The Transcriptional Signature of Kinases Inhibited by the Multi-Targeted Kinase Inhibitor AS703569 Is Associated with Clinical Outcome in Multiple Myeloma (MM): Anti-MM Activity of AS703569 in Preclinical Studies.

Abstract 730

Multi-targeted kinase inhibitors, when associated with manageable toxicity, offer the therapeutically desirable option of targeting, through a single chemical entity, several pathways that may contribute to the complexity and heterogeneity of molecular lesions harbored by neoplasias such as multiple myeloma (MM). However, intractable questions often emerge while prioritizing for preclinical studies different multi-targeted agents with extensive and/or only partially overlapping of sets of known targets. We have hypothesized that the potential therapeutic relevance of a multi-targeted inhibitor may be reflected on the prognostic relevance of its targets' transcriptional signature. We applied this concept in the case of the orally bioavailable multi-targeted kinase inhibitor AS703569, which targets (with IC50 in low nM range) all 3 Aurora kinase (AK) isoforms as well as various other kinases (e.g. cSRC, FGFR1, Flt3, Fyn, Lyn, Rsk1-3, Yes, Axl, et.c.) and evaluated the transcriptional signature of AS703569 kinase targets (with IC50 <10 nM) in MM cells of patients receiving Bortezomib as part of Phase II/III trials (specifically SUMMIT/APEX). We observed that patients with high transcriptional signature of AS703569 targets had inferior progression-free and overall survival (p=0.005 and p=0.012, log-rank test) and also validated that, in a study of tandem autologous transplant, a subset of patients with high levels of this AS703569 target transcriptional signature also have inferior overall survival (p=0.032, log-rank test) compared to cases with low levels of the signature. These observations supported the notion that the kinome space targeted by AS703569 is enriched for targets associated with adverse clinical outcome in MM. In preclinical assays, we observed that AS703569 decreased the viability of MM cell lines and primary CD138+ MM tumor cells in a time- and dose-dependent manner, with IC50 values <50 nM for the majority of cell lines tested; and without evidence of cross-resistance with established anti-MM agents. Combinations of AS703569 with dexamethasone, doxorubicin, or bortezomib did not exhibit antagonism, suggesting that AS703569 can be incorporated in regimens with these established anti-MM drug classes. Interestingly, in vitro compartment-specific bioluminescence imaging (CS-BLI) assays showed that against MM cells which respond to stromal cells with increased proliferation and survival, the anti-MM activity of AS703569 is more pronounced when these MM cells are co-cultured with bone marrow stromal cells than in conventional cultures in isolation. This indicated that AS703569 is capable of overcoming the protective effects that BMSCs confer to MM tumor cells and prompted in vivo validation studies in our orthotopic SCID/NOD model of diffuse MM bone lesions established by i.v. injection of MM-1S-GFP/Luc cells monitored by whole body bioluminescence imaging. AS703569 (50 mg/kg p.o. once weekly)-treated mice had longer overall survival than vehicle-treated mice (median 50.0 days, 95% C.I. 40.3-59.7 days vs. 39.0 days, 95% C.I., 35.4-42.6 days, p=0.019, log-rank test). An alternative schedule of AS703569 at 16.7 mg/kg 3 times/week also resulted in longer overall survival (median 54.0 days, 95% C.I. 33.2-74.8 days, p=0.023, log-rank test). These data indicate that AS703569 exhibits anti-MM activity in vitro and in orthotopic in vivo MM models, and suggests that this multi-targeted inhibitor merits considerations for further preclinical studies, as well as potential clinical studies in MM, especially given the otherwise adverse outcome associated with the inhibitor's target transcriptional signature.