Adam Willardsen

Discovery of a new HIV-1 inhibitor scaffold and synthesis of potential prodrugs of indazoles

A new oxazole scaffold showing great promise in HIV-1 inhibition has been discovered by cell-based screening of an in-house library and scaffold modification. Follow-up SAR study focusing on the 5-aryl substituent of the oxazole core has identified 4k (EC50=0.42μM, TI=50) as a potent inhibitor. However, the analogues suffered from poor aqueous solubility. To address this issue, we have developed broadly applicable potential prodrugs of indazoles. Among them, N-acyloxymethyl analogue 11b displayed promising results (i.e., increased aqueous solubility and susceptibility to enzymatic hydrolysis). Further studies are warranted to fully evaluate the analogues as the potential prodrugs with improved physiochemical and PK properties.

Abstract B137: Pharmacokinetics, antitumor activity, and therapeutic index of Nampt inhibitor MPC-8640 in mice.

Background: MPI-0487316 is a potent and orally bioavailable small molecule inhibitor of nicotinamide phosphoribosyltransferase (Nampt), an enzyme which catalyzes the rate-limiting step for synthesis of NAD from nicotinamide. Inhibition of Nampt by MPI-0487316 results in cell death as a consequence of NAD depletion and inhibition of ATP synthesis. We have previously reported that MPI-0487316 can induce regressions in a xenograft model. MPC-8640, a prodrug of MPI-0487316, was developed to increase solubility for improved formulation. Myrexis has recently initiated preclinical development of this prodrug and here we present data on the pharmacokinetic and anti-tumor activity of MPC-8640 in mice. Methods: MPI-0487316 concentration in plasma was measured using LC-MS/MS. For xenograft studies, HT1080 human fibrosarcoma cells were implanted subcutaneously into nude mice and mice were administered vehicle or MPC-8640 by oral gavage at the times and doses indicated. Results: Oral administration of MPC-8640 to mice resulted in substantial plasma concentrations of the active moiety MPI-0487316 with increasing AUC and Cmax over a wide range of doses. MPC-8640 concentration itself was negligible in plasma when dosed orally at 300 mg/kg. MPC-8640 demonstrated strong activity in the HT1080 human fibrosarcoma xenograft model when dosed qd or bid for one to two weeks. After bid dosing for one week, complete tumor growth inhibition (TGI) was observed at 6 mg/kg and substantial regression at 10 mg/kg. There was no difference between responses after seven or 14 doses bid. For qd dosing, complete tumor growth inhibition required 20 mg/kg MPC-8640 and ≥24 mg/kg for tumor regression. The anti-tumor response seen at the end of seven days of qd dosing was subsequently maintained for at least one week. TGI was observed with three or four doses qd, but with lesser potency than for five or more consecutive qd doses. In studies to determine maximum tolerated dose, 98% of mice survived up to 90 mg/kg MPC-8640 qd for one week, whereas only 60% survived doses >90 mg/kg. Conclusions: Oral MPC-8640 is an effective prodrug in mice for systemic delivery of its active moiety Nampt inhibitor MPI-0487316. The lack of significant plasma concentrations of MPC-8640 indicates that the prodrug is effectively converted to active moiety in the gut or immediately after absorption and that anti-tumor activity of MPC-8640 against subcutaneous xenografts is through its active moiety. A one week on/one week off, daily dosing schedule appears optimal, since one week of dosing, either qd or bd, was maximally effective and the anti-tumor response was sustained for at least one week after the end of dosing. Tumor regressions were induced at doses of MPC-8640 well below its maximum tolerated dose, providing promise that MPC-8640 may have anti-tumor activity in the clinic at well-tolerated doses. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B137.

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

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 mm 3 . 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 ED 50 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 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