Human monocytes exposed to Biostim (RU 41740) alter lymphocyte mitogenesis: mechanisms of action

Route of administration may determine the biological effects of RU 41,740 (Biostim). Trapping of 99mTc-labelled human albumin colloids in mice

Experiments have been conducted in mice to examine whether treatment with the immunostimulating drug RU 41,740 (Biostim) may change the distribution of i.v. injected radiolabelled human albumin colloids. It was observed that a single i.p. injection of Biostim (1 ng-1000 micrograms) significantly enhanced trapping of the particles in spleen and lungs. The effect, which was dose-dependent, was most pronounced in the lungs where more than a 10-fold increase could take place. On the contrary, oral administration of Biostim caused a dose-dependent decrease of colloid trapping in the lungs. Further experiments showed that oral administration of Biostim resulted in the appearance of soluble factors in the blood which inhibited the phagocytic activity of lung macrophages, for example, sera from such mice inhibited lung colloid trapping when injected into new hosts. I.p. administration of Biostim, however, resulted in the appearance of factors in the blood which enhanced phagocytosis of lung macrophages. Our conclusion is that the biological activity of Biostim in vivo may be highly dependent on its route of administration.

Ru 41.740 triggers human mononuclear blood cells to release tumor growth inhibitory factors in vitro

Ru 41.740 (Biostim) is an immunostimulating drug of microbial origin which may stimulate human mononuclear blood cells (mainly monocytes) to release soluble factors which inhibit replication of several tumor cell lines in vitro. Since this effect may be of clinical importance in the treatment of cancer a number of tests have been conducted in order to find methods to augment this secretion. In vitro tests suggested that this non-specific antitumor activity of Biostim may not be enhanced by concomitant treatment of patients with inhibitors of cyclo-oxygenase and lipoxygenases or by interferons alpha, beta, gamma or the hemopoietic growth factors GM-CSF and G-CSF.

Influence of RU 41.740 on human monocytes in vitro: release of soluble factors which retard multiplication of tumor cells in culture

RU 41.740 (Biostim) is an immunostimulating substance of bacterial origin with a reported protective activity against bacterial infections in man. The aim of the present investigation was to determine if Biostim-exposed blood mononuclear cells release soluble factors in vitro which may inhibit growth of tumor cells in culture. It was observed that exposure of mononuclear cells to Biostim at concentrations as low as 1 ng/ml for 24 h resulted in the release of factors capable of retarding growth of K562 cells. Three human glioma cell lines tested also appeared to be sensitive whereas three other cell lines were less sensitive or resistant. The growth inhibitory factors were shown to be produced by monocytes which is in line with previous findings showing that Biostim is a potent activator of monocytes-macrophages. Biostim-exposed monocytes, however, did not express any cytotoxic activity for K562 cells using a short-term 51Cr-release assay. It is concluded that Biostim may trigger monocytes to release factors with anti-tumor activity. These factors have not yet been identified and it remains to be determined if their production increases during Biostim treatment and whether this is correlated to an anti-tumor activity in man.