RNAi-based knockdown of multidrug resistance-associated protein 1 is sufficient to reverse multidrug resistance of human lung cells

Mechanisms of Drug Resistance in Ovarian Cancer and Associated Gene Targets

In the United States, over 100,000 women are diagnosed with a gynecologic malignancy every year, with ovarian cancer being the most lethal. One of the hallmark characteristics of ovarian cancer is the development of resistance to chemotherapeutics. While the exact mechanisms of chemoresistance are poorly understood, it is known that changes at the cellular and molecular level make chemoresistance challenging to treat. Improved therapeutic options are needed to target these changes at the molecular level. Using a precision medicine approach, such as gene therapy, genes can be specifically exploited to resensitize tumors to therapeutics. This review highlights traditional and novel gene targets that can be used to develop new and improved targeted therapies, from drug efflux proteins to ovarian cancer stem cells. The review also addresses the clinical relevance and landscape of the discussed gene targets.

XIAP underlies apoptosis resistance of renal cell carcinoma cells

X-linked inhibitor of apoptosis (XIAP), a key member of the inhibitors of apoptosis protein family, can inhibit apoptosis by directly binding to the initiator caspase-9, −3 and −7, thereby promoting tumor cell survival during tumor progression. In the present study, XIAP basal expression levels were investigated and its contribution to the resistance to apoptosis was evaluated, in the RCC cell lines exposed to apoptosis-inducing drugs. This was investigated by histological methods and western blot analysis. Using RNA interference, elimination of XIAP in Caki-1 cells was also studied, and its contribution to the sensitivity to apoptosis induced through the intrinsic pathway was observed. Differences in XIAP expression were detected between ClearCa-2 and ClearCa-6 cell lines. ClearCa-6 cells with lower expression of XIAP were more sensitive to apoptosis-inducing drugs, compared with ClearCa-2 cells. However, the levels of XIAP expression in both cell lines were stable during apoptosis. Furthermore, a Caki-1 cell line with no XIAP expression was used, and was demonstrated to be more sensitive to the apoptosis induced by the mitochondrial pathway. These results suggested that downregulation of XIAP expression could enhance the sensitivity of RCC cells to apoptosis, and the basal expression of XIAP during apoptosis is stable. This may provide novel insight for targeted gene therapy against XIAP, in the clinic.

Proadifen sensitizes resistant ovarian adenocarcinoma cells to cisplatin

Proadifen (SKF-525A) is a P450 monooxygenase inhibitor with potential anti-proliferative activity and the ability to potentiate the toxicity of hypericin-mediated photodynamic therapy and mitoxantrone via alteration of ABC transport proteins. Elevated expression of some ABC transporters may also determine the efficacy of cisplatin-based chemotherapy. Thus, the purpose of this study was to investigate the ability of proadifen to sensitize A2780 and A2780cis ovarian cancer cells to cisplatin (CDDP). Herein, we show for the first time that proadifen sensitized resistant ovarian cancer cells to CDDP-induced cell death. The chemosensitizing effect of proadifen on CDDP action was also confirmed by MTT assays in multicellular spheroids. The possible mechanisms responsible for the enhanced cytotoxicity of proadifen/CDDP combined treatment may be attributed to a decrease of reduced relative glutathione levels, downregulation of multidrug resistance-associated proteins 1 and 2 (MRP1, MRP2) and attenuation of survivin expression. Taken together, our results indicate that proadifen is a promising compound for further in vivo experiments related to overcoming multidrug resistance and sensitization of resistant ovarian carcinoma to CDDP.

Cisplatin-mediated c-myc overexpression and cytochrome c (cyt c) release result in the up-regulation of the death receptors DR4 and DR5 and the activation of caspase 3 and caspase 9, likely responsible for the TRAIL-sensitizing effect of cisplatin

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) reverses multidrug resistance (MDR) and induces apoptosis in MDR gastric carcinoma cells. In our previous study, cisplatin proved to be a sensitizing agent for TRAIL. To study the synergistic effects of cisplatin and TRAIL, we investigated the mechanism by which TRAIL reverses multidrug resistance, the role of c-myc in modulating the death receptors DR4 and DR5 and the relationship between cisplatin and cytochrome c (cyt c) release in SGC7901/VCR and SGC7901/DDP cells. We found that after treatment with TRAIL, the DNA-PKcs/Akt/GSK-3β pathway, which is positively correlated with the levels of MDR1 and MRP1, was significantly inhibited and that this tendency can be abolished by Z-DEVD-FMK (a specific caspase 3 inhibitor). We also found that suppression of c-myc by siRNA reduced the expression of DR4 and DR5 and that transfection with a pAVV-c-myc expression vector increased the expression of DR4 and DR5. Moreover, cisplatin increased the expression of c-myc in the presence of TRAIL, and there is a clear increase in cyt c release from mitochondria with the increasing concentrations of cisplatin. Meanwhile, the intrinsic death receptor pathway of caspase 9, as well as the common intrinsic and extrinsic downstream target, caspase 3, was potently activated by the release of cyt c. Together, we conclude that in TRAIL-treated MDR gastric carcinoma cells, cisplatin induces the death receptors DR4 and DR5 through the up-regulation of c-myc and strengthens the activation of caspases via promoting the release of cyt c. These effects would then be responsible for the TRAIL sensitization effect of cisplatin.