Synthesis and Biological Evaluation of Anticancer Agents

Within the last ten years intense research has led to a greater understanding of the signalling pathways that control normal cell division and cancerous cell proliferation. Enzymes known as protein tyrosine kinases (PTKs) play a key role in such growth-related processes by catalysing the phosphorylation of tyrosine residues on intracellular protein substrates. This knowledge has led to the search for selective PTK inhibitors in the hope of generating chemotherapeutic agents of potential use in the treatment of cancer. Particular attention has focused on the signalling events that occur at a receptor tyrosine kinase (RTK) called the epidermal growth factor (EGF) receptor since a number of studies have implicated its involvement in many types of human cancer. Compounds found to possess anticancer activity by acdng as PTK inhibitors with a structural resemblance to tyrosine are known as the tyrphostins. In this project, an extensive array of 3-arylpropenonitriles (approximately 140 compounds) akin to the tyrphostins have been synthesised and biologically evaluated in cell assays designed to correlate PTK inhibition at the EGF receptor to antiproliferative activity. Efforts were directed at producing more stable tyrphostin analogues as well as those that incorporate a heterocyclic moiety. From initial studies, tyrphostins incorporadng a nitrothiophene portion were shown to be highly potent antiproliferative agents and gave sub-nanomolar IC50 values against the breast adenocarcinoma MCF-7 cell line. Consequently, structurally isomeric tyrphostin sets were synthesised. More detailed biological analysis demonstrated that some of these compounds were acting in a non-selective cytotoxic fashion. Presently, the compound ethyl 2-cyano-3-[5-(2-nitrothienyl)]propenoate (A) has been accepted by the National Cancer Institute to undergo an in vivo evaluation and represents an interesting new cytotoxic anticancer agent. During a search for heterocyclic tyrphostins some quinoline derivatives were found to display encouraging antiproliferative activities against the MCF-7 cell line (IC50 values < 1 muM). The most potent compounds contained the 2-aminoethene-1,1-dicarbonitrile unit and, although they produced an additional cytotoxic action, they were found to inhibit selectively the phosphorylation of an unknown signalling protein that was found to be linked to EGF receptor activation. The 2-substituted quinoline (B) also displayed a certain degree of selectivity within a panel of 60 tumour cell lines (held at the US National Cancer Institute) and may act as an interesting lead for future studies. In order to determine the stereochemical requirement preferred for biological activity, attempts were made to synthesise geometric isomers of some tyrphostins. In particular, the cis- and trans- forms of the known tyrphostin (C) were synthesised and characterised by detailed NMR spectroscopy and X-ray crystallography. Interestingly, the isomer (C) was about 3.5 times more potent than its geometric panner in an antiproliferative assay against a cell line (HN5) that overexpresses the EGF receptor. Also, synthesised were other 2,3-diaryIpropenonitriles akin to compound (C) and some of these displayed equally effective IC50 values against the MCF-7 cell line