Bisphosphonates regulate cell growth and gene expression in the UMR 106-01clonal rat osteosarcoma cell line

Local growth of osteosarcoma involves destruction of host bone by proteolyt ic mechanisms and/or host osteoclast activation. Osteoclast formation and a ctivity are regulated by osteoblast-derived factors such as the osteoclast differentiating factor, receptor activator of NF-kappaB ligand (RANKL) and the inhibitor osteoprotegerin (OPG). We have investigated the in vitro effe cts of bisphosphonates on a clonal rat osteosarcoma cell line. The aminobis phosphonate pamidronate was added to UMR 106-01 cell cultures (10(-8) M to 10(-4) M up to 5 days). The non-aminobisphosphonate clodronate was administ ered for the same time periods (10(-6) M to 10(-2) M). Cell proliferation, apoptosis and mRNA expression was assessed. Both agents inhibited cell prol iferation in a time- and dose-dependent manner. ELISA analysis demonstrated an increase in DNA fragmentation although there was no significant dose-re lated difference between the doses studied. Bisphosphonate-treated cultures had a greater subpopulation of cells exhibiting morphological changes of a poptosis. Expression of mRNA for osteopontin and RANKL was down-regulated b y both agents, while the expression of mRNA for alkaline phosphatase, pro-c alpha1(I) collagen and OPG was not altered. Out in vitro work suggests the bisphosphonates not only have direct effects on osteosarcoma cell growth a nd apoptosis, but also, by altering the relative expression of osteoclast-r egulating factors, they may inhibit the activity of osteoclasts and their r ecruitment. (C) 2001 Cancer Research Campaign.