BALL-1, a human B leukemia/lymphoma cell line, was transplanted into nude and SCID mice under various conditions. The transplantation was substantially improved by preadaptation of BALL-1 by serial passages in newborn and young nude mice. We were able to establish the desirable conditions where 100% of SCID and nude mice that were inoculated i.p. with various doses of the adapted BALL-1 (termed BALL-1a) developed tumors. Tumors in SCID mice were disseminated to various tissues in a manner analogous to tumors in patients with B leukemia/lymphoma, whereas tumors in nude mice were not as widely disseminated and grew mainly as ascites. Flow cytometric analyses showed that all of the 11 tested cell surface markers of the parental BALL-1 were well maintained on the tumor cells recovered from the SCID and nude mice.

The utility of the developed tumor models for the therapeutic studies was investigated by i.p. or i.v. administration of an anti-B leukemia/lymphoma monoclonal antibody, termed SN7 (IgG1κ), and SN7 immunotoxin (IT) that was prepared by conjugating SN7 to ricin A chain (RA) or deglycosylated RA (dgRA). In the nude mouse model study, SN7-RA that had been administered i.p. suppressed the tumor growth completely in all of the treated mice (n = 5) without any sign of tumor or undesirable side effects for as long as followed (i.e., 350 days), whereas unconjugated SN7 showed only a slight therapeutic effect. A control RA conjugate was not effective. In the SCID mouse model studies, several sets of experiments were carried out by i.p. or i.v. administration of IT, monoclonal antibody, or control IT. In the first three sets of experiments, SCID mice inoculated with 1.1 × 106 BALL-1a cells received an i.p. administration of phosphate-buffered saline or three different doses (i.e., 4 × 10 µg, 4 × 20 µg, and 4 × 30 µg) of therapeutic agents (SN7-RA and SN7). Virtually an identical result was obtained from the three experiments. All of the phosphate-buffered saline control group mice (n = 15) died within 35 days post tumor inoculation. In contrast, all of the mice that were treated with SN7-RA (n = 19) or with SN7 (n = 15) survived for as long as followed (i.e., 250 days). However, the unconjugated SN7 was less effective than SN7 IT for tumor suppression in SCID mice that were inoculated with a larger tumor burden (i.e., 4 × 107 BALL-1a cells). The efficacy of SN7 and SN7 IT in the SCID mouse model was further studied by the systemic i.v. administration of the therapeutic agents. The i.v. therapy experiments were carried out using SN7 IT and control IT containing dgRA. In the first two sets of the experiments, therapy of SCID mice that were inoculated i.p. with 1.1 × 106 tumor cells was initiated one day post tumor inoculation by i.v. administration of different doses (i.e., a total of 120 and 80 µg, respectively) of the therapeutic agents. In each experiment, all of the mice (n = 6 and 7) that were treated with SN7-dgRA survived for as long as followed (i.e., 200 and 140 days, respectively). Of the mice that were treated with 120 and 80 µg, respectively, unconjugated SN7, 66.7% (n = 6) and 42.9% (n = 7) survived. In the third i.v. therapy experiment, the dose of SN7-dgRA was reduced to a total of 60 µg (i.e., 3 × 20 µg), and the initiation of the therapy with SN7-dgRA was delayed until 2 days or 3 days post tumor inoculation. All of the IT-treated mice (n = 8) survived for 110 days. Thus, the i.v. administered SN7-dgRA induced complete tumor suppression in all of the treated mice for as long as followed. In addition, the i.v.-injected unconjugated SN7 was effective for tumor suppression, although it is less effective than SN7-dgRA.

The present results demonstrate that SN7 IT is highly effective for tumor suppression in both animal models by i.p. or i.v. administration. Unconjugated SN7 was only marginally effective for tumor suppression in nude mice but strongly effective in SCID mice.

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This work was supported by ACS Grant CH-514.

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