REWIRING ONCOGENIC PATHWAYS TO INDUCE CELL DEATH IN CHRONIC LYMPHOCYTIC LEUKEMIA

Crabtree, Kay, Gray and Woyach REWIRING ONCOGENIC PATHWAYS TO INDUCE CELL DEATH IN CHRONIC LYMPHOCYTIC LEUKEMIA ASSIST ID1959504 Summary Chronic lymphocytic leukemia (CLL) is the most common chronic leukemia in the US. CLL remains incurable with ~4,500 death per year. The most urgent need for new therapies involves patients who have progressed after targeted therapies that now define modern care - BTK inhibitors and BCL-2 antagonists. The second major unmet need concerns patients with Richter transformation (RT), particularly because the incidence of RT climbs to ~ 15 % after six years of BTK-inhibitor therapy. Once CLL evolves into this aggressive lymphoma, median overall survival falls below 1 year. Taken together, progressive or relapsed CLL, particularly BTK/BCL- 2 double-refractory disease and RT, is a critical unmet medical need that demands new and innovative therapeutic strategies. The Crabtree and Gray laboratories have produced a new class of small molecules that rewire mutated cancer drivers to directly activate precise and powerful pathways of programmed cell death using chemically induced proximity (CIP). This class of molecules, called TCIPs (Transcriptional/Epigenetic Chemical Inducers of Proximity) uses a unique dominant gain-of-function mechanism designed to eliminate cancer cells containing the driving mutation in the face of secondary driver mutations or alternate oncogenic pathways (Gourisankar et al Nature 2023; Sarott et al Science, 2024). Indeed, in DLBCL (Diffuse Large B Cell Lymphoma), TCIP1 eliminates triple-hit PDX models as a single agent in only 21 days without recurrence or evidence of toxicity in mice. These molecules use chemically induced proximity (CIP) to bring epigenetic or transcriptional activators to the promoters of cell death genes normally bound and repressed by the BCL6 oncogenic transcription factor. By this means the BCL6 protein is rewired to be an activator rather than a repressor of proapoptotic genes, stimulating their expression and specifically killing the malignant cells. Since the original submission of this application, we have surveyed our combinatorial library of TCIP molecules and have found that TCIP2 (BCL6-CDK9, BAK-04-232) is highly effective (IC50 1 -20 nM) at selectively killing leukemic CLL cells. Recent studies, that showed BCL6 to be the most frequently mutated non-Immunoglobulin (Ig) gene in CLL B cells, suggest that non-coding mutations in the BCL6 gene are positively selected and that BCL6 contributes to the pathogenesis of CLL. We will define the mechanism underlying killing of CLL cells and explore the way that antiapoptotic epigenetic states are rewired by TCIP2 to become proapoptotic. To understand the potential role of TCIPs in CLL therapy, we will define the molecular features of cells sensitive to TCIP2 with the goal of identifying patient selection criteria that predict responses. For further mechanistic understanding of TCIP killing, we will explore the role of somatic hypermutation and negative autofeedback at the BCL6 locus of CLL B-cells in the pathogenesis of CLL and in producing sensitivity to TCIPs. Finally, we will use robust murine models to test the efficacy of TCIP2 in vivo. At the conclusion of our studies, we expect to have laid the foundation for clinical trials that will define the potential use of TCIPs in the treatment of CLL. Project Number: 1R01CA304428-01A1 | Fiscal Year: 2026 | NIH Institute/Center: National Cancer Institute (NCI) | Principal Investigator: Gerald Crabtree (+1 co-PI) | Institution: STANFORD UNIVERSITY, STANFORD, CA | Award Amount: $661,135 | Activity Code: R01 | Study Section: Advancing Therapeutics A Study Section [ATA] View on NIH RePORTER: https://reporter.nih.gov/project-details/11367607