Comparison of Glutathione Levels in Rodent and Human Tumor Cells Grown in Vitro and in Vivo

Abstract

Cellular glutathione (GSH) levels were compared in human and rodent tumor cells grown both in vivo and in vitro. Three human (A431, HEp3, ME180) and two murine (KHT and RIF-1) tumor cell lines were used. The average GSH contents for exponentially growing human cells in vitro were 14.2, 10.9, and 17.0 fmol/cell for ME180, A431, and HEp3 cells, respectively. These cells also were grown as tumors in nude mice. Following dissociation, >90% pure populations of neoplastic and nonneoplastic cells were isolated by centrifugal elutriation prior to GSH determination. The data showed that the GSH levels of the tumor associated host cells were appreciably lower than those of the neoplastic cells. In addition, in contrast to the values obtained for the exponential cells, neoplastic cells grown in vivo showed a 2- to 3-fold reduction in GSH. However, the values for in vivo cells were similar to those obtained for the same tumor cells grown in vitro in the plateau phase. Compared to the human tumor cells the GSH contents of murine tumor cells always were lower. For example, RIF-1 and KHT cells in the exponential growth phase had GSH contents of 3.3 and 7.5 fmol/cell, respectively. Also, as was observed with the human cells, the GSH content of KHT cells in plateau phase of growth was 2–3 times less than that of cells in the exponential phase of growth. Similarly, the GSH content of KHT cells grown as in situ tumors prior to dissociation and isolation by centrifugal elutriation also was reduced by a factor of 3 compared to exponential phase cells. Although the average volume of tumor cells grown in vivo was less than that of cells grown in vitro, this did not account for the differences in GSH values observed when in vitro and in vivo derived cells were compared. Finally, GSH measurements made on multiple biopsies of individual human tumor xenografts varied by a factor of 2–3 within each tumor type studied. This variation, likely due to host cell fluctuations, may present a complicating feature in the interpretation of solid tumor GSH levels.