Mechanisms of PARP inhibitor resistance in cancer and insights into the DNA damage response.

Inhibitors of poly(ADP-ribose) polymerase (PARPi) have entered the clinic for the treatment of patients with cancers that lack homology-directed DNA repair, but drug resistance remains a clinical hurdle. Recent advances in the identification of PARPi resistance mechanisms have yielded a better understanding of DNA end protection and the relevance of endogenous poly(ADP-ribose) glycohydrolase, highlighting new vulnerabilities

DNA Damage Response and Mismatch Repair Gene Defects in Advanced and Metastatic Prostate Cancer.

Alterations in DNA damage response (DDR) and related genes are present in up to 25% of advanced prostate cancers (PCa). Most frequently altered genes are involved in the homologous recombination repair, the Fanconi anemia, and the mismatch repair pathways, and their deficiencies lead to a highly heterogeneous spectrum of DDR-deficient phenotypes. More than half of these alterations concern non-BRCA DDR genes. From a therapeutic perspective, poly-ADP-ribose polymerase inhibitors have demonstrated robust clinical efficacy in tumors with BRCA2 and BRCA1 alterations. Mismatch repair-deficient PCa, and a subset of CDK12-deficient PCa, are vulnerable to immune checkpoint inhibitors. Emerging data point to the efficacy of ATR inhibitors in PCa with ATM deficiencies. Still, therapeutic implications are insufficiently clarified for most of the non-BRCA DDR alterations, and no successful targeted treatment options have been established

Baseline risk factors of in-hospital mortality after surgery for acute type A aortic dissection: an ERTAAD study

Background Surgery for type A aortic dissection (TAAD) is associated with high risk of mortality. Current risk scoring methods have a limited predictive accuracy.Methods Subjects were patients who underwent surgery for acute TAAD at 18 European centers of cardiac surgery from the European Registry of Type A Aortic Dissection (ERTAAD).Results Out of 3,902 patients included in the ERTAAD, 2,477 fulfilled the inclusion criteria. In the validation dataset (2,229 patients), the rate of in-hospital mortality was 18.4%. The rate of composite outcome (in-hospital death, stroke/global ischemia, dialysis, and/or acute heart failure) was 41.2%, and 10-year mortality rate was 47.0%. Logistic regression identified the following patient-related variables associated with an increased risk of in-hospital mortality [area under the curve (AUC), 0.755, 95% confidence interval (CI), 0.729-0.780; Brier score 0.128]: age; estimated glomerular filtration rate; arterial lactate; iatrogenic dissection; left ventricular ejection fraction <= 50%; invasive mechanical ventilation; cardiopulmonary resuscitation immediately before surgery; and cerebral, mesenteric, and peripheral malperfusion. The estimated risk score was associated with an increased risk of composite outcome (AUC, 0.689, 95% CI, 0.667-0.711) and of late mortality [hazard ratio (HR), 1.035, 95% CI, 1.031-1.038; Harrell's C 0.702; Somer's D 0.403]. In the validation dataset (248 patients), the in-hospital mortality rate was 16.1%, the composite outcome rate was 41.5%, and the 10-year mortality rate was 49.1%. The estimated risk score was predictive of in-hospital mortality (AUC, 0.703, 95% CI, 0.613-0.793; Brier score 0.121; slope 0.905) and of composite outcome (AUC, 0.682, 95% CI, 0.614-0.749). The estimated risk score was predictive of late mortality (HR, 1.035, 95% CI, 1.031-1.038; Harrell's C 0.702; Somer's D 0.403), also when hospital deaths were excluded from the analysis (HR, 1.024, 95% CI, 1.018-1.031; Harrell's C 0.630; Somer's D 0.261).Conclusions The present analysis identified several baseline clinical risk factors, along with preoperative estimated glomerular filtration rate and arterial lactate, which are predictive of in-hospital mortality and major postoperative adverse events after surgical repair of acute TAAD. These risk factors may be valuable components for risk adjustment in the evaluation of surgical and anesthesiological strategies aiming to improve the results of surgery for TAAD.Clinical Trial Registration https://clinicaltrials.gov, identifier NCT04831073

Meiotic genes and DNA double strand break repair in cancer

Tumor cells show widespread genetic alterations that change the expression of genes driving tumor progression, including genes that maintain genomic integrity. In recent years, it has become clear that tumors frequently reactivate genes whose expression is typically restricted to germ cells. As germ cells have specialized pathways to facilitate the exchange of genetic information between homologous chromosomes, their aberrant regulation influences how cancer cells repair DNA double strand breaks (DSB). This drives genomic instability and affects the response of tumor cells to anticancer therapies. Since meiotic genes are usually transcriptionally repressed in somatic cells of healthy tissues, targeting aberrantly expressed meiotic genes may provide a unique opportunity to specifically kill cancer cells whilst sparing the non-transformed somatic cells. In this review, we highlight meiotic genes that have been reported to affect DSB repair in cancers derived from somatic cells. A better understanding of their mechanistic role in the context of homology-directed DNA repair in somatic cancers may provide useful insights to find novel vulnerabilities that can be targeted

Senescence as biologic endpoint following pharmacological targeting of receptor tyrosine kinases in cancer.

Cellular senescence was first described in 1961 in a seminal study by Hayflick and Moorhead as a limit to the replicative lifespan of somatic cells after serial cultivation. Since then, major advances in our understanding of senescence have been achieved suggesting that this mechanism is activated also by oncogenic stimuli, oxidative stress and DNA damage, giving rise to the concept of premature senescence. Regardless of the initial trigger, numerous experimental observations have been provided to support the notion that both replicative and premature senescence play pivotal roles in early stages of tumorigenesis and in response of tumor cells to anticancer treatments. Moreover, various studies have suggested that the induction of senescence by both chemo- and radiotherapy in a variety of cancer types correlates with treatment outcome. As it is widely accepted that cellular senescence may function as a fundamental barrier of tumor progression, the significance of senescence for clinical interventions that make use of novel molecular targeting-based modalities needs to be well defined. Interestingly, despite numerous studies evaluating efficacies of receptor tyrosine kinases (RTKs) targeting strategies in both preclinical and clinical settings, the relevance of RTKs inhibition-associated senescence in tumors remains less characterized. Here we review the available literature that describes premature senescence as a major mechanism following targeting of RTKs in preclinical as well as in clinical settings. Additionally, we discuss the possible role of diverse RTKs in regulating the induction of senescence following cellular stress and possible implications of this crosstalk in identification of biomarkers of inhibitor-mediated chemo- and radiosensitization approaches

Targeting the receptor tyrosine kinase RET in combination with aromatase inhibitors in ER positive breast cancer xenografts.

The majority of breast cancers are estrogen receptor positive (ER+). Blockade of estrogen biosynthesis by aromatase inhibitors (AIs) is the first-line endocrine therapy for post-menopausal women with ER+ breast cancers. However, AI resistance remains a major challenge. We have demonstrated previously that increased GDNF/RET signaling in ER+ breast cancers promotes AI resistance. Here we investigated the efficacy of different small molecule RET kinase inhibitors, sunitinib, cabozantinib, NVP-BBT594 and NVP-AST487, and the potential of combining a RET inhibitor with the AI letrozole in ER+ breast cancers. The most effective inhibitor identified, NVP-AST487, suppressed GDNF-stimulated RET downstream signaling and 3D tumor spheroid growth. Ovariectomized mice were inoculated with ER+ aromatase-overexpressing MCF7-AROM1 cells and treated with letrozole, NVP-AST487 or the two drugs in combination. Surprisingly, the three treatment regimens showed similar efficacy in impairing MCF7-AROM1 tumor growth in vivo. However in vitro, NVP-AST487 was superior to letrozole in inhibiting the GDNF-induced motility and tumor spheroid growth of MCF7-AROM1 cells and required in combination with letrozole to inhibit GDNF-induced motility in BT474-AROM3 aromatase expressing cells. These data indicate that inhibiting RET is as effective as the current therapeutic regimen of AI therapy but that a combination treatment may delay cancer cell dissemination and metastasis

Targeting of the MET receptor tyrosine kinase by small molecule inhibitors leads to MET accumulation by impairing the receptor downregulation.

The MET receptor tyrosine kinase is deregulated primarily via overexpression or point mutations in various human cancers and different strategies for MET inhibition are currently evaluated in clinical trials. We observed by Western blot analysis and by Flow cytometry that MET inhibition by different MET small molecule inhibitors surprisingly increases in a dose-dependent manner total MET levels in treated cells. Mechanistically, this inhibition-related MET accumulation was associated with reduced Tyr1003 phosphorylation and MET physical association with the CBL ubiquitin ligase with concomitant decrease in MET ubiquitination. These data may suggest careful consideration for design of anti-MET clinical protocols

PIK3CA hotspot mutations differentially impact responses to MET targeting in MET-driven and non-driven preclinical cancer models

Abstract Background The MET receptor tyrosine kinase represents a promising target in cancer. PIK3CA activating mutations are common in several tumor types and can potentially confer resistance to anti-receptor tyrosine kinase therapy. Methods MET and/or PI3K pathway inhibition was assessed in NIH3T3 cells harboring MET-activating point mutation with or without ectopic expression of PIK3CAE545K and PIK3CAH1047R, as well as in MET-expressing head and neck cancer cells with endogenous PIK3CA mutations. Endpoints included PI3K pathway activation, cell proliferation, colony-forming ability, cell death, wound-healing, and an in vivo model. Results PIK3CAE545K and PIK3CAH1047R confer resistance to MET inhibition in MET-driven models. PIK3CAH1047R was more potent than PIK3CAE545K at inducing resistance in PI3K pathway activation, cell proliferation, colony-forming ability, induction of cell death and wound-healing upon MET inhibition. Resistance to MET inhibition could be synergistically overcome by co-targeting PI3K. Furthermore, combined MET/PI3K inhibition led to enhanced anti-tumor activity in vivo in tumors harboring PIK3CAH1047R. In head and neck cancer cells the combination of MET/PI3K inhibitors led to more-than-additive effects. Conclusions PIK3CA mutations can lead to resistance to MET inhibition, supporting future clinical evaluation of combinations of PI3K and MET inhibitors in common scenarios of malignant neoplasms featuring aberrant MET expression and PIK3CA mutations