Program: Oral and Poster Abstracts
Session: 802. Chemical Biology and Experimental Therapeutics: Poster III
Methods: To test the effect of TPZ on tumor survival in vitro, MM cell lines (MM1.s, H929, OPM1, RPMI8226) were exposed to normoxia (21% O2) or hypoxia (1% O2) for 24 hours with different concentrations of TPZ in order to obtain an IC50, and cell survival was assessed using MTT assay. Also, a combination of bortezomib and carfilzomib with or without TPZ was tested on cell survival. For in vivo study, 5 x 106 MM1s-Luc-GFP cells were injected intravenously (IV) into SCID mice and tumor progression was monitored for 3 weeks by bioluminescent imaging. First, we tested the hypoxic status of mice treated with and without a high-dose bortezomib (1.5mg/kg). Pimonidazole (PIM) was injected intraperitoneally (IP) into mice and 4 hours later BM was harvested, stained with anti-PIM-APC antibody and followed by measuring PIM signal in MM1s-GFP+ cells using flow cytometry. Second, we developed drug resistant cells by treating mice with a high-dose bortezomib (1.5mg/kg), and then treated with (1) bortezomib only (0.5mg/kg; n=3), or (2) bortezomib and TPZ (40mg/kg; n=3), all administered IP sequentially twice a week. The number of residual MM1s-GFP+ cells was calculated by flow cytometry.
Results: We found that TPZ was active in a dose-dependent manner only in hypoxic conditions in MM cell lines. We showed that residual MM cells in the BM after high-dose bortezomib are hypoxic, as demonstrated by PIM staining. The combination of TPZ with bortezomib and carfilzomib resensitized cancer cells to death in hypoxia, overcoming hypoxia-induced drug resistance in vitro. Moreover, TPZ-treatment in combination with bortezomib further decreased residual MM cells in vivo.
Conclusions: We reported that MRD was hypoxic and that TPZ, which was cytotoxic for MM cells only in hypoxic conditions, overcame hypoxia-induced drug resistance in vitro and killed bortezomib-resistant residual MM cells in vivo. This is the first study to show the efficacy of TPZ in MM. This data provides a preclinical basis for future clinical trials testing efficacy of TPZ in MM.
Disclosures: Azab: Selexys: Research Funding ; Karyopharm: Research Funding ; Cell Works: Research Funding ; Targeted Therapeutics LLC: Other: Founder and owner ; Verastem: Research Funding .
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