P-207: Identification of uniquely expressed proteins in bone marrow mesenchymal stromal cells of multiple myeloma patients with poor therapeutic response.

Introduction: Bone marrow microenvironment, especially the bone marrow mesenchymal stromal cells (BMMSCs), have been implicated in modulation of homing, growth, proliferation, egression, and even treatment response of tumor plasma cells in patients of multiple myeloma (MM). The proteomic profiling of cultured-BMMSCs from patients of MM may provide insight into proteins and molecular-pathways associated with risk category of MM and also with their response to therapy.

Methods: Ten newly diagnosed patients of MM (NDMM) were enrolled. The BMMSCs were isolated and cultured from bone marrow aspirate sample taken at the time of diagnostic work-up. The purity of cultured BMMSCs was confirmed by flow cytometry. Proteomic profiling of cultured BMMSCs was carried out using Liquid Chromatography-Mass Spectrometry. The risk categorization based on cytogenetics (FISH) revealed five patients each in cytogenetic high-risk (cHR) & standard-risk (cSR) categories. The data from proteomic-profiling was statistically compared between the two risk categories. All patients were started with bortezomib-based induction. Treatment response for three cSR and all five cHR patients was available at six months. Four patients, including one from cHR category achieved stringent complete response (sCR) [good responder (GR) group], and the rest four failed to achieve sCR [poor responder (PR) group]. The data from proteomic-profiling was statistically compared between the two response category-groups.

Results: The cHR patients revealed significantly higher levels of proteins involved in cholesterol biosynthesis, steroid metabolism, lipid metabolism, rRNA processing as compared to cSR patients. Whereas, the proteins involved in glycosaminoglycan & aminoglycan catabolism, and glycosphingolipid metabolism were significantly lower. Analysis amongst PR and GR revealed same results corresponding to cHR & cSR, except for absence of difference in rRNA processing pathway amongst response categories. There were some unique proteins, expressed only in PR and not in GR group, notably, ABCC3, ATXN7L3B ,BCAR3, H2BC12, IREB2, PATL1, RABGAP1L, S100A8, SIRPA, TFB1M, H2BC3, SEPTIN6, NCAM1, MFN1, TSYPL1, NOP14, AKTIP, ABHD5, MPHOSPH10, SLC35B3, IMP3. Conversely, PARVB, APOH, LZTR1, PPP1R14A, CYB561D2, UBTD2, UBTD1, TMEM14A were only present in GR group.Validation of some of these proteins on freshly enrolled NDMM patients was carried out.

Conclusions: Proteomic profiling of BMMSCs from patients of MM with poor response to therapy reveal expression of unique proteins which may provide more insight into pathobiology of disease, molecular pathways involved in resistance to therapy, and possibly potential new therapeutic targets.