Modulation of immune effector cell cytolytic activity and tumour growth inhibition in vivo by Ukrain (NSC 631570)

Ukrain is a semisynthetic compound consisting of alkaloids from Chelidonium majus L. conjugated to thiophosphoric acid, with immunomodulatory and therapeutic properties in cancer patients. The present in vitro studies demonstrate that Ukrain is an effective biological response modifier augmenting, by up to 48-fold, the lytic activity of splenic lymphocytes obtained from alloimmunized mice. The lytic activities of interleukin-2 (IL-2) treated spleen cells and peritoneal exudate lymphocytes were also significantly increased by the addition of Ukrain to the cell mediated lysis (CML) assay medium. The highest Ukrain-induced enhancement of splenic lymphocytolytic activity in vitro was found to occur at day 18 after alloimmunization was dose-dependent and specific for the immunizing P815 tumour cells. Since Ukrain was present only during the CML assays, its mode of action is thought to be via direct activation of the effector cells' lytic mechanism(s). The effect of Ukrain on the growth of Balb/c syngenic mammary adenocarcinoma was also evaluated. Intravenous, but not subcutaneous or intraperitoneal, administration of this drug was found to be effective in delaying tumour growth 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 retardation of tumour development was investigated, using peritoneal exudate 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 homologous tumour cells (DA-3). Pretreatment of PEM from normal mice with 2.5 microM Ukrain for 24 h, followed by stimulation with either IFN-gamma or with lipopolysaccharide (LPS) plus IFN-gamma enhanced their cytotoxic activity. Treatment of PEM from tumour-bearing mice with 2.5 microM Ukrain and LPS results in a reversal of their defective cytotoxic response against DA-3 target cells. Furthermore, Ukrain alone, in the absence of a secondary signal, induced the activation of tumouricidal function of PEM from tumour-bearing, but not from normal, mice. These data indicate that Ukrain's in vivo effects against the development of mammary tumours may be due, at least in part, to its ability to restore macrophage cytolytic function.