Reducing regorafenib toxicity by combining with dual JAK-HDAC inhibitor in colorectal cancer.

e15597 Background: In the US, colorectal cancer (CRC) is the third most common cancer. Patients receiving regorafenib, a multiple-kinase inhibitor, recommended to manage metastatic CRCs (mCRCs), has a modest improvement in median overall survival but it is associated with several toxicities. Our present study addresses regorafenib-induced toxicity concerns by combining regorafenib with a novel dual JAK-HDAC inhibitor (JAK-HDACi). The rationale for the dual inhibitor drug selection is due to the facts that the JAK/STAT/SOCS pathway is modulated in CRCs, and concurrent inhibition of JAK sensitizes solid tumors to HDACi. This study focused on evaluating the efficacy and reducing regorafenib-induced toxicity with this novel therapeutic combination in CRC preclinical models. Methods: We evaluated the toxicity of the JAK-HDACi, regorafenib, and their combination in normal colonic cells (CRL-1807) and their efficacy in CRC cell lines (HCT116, RKO, HT29, and SW480) exhibiting various statuses of p53, KRAS, BRAF, EGFR, and microsatellite instability, by conducting colony formation, cell proliferation, and cell cycle arrest assays. Kinome profiling and whole transcriptomic analysis were performed. Their efficacy was assessed in vivo in a CRC patient-derived xenograft (PDX) model, and experimental metastasis was evaluated in NSG mice using luciferase-tagged HT29 cells. Non-invasive, whole-body bioluminescence imaging was performed. Tumor tissues were harvested and stored at −80°C or prepared formalin-fixed paraffin-embedded blocks for Hematoxylin and Eosin (H&E) and immunostaining. Serum analysis was performed to evaluate liver and kidney functions to assess the toxicity. Results: At 500 nM concentrations, there was no pronounced death of CRL-1807 cells, but reduced number of colonies in CRC cells. Drug treatments decreased phosphorylation of STAT3 and ERK1/2 and cell viability, wherein the reduction was robust in the combination. The combination reduced activity of various kinases, as evident through kinome profiling. In SW480 cells, the combination caused G0-G1 cell arrest and decreased the S phase. RNA-seq results revealed modulation of key pathways: apoptosis, ECM-receptor interaction, and focal adhesion. The PDX model showed that the combination treatment reduced tumor growth, as evidenced in H&E staining with higher necrosis and reduced Ki67 staining. Experimental metastasis, bioluminescence imaging, and histological examination showed pronounced reduction in metastasis in mice treated with the combination. Serum chemistry profiles showed that the treatments did not cause systemic toxicity to mice used in either model. Conclusions: The combination therapy with the JAK-HDACi and regorafenib was more effective than the single agents with no evident toxicity. These findings lend credence to a clinical trial to assess this combination for treatment of patients with advanced CRC.