Effects of 3′-(4-morpholinyl)-3′-deaminodaunorubicin, 3′-(4-methoxy-1-piperidinyl)-3′-deaminodaunorubicin and daunorubicin on nuclear and polysomal RNA synthesis in human colon carcinoma cells in vitro

Abstract

The sugar amine modified anthracyclines, 3′-(4-morpholinyl)-3′-deaminodaunorubicin (MD) and 3′-(4-methoxy-1-piperidinyl)-3′-deaminodaunorubicin (MEO), are 10-fold more potent than daunorubicin (DAU) as inhibitors of RNA synthesis in human colon carcinoma (HT-29) cells in vitro, although they are 10-fold less cytocidal. In this study, HT-29 cells were exposed for 2 h to 5 × 10 −8 M MD or MEO, or 5 × 10 −7 M DAU; under these conditions total RNA synthesis is decreased by each drug by 50%, whereas cell viability is reduced more than 99% by DAU, but less than 10% by MD and MEO. Following the 2-h exposure, the cellular content of DAU was 2–4-fold greater than that of MEO and MD, respectively. All three drugs had a similar inhibitory effect on the different nuclear RNA fractions and preferentially reduced nucleolar RNA synthesis (44–49% inhibition) compared to heterogeneous RNA synthesis (5% inhibition). Polysomal RNA synthesis was inhibited to a greater degree than nuclear RNA synthesis by all the anthracyclines, and non-poly RNA synthesis was decreased by 50–60% and poly(A) RNA synthesis by 30%. When treated cells were incubated in drug-free medium for 2 h, RNA synthesis returned to 80% of the pretreatment level in MD and DAU treated cells, but by less than 10% in cells treated with MEO, and this difference was due to the more rapid cellular efflux of MD and DAU versus MEO. Thus, MD and MEO are inherently more potent inhibitors than DAU of RNA synthesis in HT-29 cells, but their reduced cytotoxicity cannot be attributed to differing effects on nucleolar or heterogeneous RNA synthesis, the nucleocytoplasmic transport of RNA, or the rate of return of RNA synthesis following drug treatment.