Enhancement of antineoplastic effect and attenuation of sister chromatid exchanges by prostaglandin E2 in Ehrlich ascites tumour cells treated with cyclophosphamide in vivo.

Reduced sister chromatid exchanges (SCE) frequency in response to cyclophosphamide (CP) was observed when Ehrlich ascites tumour (EAT) cells were exposed in vivo to 2 micrograms/g body weight of prostaglandin E2 (PGE2). 1 h before i.p. injection of 5-bromodeoxyuridine (BrdUrd) adsorbed to activated charcoal, EAT-bearing mice treated i.p. with CP appeared to have increased SCE rates and cell division delays. PGE2 had no effect on survival and in inhibiting tumour growth. CP had only a slight non-significant effect on survival and in inhibiting tumour growth. In mice treated with the combined CP (5 micrograms/g bd wt) plus PGE2 (2 micrograms/g bd wt) a significant enhancement (P < 0.01) of survival time was accompanied by inhibition of tumour growth (P < 0.01) in comparison with the untreated controls. These data imply that SCEs might result from errors in a repair process which might involve a PGE2 sensitive step.