[Pharmacological aspects in the development of liposomal medicinal preparations for the internal injection of hydrophobic cytostatics]. / Farmatsevticheskie aspekty razrabotki liposomal'nykh lekarstvennykh form dlia vnutrivennogo vvedeniia hidrofobnykh tsitostatikov.

To improve the action and selectivity of new drugs on tumor cells and the use of currently available pharmaceutical technologies to develop the systems of controlled transport of well-known antitumor compounds is one of the ways of enhancing the efficiency of drug therapy for tumors. The tropicity of steroid hormones to definite organs and tissues makes it possible to use them as specific messengers of alkylating groups to target tissues and tumors. Hormone cytostatics synthesized by this principle have a double mechanism of hormonal and cytotoxic actions. The original Russian water-insoluble hormone cytostatistics testifenon, kortifen, and cytestrol acetate demonstrated local tissue irritation together with high antitumor activity. No rational dosage forms make it possible to conduct clinical trials by parenteral administration. The aim of this paper is to summarize the authors' results of designing hydrophobic antitumor hormone cytostatics. The advantages and disadvantages of different approaches to designing traditional dosage forms and to applying colloid liposomal systems for intravenous administration of water-insoluble agents are shown.

Metallothionein expression and transient resistance to electrophilic antineoplastic drugs.

Intrinsic and acquired resistance to antineoplastic agents remains an important impediment to cancer therapy. Intracellular metallothioneins appear to be one factor in determining the responsiveness of malignant and normal cells to electrophilic anticancer agents. Metallothioneins are not only constitutively expressed but their expression can be transcriptionally activated by a host of endogenous and exogenous substances; this is a reversible phenomenon. This inducibility affords the possibility that cells can respond quickly to toxic substances and that under certain conditions transient drug resistance may occur. We review the evidence implicating metallothioneins in anticancer drug resistance and discuss this in the context of the possibility of transient resistance.

Protective function of metallothionein against certain anticancer agents.

The possible role of metallothioneins (MT) in the cellular protection against ionizing radiation and alkylating agent cytotoxicity has been investigated by the use of cultured cells with either low or high levels of MT. The cytotoxic activity of the drugs cis-dichlorodiammineplatinum (cis-DDP), chlorambucil and prednimustine was reduced 1,5-3 fold in cells containing high levels of MT, and furthermore about 70% of platinum and 30% chlorambucil was shown to be associated with the protein. Increased resistance was also demonstrated in MT-rich cells during exposure to ionizing radiation. Evidence that MT also may play a role in vivo as a resistance mechanism, was provided in studies of tumors derived from either the MT-rich or MT-poor cells which had been inoculated in nude mice. During treatment of the animals with cis-DDP, the MT-rich tumors exhibited a significant degree of resistance. These results indicate that MT may play an important role in the intrinsic protection of cells against these agents, and raises the question whether it also may be a factor in the acquired resistance of tumors against chemotherapy.

The antitumor effect of prednimustine in vitro and in vivo.

Prednimustine is active against a wide variety of experimental tumors both in vivo and in vitro. In many of these tumor systems, prednimustine exhibits distinct advantages over a mixture of its constituents, chlorambucil and prednisolone. In vitro, a higher cell kill is obtained, and in vivo, at doses that are equally effective, prednimustine is less toxic. These differences could be connected with the different pharmacokinetic profiles found between prednimustine and chlorambucil plus prednisolone.

Hormone cytostatic agents.

Antitumour agents in which various steroids were used as carriers for different cytostatic groups have been synthesized at the Research Laboratories of AB Leo, Helsingborg, Sweden. The chemical and pharmacological properties of two of these agents, estramustine phosphate and prednimustine, are reported. These agents have been shown to have good effects in the treatment of advanced hormone-resistant cancer.