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.

Responsiveness of human monocytes to Ru 41.740 (Biostim). Influence of preincubation in vitro.

Biostim, which is a glucoprotein extract of Klebsiella pneumoniae, is known to trigger human monocytes to increased secretion of metabolites, which inhibit lymphocyte mitogenesis and which augment NK-activity of lymphocytes. Some aspects of this monocyte activation have been examined in this study. The conclusion of the present investigation is that preincubation of human monocytes for 6-24 h in serum-free medium at 37 degrees C renders them unresponsive to Biostim, as assessed by secretion of the above factors. Monocytes which were preincubated in 100% serum or in serum-free medium at 3 degrees C retained their responsiveness to Biostim. Loss of Biostim responsiveness could not be prevented by interferon alpha, beta, gamma or by granulocyte-monocyte and granulocyte colony stimulating factors. One interpretation of these results is that human monocytes possess distinct receptors for Biostim whose expression is lost under suboptimal culture conditions. Expression of these receptors is a prerequisite for responsiveness to the drug.

Oral treatment with RU 41.740 (Biostim) in patients with advanced colorectal cancer: influence on the blood lymphocyte population.

Twelve patients with advanced colorectal carcinoma received oral treatment with RU 41.740, an immunomodulatory drug obtained from Klebsiella pneumoniae. The patients received three courses of RU 41.740, each consisting of 8 mg daily for 7 consecutive days, with free intervals of 3 weeks. This treatment did not significantly change the distribution of various lymphocyte subsets in the blood or the NK activity of the lymphocytes. However, PHA reactivity of purified lymphocytes increased significantly and exhibited a 2-3-fold enhancement 3 weeks after the last course. Such an increase was not observed in lymphocyte preparations which were not depleted of monocytes. It is concluded that 41.740 may be immunopharmacologically active in man when administered by the oral route.

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

The immunomodulatory agent RU 41740 (Biostim), which is derived from Klebsiella pneumoniae, may augment mitogenic responses of purified human blood lymphocytes. In non-purified preparations, however, responses may be sharply reduced due to the fact that Biostim induces monocytes to secrete immunosuppressive factors. This investigation has shown that both these biological activities can be exerted by a single, major glucoprotein fraction of Biostim termed F1. The Biostim-induced suppression of mitogen responses was not blocked by antibodies directed against IFN alpha or IFN gamma, thus speaking against IFN as being a mediator of suppression. Reduced suppression, however, was observed in the presence of drugs which inhibit arachidonic acid transformation. The cyclo-oxygenase inhibitors meclofenamic acid and indomethacin, which diminish biosynthesis of prostaglandins, could partially block the Biostim-induced suppression. Such an effect was not observed with 5,8,11-eicosatrynoic acid (ETI) which is an inhibitor of 12-lipoxygenase and leukotriene biosynthesis. Combinations of ETI and meclofenamic acid, however, were more potent than the latter tested separately. Another drug termed diclofenac Na, which apart from being an inhibitor of cyclo-oxygenase, rapidly clears cells of free arachidonic acid by binding to triglycerides, was found to be the most potent in preventing Biostim-induced suppression of mitogen responses. It is concluded that Biostim-exposed monocytes liberate increased amounts of immunosuppressive eicosanoids such as prostaglandins.

Augmentation of spontaneous cytotoxicity of human lymphocytes by RU 41.740, a glucoprotein extract of Klebsiella pneumoniae.

RU 41.740 (Biostim) is an extract of Klebsiella pneumoniae with immunomodulating properties. This substance was observed to augment spontaneous cytotoxicity of human blood lymphocytes provided that monocytes were present during Biostim treatment. Maximal augmentation was observed after 2 h of incubation. The F1 fraction, a glucoprotein which comprises approximately 20% of Biostim, and LPS from Klebsiella pneumoniae were also observed to augment spontaneous cytotoxicity of lymphocytes. Biostim treatment of K562 cells, which were used as target cells for killing, did not change their sensitivity to the lytic action of spontaneously cytotoxic cells.

Augmentation of spontaneous cytotoxicity of human lymphocytes by RU 41.740 is due to monocyte-derived factors distinct from interleukin 2, interferon alpha and gamma.

In vitro exposure of human blood lymphoid cells to RU 41.740 (Biostim), a glucoprotein extract of Klebsiella pneumoniae, augments spontaneous cytotoxicity of the lymphocytes. It was observed that the augmentation could be blocked by inhibitors of RNA- and protein-synthesis, but not by an inhibitor of DNA-synthesis. The increased cytotoxicity of Biostim-treated cells could not be explained by an increased proportion of lymphocytes binding to the target cells (K562). This indicates that Biostim acts by increasing the lytic activity of lymphocytes rather than by increasing the expression of target cell recognition structures. Further, it was shown that culture supernatants of Biostim-exposed monocytes, but not purified lymphocytes, contain factors that augment cytotoxicity of purified lymphocytes. This finding is in line with the previously reported monocyte-dependence of Biostim-induced augmentation of lymphocyte cytotoxicity. Interleukin-2 (IL-2) activity was not observed in supernatants of Biostim-exposed lymphoid cells and augmentation of lymphocyte cytotoxicity could not be inhibited by antibodies directed against interferon (IFN) alpha or gamma. This indicates that Biostim stimulates monocytes to liberate factors other than IL-2 or IFN which augment spontaneous cytotoxicity of lymphocytes.