Abstract 1874: The PIM kinase inhibitor TP-3654 demonstrates efficacy in a murine model of myelofibrosis

Myelofibrosis (MF) is the deadliest form of myeloproliferative neoplasms (MPN). The JAK2V617F mutation has been found in ~50% patients with MF. Ruxolitinib, a JAK1/JAK2 inhibitor, has been approved for treatment of MF. However, Ruxolitinib treatment has failed to induce disease remission or cure fibrosis. Therefore, there is a need to develop novel targeted therapies for MF. We found that PIM1 expression is significantly increased in mouse and human MPN/MF hematopoietic progenitor cells. Moreover, PIM1 knockdown markedly inhibited proliferation in JAK2V617F-expressing cells but not in wild-type JAK2-expressing cells. In this study, we investigated the efficacy of the second-generation pan-PIM kinase inhibitor, TP-3654, in hematopoietic cells expressing JAK2V617F and in a murine model of MF. We found that TP-3654 (0.5-1.0 μM) treatment significantly reduced proliferation of murine Ba/F3-EpoR cells expressing JAK2V617F or human JAK2V617F-positive HEL and UKE-1 cells. TP-3654 Treatment also resulted in marked apoptosis in Ba/F3-EpoR-JAK2V617F, HEL and UKE-1 cells but not in wild-type JAK2 expressing Ba/F3-EpoR cells. Additionally, TP-3654 and Ruxolitinib synergistically induced apoptosis in JAK2V617F-expressing hematopoietic cells. Furthermore, TP-3654 significantly inhibited MPN/MF CD34+ hematopoietic progenitor colony growth. We previously reported the generation of JAK2V617F knock-in mice. Whereas heterozygous JAK2V617F knock-in mice exhibit a polycythemia vera phenotype, mice expressing homozygous JAK2V617F rapidly develop high-grade MF. We have utilized the homozygous JAK2V617F mice to test the in vivo efficacy of TP-3654 alone or in combination with Ruxolitinib against MF. Treatment of TP-3654 alone significantly reduced the increase in white blood cell (WBC) and neutrophil counts as well as spleen size in mice expressing homozygous JAK2V617F compared with vehicle treatment. Combined treatment of TP-3654 and Ruxolitinib almost completely normalized the WBC and neutrophil counts and the spleen size in homozygous JAK2V617F mice. Histopathologic analysis revealed marked reduction in fibrosis in the bone marrow and spleens of TP-3654-treated mice whereas Ruxolitinib treatment did not significantly reduce fibrosis. Combined TP-3654 and Ruxolitinib treatment almost completely eliminated fibrosis in the bone marrow and spleens of homozygous JAK2V617F mice. TP-3654 treatment was well tolerated and did not cause any significant toxicity in wild type mice. RNA-sequencing analysis on purified LSK (Lin-Sca-1+c-kit+) cells from these drug-treated mice revealed that the genes related to TNFα and WNT signaling pathways were significantly down-regulated by treatment of TP-3654 alone or TP-3654 and Ruxolitinib combination compared with vehicle. Overall, our results suggest that TP-3654 alone or in combination with Ruxolitinib may have therapeutic potential for treatment of MF. Citation Format: Avik Dutta, Dipmoy Nath, Yue Yang, Golam Mohi. The PIM kinase inhibitor TP-3654 demonstrates efficacy in a murine model of myelofibrosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1874.