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Mononuclear ruthenium-dmso compounds showed interesting antimetastatic properties on experimental models of solid tumours. In line with the interesting results with multinuclear platinum complexes, which proved to overcome cisplatin resistance, we thought it worthwhile to test the pharmacological properties of some dinuclear ruthenium complexes to ascertain the possible advantages due to the introduction of a second metal centre over NAMI-A and its mononuclear analogues. These compounds belong to the general formula X2[[RuCl4(dmso-S)]2(mu-L)] or [X][[RuCl4(dmso-S)](mu-L)[RuCl3(dmso-S)(dmso-O)]] where L is a nitrogen donor ligand (pyrazine; pyrimidine; 4,4'-bipyridine; 1,2-bis(4-pyridyl)ethane; 1,2-bis(4-pyridyl) ethylene; 1,3-bis(4-pyridyl)propane) and X a counterion. We focused on parameters related to metastatic ability such as gelatinase activity, detected by zymography, and invasive potential, measured by means of a transwell chamber. These activities were correlated to the ability to inhibit tumour metastases in vivo. All dinuclear complexes, except compound D8 ([NH4]2[[RuCl4(dmso-S)]2(mu-pyz]), decrease the number of tumour cells that cross a matrigel barrier, and inhibit MMP-9 gelatinolytic activity at concentrations lower than that of NAMI-A and of other mononuclear ruthenium complexes. In vivo compounds D5 (Na2[[RuCl4(dmso-S)]2(mu-ethylbipy)]) and D7 ([NH4][[RuCl4(dmso-S)](mu-pyz)[RuCl3(dmso-S) (dmso-O)]]) show anti-metastasis activity, at two dose levels, with mild or null effect on primary tumour growth; compound D8 is the weakest active. All compounds tend to accumulate in liver and kidneys, rather than in tumour and lungs. However, compound D5, the most active in vitro on invasion and gelatinases and active in vivo on metastasis, is better concentrated in the lungs than compound D8 which is less active or inactive in vitro and in vivo. Histological analysis show liver, as well as kidney toxicities that limit in vivo activity. These data thus suggest dinuclear ruthenium complexes as promising anti-invasive agents for cancer treatment.

A series of analogues of NAMI-A, a reference compound active on solid tumor metastases, were synthesized (NAMI-A type complexes). They share the same chemical structure of NAMI-A, and differ from it in the nature of the coordinated nitrogen ligand, such as pyrazole, thiazole and pyrazine, which are less basic than imidazole. This modification confers to the new NAMI-A type complexes a better stability in aqueous solution compared to the parent compound, a very important characteristic for a class of compounds that, with NAMI-A, is currently completing a phase I clinical trial at the Netherlands Cancer Institute of Amsterdam. Cytotoxicity and the effects on cell cycle and invasion were investigated on TS/A, B16-F10 and MCF-7 tumor cell lines, while the inhibition of lung metastases was determined on the mouse experimental tumors Lewis lung carcinoma and MCa mammary carcinoma. The new complexes show a pharmacological activity very similar to that of the parental compound NAMI-A: in vitro they are devoid of meaningful cytotoxicity against tumor cells, and in vivo they inhibit metastasis formation and growth approximately to the same extent as NAMI-A. Thus the new NAMI-A type complexes retain the same potent characteristic of NAMI-A to selectively interact with solid tumor metastases. However, compared to NAMI-A they do not stop cell cycle progression at G2-M level and are more active in preventing the spontaneous invasion of Matrigel by tumor cells exposed for 1 h to 10(-4) M concentration. Globally, these complexes take advantage of the knowledge on NAMI-A and appear particularly interesting for future clinical handling and applications.

Two new adamantyl-peptides, D-(2-adamantyl)-glycyl-L-alanyl-D-isoglutamine hydro-chloride (Isomer-1) and L-(2-adamantyl)-glycyl-L-alanyl-D-isoglutamine hydrochloride (Isomer-2), were tested in the model of the MCa mammary carcinoma of the CBA mouse. These compounds, and particularly Isomer-2 showed to be more effective in reducing lung metastases than primary tumor growth and to be active in conditions in which a low number of metastases are formed, a condition that is seen when the tumor is implanted s.c. or when its growth is slowed down by a lower inoculum size. The apparent lack of any correlation between the effect of Isomer-2 on tumor growth and metastasis formation and that on the response to ConA of in vitro IL-2 selected spleen lymphocytes seems to suggest that the dose and treatment schedule chosen might not be the most appropriate. In fact, the immunopotentiation observed a 2nd drug injection is virtually lost at the end of treatment and this fact might explain the limited effect on tumor growth, and could probably account for the lack of macroscopical effects on lung metastases and on survival time.