Azaphilones produced by Penicillium maximae with their cell death-inducing activity on Adriamycin-treated cancer cell

Background Heat shock proteins (Hsps) are overexpressed in several tumors and contribute to cell proliferation, metastasis, and anticancer drug resistance. Therefore, Hsp inhibitors have enhanced cytotoxicity as chemotherapeutic agents and may be effective with a reduced dosage for tumor therapy to avoid side effects. Results Four new azaphilones, maximazaphilones I–IV (1–4), and three known compounds (5–7) have been isolated from the airborne-derived fungus Penicillium maximae. Inhibitory effects of isolated compounds against induction of Hsp105 were evaluated by the luciferase assay system using Hsp105 promoter. In this assay, 2–4, 6, and 7 significantly inhibited hsp105 promoter activity without cytotoxicity. In addition, all isolated compounds except for 5 significantly induced the death of Adriamycin (ADR)-treated HeLa cells. Interestingly, 1–4, 6, and 7 didn’t show anti-proliferative and cell death-inducing activity without ADR. Conclusion This study revealed the chemical structures of maximazaphilones I–IV (1–4) and the potency of azaphilones may be useful for cancer treatment and reducing the dose of anticancer agents. In addition, one of the mechanisms of cell death-inducing activity for 2–4, 6, and 7 was suggested to be inhibitory effects of Hsp105 expression.