Targeting COX-2 potently inhibits proliferation of cancer cells in vivo but not in vitro in cutaneous squamous cell carcinoma.

BACKGROUND: Cyclooxygenase 2 (COX-2) is an inducible enzyme which promotes tumorigenesis in many types of cancers. Genetic knockout of COX-2 significantly suppresses the tumorigenesis of skin squamous cell carcinoma (SCC). However, COX-2 inhibitor treatment only showed mild to moderate inhibition on SCC in previous reports. The aim of this study is to solve this contradiction and to re-evaluate the therapeutic potential of targeting COX-2 in SCC. METHODS: COX-2 was knocked down by shRNA in two different SCC cell lines, A431 and SCC-13. The cells proliferation and migration capacity were evaluated by cell growth curves and monolayer scratch assay, respectively. Cancer cells with COX-2 knockdown were also xenografted into Balb/c nude mice and tumor growth curves were recorded over time. In addition, we changed the drug administration route and intraperitoneally injected COX-2 inhibitor celecoxib into mice to evaluate its anti-cancer activity. RESULTS: Knockdown of COX-2 exhibited mild or even no effect on cell proliferation and migration in two different SCC cell lines in vitro. However, when cancer cells were xenografted into nude mice, knockdown of COX-2 significantly suppressed proliferation of cancer cells in tumors. At last, intraperitoneal injection instead of oral administration of COX-2 inhibitor celecoxib potently suppressed tumor growth. CONCLUSIONS: Our results indicate that COX-2 might impact on the interaction between cancer cells and surrounding microenvironments rather than on cancer cells directly, and demonstrate that targeting COX-2 is a very promising therapeutic approach for SCC treatment.

Inhibition of the prolyl isomerase Pin1 enhances the ability of sorafenib to induce cell death and inhibit tumor growth in hepatocellular carcinoma.

Hepatocellular carcinoma (HCC) is the sixth most common cancer, but is the second leading cause of cancer deaths, partially due to its heterogeneity and drug resistance. Sorafenib is the only medical treatment with a proven efficacy against advanced HCC, but its overall clinical efficacy is still modest. Therefore, a major challenge is how to improve its therapeutic efficacy. The unique prolyl isomerase Pin1 regulates numerous cancer-driving pathways. Notably, Pin1 is overexpressed in about 70% HBV-positive HCC patients and contributes to HCC tumorigenesis. However, the role of Pin1 in the efficacy of sorafenib against HCC is unknown. Here we found that sorafenib down-regulated Pin1 mRNA and protein expression, likely through inhibition of Pin1 transcription by the Rb/E2F pathway. Importantly, Pin1 knockdown potently enhanced the ability of sorafenib to induce cell death in HCC, which was further supported by the findings that Pin1 knockdown led to stabilization of Fbxw7 and destabilization of Mcl-1. Furthermore, all-trans retinoic acid (ATRA), a known anticancer drug that inhibits and ultimately induces degradation of active Pin1 in cancer cells, also potently sensitized HCC cells to sorafenib-induced cell death at least in part through a caspase-dependent manner. Moreover, ATRA also synergistically enhanced the ability of sorafenib to reduce Pin1 and inhibit tumor growth of HCC in mouse xenograft models. Collectively, these results not only demonstrate that Pin1 down-regulation is a key event underlying the anti-tumor effects of sorafenib, but also uncover that Pin1 inhibitors offer a novel approach to enhance the therapeutic efficacy of sorafenib against HCC.

Chemical or genetic Pin1 inhibition exerts potent anticancer activity against hepatocellular carcinoma by blocking multiple cancer-driving pathways.

Hepatocellular carcinoma (HCC) is one of the most prevalent and malignant cancers with high inter- and intra-tumor heterogeneity. A central common signaling mechanism in cancer is proline-directed phosphorylation, which is further regulated by the unique proline isomerase Pin1. Pin1 is prevalently overexpressed in human cancers including ~70% of HCC, and promotes tumorigenesis by activating multiple cancer-driving pathways. However, it was challenging to evaluate the significance of targeting Pin1 in cancer treatment until the recent identification of all-trans retinoic acid (ATRA) as a Pin1 inhibitor. Here we systematically investigate functions of Pin1 and its inhibitor ATRA in the development and treatment of HCC. Pin1 knockdown potently inhibited HCC cell proliferation and tumor growth in mice. ATRA-induced Pin1 degradation inhibited the growth of HCC cells, although at a higher IC50 as compared with breast cancer cells, likely due to more active ATRA metabolism in liver cells. Indeed, inhibition of ATRA metabolism enhanced the sensitivity of HCC cells to ATRA. Moreover, slow-releasing ATRA potently and dose-dependently inhibited HCC growth in mice. Finally, chemical or genetic Pin1 ablation blocked multiple cancer-driving pathways simultaneously in HCC cells. Thus, targeting Pin1 offers a promising therapeutic approach to simultaneously stop multiple cancer-driving pathways in HCC.