INVIVO AND INVITRO ERYTHROPOIETIN ACTIVITIES IN CULTURES OF A HEPATOCELLULAR-CARCINOMA CELL-LINE

The present studies were undertaken to characterize erythropoietin (Ep ) production in an Ep-producing hepatocellular carcinoma (Hep3B) cell line. Hep3B cells which had been maintained in culture were transplant ed under the renal capsule and subcutaneously in nude mice. The Hep3B xenograft doubling time is approximately 7 days. The mean hematocrit v alue of the Hep3B tumor-bearing nude mice was 33.2 +/- 1.1% (n = 8), w hich was significantly lower than that of control nongrafted nude mice (40.8 +/- 1.7%, n = 5). The Hep3B tumor-bearing nude mice showed sign ificantly higher Ep levels in the sera (37.5 +/- 5.5 munits/ml, n = 8) than control nude mice (13.5 +/- 2.7 munits/ml, n = 5). Ep levels in the sera were correlated (R = 0.714) with the total Ep in the tumor ex tracts, whereas no Ep was detectable in any of the kidney extracts. On the other hand, an inverse linear relationship (R = -0.811) between t he hematocrit values and Ep levels in the sera was demonstrated in the Hep3B tumor-bearing nude mice. The Hep3B cells recultured after growi ng in the nude mice were capable of enhancing Ep production in respons e to hypoxia, very similar to the original Hep3B cells which had been maintained in culture during the same time period. In addition, 15-met hylprostaglandin E1 at a concentration range of 4-400 ng/ml produced s ignificant increases in Ep secretion and cAMP accumulation in Hep3B cu ltures under hypoxic conditions (1% O2). The Ep produced by Hep3B cell s expressed 3.7 times higher in vitro bioactivity than immunoactivity. The bioactivity of Hep3B Ep was completely neutralized by an antibody to highly purified human recombinant Ep. In contrast, the in vivo bio activity of the Hep3B Ep was less than one tenth of its immunoactivity . These results indicate that the Hep3B tumor-bearing nude mice and th e in vitro Hep3B culture system may provide a reproducible model syste m which should be useful for studies of the mechanism of Ep production .