Influence of the implantation site on the sensitivity of patient pancreatic tumor xenografts to Apo2L/TRAIL therapy

OBJECTIVES

We have previously demonstrated activity of Apo2L/TRAIL against patient pancreatic tumor xenografts. Here, we have examined the influence of the tumor implantation site on therapeutic response of orthotopic tumors and their metastases to Apo2L/TRAIL.

METHODS

Sensitivity of 6 patient pancreatic tumor xenografts to Apo2L/TRAIL was determined in a subcutaneous model. To compare the response of orthotopic tumors, cells from subcutaneous xenografts were injected into the pancreas. Tumor growth was confirmed by histological examination of selected mice, and then treatment was started. When all control mice developed externally palpable tumors, the experiment was terminated, and pancreatic weights compared between control and treated groups. Magnetic resonance imaging was used to quantitate the response of orthotopic and metastatic tumors.

RESULTS

The sensitivity to Apo2L/TRAIL observed in subcutaneous tumors was maintained in orthotopic tumors. Metastatic spread was observed with orthotopic tumor implantation. In an orthotopic model of a sensitive tumor, primary and metastatic tumor burden was significantly reduced, and median survival significantly extended by Apo2L/TRAIL therapy.

CONCLUSIONS

Our data provide evidence that the site of tumor engraftment does not alter the inherent sensitivity of patient xenografts to Apo2L/TRAIL, and these results highlight the potential of Apo2L/TRAIL therapy against primary and metastatic pancreatic cancer.

Anticancer efficacy of Apo2L/TRAIL is retained in the presence of high and biologically active concentrations of osteoprotegerin in vivo

Osteoprotegerin (OPG) is a secreted member of the tumor necrosis factor (TNF) receptor superfamily that binds to the ligand for receptor activator of nuclear factor κB (RANKL) and inhibits bone resorption. OPG can also bind and inhibit the activity of the TNF-related apoptosis-inducing ligand (Apo2L/TRAIL), raising the possibility that the anticancer efficacy of soluble Apo2L/TRAIL may be abrogated in the bone microenvironment where OPG expression is high. In this study we used a murine model of breast cancer growth in bone to evaluate the efficacy of recombinant soluble Apo2L/TRAIL against intratibial tumors that were engineered to overexpress native full-length human OPG. In vitro, OPG-overexpressing breast cancer cells were protected from Apo2L/TRAIL-induced apoptosis, an effect that was reversed with the addition of soluble RANKL or neutralizing antibodies to OPG. In vivo, mice injected intratibially with cells containing the empty vector developed large osteolytic lesions. In contrast, OPG overexpression preserved the integrity of bone and prevented breast cancer-induced bone destruction. This effect was due primarily to the complete absence of osteoclasts in the tibias of mice inoculated with OPG-transfected cells, confirming the biologic activity of the transfected OPG in vivo. Despite the secretion of supraphysiologic levels of OPG, treatment with Apo2L/TRAIL resulted in strong growth inhibition of both empty vector and OPG-overexpressing intratibial tumors. While Apo2L/TRAIL-induced apoptosis may be abrogated in vitro by OPG overexpression, the in vivo anticancer efficacy of recombinant soluble Apo2L/TRAIL is retained in the bone microenvironment even in the presence of biologically active OPG at supraphysiologic concentrations.

Progressive resistance of BTK-143 osteosarcoma cells to Apo2L/TRAIL-induced apoptosis is mediated by acquisition of DcR2/TRAIL-R4 expression: resensitisation with chemotherapy

Apo2 ligand (Apo2L, also known as TRAIL) is a member of the tumour necrosis factor (TNF) family of cytokines that selectively induces the death of cancer cells, but not of normal cells. We observed that recombinant Apo2L/TRAIL was proapoptotic in early-passage BTK-143 osteogenic sarcoma cells, inducing 80% cell death during a 24 h treatment period. Apo2L/TRAIL-induced apoptosis was blocked by caspase inhibition. With increasing passage in culture, BTK-143 cells became progressively resistant to the apoptotic effects of Apo2L/TRAIL. RNA and flow cytometric analysis demonstrated that resistance to Apo2L/TRAIL was paralleled by progressive acquisition of the decoy receptor, DcR2. Blocking of DcR2 function with a specific anti-DcR2 antibody restored sensitivity to Apo2L/TRAIL in a dose-dependent manner. Importantly, treatment of resistant cells with the chemotherapeutic agents doxorubicin, cisplatin and etoposide reversed the resistance to Apo2L/TRAIL, which was associated with drug-induced upregulation of mRNA encoding the death receptors DR4 and DR5. BTK-143 cells thus represent a useful model system to investigate both the mechanisms of acquisition of resistance of tumour cells to Apo2L/TRAIL and the use of conventional drugs and novel agents to overcome resistance to Apo2L/TRAIL.

Role of Apo2L/TRAIL and Bcl-2-family proteins in apoptosis of multiple myeloma

Apo2 Ligand or Tumour Necrosis Factor (TNF)-Related Apoptosis-Inducing Ligand (Apo2L/TRAIL) is a member of the TNF gene superfamily that selectively induces apoptosis in tumor cells of diverse origins through engagement of death receptors. We have recently demonstrated that Type I interferons (IFN-alpha and beta) induce apoptosis in multiple myeloma (MM) cell lines and in plasma cells from MM patients. Moreover, Apo2L selectively induces apoptosis of patient MM tumor cells while sparing non-malignant cells. Apo2L induction is one of the earliest events following IFN administration in these cells. IFNs activate Caspases and the mitochondrial-dependent apoptotic pathway mediated by Apo2L production. Cell death induced by IFNs and Apo2L can be blocked by a dominant-negative Apo2L receptor, DRS, and is regulated by members of the Bcl-2 family of proteins. This review is focused on the apoptotic signaling pathways regulated by Apo2L and Bcl-2-family proteins and summarizes what is known about their clinical role.