Design, Synthesis and Biological Evaluation of Some Topoisomerase Type 1 Poisons, Cox-2 Selective Agents, and Protein Kinase Inhibitors

Mohamed S. A Elsayed, Purdue University

Abstract

Topoisomerase type 1 inhibitors represent very important chemotherapeutic agents for various oncological indications. The indenoisoquinoline class of Top1 inhibitors has been extensively developed in our lab to enhance its potency and safety profile. The 7-azaindenoisoquinolines are cytotoxic topoisomerase I (Top1) inhibitors. Previously reported representatives bear a 3-nitro group. The first chapter of this thesis documents the replacement of the genotoxic 3-nitro group by 3-chloro and 3-fluoro substituents, resulting in compounds with high Top1 inhibitory activities and potent cytotoxicities in human cancer cell cultures, and reduced lethality in an animal model. Some of the new Top1 inhibitors also possess moderate inhibitory activities against tyrosyl-DNA phosphodiesterase 1 (TDP1) and tyrosyl-DNA phosphodiesterase 2 (TDP2), two enzymes that are involved in DNA damage repair resulting from Top1 inhibitors, and they produce significantly more DNA damage in cancer cells than in normal cells. Possible binding modes to Top1 and TDP1were investigated by molecular modeling. DNA repair is a complex process that involves many enzymes. Several kinases play key roles in this process. For the purpose of enhancing the activity of Top1 inhibitors as DNA damaging agents, we aimed to design some compounds with dual activity against Top1 and a key class of enzymes involved in the DNA repair process called Checkpoint kinases. Unfortunately, the designed compounds didn’t show activity against the targets of interest but they showed very good activity against another important class of kinases, the Janus kinases. Since the discovery of the pivotal role of the Janus kinase (JAK) family in the immune response, a significant amount of effort has been focused on targeting these kinases for the treatment of autoimmune disorders and cancer. The second chapter of the thesis describes the discovery and development of a new JAK inhibitory chemotype that has produced selective JAK inhibitors. Sequential palladium chemistry was optimized for the rapid access to a focused library of derivatives to explore the structure-activity relationships of the new scaffold. Several compounds from the series displayed potencies in the low nanomolar range against the four members of the JAK family with various selectivity profiles. The efficacious inhibitory activities of many of the compounds were confirmed on the production of inflammatory cytokines and proliferation of primary T cells. Molecular modelling was used to explain and illustrate the differential activities and binding of these compounds. In chapter three, a novel indolophenanthridine ring system has been synthesized via the Schiff base-homophthalic anhydride cyclization followed by thionyl chloride-mediated dehydrogenation and intramolecular Friedel-Crafts acylation. This adds to the array of heterocyclic systems that are available through the cycloaddition reaction of imines with cyclic dicarboxylic acid anhydrides. The cytotoxicities of the indolophenanthridines were investigated in human cancer cell cultures, and the results documented significant antitumor activity in a variety of human cancer cell lines. This provides a new heterocyclic scaffold for anticancer drug design. In the last chapter of this dissertation, the discovery of selective cyclooxygenase 2 inhibitors is described. A similarity search and molecular modeling study suggested the 2'-aryl-2-aryl benzothiazole framework as a novel scaffold for the design of COX-2-selective inhibitors. Conventional Suzuki coupling conditions did not furnish the designed compounds in good yield from 2'-bromo-2-aryl benzothiazole as the starting material. A novel ligand-free Suzki-Miyaura coupling methodology was developed for sterically hindered 2'-bromo-2-aryl benzothiazoles. The reaction depends on the coordination properties of the benzothiazole ring nitrogen, which is involved in the formation of a palladacyclic intermediate that was synthesized independently and converted to the final product. The new method provides good to excellent yields (up to 99%) with favorable functional group tolerability. Six compounds had potencies in the submicromolar range against COX-2 and higher selectivity for COX-2 vs. COX-1 compared to the currently used drug celecoxib. Molecular modeling was used to investigate the possible binding mode with COX-2.

Degree

Ph.D.

Advisors

Cushman, Purdue University.

Subject Area

Chemistry|Pharmaceutical sciences|Organic chemistry|Pharmacology

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