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Cogent Biosciences Announces Initial Clinical Data From Ongoing Phase 2 APEX Trial Evaluating Bezuclastinib In Patients With Advanced Systemic

All patients treated with bezuclastinib achieved ≥50% reduction in serum tryptase, with a median reduction of 89%, regardless of prior KIT D816V inhibitor treatment All bone marrow biopsy-assessed

Benzinga · 06/10/2022 07:01

All patients treated with bezuclastinib achieved ≥50% reduction in serum tryptase, with a median reduction of 89%, regardless of prior KIT D816V inhibitor treatment

All bone marrow biopsy-assessed patients achieved ≥50% bone marrow mast cell reduction and decreases in blood KIT D816V variant allele fraction (VAF)

Bezuclastinib demonstrates favorable initial safety and tolerability profile with no reported periorbital or peripheral edema, cognitive effects or intracranial bleeding events 

Cogent to host investor conference call and webcast today at 8:00 a.m. ET 

CAMBRIDGE, Mass. and BOULDER, Colo., June 10, 2022 (GLOBE NEWSWIRE) -- Cogent Biosciences, Inc. (NASDAQ:COGT), a biotechnology company focused on developing precision therapies for genetically defined diseases, today announced positive initial data from its ongoing Phase 2 APEX clinical trial evaluating the selective KIT D816V inhibitor bezuclastinib in patients with advanced systemic mastocytosis (AdvSM). The data are being presented today in a poster presentation at the 2022 European Hematology Association (EHA) Congress in Vienna, Austria.

"Advanced systemic mastocytosis is a severe, debilitating hematologic disorder and physicians and patients remain in search of more effective and better tolerated treatment options to fight this disease," said Daniel DeAngelo, M.D., Ph.D., Chief of the Division of Leukemia at the Dana-Farber Cancer Institute and APEX clinical trial investigator. "I am very impressed with the early, encouraging results presented today from the APEX study. If results like these can be shown in a larger set of patients with AdvSM, I believe bezuclastinib has the potential to help us take a big step forward in treating systemic mastocytosis patients." 

"We are very excited to present initial clinical data from the APEX study of bezuclastinib in advanced systemic mastocytosis," said Andrew Robbins, Chief Executive Officer at Cogent Biosciences. "These results reinforce the hypothesis that a potent, selective KIT D816V inhibitor with limited CNS penetration has the potential to provide meaningful clinical activity to all systemic mastocytosis patients, without the tolerability challenges seen with other available treatment options. Based on these results, we expect to accelerate our timelines and investment and look forward to providing another APEX clinical update by the end of 2022, and to presenting SUMMIT clinical data in non-advanced systemic mastocytosis (NonAdvSM) patients in the first half of 2023."

Data from Ongoing Phase 2 APEX Clinical Trial

APEX is a global, open-label, multi-center, two-part Phase 2 clinical trial in patients with AdvSM evaluating the safety, efficacy, pharmacokinetic, and pharmacodynamic profiles of bezuclastinib. As of the data cutoff date of May 24, 2022, 11 patients had been treated in Part 1 at one of four dose levels (50 mg BID, 100 mg BID, 200 mg BID or 400 mg QD). The median age of patients at study entry was 70 years (ranging from 48-87 years). Patients were enrolled with the following sub-types: two patients with aggressive systemic mastocytosis (ASM), eight patients with systemic mastocytosis with associated hematologic neoplasm (SM-AHN), and one patient with mast cell leukemia (MCL). Two patients had received prior avapritinib and midostaurin treatment.

Initial Safety Data 

As of the cutoff date, May 24, 2022, bezuclastinib was generally well-tolerated at all doses. The majority of adverse events were Grade 1/2 and seen in no more than one patient with one serious adverse event and no Grade 4 events reported. Grade 3 events reported as at least possibly related were anemia (1 patient), neutropenia (1 patient) and hypersensitivity/mediator flare (1 patient). There were no reported cases of periorbital/peripheral edema, cognitive effects or intracranial bleeding events, which have been associated with other KIT inhibitors. As of the cutoff date, all patients remained on study. Subsequently, one SM-AHN patient with chronic myelomonocytic leukemia (CMML) transformed to acute myeloid leukemia (AML) and discontinued participation in the trial.

Initial Clinical Activity Data

As of the data cutoff date of May 24, 2022, all 11 patients treated were evaluated for signs of clinical activity. Eight of 11 patients had been treated for at least two cycles, had available data from bone marrow biopsy, and were evaluated for additional endpoints Cycle 3 Day 1 (C3D1) evaluable.

  • 11/11 patients achieved ≥50% reduction in serum tryptase levels by central assessment
    • 89% median reduction in serum tryptase
    • Six of these patients achieved reduction to <20 ng/mL
  • 8/8 patients (C3D1 evaluable) achieved ≥50% reduction in bone marrow mast cells by central review 
    • Six of these patients achieved complete clearance of bone marrow mast cell aggregates
  • 8/8 patients (C3D1 evaluable) demonstrated decreases in KIT D816V variant allele fraction (VAF) by droplet digital polymerase chain reaction (ddPCR)
  • All patients remained on treatment with treatment duration ranging from 0.5 - 4.8 months 

Two patients enrolled had previously received and discontinued avapritinib for toxicity reasons (intracranial hemorrhage, thrombocytopenia). Both patients have demonstrated clinical outcomes consistent with the avapritinib-naïve patients, including similar magnitude reductions in serum tryptase.

Bezuclastinib Clinical Development 

Based on the favorable initial safety and tolerability profile and clinical activity observed to date in the Phase 2 APEX clinical trial with bezuclastinib for AdvSM, Cogent will continue enrolling patients in Part 1 of APEX to determine a recommended dose for use in Part 2 of the trial. A pre-planned interim analysis is scheduled once approximately 28 patients have received at least two cycles of study treatment in Part 1. Cogent plans to present additional data from APEX by the end of 2022. In addition, Cogent continues to actively enroll patients in SUMMIT, a Phase 2 clinical trial with bezuclastinib for NonAdvSM, and PEAK, a registrational randomized, open-label, global, Phase 3 clinical trial in patients with imatinib-resistant Gastrointestinal Stromal Tumors (GIST). Cogent plans to present initial data from SUMMIT and lead-in data from PEAK in the first half 2023.

Conference Call Information & EHA poster

Cogent will host a webcast today at 8:00 am ET to discuss today's APEX results. The webcast will be accessible through the Investors and Media section of Cogent's website at https://investors.cogentbio.com/events. Following the live webcast, an archived replay will also be available.

Dial-in Number

U.S./Canada Dial-in Number: 844-686-3753

International Dial-in Number: 704-753-0395

Conference ID: 2951969

The APEX poster to be presented at EHA is available to registered conference attendees as well as on the Cogent Biosciences website in the Posters and Publications section of www.cogentbio.com/research.