We have also been investigating anticancer therapy using the death ligand tumor necrosis factor-related apoptosis-inducing ligand(TRAIL) in combination with the proteasome inhibitor bortezomib (Velcade). We have observed that these 2 agents synergize to promote tumor cell apoptosis in a variety of human and murine cancer cell lines. The molecular mechanism whereby this combination promotes apoptosis has been further investigated. Surprisingly this does not seem to involve inhibition of NFkB. Preliminary in vivo studies suggest this combination may have some promise for future therapeutic utililty.Screening of a large number of human tumor cell lines shows that 20-30% are sensitized to TRAIL by bortezomib. The molecular basis for sensitivity and resistance is being investigated further.There does seem to be a good correlation with the amplification of a very proximal apoptotic signal (activation of caspase 8) and sensitization. The molecular basis as to why this occurs in sensitized but not resistant cells is under investigation. A clinical trial of bortezomib and an agonist antibody to one of the TRAIL death receptors was recently initiated by Human Genome Sciences. The laboratory has been focused during the last year on immune-mediated tumor cell destruction. Natural killer (NK) cells and cytotoxic T cells (CTL) lyse virally-infected and tumor cells by 2 main mechanisms:(1) the exocytosis of lytic granules and (2) the expression of cytotoxic molecules like tumor necrosis factor (TNF) or related molecules like Fas-ligand. We have investigated the importance of these mechanisms in cytotoxic immune responses to various mouse and human tumors. We are currently using a tumor model system in an attempt to simplify these types of experiment. This involves expression by the tumor cells of viral hemagglutinin (HA) as a surrogate tumor antigen. CD 8 T cells specific for a particular HA peptide are then to be derived from various gene-targeted mice and adotively transfered to tumor-bearing mice. This should help us determine which effector functions of these T cells are crucial for tumor destruction in vivo. In addition we are treating the tumor-bearing mice with bortezomib prior to T cell transfer in an attempt to pre-sensitize the tumor cells to cytotoxic effector molecules derived from the T cells.
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