Background/Objectives: Multidrug resistance is one the leading problems in cancer treatment, where the overexpression of P-gp and other drug efflux pumps is regarded as the primary cause. With the intention to develop transporter inhibitors, natural products such as phenolics have shown great potential and diverse attention recently. Among these, isorhamnetin (ISO), an O-methylated flavonol, is predominantly found in the fruits and leaves of various plants. Thus, this study aimed to investigate the effects of ISO on the mRNA expression of membrane transporters P-gp, BCRP, MRP 1, 2, and 5, the protein expression of P-gp, as well as the GSTP1 and GSH content in DLD1 and HCT-116 colon cancer cells. Methods: The cytotoxic effect of isorhamnetin is assessed using an MTT test, while qPCR and immunocytochemistry methods were used to determine gene and protein expression levels. The concentration of reduced glutathione was determined using the colorimetric method. Results: Based on the results, ISO can modulate the expression of transporters responsible for the resistance development (all transporters on the transcriptional level were downregulated in DLD1 cells, while only MRP1 on HCT-116 cells, and reduced P-gp protein expression on both investigated cell lines). Increased glutathione content in treated cells and GSTP1 expression suggest metabolizing the ISO and potential ejection with GSH-dependent pumps. Conclusions: Thus, in future experiments, ISO as a natural medicinal compound could be used as a chemosensitizer to prevent or overcome membrane transporter-mediated drug resistance.

The development of resistance to standard cytostatics, such as 5-fluorouracil (5-FU), significantly limits the efficacy of colon cancer therapy, prompting the search for novel anticancer agents, particularly among natural compounds. This study evaluated the anticancer effects of isorhamnetin, a plant-derived flavonol, and its ability to modulate the expression of drug-resistance-related biomarkers in SW-480 and HT-29 colon cancer cells, with a focus on ATP-binding cassette (ABC) transporters. Isorhamnetin demonstrated strong cytotoxic and proapoptotic activity on both cell lines, while showing lower toxicity toward normal HaCaT cells. In addition to suppressing the mRNA expression of drug-metabolizing enzymes (CYP1A1 and CYP1B1), isorhamnetin significantly reduced the mRNA levels of multidrug resistance-associated proteins 1 and 5 (MRP1 and MRP5), as well as the P-glycoprotein (P-gp) level in SW-480 and HT-29 cells. Molecular docking analysis revealed a high binding affinity of isorhamnetin to CYP1A1, CYP1B1, P-gp, MRP1, MRP5, and glutathione S-transferase (GST) proteins, with stronger interactions than those observed for 5-FU, suggesting potential interference with their function. These results provide a solid basis for future investigations to confirm the therapeutic potential of isorhamnetin as a modulator of drug resistance in colon cancer cells.

The insect silk protects the larvae that produce it. This implies that it may contain biologically active substances that can be used in medicine. In this paper, the cytotoxic and proapoptotic potential of Indian meal moth (Plodia interpunctella) silk extract was examined after 72 h of exposure to the SW-480 human colorectal adenocarcinoma cell line. Apoptosis was examined by monitoring the cell morphological changes by fluorescent staining, acridine orange/ethidium bromide, and DAPI, as well as by flow cytometry. The results showed that silk extract has a very good cytotoxic and proapoptotic activity. The selective effect of silk indicates the presence of a high level of biocompatibility with normal human cells. Based on the results of increased gene expression for caspase 8 and 9 in silk extract-treated cells compared to control, apoptosis was induced by a caspase-dependent pathway.