Activation of lysosomal enzymes and tumour regression caused by irradiation and steroid hormones.

The lysosomal enzyme activity and membrane permeability of mouse C3H mammary tumours has been studied using quantitative cytochemical methods following irradiation of the tumours with doses of 1500, 3500 or 6000 rad gamma rays. No change in the lysosomal enzyme activity was observed immediately after irradiation, but increased enzyme activity and increased membrane permeability were observed 24 hr after irradiation with doses of 3500 or 6000 rad. Twenty-four hours after injection of prednisolone there was a marked increase of lysosomal membrane permeability and enzyme activity, and injection of prednisolone soon after irradiation enhanced the effect of irradiation. After a dose of 6000 rad and prednisolone, the lysosomal membrane permeability increased to 191% of the control and the enzyme activity to 326% of the value of the controlled tumours. Measurement of tumour size after irradiation or after a combined treatment with irradiation and prednisolone showed that a close correlation exists between tumours regression and lysosomal enzyme activity. The experiments support the view that lysosomal enzymes play an important role in tumour regression following irradiation.