Pradimicin-IRD as a DNA Damaging Anticancer Agent

DNA-damaging agents are widely used in cancer therapy; however, their use is limited by dose-related toxicities, as well as the development of drug resistance. Drug discovery is essential to overcome these limitations and offer novel therapeutic options. In a previous study by our research group, pradimicin-IRD—a new polycyclic antibiotic produced by the actinobacteria Amycolatopsis sp.—displayed antimicrobial and potential anticancer activities. In the present study, cytotoxic activity was further confirmed in a panel of five colon cancer, including those with mutation in TP53 and KRAS, the most common ones observed in cancer colon patients. While all tested colon cancer cells were sensitive to pradimicin-IRD treatment with IC50 in micromolar range, non-tumor fibroblasts were significantly less sensitive (p < 0.05). The cellular and molecular mechanism of action of pradimicin-IRD was then investigated in the colorectal cancer cell line HCT 116. Pradimicin-IRD presented antitumor effects occurring after at least 6 hours of exposure. Pradimicin-IRD induced statistically significant DNA damage (γH2AX and p21), apoptosis (PARP1 and caspase 3 cleavage) and cell cycle arrest (reduced Rb phosphorylation, cyclin A and cyclin B expression) markers. In accordance with these results, pradimicin-IRD increased cell populations in the subG1 and G0/G1 phases of the cell cycle. Additionally, mass spectrometry analysis indicated that pradimicin-IRD interacted with the DNA double strand and comet assay confirms double strand breaks and also suggests singles strand breaks. Induction o FANCG gene expression suggests crosslink alkylation of pradimicin-IRD, since FANCG is phosphorylated by ATR to promote efficient crosslink repair. In summary, pradimicin-IRD exhibits multiple antineoplastic activities—including DNA damage, cell cycle arrest, reduction of clonal growth and apoptosis—in the HCT 116 cell line. Furthermore, pradimicin-IRD displays a TP53-independent regulation of p21 expression in HCT 116 TP53-/-, HT-29, SW480, and Caco-2 cells, promoting activation of Chk2 in HCT 116. This exploratory study identified novel targets for pradimicin-IRD and provided insights for its potential anticancer activity as a DNA-damaging agent.