Novel Animal Model And In Vivo Imaging System To Study Inflammatory Response-mediated Cancer Metastasis
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Cancer metastasis is the leading cause of death in cancer patients. A vast majority of cancer-related mortality is attributed to this rather than the primary tumor itself, making the understanding of cancer metastasis critically important. Inflammatory responses have been implicated to play an important role in cancer metastasis. However, the investigation of the relationship between inflammation and cancer cell migration is limited by the lack of a reproducible cancer metastasis animal model. To fill the gap, we have recently developed an animal model. This model is composed of a two-step procedure. First, poly-L lactic acid (PLA) microspheres were implanted subcutaneously on the back of mice to induce localized inflammatory responses. Second, after PLA microsphere implantation for 24 hours, melanoma B16F10 cancer cells were transplanted in the peritoneal cavity. After cell implantation for different periods of time, animals were sacrificed and all tissues/organs were isolated for assessing the distribution of metastatic cancer cells. In addition, an imaging model was established to visualize and also quantify the cancer cell migration in vivo. For that, cancer cells were labeled with X-sight fluorescence agent. Following transplantation, the distributions of the X-sight labeled cells could be monitored using Kodak In-Vivo Imaging System. A relationship between fluorescence intensity and cell numbers was established to quantify the numbers of recruited cancer cells.Our studies have shown that inflammatory responses are one of the critical determinants of cancer cell metastasis. First, by implanting materials with varying proinflammatory properties, we found that there was a good relationship between the degree of biomaterial-mediated inflammatory responses and the numbers of immigrated cancer cells in vivo. Inflammatory responses exert similar migration responses of various cancer cells, including B16F10 melanoma cells, Lewis lung carcinoma cell line (LLC), rat prostate cancer cell line (JHU-31), human prostate adenocarcinoma (PC-3), and human breast cancer cell line (MDA-MB231).Studies were carried out to decipher the mechanisms governing inflammatory responses-mediated cancer metastasis. Our results have uncovered that cancer cells migrated out of the primary transplantation site - peritoneal cavity - via lymphatic system and CCR7/CCL21 pathways. Upon entering the circulation, cancer cells navigated to the inflammatory tissue via CXCR4/CXCL12 pathway. Rather surprisingly, we found that lymphocytes play an important role in cancer cell migration to inflamed tissue. Such lymphocyte-associated cancer cell migration is mediated, at least partially, by RANTES.Based on the results obtained from previous work, we have been working on the development of two novel strategies to reduce cancer metastasis. First, using scaffolds to release different cancer cell chemokines, we tested the influence of chemokine release on cancer cell recruitment. Interestingly, we found that erythropoietin (EPO) -releasing scaffold not only attracts more cancer cells immigrating to the implant area but also prolong the animal survival duration. On the other hand, the stromal cell-derived factor-1 alpha (SDF-1 alpha) releasing scaffolds had no significant influence on cancer cell migration. The second approach was aimed to study the potential effect of vascular permeability on cancer cell migration. The feasibility of this approach is supported by the fact that localized release of histamine significantly increase the numbers of recruited cancer cell to the implantation sites. Since mast cells are the main source of histamine, we further tested the influence of mast cell inactivator/stabilizer (cromolyn) on cancer cell recruitment. Indeed, cromolyn substantially reduced the cancer cell recruitment to the subcutaneous implants. It is our belief that the novel inflammation-induced cancer metastasis model along with in vivo imaging systems using either exogenous or endogenous labeling methods should be able to perform high throughput of different categories anti-inflammatory drugs for the treatment of cancer therapy.