Purpose: To evaluate sunitinib activity and potential cellular and molecular correlates in gastrointestinal stromal tumor (GIST) patients after imatinib failure, in addition to assessing the safety and pharmacokinetics (PK) of different dose schedules.

Experimental Design: In this open-label, dose-ranging, phase I/II study, 97 patients with metastatic imatinib-resistant/intolerant GIST received sunitinib at doses of 25, 50, or 75 mg/d on one of three schedules. Serial tumor imaging was done using computed tomography and [18F]fluoro-2-deoxy-d-glucose positron emission tomography scanning. PK and cell proliferation and KIT phosphorylation status in tumor biopsies were also analyzed.

Results: Clinical benefit was observed in 52 patients (54%: 7 objective partial responses, 45 stable disease ≥6 months). Decreased tumor glycolytic activity was shown in most patients within 7 days of starting sunitinib using [18F]fluoro-2-deoxy-d-glucose positron emission tomography. Sunitinib treatment was associated with reduced tumor cell proliferation by >25% in 52% of cases analyzed and reduced levels of phospho-KIT in tumor biopsies (indicating target modulation). The recommended dose schedule was 50 mg/d for 4 weeks followed by 2 weeks off treatment. On the 50-mg dose across all schedules, 79% of PK-evaluable patients achieved total drug trough concentrations above the target concentration (50 ng/mL) within 14 days of dosing. In addition, adverse events were generally mild to moderate in severity.

Conclusion: Cellular and molecular analyses showed that sunitinib clinical activity is associated with inhibition of KIT in GIST following imatinib failure, illustrating the rational approach used to develop a therapy aimed at the underlying oncogenic signaling pathway aberrancy. (Clin Cancer Res 2009;15(18):5902–9)

Translational Relevance

This phase I/II study played a pivotal role in the clinical development of sunitinib malate for patients with gastrointestinal stromal tumors following failure of imatinib, supporting both the subsequent randomized, placebo-controlled phase III study that confirmed the clinical benefit of sunitinib and multinational approval of sunitinib in this patient population. In addition to providing the final analysis of safety, pharmacokinetics, and clinical activity from this trial, we present correlative science results comprising functional imaging outcomes, cell proliferation status, and phosphorylation status of the primary target, KIT, in serial tumor biopsy specimens obtained from patients in the study. These results showed that sunitinib clinical activity may be associated with modulation of the primary target and illustrate the rational approach used to develop a new therapy aimed at the fundamental molecular lesion responsible for the malignancy.

Gastrointestinal stromal tumor (GIST) represents an ideal solid tumor model to apply the understanding of aberrant signal transduction to drug discovery and development. Most GISTs (∼95%) express the KIT receptor tyrosine kinase (RTK), and activating KIT gene mutations represent a key etiologic mechanism in 80% to 85% of GIST patients (1). Approximately 8% of GIST patients have activating mutations in the PDGFRA gene encoding the related RTK platelet-derived growth factor receptor-α (PDGFRA; refs. 2, 3). In ∼10% of patients, no kinase mutations are detectable in either of these two genes, although uncontrolled KIT kinase activation has been noted even in the absence of mutation (2, 4).

The survival of metastatic GIST patients was dramatically improved by treatment with the KIT and PDGFRA inhibitor imatinib mesylate (Gleevec; refs. 5, 6). However, imatinib resistance emerges due most commonly to evolution of secondary KIT or PDGFRA mutations (710). Therefore, systemic therapies are needed for GIST patients once imatinib resistance appears and for the small subset who are imatinib intolerant.

Sunitinib malate (SUTENT) is an oral, multitargeted tyrosine kinase inhibitor with potent activity against KIT, PDGFRs, vascular endothelial growth factor receptors (VEGFRs), and several other RTKs (1115). Sunitinib may exert antitumor activity in imatinib-resistant GIST by inhibiting imatinib-resistant RTK mutants and/or RTKs involved in tumor angiogenesis (including VEGFRs and PDGFRB). Here, we present the final analysis of safety, pharmacokinetics (PK), and clinical and biological activity of sunitinib in a phase I/II trial of GIST patients after imatinib failure due to resistance or intolerance, following earlier reports from this study (16, 17). These results supported both the subsequent randomized, placebo-controlled, phase III study that confirmed the clinical benefit of sunitinib (18) and multinational approval of sunitinib in this patient population (19).

Patients

Adults with histologically confirmed metastatic and/or unresectable GIST with documented imatinib failure due to resistance or intolerance were eligible for the study. Inclusion criteria included measurable disease, Eastern Cooperative Oncology Group performance status 0 to 2 (amended to 0 to 1), adequate nutritional and hematologic status, and adequate major organ function. Discontinuation of imatinib ≥2 wk before initiating sunitinib was required. The study was approved by the institutional review boards of the participating institutions; written informed consent was obtained from all patients.

Procedures

This was an open-label, single-arm, sequential cohort, dose-escalation phase I and early phase II trial to establish a phase II sunitinib dosing schedule based on safety, PK, and preliminary biological and clinical activity. Secondary objectives included doing [18F]fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET), histologic review, assessments of KIT phosphorylation and tumor cell proliferation, and tumor kinase genotyping to explore possible correlations with clinical activity. The relationship between kinase genotype and sunitinib activity in this study has been reported elsewhere (20).

Separate patient cohorts received sunitinib orally on one of three cyclical treatment schedules: Schedule 2/2 (2 wk on sunitinib, 2 wk off), Schedule 4/2 (4 wk on, 2 wk off), or Schedule 2/1 (2 wk on, 1 wk off). Schedule 2/2 dosing started at 25, 50, or 75 mg/d; Schedules 4/2 and 2/1 started at 50 mg/d. Patients experiencing clinical benefit [complete response (CR), partial response (PR), or stable disease (SD) ≥6 mo] at study end were eligible for extended treatment in a treatment continuation study.

Patients underwent regular physical examinations and evaluations of performance status, body weight, complete blood counts, and serum biochemistry. Cardiac monitoring included serial weekly measurements of cardiac troponin (TnT and/or TnI) and total creatinine kinase, electrocardiograms, and determination of left ventricular ejection fraction (by electrocardiogram or multigated acquisition scan) in each cycle. Adverse events were graded according to National Cancer Institute Common Toxicity Criteria, version 2.0 (21).

Tumor imaging and response assessments

Objective response was assessed by computed tomography (CT) or magnetic resonance imaging at baseline and the end of every even-numbered cycle. Disease status was assessed using Response Evaluation Criteria in Solid Tumors as CRs, PRs, SD, or progressive disease (PD; ref. 22). The results reported include follow-up through February 2005 and longer-term follow-up through March 2006 for patients on the treatment continuation study.

Tumor metabolic response was examined by FDG-PET on an ECAT Exact HR+ tomograph (Siemens/CTI). Serial FDG-PET scans were done in a fasting state 1 h following i.v. administration of FDG (15-20 mCi) at baseline, after the first 7 d of sunitinib dosing, at the end of cycle 1 dosing, and once during subsequent cycles.

Plasma drug concentrations

Plasma samples collected in K3EDTA were assayed to determinate concentrations of sunitinib and active metabolite SU12662 using a validated, sensitive, and specific liquid chromatographic tandem mass spectrophotometric method as previously described (23).

Histologic and correlative science studies

Tumor biopsy samples were collected at baseline and (with patient consent) at other time points for conventional histologic review and immunoblotting/immunohistochemical studies.

For immunoblotting studies, protein lysates were prepared from snap-frozen core biopsies as described previously (24). Protein concentrations were determined using the Bio-Rad Protein Assay (Bio-Rad Laboratories). Phosphorylated and total proteins were detected on immunoblots by enhanced chemiluminescence (Amersham), and chemiluminescence signals were captured and quantified using a FUJI LAS1000plus system with Science Lab 2001 ImageGauge 4.0 software (Fujifilm Medical Systems). Antibodies for immunoblotting analyses were polyclonal rabbit antibodies to phospho-KIT Y703 (Zymed Laboratories), polyclonal rabbit antibodies to phospho-AKT S473 (Cell Signaling), mouse monoclonal anti-p27 (clone 57; BD Transduction Laboratories), mouse monoclonal anti–cyclin A (clone 6E6; Novocastra), and polyclonal rabbit antibodies to total KIT (DAKO).

Immunohistochemical analysis of KIT was done using the rabbit polyclonal antibody A4502 (1:250; DAKO) and routine immunohistochemical methods without antigen retrieval (25). Tumor cell proliferation was assessed by detection of Ki67 using the MIB-1 antibody (monoclonal; 1:200; pressure cooker antigen retrieval; Immunotech).

Tumor genotyping

Primary and secondary KIT mutations were determined using PCR analysis of genomic DNA obtained from tumor biopsies as described (20).

Statistical analysis

All patients receiving at least one dose of sunitinib were included in these analyses. Descriptive statistics were used to summarize baseline characteristics, clinical responses, and adverse events. Time-to-event data were analyzed using Kaplan-Meier methods.

Patients and treatment

Between March 2002 and December 2003, 97 patients were enrolled in the treatment cohorts described in Materials and Methods as shown in Table 1. All patients had advanced GIST with bulky metastatic disease, including 94% with liver metastases. Patients had previously received imatinib at a median maximum dose of 600 mg/d. Prior imatinib failure was due to resistance in 96% of patients and intolerance in the remaining 4%. Table 1 provides additional baseline characteristics.

Table 1.

Baseline characteristics and clinical response to sunitinib treatment in patients with imatinib-resistant GIST

CharacteristicAll patients (N = 97), n (%)
Sex 
    Male 64 (66) 
    Female 33 (34) 
Age (y) 
    Median 55 
    Range 26-76 
ECOG performance status 
    0 50 (52) 
    1 41 (42) 
    2 6 (6) 
Time since original diagnosis (mo) 
    Median 33 
    Range 5-212 
Most common sites of metastatic GIST at study entry 
    Liver 91 (94) 
    Soft tissue 43 (44) 
    Peritoneum 42 (43) 
Total no. metastatic sites 
    1 5 (5) 
    2 17 (18) 
    ≥3 75 (77) 
Reason for discontinuing imatinib 
    Tumor progression 93 (96) 
    Intolerance 4 (4) 
Maximum daily dose of prior imatinib (mg) 
    Median 600 
    Range 400-1,000 
Duration of prior imatinib treatment (mo) 
    Median 19 
    Range 2-38 
Starting sunitinib dosing schedule 
    25 mg (Schedule 2/2) 6 (6) 
    50 mg (Schedule 2/2) 23 (24) 
    50 mg (Schedule 4/2) 55 (57) 
    50 mg (Schedule 2/1) 9 (9) 
    75 mg (Schedule 2/2) 4 (4) 
Tumor response to sunitinib 
    CR 0 (0) 
    PR 7 (7) 
    SD 73 (75) 
        ≥6 mo 28 (29) 
    PD 6 (6) 
    Not evaluable or missing 11 (11) 
Clinical benefit* 35 (36) 
CharacteristicAll patients (N = 97), n (%)
Sex 
    Male 64 (66) 
    Female 33 (34) 
Age (y) 
    Median 55 
    Range 26-76 
ECOG performance status 
    0 50 (52) 
    1 41 (42) 
    2 6 (6) 
Time since original diagnosis (mo) 
    Median 33 
    Range 5-212 
Most common sites of metastatic GIST at study entry 
    Liver 91 (94) 
    Soft tissue 43 (44) 
    Peritoneum 42 (43) 
Total no. metastatic sites 
    1 5 (5) 
    2 17 (18) 
    ≥3 75 (77) 
Reason for discontinuing imatinib 
    Tumor progression 93 (96) 
    Intolerance 4 (4) 
Maximum daily dose of prior imatinib (mg) 
    Median 600 
    Range 400-1,000 
Duration of prior imatinib treatment (mo) 
    Median 19 
    Range 2-38 
Starting sunitinib dosing schedule 
    25 mg (Schedule 2/2) 6 (6) 
    50 mg (Schedule 2/2) 23 (24) 
    50 mg (Schedule 4/2) 55 (57) 
    50 mg (Schedule 2/1) 9 (9) 
    75 mg (Schedule 2/2) 4 (4) 
Tumor response to sunitinib 
    CR 0 (0) 
    PR 7 (7) 
    SD 73 (75) 
        ≥6 mo 28 (29) 
    PD 6 (6) 
    Not evaluable or missing 11 (11) 
Clinical benefit* 35 (36) 

Abbreviation: ECOG, Eastern Cooperative Oncology Group.

*Defined as CR, PR, or SD ≥6 mo.

All 97 study patients received at least one sunitinib dose. Of these, 36 (37%) completed treatment (and entered the treatment continuation protocol) and 61 (63%) discontinued treatment: 47 (48%) due to lack of efficacy, 8 (8%) to adverse events, and 6 (6%) to withdrawal of consent. As of March 2006, patients had started a median of six cycles of treatment (range, 0-43) and had been on sunitinib for a median of 4.4 months (range, 0.3-24), excluding off-treatment periods. Treatment was interrupted in 59 patients (61%), and the dose was reduced in 13 patients (13%).

The maximum tolerated dose was identified as 50 mg/d after two of four patients treated at 75 mg/d on Schedule 2/2 experienced transient dose-limiting toxicities (DLT; fatigue, nausea, and vomiting) during cycle 1. Patients on 25 or 75 mg/d were switched to the 50-mg dose after one or two treatment cycles; successive patient cohorts on Schedules 4/2 and 2/1 received 50 mg/d. Schedule 4/2 at 50 mg/d was selected for phase II evaluation to maximize duration of sunitinib exposure following evidence of promising clinical activity with acceptable safety.

Clinical benefit and antitumor imaging response

By February 2005, clinical benefit from sunitinib was observed in 35 patients (36%): 7 (7%) with confirmed objective PRs and 28 (29%) with durable SD lasting ≥6 months (Table 1). Patients on Schedules 2/2 (50 mg/d) and 4/2 had clinical benefit rates of 48% and 31%, respectively. All 7 PRs and 21 of 28 durable SDs occurred in these two dosing groups. Clinical benefit rates in the remaining dosing groups [Schedules 2/2 (25 and 75 mg/d) and 2/1] ranged from 25% to 44%. Median time to objective response in patients who achieved PRs was 8.3 months (range, 3.7-12.0 months). In the overall study population, median progression-free survival was 7.8 months (95% confidence interval, 5.1-10.6 months).

With follow-up through March 2006, the number of patients obtaining clinical benefit increased to 52 (54%: 7 objective PRs, 45 durable SD). Median progression-free survival was 7.8 months (95% confidence interval, 5.1-10.4 months); median overall survival was 19.0 months (95% confidence interval, 12.9-21.5 months).

Sixty-seven patients (69%) had FDG-PET imaging data available from baseline and at least one postbaseline scan. Of 60 patients with data available on day 7 of cycle 1, FDG-PET revealed partial metabolic responses (PMR) to sunitinib in 43 patients (72%; Schedule 2/1, 5 of 7; Schedule 2/2, 22 of 31; Schedule 4/2, 16 of 22), as evidenced by a decline in maximum standardized uptake volume (SUVmax) of ≥25% relative to baseline (as defined by the European Organization for Research and Treatment of Cancer; ref. 26) and visualized as a marked decline in FDG avidity (Fig. 1A and B). With temporary cessation of sunitinib dosing during the first cycle, many patients whose tumors had shown decreased FDG avidity exhibited a rebound of metabolic activity followed by another decline in tracer uptake when dosing resumed (Fig. 1C and D). Early changes in tumor metabolism correlated with improved clinical outcome: most of the 43 patients with PMRs subsequently showed clinical benefit based on CT or magnetic resonance imaging scans, with 6 PRs and 25 SD ≥6 months by February 2005.

Fig. 1.

Sequential FDG-PET scans in a patient receiving sunitinib (Schedule 2/2) with corresponding CT scans at baseline and end cycle 2 dosing. A, baseline. B, cycle 1, day 7. C, cycle 1, day 28 (end of off-treatment period). D, cycle 2, day 14 (end of 2-wk dosing period).

Fig. 1.

Sequential FDG-PET scans in a patient receiving sunitinib (Schedule 2/2) with corresponding CT scans at baseline and end cycle 2 dosing. A, baseline. B, cycle 1, day 7. C, cycle 1, day 28 (end of off-treatment period). D, cycle 2, day 14 (end of 2-wk dosing period).

Close modal

PK analysis

Steady-state conditions were achieved by days 7 to 10 for sunitinib and by days 7 to 21 for SU12662 across all dosing schedules. At 50 mg/d, 79% of PK-evaluable patients (38 of 48) achieved total drug (sunitinib + SU12662) trough concentrations above 50 ng/mL by day 14, with 33% (13 of 40) achieving this within the first 7 days. Median trough concentrations of total drug at 50 mg/d were in the range of 48 to 63 ng/mL on Schedule 2/1, 32 to 47 ng/mL on Schedule 2/2, and 38 to 66 ng/mL on Schedule 4/2 over the remainder of the dosing period (day 7 to days 14 or 28).

Increasing exposure seemed to correlate with increased DLTs. At 75 mg/d on day 14, the median total drug trough concentration was 93.4 ng/mL, with the two patients who experienced DLTs having concentrations of 107 and 102 ng/mL. One patient who experienced a DLT (diarrhea) at 50 mg/d had a trough concentration of 84.0 ng/mL on day 14.

Cellular and molecular analyses of GIST lesions

Forty-eight patients (49%) had matched baseline (post-imatinib, pre-sunitinib) and post-sunitinib biopsies. In 11 additional patients, either the pre- or post-sunitinib biopsy contained no demonstrable tumor.

Before sunitinib dosing, the biopsies showed KIT expression in 43 cases (90%; example shown in Fig. 2), whereas 5 cases were KIT negative; 4 of the latter cases had very limited biopsy material, raising the possibility of sampling error. Three post-sunitinib biopsies were KIT negative, although the corresponding pre-sunitinib biopsies had been KIT positive. However, in the majority of tumors, changes in KIT expression (if any) were subtle (Fig. 2).

Fig. 2.

Biopsy specimens stained with H&E (top) or analyzed by immunohistochemistry (IHC) using an anti-KIT antibody (bottom) show little, if any, difference before and after 1 wk of sunitinib treatment.

Fig. 2.

Biopsy specimens stained with H&E (top) or analyzed by immunohistochemistry (IHC) using an anti-KIT antibody (bottom) show little, if any, difference before and after 1 wk of sunitinib treatment.

Close modal

Tumor cell proliferation, assessed by MIB-1 antibody detection of Ki67, was reduced by >25% in 25 cases (52%) after 1 week of sunitinib treatment (example shown in Fig. 3). In 13 cases (27%), the MIB-1 score was relatively unchanged; in 10 cases (21%), it increased by >25%.

Fig. 3.

Detection of Ki67 in a GIST biopsy specimen by MIB-1 immunohistochemical staining at baseline and after 1 wk of sunitinib treatment indicates a decline in tumor cell proliferation.

Fig. 3.

Detection of Ki67 in a GIST biopsy specimen by MIB-1 immunohistochemical staining at baseline and after 1 wk of sunitinib treatment indicates a decline in tumor cell proliferation.

Close modal

Sufficient material for immunoblotting assays was obtained from 28 patients with matched pre- and post-sunitinib biopsies. Nine of these matched sets showed reduced levels of phospho-KIT after 1 week of sunitinib treatment accompanied by changes in the phosphorylation or expression of proteins involved in cell proliferation (AKT, cyclin A, and p27) that were consistent with growth inhibition (examples shown in Fig. 4). Eight patients had matched biopsy sets with no evidence of response by immunoblotting, and biopsies from 11 patients were inevaluable because either the pre- or post-sunitinib biopsy was judged to represent residual tumor with few viable GIST cells. Of the two patients for whom immunoblotting results are shown in Fig. 4A, patient 14 had a primary KIT exon 9 mutation without detectable secondary mutations at the time of study entry and achieved an objective PR. In patient 2, in addition to a primary KIT exon 11 V560D mutation, a supraclavicular metastasis had a secondary exon 13 V654A imatinib resistance mutation (which involves the kinase ATP-binding pocket), whereas a hepatic metastasis had a different imatinib resistance mutation (exon 17 D816H) involving the activation loop domain. This patient had SD as best response, but the hepatic metastasis progressed within 4 months, whereas the supraclavicular GIST lesion continued to be well controlled on sunitinib.

Fig. 4.

A, activation of KIT signaling pathway components in GISTs, shown by immunoblotting before and after sunitinib treatment as indicated. Decline in phospho-KIT is accompanied by inhibition of the survival protein AKT, decreased expression of the cyclin A proliferation protein, and increased expression of the p27 antiproliferation protein in sunitinib-sensitive tumors [patient (Pt) 2, supraclavicular (supraclav.) metastasis; patient 14, lesion]. This pattern is reversed in a progressing lesion (patient 2, hepatic metastasis). In contrast, actin expression is not affected by sunitinib treatment. B, decline in phospho-KIT shown by immunohistochemistry after 1 wk of sunitinib treatment.

Fig. 4.

A, activation of KIT signaling pathway components in GISTs, shown by immunoblotting before and after sunitinib treatment as indicated. Decline in phospho-KIT is accompanied by inhibition of the survival protein AKT, decreased expression of the cyclin A proliferation protein, and increased expression of the p27 antiproliferation protein in sunitinib-sensitive tumors [patient (Pt) 2, supraclavicular (supraclav.) metastasis; patient 14, lesion]. This pattern is reversed in a progressing lesion (patient 2, hepatic metastasis). In contrast, actin expression is not affected by sunitinib treatment. B, decline in phospho-KIT shown by immunohistochemistry after 1 wk of sunitinib treatment.

Close modal

Safety

DLTs (predominantly nausea, fatigue, and vomiting) were documented primarily at the 75-mg sunitinib dose level; otherwise, treatment-related adverse events were generally mild to moderate in severity, the most common of which were fatigue, diarrhea, and nausea (Table 2). Grade 3 or 4 increases in lipase occurred in 13% of patients; these events were generally asymptomatic, although one patient experienced clinical symptoms of pancreatitis. Thirty-seven percent of patients experienced hand-foot syndrome.

Table 2.

Treatment-related adverse events occurring in ≥10% of patients

Adverse eventAny grade, n (%)Grade 3 or 4, n (%)
Fatigue 59 (61) 10 (10) 
Diarrhea 51 (53) 7 (7) 
Nausea 38 (39) 3 (3) 
Skin discoloration 37 (38) 0 (0) 
Hand-foot syndrome 36 (37) 7 (7) 
Hypertension 28 (29) 16 (16) 
Stomatitis 28 (29) 2 (2) 
Asymptomatic increase in lipase* 26 (27) 13 (13) 
Vomiting 20 (21) 1 (1) 
Dermatitis 19 (20) 0 (0) 
Increased serum creatinine phosphokinase 18 (19) 1 (1) 
Taste disturbance 18 (19) 0 (0) 
Hypothyroidism 17 (18) 0 (0) 
Dyspepsia 15 (15) 1 (1) 
Increased serum amylase 15 (15) 4 (4) 
Anemia 14 (14) 3 (3) 
Flatulence 14 (14) 0 (0) 
Headache 14 (14) 2 (2) 
Decreased hemoglobin 13 (13) 3 (3) 
Glossodynia 13 (13) 0 (0) 
Limb pain 13 (13) 0 (0) 
Decreased leukocyte count 12 (12) 3 (3) 
Hair color changes 11 (11) 0 (0) 
Paresthesia 11 (11) 0 (0) 
Abdominal pain 10 (10) 3 (3) 
Anorexia 10 (10) 1 (1) 
Decreased neutrophil count 10 (10) 4 (4) 
Adverse eventAny grade, n (%)Grade 3 or 4, n (%)
Fatigue 59 (61) 10 (10) 
Diarrhea 51 (53) 7 (7) 
Nausea 38 (39) 3 (3) 
Skin discoloration 37 (38) 0 (0) 
Hand-foot syndrome 36 (37) 7 (7) 
Hypertension 28 (29) 16 (16) 
Stomatitis 28 (29) 2 (2) 
Asymptomatic increase in lipase* 26 (27) 13 (13) 
Vomiting 20 (21) 1 (1) 
Dermatitis 19 (20) 0 (0) 
Increased serum creatinine phosphokinase 18 (19) 1 (1) 
Taste disturbance 18 (19) 0 (0) 
Hypothyroidism 17 (18) 0 (0) 
Dyspepsia 15 (15) 1 (1) 
Increased serum amylase 15 (15) 4 (4) 
Anemia 14 (14) 3 (3) 
Flatulence 14 (14) 0 (0) 
Headache 14 (14) 2 (2) 
Decreased hemoglobin 13 (13) 3 (3) 
Glossodynia 13 (13) 0 (0) 
Limb pain 13 (13) 0 (0) 
Decreased leukocyte count 12 (12) 3 (3) 
Hair color changes 11 (11) 0 (0) 
Paresthesia 11 (11) 0 (0) 
Abdominal pain 10 (10) 3 (3) 
Anorexia 10 (10) 1 (1) 
Decreased neutrophil count 10 (10) 4 (4) 

*Grade 3/4 lipase increase was accompanied by pancreatitis in one patient.

Cardiovascular events included hypertension (>150/100 mmHg per National Cancer Institute Common Toxicity Criteria version 2.0), which was detected in 52% of patients and reported as a treatment-related adverse event in 29%, and left ventricular ejection fraction below the lower limit of normal (as measured using multigated acquisition scans) in 14% of patients. Left ventricular ejection fraction declines were generally reversible with medical management; however, some patients showed transient elevations in serum TnI levels, generally without symptoms. Two patients developed signs or symptoms of myocardial infarction (electrocardiogram changes with new Q waves and/or TnI elevation with accompanying chest pain or ischemic ST-T wave changes).

Hypothyroidism was reported as a treatment-related adverse event in a subset of patients (18%) with prolonged sunitinib dosing and was managed with thyroid hormone replacement therapy.

Eleven patients died within 30 days of their last sunitinib dose, and 1 patient died afterwards on follow-up; none of these events were considered to be treatment related.

This study shows that sunitinib has biological and clinical activity across multiple dosing schedules in GIST patients after imatinib failure. Without exception, the patients in this trial had advanced metastases with bulky disease progressing at the time of study entry. Although only a small subset exhibited tumor shrinkage after initiation of sunitinib treatment, 54% ultimately received clinical benefit (objective response or durable SD). In the majority of patients, reduced tumor glycolytic activity was evident on FDG-PET imaging within 1 week of starting sunitinib. Overall, 43 of 60 patients (72%) who had FDG-PET imaging on day 7 of cycle 1 (when concentrations of sunitinib and its metabolite were approaching steady state) achieved PMRs, with reductions in tumor SUVmax of ≥25% relative to baseline. As defined in European Organization for Research and Treatment of Cancer guidelines in 1999 (26), acceptable SUVmax cutoffs for PMRs in the first cycle of treatment range from 15% to 25%, with the latter value being the currently recognized standard. In contrast to PMRs, objective responses on CT took much longer to detect and evolved over several months, similar to the pattern observed in studies of imatinib-treated GIST patients (5, 6, 27). Moreover, early PMRs correlated with improved clinical outcome: 31 of the 43 patients with PMRs experienced clinical benefit as determined subsequently by CT. This is also similar to what has been reported in studies of first-line treatment with imatinib, in which early metabolic responses have been found to correlate with subsequent anatomic responses (5, 27).

KIT expression in most GISTs analyzed (94%) was unaffected after 10 days of sunitinib therapy. Nevertheless, in 32% of cases analyzed, levels of phospho-KIT were reduced after 1 week of sunitinib treatment, indicating effective target modulation. Moreover, these changes were accompanied by changes in the activity or expression of proteins involved in cell proliferation (AKT, cyclin A, and p27) consistent with growth inhibition. These results correlated both with previous preclinical observations (11) and with the observation that, after 1 week of sunitinib therapy, tumor cell proliferation was reduced by >25% in 52% of cases. They also correlated with clinical outcome in several cases, such as the two cases presented in Fig. 4, although correlations between KIT signaling pathway changes and clinical outcome were not formally assessed. Taken together, the results suggest that sunitinib clinical activity may be associated with inhibition of KIT kinase activity, although a direct causal link remains to be established.

Results of this study showed that as early as day 7, steady-state conditions of sunitinib and active metabolite SU12662 were achieved across all dosing schedules. By day 14, 79% of patients on 50 mg/d had achieved total drug trough concentrations above 50 ng/mL, the concentration providing target RTK inhibition in preclinical studies (12). Dose responses were observed in terms of both efficacy and safety.

Overall, sunitinib treatment was associated with acceptable safety in these patients with advanced metastatic GIST. In most patients, adverse events were mild to moderate in severity, most commonly constitutional symptoms such as nausea, vomiting, diarrhea, and fatigue or skin toxicities such as skin discoloration and hand-foot syndrome. DLTs (fatigue, nausea, and vomiting) were seen primarily at 75 mg/d, leading to selection of 50 mg/d as the recommended phase II dose, consistent with other sunitinib dose-finding studies (28, 29). Schedule 4/2 was selected for further phase II evaluation to maximize duration of sunitinib exposure following evidence of promising clinical activity with acceptable safety.

Hypertension, known to be a class effect of angiogenesis inhibitors (30), was detected in 52% of patients and was managed with conventional antihypertensive medications. Decreased cardiac function, when observed, generally reversed after sunitinib discontinuation or dose reduction, along with addition of agents such as angiotensin-converting enzyme inhibitors, β-blocking agents, and/or diuretics. Cardiovascular toxicities that occurred among the 75 patients at one of the participating institutions in this study have been examined in more detail and reported elsewhere (31).

Hypothyroidism, reported as a treatment-related adverse event in 18% of patients in this study, is now known to be associated with long-term sunitinib therapy (19, 32) and is manageable through thyroid hormone replacement therapy. The mechanism has yet to be determined, although inhibition of iodine uptake, peroxidase activity, and VEGFR within the thyroid are among several that have been proposed (3234).

In conclusion, inhibition of multiple RTKs with sunitinib in GIST patients following imatinib failure was achieved with acceptable safety and promising evidence of antitumor activity. Based on the results of this study, a randomized, double-blind, placebo-controlled phase III study was conducted to evaluate the efficacy of sunitinib (50 mg/d, Schedule 4/2) in imatinib-resistant/intolerant GIST patients, and the interim results were positive (18), resulting in multinational approval of sunitinib for the treatment of this patient population (19). Additional research is needed to elucidate the specific mechanisms underlying the activity of sunitinib; it is unclear whether sunitinib inhibits different conformations of mutant KIT or PDGFRA more potently than imatinib or whether inhibition of other RTKs, such as the VEGFRs, accounts for this activity in imatinib-resistant GIST. Further research on the effects of primary and secondary tumor kinase mutations on GIST response to sunitinib may provide important insights on which to improve the clinical outcomes of GIST patients after imatinib failure as well as other kinase-driven malignancies.

C.L. Bello, X. Huang, D.P. Cohen, and C.M. Baum: employment and ownership interest, Pfizer. G.D. Demetri: commercial research grants, Pfizer, Novartis, Bristol-Myers Squibb, Infinity, and Exelixis; honoraria, Pfizer, Novartis, Bayer, and Infinity. M.C. Heinrich: commercial research grants, Pfizer and Novartis; ownership interest, Molecular MD; honoraria, Pfizer and Novartis; other, Pfizer, Novartis, and Molecular MD. R.G. Maki: commercial research grants, Pfizer, Novartis, and Roche; honoraria, Novartis. C.L. Corless: commercial research grant, Novartis; honoraria, Novartis. M.H. Chen: other, Bayer/Onyx.

We thank all the patients, families, and advocates who supported this work for their generous participation and encouragement and the teams of physicians, research nurses, study coordinators, and other collaborators at each of the participating institutions: M. St. Amand; L. Yiankos; M. Pevear; R. Photopoulos; K. Polson; M.T. Quigley; J. Jackson; A. Kazanovicz; J. Desai, M.D.; P. Dileo, M.D.; J. Yap, Ph.D.; Y. Melenevsky, M.D.; D.J. de Vries, Ph.D.; R. Badawi, Ph.D.; R. Tetrault, M.S. CNMT; J. Manola; S. Silverman, M.D.; K. Tuncali, M.D.; D. Ryan, M.D.; D. Harmon, M.D.; L. Blaszkowsky, M.D.; A. Zhu, M.D.; M. Thyne; L. Yu; K. Savage; D. Collins; P. Harrell; L. McGreevey; A. Town; J. Morich; D. D'Adamo, M.D., Ph.D.; M.L. Keohan, M.D.; K. Scheu; R. Vallury; A.-M. Martino; V. Tassell; M. Collier; Z. Aguilar, Ph.D.; J. Cherrington, Ph.D.; W. Manning, Ph.D.; J. McMahon, Ph.D.; P. Scigalla, M.D.; R. Allred, Ph.D.; L. Strawn, Ph.D.; and W. Sargent, Ph.D. Medical writing services were provided by B. Janas, Ph.D., as well as ACUMED (Tytherington, United Kingdom) with funding from Pfizer, Inc.

1
Corless
CL
,
Fletcher
JA
,
Heinrich
MC
. 
Biology of gastrointestinal stromal tumors
.
J Clin Oncol
2004
;
22
:
3813
25
.
2
Heinrich
MC
,
Corless
CL
,
Duensing
A
, et al
. 
PDGFRA activating mutations in gastrointestinal stromal tumors
.
Science
2003
;
299
:
708
10
.
3
Hirota
S
,
Ohashi
A
,
Nishida
T
, et al
. 
Gain-of-function mutations of platelet-derived growth factor receptor α gene in gastrointestinal stromal tumors
.
Gastroenterology
2003
;
125
:
660
7
.
4
Rubin
BP
,
Singer
S
,
Tsao
C
, et al
. 
KIT activation is a ubiquitous feature of gastrointestinal stromal tumors
.
Cancer Res
2001
;
61
:
8118
21
.
5
Demetri
GD
,
von Mehren
M
,
Blanke
CD
, et al
. 
Efficacy and safety of imatinib mesylate in advanced gastrointestinal stromal tumors
.
N Engl J Med
2002
;
347
:
472
80
.
6
Verweij
J
,
Casali
PG
,
Zalcberg
J
, et al
. 
Progression-free survival in gastrointestinal stromal tumours with high-dose imatinib: randomised trial
.
Lancet
2004
;
364
:
1127
34
.
7
Debiec-Rychter
M
,
Cools
J
,
Dumez
H
, et al
. 
Mechanisms of resistance to imatinib mesylate in gastrointestinal stromal tumors and activity of the PKC412 inhibitor against imatinib-resistant mutants
.
Gastroenterology
2005
;
128
:
270
9
.
8
Heinrich
MC
,
Corless
CL
,
Blanke
CD
, et al
. 
Molecular correlates of imatinib resistance in gastrointestinal stromal tumors
.
J Clin Oncol
2006
;
24
:
4764
74
.
9
Chen
LL
,
Trent
JC
,
Wu
EF
, et al
. 
A missense mutation in KIT kinase domain 1 correlates with imatinib resistance in gastrointestinal stromal tumors
.
Cancer Res
2004
;
64
:
5913
9
.
10
Antonescu
CR
,
Besmer
P
,
Guo
T
, et al
. 
Acquired resistance to imatinib in gastrointestinal stromal tumor occurs through secondary gene mutation
.
Clin Cancer Res
2005
;
11
:
4182
90
.
11
Abrams
TJ
,
Lee
LB
,
Murray
LJ
, et al
. 
SU11248 inhibits KIT and platelet-derived growth factor receptor β in preclinical models of human small cell lung cancer
.
Mol Cancer Ther
2003
;
2
:
471
8
.
12
Mendel
DB
,
Laird
AD
,
Xin
X
, et al
. 
In vivo antitumor activity of SU11248, a novel tyrosine kinase inhibitor targeting vascular endothelial growth factor and platelet-derived growth factor receptors: determination of a pharmacokinetic/pharmacodynamic relationship
.
Clin Cancer Res
2003
;
9
:
327
37
.
13
O'Farrell
AM
,
Abrams
TJ
,
Yuen
HA
, et al
. 
SU11248 is a novel FLT3 tyrosine kinase inhibitor with potent activity in vitro and in vivo
.
Blood
2003
;
101
:
3597
605
.
14
Murray
LJ
,
Abrams
TJ
,
Long
KR
, et al
. 
SU11248 inhibits tumor growth and CSF-1R-dependent osteolysis in an experimental breast cancer bone metastasis model
.
Clin Exp Metastasis
2003
;
20
:
757
66
.
15
Kim
DW
,
Jo
YS
,
Jung
HS
, et al
. 
An orally administered multi-target tyrosine kinase inhibitor, SU11248, is a novel potent inhibitor of thyroid oncogenic RET/PTC kinases
.
J Clin Endocrin Metab
2006
;
91
:
4070
6
.
16
Demetri
GD
,
George
S
,
Heinrich
MC
, et al
. 
Clinical activity and tolerability of the multi-targeted tyrosine kinase inhibitor SU11248 in patients (pts) with metastatic gastrointestinal stromal tumor (GIST) refractory to imatinib mesylate [abstract 3273]
.
Proc Am Soc Clin Oncol
2003
;
22
:
814
.
17
Maki
RG
,
Fletcher
JA
,
Heinrich
MC
, et al
. 
Results from a continuation trial of SU11248 in patients with imatinib-resistant gastrointestinal stromal tumor (GIST) [abstract 9011]
.
J Clin Oncol
2005
;
23
:
818s
.
18
Demetri
GD
,
van Oosterom
AT
,
Garrett
CR
, et al
. 
Efficacy and safety of sunitinib in patients with advanced gastrointestinal stromal tumour after failure of imatinib: a randomised controlled trial
.
Lancet
2006
;
368
:
1329
38
.
19
SUTENT® (sunitinib malate) full prescribing information
.
New York (NY)
:
Pfizer, Inc.
; 
2008
.
20
Heinrich
MC
,
Maki
RG
,
Corless
CL
, et al
. 
Primary and secondary kinase genotypes correlate with the biological and clinical activity of sunitinib in imatinib-resistant gastrointestinal stromal tumor
.
J Clin Oncol
2008
;
26
:
5352
9
.
21
Cancer Therapy Evaluation Program. Common Toxicity Criteria (CTC) version 2.0
.
Bethesda (MD)
:
National Cancer Institute
; 
1999
.
22
Therasse
P
,
Arbuck
SG
,
Eisenhauer
EA
, et al
. 
New guidelines to evaluate the response to treatment in solid tumors. European Organization for Research and Treatment of Cancer, National Cancer Institute of the United States, National Cancer Institute of Canada
.
J Natl Cancer Inst
2000
;
92
:
205
16
.
23
O'Farrell
AM
,
Foran
JM
,
Fiedler
W
, et al
. 
An innovative phase I clinical study demonstrates inhibition of FLT3 phosphorylation by SU11248 in acute myeloid leukemia patients
.
Clin Cancer Res
2003
;
9
:
5465
76
.
24
Duensing
A
,
Joseph
NE
,
Medeiros
F
, et al
. 
Protein kinase Cθ (PKCθ) expression and constitutive activation in gastrointestinal stromal tumors (GISTs)
.
Cancer Res
2004
;
64
:
5127
31
.
25
Hornick
JL
,
Fletcher
CD
. 
Immunohistochemical staining for KIT (CD117) in soft tissue sarcomas is very limited in distribution
.
Am J Clin Pathol
2002
;
117
:
188
93
.
26
Young
H
,
Baum
R
,
Cremerius
U
, et al
. 
Measurement of clinical and subclinical tumour response using [18F]-fluorodeoxyglucose and positron emission tomography: review and 1999 EORTC recommendations
.
Eur J Cancer
1999
;
35
:
1773
82
.
27
Stroobants
S
,
Goeminne
J
,
Seegers
M
, et al
. 
18FDG-positron emission tomography for the early prediction of response in advanced soft tissue sarcoma treated with imatinib mesylate (Glivec)
.
Eur J Cancer
2003
;
39
:
2012
20
.
28
Rosen
L
,
Mulay
M
,
Wittner
J
, et al
. 
Phase I trial of SU11248, a novel tyrosine kinase inhibitor in advanced solid tumors [abstract 765]
.
Proc Am Soc Clin Oncol
2003
;
22
:
191a
.
29
Faivre
S
,
Delbaldo
C
,
Vera
K
, et al
. 
Safety, pharmacokinetic, and antitumor activity of SU11248, a novel oral multitarget tyrosine kinase inhibitor, in patients with cancer
.
J Clin Oncol
2006
;
24
:
25
35
.
30
Sica
DA
. 
Angiogenesis inhibitors and hypertension: an emerging issue
.
J Clin Oncol
2006
;
24
:
1329
31
.
31
Chu
TF
,
Rupnick
MA
,
Kerkela
R
, et al
. 
Cardiotoxicity associated with tyrosine kinase inhibitor sunitinib
.
Lancet
2007
;
370
:
2011
9
.
32
Desai
J
,
Yassa
L
,
Marqusee
E
, et al
. 
Hypothyroidism after sunitinib treatment for patients with gastrointestinal stromal tumors
.
Ann Intern Med
2006
;
145
:
660
4
.
33
Mannavola
D
,
Coco
P
,
Vannucchi
G
, et al
. 
A novel tyrosine-kinase selective inhibitor, sunitinib, induces transient hypothyroidism by blocking iodine uptake
.
J Clin Endocrinol Metab
2007
;
92
:
3531
4
.
34
Wong
E
,
Rosen
LS
,
Mulay
M
, et al
. 
Sunitinib induces hypothyroidism in advanced cancer patients and may inhibit thyroid peroxidase activity
.
Thyroid
2007
;
17
:
351
5
.
35
Rini
BI
,
Tamaskar
I
,
Shaheen
P
, et al
. 
Hypothyroidism in patients with metastatic renal cell carcinoma treated with sunitinib
.
J Natl Cancer Inst
2007
;
99
:
81
3
.

Competing Interests

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.

Supplementary data