Intra-tumoral delivery of Cas9 and sgRNA targeting mutant KRAS suppresses tumor growth in vivo in immunodeficient mice. Cancer cells containing mutant KRAS (A–C) or wild-type KRAS (D–F) were subcutaneously injected into immunodeficient mice, after which tumors were allowed to form over 14 d. Lentivirus expressing both Cas9 and sgRNA (35T9P17) (Lenti_Cas9-sgRNA) or control lentivirus expressing only Cas9 (Lenti_Cas9) were injected into the tumors three times every 3 d. (A,D) Tumor growth curves. Black arrowheads indicate the times when the lentivirus was injected. The number of tested tumors (n) = 6. (B,C,E,F) Representative photographs (B,E) and weights (C,F) of tumors removed from euthanized mice 15 d (B,C) or 12 d (E,F) after the first lentiviral injection. Error bars represent SEM. (**) P < 0.01, (***) P < 0.001; (ns) not significant.