MODULATION OF IMMUNE EFFECTOR CELL CYTOLYTIC ACTIVITY AND TUMOR-GROWTH INHIBITION IN-VIVO BY UKRAIN (NSC-631570)

Ukrain is a semisynthetic compound consisting of alkaloids from Chelid onium majus L. conjugated to thiophosphoric acid, with immunomodulator y and therapeutic properties in cancer patients. The present in vitro studies demonstrate that Ukrain is an effective biological response mo difier augmenting, by up to 48-fold, the lytic activity of splenic lym phocytes obtained from alloimmunized mice. The lytic activities of int erleukin-2 (IL-2) treated spleen cells and peritonea( exudate lymphocy tes were also significantly increased by the addition of Ukrain to the cell mediated lysis (CML) assay medium. The highest Ukrain-induced en hancement of splenic lymphocytolytic activity in vitro was found to oc cur at day 18 after alloimmunization, was dose-dependent and specific for the immunizing P815 tumour cells. Since Ukrain was present only du ring the CML assays, its mode of action is thought to be via direct ac tivation of the effector cells' lytic mechanism(s). The effect of Ukra in on the growth of Balb/c syngenic mammary adenocarcinoma was also ev aluated. Intravenous, but not subcutaneous or intraperitoneal, adminis tration of this drug was found to be effective in delaying tumour grow th in an actual therapeutic protocol initiated five days after tumour implantation. No deleterious side-effects were observed using these in vivo treatment modalities. The role of macrophages in the observed re tardation of tumour development was investigated using peritoneal exud ate macrophages (PEM) in cytotoxicity assays. Previous studies showed that PEM of mammary tumour-bearing mice lose their capacity to kill a variety of tumour target cells including the in vitro cultured homolog ous tumour cells (DA-3). Pretreatment of PEM from normal mice with 2.5 mu M Ukrain for 24 h, followed by stimulation with either IFN-gamma o r with lipopolysaccharide (LPS) plus IFN-gamma enhanced their cytotoxi c activity. Treatment of PEM from tumour-bearing mice with 2.5 mu M Uk rain and LPS results in a reversal of their defective cytotoxic respon se against DA-3 target cells. Furthermore, Ukrain alone, in the absenc e of a secondary signal, induced the activation of tumouricidal functi on of PEM from tumour-bearing, but not from normal, mice. These data i ndicate that Ukrain's in vivo effects against the development of mamma ry tumours may be due, at least in part, to its ability to restore mac rophage cytolytic function.