Anti-Leukemia Effect of FF-10501-01, a Novel Inosine 5'-Monophosphate Dehydrogenase Inhibitor, in Advanced Acute Myeloid Leukemia (AML) and Myelodysplastic Syndromes (MDS), Including Hypomethylating Agent (HMA) Failures

Inosine 5'- monophosphate dehydrogenase (IMPDH) is a rate-limiting enzyme that catalyzes de novo synthesis of the guanine nucleotide and is overexpressed in both hematologic and solid tumors. FF-10501-01 is a potent new competitive IMPDH inhibitor. We investigated the anti-leukemia effect of FF-10501-01 in AML cell lines and in a Phase 1 clinical study in advanced AML and MDS, including HMA failures.

Thirteen leukemia cell lines were studied, including 5 parental AML cell lines and their HMA-resistant derivatives (MOLM13, SKM1, HL60, TF1, and U937), and 3 other AML cell lines (KG1, HEL, and OCI-AML3). Cell proliferation was determined using trypan blue analysis. Flow cytometry was performed to detect drug-induced apoptosis and cell cycle analysis. High-performance liquid chromatography (HPLC) was performed to detect the intracellular concentrations of guanine nucleotides. Mycophenolic acid-treated cells were used as positive control. Effect of guanosine supplement on FF-10501-01 treatment was evaluated. Within 72 hours of treatment, FF-10501-01 inhibited proliferation of all 13 AML cell lines. The IC₅₀ of FF-10501-01 ranged between 4.3 and 144.5 µM. MOLM13 was the most sensitive leukemia cell line, whereas the decitabine-resistant TF1 cell line was the most resistant. FF-10501-01-induced apoptosis was observed in all cell lines. Increased numbers of cells in G1 phase and decreased numbers in S phase were observed in MOLM13, SKM1 and TF1 cell lines treated with <100 µM FF-10501-01. Decreased intracellular concentrations of guanine nucleotides were observed in MOLM13 and SKM1 cell lines treated with 3 to 30 µM of FF-10501-01 for 24 hours. Proliferation was partially rescued after 72 hours of treatment with 3 µM guanosine and FF-10501-01 in MOLM-13, HL60 cells and their HMA-resistant derivatives. No treatment synergy was observed with the combination of FF-10501-01 with HMAs in MOLM-14 and HL-60 or their HMA-resistant cell lines.

In summary, FF-10501-01 produced potent anti-proliferative and apoptotic effects on AML cell lines through inhibition of de novo guanine nucleotide synthesis.

In view of these pre-clinical findings, we performed a standard 3+3 dose-escalation Phase 1 trial to access the safety and clinical activity of FF-10501-01 in patients with advanced AML, MDS and chronic myelomonocytic leukemia (CMML). Eligibility criteria: age ³ 18 years, high risk MDS/CMML, AML with documented PD following previous therapy, AML ≥ 60 years of age and not a candidate for other therapy, adequate renal and hepatic function, and no known history of significant cardiac disease. Sixteen patients (12 AML, 4 MDS) have been enrolled in 5 dose cohorts (50 - 400 mg/m² PO BID) for 14 days on/14 days off each 28-day cycle, including 8 M and 8 F. Median (range) values: age 75.3 yrs (59.1 - 88.6); bone marrow blasts for AML patients 40.5% (12 - 71), for MDS patients 10% (6 - 13), or 30% overall (6 - 71); and prior treatment regimens 2.5 (1 - 6). All patients relapsed from, or progressed on, prior HMAs. Mutations in FLT3, NPM1, GATA2, TET2, ASXL1, DNMT3A and/or MDM2 were present in 4/16 (25%) patients.

The median number of FF-10501-01 cycles received to date is 1.5 (range 1 - 10). No DLTs or drug-related serious adverse events (AEs) have been observed and FF-10501-01 has been very well tolerated through 5 - 10 cycles. The most frequent drug-related AEs have been Gr 1-2 nausea, diarrhea and fatigue. Drug-related Gr 4 prolonged thrombocytopenia and Gr 4 prolonged neutropenia were reported in one patient at 200 mg/m² BID.

Two partial responses (PRs) have been achieved in 1 patient each at 50 and 100 mg/m² BID after 3 cycles, 7 (50%) patients demonstrated long-term stable disease over 2 - 10 cycles, and 4 patients have remained on study drug through 5 - 10 cycles and are still ongoing. Updated safety and efficacy data, including PK/PD, will be presented at the meeting.

FF-10501-01 is a promising new agent for the treatment of advanced AML and MDS. Preclinical activity was seen in multiple leukemia cell lines. In a Phase 1 trial, clinical activity with PRs, prolonged disease stabilization and a highly tolerable safety profile were observed. The Phase 2 expansion phase will be initiated soon.