Pan-PIM Kinase Inhibitors Enhance Lenalidomide's Anti-Myeloma Activity Via Cereblon-IKZF1/3 Cascade

Pan-PIM Kinase Inhibitors Enhance Lenalidomide's Anti-myeloma Activity Via Cereblon-IKZF1/3 Cascade

Yonggang Sha¹, Jing Zheng², Jianda Hu²⁺, and Yubin Kang¹⁺

¹Division of Hematologic Malignancies and Cellular Therapy, Department of Medicine, Duke University Medical Center, Durham, North Carolina, USA; ²Fujian Institute of Hematology, Fujian Provincial Key Laboratory of Hematology, Fujian Medical University Union Hospital, China

⁺ Corresponding author: Yubin Kang, MD, Email: yubin.kang@duke.edu; and Jianda Hu, Email: drjiandahu@163.com.

ABSTRACT

Purpose: Multiple myeloma (MM) remains an incurable disease, and continuous efforts are required to develop novel therapeutic agents and novel drug combinations with more effective anti-myeloma activity. Immunomodulatory agents (IMiDs) including lenalidomide are one of the mainstays in the treatment of MM. It is important to identify and develop novel agents that can work with IMiDs for enhanced anti-myeloma effects. Here, we determined anti-myeloma effect of pan-PIM inhibitors and the synergistic anti-myeloma effects of pan-PIM inhibitors with IMiDs (lenalidomide).

Experimental Design: The anti-myeloma activities of pan-PIM inhibitors (SGI1776 and CX6258) and the synergistic anti-myeloma effects of pan-PIM inhibitors with lenalidomide were determined in human myeloma cells, transplanted VK*MYC myeloma mice, and myeloma xenograft mouse models. Western blot, protein stability assay, shRNA specific gene knockdown, and ubiquitination assay were performed to determine the molecular mechanisms involved.

Results: Pan-PIM inhibitors (SGI1776 and CX6258) induced the apoptosis of MM cells and exhibited significant anti-myeloma activities in human myeloma cells and in transplanted VK*MYC myeloma mice. Combination of PIM inhibitors with lenalidomide showed synergistic anti-myeloma effects without additional hematological or liver toxicities in vivo in myeloma xenograft mouse models. The treatments of pan-PIM inhibitors promoted ubiquitination and degradation of IKZF1 and IKZF3, the two transcription factors important for the survival of myeloma cells, and combining Pan-PIM inhibitors with lenalidomide leds to more effective degradation of IKZF1 and IKZF3 in vitro in human multiple myeloma cells and in vivo in myeloma xenograft mouse model. We further demonstrated that treatments with pan-PIM inhibitors resulted in an increased expression of Cereblon, and knockdown of Cereblon with shRNA abolished the effects of pan-PIM inhibitors on IKZF1 and IKZF3, demonstrating a central role of Cereblon in Pan-PIM inhibitor-mediated IKZF1/3 degradation.

Conclusions: We demonstrated that pan-PIM inhibitors (SGI1776 and CX6258) exhibited significant anti-myeloma activities and combination of pan-PIM inhibitors with lenalidomide showed synergistic anti-myeloma effects without additional hematological or liver toxicities. Mechanistically, pan-PIM kinase inhibitors enhance lenalidomide's anti-myeloma activity via Cereblon-IKZF1/3 Cascade. Our study provides molecular rationale and justification for clinical trials combining pan-PIM inhibitors and lenalidomide for the treatment of myeloma.