Associate Professor Cleveland Clinic Lerner Research Institute
Introduction: Monoclonal antibody (mAb) drugs are already in clinical use to treat multiple myeloma (MM) but all MM patients eventually develop drug resistance. Therefore, novel targeted therapy is urgently needed to overcome the drug resistance. The plasma cell-induced ER resident protein 1 (pERP1) is one of the co-chaperone proteins specifically required for the differentiation and function of antibody-secreting cells in a T cell independent immune response. High pERP1 expression has been specifically linked to B cell malignancy such as chronic lymphocytic leukemia, follicular lymphoma, and diffuse large B-cell lymphoma correlates with poorer prognosis and shorter survival times in patients. The expression pattern of pERP1 in MM patients is unclear.
Methods: We performed 10X scRNA seq analysis to simultaneously identify distinct immune cell populations and MM cells using bone marrow samples from patients. Through scRNA seq analysis, we identified the most highly upregulated and downregulated genes in each immune cell cluster. To test whether pERP1 might be a novel immunotarget for MM treatment, we have developed an pERP1 antibody drug conjugate (ADC). We further tested pERP1 ADC in our newly developed preclinical third generation AIDCreERT2+/-, EYFP LSL/-, P53L/L, BrafV600ELSL/-, cMYCLSL/- (AEY-PVM) MM mouse model.
Results: By means of single cell RNA seq analysis, we identified the most upregulated gene signatures in patients to include those of CD138, CD38, BCMA, and pERP1. When we look for other chaperone proteins including GRP78 and GRP94, we found them to be broadly expressed in bone marrow cells while not finding specific expression in the MM cell population, which underscoring the importance of pERP1 in the development of MM and its potential as a therapeutic target. Our studies further demonstrate high expression of pERP1 on the surface of MM cell lines and on CD138+ plasma cells in MM patients as compared with those from healthy donors. Then, we developed a pERP1 ADC against human pERP1 antigen, verified by using Biacore S200 Surface Plasmon Resonance (SPR) assay. We determined the IC50 of the pERP1 ADC drug against the human cell line RPM18226 to be 1.034 nM. We then tested the pERP1ADC drug in our third generation AEY-PVM mice after they developed MM disease as determined by M spike detection on an SPE gel. We used only 1.25mg/kg of the pERP1 ADC drug, which is lower than the dose of the currently clinically used ADC drugs belantamab mafodotin (2.5-3.4 mg/kg), to treat the AEY-PVM MM mice. Furthermore the survival data from 5 MZB1-ADC treated AEY-PMV mice and 5 control mice confirmed that pERP1 mAb can significantly prolong the survival of AEY-PMV MM mice.
Conclusions: In conclusion, we have found pERP1 to be highly expressed on the surface of MM cell lines in culture and of MM cells from patients in comparison with plasma cells from healthy donors, underscoring the potential of pERP1 as a novel immunotherapy target by using mAb or ADC.
