Treatment with β-Catenin Antagonist BC2059 Exerts Single Agent Efficacy and Exerts Improved Activity with Tyrosine Kinase Inhibitor (TKI) or Pan-Histone Deacetylase (HDAC) Inhibitor Against Human CML and Myeloproliferative Neoplasm (MPN) Progenitor Cells
Authors: Fiskus Warren , Smith Jacqueline , Mudunuru Uma , Hembruff Stacey , Reyes Ruben , Abhyankar Sunil , McGuirk Joseph , Aljitawi Omar S. , Ganguly Siddhartha , Horrigan Stephen K. , Sharma Sunil , Bhalla Kapil N. 
Published: October 2019

Abstract
Abstract 65
The canonical WNT-β-catenin pathway is essential to the cellular processes of self-renewal, growth and survival. Deregulated WNT-β-catenin in transformed hematopoietic progenitor cells inhibits the multi-protein degradation complex formed by axin, adenomatous polyposis coli (APC) and glycogen synthase kinase 3β (GSK3β). This results in the preservation, nuclear translocation and interaction of β-catenin with the T-cell factor (TCF)/lymphoid enhancer factor (LEF) transcription factor, which regulates the expression of genes such as cyclin D1, Myc, survivin and Axin. BC2059 (β-Cat Pharmaceuticals) is a potent small molecule, anthraquinone oxime-analog inhibitor of the WNT-β catenin pathway. Treatment with BC2059 mediates the degradation of β-catenin. In the present studies, we determined the activity of BC2059 in human cultured and primary CML and advanced MPN versus normal progenitor cells. Exposure to 50 to 100 nM of BC2059 induced cell cycle G1 phase accumulation and apoptosis (40 to 80%) of the cultured MPN cells HEL92.1.7 (HEL) and UKE1 cells expressing the mutant JAK2V617F, as well as of the CML K562 and LAMA-84 cells expressing BCR-ABL. BC2059 treatment also induced apoptosis of CD34+ primary MPN cells derived from the peripheral blood of patients with advanced MPN expressing mutant JAK2, as well as of primary CD34+ CML progenitor cells. In contrast, as compared to the untreated controls, BC2059 treatment did not induce apoptosis of normal CD34+ progenitor cells. Exposure to BC2059 resulted in marked down regulation of β-catenin protein levels and the activity of the LEF1/TCF4 transcription factor, which was accompanied with reduced levels of cyclin D1, MYC, survivin and up regulation of Axin 2 levels, as detected by immunoblot analyses of the cell lysates of BC2059-treated CML and MPN cells. We also determined the in vivo anti-MPN activity of BC2059. Following the tail vein infusion of HEL cells and establishment of MPN, NOD-SCID mice were treated with 15 or 20 mg/Kg of BC2059 administered b.i.w for three weeks via the tail vein. As compared to the control, BC2059-treated mice demonstrated significantly improved survival (p <0. 001). Next, we examined the effects of co-treatment with BC2059 (20 to 50 nM) and JAK2-targeted TKI TG101209 (TG) (200–1000 nM) or BCR-ABL-targeted TKI nilotinib (10–20 nM) against MPN or CML cells, respectively. As compared to treatment with each agent alone co-treatment with BC2059 and TG synergistically induced apoptosis of HEL and primary CD34+ MPN cells. Additionally, co-treatment with BC2059 and nilotinib induced synergistic apoptosis of K562 and primary CML progenitor cells. Further, combined treatment with BC2059 and the HDAC inhibitor panobinostat (10 to 20 nM) also induced significantly more apoptosis of HEL and K562 (p < 0.01), as well as of the primary CD34+ MPN and primary CML progenitor cells. In normal CD34+ progenitor cells, the BC2059-based combinations were remarkably less toxic (p < 0.01). These findings demonstrate that BC2059 exerts notable in vitro and in vivo activity against human MPN and CML versus normal CD34+ progenitor cells. Additionally, BC2059 may exert superior activity in combination with JAK2 or BCR-ABL-targeted TKI, or with pan-HDAC inhibitor against human MPN or CML progenitor cells.

Disclosures:
Reyes: Millennium, Sanofi Aventis: Consultancy. Horrigan:BetaCat Pharmaceuticals: Employment, Equity Ownership. Sharma:Beta Cat Pharmaceuticals: Equity Ownership.