A novel RET inhibitor with potent efficacy against medullary thyroid cancer in vivo

BackgroundMost medullary thyroid carcinomas (MTC) recur or progress despite curative resection. Current targeted therapies show promise but lack durable efficacy and tolerability. The purpose of this study was to build on previous in vitro work and evaluate withaferin A (WA), a novel RET inhibitor, in a metastatic murine model of MTC.MethodsA total of 5 million DRO-81-1 human MTC cells injected in the left posterior neck of nu/nu mice generated metastases uniformly to the liver, spleen, and/or lungs. Treatment with WA (8 mg/kg/day, intraperitoneally, for 21days) was started for neoplasms >100 mm3. Endpoints were survival, neoplasm >15,00 mm3, decreased body weight, or body score (all measured three times/wk).ResultsAll controls (saline; n = 5) died or deteriorated from metastatic disease by 7 weeks postinjection. All treated animals were alive (WA; n = 5), having tumor regression and growth delay without toxicity or weight loss at 6 weeks posttreatment (P < .01). Tumor cells treated with WA demonstrated inhibition of total and phospho-RET levels by Western blot analysis in a dose-dependent manner (almost complete inhibition with treatment of 5 μM WA) as well as potent inhibition of phospho-ERK and phospho-Akt levels.ConclusionWA is a novel natural-product RET-inhibitor with efficacy in a metastatic murine model of MTC. Further long-term efficacy/toxicity studies are warranted to evaluate this compound for clinical translation.