JNJ-26483327 is a novel oral Pan Her/Src/VEGFR-3 inhibitor which has previously been shown in preclinical models to cross the blood-brain barrier and to reach high levels in brain, solid tumor, and bone marrow sites. JNJ-26483327 is not an active substrate for P-glycoprotein pumps and has been well tolerated to date in an ongoing phase I trial. VEGF-C signaling through the VEGFR-3 (FLT-4) receptor has been shown to promote growth of acute myeloid leukemia (AML) cells and to mediate resistance to multiple chemotherapy drugs in vitro. Anti-VEGFR-3 antibody therapy decreased angiogenesis, increased hypoxia and necrosis, and reduced lymph node metastases in solid tumor xenografts. To date, however, VEGF-C/VEGFR-3 inhibition has not been actively been investigated for treatment of hematological malignancies. We hypothesized that JNJ- 26483327 treatment of VEGFR-3 expressing systemic AML would limit tumor growth and lymphatic spread via VEGF-C/VEGFR-3 mechanisms. An initial dose-finding pilot experiment was performed using SCID mice engrafted via tail vein with ten million HELluc cells, human acute myeloid leukemia cells with known expression of VEGF-A/C and VEGFR-2/3 and stably transfected with luciferase constructs to facilitate small animal imaging. Mice were treated with PBS, vehicle (200 mL by mouth twice daily), low dose JNJ-26483327 (75 mg/kg by mouth twice daily, total 150 mg/kg/day) and high dose JNJ- 26483327 (125 mg/kg by mouth daily, total 250 mg/kg/day) for 10 consecutive days. We found that low dose JNJ-26483327 therapy significantly improved the median survival of HELluc systemic xenografts by 46% (26 days longer than vehicle-treated controls) (p<0.05). Although high dose JNJ-26483327 prolonged median survival over vehicletreated controls, the difference was not statistically significant. Moreover, although JNJ- 26483327 improved survival, HELluc leukemia burden (as measured by bioluminescent imaging) was not significantly reduced or eradicated as compared to control, consistent with cytostatic but not cytotoxic anti-tumor effects. VEGFR-3 signaling has also been shown to mediate leukemia cell proliferation, survival, and resistance to chemotherapy. Based on preclinical and clinical data demonstrating improved anti-tumor activity of VEGF inhibitors when combined with chemotherapy, we hypothesized that combining JNJ-26483327 with chemotherapy used in conventional AML therapy may result in additive synergistic anti-tumor effects. To determine if JNJ-26483327 inhibition enhanced the effects of cytotoxic chemotherapy, systemic HELluc tumor bearing mice were treated with low dose JNJ-26483327 (150 mg/kg/day for 10 days) and a single maximally tolerated dose of doxorubicin (1.5mg/kg). Both single agent doxorubicin and single agent JNJ-26483327 treatment resulted in significant reduction of HELluc tumor burden. However, no significant decrease in leukemia burden was observed after combination JNJ-26483327+doxorubicin treatment when compared to single agent groups. Lastly we postulated that combination therapies of JNJ-26483327 with other anti-VEGF therapies directed at inhibition of VEGF-A, VEGFR-1, or VEGFR-2 would result in inhibition of all known VEGFR signaling pathways and result in improved anti-leukemic effects of JNJ-26483327 therapy. Systemic HELluc bearing mice were treated with PBS, vehicle, low dose JNJ-26483327, an anti-hVEGF-A antibody BV (bevacizumab, Genentech) or combination JNJ-26483327+ BV. Results showed that single agent low dose JNJ- 26483327 or single agent BV significantly reduced HELluc tumor burden up until day 20. Combination JNJ-26483327+BV treatment, however, did not result in additive/synergistic anti-leukemic effects as compared to single agent therapy and may in fact have resulted in possible antagonistic effects.

Conclusions: Single agent JNJ-26483327 therapy prolongs survival of mice engrafted with VEGFR-3+ HEL AML cells. Limitations of the above studies include the short duration of JNJ-26483327 administration (10 days only) and lack of synergistic effects of JNJ-26483327 when combined with doxorubicin and anti-hVEGF-A antibody therapy. Future studies will address the effects of long-term JNJ-26483327 administration on AML stem cell growth using NOD/SCID mouse models engrafted with patient samples and combination JNJ-26483327+ cytarabine/anthracycline chemotherapy.

Disclosures: King:Ortho Biotech: Employment. Freyne:Ortho Biotech: Employment. Perera:Ortho Biotech: Employment.

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