Separation of Parathyroid Hormome-Like Activity from Transforming Growth Factor-α and -β in the Canine Adenocarcinoma (CAC-8) Model of Humoral Hypercalcemia of Malignancy*

Abstract

A canine adenocarcinoma model (CAC-8) of humoral hypercalcemia of malignancy was evaluated for transforming growth factors (TGF)-alpha and -beta, PTH-like activity [adenylate cyclase-stimulating activity (ACSA)], and in vitro bone-resorbing activity. Biological activities present in CAC-8 were separated by reverse phase or cation exchange HPLC. TGF alpha in tumor extract was separated from TGF beta and ACSA by reverse phase HPLC. TGF alpha eluted between 26-30% acetonitrile and was identified by RIA. After the initial reverse phase separation, TGF beta and ACSA in tumor extract coeluted between 36-38% acetonitrile. Sequential cation exchange followed by reverse phase HPLC separated TGF beta from ACSA. Evaluation of fractions containing ACSA using an in vitro bone-resorbing assay demonstrated copurification of ACSA and bone-resorbing activity. The PTH receptor antagonist [Nle8,18,Tyr34]bovine PTH-(3-34)-amide, but not [Nle8,18,Tyr34]bovine PTH-(7-34)-amide, completely inhibited ACSA in column eluates. Conditioned cell culture medium from CAC-8 primary cultures contained predominantly latent TGF beta that could be activated by acidification. These findings indicate that the CAC-8 model of cancer-associated hypercalcemia produces a PTH-like factor, TGF alpha, and TGF beta that were separable by reverse phase or cation exchange HPLC. This feature should be useful to investigate the role of TGFs and PTH-like proteins in the pathogenesis of humoral hypercalcemia of malignancy.