An investigation of the possible anticancer activity of seven novel bi(amido) gold(I) complexes derived from a purine or azole base

Abstract

Gold(I)phosphines, nucleoside analogues, and azole derivatives have been identified as promising anticancer compounds. The clinical use of these individual compounds is, however, limited due to non-selectivity associated with adverse effects and developed resistance. This study investigated seven novel gold compounds that contain either a nucleoside analogue or an azole, bound via a gold nitrogen bond, which have been designed and synthesized by Dr. Horvath under the supervision of Prof. Raubenheimer from the University of Stellenbosch. The novel compounds are divided into purinecontaining/ nucleoside analogue compounds (UH 86.2, UH 75.1, UH 58.1, UH 145.1) and azole-containing compounds (UH 107.1, UH 126.1, UH 127.1). The anticancer effects of these novel compounds were compared with that of previously described anticancer compounds [Au(dppe)2]Cl and cisplatin. The octanol/water partition coefficients (PC) of the compounds were measured in order to determine whether a correlation between the lipophilicity of the structures and the cytotoxic potency and selectivity exists. This might provide further insight for structural alterations of the compounds in order to improve their anticancer activity. The results from octanol/water PC determinations, revealed that the purine-containing compounds (UH 86.2, UH 75.1, UH 58.1, and UH 145.1), as well as the azole-containing compound, UH 127.1, exhibited hydrophilic properties, while the azole-containing compounds, UH 107.1 and UH 126.1 are lipophilic. In contrast to results by Berners-Price et al. (1999), that reported a direct proportionality between lipophilicity and cytotoxicity, for the current study, involving HeLa cells, CoLo cells, normal resting and PHA stimulated lymphocytes, no correlation was observed. For the Jurkat cell line, however, an increase in lipophilicity for the series of compounds studied was accompanied by an increase in cytotoxicity. The reason for the exception is not yet fully understood. The in vitro tumour specificity of each compound was established with cytotoxicity assays on various cancer cell lines and normal cell cultures. The cancer cell lines included human cervical cancer (HeLa) cells, human colon cancer (CoLo) cells, and human lymphocytic leukaemia (Jurkat) cells. The normal cell cultures included human resting lymphocytes and human phytohemaglutin (PHA) stimulated lymphocytes. From this data, the four most promising novel compounds were identified. Additional tests were performed by adding these four compounds to cancer cells including human breast cancer (MCF-7) cells, and cisplatin sensitive and resistant human ovarian cancer (A2780 and A2780cis) cells as well as normal chicken embryo fibroblasts. The tumour specificity of each compound was determined from the results obtained via the cytotoxicity assays. The compound is more selective the higher the tumour specificity. Cisplatin exhibited the highest tumour specificity, and [Au(dppe)2]Cl, the lowest. The two most promising novelcompounds were identified as UH 126.1 and UH 127.1, which was evidenced by their high tumour specificities. Further experiments were conducted with these two azolecontaining compounds by using Jurkat cells. The possible mechanism by which the novel compounds induce cytotoxicity was investigated with flow cytometric analysis. The effects of the compounds on the cell death pathway, the mitochondrial membrane potential and the cell cycle were determined. These results indicated that the novel compounds, UH 126.1 and UH 127.1 initiate the apoptotic cell death pathway rather than the necrotic cell death pathway. According to results, UH 126.1 and UH 127.1 influenced the status of the mitochondrial membrane potential (MMP) non-selectively and only at high concentrations. Although involvement of mitochondria in the mechanism of action cannot be excluded, results indicated that it is most likely not the primary target. After investigating the effects of the two novel azole-containing compounds on the cell cycle in Jurkat cells, it was detected that these compounds induce cell accumulation in the G1 phase of the cell cycle. It was concluded that UH 126.1 and UH 127.1 might interfere with the cell cycle indirectly, possibly by inhibition of cyclin-dependent kinases and/or other enzymes necessary for DNA replication. In an acute in vivo toxicity test during this study, results revealed drug induced adverse effects (such as significant weight loss, piloerection and diarrhoea), in the mice that received 3 and 6ìmol/kg of both UH 126.1 and UH 127.1. Evidence also revealed signs of nephrotoxicity and epatotoxicity. Due to minimal adverse effects observed in the groups that received UH 126.1 and UH 127.1 at the concentration of 1,5ìmol/kg, this is the suggested maximum tolerated dose (MTD) for these compounds. Further dose-range studies with UH 126.1 and UH 127.1 are, however, needed in order to evaluate clinicalefficacy. Copyright