Purpose: A novel regimen designed to maximize antileukemia activity of carboplatin through inhibiting repair of platinum-DNA adducts was conducted in poor prognosis, acute leukemia patients.

Experimental Design: Patients received fludarabine (10 to 15 mg/m2 × 5 days), carboplatin (area under the curve 10 to 12 by continuous infusion over 5 days), followed by escalated doses of topotecan infused over 72 hours (fludarabine, carboplatin, topotecan regimen). Twenty-eight patients had acute myelogenous leukemia (7 untreated secondary acute myelogenous leukemia, 11 in first relapse, and 10 in second relapse or refractory), 1 patient had refractory/relapsed acute lymphoblastic leukemia, and 2 patients had untreated chronic myelogenous leukemia blast crisis. Six patients had failed an autologous stem cell transplant. Patients ranged from 19 to 76 (median 54) years. Measurement of platinum-DNA adducts were done in serial bone marrow specimens.

Results: Fifteen of 31 patients achieved bone marrow aplasia. Clinical responses included 2 complete response, 4 complete response with persistent thrombocytopenia, and 2 partial response. Prolonged myelosuppression was observed with median time to blood neutrophils ≥200/μl of 28 (0 to 43) days and time to platelets ≥20,000/μl (untransfused) of 40 (24 to 120) days. Grade 3 or greater infections occurred in all of the patients, and there were 2 infection-related deaths. The nonhematologic toxicity profile was acceptable. Five patients subsequently received allografts without early transplant-related mortality. Maximum tolerated dose of fludarabine, carboplatin, topotecan regimen was fludarabine 15 mg/m2 × 5, carboplatin area under the curve 12, and topotecan 2.55 mg/m2 over 72 hours. An increase in bone marrow, platinum-DNA adduct formation between the end of carboplatin infusion and 48 hours after the infusion correlated with bone marrow response.

Conclusions: Fludarabine, carboplatin, topotecan regimen is a promising treatment based on potential pharmacodynamic interactions, which merits additional study in poor prognosis, acute leukemia patients.

Treatment options are limited for the majority of patients with acute leukemia developing after pre-existing hematologic conditions or relapsed after initial induction chemotherapy. New promising approaches include combinations of novel agents designed to modulate DNA repair mechanisms and thereby provide synergistic cytotoxicity. In early clinical trials the topoisomerase I inhibitor, topotecan, and the platinum analog, carboplatin, have successfully induced clinical remission in a small, but substantial number of patients with refractory or relapsed acute leukemia (1, 2, 3, 4, 5, 6, 7, 8). Moreover, combined administration of cisplatin or carboplatin with topotecan in Phase I studies is associated with profound myelosuppression, suggesting a potential role in the treatment of acute leukemia, where bone marrow aplasia is generally required to achieve remission (9, 10).

DNA cross-linking is believed to be the primary cytotoxic mechanism of platinum-based chemotherapy, and differences in the ability of a cell to repair DNA damage may affect the magnitude of tumor cell kill (11, 12). In tumor cell lines, combinations of cisplatin analogs and topoisomerase I inhibitors are synergistic, in part, because of a decreased ability to repair platinum-DNA adducts (13, 14, 15, 16, 17). Concurrent administration of cisplatin and fludarabine has also been shown to enhance formation of platinum-DNA cross-links (18, 19). Therefore, addition of fludarabine and topotecan to carboplatin-based chemotherapy for acute leukemia may provide a way to circumvent both intrinsic and acquired platinum resistance through inhibition of platinum-DNA cross-link repair.

Based on these preliminary data, we designed a Phase I pharmacodynamic study of 5 days of concurrent fixed-dose fludarabine and continuous infusion carboplatin followed by a 72-hour infusion of escalating doses of topotecan for patients with relapsed or refractory acute leukemia, secondary acute myelogenous leukemia, or chronic myelogenous leukemia blast crisis. Pharmacodynamic and platinum-DNA adduct companion studies were correlated with bone marrow aplasia and patient outcome.

Research Participants

Adult patients (≥18 years) with relapsed or refractory acute myelogenous leukemia or acute lymphoblastic leukemia were eligible for treatment. In addition, patients with acute leukemia secondary to pre-existing hematologic disorders or chemotherapy, high-grade myelodysplastic syndromes, or chronic myelogenous leukemia in blast crisis were eligible for treatment at diagnosis or after no more than 2 prior induction regimens. Patients who had failed autologous transplantation were eligible provided that they had recovered from acute toxicities of treatment. Adequate cardiac, pulmonary, hepatic, and renal function (defined as calculated creatinine clearance ≥50 ml/minutes, total serum bilirubin ≤2.0 mg/dl, and blood transaminase ≤3 times the upper limit of normal), Eastern Cooperative Oncology Group performance status ≤3, and a life expectancy of at least 1 month without definitive treatment were required. Prior chemotherapy including camptothecin analogs was allowed, and a minimum of 2 weeks must have elapsed since the last cytotoxic therapy (excluding hydroxyurea and corticosteroids). Exclusion criteria included previous allogeneic transplant, uncontrolled infections, or central nervous system leukemia. The clinical protocol was approved by the Institutional Review Board at University Hospitals (Case Western Reserve University), and all of the patients gave written informed consent.

Treatment Plan and Dose Escalation Schema

Treatment schema, schedule of correlative laboratory studies, and dose escalation schedule are described in Fig. 1 and Table 1. Drug dosages were calculated according to body surface area calculation with the lesser of actual or corrected body weight [ideal body weight + 25% (actual-ideal body weight)]. For dose levels 1 to 3, carboplatin was administered by continuous infusion over 120 hours for a total dose calculated to achieve an area under the curve of 10 according to the Calvert formula (20), and fludarabine at a dose of 10 mg/m2 was administered over 30 minutes daily. For dose levels 4 and above, carboplatin was given to achieve an area under the curve of 12, and the daily fludarabine dose was raised to 15 mg/m2/day. Topotecan at the assigned dose (see schema in Fig. 1) was administered by continuous infusion for 72 hours beginning immediately after the carboplatin infusion was completed. An early treatment assessment bone marrow aspirate and biopsy were obtained 7 days after the completion of topotecan (day 15 to 18 after the beginning of treatment). Patients with residual leukemia at this evaluation were eligible for a second induction cycle to begin no sooner than day 16 and no later than day 35 after the beginning of induction cycle 1. Treatment with hematopoietic growth factors was initiated in patients who achieved bone marrow aplasia, defined as marrow cellularity ≤5% and/or ≤5% blasts 15 to 18 days from the initiation of treatment. Patients who achieved a complete or partial response could receive one cycle of consolidation therapy with fludarabine, carboplatin, and topotecan within 4 to 8 weeks of hospital discharge or recovery of peripheral blood counts to neutrophils ≥1200/μl and platelets ≥75,000/μl. Dose modifications for consolidation therapy were made according to toxicities encountered during the initial induction therapy. No dose escalations were allowed within individual patients.

Toxicities were graded by the NCI common toxicity criteria (version 1.0). Dose-limiting toxicity was defined as a grade 3 or worse nonhematologic toxicity. Grade 3 or greater stomatitis, diarrhea, or infectious complications (unless greater than 7 days duration) were not considered dose limiting because these are commonly observed during leukemia induction therapy. Dose-limiting hepatoxicity was defined as ≥grade 4 hyperbilirubinemia or ≥grade 3 transaminase elevation, which did not resolve to <3× the upper limit of normal by day 35 of treatment. Dose-limiting hematologic toxicity was defined as an absolute neutrophil count ≤200/μl or an unsupported platelet count ≤20,000/μl with a ≤5% cellular bone marrow without evidence of residual leukemia lasting 35 days or greater from the beginning of the most recent cycle of chemotherapy. Deaths occurring within 6 weeks of the beginning of protocol treatment were classified into 3 categories: (1) disease related, for example, because of leukostasis; (2) cytopenia-related, such as infection or bleeding (providing cytopenia was <5 weeks duration); and (3) treatment-related, for example, because of organ toxicities such as mucositis, hepatotoxicity, and cytopenia ≥35 days or unexpected toxicities not related to bleeding and infection. The dose escalation schema was modified for category 3 deaths only. If no patient at an individual dose level developed a dose-limiting toxicity, dose escalation proceeded. If 1 of 3 patients developed a dose-limiting toxicity as defined above, 3 additional patients were enrolled at the same dose level. If <2 of 6 patients developed dose-limiting toxicity, dose escalation continued. If 2 or greater dose-limiting toxicity developed, the dose of topotecan was reduced either a full step for moderate or severe toxicities or half step for mild toxicities observed at the next lowest dose level. Moderate toxicity was defined as grade 2 or worse nonhematologic toxicity, grade 3 or worse stomatitis, diarrhea, or hepatotoxicity. Infectious complications were excluded unless caused by prolonged aplasia unrelated to persistent leukemia. Each individual in a cohort was followed for a minimum of 6 weeks before the next cohort was entered. Maximum tolerated dose was defined as the dose level at which no more than 1 of 6 patients experienced dose-limiting toxicity.

Clinical Evaluation

Complete response was defined as neutrophil count ≥1200/μl, platelet count ≥100,000/μl, without circulating leukemic blasts, and bone marrow cellularity of ≥20% with ≤5% blasts. A partial response included all of the criteria listed above except that the bone marrow contained 5 to 25% blasts. There was also a category of a complete response with the exception of persistent thrombocytopenia. Other responses of interest included achievement of an early aplastic bone marrow defined as bone marrow cellularity on day 16 to 18 of treatment to <5% and/or blast percentage to <5%. All clinical responses were reviewed by a clinical hematopathologist (H.J.M.).

Laboratory Studies

Topoisomerase I Activity Assays.

Topoisomerase I activity levels were assayed from bone marrow aspirates before treatment, at the end of the carboplatin infusion, and ∼48 hours after the start of the topotecan infusion. Five milliliters of bone marrow or 10 ml of peripheral blood were collected in an EDTA tube and diluted 1:1 with PBS. Marrow mononuclear cells were separated by a Ficoll-Hypaque discontinuous gradient and then washed in PBS at 4°C (21). Contaminating red blood cells were lysed with RBC lysis buffer (Sigma, St. Louis, MO). Cell pellets were flash frozen in liquid nitrogen and stored at −80°C. Topoisomerase I was quantitated from specimens containing a minimum of 1 × 107 mononuclear cells by measuring enzymatic activity as ATP-independent relaxation of supercoiled φX174 DNA according to previously described methods (22). Gels were stained with ethidium bromide, photographed under short wave UV light, and densitometric profiles of the negatives were quantitated. One unit of topoisomerase activity was defined as the amount of enzyme needed to relax 0.6μg of supercoiled DNA in 30 minutes at 37°C (22, 23, 24). Topoisomerase I activity was expressed relative to DNA and protein content of cell samples. All samples were run against a standard control colon cancer cell line. Because of the limited amount of DNA, most samples were analyzed once. Variability of the assay was within 5% in samples run in duplicate or triplicate.

Topotecan Total and Lactone Concentration

Samples of blood for topotecan total and lactone concentration were obtained before the start of the topotecan infusion and at 24, 48, and 68 hours after the start of the topotecan infusion (where possible). Whole blood (3 ml) was collected in a heparinized syringe, transferred to a 5-ml red top tube, centrifuged at 4°C for 5 minutes at 3,000 rpm, and transferred into a glass tube. Exactly 1 ml of plasma was immediately pipetted into a borosilicate glass tube containing 5 ml of methanol (from −20°C freezer), vortex mixed for 10 seconds, and spun in 4°C centrifuge at 3,000 rpm for 5 minutes. The resulting supernatant was stored at −70°C until analysis. Topotecan lactone and total topotecan were determined with high-pressure liquid chromatography (model 1050 pump, 1046A fluorescence detector, Hewlett Packard, Wilmington, DE) with minor modifications of sample quantify and reconstitution and volumes of previously published procedures (25). Quality control samples of high- and low-concentration plasma total topotecan and topotecan lactone were determined with each set of patient samples. The control limits (mean ± SD) for the high and low total topotecan concentration were 7.4 ± 0.7 and 1.1 ± 0.1 ng/ml, respectively. For topotecan lactone the control limits were 5.8 ± 0.8 ng/ml and 1.0 ± 0.2 ng/ml for the high and low concentrations, respectively.

Evaluation of Platinum-DNA Adducts

Bone marrow aspirates were taken before the beginning of treatment, at the completion of the carboplatin infusion on day 5, and at 48 hours after the start of the topotecan infusion. DNA was isolated from these aspirates with a Qiagen DNA Mini kit (Qiagen, Valencia, CA), and the concentration of DNA in each sample was quantified by UV absorption (A260). DNA samples were diluted in 3.5% nitric acid and hydrolyzed overnight at 70°C. Platinum-DNA adduct levels were determined with a ThermoFinnigan Neptune plasma ionization multicollector mass spectrometer as described previously (26). This inductively coupled plasma mass spectrometry approach allows a substantial improvement in sensitivity to that observed with previous methods, such as atomic absorption spectrophotometry and ELISA, with detection limits in the single femtogram range being obtainable. Because of the labor-intensive nature of running these samples on the inductively coupled plasma mass spectrometry and, in some cases, limitations in the amount of DNA sample available, most samples were analyzed once. However, at the beginning and end of the analytical run, a number of samples were run in duplicate, with replicates within 5% in all of the cases. Final platinum-DNA adduct levels were calculated as nmoles/g DNA.

Statistical Analyses

The nonparametric, one-way ANOVA Kruskal-Wallis test was used to test for differences in topotecan plasma concentration medians across the topotecan dose groups. This test was also used to compare clinical and early bone marrow response groups with median absolute platinum adduct levels at 120 hours. Linear regression was used to test the correlation between the mean plasma topotecan concentration and the time in days to recover to an absolute neutrophil count >200/μl. Fisher’s exact test was used to test the dependency on bone marrow response and clinical response of the proportion of patients with increases in adduct levels between 120 and 168 hours.

Patient Characteristics

Thirty-one patients were enrolled between September 1998 and November 2001 (Table 2). Fourteen men and seventeen women were treated of whom 27 were Caucasian and 4 were African American. Median age was 54 (range, 19 to 76) years. Twenty-eight patients had acute myelogenous leukemia as follows: 7 untreated, 11 in first relapse, and 10 in second relapse or refractory. All untreated patients had acute myelogenous leukemia secondary to myelodysplastic syndrome or previous cytotoxic chemotherapy for other malignancies. Two patients had chronic myelogenous leukemia in untreated blast crisis and 1 patient had refractory/relapsed acute lymphoblastic leukemia. Ten patients had antecedent myelodysplastic syndromes, and 6 patients had failed autologous stem cell transplant. Median duration of remission of the patients treated in first relapse was 5 (range, 2 to 10) months.

Clinical Response

Two patients at each of the dose levels 3 and higher achieved a clinical response. Four patients achieved a complete response, 2 achieved a complete response with the exception of persistent thrombocytopenia, and 2 patients achieved a partial response. No responses were seen at dose levels 1 and 2 of treatment. Five of 9 previously untreated patients achieved a clinical response compared with 2 of 11 patients treated in first relapse and 1 of 11 patients with later stage disease. Patient characteristics and description of treatment response are included in Table 3. Nine additional patients achieved an early aplastic bone marrow response without subsequent remission. Of these patients, 1 died of infection on day 35 of the second cycle of induction treatment without any evidence of hematopoietic recovery, 1 received alternate salvage treatment, 2 recovered only circulating blasts, 3 achieved transient recovery of neutrophils with persistent grade 4 thrombocytopenia, and 2 patients had transient recovery of absolute neutrophil count ≥1500/μl and platelets ≥100,000/μl with persistent circulating blasts.

Five patients (3 with clinical responses and 2 with persistent disease after fludarabine, carboplatin, topotecan regimen treatment) underwent allogeneic transplantation shortly after receiving protocol therapy. Two of these patients remain alive in complete remission at 46 months after receiving an allogeneic transplant from an HLA identical sibling in first partial response and at 36 months after an umbilical cord blood donor in the setting of persistent disease. One patient with chronic myelogenous leukemia blast crisis died of extensive chronic graft versus host disease without evidence of disease recurrence ∼12 months after receiving an allogeneic transplant from a matched unrelated donor. Two additional patients died from recurrent leukemia. There were no early (first 100 days) transplant-related deaths or excessive end-organ toxicities observed in the patients who underwent allogeneic stem cell transplantation after receiving the fludarabine, carboplatin, topotecan regimen.

Toxicity Evaluation

Two of 31 patients died within the first 6 weeks of receiving induction chemotherapy. One patient treated at dose level 5 died of overwhelming pseudomonas pneumonia on day 35 after a second cycle of induction fludarabine, carboplatin, topotecan regimen without evidence of hematopoietic recovery. This was considered a dose-limiting hematologic and pulmonary toxicity and category 3 death (see Patients and Methods). A patient with relapsed/refractory acute lymphoblastic leukemia treated at dose level 5A also died. This death was coded as a category 2 death as it was caused by overwhelming infection on day 22.

Nonhematologic toxicities of grade 3 or greater are summarized in Table 4. Grade 3 or greater infections were observed in all of the patients. Two episodes of atrial fibrillation were observed at dose levels 2 and 4 and were not considered dose-limiting because they occurred after amphotericin administration in the setting of a prior cardiac history in 1 patient and multiple electrolyte abnormalities and infections in the second patient. Two episodes of grade 3 neurologic toxicity (lethargy that was possibly therapy-related) lasting 3 days at dose level 3 and grade 3 headache at dose level 5 prompted treatment of an additional 3 patients on each of these dose levels. Another patient treated at dose level 4 had a malignant pleural effusion (grade 3) before starting protocol treatment. Because of an error in topotecan administration (1 of 3 doses given as a bolus rather than infusion), seven patients were treated at dose level 5. Grade 3 to 4 hypocalcemia was common. Hepatic and gastrointestinal toxicities, which were not considered dose-limiting according to protocol guidelines, included grade 3 elevation of alanine aminotransferase for 3 days, 3 episodes of grade 3 hyperbilirubinemia of 1 day’s duration, and 1 episode of grade 3 neutropenic enterocolitis.

Hematologic recovery after induction therapy in patients who achieved clinical response is described in Table 5 A. The time to recover neutrophils ≥200/μl ranged from 20 to 43 days (median 28), and time to platelet transfusion independence ranged from 24 to 120 days (median 40) from the first day of the most recent cycle of induction chemotherapy. One of 6 patients at dose level 3, none of the first 3 patients who received dose level 4, and 2 of 6 patients treated at dose level 5 experienced dose-limiting hematologic toxicity. Dose level 5A, which included a half-step reduction of topotecan between dose 4 and 5 was added, and 2 of 6 patients developed dose-limiting hematologic toxicity. Three additional patients were then accrued to dose level 4, and a total of 1 of 6 patients treated at this dose experienced prolonged platelet recovery. Therefore, the maximum tolerated dose of the regimen was defined as dose level 4.

Four patients received fludarabine, carboplatin, topotecan regimen as consolidation therapy (Table 5 B). One of these patients died with an aplastic bone marrow 81 days after receiving fludarabine, carboplatin, topotecan regimen chemotherapy without evidence of leukemia.

Laboratory Studies

Pharmacokinetics.

Topotecan and lactone plasma concentration were available for 21 patients. The mean ratio of total topotecan to plasma lactone was 2.33 (SD, 0.51). The average of topotecan and lactone plasma determinations at 24, 48, and 72 hours was used for pharmacokinetic correlations. There was no significant relationship between dose of topotecan administered and plasma concentration of topotecan (P = 0.19). There was, however, a significant correlation between topotecan plasma concentration and recovery of neutrophils (n = 9; P = 0.016; Fig. 2).

Pharmacodynamic Studies

Topoisomerase I Activity.

Topoisomerase I activity from mononuclear cell fractions of bone marrow aspirates was analyzed as shown in the schema (Fig. 1). For these studies the blast percentage of the mononuclear cell fractions was not determined. A change in topoisomerase I activity was defined as a 15% increase or decrease from baseline. Topoisomerase activity decreased in 9 patients, increased in 2 patients, and remained the same in 2 patients between the start of treatment and the completion of the carboplatin infusion. Changes in topoisomerase I activity also was compared before treatment and 48 hours after the beginning of the topotecan infusion in 9 patients and was found to decrease in 9 patients and increase in 2 patients. Modulation of topoisomerase I activity did not correlate with clinical or bone marrow response at either time point analyzed (Wilcoxan and t test, P > 0.1).

Platinum-DNA Adducts

Mononuclear cells isolated from bone marrow aspirates taken before, on completion of, and 48 hours after the end of the carboplatin infusion were analyzed for determination of in vivo platinum-DNA adduct levels in 19 patients (Table 6). One 48-hour sample was not available for analysis. A large interpatient variation in platinum-DNA adduct levels was observed, with ∼130- and 225-fold variations in adduct levels determined at the end of carboplatin infusion on day 5 and 48 hours after completion of carboplatin infusion, respectively (range, 0.22 to 28.61 nmol/L/g DNA at end of carboplatin infusion; 0.53 − 120.1 nmol/L/g DNA at 48 hours post infusion; Fig. 3). A mean pretreatment platinum-DNA adduct level of 0.10 ± 0.15 moles/g DNA was determined from mononuclear cells isolated from bone marrow samples obtained before carboplatin administration in these patients. Platinum-DNA adduct levels, either determined at the end of carboplatin infusion or 48 hours after completion of infusion, did not show a clear relationship with the actual dose of carboplatin administered. No significant correlations were observed between the extent of platinum-DNA adduct formation and either bone marrow response or clinical response. Furthermore, time to hematopoetic recovery (neutrophils ≥200/μl or platelets ≥20,000/μl) was not influenced by the platinum-DNA adduct level attained at the end of the carboplatin infusion or the 48 hours post-infusion sample. An increase or decrease in adduct level at 48 hours post infusion was defined as a change of >15% from the value determined at the end of carboplatin infusion. In those patients in whom adduct concentration increased between the end of carboplatin infusion and the 48 hours post-infusion sample, 7 of 8 patients achieved an aplastic day 16 bone marrow response compared with only 4 of 10 patients in whom the adduct levels decreased (P = 0.065, Fisher’s exact test). Furthermore, 4 of 7 patients whose platinum-adduct levels increased showed a clinical response compared with 1 of 9 patients in whom platinum-DNA adducts decreased between those two time points (P = 0.106). In addition, we did not observe any correlation between the dose of topotecan administered and the change in platinum-DNA adduct levels determined between the end of the carboplatin infusion and 48 hours after infusion.

The combination of a topoisomerase I inhibitor and DNA damaging agent such as carboplatin has been shown to possess synergistic antitumor activity in multiple in vitro and in vivo studies (13, 14, 15, 16, 17). We designed a Phase I and translational study of fludarabine, carboplatin, and escalating doses of topotecan (fludarabine, carboplatin, topotecan regimen) given in a sequential fashion for patients with acute leukemia. Pharmacodynamic studies of topoisomerase I activity and platinum-DNA adduct formation were included to explore potential mechanisms of synergy between carboplatin and topotecan.

In comparison to other salvage chemotherapy regimens for acute leukemia, fludarabine, carboplatin, topotecan regimen was well tolerated with acceptable nonhematologic toxicity. Hematologic toxicity was dose-limiting and, in fact, defined the maximum tolerated dose and recommended dose for Phase II studies as fludarabine 15 mg/m2 for 5 consecutive days, carboplatin area under the curve of 12 over 120 hours, followed by topotecan 0.85 mg/m2/day by continuous infusion over 72 hours. The median time to achieve an absolute neutrophil count of ≥200/μl was 28 (range, 20 to 43) days, and the median time to platelet transfusion independence was 40 (range, 29 to 120) days. The most commonly observed nonhematologic toxicities included infections, hypocalcemia, and hypomagnesemia. The observed treatment-related mortality of 6% (2 to 31) during induction chemotherapy in this heavily treated group of patients compares favorably to other leukemia induction or salvage regimens (27). One patient who received fludarabine, carboplatin, topotecan regimen with a 25% dose reduction as consolidation therapy died of bone marrow aplasia 81 days after receiving treatment, raising a concern that hematologic toxicity of the regimen may be cumulative. The maximum tolerated dose of topotecan and carboplatin in the fludarabine, carboplatin, topotecan regimen for acute leukemia appears to be approximately twice that observed for solid tumors (10).

At the dose range studied, we found significant interpatient variation of steady-state lactone and total topotecan plasma concentrations within dose levels and did not observe a significant relationship between dose and plasma concentration of topotecan. The consistent ratio of steady-state total topotecan to plasma lactone concentration suggests that sample processing and analysis were accurate. However, the number of patients available for analysis may not have been sufficient to determine any significant correlation between steady-state plasma topotecan concentration and early treatment bone marrow or clinical response. On the other hand, it is of interest that all of the clinical responses were observed at dose level 3 or greater, suggesting that topotecan added significantly to the antileukemic activity of the regimen. In our study, increased plasma concentrations of topotecan correlated significantly with days to neutrophil recovery. Other investigators have observed up to a 10-fold interpatient variability between dose administered and topotecan pharmacokinetics (28, 29, 30). Moreover, topotecan plasma concentrations rather than dose administered have been shown to correlate with the development of hematologic and gastrointestinal toxicities (28, 31, 32, 33, 34), suggesting that future studies may warrant consideration of dosing of topotecan based on pharmacokinetics (35).

Enhanced cytotoxicity between carboplatin and topotecan in the fludarabine, carboplatin, topotecan regimen may be related to the potential for DNA damaging agents such as carboplatin to increase topoisomerase I activity. However, in the current study we did not observe a correlation between up-regulation of topoisomerase I activity and tumor response among the 13 paired patient samples analyzed. Kanzawa et al.(36) found that the topoisomerase I inhibitory effect of irinotecan in small cell lung cancer cell lines was enhanced 10-fold in the presence of the cisplatin analog nedaplatin, potentially explaining the marked synergy of the two agents. In contrast, Ma et al.(37) were unable to correlate synergistic cytotoxicity between cisplatin and topoisomerase I inhibitors in a panel of solid-tumor cell lines with up to a 4-fold difference in topoisomerase I activity. These data suggest that the amount of the target topoisomerase I/DNA complex is not a major contributor to the enhanced cytotoxic activity of these combinations.

As a secondary objective of this Phase I study, bone marrow aspirates were obtained during and after treatment with carboplatin to investigate the potential correlation between platinum-DNA adduct formation as well as previously reported DNA-based synergistic interactions between topotecan and platinum agents (15, 16) and clinical response. Platinum-DNA adduct levels determined in our study were comparable with data from 6 patients receiving high-dose carboplatin chemotherapy, with a similar inductively coupled plasma mass spectrometry method (38). A large, interpatient variation in DNA adduct levels was observed, although carboplatin was dosed to achieve standardized carboplatin exposures (area under the curve of 10 or 12 depending on the dose level). This suggests that platinum-DNA adduct formation is not closely related to drug pharmacokinetics, a finding also previously reported for cisplatin (39). In contrast to the study by Veal et al.(39), in which single-agent cisplatin was administered, we did not observe any correlation between the degree of myelosuppression and extent of platinum-DNA adduct formation. No statistically significant correlations were observed between the concentration of adduct formation and either an aplastic early bone marrow response or clinical response. However, in this relatively limited study group, there appeared to be an association between achievement of early bone marrow aplasia and clinical responses in the patients whose adduct levels increased between the end of carboplatin infusion and 48 hours after the end of infusion. This may suggest an important role for DNA adduct-repair processes in this group of patients. Because our studies were obtained on mononuclear cell fractions of the bone marrow aspirates, changes in platinum-DNA adduct formation observed could be influenced, in part, by variations in blast cell content of the bone marrow during treatment. Furthermore, we did not observe correlations between platinum-DNA adduct formation and either topotecan dose or topotecan plasma concentration in the patients studied. These data are in agreement with a recently published Phase I study showing that sequence of topotecan given in combination with cisplatin did not influence peak platinum-DNA adduct formation in peripheral blood leukocytes of patients (9).

In contrast to our study, Welters et al. (40) found significant correlations between platinum-DNA adducts and tumor response in xenografted tumor tissues and in cultured tumor cells of head and neck squamous cell cancer. Other investigators have explored the relationship between platinum-DNA adduct formation in peripheral blood leukocytes and clinical response in patients undergoing chemotherapy. Reed et al. (41) found a highly statistically significant correlation between platinum-DNA adduct levels in peripheral blood leukocytes during cycle 1 of chemotherapy and disease response in patients with a variety of solid tumors. No such correlation was found by other investigators in similar studies (38, 42). It should be noted that in many of these studies, including the present report, platinum agents are being administered as one of a combination of different anticancer agents.

The apparently anomalous relationship we observed between clinical response and level of platinum-DNA adduct formation has been reported by others. Johnson et al. (12) found 20- to 40-fold higher DNA platination levels in cisplatin-resistant compared with cisplatin-sensitive human ovarian cancer cell lines. Increased adduct levels in more resistant cell lines, compared with sensitive cell lines, have also been observed in other tumor cell types, including colon, bladder, testicular, and leukemia, after exposure to cisplatin (42, 43, 44, 45, 46, 47). This may suggest that resistant tumor cell lines are able to tolerate higher levels of DNA damage. On the other hand, as in our study, deficiencies in the ability to repair platinum-DNA adducts have been associated with sensitivity to cisplatin in multiple tumor cell lines (12, 48, 49, 50).

We are encouraged by the clinical activity of fludarabine, carboplatin, topotecan regimen in this group of patients with high-risk leukemia. Eight of 25 patients treated at dose level 3 or higher achieved clinical response. This included 5 of 9 patients who had leukemia secondary to antecedent hematologic conditions or cytotoxic chemotherapy and had not previously received leukemia induction therapy, 2 of 11 patients in first relapse, and 1 patient in second relapse. The duration of response was limited in these high-risk patients, and prolonged thrombocytopenia was observed. In this small study, the response rate we observed, particularly in previously untreated patients, compares favorably to cytarabine-based regimens. Furthermore, there were no early transplant-related deaths among the 5 patients who underwent allogeneic stem cell transplantation shortly after receiving protocol treatment, which we believe was due in large part to the favorable toxicity profile of the fludarabine, carboplatin, topotecan regimen. Phase II studies are planned to additionally define the antileukemia activity and toxicity of this regimen.

Fig. 1.

Treatment schema and schedule of correlative laboratory studies. Topotecan levels were obtained from plasma. Topoisomerase I activity and platinum-DNA adducts were done on bone marrow aspirates. Please also see Table 1.

Fig. 1.

Treatment schema and schedule of correlative laboratory studies. Topotecan levels were obtained from plasma. Topoisomerase I activity and platinum-DNA adducts were done on bone marrow aspirates. Please also see Table 1.

Close modal
Fig. 2.

Correlation between topotecan plasma concentration and neutrophil recovery (n = 9). P = 0.016 for the plotted linear regression. (ANC, absolute neutrophil count)

Fig. 2.

Correlation between topotecan plasma concentration and neutrophil recovery (n = 9). P = 0.016 for the plotted linear regression. (ANC, absolute neutrophil count)

Close modal
Fig. 3.

Change in platinum-DNA adduct levels obtained from bone marrow mononuclear cells on day 5 of carboplatin infusion and 48 hours after the carboplatin infusion was completed. Platinum-DNA adduct levels increased in 8 of the 18 patients.

Fig. 3.

Change in platinum-DNA adduct levels obtained from bone marrow mononuclear cells on day 5 of carboplatin infusion and 48 hours after the carboplatin infusion was completed. Platinum-DNA adduct levels increased in 8 of the 18 patients.

Close modal

Grant support: NIH Grant R21-CA81500-02 (B. Cooper), the Hematopoietic Stem Cell Core Facility of the Comprehensive Cancer Center of Case Western Reserve University and University Hospitals of Cleveland, NIH Grant P30 CA43703 (Ireland Cancer Center, Cleveland, OH), and Clinical Research Grants from SmithKline Beecham, Bristol Myers Squibb, and Berlex.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Requests for reprints: Brenda W. Cooper, Department of Medicine, University Hospitals of Cleveland, 11100 Euclid Avenue, Cleveland, OH 44106. Phone: (216) 844-3213; Fax: (216) 844-1256; E-mail: bxc12@po.cwru.edu

Table 1

Dose escalation schema

Dose levelTopotecan (mg/m2 daily)Carboplatin (total AUC)Fludarabine (mg/m2/daily)
10 10 
0.7 10 10 
0.85 10 10 
0.85 12 15 
1.0 12 15 
5A 0.925 12 15 
Dose levelTopotecan (mg/m2 daily)Carboplatin (total AUC)Fludarabine (mg/m2/daily)
10 10 
0.7 10 10 
0.85 10 10 
0.85 12 15 
1.0 12 15 
5A 0.925 12 15 
Table 2

Patient characteristics (N = 31)

Male:Female 14:17 
Median age (range) 54 (19–76) years 
Race  
 Caucasian 27 
 African American 
Diagnosis  
AML 28 
 Untreated 
 First relapse 11 
 Second relapse 
 Refractory 
ALL 
CML blast crisis 
 Prior myelodysplasia 10 
 Prior autotransplant 
 Duration of first CR 5 (2–10) months 
Male:Female 14:17 
Median age (range) 54 (19–76) years 
Race  
 Caucasian 27 
 African American 
Diagnosis  
AML 28 
 Untreated 
 First relapse 11 
 Second relapse 
 Refractory 
ALL 
CML blast crisis 
 Prior myelodysplasia 10 
 Prior autotransplant 
 Duration of first CR 5 (2–10) months 

Abbreviations: AML, acute myelogenous leukemia; ALL, acute lymphoblastic leukemia; CML, chronic myelogenous leukemia; CR, complete response.

Table 3

Description of clinical response in 8 patients

UPN no.Dose levelDiagnosisPrior treatmentResponse descriptionDuration
3 (2 cycles) AML relapse 2 Autotransplant Complete response with the exception of persistent thrombocytopenia 4 months 
   Mitoxantrone-VP-16   
12 CML blast crises None Complete response 2 months, died of extensive GVHD 12 months after allogeneic transplant performed in early relapse 
13 Secondary AML Extramedullary leukemia (liver) None Partial response (complete response in bone marrow) with resolution of cytogenetic abnormalities. Microscopic residual focus of suspicious cells in liver Remains in CR 46+ months after allogeneic transplant 
17 Secondary AML None Complete response then reversion to MDS with clearing of blasts 3 months 
18 5 (2 cycles) Secondary AML None Complete response 5 months 
24 5A AML relapse 1 Extramedullary (skin) High-dose cytarabine Complete response Died from prolonged aplasia after receiving consolidation cycle of FCT without leukemia 
27 5A AML relapse 1 Conventional cytarabine idarubicin, high-dose cytarabine consolidation Complete response with the exception of persistent thrombocytopenia Relapsed 4 months after allogeneic transplantation 
31 Secondary AML None Partial response, recovery of normal blood counts with persistent bone marrow blasts 1 month 
UPN no.Dose levelDiagnosisPrior treatmentResponse descriptionDuration
3 (2 cycles) AML relapse 2 Autotransplant Complete response with the exception of persistent thrombocytopenia 4 months 
   Mitoxantrone-VP-16   
12 CML blast crises None Complete response 2 months, died of extensive GVHD 12 months after allogeneic transplant performed in early relapse 
13 Secondary AML Extramedullary leukemia (liver) None Partial response (complete response in bone marrow) with resolution of cytogenetic abnormalities. Microscopic residual focus of suspicious cells in liver Remains in CR 46+ months after allogeneic transplant 
17 Secondary AML None Complete response then reversion to MDS with clearing of blasts 3 months 
18 5 (2 cycles) Secondary AML None Complete response 5 months 
24 5A AML relapse 1 Extramedullary (skin) High-dose cytarabine Complete response Died from prolonged aplasia after receiving consolidation cycle of FCT without leukemia 
27 5A AML relapse 1 Conventional cytarabine idarubicin, high-dose cytarabine consolidation Complete response with the exception of persistent thrombocytopenia Relapsed 4 months after allogeneic transplantation 
31 Secondary AML None Partial response, recovery of normal blood counts with persistent bone marrow blasts 1 month 

Abbreviations: AML, acute myelogenous leukemia; CML, chronic myelogenous; FCT, fludarabine, carboplatin, topotecan regimen.

Table 4

Grade 3 to 4* nonhematologic toxicities according to dose level of topotecan (induction only)

ToxicitiesDose level
123455A
Cardiac  1 (3)  1 (3)   
Gastrointestinal     1 (3) 1 (3) 
Hepatic   1 (3) 1 (3) 1 (3) 1 (3) 
Hypocalcemia   1 (3) 1 (3) 1 (4) 2 (3) 
Infection 3 (3) 3 (3) 4 (3) 6 (3) 7 (3,5)§ 6 (3,5) 
Neurologic   1 (3)§  1 (3)§  
Pulmonary    1 (3) 1 (5)  
Patients/cycles 6/8 7/9 
ToxicitiesDose level
123455A
Cardiac  1 (3)  1 (3)   
Gastrointestinal     1 (3) 1 (3) 
Hepatic   1 (3) 1 (3) 1 (3) 1 (3) 
Hypocalcemia   1 (3) 1 (3) 1 (4) 2 (3) 
Infection 3 (3) 3 (3) 4 (3) 6 (3) 7 (3,5)§ 6 (3,5) 
Neurologic   1 (3)§  1 (3)§  
Pulmonary    1 (3) 1 (5)  
Patients/cycles 6/8 7/9 
*

NCI common toxicity criteria (version 1.0).

Dose level 5A was added after dose-limiting hematologic and neurologic toxicity in an individual patient and 1 patient death because of prolonged aplasia was observed at dose level 5 and includes a half-step reduction of topotecan.

Number of patients (grade of toxicity).

§

Dose-limiting toxicity.

Table 5

Hematologic recovery in patients achieving clinical response

A. Days to hematopoietic recovery* (induction)
Dose levelNo. of cyclesANC ≥ 200Platelets ≥ 20,000ANC ≥ 1,200Platelets ≥ 75,000
40 120 45 NR 
 20 24 22 24 
32 33 34 37 
 22 42 22 60 
29 23 36 27 
 28 40 39 52 
5A 29 40 33 61 
 40 70 48 NR (50,000/μl on day 83) 
A. Days to hematopoietic recovery* (induction)
Dose levelNo. of cyclesANC ≥ 200Platelets ≥ 20,000ANC ≥ 1,200Platelets ≥ 75,000
40 120 45 NR 
 20 24 22 24 
32 33 34 37 
 22 42 22 60 
29 23 36 27 
 28 40 39 52 
5A 29 40 33 61 
 40 70 48 NR (50,000/μl on day 83) 
B. Days to hematopoietic recovery (consolidation)
Patients IDCycle no.DoseANC ≥ 200Platelets ≥ 20,000
12 Never dropped 22 
17 31 25 
18 46 44 
24 5A 81+ 81+ 
B. Days to hematopoietic recovery (consolidation)
Patients IDCycle no.DoseANC ≥ 200Platelets ≥ 20,000
12 Never dropped 22 
17 31 25 
18 46 44 
24 5A 81+ 81+ 

Abbreviations: ANC, absolute neutrophil count; NR, not reached.

*

Recovery in days from most recent course of induction.

Dose-limiting hematologic toxicity defined as ANC ≤ 200/μl or an unsupported platelet count ≤ 20,000/μl lasting 35 or more days from the beginning of the most recent cycle of chemotherapy.

Given at 25% dose reduction, patient died without evidence of leukemia or marrow recovery.

Table 6

Platinum-DNA adduct levels, bone marrow response, and clinical response in 19 patients

PatientPlatinum-DNA adducts (nmoles/g DNA)Bone marrow responseClinical responseTopotecan dose level
End carboplatin infusion48 h after carboplatin infusion
1.08 38.35 
12 0.37 ND 
13 7.72 120 
14 3.18 1.09 
15 10.4 7.77 
16 0.22 0.72 Early death 
17 2.05 0.53 
18 1.02 2.70 
20 28.6 4.27 
21 2.43 3.67 
22 4.28 1.43 
23 10.2 1.89 5A 
25 16.6 13.6 Early death 5A 
26 1.97 0.53 5A 
27 0.84 0.98 5A 
28 7.36 73.0 5A 
29 2.34 0.84 
30 1.74 1.43 
31 3.16 3.61 
PatientPlatinum-DNA adducts (nmoles/g DNA)Bone marrow responseClinical responseTopotecan dose level
End carboplatin infusion48 h after carboplatin infusion
1.08 38.35 
12 0.37 ND 
13 7.72 120 
14 3.18 1.09 
15 10.4 7.77 
16 0.22 0.72 Early death 
17 2.05 0.53 
18 1.02 2.70 
20 28.6 4.27 
21 2.43 3.67 
22 4.28 1.43 
23 10.2 1.89 5A 
25 16.6 13.6 Early death 5A 
26 1.97 0.53 5A 
27 0.84 0.98 5A 
28 7.36 73.0 5A 
29 2.34 0.84 
30 1.74 1.43 
31 3.16 3.61 

Abbreviations: ND, not determined; N, no response; Y, response.

1
Rowinsky EK, Adjei A, Donehower RC, et al Phase I and pharmacodynamic study of the topoisomerase I-inhibitor topotecan in patients with refractory acute leukemia.
J Clin Oncol
1994
;
2
:
2193
-203.
2
Kantarjian HM, Beran M, Ellis A, et al Phase I study of topotecan, a new topoisomerase I inhibitor in patients with refractory or relapsed acute leukemia.
Blood
1993
;
81
:
1146
-51.
3
Beran M, Kartarjian H, O’Brien S, et al Topotecan, a topoisomerase I inhibitor is active in the treatment of myelodysplastic syndrome and chronic myelomonocytic leukemia.
Blood
1996
;
88
:
2473
-9.
4
Meyers FJ, Welborn J, Lewis JP, et al Infusion carboplatin treatment of relapsed and refractory acute leukemia: evidence of efficacy with minimal extramedullary toxicity at intermediate doses.
J Clin Oncol
1989
;
7
:
173
-8.
5
Martinez JA, Martin G, Sanz GF, et al A phase II clinical trial of carboplatin infusion in high-risk acute nonlymphoblastic leukemia.
J Clin Oncol
1991
;
9
:
39
-43.
6
Vogler WR, Harrington DP, Winton EF, et al A phase II clinical trial of carboplatin in relapsed and refractory leukemia.
Leukemia (Baltimore)
1992
;
6
:
1072
-5.
7
Ettinger LJ, Krailo M, Gaynon PS, et al A phase I study of carboplatin in childhood leukemia: a report from the Children’s Cancer Study Group.
Cancer (Phila)
1993
;
71
:
3377
-89.
8
Kaufmann S, Letendre L, Litzow M, et al Phase I study of continuous infusion topotecan and carboplatin for relapsed or refractory acute leukemia[abstract 107].
Proc Am Soc Clin Oncol Annu Meet
1998
;
17
:
28a
9
de Jonge MJ, Loos WJ, Gelderblom H, et al Phase I pharmacologic study of oral topotecan and intravenous cisplatin: sequence-dependent hematologic side effects.
J Clin Oncol
2000
;
18
:
2104
-115.
10
Athale UH, Stewart C, Kuttesch JF, et al Phase I study of combination topotecan and carboplatin in pediatric solid tumors.
J Clin Oncol
2002
;
20
:
88
-95.
11
Reed E, Parker RJ, Gill I, et al Platinum-DNA adduct in leukocyte DNA of a cohort of 49 patients with 24 different types of malignancies.
Cancer Res
1993
;
53
:
3694
-9.
12
Johnson SW, Swiggard PA, Handel LM, et al Relationship between platinum-DNA adduct formation and removal and cisplatin cytotoxicity in cisplatin-sensitive and resistant human ovarian cancer cells.
Cancer Res
1994
;
54
:
5911
-6.
13
Fukuda M, Nishio K, Kanzawa F, et al Synergism between cisplatin and topoisomerase I inhibitors, NB-506 and SN-38, in human small cell lung cancer cells.
Cancer Res
1996
;
56
:
789
-93.
14
Kano Y, Akutsu M, Suzuki K, Yoshida M. Effects of carboplatin in combination with other anticancer agents on human leukemia cell lines.
Leuk Res
1993
;
17
:
113
-9.
15
Kaufman SH, Peereboom D, Buckwalter CA, et al Cytotoxic effects of topotecan combined with various anticancer agents in human cancer cell lines.
J Natl Cancer Inst (Bethesda)
1996
;
88
:
734
-41.
16
Jonsson E, Fridborg H, Nygren P, Larsson R. Synergistic interactions of combinations of topotecan with standard drugs in primary cultures of human tumor cells from patients.
Eur J Clin Pharmacol
1998
;
54
:
509
-14.
17
Cheng MF, Chatterjee S, Berger NA. Schedule-dependent cytotoxicity of topotecan alone and in combination chemotherapy regimens.
Oncol Res
1994
;
6
:
269
-79.
18
Li L, Liu X, Glassman AB, et al Fludarabine triphosphate inhibits nucleotide excision repair of cisplatin-induced DNA adducts in vitro.
Can Res
1997
;
57
:
1487
-94.
19
Li L, Keating MJ, Plunkett W, Yang LY. Fludarabine-mediated repair inhibition of cisplatin-induced DNA lesions in human chronic myelogenous leukemia-blast crisis K 562 cells: induction of synergistic cytotoxicity independent of reversal of apoptosis resistance.
Mol Pharmacol
1997
;
52
:
798
-806.
20
Calvert AH, Newell DR, Gumbrell LA, et al Carboplatin dosage: prospective evaluation of a simple formula based on renal function.
J Clin Oncol
1989
;
17
:
1748
-56.
21
Boyum A. Separation of leukocytes from blood and bone marrow.
Scand J Clin Lab Investig
1968
;
21
:
97
22
Willson J, Gerson S, Haaga J, Berger S, Berger N. Biochemical modulation of drug resistance in colon cancers.
Proc Am Assoc Cancer Res
1992
;
33
:
236
23
Duget M, Lavenot C, Harper F, et al DNA topoisomerases from rat liver: physiologic variation.
Nucleic Acids Res
1983
;
11
:
1059
-75.
24
Champoux JJ, McConaughy B. Purification and characterization of the DNA untwisting enzyme for rat liver.
Biochemistry
1976
;
15
:
4638
-42.
25
Beijnen JH, Smith BR, Keijer WJ, et al High performance liquid chromatographic analysis of the new anti-tumor drug SK&F 104864-A (NSC 609699) in plasma.
J Pharm Biomed Anal
1990
;
8
:
789
-94.
26
Nowell GM, Pearson DG, Ottley CJ, Schweiters J, Dowall D. Long-term performance characteristics of plasma ionization multicollector mass spectrometer (PIMMS): the ThermoFinnigan Neptune Holland JG Tanner SD Vincent JL eds. .
Plasma Source Mass Spectrometry: Applications and Emerging Technologies
2003
p. 307
-20. Royal Society of Chemistry Cambridge, UK
27
Anderson JE, Kopecky KJ, Willman CL, et al Outcome. After induction chemotherapy for older patients with acute myeloid leukemia is not improved with mitoxantrone and etoposide compared to cytarabine and daunorubicin: a Southwest Oncology Group study.
Blood
2002
;
100
:
3869
-76.
28
Stewart CF, Baker SD, Heideman RL, et al Clinical pharmacodynamics of continuous infusion topotecan in children: systemic exposure predicts hematologic toxicity.
J Clin Oncol
1994
;
12
:
1946
-54.
29
Montazeri A, Boucard M, Lokiec F, et al Population pharmacokinetics of topotecan: intraindividual variability in total drug.
Cancer Chemother Pharmacol
2000
;
46
:
375
-81.
30
Van Warmerdam LJ, Creemers GJ, Rodenhuis S, et al Pharmacokinetics and pharmacodynamics of topotecan given on a daily times five schedule I phase II clinical trials using a limited sampling procedure.
Cancer Chemother Pharmacol
1996
;
38
:
254
-60.
31
Haas NB, LaCreta FP, Walczak J, et al Phase I/pharmacokinetic study of topotecan by 24-hour continuous infusion weekly.
Cancer Res
1994
;
54
:
1220
-6.
32
Rose PG, Gordon NH, Fusco N, et al A phase II and pharmacokinetic study of weekly 72 hours topotecan infusion in patients with platinum-resistant ovarian carcinoma.
Gynecol Oncol
2000
;
78
:
228
-34.
33
Furman WL, Baker SD, Pratt CB, et al Escalating systemic exposure of continuous infusion topotecan in children with recurrent acute leukemia.
J Clin Oncol
1996
;
14
:
1504
-11.
34
Cooper BW, Donaher E, Lazarus HM, et al A phase I and pharmacodynamic study of sequential topotecan and etoposide in patients with relapsed or refractory acute myelogenous and lymphoblastic leukemia.
Leuk Res
2003
;
27
:
35
-44.
35
Gallo JM, Laub PB, Rowinsky EK, Grochow LB, Baker SD. Population pharmacokinetic model for topotecan derived from phase I clinical trials.
J Clin Oncol
2000
;
18
:
2459
-67.
36
Kanzawa F, Koizumi F, Koh Y, et al In vitro synergistic interactions between the cisplatin analogue nedaplatin and the DNA topoisomerase I inhibitor irinotecan and the mechanism of this interaction.
Clin Cancer Res
2001
;
7
:
202
-9.
37
Ma J, Maliepaard M, Nooter K, et al Synergistic cytotoxicity of cisplatin and topotecan or SN-38 in a panel of eight solid-tumor cell lines in vitro.
Cancer Chemother Pharmacol
1998
;
41
:
307
-16.
38
Bonetti A, Apostoli P, Zaninelli M, et al Inductively coupled plasma mass spectroscopy quantitation of platinum-DNA adducts in peripheral blood leucocytes of patients receiving cisplatin or carboplatin-based chemotherapy.
Clin Cancer Res
1996
;
2
:
1829
-35.
39
Veal GJ, Dias C, Price L, et al Influence of cellular factors and pharmacokinetics on the formation of platinum-DNA adducts in leukocytes of children receiving cisplatin therapy.
Clin Cancer Res
2001
;
7
:
2205
-12.
40
Welters MJ, Fichtinger-Schepman AM, Baan RA, et al Pharmacodynamics of cisplatin I human head and neck cancer: correlation between platinum content, DNA adduct levels and drug sensitivity in vitro and in vivo.
Br J Cancer
1999
;
79
:
82
-8.
41
Reed E, Ozols RF, Tarone R, Yuspa SH, Poirier MC. Platinum-DNA adducts in leukocyte DNA correlate with disease response in ovarian cancer patients receiving platimum-based chemotherapy.
Proc Natl Sci USA
1987
;
84
:
5024
-8.
42
Fisch MJ, Howard KL, Einhorn LH, Sledge GW. Relationship between platinum-DNA adducts in leukocytes of patients with advanced germ cell cancer and survival.
Clin Cancer Res
1996
;
2
:
1063
-6.
43
Shellard SA, Hosking LK, Hill BT. Anomalous relationship between cisplatin sensitivity and the formation and removal of platinum-DNA adducts in two human ovarian carcinoma cell lines in vitro.
Cancer Res
1991
;
51
:
4557
-64.
44
Bedford P, Fichtinger-Schepman AM, Shellard SA, et al Differential repair of platinum-DNA adducts in human bladder and testicular tumor continuous cell lines.
Cancer Res
1988
;
48
:
3019
-24.
45
Hill BT, Shellard SA, Hosking LK, Fichtinger-Schepman AM, Bedford P. Enhanced DNA repair and resistance to cis-diamminedichloroplatinum (II) after in vivo exposure of a human teratoma cell line to fractionated X-irradiation.
Int J Radiat Oncol Biol Phys
1990
;
19
:
75
-83.
46
Fram RJ, Woda BA, Wilson JM, Robichaud N. Characterization of acquired resistance to cis-diamminedichloroplatinum (II) in BE human colon carcinoma cells.
Cancer Res
1990
;
50
:
72
-7.
47
Strandberg MC, Bresnick E, Eastman A. The significance of DNA crosslinking to cis-diamminedichloroplatinum (II)-induced cytotoxicity in sensitive and resistant lines of murine leukemia L1210 cells.
Chem-Biol Interact
1982
;
39
:
169
-80.
48
Hill BT, Scanlon KJ, Hansson J, et al Deficient repair of cisplatin-DNA adducts identified in human testicular teratoma cell lines established from tumours from untreated patients.
Eur J Cancer
1994
;
30A
:
832
-7.
49
Parker RJ, Eastman A, Bostick-Bruton F, Red E. Acquired cisplatin resistance in human ovarian cancer cells is associated with enhanced repair of cisplatin-DNA lesions and reduced drug accumulation.
J Clin Investig
1991
;
87
:
772
-7.
50
Zeng-Rong N, Paterson J, Alpert L, et al Elevated DNA repair capacity is associated with intrinsic resistance of lung cancer to chemotherapy.
Cancer Res
1995
;
55
:
4760
-4.