Bisphosphonates, which are specifically internalised into osteoclasts (Sato et al, 1991), lead to inhibition of cell function because of changes following website in the cytoskeleton and loss of the ruffled border (Carano et al, 1990), as well as apoptosis (Hughes et al, 1995). Third-generation, nitrogen-containing BPs, such as zoledronic acid (ZOL) (Green et al, 1994), inhibit farnesyldiphosphate (FPP) synthase, an enzyme involved in the mevalonate pathway (Luckman et al, 1998; Benford et al, 1999), preventing post-translational events of prenylation of small GTP-binding proteins such as p21ras, Rab, Rho, Rac and cdc42 (Luckman et al, 1998), which are required for a variety of biological functions including signal transduction and cell adhesion.
In addition to the potent antiresorptive effects of nitrogen-containing BPs, recent reports have also shown that these compounds induce antiproliferative and apoptotic effects in multiple myeloma cells in vitro (Shipman et al, 1997; Aparicio et al, 1998), may synergise with chemotherapeutic or biological agents (Tassone et al, 2000, 2002), and may offer clinical benefits (Dhodapkar et al, 1998; Berenson et al, 1998). A direct effect induced by BPs has also been demonstrated on tumour cells of nonhaematopoietic origin. Bisphosphonates induce inhibition of adhesion of breast and prostate cancer cells to bone matrix (Van Der et al, 1996; Boissier et al, 1997). In a mouse model of breast cancer, BPs inhibited the progression and the development of bone metastasis (Sasaki et al, 1995).
Other studies have also suggested that BPs may interfere with the growth and survival of metastatic cancer cells in bone (Pelger et al, 1998). More recently, a variety of studies have focused on the direct effect of BPs on growth and survival of cancer cells from solid tumours. ZOL induces a significant reduction of cell viability, increases apoptotic cell death and downregulation of bcl-2 protein, p21ras delocalisation from the cell membrane and proteolytic cleavage of PARP, indicating direct antitumour effects on human breast cancer cells (Senaratne et al, 2000; Senaratne et al, 2002). In prostate cancer cells, ZOL has shown a remarkable inhibitory effect on cell proliferation by induction of cell death and/or cytostasis in vitro (Lee et al, 2001).
In this scenario, since there have been no studies addressing the possibility Brefeldin_A of a direct effect of BPs on growth and survival of human PC cells, we studied the activity of the most potent BP, ZOL, on a panel of different human PC cell lines (BxPC-3, CFPAC-1 and PANC-1). We have additionally studied whether the nitrogen-containing ZOL might induce effects on the p21ras/raf1/MEK1/ERK and on the pkB/Akt pathways, and if apoptosis should be related to caspase-9/-3 and PARP cleavage/activation in these cancer cells.