8-K: Nurix Therapeutics Unveils Robust Phase 1 Data for Bexobrutideg in Relapsed/Refractory CLL and WM, Paving Way for Pivotal Trials

Nurix Therapeutics announced compelling updated Phase 1 clinical data for its investigational BTK degrader, bexobrutideg (NX-5948), demonstrating high objective response rates and a favorable safety profile in heavily pretreated patients with relapsed or refractory Chronic Lymphocytic Leukemia (CLL) and Waldenström Macroglobulinemia (WM), with pivotal trials slated for 2025.

Summary

• Bexobrutideg (NX-5948) is an investigational, orally bioavailable, brain penetrant, small molecule degrader of Bruton's tyrosine kinase (BTK).
• Updated clinical data from the fully enrolled Phase 1a dose escalation study (n=48) in relapsed/refractory CLL/SLL patients was presented.
• This CLL/SLL cohort was heavily pretreated, with a median of four prior lines of therapy (range 2-12), including prior covalent BTK inhibitors (97.9%), BCL2 inhibitors (83.3%), and non-covalent BTK inhibitors (27.1%).
• Many CLL/SLL patients had BTK inhibitor resistance mutations (BTK 38.3%, PLCG2 14.9%) and poor prognostic features (TP53 mutations 44.7%, CNS involvement 10.4%).
• As of the March 12, 2025 data cut, the median follow-up for CLL/SLL was 9.0 months, with most patients still on treatment.
• Bexobrutideg was well tolerated across all doses (50 mg to 600 mg once daily) in CLL/SLL, with the most common treatment emergent adverse events being purpura/contusion (45.8%), neutropenia (29.2%), and thrombocytopenia (22.9%), primarily low grade. No new onset atrial fibrillation was observed.
• Among efficacy evaluable CLL/SLL patients (n=47), bexobrutideg treatment resulted in an objective response rate (ORR) of 80.9% across all doses, with a median time to first response of 1.9 months.
• Many patients experienced deepening of their response with longer time, with multiple conversions from stable disease to partial responses and one patient, on treatment for over two years, experienced a complete response.
• The median duration of response has not been reached in CLL/SLL, with 18 patients on treatment for more than a year.
• Responses were observed across all CLL/SLL populations regardless of prior treatment, baseline mutations, or CNS involvement.
• Data for WM patients (n=22) from Phase 1a/1b cohorts showed a median age of 72.5 years and a median of 3 prior lines of therapy, with all (100%) having received a covalent BTK inhibitor.
• In WM, bexobrutideg was well tolerated, consistent with the overall study population, with common AEs being petechiae (27.3%), diarrhea (22.7%), purpura/contusion (18.2%), neutropenia (18.2%), and thrombocytopenia (18.2%). No new onset atrial fibrillation or Grade 5 AEs were observed.
• In 19 efficacy evaluable WM patients, the ORR was 84.2%, including two patients (10.5%) with very good partial response (VGPR), 11 patients (57.9%) with partial response (PR), and three patients (15.8%) with minor response (MR).
• Steady reductions in IgM levels were observed in WM patients, with three achieving greater than 90% reduction.
• The median duration of response for WM has not been reached.

Sentiment

Score: 9

Explanation: The document presents overwhelmingly positive clinical data for bexobrutideg, demonstrating high efficacy and a favorable safety profile in difficult-to-treat patient populations. The company's clear path to pivotal trials and strategic positioning in a growing market indicate strong future prospects. The tone is confident and the results appear to exceed typical expectations for Phase 1 data in this therapeutic area.

Positives

• High objective response rates (ORR) of 80.9% in heavily pretreated CLL/SLL patients and 84.2% in WM patients.
• Demonstrated deepening of responses over time, including a complete response in a CLL patient and very good partial responses in WM patients.
• Bexobrutideg was well tolerated across all doses in both CLL/SLL and WM, with adverse events primarily low grade and no new safety signals observed with longer duration or higher doses.
• No new onset atrial fibrillation observed in either patient population, which is a known side effect of some BTK inhibitors.
• Responses observed across all CLL/SLL populations regardless of prior treatment, baseline mutations (including BTK and PLCG2 resistance mutations), or CNS involvement.
• Ability to overcome treatment-emergent BTKi resistance mutations and disrupt BTK scaffolding, addressing an unmet medical need.
• Fast Track Designation from the FDA for CLL (January 2024) and WM (December 2024), and EU PRIME designation from EMA (November 2024), indicating potential for accelerated development.
• Orphan Drug Designation from the FDA for WM (March 2025).
• Company remains on track to initiate pivotal trials of bexobrutideg in 2025.
• Bexobrutideg is brain penetrant and shows clinical CNS activity.

Negatives

• The data presented is from Phase 1a/b studies, which are early-stage trials, and larger, later-stage trials are needed to confirm efficacy and safety.
• Two treatment emergent adverse events led to drug discontinuation in WM patients.

Risks

• Risks inherent in the drug development process, including the unexpected emergence of adverse events or other undesirable side effects during clinical development.
• Uncertainties related to the timing and results of clinical trials.
• Whether Nurix will be able to fund its research and development activities and achieve its research and development goals.
• The impact of economic and market conditions and global and regional events on Nurix's business, clinical trials, financial condition, liquidity, and results of operations.
• Whether Nurix will be able to protect intellectual property.
• Risks and uncertainties relating to the timing and receipt of payments from Nurix's collaboration partners, including milestone payments and royalties on future potential product sales.
• The extent animal model data predicts human efficacy.

Future Outlook

Nurix Therapeutics remains on track to initiate pivotal trials for bexobrutideg in 2025, with plans for a streamlined clinical development path covering all lines of therapy. This includes a single-arm monotherapy trial in post-BTKi/post-BCL2i patients for potential accelerated approval, a randomized head-to-head trial in the post-cBTKi, 2L+ population, and potential expansion to 1L+ with combination studies. The company is also laying the foundation for commercialization, aiming to establish bexobrutideg as a differentiated treatment option and lead a new class of therapeutics in CLL with best-in-class ambition.

Management Comments

• Dr. Talha Munir stated that the data demonstrate an impressive safety and efficacy profile for bexobrutideg with improvement in responses in patients over time, including a complete response in a CLL patient, and that bexobrutideg has the potential to address the unmet need for patients with relapsed or refractory CLL and WM who have failed prior treatments.
• Dr. Paula G. OConnor, Chief Medical Officer, commented that with longer time on treatment, the company is encouraged by the continued favorable safety profile and high ORR with deepening responses in CLL and WM, including those with high-risk features, and that they remain on track to initiate pivotal studies in 2025.
• Dr. Arthur T. Sands, President and CEO, highlighted that bexobrutideg offers a next-generation approach to BTK targeting with exquisite selectivity, superior preclinical potency, broad coverage of mutations, and demonstrated clinical activity in areas of high unmet medical need, and that Nurix is preparing to initiate pivotal studies and laying the foundation for commercialization.

Industry Context

Bexobrutideg is positioned as a novel Bruton's tyrosine kinase (BTK) degrader, a new therapeutic modality designed to overcome limitations of existing BTK inhibitors, particularly resistance mutations (e.g., C481S, T474I) and the scaffolding function of BTK. It aims to address the growing unmet need in heavily pretreated relapsed/refractory CLL and WM patients who have failed prior covalent and non-covalent BTK inhibitors and BCL2 inhibitors. The company believes it can displace current BTK inhibitors and potentially expand into earlier lines of therapy, including combinations with BCL2 inhibitors, in a market projected to grow from over $9 billion in 2024 to over $15 billion by 2028 for BTK-targeting agents in CLL.

Comparison to Industry Standards

• Bexobrutideg is designed to overcome treatment-emergent BTKi resistance mutations and disrupt BTK scaffolding, which are limitations of current BTK inhibitors.
• It exhibits exquisite selectivity and superior potency against wild-type BTK compared to other BTK degraders.
• It offers the broadest coverage of BTK resistance mutations and is the only degrader with demonstrated clinical CNS activity and blood-brain barrier penetration.
• The high ORR (80.9% in CLL, 84.2% in WM) and deepening responses, including complete response, in heavily pretreated, high-risk patient populations suggest a strong competitive profile against existing therapies where patients have limited options due to intolerance or acquired resistance.
• The absence of new onset atrial fibrillation is a notable safety advantage compared to some existing BTK inhibitors.

Stakeholder Impact

• Shareholders: Positive impact due to strong clinical data, potential for accelerated approval, and entry into a large and growing market, which could lead to increased valuation and future revenue.
• Patients: Significant positive impact by offering a potentially life-changing treatment option for heavily pretreated patients with relapsed/refractory CLL and WM, especially those with resistance mutations or CNS involvement, who currently have limited therapeutic options.
• Healthcare Providers: Provides a novel, effective, and well-tolerated treatment option for challenging B-cell malignancies.
• Competitors: Introduces a new class of BTK degraders that could disrupt the existing BTK inhibitor market.

Next Steps

• Initiate pivotal trials of bexobrutideg in 2025.
• Conduct a single-arm monotherapy trial in post-BTKi/post-BCL2i patients (Fast Track population) for potential accelerated approval.
• Conduct a randomized head-to-head trial versus comparator(s) in the post-cBTKi, 2L+ population.
• Explore potential expansion to 1L+ with bexobrutideg in combination with BCL2i head-to-head versus standard of care.
• Continue enrollment in additional Phase 1b sub-population cohorts for CLL (e.g., high-risk genetic profiles, 2L+ disease with prior BTKi but no BCL2i, BTKi-naive, wAIHA, prior BTKi with CNS involvement).
• Lay the foundation for the commercialization of bexobrutideg.

Key Dates

Recommendation

Keywords

Nurix Therapeutics, NRIX, Bexobrutideg, NX-5948, BTK degrader, Chronic Lymphocytic Leukemia, CLL, Waldenström Macroglobulinemia, WM, B-cell malignancies, Phase 1 clinical trial, targeted protein degradation, oncology, hematology, clinical data, drug development, biopharmaceutical, SEC filing, 8-K, EHA2025