Sorafenib and its derivative SC-49 sensitize hepatocellular carcinoma cells to CS-1008, a humanized anti-TNFRSF10B (DR5) antibody.

BACKGROUND AND PURPOSE: Previously, we have shown that sorafenib sensitizes hepatocellular carcinoma (HCC) to apoptosis induced by TNF-related apoptosis-inducing ligand (TNFSF10; TRAIL). Here, we report that sorafenib and SC-49 sensitize HCC cells to CS-1008, a novel anti-human death receptor 5 (TNFRSF10B) antibody. EXPERIMENTAL APPROACH: HCC cell lines (PLC5, Huh-7, and Hep3B) were treated with CS-1008 and/or sorafenib and analysed in terms of apoptosis and signal transductions. KEY RESULTS: SC-49 is a sorafenib derivative, which is devoid of kinase inhibitory activity. Both sorafenib and SC-49 down-regulated the phosphorylation of STAT3 at Tyr(705) and subsequently reduced the levels of STAT3-regulated proteins, Mcl-1, survivin and cylcin D1, in CS-1008-treated HCC cells. Knockdown of STAT3 by RNA interference overcame apoptotic resistance to CS-1008 in HCC cells, and ectopic expression of STAT3 in HCC cells abolished the sensitizing effects of sorafenib and SC-49 on CS-1008-induced apoptosis, indicating that inhibition of STAT3 mediates the enhancing effects of these compounds when combined with CS-1008. Importantly, inhibition of SHP-1 by adding a specific SHP-1 inhibitor reduced the effects of SC-49 and CS-1008 on p-STAT3 and apoptosis, whereas co-treatment of CS-1008 with SC-49 increased the activity of SHP-1. These data indicate that the combined effects of CS-1008 and SC-49 on HCC are mediated by SHP-1. Moreover, the combination of CS-1008 and SC-49 inhibited HCC xenograft tumour growth in vivo. CONCLUSIONS AND IMPLICATIONS: Sorafenib and its derivative SC-49 sensitize HCC cells to the antitumour effects of CS-1008 through SHP-1-dependent inactivation of STAT3.

Modulation of TRAIL resistance in colon carcinoma cells: different contributions of DR4 and DR5.

BACKGROUND: rhTRAIL is a therapeutic agent, derived from the TRAIL cytokine, which induces apoptosis in cancer cells by activating the membrane death receptors 4 and 5 (DR4 and DR5). Here, we investigated each receptor's contribution to rhTRAIL sensitivity and rhTRAIL resistance. We assessed whether agonistic DR4 or DR5 antibodies could be used to circumvent rhTRAIL resistance, alone or in combination with various chemotherapies. METHODS: Our study was performed in an isogenic model comprised of the SW948 human colon carcinoma cell line and its rhTRAIL resistant sub-line SW948-TR. Effects of rhTRAIL and agonistic DR4/DR5 antibodies on cell viability were measured using MTT assays and identification of morphological changes characteristic of apoptosis, after acridine orange staining. Sensitivity to the different death receptor ligands was stimulated using pretreatment with the cytokine IFN-gamma and the proteasome inhibitor MG-132. To investigate the mechanisms underlying the changes in rhTRAIL sensitivity, alterations in expression levels of targets of interest were measured by Western blot analysis. Co-immunoprecipitation was used to determine the composition of the death-inducing signalling complex at the cell membrane. RESULTS: SW948 cells were sensitive to all three of the DR-targeting agents tested, although the agonistic DR5 antibody induced only weak caspase 8 cleavage and limited apoptosis. Surprisingly, agonistic DR4 and DR5 antibodies induced equivalent DISC formation and caspase 8 cleavage at the level of their individual receptors, suggesting impairment of further caspase 8 processing upon DR5 stimulation. SW948-TR cells were cross-resistant to all DR-targeting agents as a result of decreased caspase 8 expression levels. Caspase 8 protein expression was restored by MG-132 and IFN-gamma pretreatment, which also re-established sensitivity to rhTRAIL and agonistic DR4 antibody in SW948-TR. Surprisingly, MG-132 but not IFN-gamma could also increase DR5-mediated apoptosis in SW948-TR. CONCLUSIONS: These results highlight a critical difference between DR4- and DR5-mediated apoptotic signaling modulation, with possible implications for future combinatorial regimens.

DR5 activation of caspase-8 induces DC maturation and immune enhancement in vivo.

Non-homeostatic tissue apoptosis in vivo has been shown to induce inflammatory responses and facilitate the cross-presentation of proteins within apoptotic bodies. We hypothesize that in the presence of foreign antigens, the apoptotic-inflammatory process improves immune priming; further, molecules that trigger apoptosis may be adapted for use as immune adjuvants. One very attractive molecule in this context is the tumor necrosis factor receptor (TNFR) family molecule DR5/TRAIL-receptor 2. We show a significant improvement in CD8(+) T-cell mediated vaccine immunity with the use of death receptor-5 (DR5) as an immune adjuvant, a property that is correlated with the activation of caspases-8 (casp8) and dependent on its ability to induce apoptosis in vivo.