DNA damage and breast cancer

Cancer is intimately related to the accumulation of DNA damage,and repair failures(including mutation prone repair and hyperactive repair systems).This article relates current clinical categories for breast cancer and their common DNA damage repair defects.Information is included on the potential for accumulation of DNA damage in the breast tissue of a woman during her lifetime and the role of DNA damage in breast cancer development.We then cover endogenous and exogenous sources of DNA damage,types of DNA damage repair and basic signal transduction pathways for three gene products involved in the DNA damage response system;namely BRCA1,BRIT1 and PARP-1.These genes are often considered tumor suppressors because of their roles in DNA damage response and some are under clinical investigation as likely sources for effective new drugs to treat breast cancers.Finally we discuss some of the problems of DNA damage repair systems in cancer and the conundrum of hyper-active repair systems which can introduce mutations and confer a survival advantage to certain types of cancer cells.

New insights into tumor dormancy:Targeting DNA repair pathways

Over the past few decades, major strides have advanced the techniques for early detection and treatment of cancer. However, metastatic tumor growth still accounts for the majority of cancer-related deaths worldwide. In fact, breast cancers are notorious for relapsing years or decades after the initial clinical treatment, and this relapse can vary according to the type of breast cancer. In estrogen receptor-positive breast cancers, late tumor relapses frequently occur whereas relapses in estrogen receptor-negative cancers or triple negative tumors arise early resulting in a higher mortality risk. One of the main causes of metastasis is tumor dormancy in which cancer cells remain concealed, asymptomatic, and untraceable over a prolonged period of time. Under certain conditions, dormant cells can re-enter into the cell cycle and resume proliferation leading to recurrence. However, the molecular and cellular regulators underlying this transition remain poorly understood. To date, three mechanisms have been identified to trigger tumor dormancy including cellular, angiogenic, and immunologic dormancies. In addition, recent studies have suggested that DNA repair mechanisms may contribute to the survival of dormant cancer cells. In this article, we summarize the recent experimental and clinical evidence governing cancer dormancy. In addition, we will discuss the role of DNA repair mechanisms in promoting the survival of dormant cells. This information provides mechanistic insight to explain why recurrence occurs, and strategies that may enhance therapeutic approaches to prevent disease recurrence.

Exploiting the homologous recombination DNA repair network for targeted cancer therapy

Genomic instability is a characteristic of cancer cells.In order to maintain genomic integrity,cells have evolved a complex DNA repair system to detect,signal and repair a diversity of DNA lesions.Homologous recombination(HR)-mediated DNA repair represents an error-free repair mechanism to maintain genomic integrity and ensure high-fidelity transmission of genetic information.Deficiencies in HR repair are of tremendous importance in the etiology of human cancers and at the same time offer great opportunities for designing targeted therapeutic strategies.The increase in the number of proteins identified as being involved in HR repair has dramatically shifted our concept of the proteins involved in this process:traditionally viewed as existing in a linear and simple pathway,today they are viewed as existing in a dynamic and interconnected network.Moreover,exploration of the targets within this network that can be modulated by small molecule drugs has led to the discovery of many effective kinase inhibitors,such as ATM,ATR,DNA-PK,CHK1,and CHK2 inhibitors.In preclinical studies,these inhibitors have been shown to sensitize cancer cells to chemotherapy and radiation therapy.The most exciting discovery in the field of HR repair is the identification of the synthetic lethality relationship between poly(ADPribose)polymerase(PARP)inhibitors and HR deficiency.The promises of clinical applications of PARP inhibitors and the concept of synthetic lethality also bring challenges into focus.Future research directions in the area of HR repair include determining how to identify the patients most likely to benefit from PARP inhibitors and developing strategies to overcome resistance to PARP inhibitors.