CELL CYCLE-SPECIFIC GROWTH-INHIBITION OF HUMAN BREAST-CANCER CELLS INDUCED BY METABOLIC-INHIBITORS

Proliferation of exponentially growing breast cancer cells (line Hs578T) was blocked specifically in G1 by 3-hydroxy-3-methylglutaryl Coenzyme A (HMG CoA) reductase inhibition, as well as by inhibition of N-linked glycosylation. As a consequence of these inhibitory conditions, the cells were synchronized in the G1 stage of the cell cycle. The similarities in the kinetic responses point to the possibility that the two different types of metabolic inhibitions block cell cycle progression by common mechanisms. One possibility is that the inhibition of HMG CoA reductase activity also leads to a depressed rate of N-linked glycosylation, which in turn may constitute the critical event for cell cycle progression and cell growth. In order to investigate whether this relationship exists in breast cancer cells, cells synchronized in G1 by mevinolin (an inhibitor of HMG CoA reductase) were used. Upon addition of mevalonate, whose endogenous synthesis is catalysed by HMG CoA reductase, the cells entered S phase after a 4 h pre-replicative period. Mevalonate stimulation also led to a rapid and substantial increase in N-linked glycosylation, measured by determining the uptake of radioactive glucosamine. This metabolic event was found to be of critical importance for the initiation of DNA synthesis. However, as soon as the cells had entered S phase, they were independent of the level of N-linked glycosylation.