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1611 Mitochondrial Electron Transport Chain Inhibition Promotes Resistance to Proteasome Inhibitors in Multiple Myeloma

Program: Oral and Poster Abstracts
Session: 651. Multiple Myeloma and Plasma Cell Dyscrasias: Basic and Translational: Poster I
Hematology Disease Topics & Pathways:
Non-Biological, Translational Research, Plasma Cell Disorders, Chemotherapy, Diseases, Metabolism, Therapies, Lymphoid Malignancies, Biological Processes
Saturday, December 11, 2021, 5:30 PM-7:30 PM

Aditi Sharma, PhD1*, Abhinav Achreja, PhD2,3*, Remya Nair, PhD1*, Pulkit Gupta1*, Claudia L Edgar, BS1*, Olamide Animasahun, BS3,4*, Anjali Mittal, BS3,4*, Bhakti Dwivedi, PhD5*, Manoj Bhasin, PhD6, Vikas A Gupta, MD, PhD1*, Benjamin G Barwick, PhD1, Shannon M Matulis, PhD1*, Sagar Lonial, MD, FACP1, Lawrence H. Boise, PhD1, David L Jaye, MD7, Arun P Wiita, MD, PhD8, Ajay K. Nooka9, Deepak Nagrath, MS, PhD2,3,4* and Mala Shanmugam, PhD10

1Department of Hematology and Medical Oncology, Winship Cancer Institute, Emory University School of Medicine, Atlanta, GA
2Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI
3Biointerfaces Institute, University of Michigan, Ann Arbor, MI
4Department of Chemical Engineering, University of Michigan, Ann Arbor, MI
5Department of Biostatistics and Bioinformatics Shared Resource, Winship Cancer Institute, Emory University, Atlanta, GA
6Department of Pediatrics, Emory University School of Medicine, Atlanta, GA
7Department of Pathology and Laboratory Medicine, Emory University School of Medicine, Dunwoody, GA
8Department of Laboratory Medicine, UCSF, San Francisco, CA
9Department of Hematology and Medical Oncology, Winship Cancer Insitute, Emory University School of Medicine, Atlanta, GA
10Department of Hematology and Medical Oncology, Winship Cancer Institute, Emory University School of Medicine, Winship Cancer Institute, Atlanta, GA

INTRODUCTION

Proteasome inhibitors (PI) such as bortezomib (Velcade), carfilzomib (Kyprolis) and ixazomib (Ninlaro)) have been shown to be efficacious in multiple myeloma (MM) therapy. However, despite being an effective first line therapy, resistance to PI usually develops, leading to relapse and refractory disease. Previous studies have implicated a role of OXPHOS, glycolysis, antioxidants and serine metabolism in PI resistance. Mitochondrial metabolism plays a central role in malignant progression not only by generating ATP but also by providing precursors for synthesis of several biomolecules such as proteins, nucleotides, fatty acids and antioxidants that can influence the efficacy of MM therapies. We previously determined reduced mitochondrial electron transport chain (ETC) activity promotes sensitivity to the BCL-2 antagonist, venetoclax. However, the relationship between the metabolic state of the mitochondria and proteasome inhibitor (PI) sensitivity is not fully understood. Unexpectedly, we found ETC inhibition or reduced ETC activity to promote resistance to PIs. Here, we investigate the mechanistic basis for divergent effects of mitochondrial stress on sensitivity to PIs and venetoclax.

METHODS

We have used RNA-Seq and carbon isotope tracing using labeled U13C-glucose or U13C-glutamine, flow cytometry and western blot analysis in MM cell lines treated with mitochondrial Complex I inhibitor, IACS-010759 (IACS) +/- Bortezomib; and immunostaining of MM patient samples and interrogation of Multiple Myeloma Research Foundation’s CoMMpass Study (NCT01454297, Interim Analysis 15).

RESULTS

We find that mitochondrial ETC (complex I-V) inhibition antagonizes bortezomib (BTZ) and carfilzomib (CFZ) induced cell death in MM in contrast to promoting sensitivity to venetoclax. Additionally, cell lines exhibiting intrinsically reduced ETC activity were more resistant to PI in comparison to cell lines with higher ETC activity. Evaluation of CoMMpass MM trial (NCT0145429, IA15) and serial samples from 50 patients before PI treatment and after relapse, show pathways related to OXPHOS and TCA cycle to be downregulated in poor survival patients, corroborating our in vitro observations on reduced ETC activity promoting resistance to PI. To elucidate the mechanistic basis of ETC-inhibition induced PI resistance we performed RNA-Seq and U13C-glucose and glutamine tracing in L363 cells treated with the ETC Complex I inhibitor IACS +/- BTZ. RNA-Seq analysis and further confirmation by western blot analysis reveals integrated stress response (ISR) upregulation, ATF4 induction, and suppression of protein translation and global protein ubiquitination levels, likely responsible for resistance to proteasome inhibition in cells co-treated with IACS and BTZ compared to BTZ alone. Stable isotope tracing reveals an upregulation of reductive carboxylation; while RNA-Seq data and flow cytometry demonstrate increase in the cystine/glutamate transporter SLC7A11. The ensuing metabolic rewiring in mitochondrially suppressed MM induces several metabolic vulnerabilities including sensitivity to the SLC7A11 inhibitor, erastin. We also show that knockdown of ATF4 re-sensitizes ETC-inhibited cells to BTZ while ablating sensitivity to venetoclax (previously reported). Furthermore, examination of patient samples demonstrates inter-cellular heterogeneity in ATF4 expression. Our results thus, support the role ATF4 as key determinants of PI and BCL-2 antagonist efficacy.

CONCLUSION

We show mitochondrial ETC inhibition induces ISR mediated resistance to PI. These ETC-inhibited cells are however sensitive to BCL-2 antagonists and afford additional metabolic vulnerabilities that can be capitalized upon to target metabolic heterogeneity in MM. Our study underscores the need for implementing combinatorial regimens in MM cognizant of mitochondrial metabolic heterogeneity-mediated resistance.

Disclosures: Bhasin: Sanofi Genzyme: Consultancy; Canomiks: Membership on an entity's Board of Directors or advisory committees; Anxomics: Membership on an entity's Board of Directors or advisory committees. Lonial: Janssen: Consultancy, Honoraria, Research Funding; BMS/Celgene: Consultancy, Honoraria, Research Funding; AMGEN: Consultancy, Honoraria; GlaxoSmithKline: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Abbvie: Consultancy, Honoraria; TG Therapeutics: Membership on an entity's Board of Directors or advisory committees; Merck: Honoraria. Boise: AstraZeneca: Consultancy, Research Funding; Abbvie: Consultancy. Jaye: Stemline Therapeutics: Honoraria. Nooka: Janssen Oncology: Consultancy, Research Funding; GlaxoSmithKline: Consultancy, Other: Travel expenses; Sanofi: Consultancy; Bristol-Myers Squibb: Consultancy; Takeda: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Oncopeptides: Consultancy; Adaptive technologies: Consultancy; Karyopharm Therapeutics: Consultancy.

*signifies non-member of ASH