Fig. 6. The combination of ALK and PARP inhibitors effectively suppresses tumor growth in vivo.
a–d, Tumor volume and Kaplan–Meier survival curves of mice bearing subcutaneous injected SKOV3 ovarian tumors (a and b) and orthotopic PARP inhibitor-resistant (acquired resistance) SUM149 tumors (nos. 6 and 15; c and d). Mice were treated with oral talazoparib (0.33 mg kg−1) and lorlatinib (5 mg kg−1), either alone or in combination, five times per week (a, c and d), or with oral olaparib (50 mg kg−1) and ceritinib (7.5 mg kg−1), either alone or in combination, five times per week (b). Tumor volume data were reported as mean ± s.e.m. Statistical analysis was carried out using two-tailed, unpaired Student’s t-test (n = 5 mice in each treatment group). e,f, Tumor volume curves (e) and representative images of IHC staining (f) of PARP inhibitor-sensitive SUM149 (parental) tumors from mice with the indicated antibodies. Mice were treated with oral talazoparib (0.33 mg kg−1) five times per week. Scale bar, 20 µm. Tumor volume data were reported as mean ± s.e.m. (n = 5 mice in each treatment group). Statistical analysis was carried out using the two-tailed, unpaired Student’s t-test: **P = 0.0052. g, Representative IHC images stained with indicated antibodies in tumor tissues from mice bearing orthotopic PARP inhibitor-resistant (acquired resistance) SUM149 cells. Data represent images of n = 3 mice. Scale bar, 20 µm. h, Model of PARP inhibitor-resistant mechanism mediated by the ALK–p-Tyr19-CDK9 axis: (1) inactivation of PARP leads to PARP1 trapping on the DNA and increases unrepaired DNA lesions; (2) in PARP inhibitor-resistant cells, p-ALK interacts with and tyrosine phosphorylates CDK9 at Tyr19 to increase the protein stability and kinase activity of CDK9; p-Tyr19-CDK9 regulates formation and nuclear localization of P-TEFb and transcriptionally activates HR-repair genes by phospho-Ser2-RNA Pol II, which in turn contributes to HR proficiency and PARP inhibitor resistance; (3) p-ALK is inhibited by treatment with ALK inhibitors, and the ubiquitination and proteasomal degradation of CDK9 are increased by binding of the E3 ligase Skp2, which in turn blocks the transcription of HR-repair genes and increases PARP inhibitor sensitivity and cell death; and (4) ALK inhibitors induce synthetically lethal PARP inhibitors via induction of HR deficiency.