6-acetoxy-anopterine: A novel structure class of mitotic inhibitor disrupting microtubule dynamics in prostate cancer cells

The lack of a cure for metastatic prostate cancer (PCa) highlights the urgent need for more efficient drugs to fight this disease. Here, we report the molecular mechanism of action of the natural product 6-acetoxy-anopterine (6-AA) in malignant cells of the prostate. This potent cytotoxic alkaloid from the endemic Australian tree Anopterus macleayanus induced at low nanomolar doses a strong accumulation of LNCaP and PC3 PCa cells in mitosis, severe mitotic spindle defects and asymmetric cell divisions, ultimately leading to mitotic catastrophe accompanied by cell death through apoptosis. DNA microarray of 6-AA treated LNCaP cells combined with pathway analysis identified very similar transcriptional changes when compared to vinblastine, highlighting pathways involved in mitosis, microtubule spindle organisation and microtubule binding. Like vinblastine, 6-AA inhibited microtubule polymerization in a cell-free system and reduced microtubule polymer mass in vitro. Yet, microtubule alterations that are associated with resistance to microtubule-destabilizing drugs like vinca alkaloids or 2-methoxyestradiol did not confer cross-resistance to 6-AA, suggesting a different mechanism of microtubule interaction. Finally, 6-AA is the first-in-class microtubule inhibitor that features the unique anopterine scaffold. Altogether, this study provides a strong rationale to further develop this novel structure class of microtubule inhibitor for the treatment of malignant disease. The dataset was derived from three biological repeats of each of the treatment groups DMSO and vinblastine and four repeats of the treatment group 6-AA.