Abstract 3726: INCB52793 JAK1 inhibitor synergizes with ATRA to inhibit expansion of AML
Authors: Ramsey Haley E. , Ferrell P. Brent , Fischer Melissa A. , Gorska Agnieszka E. , Maier Caroline , Norris Jeremy , Farrow Melissa , Guiterrez Danielle , Pino James , Zinkel Sandra , Lopez Carlos , Koblish Holly , Stubbs Matthew , Scherle Peggy , Irish Jonathan M. , Caprioli Richard , Savona Michael R. 
Published: July 2017

Abstract
Dysregulated JAK/STAT signaling is known to drive myeloproliferative neoplasms, and targeting JAK1 and JAK2 has led to improvement in morbidity and mortality in these diseases. While dose-dependent anemia and thrombocytopenia limit the use of JAK2 inhibition, selectively targeting JAK1 has been explored as a means to suppress inflammation and STAT-associated neoplastogenesis. Recently, INCB52793 was found to be 100-fold selective for JAK1 over JAK2, and it has recently been explored in the clinic in solid tumors and acute myeloid leukemia (AML). In a large high throughput screen, we detected synergistic effects between INCB52793 and all-trans retinoic acid (ATRA) in several non-promyelocytic AML cell lines. In another in vitro assay, human primary AML blasts exposed to INCB52793 exhibited a marked increase in both CD13 and CD86, two markers indicative of cellular differentiation.
Given these findings, we tested this combination in an in vivo murine model of AML. Human leukemia cells were injected into the tail vein of sublethally irradiated NSGS mice which were then treated days 7-35 post-transplant with ATRA, INCB52793, ATRA/INCB52793, or vehicle. Weekly monitoring for peripheral human CD45+ cells revealed that the INCB52793/ATRA combination effectively decreased the expansion of leukemic cells. At 35-40 days, significant decreases in tumor burden were seen within the bone marrow (BM) and spleens of INCB62793/ATRA treated mice. Bone marrow and splenic cells were also analyzed by mass cytometry, simultaneously measuring 35 signaling, differentiation, and cell death attributes per-cell. The few remaining human cells in the INCB62793/ATRA combo group synergistically displayed 30-fold decreases in CD38, 8-fold increases in CD34, and attained high levels of p-STAT3 and p-STAT5, potentially implying a resistant progenitor population.
Label free proteomics revealed significant fold changes in in vitro INCB52793/ATRA treated cells. Proteins related to cellular differentiation mechanisms, such as SMAD3, BCL11A, RUNX2, HNRNPLL, and SAMHD1, were elevated between 24 to 48 hours post treatment supporting our hypothesis that JAK1 inhibition enhanced ATRA induced differentiation.
Targeting retinoic acid receptor and JAK1 together synergistically resulted in the decreased expansion of multiple AML cell lines, and preferential reduction of AML cells from the blood, spleen and bone marrow of treated mice in vivo. Common CD34-CD38+ tumor cells were eliminated, and rare remaining CD34+ AML cells displayed high p-STAT3 and p-STAT5 levels after INCB52793/ATRA therapy. While ATRA is a critical component in the therapy of acute promyelocytic leukemia (M3), it has not been successfully employed in other AML. These preliminary data represent a potential for INCB52793/ATRA therapy in non-M3 AML.
Citation Format: Haley E. Ramsey, P. Brent Ferrell, Melissa A. Fischer, Agnieszka E. Gorska, Caroline Maier, Jeremy Norris, Melissa Farrow, Danielle Guiterrez, James Pino, Sandra Zinkel, Carlos Lopez, Holly Koblish, Matthew Stubbs, Peggy Scherle, Jonathan M. Irish, Richard Caprioli, Michael R. Savona. INCB52793 JAK1 inhibitor synergizes with ATRA to inhibit expansion of AML [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3726. doi:10.1158/1538-7445.AM2017-3726