Rolfe, Mark

Abstract Hematological malignancies such as multiple myeloma (MM) have an increased reliance on the ubiquitin proteasome system (UPS) presumably as a consequence of their high protein synthetic and secretory burden. Chemical agents that target the proteasome, such as bortezomib and carfilzomib, have been successful in treating multiple myeloma; however patients treated with these drugs ultimately relapse. The AAA-ATPase p97/VCP (p97) facilitates ATP-dependent extraction and degradation of ubiquitinated proteins destined for proteasomal elimination. In addition to ubiquitin-dependent protein degradation, p97 is also closely involved in other aspects of protein homeostasis, including endoplasmic reticulum-associated degradation (ERAD) and autophagy. Pharmacologic inhibition of p97 provides a compelling therapeutic approach for hematological malignancies that rely on tight regulation of protein homeostasis as a component of their survival. CB-5083 is a novel small molecule inhibitor of p97 ATPase activity with nanomolar enzymatic and cellular potency. Treatment of cancer cells with CB-5083 causes a dramatic increase in poly-ubiquitinated proteins as well as an accumulation of substrates of the UPS and ERAD. CB-5083 causes a profound induction of the unfolded protein response (UPR) with consequent activation of the DR5 death receptor, caspase 8, caspase 3/7 and ultimately cell death. Induction of the UPR occurs to a greater magnitude with CB-5083 when compared to the proteasome inhibitor, bortezomib, suggesting the potential for increased efficacy in cancers with sensitivity to UPR-mediated cell death. In addition, activation of apoptosis and cell death occur more rapidly with CB-5083 than with bortezomib. Sequencing of cell lines made resistant to CB-5083 reveals missense mutations mapping to the D2 ATPase site in p97, supporting on-target association with cytotoxicity. In an expanded panel of MM cell lines there is no correlation between the cytotoxic sensitivity to CB-5083 and the cytotoxic sensitivity to proteasome inhibitors, suggesting differential mechanisms of cytotoxicity and potential activity of CB-5083 in proteasome inhibitor resistant settings. Compared to myeloma cell lines, CB-5083 has reduced cytotoxic potency in immortalized stromal cell lines and in patient-derived CD138-negative bone marrow mononuclear cells. Furthermore, unlike the reduced potency demonstrated by carfilzomib in the context of MM cell-bone marrow stromal cell (BMSC) interactions, the cyto-reductive potential of CB-5083 is unaffected in co-cultures of MM cells with patient-derived BMSCs or immortalized BMSCs from healthy donors. In vivo, CB-5083 is orally bioavailable, shows a pharmacodynamic effect in tumor tissue (as measured by poly-ubiquitin accumulation) and demonstrates robust anti-tumor activity across several MM models. CB-5083 treatment of mice bearing subcutaneous xenografts leads to tumor stasis and regression in RPMI8226 and AMO1 MM models, respectively. In advanced models of disseminated, ortho-metastatic disease, intermittent oral administration of CB-5083 demonstrates significant inhibition of myeloma burden and improves survival, with an overall efficacy profile that compares favorably to that of clinically approved proteasome inhibitors. Furthermore, in the Vk*Myc genetically engineered mouse model of MM, treatment with CB-5083 results in a significant reduction in M-spike by 55%. Combination treatment of mice bearing the RPMI8226 subcutaneous xenograft model with CB-5083, dexamethasone and lenalidomide results in tumor regression. Taken together, these data demonstrate that CB-5083 is a potent and selective inhibitor of the p97 ATPase with robust activity in vitro and in vivo in numerous MM models and strongly support clinical evaluation. Based on these observations, a phase 1 dose-escalation trial has recently been initiated and is currently underway in patients with relapsed/refractory multiple myeloma. Disclosures Anderson: Cleave Biosciences: Employment. Le Moigne:Cleave Biosciences: Employment. Djakovic:Cleave Biosciences: Employment. Rice:Cleave Biosciences: Employment. Wong:Cleave Biosciences: Employment. Kumar:Cleave Biosciences: Employment. Valle:Cleave Biosciences: Employment. Menon:Cleave Biosciences: Employment. Kiss von Soly:Cleave Biosciences: Employment. Wang:Cleave Biosciences: Employment. Yao:Cleave Biosciences: Employment. Soriano:Cleave Biosciences: Employment. Bergsagel:ONYX: Consultancy; Janssen: Consultancy; BMS: Consultancy; Novartis: Research Funding. Yakes:Cleave Biosciences: Employment. Zhou:Cleave Biosciences: Employment. Wustrow:Cleave Biosciences: Employment. Rolfe:Cleave Biosciences: Employment.

Abstract Inhibition of the AAA ATPase, p97, was recently shown to be a novel method for targeting the ubiquitin proteasome system, and CB-5083, a first-in-class inhibitor of p97, has demonstrated broad antitumor activity in a range of both hematologic and solid tumor models. Here, we show that CB-5083 has robust activity against multiple myeloma cell lines and a number of in vivo multiple myeloma models. Treatment with CB-5083 is associated with accumulation of ubiquitinated proteins, induction of the unfolded protein response, and apoptosis. CB-5083 decreases viability in multiple myeloma cell lines and patient-derived multiple myeloma cells, including those with background proteasome inhibitor (PI) resistance. CB-5083 has a unique mechanism of action that combines well with PIs, which is likely owing to the p97-dependent retro-translocation of the transcription factor, Nrf1, which transcribes proteasome subunit genes following exposure to a PI. In vivo studies using clinically relevant multiple myeloma models demonstrate that single-agent CB-5083 inhibits tumor growth and combines well with multiple myeloma standard-of-care agents. Our preclinical data demonstrate the efficacy of CB-5083 in several multiple myeloma disease models and provide the rationale for clinical evaluation as monotherapy and in combination in multiple myeloma. Mol Cancer Ther; 16(11); 2375–86. ©2017 AACR.

Abstract Background: The AAA-ATPase p97/VCP facilitates the extraction and degradation of ubiquitinated proteins by converting chemical energy into mechanical force. p97 is closely involved in several facets of protein homeostasis, including ubiquitin-dependent protein degradation, endoplasmic reticulum-associated degradation (ERAD) and autophagy. p97 has been increasingly linked to cancer: it showed elevated protein expression in tumors, it can mediate the degradation of proteins in cancer-relevant pathways and is required for orchestrating the ubiquitin-governed DNA-damage response. In this context, p97 inhibitors may have an advantage versus other protein homeostasis inhibitors and may be active in solid tumors where 26S proteasome inhibitors, bortezomib and carfilzomib, have shown poor efficacy. We report here p97 inhibition as a novel approach to exploit cancer cell addiction to protein homeostatic mechanisms. Results: We have discovered novel small molecule inhibitors of p97 ATPase activity with nanomolar enzymatic and cellular potency. In cellular models, treatment of cancer cells with our lead compound CB-5083 causes disruptions in specific p97 functions, including ubiquitin-dependent protein degradation, ERAD, endocytosis and autophagy. In mouse models, CB-5083 is orally bio-available and causes rapid and sustained accumulation of poly-ubiquitin in tumor xenografts after a single administration. Concurrent with increases in polyubiquitin levels, activation of ER stress response pathways and induction of apoptosis markers are also observed. Sub-chronic oral administration of CB-5083 is generally well-tolerated with <10% body weight loss and results in potent tumor growth inhibition in several solid tumor xenograft models. This result is in marked contrast to proteasome inhibitors that are inactive in the same solid tumor models. In the Vk*MYC transgenic mouse model of multiple myeloma, CB-5083 treatment resulted in >50% reduction in M-spike. Additional efforts are focused on the development of translational assays to monitor p97 target engagement and antitumor efficacy in upcoming clinical trials of CB-5083. Conclusion: These data demonstrate that CB-5083 is a potent inhibitor of p97 that translates to tumor growth inhibition in multiple rodent models of human cancer. Furthermore, CB-5083 appears to exhibit greater potency over current proteasome inhibitors that further validate targeting p97 and protein homeostasis in the treatment of cancer. Citation Format: Ronan Le Moigne, Steve Wong, Ferdie Soriano, Eduardo Valle, Daniel J. Anderson, Stevan Djakovic, Mary-Kamala Menon, Bing Yao, Julie Rice, Jinhai Wang, Szerenke Kiss Von Soly, Brajesh Kumar, Marta Chesi, P. Leif Bergsagel, Han-Jie Zhou, David Wustrow, Mark Rolfe, F. Michael Yakes. CB-5083 is a novel first in class p97 inhibitor that disrupts cellular protein homeostasis and demonstrates anti-tumor activity in solid and hematological models. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 951. doi:10.1158/1538-7445.AM2014-951