No abstract

Bisphosphonates (BPs) are widely used in the treatment of osteolytic bone disease associated with multiple myeloma, and have been demonstrated to exert antitumor effects both in vitro and in vivo. However, the precise molecular mechanisms involved in the direct antitumor effects of BPs in vitro are not known. Nitrogen‐containing BPs, such as risedronate (RIS), act by inhibiting protein prenylation. A phosphonocarboxylate analogue of RIS, 3‐PEHPC, has previously been shown in osteoclasts and macrophages to specifically inhibit prenylation of Rab GTPases. The aim of this study was to identify the molecular targets of RIS and 3‐PEHPC in human myeloma cells and to determine the cellular effects of selective inhibition of Rab prenylation by 3‐PEHPC as compared to nonspecific inhibition of protein prenylation by RIS in human myeloma cells. RIS dose‐dependently inhibited prenylation of both Rap1A and Rab6, whereas 3‐PEHPC only inhibited Rab6 prenylation. Both RIS and 3‐PEHPC dose‐dependently increased apoptosis in human myeloma cells. RIS induced an accumulation of cells in the S‐phase of the cell cycle, associated with inhibition of DNA replication. In contrast, 3‐PEHPC did not cause cell‐cycle arrest. Furthermore, geranylgeraniol could prevent inhibition of prenylation, induction of apoptosis, and cell‐cycle arrest in response to RIS, but not inhibition of Rab prenylation and apoptosis induced by 3‐PEHPC, consistent with specific inhibition of Rab geranylgeranyl transferase by 3‐PEHPC. In conclusion, our studies demonstrate that selective inhibition of Rab prenylation induces apoptosis, but not S‐phase arrest, thus identifying distinct molecular pathways that mediate the antimyeloma effect of nitrogen‐containing BPs. © 2006 Wiley‐Liss, Inc.

Background: Tumour cell-selective activation of apoptosis by recombinant human TNF-related apoptosis-inducing ligand (rhTRAIL) is enhanced through co-activation of p53 by chemotherapeutic drugs. The novel anticancer agent nutlin-3 provides a promising alternative for p53 activation by disrupting the interaction between p53 and its negative feedback regulator MDM2.

Background:Drug resistance is a major problem in ovarian cancer. Triggering apoptosis using death ligands such as tumour necrosis factor-related apoptosis inducing ligand (TRAIL) might overcome chemoresistance.Methods:We investigated whether acquired cisplatin resistance affects sensitivity to recombinant human (rh) TRAIL alone or in combination with cisplatin in an ovarian cancer cell line model consisting of A2780 and its cisplatin-resistant subline CP70.Results:Combining cisplatin and rhTRAIL strongly enhanced apoptosis in both cell lines. CP70 expressed less caspase 8 protein, whereas mRNA levels were similar compared with A2780. Pre-exposure of particularly CP70 to cisplatin resulted in strongly elevated caspase 8 protein and mRNA levels. Caspase 8 mRNA turnover and protein stability in the presence or absence of cisplatin did not differ between both cell lines. Cisplatin-induced caspase 8 protein levels were essential for the rhTRAIL-sensitising effect as demonstrated using caspase 8 small-interfering RNA (siRNA) and caspase-8 overexpressing constructs. Cellular FLICE-inhibitory protein (c-FLIP) and p53 siRNA experiments showed that neither an altered caspase 8/c-FLIP ratio nor a p53-dependent increase in DR5 membrane expression following cisplatin were involved in rhTRAIL sensitisation.Conclusion:Cisplatin enhances rhTRAIL-induced apoptosis in cisplatin-resistant ovarian cancer cells, and induction of caspase 8 protein expression is the key factor of rhTRAIL sensitisation.