The influence of p53 status on the cytotoxicity of fluorinated pyrimidine L-nucleosides.

Fluorinated nucleoside analogues are a major class of cancer chemotherapy agents, and include the drugs 5-fluorouracil (5FU) and 5-fluoro-2'-deoxyuridine (FdUrd). The aim of this study was to examine the cellular toxicity of two novel fluorinated pyrimidine L-nucleosides that are enantiomers of D-nucleosides and may be able to increase selectivity for cancer cells as a result of their unnatural L-configuration. Two fluorinated pyrimidine L-nucleosides were examined in this study, L110 ([ß-L, ß-D]-5-fluoro-2'-deoxyuridine) and L117 (ß-L-deoxyuridine:ß-D-5'-fluoro-2'-deoxyuridine). The cytotoxicity of these L-nucleoside was determined in primary mouse fibroblasts and was compared with 5FU and FdUrd. In addition, the influence of p53 status on cytotoxicity was investigated. These cytotoxicity assays were performed on a matched set of primary mouse fibroblasts that were either wild type or null for the p53 tumour suppressor gene. It was found that cells lacking functional p53 were over 7500 times more sensitive to the drugs L110, L117 and FdUrd than cells containing wild type p53.

Plasmodium falciparum: the potential of the cancer chemotherapeutic agent cisplatin and its analogues as anti-malarials.

The anti-malarial activity of the cancer chemotherapeutic agent cisplatin and cisplatin analogues was determined in Plasmodium falciparum. The cisplatin analogues included DNA-targeted acridine-tethered platinum compounds, carboplatin and transplatin. A [(3)H]-hypoxanthine incorporation assay was utilised to determine the IC(50) of cisplatin and related analogues. The DNA-targeted Pt compounds and cisplatin were shown to have IC(50) values that were less than 1 µM in P. falciparum, with the acridine-tethered compounds having the greatest cytotoxicity. Carboplatin and transplatin had IC(50) values of 12 and 16 µM, respectively. The outcome for transplatin was particularly interesting since it is not cytotoxic in mammalian cells. These results were discussed with respect to the potential use of cisplatin and cisplatin analogues as anti-malarial agents.

Plasmodium falciparum: DNA sequence specificity of cisplatin and cisplatin analogues.

In this paper, we provided evidence that cisplatin is able to form adducts with cellular DNA in Plasmodium falciparum. The DNA sequence specificity of cisplatin adduct formation was determined in trophozoite-enriched P. falciparum cells and this paper represents the first occasion that the sequence specificity of cisplatin DNA damage has been observed in malaria cells. Utilising a sub-telomeric, 692 bp repeat sequence in the P. falciparum genome, we were able to investigate the DNA adducts formed by cisplatin and five analogues. A run of eight consecutive guanines was the most prominent site of DNA damage in the malarial cells. This study suggests that the mechanism of P. falciparum cell death caused by cisplatin involves damage to DNA and hence inhibition of DNA replication and cell division.

New malaria chemotherapy developed by utilization of a unique parasite transport system.

During its development in the host red cell, the human malarial parasite causes profound alteration in the permeability of the host cell membrane. These membrane transport systems(s) play a role in the development of the intra-erythrocytic parasite in its need to take up solutes and nutrients from the extracellular medium and the disposal of metabolic wastes. Importantly, the properties of these parasite induced transport systems are significantly different from those in normal human cells. Hence, such systems are of considerable interest for their potential use in anti-malarial chemotherapy, both by (i). inhibiting the transport and hence depriving the parasite of nutrients essential for its development, or (ii). by designing cytotoxic drugs which selectively enter the parasite through these induced transporter routes and hence cannot enter normal mammalian cells. Since our discovery that optical isomers of nucleosides (such as L- adenosine or L- thymidine) were selectively transported into malaria infected cells through the induced transporter, L-nucleoside drug "carriers" were actively synthesized as potentially new therapeutic agents. The compounds are dinucleoside phosphate dimers, where each "carrier" (a L-nucleoside) has been conjugated to known anti-malarial agents, such as 5'-fluro-uridine through the 3' and 5'-OH and a phosphate group. A very large series of these drugs have been synthesized with varying conjugations. The dimers are extremely toxic against malaria and experimental evidence has confirmed that they are incapable of entering normal mammalian cells. This review discusses their mechanism of action and potential as new anti-malarial chemotherapy as well as the role played by the membrane transport system of malaria infected cells as a target for malaria chemotherapy.