Identification of resistance mechanisms and targeting of DNA repair proteins for cancer therapy

Abstract

Cancers have the ability to develop resistance to traditional therapies, and the increasing prevalence of these drug-resistant cancers necessitates further research and treatment advancement. Various cellular pathways are involved in the development of drug resistance in cancer cells. DNA replication and repair pathways are crucial to maintaining the cellular integrity by the involvement of several proteins. Human topoisomerase 1 and human DNA ligase I are the essential enzymes involved in DNA replication and repair. Here, we report the interplay of these enzymes during drug resistance. In the present study, we have identified a novel combinational approach to compensate for the topoisomerase 1 DNA relaxation activity. Also characterized the novel human DNA ligase I inhibitor (Compound 27) by using various in-silico, invitro, ex-vivo and 3D culture approaches. The whole study has been divided into six chapters. Chapter 1 contains a detailed description of Topoisomerases, their mechanism of action and different strategies to inhibit the topoisomerases function. This chapter also shares a brief knowledge about the known topoisomerase 1 inhibitors and their resistance mechanism. Chapter 2 covers a brief description of all the major techniques and experimental approaches used in the identification of the topoisomerase 1 drug resistance mechanism. Chapter 3 describes the DNA relaxation activity and overexpression of human DNA ligase I during topoisomerase 1 inhibition. It also describes the effect of human DNA Ligase I inhibitor (Compound 27 {C 27}) on DNA relaxation activity. Chapter 4 contains the identification of novel hLigI inhibitors from our in-house (CSIR-CDRI) small molecule library. This study extensively characterizes the human DNA Ligase I inhibitor by using in-vitro, ex-vivo and 3D methods. Chapter 5 reports the combination effect of topoisomerase 1 inhibitor and human DNA Ligase I inhibitor. It also showed a higher effect of topoisomerase 1 inhibitor on human DNA Ligase I deficient cell line. Defines the compensatory activity of human DNA Ligase I during topoisomerase 1 inhibition. Chapter 6 contains miscellaneous / supplementary data. Parts of the results described in this thesis have already been reported in the following