TP53 and cancer: NDI1-HCT 116 p53−/− xenograft growth was resistant to metformin therapy (Figure 7A,B), suggesting that the metformin carries out its tumor inhibitory effects in a cancer cell autonomous manner through inhibition of mitochondrial complex I. Importantly, the consumption of water containing metformin was similar between control and NDI1 tumor barring mice (Figure 7C).