Targeting CREB-Binding Protein (CREBBP) Overcomes Resistance to Azacitidine and Venetoclax Therapy in Acute Myeloid Leukemia (AML)
Authors: LeBlanc Francis , Bennett Josh , Choi Kwangmin , Starczynowski Daniel T. 
Published: December 2023

Acute myeloid leukemia (AML) is a clonal myeloid malignancy arising from hematopoietic stem or progenitor cells (HSPC) within the bone marrow (BM). Despite advancements in our understanding of AML pathogenesis, patients continue to face grim outcomes, with a five-year relative survival rate of approximately 20%. This highlights the pressing need to identify molecular features of AML that are amenable to therapeutic intervention. The ideal molecular targets would be those broadly dysregulated and integral to multiple signaling pathways implicated in AML pathogenesis. Recent therapeutic regimens have incorporated venetoclax, a small molecule inhibitor of BCL2, in combination with hypomethylating agents, showing moderate success. Venetoclax (VEN) acts as a BH3 mimetic, specifically inhibiting BCL2. While clinical outcomes of VEN combined with hypomethylating agents (decitabine or azacitidine - AZA) have been promising, a substantial subset of patients remains refractory or experiences relapse following treatment with these regimens. Due to the molecular and cellular heterogeneity of AML, identifying ideal mechanisms to circumvent resistance remains elusive.

In our investigations, we have observed that patient-derived cells from AML exhibit a higher frequency of dysregulated immune and inflammatory pathways than previously appreciated, referred to as “oncogenic immune signaling states.” Furthermore, immune and inflammatory-related pathways are preferentially expressed in AML patients who are resistant/refractory to VEN/AZA compared to those who respond favorably. To identify critical immune and inflammatory-related pathways contributing to VEN/AZA responses, we developed an oncogenic immune signaling-targeted CRISPR-library, aimed at identifying potential therapeutic targets involved in VEN/AZA resistance in AML. Utilizing this targeted CRISPR-screen approach, we successfully identified CREB-binding protein (CREBBP) as the top candidate linked to resistance to VEN/AZA therapy.

Notably, CREBBP alterations have been associated with a poor prognosis in de novo AML, making it a compelling target for further investigation. To validate CREBBP's role in VEN/AZA resistance, we treated a VEN/AZA-resistant AML cell line, THP1 (FAB subtype M5, KMT2A-r), with commercially available pharmacologic inhibitors of CREBBP, A485, and CCS1477, and assessed the response. Remarkably, inhibition of CREBBP with either A485 or CCS1477 significantly decreased cell proliferative ability and clonogenic potential. Importantly, co-treatment with either A485 or CCS1477 and VEN/AZA synergistically abrogated cell proliferation and clonogenic potential of THP1 cells, effectively overcoming resistance (Figure 1).

Our ongoing studies include validating CREBBP as a potential therapeutic target for overcoming VEN/AZA resistance in AML. We have created CREBBP-knockdown cell lines through genetic manipulation (shRNA) and will utilize these to confirm the specificity of CREBBP in modifying resistance to VEN/AZA. In addition we will utilize patient-derived xenograft studies in immunocompromised (NRG) mouse models. By investigating CREBBP's role in mediating resistance, we aim to unlock new avenues for enhancing the efficacy of VEN/AZA therapy in AML patients, particularly those facing resistance to current therapies.

In conclusion, our research highlights the critical involvement of CREBBP in VEN/AZA resistance in AML. Targeting this molecular pathway holds the promise of offering a potential therapeutic approach to improve treatment outcomes for AML patients, particularly those facing resistance to current therapies. Understanding and harnessing CREBBP's influence could pave the way for developing personalized and effective strategies to combat this challenging hematological malignancy.