Annexin A4 induces platinum resistance in a chloride-and calcium-dependent manner.

Platinum resistance has long been a major issue in the treatment of various cancers. We previously reported that enhanced annexin A4 (ANXA4) expression, a Ca2+-regulated phospholipid-binding protein, induces chemoresistance to platinum-based drugs. In this study, we investigated the role of annexin repeats, a conserved structure of all the annexin family, responsible for platinum-resistance as well as the effect of knockdown of ANXA4. ANXA4 knockdown increased sensitivity to platinum-based drugs both in vitro and in vivo. To identify the domain responsible for chemoresistance, ANXA4 deletion mutants were constructed by deleting annexin repeats one by one from the C terminus. Platinum resistance was induced both in vitro and in vivo in cells expressing either full-length ANXA4 or the deletion mutants, containing at least one intact annexin repeat. However, cells expressing the mutant without any calcium-binding sites in the annexin repeated sequence, which is essential for ANXA4 translocation from the cytosol to plasma membrane, failed to acquire platinum resistance. After cisplatin treatment, the intracellular chloride ion concentration, whose channel is partly regulated by ANXA4, significantly increased in the platinum-resistant cells. These findings indicate that the calcium-binding site in the annexin repeat induces chemoresistance to the platinum-based drug by elevating the intracellular chloride concentration.

Annexin A4-conferred platinum resistance is mediated by the copper transporter ATP7A.

Although platinum drugs are often used for the chemotherapy of human cancers, platinum resistance is a major issue and may preclude their use in some cases. We recently reported that enhanced expression of Annexin A4 (Anx A4) increases chemoresistance to carboplatin through increased extracellular efflux of the drug. However, the precise mechanisms underlying that chemoresistance and the relationship of Anx A4 to platinum resistance in vivo remain unclear. In this report, the in vitro mechanism of platinum resistance induced by Anx A4 was investigated in endometrial carcinoma cells (HEC1 cells) with low expression of Anx A4. Forced expression of Anx A4 in HEC1 cells resulted in chemoresistance to platinum drugs. In addition, HEC1 control cells were compared with Anx A4-overexpressing HEC1 cells in xenografted mice. Significantly greater chemoresistance to cisplatin was observed in vivo in Anx A4-overexpressing xenografted mice. Immunofluorescence analysis revealed that exposure to platinum drugs induced relocation of Anx A4 from the cytoplasm to the cellular membrane, where it became colocalized with ATP7A, a copper transporter also well known as a mechanism of platinum efflux. ATP7A expression suppressed by small interfering RNA had no effect on HEC1 control cells in terms of chemosensitivity to platinum drugs. However, suppression of ATP7A in Anx A4-overexpressing platinum-resistant cells improved chemosensitivity to platinum drugs (but not to 5-fluorouracil) to a level comparable to that of control cells. These results indicate that enhanced expression of Anx A4 confers platinum resistance by promoting efflux of platinum drugs via ATP7A.

Therapeutic strategies in epithelial ovarian cancer.

Ovarian cancer is the most lethal gynecologic malignancy. It appears that the vast majority of what seem to be primary epithelial ovarian and primary peritoneal carcinomas is, in fact, secondary from the fimbria, the most distal part of the fallopian tube. Treatment of epithelial ovarian cancer is based on the combination of cytoreductive surgery and combination chemotherapy using taxane and platinum. Although clear cell type is categorized in indolent type, it is known to show relatively strong resistance to carboplatin and paclitaxel regimen and thus poor prognosis compared to serous adenocarcinoma, especially in advanced stages. Irinotecan plus cisplatin therapy may effective for the clear cell adenocarcinoma. The larger expectation for improved prognosis in ovarian carcinoma is related to the use of the new biological agents. One of the most investigated and promising molecular targeted drugs in ovarian cancer is bevacizumab, a monoclonal antibody directed against VEGF. PARP inhibitor is another one. A few recent studies demonstrated positive results of bevacizumab on progression-free survival in ovarian cancer patients, however, investigation of molecular targeting drugs in patients with ovarian cancer are still underway.

Targeting annexin A4 to counteract chemoresistance in clear cell carcinoma of the ovary.

IMPORTANCE OF THE FIELD: Epithelial ovarian cancer (EOC) is the leading cause of death from gynecological malignancies in Western countries. Among the four major histological subtypes of EOC, clear cell carcinoma (CCC) of the ovary is highly resistant to platinum-based chemotherapy and is consequently associated with poor patient prognosis in advanced stages. AREAS COVERED IN THIS REVIEW: An overview of the clinical characteristics of ovarian CCC; the role of annexin family proteins in tumor development and progression; the role of annexin A4 in enhancing cellular drug resistance; recent studies linking annexin A4 overexpression to chemoresistance in tumors of ovarian CCC. WHAT THE READER WILL GAIN: Insight into the emerging role for annexin A4 in enhancing chemoresistance in ovarian CCC. TAKE HOME MESSAGE: Annexin A4 enhances cancer cell chemoresistance and is overexpressed in tumors of patients with ovarian CCC. Targeting of annexin A4 may represent a future strategy to counteract resistance to chemotherapy in ovarian CCC.

Enhanced expression of Annexin A4 in clear cell carcinoma of the ovary and its association with chemoresistance to carboplatin.

Clear cell carcinoma (CCC) of the ovary is known to be highly resistant to platinum-based chemotherapy. The purpose of our study was to identify a candidate protein that is associated with chemoresistance of CCC and to investigate the specific mechanism of chemoresistance conferred by the identified protein. Enhanced expression of Annexin A4 (Anx A4) was identified in ovarian CCC cells using 2-D differential gel electrophoresis (2D-DIGE) and mass spectrometry. Anx A4 levels were elevated in CCC cells compared with non-CCC cells as determined by real-time RT-PCR and Western blot analysis. Immunohistochemical analysis of Anx A4 was performed in 126 epithelial ovarian cancer tissue samples and demonstrated significantly elevated levels of Anx A4 protein levels in ovarian CCC tumors compared with ovarian serous and endometrioid tumors (p < 0.01). Anx A4-transfected ovarian non-CCC cells were more resistant to carboplatin (IC50 = 42 microM) compared with control cells (IC50 = 23 microM) as determined by modified MTT assay. Intracellular platinum levels were significantly lower in Anx A4-transfected cells compared with control cells after carboplatin treatment (p = 0.0020) and after an additional 360 min of carboplatin-free incubation (p = 0.0004), as measured by atomic absorption spectrophotometry. Expression of Anx A4 is elevated in ovarian CCC tumors and is associated with chemoresistance in cultured ovarian cancer cells. These results demonstrate that Anx A4 confers chemoresistance in ovarian cancer cells in part by enhancing drug efflux. Thus, Anx A4 may represent a novel therapeutic target of chemoresistance in patients with ovarian CCC.

PIK3CA gene mutations and amplifications in uterine cancers, identified by methods that avoid confounding by PIK3CA pseudogene sequences.

PIK3CA codes for a Class IA p110-alpha catalytic subunit of the PI3Ks (phosphatidylinositol 3-kinases) that regulate various signaling pathways important for neoplasia, including cell proliferation, motility, adhesion, and survival. Pro-oncogenic mutations in exons 9 and 20 of the PIK3CA gene have been frequently observed in numerous types of human malignancies. Amplification of the PIK3CA gene has been reported in uterine cervical cancers. In this study, we have done in depth analysis of uterine cervical and endometrial cancers for PIK3CA gene mutations and amplifications. In uterine cervical cancers, PIK3CA mutations were found in 3 of 22 cases (14%), all of them in exon 9. In endometrial cancers, a similar incidence of mutations was found, in 3 of 29 cases (10%), however they were all within exon 20. Amplification of the PIK3CA gene was also detected in 2 out of 22 (9%) cervical cancers and 3 out of 29 (10%) endometrial cancers. In this study, we were unable to find a clear association between PIK3CA mutations and gene amplifications, nor with tumor histological subtypes or staging. Mutations and amplifications of the PIK3CA gene are relatively infrequent in human cervical and endometrial cancers; however, PIK3CA gene alteration may still play a role in some subset of uterine cancers.