CRISPR Screens in Synthetic Lethality and Combinatorial Therapies for Cancer

Abstract

Cancer is a complex disease resulting from the accumulation of genetic dysfunctions. Tumor heterogeneity causes the molecular variety that divergently controls responses to chemotherapy, leading to the recurrent problem of cancer reappearance. For many decades, efforts have focused on identifying essential tumoral genes and cancer driver mutations. More recently, prompted by the clinical success of the synthetic lethality (SL)-based therapy of the PARP inhibitors in homologous recombinant deficient tumors, scientists have centered their novel research on SL interactions (SLI). The state of the art to find new genetic interactions are currently large-scale forward genetic CRISPR screens. CRISPR technology has rapidly evolved to be a common tool in the vast majority of laboratories, as tools to implement CRISPR screen protocols are available to all researchers. Taking advantage of SLI, combinatorial therapies have become the ultimate model to treat cancer with lower toxicity, and therefore better efficiency. This review explores the CRISPR screen methodology, integrates the up-to-date published findings on CRISPR screens in the cancer field and proposes future directions to uncover cancer regulation and individual responses to chemotherapy.

Exploiting DNA Endonucleases to Advance Mechanisms of DNA Repair

“…In this article, we present a small snapshot of the utility of gene editing tools that can be brought to bear to further our knowledge of two DNA repair pathways, MMR and BER. The far-reaching implications of CRISPRbased gene editing go well beyond basic science research with roles in medicine and therapeutics [423], gene therapy [424], agriculture [425], advances in animal modeling [426], and cancer discovery [427]. CRISPR methods open the door to the personalized treatment of genetic diseases.…”

Synthetic Vulnerabilities in the KRAS Pathway

“…A number of studies have confirmed that CRISPR-based screens have improved reproducibility compared to RNAi screening approaches, likely due to the lower off-target frequency of gRNAs and the higher efficiency of CRISPR reagents from creating knockout mutants rather than RNA-targeted knockdowns [ 112 , 113 , 114 ]. Thus, large-scale CRISPR/Cas9 screens have proven to be a powerful method identifying genetic defects in tumors harboring oncogenic mutations such as KRAS [ 115 , 116 ]. Table 2 summarizes a selection of the most relevant CRISPR/Cas9 screens carried out to date, focusing on a few illustrative examples below.…”

“…During the last several years, the use of biocomputational methods in combination with CRISPR/Cas9 knockout screens has become a highly powerful technique to elucidate essential cancer genes and define important therapeutic targets [ 116 , 140 , 141 , 142 ]. Although many studies have enumerated interesting KRAS synthetic lethal targets, these findings are not applicable to all KRAS -mutant cancer contexts because of the heterogeneity associated to this oncogenic mutation.…”

Functional Roles of Bromodomain Proteins in Cancer

“…Cancer heterogeneity presents major challenges for the development of personalized treatments [ 1 , 2 , 3 , 4 ]. Current precision therapies used in the treatment of cancer are designed to exploit a variety of different biological entities characteristic to individual cancer types, such as activated protein kinases, estrogen receptor, and defective DNA repair enzymes [ 4 , 5 , 6 ]. Understanding the mechanistic details of cancer biology is critical for improving diagnostic tools and for developing new therapeutic interventions.…”