PTC596 is an orally active small molecule that targets tumor stem cell populations by reducing the function, activity and amount of BMI1. PTC596 acts by altering and destroying the BMI1 protein through a process called phosphorylation. PTC596 has potently inhibited BMI1 function in multiple tumor cell lines. In in vitro tests, PTC596 has preferentially targeted chemotherapy resistant cancer stem cells. Specifically, PTC596 preferentially depleted cancer stem cells in assays with tumor cell lines from fibrosarcoma, prostate and colon cancers. Conversely, the cytotoxic chemotherapies carboplatin, temozolomide, methotrexate and indibulin enriched the population of cancer stem cells in this assay.
In animal cancer models using human tumors, weekly oral dosing of PTC596 provided tumor control, including reduction of tumor size. PTC596 and the commonly used chemotherapy paclitaxel were both effective at controlling tumor growth in these animal models. However, PTC596, but not paclitaxel, decreased BMI1 levels, indicating a reduction in cancer stem cells. Consistent with this reduction in BMI1 levels, after transplanting tumor cells from one animal to another, the resulting tumors treated with PTC596 had lower levels of cancer stem cells than either untreated tumors or tumors treated with paclitaxel.
PTC596 has been well tolerated at effective doses in animals. Preliminary data from these animal models suggest that PTC596 may preferentially target cancer stem cells without targeting normal stem cells.