Inhibition of Friend erythroleukaemia-cell tumours in vivo by a synthetic analogue of prostaglandin E2.

The effect of 16,16-dimethyl-PGE2-methyl ester (di-M-PGE2), a long-acting synthetic analogue of prostaglandin E2, on the replication of Friend erythroleukaemia cells (FLC) in vivo has been studied. Pre-treatment in vitro of both undifferentiated and differentiated FLC with di-M-PGE2 (1 microgram/ml) did not alter rates of tumour appearance or growth, but increased the median survival of DBA/2J mice. Systemic administration of di-M-PGE2 (10 microgram/mouse/day) was not toxic to the mice, but significantly inhibited tumour growth and increased median survival in mice injected s.c. with undifferentiated FLC. These effects of di-M-PGE2 were much more pronounced in mice receiving differentiated (DMSO-treated) FLC. In this latter group, the appearance of tumour was also significantly delayed by di-M-PGE2. The different effects of di-M-PGE2 treatment on tumours derived from undifferentiated and differentiated cells suggest that the analogue is acting directly on tumour-cell replication rather than on factors related to the host response.