On July 18, 2023 ENB Therapeutics, Inc., a biotechnology company pioneering a new and differentiated class of therapeutics targeting the endothelin B receptor (ETBR) inhibitor, reported that the company has completed enrollment of its international Phase 1 ENBOLDEN-101 trial investigating the safety and efficacy of lead product ENB-003 in combination with KEYTRUDA (pembrolizumab), Merck’s anti-PD-1 therapy (Press release, ENB Therapeutics, JUL 18, 2023, View Source [SID1234633304]). The Phase ½a study is a multicenter, open-label study conducted in the US and Australia and is comprised of two parts. Part 1 recruited 46 patients and was a dose-escalation study to determine the recommended dose for the Part 2 expansion phase of the study. The results of this study will be presented by ENB Therapeutics in a poster titled, "ENB-003, an ETBR antagonist, in combination with pembrolizumab for refractory advanced solid tumors: Topline data from the ENBolden-101 Phase 1B study" at the Immuno-oncology Summit which is being held August 7-9, 2023 in Boston, Massachusetts.

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ENB-003 in combination with pembrolizumab was well tolerated in the dose escalation study and demonstrated no DLTs across the 6 dosing cohorts. The most common treatment emergent adverse events irrespective of grade or causality included fatigue (28.2%), constipation (26.1%), abdominal pain (26.1%), nausea (23.9%), anemia 17.4%, diarrhea (17.4%). Serious adverse events, grade 3 and above considered possibly related to study treatment included fatigue (n=4), diarrhea (n=3), dyspnea (n=3) constipation (n=2), rash (n=2). 15 patients with evaluable disease were enrolled in cohorts 1-5 (ENB-003 dose range 150ug-1000ug) and 15 patients with evaluable disease were enrolled in the 6th cohort (ENB-003 dose 2000ug). The dosing frequency for cohort 6 was doubled to 6 doses every 3 weeks from 6 doses every 6 weeks in cohort 1-5. The DCR across all cohorts irrespective of ETBR status was 33% (1 PR, 9 SD, 20 PD). The DCR in ETBR-Hi patients was 33% in cohorts 1-5 (4 SD, 1 PR, 10 PD) and 83% in cohort 6 (5 SD, 1 PD). The DCR for ETBR-Lo patients in cohort 6 was 0% (9 PD). ETBR-Lo patients were not enrolled in cohorts 1-5. For microsatellite stable (MSS) platinum refractory/ resistant ovarian cancer there was an 80% DCR across all cohorts (1 PR, 3 SD, 1 PD) with a trend for durable responses at higher doses of ENB-003. A platinum refractory MSS ovarian cancer patient experienced a 95% PR of 12-month duration. The sample size was not powered for statistical significance.

"The completion of enrollment of the Phase 1 ENBOLDEN-101 first-in-man study is a significant milestone for our Company. We are extremely encouraged by the results in heavily treated cancer patients refractory to standard of care treatment," stated Sumayah Jamal, MD-PhD, President, Chief Scientific Officer and Co-Founder of ENB Therapeutics. "Our data suggest potential efficacy in patients that do not historically respond to immunotherapy and support further clinical development. We are grateful to our patients and their families for their participation in our study. "

Part 2 is a dose expansion study at the recommended dose designed to evaluate the safety, tolerability and efficacy of ENB-003 in combination with pembrolizumab in cancers refractory to standard of care including MSS R/R ovarian cancer, MSS pancreatic cancer, anti-PD1 refractory HNSCC, anti-PD1 refractory melanoma and anti-PD1 refractory TNBC. For more information on this Phase 1/2a study, see NCT04205227.

KEYTRUDA is a registered trademark of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA.

About ENB-003

ENB-003 is a selective endothelin B receptor (ETBR) inhibitor that, in preclinical studies, enhances efficacy of CAR-T and anti-PD-1 in solid tumors across multiple cancer types in preclinical studies. In an ongoing multi-center Phase 1/2 clinical trial, early efficacy signals suggest that ENB-003 overcomes resistance to the anti-PD-1 therapy KEYTRUDA (pembrolizumab) in heavily pre-treated drug resistant cancer patients. The Phase 2 portion of the ENB-003 + pembrolizumab combination study is expected to start in the first half of 2024. The trial will enroll microsatellite stable platinum refractory and primary platinum resistant ovarian cancer patients, as well as microsatellite stable pancreatic cancer patients that have failed standard of care.