MTR-08MODELING TMZ RESISTANCE IN PATIENT-DERIVED BRAIN TUMOR- INITIATING CELLS

Intrinsic and required resistance hampers the inability for Temozolomide to give prolonged therapeutic response in glioblastoma. To this end we developed an in vivo model to investigate the mechanism behind TMZ resistance. Using TMZ-sensitive patient-derived brain tumor-initiating cells (BTIC; BT73 and BT206), intracranial tumors were established in immunocompromised mice. Once visible, animals were treated with TMZ [50 mg/kg/day (one cycle) followed by 5 cycles of 10 mg/kg/day (cycle = 5d on, 2d off)] and followed for recurrence. Tumor cells were isolated and re-implanted into animals for a second round of selection [TMZ 50 mg/kg/day (one cycle); 30 mg/kg/day (two cycles)]. BTICs established from these animals were termed BT73R and BT206R and confirmed for their acquired resistance to TMZ both in vitro and in vivo. Using cytokine profiling arrays and global gene expression arrays, we identified candidate genes/factors related to the development of TMZ resistance. Assessment of tumor interstitial fluid from BT73R and BT206R uncovered changes in several cytokines/chemokines including an increase in CX3CL1, IL16 and IL23 and a decrease in MDC, IFNa2, IP-10 and CCL2. In addition, we observed a greater than two-fold change in 131 genes found in common between the TMZ-resistant xenografts including 30 genes related to tumor adhesive, invasive and drug resistance that were selected for further validation. To date, of the common genes, 11 were confirmed including 7 up-regulated genes (IGFBP5, EFEMP1, TCEAL7, SLFN11, FAM129A, PCDH10 and DCX) and 4 down-regulated genes (DACH1, ICAM1, MLKL and NFTAC2). In addition, MGMT protein was detected in BT73R but not BT206R. The data presented here suggests that acquired resistance to TMZ in the BTICs may not be mediated through a single mechanism, but rather via multiple genes/pathways warranting further evaluation of these models in the hope of identifying potential therapeutic markers or targets for acquired TMZ resistance.