Anti-DR4 Antibody [DR-4-02] (FITC) (A86110)

Mesenchymal stem cells (MSC) are emerging as novel cell-based delivery agents; however, a thorough investigation addressing their therapeutic potential in medulloblastomas (MB) has not been explored to date. In this study, we engineered human MSC to express a potent and secretable variant of a tumor specific agent, tumor necrosis factor-apoptosis-inducing ligand (S-TRAIL) and assessed the ability of MSC-S-TRAIL mediated MB killing alone or in combination with a small molecule inhibitor of histone-deacetylase, MS-275, in TRAIL-sensitive and -resistant MB in vitro and in vivo. We show that TRAIL sensitivity/resistance correlates with the expression of its cognate death receptor (DR)5 and MSC-S-TRAIL induces caspase-3 mediated apoptosis in TRAIL-sensitive MB lines. In TRAIL-resistant MB, we show upregulation of DR4/5 levels when pre-treated with MS-275 and a subsequent sensitization to MSC-S-TRAIL mediated apoptosis. Using intracranially implanted MB and MSC lines engineered with different combinations of fluorescent and bioluminescent proteins, we show that MSC-S-TRAIL has significant anti-tumor effects in mice bearing TRAIL-sensitive and MS-275 pre-treated TRAIL-resistant MBs. To our knowledge, this is the first study that explores the use of human MSC as MB-targeting therapeutic-vehicles in vivo in TRAIL-sensitive and resistant tumors, and has implications for developing effective therapies for patients with medulloblastomas.

Scatter factor (SF) and its receptor c-Met are overexpressed in various tumor types, and their expression often correlates with a poor prognosis. The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), is a proposed tumor-specific chemotherapy agent, but its clinical usage is limited by acquisition of TRAIL resistance by tumors. The goals of this study were to determine whether and how SF protects tumor cells against TRAIL and whether SF-induced TRAIL resistance could be reversed. We used MTT assays, trypan blue dye exclusion assays, apoptosis assays, RNA interference, luciferase reporter assays, immunoprecipitation/western blotting, and other cell biological techniques to study SF protection of cultured human tumor cells against TRAIL. SF conferred resistance to TRAIL in various human prostate carcinoma and breast carcinoma cell lines. SF inhibited TRAIL-induced caspase-3 activation, poly (ADP-ribose) polymerase cleavage, and cell death. SF protection against TRAIL required c-Akt; but unlike protection against adriamycin, it did not require Src signaling or the classical pathway of nuclear factor-kappaB activation. Protection against TRAIL was blocked by knockdown of X-linked inhibitor of apoptosis or FLICE-inhibitor protein (FLIP) (a component of the death-inducing signaling complex). We found that c-Met physically associates with several TRAIL receptors and SF regulates their protein stability. Protection against TRAIL was blocked by a novel small molecule inhibitor of c-Met (PHA665752) and by an inhibitor of cyclooxygenase 2. In conclusion, these findings elucidate potential mechanisms of TRAIL resistance in tumors that overexpress the SF/c-Met and identify possible means of reversing this resistance.