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

Abstract

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.

FIGURE 1

Degree of tumor growth inhibition (TGI) of patient pancreatic tumors engrafted subcutaneously in SCID mice achieved by Apo2L/TRAIL treatment for 3 sensitive and 3 resistant xenografts. Tumor bearing mice were treated with 500µg/dose of Apo2L/TRAIL daily for approximately two 2-week cycles, separated by 1 week rest (the day on which the % tumor growth inhibition was calculated varied slightly between experiments as indicated). Sensitivity was designated based on the results of the Student t-test comparing average tumor size on day indicated (**p<0.005; *p<0.05). Gray bars- sensitive tumors; black bars- resistant tumors.

FIGURE 2

Histology of engrafted pancreatic xenograft #11424. A. Viable tumor cells (arrow) can be identified in the SCID mouse pancreas. B. In a serial section, these cells are positive by IHC for human mitochondria (arrow) and thus confirmed to be of human origin. C. A metastatic lesion is grossly visible in the periphery of the liver (circled). D. A metastatic lesion in a section of the liver (arrow). E–P. Histological features of individual tumors are identical in subcutaneous and orthotopic sites: for each tumor the subcutaneous (SC) sample is shown above the orthotopic (Ortho) location: (#11424 E-SC, F-Ortho; #14244 G-SC, H-Ortho; #16096 I-SC, J-Ortho; #12298 K-SC, L-Ortho; #12424 M-SC, N-Ortho; #12459 O-SC, P-Ortho).

FIGURE 3

Responses of the six patient pancreatic xenografts engrafted orthotopically to Apo2L/TRAIL treatment. Mice were treated daily with Apo2L/TRAIL and tumor burden (as indicated by weight of the pancreas) was evaluated at the end of treatment. A–C. Mice with tumors 11424 (A), 14244 (B) and 16096 (C) all showed a significant differences in pancreatic weight between control and treated mice; D–E Mice with tumors 12298 (D), 12424 (E) and 12459 (F) did not. (**p<0.005; *p<0.05).

FIGURE 4

Response of orthotopic and metastatic pancreatic cancer to Apo2L/TRAIL. The presence of both primary and metastatic tumors was confirmed prior to initiating treatment on day 94. Representative coronal T2-weighted MR images of a saline-treated mouse (A, B) and an Apo2L/TRAIL treated mouse (C, D) on day 110 (A, C) and on day 122 (B, D) in which the appearance of both primary and metastatic lesions are indicated (primary tumors are outlined in red; arrows point to metastatic lesions).

FIGURE 5

Growth of primary orthotopic tumors and metastatic lesions is inhibited by Apo2L/TRAIL and survival is extended in treated mice. A. Growth curves of primary tumors in control and Apo2/TRAIL treated mice. B. Final pancreatic weights in the mice shown in (A). C. Metastatic burden (mm³) of control and Apo2/TRAIL treated animals at different time points post implantation. Differences in metastatic burden between animals in saline and treatment groups were statistically significant on day 115 (p<0.05) and d122 (p<0.001). D. Kaplan-Meier survival curves of control and Apo2/TRAIL treated animals. A significant increase in median survival was observed following Apo2/TRAIL treatment (175 days; p=0.01) compared to control animals (130 days).