Optimizing Arsenic Therapy by Selectively Targeting Leukemia Cells.

Arsenic, in the simple form of arsenic trioxide, is currently marketed for the treatment of acute promyelocytic leukemia. Due to the multifaceted mechanisms of action of arsenic, it has also shown promise in other types of leukemias but is hindered by its toxic effects toward normal cells. This research has aimed to determine whether tumor-homing peptide complexes of arsenic can be designed and developed to strategically target specific cancers. The end goal is to achieve dose reduction and decreased side effects of the resultant arsenic therapeutic agent. In this article, we present the synthesis, characterization, and stability studies of a new class of As-peptide complexes designed to target leukemia. In vitro biological studies of the most stable complex show 1000 times greater toxicity toward leukemia cells over human blood cells, indicating potential for progression to in vivo studies.

Does cytotoxicity of metallointercalators correlate with cellular uptake or DNA affinity?

The cytotoxicity of the metallointercalators, [Pt(5,6-dimethyl-1,10-phenanthroline)(trans-1R,2R-diaminocyclohexane)](2+) ([56MERR]) and [Pt(5,6-dimethyl-1,10-phenanthroline)(trans-1S,2S-diaminocyclohexane)](2+) ([56MESS]), towards A549 human lung cancer cells was examined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The IC(50) value obtained following exposure of A549 cells to [56MESS] for 4 h was approximately three times smaller than that obtained when [56MERR] was administered under the same conditions, indicating that the former complex displayed greater cytotoxicity. Both IC(50) values were greater than that obtained after exposure of A549 cells to cisplatin, demonstrating that the latter compound was the most cytotoxic of the three examined. Microprobe synchrotron radiation X-ray fluorescence (SR-XRF) analyses of metallointercalator-treated A549 cells showed that platinum became localised in DNA-rich regions of the nucleus. In contrast, when the same cells were treated with cisplatin the metal became distributed throughout the cell. Determination of the maximum concentration of platinum present inside the cells using graphite furnace atomic absorption spectrophotometry (GFAAS) of platinum-treated cells suggested that there was greater uptake of [56MERR] compared to [56MESS] by the A549 cells, and that platinum uptake did not account for the greater toxicity of [56MESS], as assessed by the MTT assay. Electrospray ionization mass spectrometric (ESI-MS) and circular dichroism (CD) spectroscopic studies of solutions containing either [56MERR] or [56MESS], and a duplex hexadecamer molecule, showed the two metallointercalators displayed very similar affinity towards the nucleic acid. Overall these results indicate that the difference in cytotoxicity of the two platinum metallointercalators is probably the result of variations in their interactions with other cellular components.