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Mucins are high molecular weight glycoproteins expressed on the apical surface of normal epithelial cells. In cancer disease mucins are overexpressed on the entire cellular surface. Overexpression of MUC1 mucin in pancreatic tumours has been correlated with poor patient survival. Current chemotherapeutic approaches such as 5-fluorouracil (5-FU) has produced limited clinical success. In this study we investigated the role of mucin in cytotoxic drug treatment to determine whether the extracellular domain of mucin impedes cytotoxic drug action of 5-FU. Human pancreatic cancer cells revealed high and relatively moderate MUC1 levels for Capan-1 and HPAF-II, respectively, compared to MUC1 negative control (U-87 MG glioblastoma) that showed relatively non-specific anti-MUC1 uptake. Benzyl-alpha-GalNAc (O-glycosylation inhibitor) was used to reduce mucin on cell surfaces, and neuraminidase was used to hydrolyse sialic acid at the distal end of carbohydrate chains. Benzyl-alpha-GalNAc had no effect on cell morphology or proliferation at the concentrations employed. The inhibition of O-glycosylation resulted in significant 5-FU antiproliferative activity against Capan-1 and HPAF-II, but not against U-87 MG. However, the exposure of cells to neuraminidase failed to improve the cytotoxic action of 5-FU. Our experimental findings suggest that the overexpression of mucin produced by human pancreatic tumours might limit the effectiveness of chemotherapy.

Transport parameters determine the access of drugs to tumors. However, technical difficulties preclude the measurement of these parameters deep inside living tissues. To this end, we adapted and further optimized two-photon fluorescence correlation microscopy (TPFCM) for in vivo measurement of transport parameters in tumors. TPFCM extends the detectable range of diffusion coefficients in tumors by one order of magnitude, and reveals both a fast and a slow component of diffusion. The ratio of these two components depends on molecular size and can be altered in vivo with hyaluronidase and collagenase. These studies indicate that TPFCM is a promising tool to dissect the barriers to drug delivery in tumors.

Intravital microscopy coupled with chronic animal window models has provided stunning insight into tumor pathophysiology, including gene expression, angiogenesis, cell adhesion and migration, vascular, interstitial and lymphatic transport, metabolic microenvironment and drug delivery. However, the findings to date have been limited to the tumor surface (150 microm). Here, we show that the multiphoton laser-scanning microscope can provide high three-dimensional resolution of gene expression and function in deeper regions of tumors. These insights could be critical to the development of novel therapeutics that target not only the tumor surface, but also internal regions.