Acid Ceramidase (ASAH1) Is a Key Mediator of Drug Resistance in Refractory Multiple Myeloma

Despite the growing armamentarium of treatments including proteasome inhibitors (PIs), immunomodulatory imides (IMiDs) and cellular and non-cellular immunotherapies MM remains incurable, due to the emergence of drug resistance that causes patient relapse. To develop therapies that significantly extend overall survival, a clearer understanding of the mechanisms driving drug-resistance is urgently required.

Analysis of RNA-seq data derived from 672 MM Moffitt patients revealed that sphingolipid metabolism genes and in particular acid ceramidase (ASAH1), are significantly enriched in relapse MM (RMM). Further, high levels of ASAH1 in RMM patients predicted poorer overall survival when patients were treated with any PI-containing regimen (median overall survival 552 vs 1226 days). These findings were corroborated in the Multiple Myeloma Research Foundation CoMMpass dataset (IA17). Next, we queried potential mechanisms of treatment resistance using gene-set enrichment analysis (GSEA). ASAH1 High patients displayed upregulation of gene signatures involved in metabolism of lipids, sphingolipids and regulation of apoptosis. Further, PI-resistant cell lines (U266-PSR, RPMI8226-B25, and ANBL6-V10R) displayed elevated levels of ASAH1, and total and phosphorylated levels of anti-apoptotic proteins MCL-1 and BCL-2 compared to PI-sensitive parental cells (U266, RPMI8226 and ANBL6). Genetic (shRNA) and pharmacological (ceranib-2) inhibition of ASAH1 significantly decreased MM viability and reduced MCL-1/BCL-2 expression. Further, ASAH1 inhibition resensitized resistant MM cells to PI treatment. Importantly, we recapitulated our findings in CD138+ patient MM cells ex vivo (EMMA platform), with ceranib-2/PI treatment being synergistic in the majority (>75%) of patient samples tested. In vivo, ceranib-2 treatment limited PI-resistant U266-PSR MM tumor growth and extended overall survival of NSG mice. Further, ASAH1 depletion (shRNA) resensitized MM cells to PI treatment in vivo and loss of MCL-1 and BCL-2 expression was confirmed ex vivo.

To understand the mechanism through which ASAH1 mediates PI-resistance we performed total and pSTY proteomic profiling (LC-MS/MS). Proteomic analyses revealed inhibition of the endogenous phosphatase PP2A inhibitor, I2PP2A as a candidate mechanism. Notably, I2PP2A was elevated in PMRC RMM patient samples, correlating with ASAH1 expression, and predicting poorer overall survival.

In conclusion, in vitro, in vivo and patient ex vivo data demonstrate ASAH1 is a novel, clinically relevant and tractable target for the treatment of PI-resistant MM. Future studies to develop novel and potent ASAH1 inhibitors for the treatment resistant MM, in combination with current standard of care therapies are on-going and we believed warranted based on our emerging data.

Hampton:M2GEN: Current Employment. Shain:Bristol Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; GlaxoSmithKline: Speakers Bureau; Takeda: Honoraria, Speakers Bureau; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Adaptive: Honoraria; Janssen: Honoraria, Speakers Bureau; Amgen: Speakers Bureau; Karyopharm: Research Funding, Speakers Bureau; AbbVie: Research Funding.