Irinotecan plus mitomycin C as second-line chemotherapy for advanced gastric cancer resistant to fluoropyrimidine and Cisplatin: a retrospective study

Mutations in AcrR and RNA Polymerase Confer High-Level Resistance to Psoralen-UVA Irradiation

DNA interstrand cross-links, such as those formed by psoralen-UVA irradiation, are highly toxic lesions in both humans and bacteria, with a single lesion being lethal in Escherichia coli. Despite the lack of effective repair, human cancers and bacteria can develop resistance to cross-linking treatments, although the mechanisms of resistance remain poorly defined. Here, we subjected E. coli to repeated psoralen-UVA exposure to isolate three independently derived strains that were >10,000-fold more resistant to this treatment than the parental strain. Analysis of these strains identified gain-of-function mutations in the transcriptional regulator AcrR and the alpha subunit of RNA polymerase that together could account for the resistance of these strains. Resistance conferred by the AcrR mutation is mediated at least in part through the regulation of the AcrAB-TolC efflux pump. Resistance via mutations in the alpha subunit of RNA polymerase occurs through a still-uncharacterized mechanism that has an additive effect with mutations in AcrR. Both acrR and rpoA mutations reduced cross-link formation in vivo. We discuss potential mechanisms in relation to the ability to repair and survive interstrand DNA cross-links. IMPORTANCE Psoralen DNA interstrand cross-links are highly toxic lesions with antimicrobial and anticancer properties. Despite the lack of effective mechanisms for repair, cells can become resistant to cross-linking agents through mechanisms that remain poorly defined. We derived resistant mutants and identified that two gain-of-function mutations in AcrR and the alpha subunit of RNA polymerase confer high levels of resistance to E. coli treated with psoralen-UVA. Resistance conferred by AcrR mutations occurs through regulation of the AcrAB-TolC efflux pump, has an additive effect with RNA polymerase mutations, acts by reducing the formation of cross-links in vivo, and reveals a novel mechanism by which these environmentally and clinically important agents are processed by the cell.

A Quinone-Containing Compound Enhances Camptothecin-Induced Apoptosis of Lung Cancer Through Modulating Endogenous ROS and ERK Signaling

The natural compound camptothecin (CPT) derivatives have widely been used for anti-cancer treatments, including lung cancer. However, many chemoresistant cancer cells often develop a relatively higher threshold for inducing apoptosis, causing a limited efficacy of anti-cancer drugs. Likewise, lung cancer cells acquire chemoresistance against CPT analogs, such as irinotecan and topotecan, finally resulting in an unsatisfied outcome and poor prognosis of lung cancer patients. TFPP is a quinone-containing compound as a candidate for CPT-based combination chemotherapy. In this study, we examined the effect of TFPP and CPT cotreatment on non-small cell lung cancer (NSCLC) cells. Cell proliferation and flow cytometry-based Annexin-V/PI staining assays demonstrated the synergistic effect of TFPP on CPT-induced apoptosis in both NSCLC A549 and H1299 cells. The results of CPT and TFPP cotreatment cause the regulation of the ERK-Bim axis and the activation of mitochondrial-mediated caspase cascade, including caspase-9 and caspase-3. Besides, TFPP significantly enhanced CPT-induced endogenous reactive oxygen species (ROS) in the two NSCLC cells. In contrast, the treatment of N-acetyl-L-cysteine (NAC), an ROS scavenger, rescues the apoptosis of NSCLC cells induced by TFPP and CPT cotreatment, suggesting that the synergistic effect of TFPP on CPT-induced anti-NSCLC cells is through upregulating ROS production. Consequently, our results suggest that TFPP sensitizes NSCLC towards CPT-based chemotherapy may act through decreasing the apoptosis-initiating threshold. Therefore, TFPP may be a promising chemosensitizer for lung cancer treatment, and the underlying mechanism warrants further.