Ovarian cancer is the leading cause of death among all types of female reproductive system tumors. In recent years, there has been little progress in the treatment of ovarian cancer [17–18]. Chemotherapy resistance is the biggest obstacle to the treatment of ovarian cancer. Despite an initial response rate of more than 80% to first-line chemotherapy, most patients eventually develop drug resistance and undergo cancer recurrence, so new treatments are urgently needed to improve survival in ovarian cancer . In this study, we analyzed the effect of the zinc ion chaperone NSC319726 on ovarian cancer cells function and the possible mechanisms for its proliferation suppression.
P53 is a tetrameric multi-structured domain transcription factor, which plays an important role in maintaining cellular genomic integrity, and activates the expression of multiple genes. As a tumor suppressor gene, P53 encodes a DNA-binding transcription factor that induces cell growth arrest, cellular senescence, and cell death in response to cellular stress . This is achieved through transcriptional regulation of multiple target genes, including P21, which blocks cell cycle progression, and Bax and Puma, which promote apoptosis . This illustrates the critical role of P53 as a trigger that promotes cell cycle arrest or apoptosis during the development of cancer . The mutational spectrum of P53 is atypical because tumorigenic alterations are overwhelmingly missense and map to nearly every position within one of the domains of the protein (the DNA-binding domain). The DNA-binding domain possesses two unusual properties-one of the highest zinc affinities of any eukaryotic protein and extreme instability in the absence of zinc-which are predicted to poise P53 on the cusp of folding/unfolding in the cell, with a major determinant being available zinc concentration .
P53 gene is mutated in various tumors, such as serous endometrial cancer and ovarian cancer . In almost all human cancers, P53 is inactivated, and in approximately 50% of human cancers, this inactivation is a direct result of mutations in the P53 gene [25–27]. The zinc ion (coordinated by amino acids C176 and H179 on the L2 loop and C238 and C242 on the L3 loop) plays a pivotal role in the tertiary structure of wild-type P53 and the correct folding of P53 [28–29]. Deficient zinc ion and excess zinc ion both result in P53 misfolding and loss of function, while the correct zinc ion concentration will reactivate P53 and inhibit tumor cell growth [30–31]. NSC319726, as a zinc metallochaperone, can provide the zinc ion of appropriate concentration and promotes correct folding of P53 by chelating zinc ion, thereby contributing to proper folding of P53 and restoration of its physiological function .
Results in this study demonstrated that NSC319726 can effectively suppress the proliferation, migration, invasion and promote apoptosis of ovarian cancer cells A2780 and SK-OV-3, and the suppressive effect becomes more pronounced as the drug concentration increases. The result of functional restoration of P53 is either tumor cell cycle arrest or suppression of tumor cell apoptosis . It is thus seen that as the expression of P53 increases, the expression of its downstream CDK inhibitor protein P21 is overexpressed, which further inhibits the joint effort of CDK and cyclin. P21 and P27 inhibit the cyclin-CDK complex, causing retinoblastoma (Rb) to fail to fully phosphorylate, leading to G1/S phase block and causing cancer cells to undergo cycle arrest and fail to enter mitotic phase, thereby inhibiting their proliferation [32–36]. To explore the possible anti-proliferation mechanism of NSC319726 in ovarian cancer cells, we examined the effect of NSC319726 on the expression of P21, P27, CDK2, CDK4, cyclinD1, and cyclinE1. The overexpression of P21 and P27, and the down-regulation of CDK2, CDK4, cyclinD1, and cyclinE1 indicated that, NSC319726 can restore the function of P53, activate the CDK inhibitors P21 and P27, and inhibit CDK and cyclin, further suppress ovarian cancer cells growth. In addition, the activation of wild-type P53 may cause cell apoptosis through induction of a range of target genes such as BAX, PMAIP1 (NOXA), BBC3 (PUMA), P53AIP1, FAS, FDXR and TP53I3 (PIG3) , and the expression of wild-type P53 expression can promote MDM2-mediated Slug degradation to enhance E calmodulin expression thereby suppressing cell migration and invasion . This is consistent with our observations that NSC319726 suppressed ovarian cancer cells migration and invasion, and promote their apoptosis. The exact mechanism needs to be further explored.
In summary, the zinc metallochaperone NSC319726 can suppress ovarian cancer cells proliferation, migration and invasion, and promote their apoptosis, and has the potential to be a novel drug for ovarian cancer treatment.