Efficacy of camptothecin analog DX-8951f (Exatecan Mesylate) on human pancreatic cancer in an orthotopic metastatic model.

We determined the antitumor and antimetastatic efficacy of the camptothecin analogue DX-8951f in an orthotopic metastatic mouse model of pancreatic cancer. DX-8951f showed efficacy against two human pancreatic tumor cell lines in this model. These cell lines were transduced with the green fluorescent protein, enabling high-resolution visualization of tumor and metastatic growth in vivo. The DX-8951f studies included both an early and advanced cancer model. In the early model, using the human pancreatic cancer lines MIA-PaCa-2 and BxPC-3, treatment began when the orthotopic primary tumor was approximately 7 mm in diameter. DX-8951f was significantly effective against both MIA-PaCa-2 and BxPC-3. In contrast, 2', 2'-difluorodeoxycytidine (gemcitabine), the standard treatment for pancreatic cancer, did not have significant efficacy against MIA-PaCa-2. Although gemcitabine showed significant activity against BxPC-3 primary tumor growth, it was not effective on metastasis. In the model of advanced disease, using BxPC-3, treatment started when the orthotopic primary tumor was 13 mm in diameter. DX-8951f was significantly effective in a dose-response manner on the BxPC-3 primary tumor. DX-8951f also demonstrated antimetastatic activity in the late-stage model, significantly reducing the incidence of lymph node metastasis while eliminating lung metastasis. In contrast, gemcitabine was only moderately effective against the primary tumor and ineffective against metastasis at both sites in the late-stage model. Therefore, DX-8951f was highly effective against primary and metastatic growth in this very difficult-to-treat disease and showed significantly higher efficacy than gemcitabine, the standard treatment of pancreatic cancer. DX-8951f, therefore, has important clinical promise and has more positive features than the currently used camptothecin analogue CPT-11, which requires metabolic activation and is toxic.

Antimetastatic efficacy of oral 5-FU imaged by green fluorescent protein in real time.

The effectiveness of oral 5-FU in suppressing liver metastasis was assessed in a highly-metastatic mouse model. Doses of 20 and 25 mg/kg oral 5-FU significantly suppressed primary and metastatic tumor growth (p = 0.012). These inhibitory effects were more dramatic in suppressing liver metastasis (p = 0.0). The efficacy of 5-FU was visualized by whole-body fluorescence imaging of the green fluorescent protein-expressing tumor and its subsequent metastases. Toxicity was observed only in the 30 mg/kg dose. Furthermore, we showed that the non-toxic doses of 5-FU significantly prolonged survival in these animals. These data suggest the important clinical potential of oral 5-FU.

Direct external imaging of nascent cancer, tumor progression, angiogenesis, and metastasis on internal organs in the fluorescent orthotopic model.

Mouse tumor models have undergone profound improvements in the fidelity of emulating human disease. Replacing ectopic s.c. implantation with organ-specific orthotopic implantation reproduces human tumor growth and metastasis. Strong fluorescent labeling with green fluorescent protein along with inexpensive video detectors, positioned externally to the mouse, allows the monitoring of details of tumor growth, angiogenesis, and metastatic spread. However, the sensitivity of external imaging is limited by light scattering in intervening tissue, most especially in skin. Opening a reversible skin-flap in the light path markedly reduces signal attenuation, increasing detection sensitivity many-fold. The observable depth of tissue is thereby greatly increased and many tumors that were previously hidden are now clearly observable. This report presents tumor images and related quantitative growth data previously impossible to obtain. Single tumor cells, expressing green fluorescent protein, were seeded on the brain image through a scalp skin-flap. Lung tumor microfoci representing a few cells are viewed through a skin-flap over the chest wall, while contralateral micrometastases were imaged through the corresponding skin-flap. Pancreatic tumors and their angiogenic microvessels were imaged by means of a peritoneal wall skin-flap. A skin-flap over the liver allowed imaging of physiologically relevant micrometastases originating in an orthotopically implanted tumor. Single tumor cells on the liver arising from intraportal injection also were detectable. Possible future technical developments are suggested by the image, through a lower-abdominal skin-flap, of an invasive prostate tumor expressing both red and green fluorescent proteins in separate colonies.