Activity of Anticancer Drugs in Relation to the Tumour Microenvironment and Potential to Inhibit Repopulation and Enhance Therapeutic Outcome

Tumours have a disorganized and convoluted vasculature. Tumour cells that reside close to patent blood vessels are nourished by oxygen and other nutrients and are rapidly proliferating while distally located cells slowly proliferating. Anticancer drugs must be delivered in adequate (toxic) concentrations to all tumour cells to be effective, and it is therefore important to study their distribution of activity in tumours.;In order to assess the distribution of anticancer agents in tumours using immuno-histochemistry (IHC) and fluorescence imaging, drugs must be either inherently fluorescent or have antibodies that recognize their activity. As the vast majority of anticancer drugs fulfill neither of these criteria, the first objective of this thesis was to develop techniques to assess the pharmacodynamic activity of anticancer drugs in relation to distance from vasculature and hypoxic regions using biomarkers that could be recognized by antibodies using IHC. I found that GH2AX , a biomarker of DNA damage was activated in as little as 10 minutes following treatment. In addition, changes in biomarkers of apoptosis (cleaved caspase -3 or -6) and cell proliferation (Ki-67) could be used to determine drug activity at 24 hours following drug treatment.;The second objective of this thesis addressed the ability of a novel hypoxia activated pro-drug, TH-302, used alone or with chemotherapy (doxorubicin or docetaxel) to modify the distribution of biomarkers in relation to blood vessels and regions of hypoxia. It was found that TH-302 increased DNA damage and apoptosis not only in hypoxic regions but also in vascularized areas and this effect was augmented through the addition of chemotherapy. TH-302 increased growth delay due to chemotherapy of human tumour xenografts, consistent with complementary effects of the drugs in different regions of the tumour microenvironment.;The third objective of this thesis was to study changes in the tumour microenvironment after chemotherapy. I injected into tumour-bearing mice two markers of hypoxia, EF5 and pimonidazole, with a variable interval between injections. I studied the effects of chemotherapy alone on repopulation of hypoxic tumour cells and the ability of TH-302 to inhibit repopulation. It was found that (i) reoxygenation of previously hypoxic cells and repopulation of the tumour from them occurs after chemotherapy, and (ii) TH-302 was able to reduce tumour cell reoxygenation and repopulation. This supports the potential of TH-302 to increase therapeutic effects of chemotherapy.;The work presented in this thesis highlights the importance of the tumour microenvironment and its ability to impact the distribution of anticancer drugs to cells.