Synergistic effect of combination treatment with MI-219, a small molecule inhibitor of the MDM2-p53 interaction, and kinase inhibitors or chemotherapeutic agents.

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Targeting the MDM2-p53 interaction to reactivate p53 tumor suppressor function in cancer using small-molecule inhibitors is a new strategy for anti-cancer drug development. MI-219 is developed as a highly potent and orally bioavailable small molecule inhibitor of the MDM2-p53 interaction. Cell growth inhibition was measured using WST-based assays. The CalcuSyn program was used to calculate the Combination Index (CI) value (CI value<1 indicates synergy). In vivo, the anti-cancer effect of MI-219 was evaluated in a SJSA-1 xenograft and other models.
 
 MI-219 exhibited strong affinity to MDM2 with a Ki value of 5 nM and >10,000-fold selectivity over other protein-protein interactions. MI-219 induced a dose-dependent growth inhibition in wt-p53 cancer cell lines with a mean IC₅₀ of 2.65 uM in A549, 3.566 uM in H460, 2.20 uM in RKO, 1.75 uM in SJSA-1, and 5.14 uM in BC-3. MI-219 demonstrated strong synergy with targeted agents, such as the EGFR kinase inhibitor erlotinib, against NSCLC lines A549 (CI value=0.48) and H460 (CI value=0.8). Synergy was also observed with irinotecan against the colon cancer line RKO (CI value = 0.76) and against A549 (CI value=0.55). When dosed at 50 mg/kg in mice, MI-219 had an oral bioavailability of 55% with t_1/2 of 1.6 hours and a Cmax of 17.3 uM. MI-219 was stable in plasma of mice, rats, dogs and monkeys. Tissue distribution studies further demonstrated that following oral administration of MI-219, there was a wide and rapid distribution in the body and excellent penetration into tumor tissues. Consistent with its high binding affinity and excellent PK and PD profiles, when given at optimal doses for 14 days, MI-219 was capable of completely stopping tumor growth or inducing partial tumor regression as a single agent. Combined treatment with MI-219 and irinotecan synergistically suppressed SJSA-1 cells tumor growth compared with treatment of either agent alone. The combination showed anti-tumor efficacy with a T/C value of 0.35 for 50 mg/kg, 0.30 for 100 mg/kg and 0.10 for 200 mg/kg of MI-219 combined with irinotecan, whereas the single agent treatments are less effective (T/C value =0.83 for 50 mg/kg, 0.72 for 100 mg/kg, and 0.52 for 200 mg/kg of MI-219 alone, and 0.54 for irinotecan alone) (P<0.001).MI-219 was more effective than irinotecan at its MTD dose in the SJSA-1 xenograft model. Importantly, there was no significant weight loss in mice treated with MI-219 and no enhanced toxicity observed in combination treatment over chemotherapy. MI-219 was well tolerated in multi-dosing in rats and dogs.
 Thus, these studies demonstrate that a rationally designed, highly potent and specific small-molecule inhibitor of the MDM2-p53 interaction showed promising therapeutic potential preclinically as a single agent or in combination and warrants clinical investigations as a new class of therapy for the treatment of cancer.