Abstract 3684: The combination of JAK inhibitor, ruxolitinib, pan-PIM inhibitor, LGH447, and CDK4/6 inhibitor, LEE011, in a preclinical mouse model of myeloproliferative neoplasia
Authors: Pinzon-Ortiz Maria , Rong Xianhui , Saci Abdel , Schlegel Robert , Vanasse Gary , Caponigro Giordano , Cao Z. Alexander 
Published: May 2015

Abstract
The JAK/STAT axis is a critical component downstream of multiple cytokine and growth factor receptor signaling pathways. The genetic aberration of JAK2V617F and the associated activation of STAT in myeloproliferative neoplasia (MPN) is one example of the involvement of this pathway in human cancer. Activated JAKs phosphorylate STAT proteins, which then up-regulate the transcription of STAT target genes such as PIM1. Pim kinases are involved in the regulation of cell cycle and proliferation. The inhibition of JAK1/2 by the JAK inhibitor, ruxolitinib (RUX), results in the suppression of the JAK-STAT pathway and promotes significant clinical benefit in patients with myelofibrosis. Our previous preclinical studies in a Ba/F3-JAK2V617F-driven MPN model demonstrate that the combination of RUX and the pan-PIM inhibitor, LGH447, exhibits greater inhibition of spleen weight and some reduction of JAK2V617F allele burden, compared with the RUX monotherapy. Mutant JAK2V617F has been shown to increase CDC25A transcription through activated STAT5. It also regulates p27 at both the gene expression and phosphorylation levels. The activation of CDC25A and the modulation of p27 have been postulated to trigger the activation of cyclin dependent kinases (CDK), such as CDK4, to initiate cell cycle progression. Additionally, activated STATs and Pims have been shown to activate D cyclins that are upstream of CDK4/6. Here, we explored the hypothesis that CDK4/6 inhibition, in conjunction with JAK and PIM inhibition, would enhance therapeutic efficacy against MPN. LEE011 is a potent and selective inhibitor of CDK4/6. The combination of RUX and LEE011 was tested in an MPN model with Ba/F3 cells harboring EPOR-JAK2V617F. While RUX monotherapy reduced spleen weight and total tumor burden by more than 50%, it had marginal effect on JAK2V617F allele burden in this model. The combination of RUX and LEE011 resulted in an additional 2 to 3 fold reduction in spleen weight and total tumor burden. Yet, no clear modulation of JAK2V617F allele burden was observed. To further enhance the anti-tumor activity, we tested the triple combination of RUX, LGH447 and LEE011 in this MPN model. This triple combination resulted in &gt;99% reduction of total tumor burden and a ∼96% reduction of spleen weight. Furthermore, the triple combination of RUX, LGH447 and LEE011 significantly down-modulated JAK2V617F allele burden by &gt; 80%. Our preclinical data indicate that the triple combination of RUX, CDK4/6 inhibitor, LEE011, and pan-PIM inhibitor, LGH447, may preferentially impact the JAK2V617F mutant MPN clones. This combination also achieves greater reductions in tumor burden and spleen weight in our preclinical MPN model. Therefore, potentially greater therapeutic benefit in subgroups of MPN patients may be achieved with the triple combination of RUX, LEE011 and LGH447.
Citation Format: Maria Pinzon-Ortiz, Xianhui Rong, Abdel Saci, Robert Schlegel, Gary Vanasse, Giordano Caponigro, Z. Alexander Cao. The combination of JAK inhibitor, ruxolitinib, pan-PIM inhibitor, LGH447, and CDK4/6 inhibitor, LEE011, in a preclinical mouse model of myeloproliferative neoplasia. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3684. doi:10.1158/1538-7445.AM2014-3684