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Activating KRAS mutations drive colorectal cancer tumorigenesis and influence response to anti- EGFR-targeted therapy. Despite recent advances in understanding Ras signaling biology and the revolution in therapies for melanoma using BRAF inhibitors, no targeted agents have been effective in KRAS-mutant cancers, mainly due to activation of compensatory pathways. Here, by leveraging the largest synthetic lethal genetic interactome in yeast, we identify that KRAS-mutated colorectal cancer cells have augmented homologous recombination repair ( HRR) signaling. We found that KRAS mutation resulted in slowing and stalling of the replication fork and accumulation of DNA damage. Moreover, we found that KRAS-mutant HCT116 cells have an increase in MYC-mediated RAD51 expression with a corresponding increase in RAD51 recruitment to irradiation-induced DNA double-strand breaks ( DSBs) compared to genetically complemented isogenic cells. MYC depletion using RNA interference significantly reduced IR-induced RAD51 foci formation and HRR. On the contrary, overexpression of either HA-tagged wild-type (WT) MYC or phospho-mutant S62A increased RAD51 protein levels and hence IR-induced RAD51 foci. Likewise, depletion of RAD51 selectively induced apoptosis in HCT116-mutant cells by increasing DSBs. Pharmacological inhibition targeting HRR signaling combined with PARP inhibition selectivity killed KRAS-mutant cells. Interestingly, these differences were not seen in a second isogenic pair of KRAS WT and mutant cells ( DLD-1), likely due to their nondependency on the KRAS mutation for survival. Our data thus highlight a possible mechanism by which KRAS-mutant-dependent cells drive HRR in vitro by upregulating MYC- RAD51 expression. These data may offer a promising therapeutic vulnerability in colorectal cancer cells harboring otherwise nondruggable KRAS mutations, which warrants further investigation in vivo. [ABSTRACT FROM AUTHOR]

Here we investigate whether the presence of germinal vesicle-stage oocytes (GV− oocytes) reflects poor oocyte developmental competence (or quality). This was a prospective, non-randomised, cohort pilot-study involving 60 patients undergoing in vitro fertilization/ intracytoplasmic sperm injection for whom complete pregnancy outcome data were available. Patients in whom GV− oocytes were retrieved (GV+) at transvaginal oocyte retrieval (TVOR) were compared with those from whom no GVs were retrieved (GV−). We found that GV+ (n = 29) and GV− (n = 31) patients were similarly aged (35.4 vs. 36.4 years; p = 0.446). GV+ patients had a mean of 2.41 ± 2.03 GVs and comparable yields of MII oocytes to GV− patients (11 ± 6.88 vs. 8.26 ± 4.84; p = 0.077). Compared with GV− patients, GV+ patients had markedly lower implantation rates (11.8% vs. 30.2%; p = 0.022) as well as oocyte utilisation rates for clinical pregnancy (2.3% vs. 6.8%; p = 0.018) and live-birth (1.9% vs. 5.7%; p = 0.029). DNA damage levels measured using γH2AX immunostaining were not different in oocytes from women <36 years versus those ≥36 years (p = 0.606). Thus, patients who have GV− stage oocytes at TVOR exhibit poor oocyte quality reflected in reduced per-oocyte pregnancy success rates and uniformly high levels of oocyte DNA damage. [ABSTRACT FROM AUTHOR]