SiRNA screening of the kinome identified Aurora A kinase as a therapeutic target gene in cervical cancer

Abstract

HPV oncogenes disable a number of tumour suppressor pathways, including p53 and Rb, contributing to the transformed phenotype. Loss of these critical host cell functions may also provide an opportunity to selectively target the destruction of HPV-transformed cells. We have performed an siRNA screen using the kinome (779 genes) library to identify genes that when depleted are synthetically lethal with HPV transformation. The primary and validations screens have confirmed Aurora A kinase (AURKA) as a potential synthetic lethal target selective for HPV transformed cells. AURKA has been further investigated using the selective small molecule inhibitor MLN8237. We found that MLN8237 was significantly more potent towards the HPV transformed cells. The effect was not a consequence of targeting mitosis as two other mitotic inhibitors, PLK1 inhibitor (BI2536) and taxol, demonstrated no selectivity. Analysis of the nuclear structure and DNA content showed that Aurora A inhibition promoted a high level of polyploidy in non-HPV treated cells whilst this same degree of polyploidy was associate with apoptosis in the HPV-transformed cell lines. Whereas Bcl-2 over expression in HeLa cells had no effect on sensitivity to MLN8237, Mcl-1 overexpressing HeLa cells were less sensitive to the MLN8237 in comparison to the parental cell line, which may suggests the involvement of Noxa or Puma pro-apoptotic proteins in the induction of the apoptosis in the HPV-transformed cells. The transfection of the non-HPV C33A cervical cancer and SCC25 squamous cell carcinoma cell lines with the HPV16 oncogenic E7 increased sensitivity to MLN8237 between 3 >10 fold suggesting that the sensitivity to MLN8237-dependent killing was a direct consequence of HPV E7 expression. Xenograft experiments with cervical cancer cell lines in immunodeficient mice showed MLN8237 inhibited growth of HPV and non-HPV xenografts during treatment with 30mg/kg MLN8237 once a day for 10 consecutive days. However, outgrowth of tumour was noticed from the second day post-treatment in the non-HPV tumour group whereas the HPV-induced tumour group did not show cancer recurrence for 50 days post-treatment. These findings suggest that MLN8237 represent a promising novel therapeutic targeted agent against HPV-transformed cervical cancer.