Improved Efficacy Upon Combined JAK1/2 and Pan-Deacetylase Inhibition Using Ruxolitinib (INC424) and Panobinostat (LBH589) in Preclinical Mouse Models of JAK2V617F-Driven Disease
Authors: Baffert Fabienne , Evrot Emeline , Ebel Nicolas , Roelli Claudia , Andraos Rita , Qian Zhiyan , Romanet Vincent , Murakami Masato , Radimerski Thomas 
Published: October 2019

Abstract
Abstract 798FN2

Background:
Ruxolitinib (INC424), a potent and selective oral JAK1 and JAK2 inhibitor, has demonstrated rapid and durable reductions in splenomegaly and improved disease-related symptoms, role functioning, and quality of life in 2 phase 3 studies in patients with myelofibrosis. Panobinostat, a potent oral pan-deacetylase inhibitor (pan-DACi) that increases acetylation of proteins involved in multiple oncogenic pathways, has shown encouraging clinical activity in phase 1/2 trials of myelofibrosis. Here, we investigate the combination of ruxolitinib and panobinostat in mouse models of JAK2V617F-driven disease.

Methods:
Scid-beige female mice were randomized to treatment groups on the basis of baseline bioluminescence 4 days after injection of Ba/F3 EpoR JAK2V617F-luciferase cells. Mice were treated with vehicle control, panobinostat (4, 8, or 12 mg/kg intraperitoneal 3 times a week) alone or in combination with ruxolitinib (60 mg/kg orally twice daily), or ruxolitinib alone (n=7 each). Whole-body bioluminescence imaging was conducted on days 7 and 11. Spleens were weighed and extracts were obtained to determine levels of phosphorylated STAT5 (p-STAT5) and lysine acetylation.

Results:
Imaging on day 11 showed luminescence reductions (P <.05 compared with vehicle control) in all treatment groups (Table)
A dose-dependent reduction was observed in mice treated with panobinostat alone. Combination therapy produced the greatest reductions in luminescence, as low as 3% of the untreated control in the ruxolitinib + panobinostat (12 mg/kg) group (P <.05 compared with the same dose of panobinostat alone or ruxolitinib alone). Similarly, reductions in spleen weight (P <.05 compared with control) were observed with ruxolitinib alone and panobinostat (12 mg/kg) alone and in all combination groups. Treatment with ruxolitinib reduced phosphorylation of the JAK2 downstream target STAT5, whereas panobinostat treatment reduced total STAT5 levels. Mice treated with both panobinostat and ruxolitinib had reduced levels of p-STAT5 and total STAT5 in spleen extracts. Lysine acetylation, unchanged in ruxolitinib-treated mice, was markedly increased in panobinostat-treated mice. Together, the pharmacodynamic analyses indicate that ruxolitinib and panobinostat are active and have nonoverlapping and complementary effects on biological pathways. There was no major change in tolerability, as assessed by body weight, between panobinostat alone and in combination with ruxolitinib. The experiment was repeated with the 2 top doses of panobinostat and ruxolitinib and showed similar results. Based on these encouraging data, the combination is currently being tested in a mouse JAK2V617F bone marrow transplant model of myeloproliferative neoplasm (MPN) disease to assess its disease-modifying potential.

Conclusions:
The combination of ruxolitinib and panobinostat showed significant improvements in anticancer activity compared with either treatment given alone in this JAK2V617F mouse model. Further studies in a murine MPN disease model are underway.

Disclosures:
Baffert: Novartis Pharma AG: Employment. Evrot:Novartis Pharma AG: Employment. Ebel:Novartis Pharma AG: Employment. Roelli:Novartis Pharma AG: Employment. Andraos:Novartis Pharma AG: Employment. Qian:Novartis Pharma AG: Employment. Romanet:Novartis Pharma AG: Employment. Murakami:Novartis Pharma AG: Employment. Radimerski:Novartis Pharma AG: Employment.