Abstract LB-393: The cancer metabolism inhibitor MPC-9528 induces tumor regression in xenograft models with multiple dosing schedules by causing rapid and sustained reduction in tumor NAD

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Introduction : MPC-9528 is a potent, selective, orally bioavailable inhibitor of nicotinamide phosphoribosyltransferase (Nampt), which catalyzes the rate-limiting step for NAD biosynthesis from nicotinamide. Inhibition of Nampt by MPC-9528 results in cell death as a consequence of NAD depletion and inhibition of ATP synthesis. MPC-9528 is a potent tumoricidal agent of cancer cell lines of diverse origin and shows anti-tumor activity in multiple xenograft models. Here we explore the determinants of efficacy in xenograft models by comparing the effects of MPC-9528 oral dosing schedules in terms of both tumor NAD depletion and survival. Methods : HT1080 human fibrosarcoma cells were implanted subcutaneously into athymic mice (nu/nu) for tumor studies. Dosing was initiated when median tumor volume was >100 mm3. MPC-9528 was dosed orally, either once weekly, once daily, or twice daily, for a total of two or three weeks. For pharmacodynamic (PD) studies, animals were dosed with MPC-9528 and tumors were collected at various times post-dosing for NAD determination by LC-MS/MS. Results : MPC-9528 (75 mg/kg) dosed once weekly for three weeks in a HT1080 xenograft model resulted in 75% tumor regression on study Day 23, 8 days after the last dose. The ED50 for anti-tumor activity with this schedule was 44 mg/kg and doses at or below 35 mg/kg showed no anti-tumor activity. All doses were equally well-tolerated with <10% change in median body weight. In the same model, MPC-9528 dosed once daily at 10 mg/kg or twice daily at 3 mg/kg for 14 days showed 91% and 92% tumor regression, respectively, by the end of dosing on study Day 15. Two animals in each of the MPC-9528 dose groups showed complete tumor regression. MPC-9528 (4 mg/kg) dosed twice daily resulted in complete tumor regression in 9 out of 10 animals. The plasma concentration versus time profiles of MPC-9528 dosed at 3, 10 or 75 mg/kg indicated that anti-tumor activity was not dependent on maximal concentration of the compound in blood or the total absorbed dose but rather on maintenance of compound concentration above a threshold efficacious concentration. PD studies revealed a rapid and sustained reduction of NAD in tumors from mice dosed with MPC-9528 and that the magnitude and kinetics of NAD change depended on the dose and schedule. Conclusions : MPC-9528 administration results in regression of tumors when plasma concentrations of compound are maintained above a threshold. MPC-9528 shows comparable efficacy when given intermittently, on a weekly schedule, or continuously on a once, or twice daily schedule. This unique attribute of MPC-9528 reflects its mechanism of action as a cell metabolism inhibitor that functions by inhibiting NAD synthesis in tumor cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-393. doi:10.1158/1538-7445.AM2011-LB-393