Characterizing the biological effects of Apo2L/TRAIL on tumor cells in vitro and in vivo
Beachy, Sarah Hejaily
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Recently, emphasis in cancer research has been on the development of tumor targeted therapies in order to spare the toxic side effects of chemotherapy. While targeted therapies have certain advantages, they are not exempt from the problems in common with traditional therapy: quickly measuring the response of the tumor to the therapy, predicting sensitivity of the tumor to the therapy, and gaining accessibility of the drug to the tumor site. In this thesis, Apo2L/TRAIL, a cytokine that kills malignant cells while sparing normal cells, was used as a model therapy to study human tumor cell apoptosis in vitro, and in vivo using SCID mice. This thesis work investigated the following specific aims: (1) To test potential methods for detection and identification of metabolites and proteins released from tumor cells into the extracellular environment during apoptosis, (2) To identify candidate protein markers of tumor cell sensitivity and resistance to Apo2L/TRAIL, and (3) To study the tumor microenvironment during Apo2L/TRAIL treatment of tumors to evaluate new strategies for improved drug delivery. Using 1H-NMR and multivariate data analysis, metabolite profiles distinguished between the extracellular environment of control tumor cells and tumor cells undergoing apoptosis. With 2D gels, alterations in E-cadherin and fibrinogen levels were found to be useful as indicators of therapy-induced apoptosis of tumor cells. Analysis of patient tumor specimens with 2D gels and multidimensional protein identification technology revealed classes of proteins including heat shock proteins and chaperonin-containing TCP-1 (CCTs) that may be useful in predicting sensitivity to Apo2L/TRAIL. Finally, Apo2L/TRAIL can dramatically decrease tumor interstitial fluid pressure and decrease areas of hypoxia, suggesting that drug delivery could be increased following Apo2L/TRAIL treatment. Future work will identify metabolite markers for use in monitoring therapy, determine optimal sampling times, and determine whether these markers are drug-specific. Larger numbers of patient specimens are needed to investigate proteins indicative of Apo2L/TRAIL sensitivity and resistance more completely. Additional studies on the effect of Apo2L/TRAIL on blood vessels are necessary in order to further support the idea that Apo2L/TRAIL can be used as a strategy for improved drug delivery to tumors.