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Date of Award
Campus Access Dissertation
Doctor of Philosophy in Biochemistry and Molecular Biology (PhD)
Administrative Home Department
Department of Chemistry
Committee Member 1
Tarun K. Dam
Committee Member 2
Committee Member 3
Alterations in nutritional uptake and metabolism is a crucial hallmark of cancer. As cancer cells progress in their development, they exhibit increased dependency on nutrient sugar to cope with enhanced metabolic needs. These adaptations result in alterations in the expression of facilitative sugar transporters (GLUTs) and significant differences in sugar uptake activity in cancer vs. normal cells. These metabolism-linked differences provided a basis for developing new, more specific approaches to identify cancer cells and sensitize them towards chemotherapy. Considering the high need for cancer cells in glucose – a major sugar nutrient – the strategies widely explored thus far focused on targeting glucose transporters. The broad range of data obtained throughout over 60-year long research endeavors have identified the advantages of targeting glucose GLUTs and highlighted the challenges in applying this strategy due to the ubiquitous need for glucose. These findings highlighted the need for more specific approaches to target cancer cells in diagnostic and therapeutic applications. This thesis presents the studies to assess the therapeutic potential of fructose-specific transporter GLUT5 in breast cancers. Prior development of GLUT5-specific fluorescence activity reporters (ManCous) provided the necessary tools for these studies. Due to the effective competition with fructose for the uptake through GLUT5, we sought ManCous as convenient tools to explore the outcomes of inhibition of fructose uptake on cancer and the potential impact of such nutritional deprivation. We have made several observations that provides the basis for further progression in this research direction. We have found that ManCous, depending on the substitution, can serve either as GLUT5 inhibitors (ManCou Phenyl) or as inhibitors of GLUT5 and glycolysis (ManCou H). The latter was found to take place due to the effective inhiation of hexokinase II. With both type of probes, we observed a significant cytotoxic response in breast cancer cells (MCF7 and MDA-MB-231), with the magnitude of the response depending on the cell dependence on GLUT5 activity. We also found that ManCou-induced cytotoxicity contributes to the action of DNA alkylating chlorambucil, enhancing the IC50 three-fold in more aggressive MDA-MB-231 cells. The responses to the prolonged action of ManCou probes differed between the two cancer phenotypes. Namely, the more aggressive MDA-MB-231 cells were found to adapt to the action of ManCou H and recover by evading apoptosis through senescence. In contrast, mere inhibition of GLUT5 maintained the impact. We have also found that adaptations are linked with GLUT expression alterations and enhancement in glucose uptake to compensate for the induced nutritional deprivation. In a separate study, we assessed GLUT5 targeting for specific drug delivery to explore the feasibility of improving therapeutic outcomes of a bioactive agent through cancer-specific GLUT5-mediated delivery. Several glycoconjugates were synthesized to evaluate the role of conjugate size and hydrophobicity in maintaining GLUT5 mediate uptake long-term. We found that cancer-specific uptake is feasible with the hydrophilic substrates. We also found that enhanced hydrophobicity promoted alternative mechanisms of compound internalization with the loss of cancer-specific toxicity. The studies have provided substantial evidence for the feasibility of achieving cancer-specific bioactivity. Lastly, the translation of ManCou-based GLUT5 activity to flow setting for potential high-throughput applications has been explored. In the future, studies need to be undertaken to explore how ManCous sensitizes other cancer cell types and if the co-treatment is applicable to maintain irreversible impact in cancer cells long-term.
Ghosh, Avik, "EXPLORING GLUT5 TARGETING FOR CANCER DIAGNOSIS AND THERAPY", Campus Access Dissertation, Michigan Technological University, 2021.