COMBINED GROWTH-INHIBITORY RESPONSES AND ULTRASTRUCTURAL ALTERATIONS PRODUCED BY 1,3-BIS(2-CHLOROETHYL)-1-NITROSOUREA AND DEXAMETHASONE IN RAT GLIOMA CELL-CULTURES

  • 1 January 1977
    • journal article
    • research article
    • Vol. 37  (2) , 585-594
Abstract
The effect of 0.0001-10 .mu.M 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and 1 .mu.M dexamethasone on cell proliferation was studied by measuring cell densities in control and drug treated rat glioma (strain C6) monolayer cultures. When C6 cultures were exposed to 0.01-10 .mu.M BCNU, the growth rates decreased for 2 days as control cell populations continued to proliferate at log phase rates. These growth inhibitory responses were dose dependent and ranged from 20-80%, relative to control growth. Subsequently, the growth rates increased and the inhibitory responses ranged from 0-12% 4 days later. Cell densities in C6 cultures exposed to 1 .mu.M dexamethasone for 1 day did not differ significantly from controls. Cell proliferation ceased and the inhibitory response remained at 50% relative to controls in the stationary phase. When 0.03 .mu.M BCNU and 1 .mu.M dexamethasone were supplied simultaneously to C6 cultures, a 35% inhibitory response occurred after 1 day. This response did not differ significantly from that observed with 0.03 .mu.M BCNU alone. After 4 days, the inhibitory response did not decrease in cultures containing both drugs, but decreased to 13% in the 0.03 .mu.M BCNU-treated cultures. In 1 .mu.M BCNU treated cultures, the response was 66% after 1 day, which decreased to 21% 5 days later. When 1 .mu.M BCNU was supplied to C6 cultures that were pretreated for 1 day with 1 .mu.M dexamethasone, the response was 91% the following day, and this decreased to only 54% 5 days later. Dose-response curves showed that the inhibitory responses after 1 day in these pretreated cultures exposed to 0.001-10 .mu.M BCNU increased up to 22% relative to the responses produced by either drug alone. After 5 days, the responses in the pretreated cultures exposed to 0.001-1 .mu.M BCNU was 50%, which was similar to the response produced by 1 .mu.M dexamethasone alone. Ultrastructural studies revealed that control and 1 .mu.M BCNU-treated C6 cells contained 18 mitochondria, but the treated cells were 10% smaller after 1 day. Cells exposed to 1 .mu.M dexamethasone for 1 day contained 23 mitochondria which decreased to 18 the 2nd day. The amount of granular endoplasmic reticulum increased > 80% in cells treated with BCNU for 1 day or dexamethasone for 2 days. C6 cells pretreated with dexamethasone and exposed to BCNU for an additional day contained 23 mitochondria, did not decrease in size and exhibited a > 250% increase in the amount of granular endoplasmic reticulum. Combined growth inhibitory responses and ultrastructural alterations occur when C6 cells are treated sequentially with 1 .mu.M dexamethasone and BCNU.