Zentalis Pharmaceuticals Presents Phase 1b MUIR Data for Azenosertib Plus Paclitaxel in Platinum-Resistant Ovarian Cancer at ASCO 2026

Phase 1b combination data from Zentalis Pharmaceuticals signal a credible efficacy and tolerability profile for azenosertib plus paclitaxel in platinum-resistant ovarian cancer (PROC), with findings that carry formulation and manufacturing implications as WEE1 inhibitor programs move closer to registration-intended trials.

Results from Part 1 of the MUIR trial, drawn from a December 1, 2025 data cutoff, cover 46 heavily pre-treated patients across four dose cohorts: 200 mg QD continuous, and 200 mg, 250 mg, or 300 mg QD intermittent (5 days on, 2 days off), each combined with paclitaxel 80 mg/m². All patients had received prior paclitaxel. Across all cohorts, the combination produced a 39% overall response rate and a 7.3-month median progression-free survival, with a low frequency of high-grade adverse events.

The 250 mg QD intermittent cohort drew particular attention. That arm returned a 50% ORR and a 9.2-month median duration of response, a profile the investigators characterize as a potential optimal therapeutic index. Notably, clinical activity appeared comparable in both Cyclin E1-positive and Cyclin E1-negative tumors, suggesting that biomarker status may carry less predictive weight in the combination setting than in azenosertib monotherapy, where Cyclin E1 positivity anchors the registration strategy for PROC.

For drug product teams, the intermittent dosing schedule at the 250 mg level introduces scheduling complexity that will require careful attention to process validation parameters and packaging configurations as the program scales. The paclitaxel backbone is well-characterized under 21 CFR Part 211, but co-administration with a first-in-class WEE1 inhibitor at varying dose intensities will demand robust comparability data across any future manufacturing site changes or formulation adjustments.

Zentalis frames the MUIR trial as complementary to its core registration strategy rather than a pivot. The company's primary focus remains azenosertib monotherapy in Cyclin E1-positive PROC, with the combination arm representing an indication-expansion pathway into broader ovarian cancer settings and tumor types where taxanes are standard of care. Data from the other MUIR combination arms are expected to be disclosed separately.

The poster, Abstract #5529, is scheduled for the Gynecologic Cancer Poster Session on June 1, 2026, from 9:00 am to 12:00 pm CDT at the ASCO Annual Meeting in Chicago.

The 250 mg intermittent cohort's 9.2-month median duration of response will serve as a key benchmark as Zentalis determines whether to advance azenosertib-taxane combinations into later-phase, registration-enabling studies.

Source: Zentalis Pharmaceuticals via GlobeNewswire, May 21, 2026.