Pollock, Roy M.

Abstract Introduction: CFT7455 is a highly potent and novel Ikaros Family Zinc Finger Protein 1/3 (IKZF1/3) degrader. In xenograft models, CFT7455 has more potent IKZF1/3 degradation compared to other degraders. Early observations from the FIH clinical trial (NCT04756726) along with supporting translational studies are presented here. Methods: Pre-clinical studies comparing CFT7455 and CC-92480 in both in vitro and xenograft models were performed. The pre-clinical studies’ results coincided with observations from the on-going clinical trial. The clinical trial is an open-label, Phase 1/2, multi-center, FIH study in heavily pretreated relapsed/refractory (R/R) MM and non-Hodgkin’s lymphoma (NHL) patients evaluating safety, tolerability, and PK of CFT7455. Eligible MM patients are R/R to therapy and are not candidates for regimens known to provide clinical benefit. A starting dose of 50 μg QD 21 days on/7 days off (21/7) in 28-day cycles was administered. Results: CFT7455 and CC-92480 showed similar cereblon binding profiles and in vitro IKZF1/3 degradation kinetics, translating into sub-nanomolar GI50 values in proliferation assays across a panel of MM cell lines. In the NCI-H929 xenograft model, 100 μg/kg/day of CFT7455 resulted in durable tumor regressions, while 1000 μg/kg/day of CC-92480 gave tumor stasis. Similar results were seen in a systemic model of MM, MM1.S. Both compounds achieved >95% IKZF3 degradation in tumors 4h post dose. At 48h post dose, CFT7455 was more effective than CC-92480 in maintaining IKZF3 degradation (65% vs. 6% respectively). When levels of CFT7455 and CC-92480 in plasma and tumor were compared, CFT7455 concentrations were > DC80 in tumor 48h post dose, while CC-92480 levels were undetectable in tumor and plasma, demonstrating CFT7455 has longer exposure resulting in sustained IKZF1/3 degradation in pre-clinical models. In cohort A, 5 heavily pre-treated MM patients (pts) received single agent CFT7455. 4 pts have received at least 3 cycles, with 2 pts receiving 5 cycles. Neutropenia (grade 4) was observed in 3/5 pts without coincident fever or infection. Additionally, a 2-4 fold accumulation in plasma CFT7455 exposure at steady state was observed. Early pharmacodynamic (PD) data demonstrates deep persistent degradation of IKZF3 (~100%) and serum free light chain reduction (up to 72%) in response to treatment. Stable disease has been observed in 34 pts, suggesting clinical benefit. Conclusions: While CFT7455 showed clinical benefit at 50 ug with deep target degradation, neutropenia was dose limiting. PK/PD modeling suggests alternative dosing regimens may result in increased tolerability with preserved efficacy, and evaluation of them is underway. Updated results will be presented at the meeting. Citation Format: Sagar Lonial, Shambavi Richard, Jeffrey V Matous, Andrew J. Yee, Urvi Shah, Neha Mehta-Shah, Thomas Martin, Eli Muchtar, Sikander Ailawadhi, Paul G. Richardson, Manisha Bhutani, Samantha Perino, Jason Kirby, Roman V. Agafonov, Prasoon Chaturvedi, Bradley Class, Matthew Schnaderbeck, Michael R. Palmer, Cathleen Gorman, Oliver Schoenborn-Kellenberger, Amanda Hoerres, Stewart L. Fisher, Roy M. Pollock, Adam Crystal, Michelle Mahler, Jesus Bardeja. Pharmacokinetic (PK) profile of a novel IKZF1/3 degrader, CFT7455, enables significant potency advantage over other IKZF1/3 degraders in models of multiple myeloma (MM) and the results of the initial treatment cohort from a first-in-human (FIH) phase 1/2 study of CFT7455 in MM [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT186.

Abstract Introduction: Rearrangements of the MLL (mixed lineage leukemia) gene on chromosome 11q23 are present in 5-10% of either acute myeloid (AML) or acute lymphoblastic leukemia (ALL), and are associated with a poor prognosis. Fusion proteins involving the MLL histone methyltransferase (HMT) result in recruitment of another HMT, DOT1L, to a multi-protein complex leading to aberrant methylation of Histone H3 lysine 79 (H3K79) at MLL target genes and enhanced expression of leukemogenic genes such as HOXA9 and MEIS1. EPZ-5676 is a small molecule inhibitor of DOT1L with sub-nanomolar affinity and >37,000 fold selectivity against additional HMTs. EPZ-5676 treatment of cultured cells reduced histone H3K79 methylation, decreased MLL target gene expression and resulted in selective killing of MLL-rearranged (MLL-r) leukemia cells by inducing apoptosis and differentiation. EPZ-5676 administration led to tumor regression in an MLL-r leukemia xenograft model. We report preliminary results of an ongoing Phase 1 trial of EPZ-5676 in patients with advanced hematologic malignancies, including acute leukemia with MLL-r. Methods: This is a 2-part phase 1 open label dose escalation study investigating the safety, tolerability, pharmacokinetics (PK), pharmacodynamics (PD) and anti-leukemic activity of EPZ-5676 in adult patients (pts) with relapsed/refractory leukemia (CT.gov: NCT01684150). In the dose-escalation phase, patients with AML, ALL, acute mixed lineage leukemia, myelodysplastic syndrome, myeloproliferative neoplasia (MPN) or chronic myeloid leukemia were eligible. Eligibility in the expansion phase of the study was restricted to pts with MLL-r or partial tandem duplication of MLL (MLL-PTD). EPZ-5676 was administered via continuous intravenous infusion (CIV) for 21 days of a 28 day cycle in the dose escalation phase and CIV for all 28 days of a 28 day cycle in the expansion phase, until disease progression or unacceptable toxicity. Results: Between October 2012 and July 2014, 37 pts have enrolled; 36 are evaluable for safety (received at least 1 dose of EPZ-5676) and 28 pts (19 MLL-r, 4 MLL-PTD) are evaluable for anti-leukemia activity (completed at least one post baseline marrow evaluation). The median age at time of enrollment was 53 years (range: 20 to 81 years); the median number of prior systemic therapies was 2 (range: 1 to 6) and 14 pts had a prior allogeneic stem cell transplant. Of the treated pts, disease characteristics were: 31 pts with AML (21 MLL-r, 5 MLL-PTD), 4 pts with ALL (3 MLL-r) and 1 pt with MPN (MLL-r). Table 1: Number of evaluable pts per cohort Dose (mg/m2/day) 12 24 36 54 80 90 21 day CIV 1 5 4 6 3 - 28 day CIV - - - - - 17 The median time on study was 29 days (range: 5-196 days). Adverse events (AEs) reported in >15% of pts were: anemia, fever/neutropenia, thrombocytopenia, constipation, diarrhea, nausea, chills, fatigue, mucosal inflammation, peripheral edema, hypomagnesemia, dyspnea and sepsis; of which leukocytosis, nausea and hypomagnesemia were assessed by the investigator as drug related. Grade I PR interval prolongation, without associated QTc changes, was observed in 2 pts. There were no deaths attributed to study drug treatment, and there were 2 pts with treatment discontinuation for potentially drug-related AEs. Dose proportional PK was observed with rapid attainment of steady-state plasma concentrations on Day 1 of treatment. Preliminary PD data demonstrated inhibition of H3K79 methylation from baseline in marrow (median: 52%, range 0-81%) and peripheral blood mononuclear cells (median: 43%, range 25-67%) at doses above 36 mg/m2/day. PD effects were observed by day 8. The 21 day CIV pts recovered H3K79 methylation towards baseline by day 28, and the 28 day CIV pts maintained methyl-mark inhibition throughout cycle 1. To date, best responses for pts with MLL-r are morphologic CR (1 pt.), cytogenetic CR (1 pt), and resolution of leukemia cutis (2 pts). In addition, a treatment-related increase in neutrophils (PMN) and/or monocytes was observed in 6 pts with a median day of onset of 15 days (range 8-28 days). The identification of the MLL-r by split signal FISH in mature PMN suggests a differentiation effect on the leukemic clone. Conclusions: EPZ-5676 is well tolerated and exhibits anti-leukemic activity in MLL-rearranged acute leukemia. These data provide rationale for continued clinical investigation of potential utility of EPZ-5676 in patients with rearrangements of the MLL gene. Disclosures Stein: Janssen Pharmaceuticals: Consultancy. Garcia-Manero:Epizyme, Inc: Research Funding. Rizzieri:Novartis, Inc: Consultancy, Speakers Bureau; Ariad, Inc: Speakers Bureau. Savona:Karyopharm: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees. Altman:Astellas: Membership on an entity's Board of Directors or advisory committees; Ariad: Membership on an entity's Board of Directors or advisory committees; Spectrum: Membership on an entity's Board of Directors or advisory committees; Foundation Medicine: Membership on an entity's Board of Directors or advisory committees. Armstrong:Epizyme, Inc: Consultancy. Pollock:Epizyme: Employment, Equity Ownership. Waters:Epizyme, Inc: Employment, Equity Ownership. Legler:Epizyme, Inc: Employment. Thomson:Epizyme, Inc: Employment. Daigle:Epizyme, Inc: Employment, Equity Ownership. McDonald:Epizyme, Inc: Employment. Campbell:Epizyme, Inc: Employment, Equity Ownership. Olhava:Epizyme, Inc: Employment. Hedrick:Epizyme, Inc: Employment; Pharmacyclics, Inc: Equity Ownership. Copeland:New Enterprise Associates: Ad hoc consultant, Ad hoc consultant Other; Mersana: Membership on an entity's Board of Directors or advisory committees; Epizyme, Inc: Employment, Equity Ownership.

Key Points Pinometostat demonstrates first evidence of DOT1L target inhibition and clinical responses in a subset of MLL-r advanced leukemia patients. The observed safety profile of pinometostat shows potential for exploration of combination therapies in leukemia.