The effect of organophosphorus inhibitors, p-nitrophenol and cytochalasin B on cytotoxic killing of tumour cells by immune spleen cells, and the effect of shaking.

Organophosphorus (OP) agents are irreversible inhibitors of OP sensitive esterases. Their effect on the cytotoxic killing of Cr-labelled mastocytoma cells by immune spleen cells was assessed by the release of Cr. OP fluoridates inhibited cytotoxic killing whether used as a pretreatment before the addition of the labelled target cells or as a concurrent treatment. The effect of pretreatment was time, temperature and concentration dependent and was abolished by hydrolysis. It occurred at concentrations which did not inhibit the incorporation of [C] leucine and uridine. It is tentatively suggested that the OP agents inhibited an activated esterase present in the spleen cell before the cytotoxic reaction. In contrast, phosphonates inhibited cytotoxic killing when used concurrently but had little effect as a pretreatment. The chemically more reactive -nitrophenyl phosphonates and the much less reactive phenyl phosphonates inhibited cytotoxic killing to a similar degree. It was concluded that the phosphonates did not inhibit activated esterase. The effect of phosphonates was virtually abolished by hydrolysis. However the effect of the -nitrophenyl phosphonates was increased by hydrolysis. This was due to the -nitrophenol formed. Cytochalasin B, which is known to interfere with cell movements, and -nitrophenol, both of which inhibited spleen cell migration from a capillary tube, inhibited cytotoxic killing when used concurrently. This inhibition was partly reversed by shaking. It is suggested that movements of the cell surface may be essential, in the absence of shaking, to provide the contact needed for cytotoxic killing.