Design and synthesis of new polycyclic compounds with potential anticancer activity

Abstract

p53 is best known as a tumor suppressor that transcriptionally regulates, in response to cellular stresses such as DNA damage or oncogene activation, the expression of various target genes that mediate cell-cycle arrest, DNA repair, senescence or apoptosis—all of these cellular responses are designed to prevent damaged cells from proliferating and passing mutations on to the next generation. In 50% of human cancers, p53 is defective due usually to somatic mutations or deletions primarily in its DNA-binding domain and, to a lesser extent, to posttranslational modifications such as phosphorylation, acetylation and methylation that affect p53 function and stability. Altered p53 fails to regulate growth arrest and cell death upon DNA damage, directly contributing to tumor development, malignant progression, poor prognosis and resistance to treatment. Conversely, restoring endogenous p53 activity can halt the growth of cancerous tumors in vivo by inducing apoptosis, senescence, and innate inflammatory responses. cycle arrest, apoptosis, or senescence. While p53 plays a protective role in normal somatic tissues by limiting the propagation of damaged cells, its powerful growth suppressive and proapoptotic activity could be turned into a powerful weapon against cancer cells that have retained the functionality of the p53 pathway. Searching for small-molecules that activate the transcriptional activity of p53 would be expected to lead to the discovery of both DNA-damaging agents and compounds that are specific for the p53 pathway, including agents that interact directly with p53 or that inhibit MDM2 a negative regulator of p53 activity and stability. MDM2 is overexpressed in many human tumors and effectively impairs the function of the p53 pathway. Therefore, restoration of p53 function by antagonizing MDM2 has been proposed as a novel approach for treating cancer, and studies using macromolecular tools have shown its validity in vitro. II According to these findings, and as part of a wide medicinal chemistry program aimed at identifying small-molecules endowed with antitumor activity, different series of natural compound-inspired derivatives were designed as potential p53 modulators. Specifically, my PhD thesis work has been centered on two projects: the first was based on the design and synthesis of carbazole derivatives as DNA- damaging agents; while the second was based on the valuation of natural product analogues designed as both cellular cycle modulators and p53-MDM2 interaction inhibitors. The final aim of this study was to identify of suitable leads which allow us to deep on the molecular complexity of p53 network, improving the antitumor therapeutic arsenal The role of natural products as a source for remedies has been recognized since ancient times. Despite major scientific and technological progress in combinatorial chemistry, drugs derived from natural product still make an enormous contribution to drug discovery today. The development of novel agents from natural sources presents obstacles that are not usually met when one deals with synthetic compounds. For instance, there may be difficulties in accessing the source of the samples, obtaining appropriate amounts of the sample, identification and isolation of the active compound in the sample, and problems in synthesizing the necessary amounts of the compound of interest. An analysis of the number of chemotherapeutic agents and their sources indicates that over 60% of approved drugs are derived from natural compounds. During my PhD thesis work three different structural motives present in natural products have been considered to be suitable scaffold in the design of new antitumoral agents: carbazoles, acridines and spirooxindole derivatives. Carbazoles either in a pure substituted or in an annellated substituted form, represent an important and heterogeneous class of anticancer agents, which has grown considerably over the last two decades. Recently, Wong et al. have described a particular activity of a series of acridine derivatives characterized III by a polycyclic planar system and by a side chain ending with a tertiary amine, act stabilized p53 protein by blocking its ubiquitination, without phosphorylation of ser15 or ser20 on p53. Furthermore, these derivatives induced p53-dependent cell death, activating p53 transcriptional activity Based on the structural cytotoxic requirements for these class of products my first PhD project was centered on synthesis of two series of compounds in which a carbazole eskeleton were linked by an alkyl chain to an amine (series 1) or substituted amide (series 2) groups. In the other hand, small molecule natural products containing spirooxindole derivatives have demonstrated to be invaluable tools in the discovery and characterization of critical events for the progression and the regulation of the cell cycle. Based on the spirotryprostatin-A structure, during my PhD project II I designed, synthesized, and evaluated different series of compounds belonging to the diketopiperazine structural class as potential cell cycle modulators and cytotoxic agents. Starting from the spirooxindolthiazolidine scaffold, amide coupling with Pro derivatives and intramolecular cyclization reactions are suitable synthetic methods to generate chemically diverse diketopiperazine system, such as hexahydropyrrolo[1,2-a][1,3]thiazolo[3,2-d]pyrazine-5,10-dione (structure I), hexahydropyrrolo[1,2-a] [1,3]thiazolo[3,4-d]pyrazine-5,10-dione (structure II) and, spiroindol-2-one[3,30]hexahydro-5,10H-pyrrolo[1,2-a][1,3]thiazolo[3,4-d]pyrazine-5,10-dione (structure III). Some of these compounds, especially those who belong to the series I and II, showed interesting cytotoxic activity. In the last part of my project, I have designed and synthesized two libraries of compounds based on the spirooxindol-thyazolidine moiety, analogues of spirooxoindol-pyrrolidine template as p53-MDM2 inhibitors. Compounds (3R,7aR)-6-(4-chlorobenzyl)-1H-spiro[imidazo[1,5-c]thiazole-3,3‘-indoline]-2‘,5,7(6H,7aH)-trione (42c) and (3R,7aR)-50-methyl-6-(3,4,5-trimethoxybenzyl)-1H-spiro[imidazo-[1,5-c]thiazole-3,3‘-indoline]- IV 2‘,5,7(6H,7aH)-trione (43d) are the most potent compounds of this series, inhibiting cell growth of different human tumor cells at submicromolar and micromolar concentrations, respectively. Compound 42c induces apoptotic cell death in human melanoma cell line M14 at 24 h, while in the same condition, treatment with 43d shows a clear arrest at G2/M phase inducing delay of cell cycle progression. Possibly, these activities may be due to inhibition of p53-MDM2 interaction and subsequent p53 release and activation. [edited by author]