Cancer cells frequently harbor defects in DNA repair pathways, leading to genomic instability. This can foster tumorigenesis but also provides a weakness in the tumor that can be exploited ...therapeutically. Tumors with compromised ability to repair double-strand DNA breaks by homologous recombination, including those with defects in BRCA1 and BRCA2, are highly sensitive to blockade of the repair of DNA single-strand breaks via the inhibition of the enzyme poly(ADP) ribose polymerase. This provides the basis for a novel synthetic lethal approach to cancer therapy.
In the past few years, it has become clear that mutations in epigenetic regulatory genes are common in human cancers. Therapeutic strategies are now being developed to target cancers with mutations ...in these genes using specific chemical inhibitors. In addition, a complementary approach based on the concept of synthetic lethality, which allows exploitation of loss-of-function mutations in cancers that are not targetable by conventional methods, has gained traction. Both of these approaches are now being tested in several clinical trials. In this Review, we present recent advances in epigenetic drug discovery and development, and suggest possible future avenues of investigation to drive progress in this area.
PARP inhibitors Lord, Christopher J.; Ashworth, Alan
Science,
03/2017, Volume:
355, Issue:
6330
Journal Article
Peer reviewed
Open access
PARP inhibitors (PARPi), a cancer therapy targeting poly(ADP-ribose) polymerase, are the first clinically approved drugs designed to exploit synthetic lethality, a genetic concept proposed nearly a ...century ago. Tumors arising in patients who carry germline mutations in either BRCA1 or BRCA2 are sensitive to PARPi because they have a specific type of DNA repair defect. PARPi also show promising activity in more common cancers that share this repair defect. However, as with other targeted therapies, resistance to PARPi arises in advanced disease. In addition, determining the optimal use of PARPi within drug combination approaches has been challenging. Nevertheless, the preclinical discovery of PARPi synthetic lethality and the route to clinical approval provide interesting lessons for the development of other therapies. Here, we discuss current knowledge of PARP inhibitors and potential ways to maximize their clinical effectiveness.
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BFBNIB, NMLJ, NUK, ODKLJ, PNG, SAZU, UL, UM, UPUK
The genetic concept of synthetic lethality has now been validated clinically through the demonstrated efficacy of poly(ADP-ribose) polymerase (PARP) inhibitors for the treatment of cancers in ...individuals with germline loss-of-function mutations in either BRCA1 or BRCA2. Three different PARP inhibitors have now been approved for the treatment of patients with BRCA-mutant ovarian cancer and one for those with BRCA-mutant breast cancer; these agents have also shown promising results in patients with BRCA-mutant prostate cancer. Here, we describe a number of other synthetic lethal interactions that have been discovered in cancer. We discuss some of the underlying principles that might increase the likelihood of clinical efficacy and how new computational and experimental approaches are now facilitating the discovery and validation of synthetic lethal interactions. Finally, we make suggestions on possible future directions and challenges facing researchers in this field.
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NUK, OILJ, SBMB, UL, UM, UPUK
Cells carrying mutated BRCA1 or BRCA2 genes are defective in DNA repair by homologous recombination and, as a consequence, are highly sensitive to inhibitors of poly (ADP-ribose) polymerase (PARP). ...This provides the basis for a novel "synthetic lethal" approach to cancer therapy. We have recently shown that this sensitivity can be reversed, and resistance to PARP inhibition can be acquired by deletion of a mutation in BRCA2. Furthermore, a similar mechanism seems to be associated with carboplatin resistance in some BRCA2 mutation carriers with ovarian cancer.
The first wave of genetically targeted therapies for cancer focused on drugging gene products that are recurrently mutated in specific cancer types. However, mutational analysis of tumours has ...largely been exhausted as a strategy for the identification of new cancer targets that are druggable with conventional approaches. Furthermore, some known genetic drivers of cancer have not been directly targeted yet owing to their molecular structure (undruggable oncogenes) or because they result in functional loss (tumour suppressor genes). Functional genomic screening based on the genetic concept of synthetic lethality provides an avenue to discover drug targets in all these areas. Although synthetic lethality is not a new idea, recent advances, including CRISPR-based gene editing, have made possible systematic screens for synthetic lethal drug targets in human cancers. Such approaches have broad potential to drive the discovery of the next wave of genetic cancer targets and ultimately the introduction of effective medicines that are still needed for most cancers.
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FZAB, GEOZS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Synthetic lethality provides a potential mechanistic framework for the therapeutic targeting of genetic and functional deficiencies in cancers and is now being explored widely. The first clinical ...exemplification of synthetic lethality in cancer has been the exploitation of inhibitors of poly-(ADP-ribose) polymerase (PARP) for the treatment of cancers with defects in the BRCA1 or BRCA2 tumor suppressor proteins, which are involved in the repair of DNA damage. Although this approach has shown promise, multiple potential resistance mechanisms have been identified. In this Perspective, we discuss these mechanisms and their relevance to the development of selective therapies for BRCA-deficient cancers.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Drugs targeting the cell cycle-regulatory cyclin-dependent kinase (CDK) 4 and 6 have been approved for the treatment of hormone receptor-positive breast cancer, and inhibitors targeting other ...cell-cycle CDKs are currently in clinical trials. Another class of CDKs, the transcription-associated CDKs, including CDK7, CDK8, CDK9, CDK12 and CDK13, are critical regulators of gene expression. Recent evidence suggests several novel functions of these CDKs, including regulation of epigenetic modifications, intronic polyadenylation, DNA-damage responses, and genomic stability. Here, we summarize our current understanding of the transcriptional CDKs, their utility as biomarkers, and their potential as therapeutic targets. SIGNIFICANCE: CDK inhibitors targeting CDK4 and CDK6 have been approved in hormone receptor-positive breast cancer, and inhibitors targeting other cell-cycle CDKs are currently in clinical trials. Several studies now point to potential therapeutic opportunities by inhibiting the transcription-associated CDKs as well as therapeutic vulnerabilities with PARP inhibitors and immunotherapy in tumors deficient in these CDKs.
The genetic concept of synthetic lethality, in which the combination or synthesis of mutations in multiple genes results in cell death, provides a framework to design novel therapeutic approaches to ...cancer. Already there are promising indications, from clinical trials exploiting this concept by using poly(ADP-ribose) polymerase (PARP) inhibitors in patients with germline
BRCA1
or
BRCA2
gene mutations, that this approach could be beneficial. We discuss the biological rationale for BRCA-PARP synthetic lethality, how the synthetic lethal approach is being assessed in the clinic, and how mechanisms of resistance are starting to be dissected. Applying the synthetic lethal concept to target non-
BRCA
-mutant cancers also has clear potential, and we discuss how some of the principles learned in developing PARP inhibitors might also drive the development of additional genetic approaches.
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