Cancer-specific defects in DNA repair pathways as targets for personalized therapeutic approaches.

Defects in DNA repair pathways enable cancer cells to accumulate genomic alterations that contribute to their aggressive phenotype. However, tumors rely on residual DNA repair capacities to survive the damage induced by genotoxic stress. This dichotomy might explain why only isolated DNA repair pathways are inactivated in cancer cells. Accordingly, synergism has been observed between DNA-damaging drugs and targeted inhibitors of DNA repair. DNA repair pathways are generally thought of as mutually exclusive mechanistic units handling different types of lesions in distinct cell cycle phases. Recent preclinical studies, however, provide strong evidence that multifunctional DNA repair hubs, which are involved in multiple conventional DNA repair pathways, are frequently altered in cancer. We therefore propose that targeted anticancer therapies should not only exploit synthetic lethal interactions between two single genes but also consider alterations in DNA repair hubs. Such a network-based approach considerably increases the opportunities for targeting DNA repair-defective tumors.

Meta-Analysis Reveals Significant Sex Differences in Chronic Lymphocytic Leukemia Progression in the Eµ-TCL1 Transgenic Mouse Model.

The Eµ-TCL1 transgenic mouse model represents the most widely and extensively used animal model for chronic lymphocytic leukemia (CLL). In this report, we performed a meta-analysis of leukemia progression in over 300 individual Eµ-TCL1 transgenic mice and discovered a significantly accelerated disease progression in females compared to males. This difference is also reflected in an aggressive CLL mouse model with additional deletion of Tp53 besides the TCL1 transgene. Moreover, after serial adoptive transplantation of murine CLL cells, female recipients also succumbed to CLL earlier than male recipients. This sex-related disparity in the murine models is markedly contradictory to the human CLL condition. Thus, due to our observation we urge both careful consideration in the experimental design and accurate description of the Eµ-TCL1 transgenic cohorts in future studies.

Teleocidin A2 inhibits human proteinase-activated receptor 2 signaling in tumor cells.

Enhanced expression of the proteinase-activated receptor 2 (PAR2) is linked to cell proliferation and migration in many cancer cell types. The role of PAR2 in cancer progression strongly illustrates the need for PAR2-inhibiting compounds. However, to date, potent and selective PAR2 antagonists have not been reported. The natural product teleocidin A2 was characterized against PAR2-activating peptide SLIGKV-NH 2, and trypsin-induced PAR2-dependent intracellular Ca2+ mobilization in tumor and in primary endothelial or epithelial cells. Further biochemical and cell-based studies were conducted to evaluate teleocidin specificity. The antagonizing effect of teleocidin A2 was confirmed in PAR2-dependent cell migration and rearrangement of actin cytoskeleton of human breast adenocarcinoma cell line (MDA-MB 231) breast cancer cells. Teleocidin A2 antagonizes PAR2-dependent intracellular Ca2+ mobilization induced by either SLIGKV-NH 2 or trypsin with IC 50 values from 15 to 25 nmol/L in MDA-MB 231, lung carcinoma cell line, and human umbilical vein endothelial cell. Half maximal inhibition of either PAR1 or P2Y receptor-dependent Ca2+ release is only achieved with 10- to 20-fold higher concentrations of teleocidin A2. In low nanomolar concentrations, teleocidin A2 reverses both SLIGKV-NH 2 and trypsin-mediated PAR2-dependent migration of MDA-MB 231 cells, and has no effect itself on cell migration and no effect on cell viability. Teleocidin A2 further controls PAR2-induced actin cytoskeleton rearrangement of MDA-MB 231 cells. Thus, for the first time, the small molecule natural product teleocidin A2 exhibiting PAR2 antagonism in the low nanomolar range with potent antimigratory activity is described.

Label-Free Protein-RNA Interactome Analysis Identifies Khsrp Signaling Downstream of the p38/Mk2 Kinase Complex as a Critical Modulator of Cell Cycle Progression.

Growing evidence suggests a key role for RNA binding proteins (RBPs) in genome stability programs. Additionally, recent developments in RNA sequencing technologies, as well as mass-spectrometry techniques, have greatly expanded our knowledge on protein-RNA interactions. We here use full transcriptome sequencing and label-free LC/MS/MS to identify global changes in protein-RNA interactions in response to etoposide-induced genotoxic stress. We show that RBPs have distinct binding patterns in response to genotoxic stress and that inactivation of the RBP regulator module, p38/MK2, can affect the entire spectrum of protein-RNA interactions that take place in response to stress. In addition to validating the role of known RBPs like Srsf1, Srsf2, Elavl1 in the genotoxic stress response, we add a new collection of RBPs to the DNA damage response. We identify Khsrp as a highly regulated RBP in response to genotoxic stress and further validate its role as a driver of the G(1/)S transition through the suppression of Cdkn1a(P21) transcripts. Finally, we identify KHSRP as an indicator of overall survival, as well as disease free survival in glioblastoma multiforme.

A functional cancer genomics screen identifies a druggable synthetic lethal interaction between MSH3 and PRKDC.

Here, we use a large-scale cell line-based approach to identify cancer cell-specific mutations that are associated with DNA-dependent protein kinase catalytic subunit (DNA-PKcs) dependence. For this purpose, we profiled the mutational landscape across 1,319 cancer-associated genes of 67 distinct cell lines and identified numerous genes involved in homologous recombination-mediated DNA repair, including BRCA1, BRCA2, ATM, PAXIP, and RAD50, as being associated with non-oncogene addiction to DNA-PKcs. Mutations in the mismatch repair gene MSH3, which have been reported to occur recurrently in numerous human cancer entities, emerged as the most significant predictors of DNA-PKcs addiction. Concordantly, DNA-PKcs inhibition robustly induced apoptosis in MSH3-mutant cell lines in vitro and displayed remarkable single-agent efficacy against MSH3-mutant tumors in vivo. Thus, we here identify a therapeutically actionable synthetic lethal interaction between MSH3 and the non-homologous end joining kinase DNA-PKcs. Our observations recommend DNA-PKcs inhibition as a therapeutic concept for the treatment of human cancers displaying homologous recombination defects.