Efflux inhibition by IWR-1-endo confers sensitivity to doxorubicin effects in osteosarcoma cells

Osteosarcoma, the most prevalent bone tumor in children and young adults, still relies heavily on the patient’s response to neoadjuvant chemotherapy to predict outcomes. Despite the progress in combination chemotherapy regimens, overcoming resistance remains challenging. Recently, highly potent small molecule inhibitors of canonical Wnt signaling through poly(ADP-ribose) polymerase (PARP)-family enzymes, specifically tankyrases 1 & 2 (Tnks1/2), have been explored as potential agents to enhance chemotherapy sensitivity. This study aimed to evaluate the ability of the highly specific Tnks1/2 inhibitor, IWR-1-endo, to sensitize chemotherapy-resistant osteosarcoma to doxorubicin.

Our findings revealed that IWR-1-endo significantly reduced cellular efflux, as evidenced by increased retention of Calcein AM and doxorubicin within the cells. In a model of doxorubicin-resistant osteosarcoma, pre-treatment with IWR-1-endo greatly enhanced sensitivity to doxorubicin, reducing the doxorubicin IC50 in resistant cells but not in chemotherapy-naïve cells. This effect caused the doxorubicin-treated cells to accumulate at the G2/M checkpoint. Additionally, the treatment with IWR-1-endo led to an increase in γH2AX foci formation, indicating enhanced DNA damage by doxorubicin.

In summary, our results demonstrate that IWR-1-endo effectively increases cellular responses to doxorubicin by inhibiting efflux transport in a drug-resistant osteosarcoma model.