A novel transcript for DNA repair gene Ercc1 in mouse skin

Identification of small molecule inhibitors of ERCC1-XPF that inhibit DNA repair and potentiate cisplatin efficacy in cancer cells

ERCC1-XPF heterodimer is a 5′-3′ structure-specific endonuclease which is essential in multiple DNA repair pathways in mammalian cells. ERCC1-XPF (ERCC1-ERCC4) repairs cisplatin-DNA intrastrand adducts and interstrand crosslinks and its specific inhibition has been shown to enhance cisplatin cytotoxicity in cancer cells. In this study, we describe a high throughput screen (HTS) used to identify small molecules that inhibit the endonuclease activity of ERCC1-XPF. Primary screens identified two compounds that inhibit ERCC1-XPF activity in the nanomolar range. These compounds were validated in secondary screens against two other non-related endonucleases to ensure specificity. Results from these screens were validated using an in vitro gel-based nuclease assay. Electrophoretic mobility shift assays (EMSAs) further show that these compounds do not inhibit the binding of purified ERCC1-XPF to DNA. Next, in lung cancer cells these compounds potentiated cisplatin cytotoxicity and inhibited DNA repair. Structure activity relationship (SAR) studies identified related compounds for one of the original Hits, which also potentiated cisplatin cytotoxicity in cancer cells. Excitingly, dosing with NSC16168 compound potentiated cisplatin antitumor activity in a lung cancer xenograft model. Further development of ERCC1-XPF DNA repair inhibitors is expected to sensitize cancer cells to DNA damage-based chemotherapy.

Functional characterization of a novel transcript of ERCC1 in chemotherapy resistance of ovarian cancer

Approximately 15-20% of ovarian cancer patients receiving platinum-based chemotherapy are primary platinum-resistant. Identification of these patients and transfer to other more effective therapy could reduce the morbidity of ovarian cancer. ERCC1 is a DNA repair gene which can complex with XPF to repair cisplatin-induced DNA damage and cause chemotherapy resistance. In this study, we found a novel ERCC1 transcript initiated upstream of the normal transcription initiation site. The expression of this larger ERCC1 transcript dramatically increased following cisplatin treatment in ovarian cancer cells and was regulated by the MAPK pathway. This phenomenon conferred enhanced cisplatin resistance on ovarian cancer cells, and was confirmed with chemosensitive and chemoresistant patients' samples. Our data suggested that larger ERCC1 transcript levels correlated with the outcome of platinum-based chemotherapy.

Functional characterization of a novel transcript of ERCC1 in chemotherapy resistance of ovarian cancer

Approximately 15-20% of ovarian cancer patients receiving platinum-based chemotherapy are primary platinum-resistant. Identification of these patients and transfer to other more effective therapy could reduce the morbidity of ovarian cancer. ERCC1 is a DNA repair gene which can complex with XPF to repair cisplatin-induced DNA damage and cause chemotherapy resistance. In this study, we found a novel ERCC1 transcript initiated upstream of the normal transcription initiation site. The expression of this larger ERCC1 transcript dramatically increased following cisplatin treatment in ovarian cancer cells and was regulated by the MAPK pathway. This phenomenon conferred enhanced cisplatin resistance on ovarian cancer cells, and was confirmed with chemosensitive and chemoresistant patients' samples. Our data suggested that larger ERCC1 transcript levels correlated with the outcome of platinum-based chemotherapy.

Functional characterization of a novel transcript of ERCC1 in chemotherapy resistance of ovarian cancer

Approximately 15-20% of ovarian cancer patients receiving platinum-based chemotherapy are primary platinum-resistant. Identification of these patients and transfer to other more effective therapy could reduce the morbidity of ovarian cancer. ERCC1 is a DNA repair gene which can complex with XPF to repair cisplatin-induced DNA damage and cause chemotherapy resistance. In this study, we found a novel ERCC1 transcript initiated upstream of the normal transcription initiation site. The expression of this larger ERCC1 transcript dramatically increased following cisplatin treatment in ovarian cancer cells and was regulated by the MAPK pathway. This phenomenon conferred enhanced cisplatin resistance on ovarian cancer cells, and was confirmed with chemosensitive and chemoresistant patients' samples. Our data suggested that larger ERCC1 transcript levels correlated with the outcome of platinum-based chemotherapy.

Cisplatin regulates the MAPK kinase pathway to induce increased expression of DNA repair gene ERCC1 and increase melanoma chemoresistance

The incidence of malignant melanoma is growing rapidly worldwide and there is still no effective therapy for metastatic disease. Melanoma is the second most common cancer among young adults in the UK, where incidence rates have more than quadrupled since the 1970s. Increased expression of a number of DNA repair genes has been reported in melanoma and this likely contributes to its extreme resistance to conventional DNA-damaging chemotherapeutics. One such chemotherapeutic that is effective against a range of other cancers, but not melanoma, is cisplatin. The DNA repair proteins ERCC1 and XPF are needed to remove cisplatin-induced DNA damage and we have investigated the response of these proteins to cisplatin in melanoma. The expression of both genes is induced by cisplatin. Use of a MEK inhibitor showed that ERCC1, but not XPF induction was regulated by the mitogen-activated protein kinase (MAPK) pathway, with reduction in expression of DUSP6, the phosphatase that inactivates the extracellular signal-regulated kinase (ERK), being particularly important. DUSP6 overexpression prevented cisplatin induction of both ERCC1 and XPF, resulting in increased sensitivity to cisplatin. A novel ERCC1 mRNA was found that initiated upstream of the normal transcription initiation site, and was strongly regulated by both cisplatin and the MAPK pathway and its role in cisplatin resistance merits further study. The cisplatin induction of ERCC1 and XPF provides important insights into the resistance of melanoma to DNA-damaging chemotherapeutics, which is one of the major obstacles to melanoma treatment.