Results of a Phase 1, Dose-Escalation Study of FF-10501-01 in Patients with Relapsed/Refractory Acute Myeloid Leukemia (AML) or Hypomethylating Agent (HMA)-Resistant Myelodysplastic Syndrome (MDS)

Introduction

FF-10501-01 is an orally bioavailable potent inhibitor of inosine-5-monophosphate dehydrogenase (IMPDH). In vitro, FF-10501-01 reduced the proliferation of multiple human-derived myeloid leukemia parent and hypomethylating agent (HMA)-resistant cell lines in a concentration dependent manner. Incubation of cells with FF-01501-01 also reduced intracellular pools of GMP, GDP and GTP, and this effect was reversed by addition of guanosine, demonstrating that the effect was due to inhibition of IMPDH. FF-10501-01 was evaluated in a Phase 1 clinical trial in patients with relapsed/refractory AML and HMA-resistant MDS and results are presented below.

Methods

This was an open-label, single-institution, Phase 1, dose escalation study in patients with refractory AML and MDS, or in patients with AML > 60 years of age not eligible for other treatment. The study was conducted as a "3+3" design. The objectives of the study were to describe the adverse event profile, pharmacokinetics, pharmacodynamics, recommended Phase 2 dose (RP2D) and preliminary efficacy of FF-10501-01. Oral FF-10501-01 was administered in escalating doses ranging from 50 - 500 mg/m² twice daily (BID) for periods of 14, 21 or 28 days in a 28-day treatment cycle and dose escalation to the next dose cohort was governed by the decision of a safety review committee. The pharmacokinetics of FF-10501-01 and its primary active metabolite were determined by measuring blood levels at various times after administration; pharmacodynamics were based on measurements of xanthine monophosphate (XMP) at various time points. The institutional review board of the participating institution approved the protocol and all protocol amendments, and all patients provided written informed consent.

Results

Thirty-seven patients were treated with FF-10501-01. Most (78%) of patients had AML; the median age of all patients was 78 (range: 58 - 88). All patients had received prior therapy (median number 3, range: 1 - 6) and 3 patients had undergone stem-cell transplantation. FF-10501-01 was well tolerated; the most frequently observed treatment-emergent related adverse events were fatigue (22%), diarrhea (11%), nausea (11%) and oral mucositis (8%). Of all adverse events reported, only 3 were Grade 3 in severity (one episode each of neutropenia, thrombocytopenia and oral mucositis); all others were Grade 1 or 2. The RP2D was determine to be 400 mg/m² given for 21 days every 28 days. In the MDS cohort, 1 of 8 evaluable patients demonstrated a complete bone marrow response that persisted for 19 months and 3 of 24 evaluable patients with AML demonstrated partial responses; in 1 of these patients, the response persisted for 31 months. One additional patient with AML continued treatment with FF-10501-01 for 14 months without evidence of progression. FF-10501-01 displayed dose proportional pharmacokinetics with no evidence of drug accumulation; mean steady-state observed half-lives ranged from 3 - 9 hours. Blood concentrations of XMP were variable between subjects as a function of dose and time. Following a single administration of FF-10501-01, on average, there appeared to be a reduction in XMP from baseline and maximum inhibition of pre-dose blood concentrations of XMP were consistently near or above 50% following the first administration of FF-10501-01.

Conclusion

FF-10501-01, was well tolerated and demonstrated evidence of efficacy in a heavily pre-treated population of patients with AML and MDS. FF-10501-01 had predictable pharmacokinetics and pharmacodynamic testing verified its mechanism of action as an IMPDH inhibitor. FF-10501-01 in combination with other agents, is currently undergoing additional clinical testing.