MCJ localizes on the inner membrane of mitochondria and negatively regulates Complex I thus acting as an endogenous brake on mitochondrial respiration (Hatle et al., 2013) As MCJ is often downregulated in the tumors, the authors generated MCJ mimetics and investigated their capability to inhibit ABC transporter function and therapeutic efficacy in combination with doxorubicin, using ovarian and mammary cancer cells and an in vivo mouse model of mammary tumor (Giddings et al., 2021). The gene discussed is ABCG2; the disease is breast cancer.