Abstract 1327: Macromolecular transport, collagen fiber morphology, and metastasis are influenced by the tumor growth location

Abstract

Abstract Metastasis and malignant ascites are major causes of poor prognosis in prostate cancer patients. Cancer cells metastasize more readily from orthotopic sites than from heterotopic sites (1). Here we have focused on characterizing the role of the extracellular matrix (ECM) in facilitating metastatic dissemination from metastasis-permissive environments and on understanding the role of hypoxia in these environments using noninvasive MRI and optical imaging of orthotopic and subcutaneous PC3 tumor xenografts. MRI of a macromolecular contrast agent was used to characterize interstitial fluid transport, second harmonic generation (SHG) microscopy to determine collagen I fiber distribution, and enhanced green fluorescent protein (EGFP) expression to detect hypoxia. These studies will provide insights into the dynamics of interstitial transport, and the influence of collagen I fibers within these metastasis-permissive environments. PC3-HRE-EGFP cells were engineered to express EGFP under hypoxia (1). For the orthotopic implantation, we used a microsurgical method that avoids disseminating cancer cells during inoculation in the prostate. By implanting PC3 tumor tissues rather than injecting cells, the stromal tissue and the three dimensional cytoarchitecture, believed to play a critical role in tumor progression and metastasis, were maintained. Interstitial fluid transport parameters were measured on a Bruker Biospec 4.7T spectrometer as previously described (2). SHG microscopy of freshly excised xenograft slices was performed on a Zeiss 710 LSM NLO microscope system. Collagen fiber morphology was characterized in terms of the inter-fiber distance and fiber volume (3). A significantly higher number of interstitial fluid pooling voxels, and lower efflux and influx rates were observed in orthotopic tumors compared to the subcutaneous ones. SHG imaging demonstrated significantly higher fiber density and volume in orthotopic tumors. Metastases to lymph nodes, lungs and several other organs were routinely observed following orthotopic implantation, but rarely occurred after subcutaneous implantation. Overall, orthotopic prostate tumors were characterized by a higher density of collagen fibers, a higher number of interstitial fluid pooling voxels, and lower efflux and influx rates compared to subcutaneous tumors. Characterization of hypoxia in orthotopic and subcutaneous environments and its relationship to interstitial transport and collagen fiber distribution is ongoing. These data demonstrate the profound impact of the location of tumor growth on the ECM and macromolecular transport, and provide additional insights into environments that are permissive for metastasis and the accumulation of malignant ascites. (1) Raman et al, Cancer Res, 66:9929-9936, 2006. (2) Pathak et al, Cancer Res, 65:1425-32, 2005. (3) Kakkad et al, Neoplasia 12:608-17, 2010. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1327. doi:1538-7445.AM2012-1327