eFFECTOR Therapeutics Announces New Positive Interim Data from Dose Escalation and Phase 2 Expansion Cohorts of Zotatifin in ER+ Metastatic Breast Cancer Patients

Median progression free survival (mPFS) of 7.4 months in the ZFA expansion cohort evaluating zotatifin in combination with fulvestrant and abemaciclib in heavily pretreated patients Zotatifin generally well tolerated as dose escalation continues; Currently enrolling at 0.28 mg/kg in the ZF doublet evaluating zotatifin combined with fulvestrant and at 0.1 mg/kg in the ZFA triplet SOLANA BEACH, Calif. and REDWOOD CITY, Calif., Dec. 08, 2023 (GLOBE NEWSWIRE) — eFFECTOR Therapeutics, Inc. (NASDAQ: EFTR), a leader in the development of selective translation regulator inhibitors (STRIs) for the treatment of cancer, today announced new positive interim data from dose escalation and Phase 2 expansion cohorts of a Phase 1/2 clinical study of zotatifin in patients with estrogen receptor positive (ER+) metastatic breast cancer (mBC). The data, reflecting a cutoff date of Nov. 17, 2023, is being presented by Ezra Rosen, M.D., Ph.D., Medical Oncologist and Early Drug Development Specialist, Memorial Sloan Kettering Cancer Center, at the 2023 San Antonio Breast Cancer Symposium (SABCS®), held from December 5 – 9, 2023 in San Antonio, Texas. “We are extremely pleased with the positive interim data, especially the 7.4 month mPFS in the ZFA cohort of heavily pretreated patients, which builds on the responses reported earlier and underscores the potential of zotatifin as a promising treatment option for patients with ER+ metastatic breast cancer,” said Steve Worland, Ph.D., president and chief executive officer of eFFECTOR. “The safety and tolerability data are also encouraging and have led us to reopen dose escalation of the ZFA triplet.” In the ZFA triplet cohort, wherein patients with a median of four prior lines of therapy for metastatic disease received 0.07 mg/kg zotatifin dosed on Days 1 and 8 of 21-day cycles, combined with fulvestrant and abemaciclib, the mPFS was 7.4 months (95% confidence intervals 2.8 to non-estimable). As previously reported, five of 19 (26%) RECIST-evaluable patients had partial responses, including four confirmed and one unconfirmed. The ZFA triplet was generally well tolerated, with the large majority of zotatifin-related treatment-emergent adverse events (TEAEs) being Grade 1 or 2. The most common zotatifin-related TEAEs were nausea, vomiting and fatigue, all Grade 1 or 2. The most common Grade 3 or higher zotatifin-related TEAEs were anemia and blood creatinine phosphokinase increase, each in two of 20 (10%) patients. Four of 20 (20%) of patients discontinued treatment due to adverse events of any cause. In the new ZF dose escalation cohorts, three patients were enrolled at each dose level of 0.1, 0.14 and 0.2 mg/kg zotatifin administered once every two weeks, combined with fulvestrant. The patients were heavily pretreated, with a median of four prior lines of treatment for metastatic disease. There were no dose-limiting toxicities (DLTs) or serious adverse events (SAEs) observed in these nine patients and enrollment is ongoing now at 0.28 mg/kg zotatifin combined with fulvestrant. There was one confirmed partial response in the 0.1 mg/kg cohort, two instances of stable disease in the 0.14 mg/kg cohort and one instance of stable disease in the 0.2 mg/kg cohort. Based on the safety and tolerability of the ZF doublet, dose escalation has been reopened in the ZFA triplet, with enrollment ongoing at 0.1 mg/kg zotatifin dosed once every two weeks, combined with fulvestrant and abemaciclib. The company expects to report additional data from dose escalation in the first half of 2024. About the Phase 1/2 Trial The Phase 1/2 trial (NCT04092673) is an open-label randomized dose-escalation and cohort-expansion study evaluating eIF4A inhibitor, zotatifin, in patients with advanced solid tumors. The primary objectives of part one of the trial are to evaluate the safety and tolerability of zotatifin as a monotherapy in patients with defined, advanced solid tumors, determine the recommended Phase 2 dose for zotatifin as a monotherapy and to evaluate the pharmacokinetics profile. In part two of the trial, the primary objective is to evaluate the preliminary antitumor activity of zotatifin as a monotherapy and as a combination therapy in patients with defined, advanced solid tumors. About Zotatifin Zotatifin is a potent and sequence-selective small molecule inhibitor of the RNA helicase eIF4A that is designed to suppress expression of a network of cancer driving proteins, including Cyclins D and E, CDKs 2, 4 and 6 and select RTKs as well as KRAS. We are currently investigating zotatifin in ongoing clinical trials for solid tumors. About eFFECTOR Therapeutics eFFECTOR is a clinical-stage biopharmaceutical company pioneering the development of a new class of oncology drugs referred to as STRIs. eFFECTOR’s STRI product candidates target the eIF4F complex and its activating kinase, mitogen-activated protein kinase interacting kinase (MNK). The eIF4F complex is a central node where two of the most frequently mutated signaling pathways in cancer, the PI3K-AKT-mTOR and RAS-MEK-ERK pathways, converge to activate the translation of select mRNA into proteins that are frequent culprits in key disease-driving processes. Each of eFFECTOR’s product candidates is designed to act on a single protein that drives the expression of a network of functionally related proteins, including oncoproteins and immunosuppressive proteins in T cells, that together control tumor growth, survival and immune evasion. eFFECTOR’s lead product candidate, tomivosertib, is a MNK inhibitor currently being evaluated in KICKSTART, a randomized, double-blind, placebo-controlled Phase 2b trial of tomivosertib in combination with pembrolizumab in patients with metastatic non-small cell lung cancer (NSCLC). Zotatifin, eFFECTOR’s inhibitor of eIF4A, is currently being evaluated in Phase 2a expansion cohorts in certain biomarker-positive solid tumors, including ER+ breast cancer and KRAS-mutant NSCLC. eFFECTOR has a global collaboration with Pfizer to develop inhibitors of a third target, eIF4E. Forward-Looking Statements eFFECTOR cautions you that statements contained in this press release regarding matters that are not historical facts are forward-looking statements. The forward-looking statements are based on our current beliefs and expectations and include, but are not limited to: the potential therapeutic benefits of zotatifin; and the future clinical development and data readouts of zotatifin and the timing thereof. Actual results may differ from those set forth in this press release due to the risks and uncertainties inherent in our business, including, without limitation: interim results of a clinical trial are not necessarily indicative of final results and one or more of the clinical outcomes may materially change as patient enrollment continues, following more comprehensive reviews of the data and as more patient data becomes available, including the risk that unconfirmed responses may not ultimately result in confirmed responses to treatment after follow-up evaluations; potential delays in the commencement, enrollment and completion of clinical trials; our dependence on third parties in connection with product manufacturing, research and preclinical and clinical testing; the results of preclinical studies and early clinical trials are not necessarily predictive of future results; the success of our clinical trials and preclinical studies for our product candidates is uncertain; we may use our capital resources sooner than expected and they may be insufficient to allow clinical trial readouts; regulatory developments in the United States and foreign countries; unexpected adverse side effects or inadequate efficacy of our product candidates that may limit their development, regulatory approval and/or commercialization, or may result in recalls or product liability claims; our ability to obtain and maintain intellectual property protection for our product candidates; and other risks described in our prior filings with the Securities and Exchange Commission. You are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date hereof, and we undertake no obligation to update such statements to reflect events that occur or circumstances that exist after the date hereof. All forward-looking statements are qualified in their entirety by this cautionary statement, which is made under the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. Contacts:         Investors:   Media:Christopher M. CalabreseManaging DirectorLifeSci [email protected] Kevin GardnerManaging DirectorLifeSci [email protected] Mike TattoryAccount SupervisorLifeSci [email protected]