Abstract 564: Therapeutic targeting of JAK/STAT signaling and histone acetyltransferase activity in post-myeloproliferative neoplasm secondary AML

Abstract Post-myeloproliferative neoplasm secondary Acute Myeloid Leukemia (Post-MPN sAML) is an aggressive and lethal hematologic malignancy arising from myeloproliferative neoplasms (MPN). Hyperactivation of JAK/STAT signaling was identified in 50-90% of MPNs - underscoring its role in driving MPN pathogenesis and transformation to post-MPN sAML. Ruxolitinib, a Type-I JAK2 inhibitor approved for the treatment of myelofibrosis, was tested in a Phase II clinical trial in post-MPN sAML. The trial revealed that ruxolitinib improved the quality of life in patients but was not disease-modifying. Thus, there is an urgent need to find synergistic drug combinations capable of complementing the therapeutic activity of JAK2 inhibitors in post-MPN sAML. Here, we demonstrate that combination treatment of ruxolitinib and CBP30, a bromodomain inhibitor of histone acetyltransferases (HAT) CBP and p300, enhances the therapeutic activity of ruxolitinib in post-MPN sAML. Genome-wide CRISPR loss-of-function screens in JAK2-mutated HEL cells determined that knockout of CBP sensitizes leukemic cells to JAK2 inhibitors. Consistently, functional validation through CRISPR/Cas9 demonstrated that genetic deletion of CBP but not of p300 renders HEL cells sensitive to ruxolitinib treatment. Pharmacologic inhibition of JAK/STAT signaling and HAT activity through ruxolitinib and CBP30 treatment in post-MPN sAML lines HEL and SET2 decreases proliferation and induces apoptosis and cell cycle arrest. Mechanistically, the synergism between ruxolitinib and CBP30 elicits a unique transcriptome profile in HEL with significant downregulation of E2F and MYC targets. In addition, epigenetic profiling revealed that the synergism induces global changes in H3K27ac signals with downregulation and upregulation of H3K27ac signals in predicted STAT5/BCL3 and GATA-bounded regions, respectively. Remarkably, combination treatment of ruxolitinib and CBP30 in HEL luciferase NSG mouse xenografts showed significant leukemia regression and decrease in spleen size compared to mice treated with vehicle or single agents. Overall, these results substantiate the potential of targeting JAK/STAT signaling and histone acetyltransferase activity in the treatment of post-MPN sAML. Citation Format: Kalay Bertulfo, Koen Debackere, Hannah Miller, Cindy Ma, Ryan Najac, Adolfo Ferrando, Teresa Palomero. Therapeutic targeting of JAK/STAT signaling and histone acetyltransferase activity in post-myeloproliferative neoplasm secondary AML abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 564.