Characterization of Bortezomib Resistant Human Multiple Myeloma Cell Line (HMCL): A Clinically Relevant Model for Novel Drug Development in Multiple Myeloma (MM).

Introduction: Bortezomib (B) is the first in class proteasome inhibitor that received FDA approval for the treatment of MM patients with relapsed or refractory disease. Despite impressive clinical activity all patients develop resistance to B. The underlying mechanism of resistance to B remains undetermined. Mechanisms to overcome B resistance or development of new therapeutic agent(s) with activity in context of B resistance are limited due to unavailability of established preclinical B resistant MM models. To overcome this challenge we developed a B resistant HMCL.

Methods: we chronically exposed the OPM-2 HMCL to sub-lethal doses of B. Surviving cells were harvested, re-cultured and dose of B incrementally increased over prolong period of time. The resulting resistant cells were further characterized using array Comparative Genomic Hybridization (aCGH), spectral karyotyping (SKY) and gene expression profiling.

Results: After several passages we were able to induce B resistance in this HMCL. Final clone (OPM-2BR) demonstrate resistance to 2 × IC₅₀ dose of B. While SKY and aCGH analysis demonstrated significant differences when compared with parent OPM-2WT (wild type) HMCL, gene expression profiling of the resistant and parental lines demonstrated significant upregulation in the expression of a number of ATP-binding cassette transporters. For example, the breast cancer resistance protein (ABCG2) is upregulated 4-fold in the resistant cell line compared to the parental cell line. This data suggests that drug efflux mediated by drug transporters represents one potential mechanism of resistance to B.

Conclusion: Chronic in vitro B exposure results in induced resistance in HMCL-OPM-2BR. Resistant cell line demonstrates cytogenetic variability when compared to the parent cell line. Induction of resistance is stable and provides an important preclinical tool to investigate mechanism(s) of B resistance as well as new drug development for B resistant myeloma patients. Detailed analysis of this cell lines including therapeutic interventions investigating resistance reversal will be presented at the meeting.