Disruption of microtubule function in cultured human cells by a cytotoxic ruthenium(ii) polypyridyl complex.

Treatment of malignant and non-malignant cultured human cell lines with a cytotoxic IC50 dose of ∼2 µM tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(ii) chloride (RPC2) retards or arrests microtubule motion as tracked by visualizing fluorescently-tagged microtubule plus end-tracking proteins. Immunofluorescent microscopic images of the microtubules in fixed cells show substantial changes to cellular microtubule network and to overall cell morphology upon treatment with RPC2. Flow cytometry with MCF7 and H358 cells reveals only minor elevations of the number of cells in G2/M phase, suggesting that the observed cytotoxicity is not tied to mitotic arrest. In vitro studies with purified tubulin reveal that RPC2 acts to promote tubulin polymerization and when imaged by electron microscopy, these microtubules look normal in appearance. Isothermal titration calorimetry measurements show an associative binding constant of 4.8 × 106 M-1 for RPC2 to preformed microtubules and support a 1 : 1 RPC2 to tubulin dimer stoichiometry. Competition experiments show RPC2 does not compete for the taxane binding site. Consistent with this tight binding, over 80% of the ruthenium in treated cells is co-localized with the cytoskeletal proteins. These data support RPC2 acting as an in vivo microtubule stabilizing agent and sharing many similarities with cells treated with paclitaxel.

Effect of Khat (Catha edulis) Use on the Bioavailability, Plasma Levels and Antimalarial Activity of Chloroquine.

OBJECTIVES: This study aimed to evaluate the effect of khat (Catha edulis) on chloroquine (CQ) bioavailability in healthy Yemeni adults and its effect on CQ plasma levels and parasite clearance among malaria patients. METHODS: This study took place between January and April 2007 in Bajil and Sana'a, Yemen. Two CQ doses (600 mg each) were given to 15 healthy males on separate occasions; the first dose was followed by a khat-chewing session (phase one) while controls abstained from khat-chewing for the second (phase two). Additionally, 103 patients with Plasmodium falciparum-induced malaria, including both regular khat chewers (n = 57) and non-khat chewers (n = 46), were treated with CQ (25 mg/kg) over three days. Pharmacokinetic parameters were analysed among both controls and malaria patients. Parasite clearance was also investigated for the latter group. RESULTS: The mean area under the concentration-time curve (AUC) was 2,108.9 versus 2,797.4 ng/hour/mL, mean peak plasma concentration (Cmax) was 415.6 versus 508.7 ng/mL and mean time to reach Cmax was 3.8 versus 3.6 hours for controls in phase one versus phase two, respectively; both AUC and Cmax levels were significantly reduced by khat-chewing (P <0.050). For khat- versus non-khat-chewing malaria patients, mean plasma CQ concentrations were 266.4 ng/mL versus 427.5 ng/mL (P <0.001). Furthermore, CQ was effective in 71.7% and 75.4% of non-khat and khat-chewing malaria patients, respectively (P = 0.823). CONCLUSION: Khat-chewing was found to significantly reduce plasma CQ levels among healthy volunteers and malaria patients. While receiving CQ treatment, patients should be advised not to chew khat.