To establish structure-activity relationships, derivatives of bis(O-alkyldithiocarbonato)platinum(II) complexes were analyzed. Eighteen bis(O-alkyldithiocarbonato) metal complexes were synthesized, and their cytotoxic activity on two human cancer cell lines was compared with the corresponding platinum bis(O-alkyldithiocarbonato) complexes and cisplatin. Complexes were synthesized with palladium, gold, nickel, copper, rhodium, and bismuth. Palladium and bismuth complexes were found to display significant cytotoxic activity. Palladium complexes were most active with up to 10-fold lower IC50 values as compared with the corresponding platinum complexes. The other complexes were only poorly active. Palladium, bismuth, and nickel complexes were more active at pH 6.8 than at pH 7.4. This difference in activity was most pronounced with palladium complexes. A pH of 6.8 and lower has been frequently found in solid tumors. Drugs with such pH dependent activity are supposed to have an improved therapeutic index as compared to drugs that are active irrespective of pH.

Stimulation of macrophages by lipopolysaccharide (LPS) leads to the synthesis of proinflammatory cytokines and nitric oxide (NO) and, as a consequence, to endotoxic shock. We provide evidence that LPS stimulates the activity of a membrane-associated neutral sphingomyelinase (nSMase) and that this activity is mandatory for the liberation of nuclear factor-kappa B (NF kappa B) and the induction of inducible NO-synthase (iNOS). With the aid of a newly developed, selective inhibitor of nSMase, C11AG, we could distinguish between nSMase-dependent and -independent LPS-induced signals. C11AG blocked LPS-stimulated sphingomyelin degradation and NF kappa B activation without interfering with p42 tyrosine phosphorylation. Concomitantly, the expression of iNOS was found to be reduced both in mononuclear cells and in murine endotoxemia. Therefore, specific inhibitors of nSMase may define a new class of antiinflammatory substances.

Platinum complexes are essential tools for cancer treatment despite their toxic side effects. Here we describe a new platinum complex with sulphurs as complexing atoms (thioplatin). Purpose: To demonstrate that the antitumoral activity of a new sulphur-containing platinum compound (thioplatin) depends on a slightly acidic pH. Methods: Platinum uptake by tumour cells and interaction with DNA was determined at slightly acidic or alkaline pH. To demonstrate low in vivo toxicity the effects of thioplatin on body weight, blood urea nitrogen, white blood cell count and the histopathological appearance of small intestines and kidneys were evaluated at doses that displayed antitumoral effects against human small-cell lung cancer and human colorectal cancer xenotransplants in nude mice. Results: The slightly acidic pH optimum of thioplatin was proven by the altered electrophoretic mobility of plasmid DNA, quantitation of the platinum content in the DNA of tumour cells and cytotoxicity studies. Thioplatin displayed antitumoral activity without severe side effects such as weight loss, renal ischaemia, destruction of villi in the small intestine or leukopenia as observed at comparable doses of cisplatin. Furthermore, probably due to its lipophilic nature, thioplatin was taken up readily even by cisplatin-resistant cells. In vivo studies with human tumour xenografts in nude mice showed a therapeutic index of thioplatin five to ten times higher than that of cisplatin.