br Fig In vivo antitumor effects of BMS in SKOV
Fig. 4. In vivo antitumor effects of BMS-777607 in SKOV3 KRN 7000 constitutively expressing phosphorylated c-MET 50 mg/kg of BMS-777607 daily was orally administered to SKOV3 cell xenograft nude mice (water was administered to the control mice). The tumor sizes were monitored using an IVIS system. The tumor burden was proportional to the size of cell dissemination area. The results demonstrated inhibition of tumor growth (p ¼ 0.0439, control versus BMS-777607) and reduction in tumor burden (p ¼ 0.0091, control versus BMS-777607) due to BMS-777607 treatment in the ovarian cancer cells with constitutively phosphorylated c-MET. Error bars in each chart represent the standard error.
demonstrate that the growth of the SKOV3 tumor was inhibited in mice treated with BMS-777607. The tumor burden in mice treated with this compound was also reduced.
The design of targeted therapies has improved considerably after the molecular characterization of ovarian cancer [21,22]. Therapies that target multiple tumorigenesis effects are favored in drug development. c-MET was indicated to play a crucial role in tumor growth and metastasis because of crosstalk with multiple signaling pathways. Other evidence also shows that MET can regulate VEGF-A signaling and may be involved in tumor invasion and angiogenesis . All these results suggest that inhibiting c-MET activation could block multiple phenomena to achieve anti-tumor effects.
Many small molecules that target VEGF receptor or various re-ceptor tyrosine kinases were evaluated in preclinical studies and clinical trials of ovarian cancer . Although they cannot induce an immune response against tumor cells as can monoclonal anti-body drugs, small molecular inhibitors can penetrate the cyto-plasmic membrane to suppress the phosphorylation of proteins inside the cells .Compared with therapeutic monoclonal anti-body drugs, small molecular inhibitors generally possess lower specificity. Hence, these inhibitors might inhibit several signaling pathways at a clinically feasible dosage and can reduce the possi-bility of resistance. This evidence suggests that small molecular inhibitors have high clinical value in cancer therapy.
Our data demonstrate that BMS-777607 has higher cell growth inhibition effects in cells with constitutively activated c-MET than in other cells. However, the growth of cells that did not exhibit c-MET activation or expression was also affected after BMS-777607 treatment. This indicates that c-MET phosphorylation blockade was not the only method to inhibit ovarian cancer cell growth. Aurora B is the other target of BMS-777607 at concentrations higher than IC50 . Aurora B inhibition can reduce the phos-phorylation of histone H3, thus disturbing the stability of a-tubulin and inducing polyploidy [26,27]. Whether concomitant inhibition of c-MET and Aurora B could cause synergistic effects and reduce the viability of cells with constitutively activated c-MET requires further investigation.
A combination of targeted therapy and chemotherapy or different signaling inhibitors was previously a trend for tumor treatment. However, the efficacy of combinational treatment with tyrosine ki-nase inhibitors and chemotherapy is controversial. A combination of EGFR TKI and chemotherapy did not surpass monotherapy in a total of six randomized controlled trials of non-small-cell lung cancer . Although BMS-777607 possesses a moderate antitumor effect alone, research reported that cells treated with BMS-777607 may induce drug resistance to chemotherapy because of the induction of polyploidy . A combination of BMS-777607 and the mTOR in-hibitor AZD8055 was revealed to reduce cell polyploidy and achieve a maximal synergistic cytotoxic effect on cancer cells derived from pancreatic cancer and cancer stem cells . Thus, large-scale screening to identify small molecules that can induce synergistic effects with BMS-777607 is necessary.
Constitutive activation of receptor tyrosine kinases was re-ported to involve a gene mutation. Because the HGF level in the microenvironment of ovarian cancer is low, c-MET constitutive activation in ovarian cancer cells remains unexplained. Active mutation of c-MET in human cancer was first identified in both somatic and inherited forms of human renal papillary carcinomas . Identifying the mutation in the kinase domain of c-MET will facilitate the selection of a strategy for targeted therapy between c-MET and HGF blockade. In conclusion, BMS-777607 exhibits the highest inhibition of cell growth in ovarian cancer cells constitutively expressing c-MET. Treating SKOV3 cells with BMS-777607 could reduce c-MET acti-vation and inhibit downstream cell signaling, thus causing cell apoptosis and polyploidy as well as cell cycle and cell migration inhibition. This molecule also inhibited tumor growth (induced using the SKOV3 ovarian cancer cells) in a mouse xenograft model in vivo. Examining the synergistic effect of BMS-777607 with other therapeutic agents is warranted for identifying effective therapies for ovarian cancer.