The earliest reports on the therapeutic use of metals or metal-containing compounds in cancer and leukemia date from the sixteenth and nineteenth centuries. They were forgotten until the 1960s, when the anti-tumour activity of the inorganic complex cis-diammine-dichloroplatinum(II) (cisplatin) was discovered. This led to the development of other types of non-organic cytostatic drugs. Cisplatin has developed into one of the most frequently used and most effective cytostatic drugs for the treatment of solid carcinomas. Numerous other metal compounds containing platinum, other platinum metals, and even non-platinum metals were then shown to be effective against tumours in man and experimental tumours in animals. These compounds comprise main-group metallic compounds of gallium, germanium, tin, and bismuth, early-transition metal complexes of titanium, vanadium, niobium, molybdenum, and rhenium, and late-transition metal complexes of ruthenium, rhodium, iridium, platinum, copper, and gold. Several platnium complexes and four non-platnium-metal antitumour agents have so far entered early clinical trials. Gallium trinitrate and spirogermanium have already passed phase II clinical studies and have shown limited cytostatic activity against certain human carcinomas and lymphomas. The two early-transition metal complexes budotitane and titanocene dichloride have just reached the end of phase I clinical trials and have been found to have an unusual pattern of organ toxicity in man. Titanocene dichloride will soon enter phase II clinical studies.

Der überraschenden Wirkung des Kations in 1 gegen Ehrlich‐Ascites‐Tumor der Maus muß ein anderes Prinzip zugrunde liegen als der Wirkung der Metallocen‐dihalogenide d‐elektronenarmer Übergangsmetalle, denn die Anionen in 1 sind nicht koordiniert, sondern salzartig gebunden. Ferrocen ist beim gleichen Testsystem inaktiv.

The antitumor activity of a series of iron complexes, i.e., of ferrocene [Cp2Fe], of tetrachloroferrates(III) [R4N]+[FeCl4]-, and of ferricenium complexes [Cp2Fe]+X- (X- = [FeCl4]-, 1/2 [Cl3FeOFeCl3]2-, [H5Mo7O24]- X 2H2O, [2,4,6-(NO2)3C6H2O]-, or [CCl3COO]- X 2 CCl3COOH) was investigated against EAT in CF1 mice. Whereas ferrocene and the ammonium tetrachloroferrates(III) did not show recognizable tumor-inhibiting activity, such activity was exhibited by the water-soluble, salt-like ferricenium complexes; the best antineoplastic properties, with optimum cure rates of 100%, were found for ferricenium picrate and ferricenium trichloroacetate. The ferricenium compounds are the first iron complexes for which antineoplastic activity has now been shown. They represent a new type of antitumor agent insofar as they differ fundamentally from known inorganic and organometallic antitumor agents (a) by their ionic, salt-like character, which is responsible for their high water solubility, and (b) by the absence of a cis-dihalometal moiety; this moiety has been recognized as important for the intracellular action of other known inorganic cytostatics.

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