An adamantane derivative, 2, 2-Bis (4-(4-amino-3-hydroxyphenoxy) phenyl) adamantane (DPA), was found to inhibit the growth of several cancer cell lines in the National Cancer Institute (NCI) Anticancer Drug Screen system. Our previous study showed that DPA inhibited the growth of human colon cancer cell Colo 205 xenografts. DPA-treated cells were arrested at G0/G1, and the DPA-induced cell growth inhibition was irreversible after removal of DPA. Moreover, no acute toxicity was observed after an intra-peritoneal challenge of DPA in nude mice weekly. In this study, we examined the in vivo therapeutic potential of DPA combined with clinical chemotherapeutic agent CPT-11 in Colo 205 cell xenografts. The in vitro cytostatic and differentiative effects of DPA on human colon cancer cells was also evaluated. DPA exerted growth inhibitory activities in vitro against three human colon cancer cell lines (Colo 205, HT-29, and HCT-15). DPA-treated cells showed a more adhesive epithelial phenotype. The differentiation markers of carcinoembryonic antigen (CEA) and fibronectin (FN) were significantly increased in colon cancer cells after treatment with DPA. Further studies showed the induction of p21/Cip1, p27/Kip1, E-cadherin and dephosphorylated p120ctn expression was involved in DPA-induced anticancer effects. Interestingly, DPA-induced elevation of p21/Cip1 was independent of the induction of p53 in Colo 205 cells. in vivo results demonstrated that DPA enhanced the in vivo anticancer activity of the chemotherapeutic agent, CPT-11, by elevation of p53-independent p21/Cip1 and p27/Kip1 expression. Our results suggest that DPA appears to be a new potentially less toxic modality of cancer combinatory therapy.

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