On June 7, 2023 Repare Therapeutics Inc. ("Repare" or the "Company") (Nasdaq: RPTX), a leading clinical-stage precision oncology company, reported initial proof of concept monotherapy data from its Phase 1 MYTHIC clinical trial evaluating lunresertib (RP-6306), a first-in-class, oral PKMYT1 inhibitor in molecularly selected advanced solid tumors (Press release, Repare Therapeutics, JUN 7, 2023, View Source [SID1234632572]).

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"These initial proof of concept results for lunresertib monotherapy show a favorable and distinct tolerability profile and preliminary antitumor activity that support our development plans for this program," said Maria Koehler, MD, PhD, Chief Medical Officer of Repare. "The data demonstrate that lunresertib effectively inhibits PKMYT1 and offers a synthetic lethal combination with CCNE1 amplification or inactivating mutations in FBXW7 and PPP2R1a. These genetic alterations have previously been considered undruggable and represent a significant unmet medical need. These findings, along with the continued advancement of the lunresertib program across multiple ongoing combination clinical trials, validate our proprietary STEP2 platform and precision medicine approach."

"While early, these promising proof-of-concept data continue to support our belief in the potential transformative role that lunresertib could play, either alone or in combination with other therapies, in patients with molecularly selected advanced solid tumors," said Lloyd M. Segal, President and Chief Executive Officer of Repare. "We look forward to reporting initial combination data of lunresertib with camonsertib, as well as lunresertib with gemcitabine, in the fourth quarter of this year, while also advancing multiple other trials to further our understanding of our first-in-class PKMYT1 inhibitor program."

Key Initial Findings from the Phase 1 MYTHIC Clinical Trial:

MYTHIC (NCT04855656) Module 1 is a first-in-human, global, open-label Phase 1 dose-escalation study to evaluate safety, pharmacokinetics, pharmacodynamics and preliminary anti-tumor activity of a novel and potent small molecule PKMYT1 inhibitor, lunresertib. MYTHIC Module 2 will investigate lunresertib in combination with camonsertib (RP-3500/RG6526), a potent and selective oral inhibitor of ATR developed by Repare and now partnered with Roche (excluding the lunresertib combination), in molecularly selected advanced solid tumors. As of the data cutoff date of April 28, 2023, 63 patients were enrolled in lunresertib monotherapy Module 1 of the MYTHIC study, which is ongoing and accruing patients.

Tolerability profile of lunresertib monotherapy appears favorable and differentiated from other clinical cell cycle inhibitors, which have been characterized with myelotoxicity and diarrhea. No grade 4 toxicity was observed with lunresertib, where grade 3 treatment emergent adverse events of interest included rash (7.9%), anemia (6.3%) and nausea or vomiting (1.6%) The only dose limiting toxicity was reversible rash, alleviated with dose modifications and simple supportive measures.
Two recommended dose/schedules were identified – 240mg daily continuously and 80-100mg BID intermittent weekly – to offer maximum flexibility in combination studies.
Pharmacodynamic analysis confirmed lunresertib treatment results in PKMYT1 target inhibition at active doses and increases DNA damage.
Preliminary anti-tumor activity was observed, including moderate tumor shrinkages and a confirmed partial response per RECIST 1.1 criteria. Several patients demonstrated long stable disease and remain on treatment for greater than 11 months and ongoing.
Early clinical combination insights demonstrated greater anti-tumor activity in patients treated with the combination of lunresertib and camonsertib than lunresertib alone, based on higher molecular response rates and RECIST 1.1 responses. Examples of confirmed partial responses are provided for the three tested sensitivity genotypes in endometrial adenocarcinoma, cholangiocarcinoma and colorectal cancer, with more details planned for the Q4 scientific presentation.
Encouraging early responses observed across gemcitabine, camonsertib, and FOLFIRI clinical combinations in multiple tumor types and genotypes.
Favorable and distinct tolerability profile and preliminary antitumor activity demonstrated thus far support potential development plans that may include further trials of lunresertib in various combination and maintenance approaches.
Repare is also currently evaluating lunresertib in combination with gemcitabine in the Phase 1 MAGNETIC study and in combination with FOLFIRI in the Phase 1 MINOTAUR study. Repare is working with Princess Margaret Cancer Center to initiate clinical testing, as part of an investigator-sponsored trial (IST), of a fourth lunresertib combination with carboplatin and paclitaxel for the treatment of recurrent TP53 mutated ovarian and uterine cancer, with first patient dosing expected this year. The Company is also collaborating with the Canadian Cancer Trials Group in an ongoing basket Phase 2 IST that is enrolling patients with selected, advanced cancers receiving lunresertib as combination (NCT05605509), and in a second active study that will evaluate lunresertib in combination with gemcitabine in patients with CDK4/6 inhibitor treated ER+/HER2- metastatic breast cancer (NCT05601440). These studies aim to expand the treatment opportunities for lunresertib to earlier stages of cancer treatment or additional tumor types.

Company Virtual Webcast Event:

The Company will host a virtual investor webcast with accompanying slides for analysts and investors today at 4:30 p.m. Eastern Time to further discuss the lunresertib program, including initial proof-of-concept monotherapy data from MYTHIC and an update on ongoing combination clinical trials.

To access the call, please dial (877) 870-4263 (U.S. and Canada) or (412) 317-0790 (international) at least 10 minutes prior to the start time and ask to be joined to the Repare Therapeutics call. A live video webcast will be available in the Investor section of the Company’s website at View Source A webcast replay will also be archived for at least 30 days.