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The antitumor activity of the organometallic ruthenium(II)-arene complexes, RuCl(2)(eta(6)-arene)(PTA), (arene = p-cymene, toluene, benzene, benzo-15-crown-5, 1-ethylbenzene-2,3-dimethylimidazolium tetrafluoroborate, ethyl benzoate, hexamethylbenzene; PTA = 1,3,5-triaza-7-phosphaadamantane), abbreviated RAPTA, has been evaluated. In vitro biological experiments demonstrate that these compounds are active toward the TS/A mouse adenocarcinoma cancer cell line whereas cytotoxicity on the HBL-100 human mammary (nontumor) cell line was not observed at concentrations up to 0.3 mM, which indicates selectivity of these ruthenium(II)-arene complexes to cancer cells. Analogues of the RAPTA compounds, in which the PTA ligand is methylated, have also been prepared, and these prove to be cytotoxic toward both cell lines. RAPTA-C and the benzene analogue RAPTA-B were selected for in vivo experiments to evaluate their anticancer and antimetastatic activity. The results show that these complexes can reduce the growth of lung metastases in CBA mice bearing the MCa mammary carcinoma in the absence of a corresponding action at the site of primary tumor growth. Pharmacokinetic studies of RAPTA-C indicate that ruthenium is rapidly lost from the organs and the bloodstream.

Ruthenium compounds have gained large interest for their potential application as chemotherapeutic agents, and in particular the complexes of the type (X)[trans-RuCl4(dmso-S)L] (X = HL or Na, NAMI-A or NAMI, respectively, for L = imidazole) are under investigation for their antimetastatic properties. The NAMI(-A)-like compounds are prodrugs that hydrolyze in vivo, and the investigation of their hydrolytic properties is therefore important for determining the nature of the potential active species. The NAMI-A-type Ru(III) complex 1, (Hdmtp)[trans-RuCl4(dmso-S)(dmtp)] (dmtp is 5,7-dimethyl[1,2,4]triazolo[1,5-a]pyrimidine), and the corresponding sodium analogue 2, (Na)[trans-RuCl4(dmso-S)(dmtp)], were synthesized. The hydrolyses of 1 and 2 in water as well as in buffered solutions were studied, and the first hydrolysis product, [mer-RuCl3(H2O)(dmso-S)(dmtp)].H2O (3), was isolated and characterized. The molecular structures of 1 and 3 were determined by single-crystal X-ray diffraction analyses and prove the importance of the hydrogen-bonding properties of dmtp to stabilize hydrolysis products. In vitro 1 (a) is not cytotoxic on tumor cells, following challenges from 1 to 72 h and concentrations up to 100 microM, (b) inhibits matrigel invasion at 0.1 mM and MMP-9 activity with an IC50 of about 1 mM, and (c) is devoid of pronounced effects on cell distribution among cell cycle phases. In vivo compound 1, similar to NAMI-A, significantly inhibits metastasis growth in mice bearing advanced MCa mammary carcinoma tumors. In the lungs, 1 is significantly less concentrated than NAMI-A, whereas no differences between these two compounds were found in other organs such as tumor, liver, and kidney. However, 1 caused edema and necrotic areas on liver parenchyma that are more pronounced than those caused by NAMI-A. Conversely, glomerular and tubular changes on kidney are less extensive than with NAMI-A. In conclusion, 1 confirms the excellent antimetastatic properties of this class of NAMI-A-type compounds and qualifies as an interesting alternative to NAMI-A for treating human cancers.