Molecular disruption of RAD50 sensitizes human tumor cells to cisplatin-based chemotherapy

Abstract

Platinum-based drugs that induce DNA damage are commonly used first-line chemotherapy agents for testicular, bladder, head and neck, lung, esophageal, stomach, and ovarian cancers. The inherent resistance of tumors to DNA damage often limits the therapeutic efficacy of these agents, such as cisplatin. An enhanced DNA repair and telomere maintenance response by the Mre11/Rad50/Nbs1 (MRN) complex is critical in driving this chemoresistance. We hypothesized therefore that the targeted impairment of native cellular MRN function could sensitize tumor cells to cisplatin. To test this, we designed what we believe to be a novel dominantnegative adenoviral vector containing a mutant RAD50 gene that significantly downregulated MRN expression and markedly disrupted MRN function in human squamous cell carcinoma cells. A combination of cisplatin and mutant RAD50 therapy produced significant tumor cytotoxicity in vitro, with a corresponding increase in DNA damage and telomere shortening. In cisplatin-resistant human squamous cell cancer xenografts in nude mice, this combination therapy caused dramatic tumor regression with increased apoptosis. Our findings suggest the use of targeted RAD50 disruption as what we believe to be a novel chemosensitizing approach for cancer therapy in the context of chemoresistance. This strategy is potentially applicable to several types of malignant tumors that demonstrate chemoresistance and may positively impact the treatment of these patients.

Sequential Tracking of PD-L1 Expression and RAD50 Induction in Circulating Tumor and Stromal Cells of Lung Cancer Patients Undergoing Radiotherapy

“…In tissue biopsies, expression of the biomarker PD-L1 alone is not a prognostic indicator of survival in lung cancer, while RAD50 foci formation has been indicated as positively correlated with survival (14,18,20,24,29,30,32,35,39,40,42). We analyzed the clinical outcomes of patients based on expression of PD-L1, or the average number of RAD50, at both T0 and T1 time points (Fig.…”

“…Because RAD50 foci formation in tissue biopsies has been shown to be positively correlated with survival (18,20,24,26), we assessed its prognostic value in circulating cells (Fig. 6).…”

“…Cells originating from tumors receiving site-directed radiation are marked by ionizing radiation-induced DNA damage, including tumor and stromal cells (18)(19)(20)(21)(22)(23)(24). Thus, we expect that circulating cells that originate at the tumor site during radiotherapy should have evidence of DNA damage, such as ionizing radiation-induced foci (IRIF), which can be visualized with RAD50 (18)(19)(20)(21)(22)(23)(24).…”

“…Thus, we expect that circulating cells that originate at the tumor site during radiotherapy should have evidence of DNA damage, such as ionizing radiation-induced foci (IRIF), which can be visualized with RAD50 (18)(19)(20)(21)(22)(23)(24). RAD50 is a protein that complexes with the proteins NBS1 and MRE11 and is crucial in the DNA double-strand repair process following treatment with radiation and/or chemical agents.…”

“…In normal mammalian cells, RAD50 is distributed throughout both the cytoplasm and the nucleus. Following double-stranded breaks in DNA, the RAD50/NBS/MRE11 complex rapidly translocates to the sites of the breakage, forming aggregated nuclear foci until the break is repaired, for example, IRIF (18,20,23,25). Thus, RAD50 can be used as a specific identifier of cells that have been exposed to high levels of radiation, acting as a biological tag of cells from patients that have been directly exposed to radiation targeted to a tumor mass (18)(19)(20)(21)(22)(23)(24)(26)(27)(28).…”