Spiclomazine displays a preferential anti-tumor activity in mutant KRas-driven pancreatic cancer

Abstract

Ras-targeted therapy represents a ‘holy grail’ in oncology. Based on our model prediction, Spiclomazine freezing the intermediate conformation of activated Ras is central to cancer therapeutics. We show here that Spiclomazine leads to an effective suppression in Ras-mediated signaling through abrogating the KRas-GTP level in the KRas-driven pancreatic cancer. The Ras-mediated signaling inhibition leads to dramatically reduced survivals of five KRas-driven pancreatic cancer cell lines with IC₅₀ ranging 19.7~74.2 μM after 48 hours of treatment. However, no significant changes have been observed for normal cell lines. It is worth mentioning that the mutant KRas-driven cancer cells are more sensitive towards Spiclomazine than the wild-type KRas cancer cells. Subsequent cellular thermal shift and RNA interference assays show that Spiclomazine efficiently binds with and stabilizes KRas to a certain extent within the cells. This validates the effect of target engagement on drug efficacy. Furthermore, Spiclomazine arrests cell cycle at G2 phase in the cancer cells, without obvious cell-cycle arrest in the normal cells. This further demonstrates its selectively biological response to cancer cells involved in Ras-GTP-mediated target engagement. Spiclomazine completely inhibits the growth of MIA PaCa-2 tumors on renal capsule xenograft models in BALB/c mice administered 68 mg kg^-1 for 2 weeks via intra-peritoneal route. Immunohistochemical analyses reveal the reduced c-Raf and p-ERK and the increase in TUNEL staining. These observations further confirm the in vitro findings. Taken together, Spiclomazine is a selective inhibitor for mutant KRas-driven pancreatic cancer.