Targeting of GLUT5 for Transporter-Mediated Drug-Delivery Is Contingent upon Substrate Hydrophilicity

Abstract

Specific link between high fructose uptake and cancer development and progression highlighted fructose transporters as potential means to achieve GLUT-mediated discrimination between normal and cancer cells. The gained expression of fructose-specific transporter GLUT5 in various cancers offers a possibility for developing cancer-specific imaging and bioactive agents. Herein, we explore the feasibility of delivering a bioactive agent through cancer-relevant fructose-specific transporter GLUT5. We employed specific targeting of GLUT5 by 2,5-anhydro-D-mannitol and investigated several drug conjugates for their ability to induce cancer-specific cytotoxicity. The proof-of-concept analysis was carried out for conjugates of chlorambucil (CLB) in GLUT5-positive breast cancer cells and normal breast cells. The cytotoxicity of conjugates was assessed over 24 h and 48 h, and significant dependence between cancer-selectivity and conjugate size was observed. The differences were found to relate to the loss of GLUT5-mediated uptake upon increased conjugate size and hydrophobicity. The findings provide information on the substrate tolerance of GLUT5 and highlight the importance of maintaining appropriate hydrophilicity for GLUT-mediated delivery.

Transporter-Mediated Drug Delivery

“…In terms of the exploitation of individual transporters, the lack of specific binders to transporters with similar substrate specificity can be a bottleneck [74], and their development would enable the generation of more advanced drug delivery systems. Once specific binders are available, dual targeting can also be an interesting approach, especially when targeting heterogenous cell populations such as in tumors [26,125].…”

“…For example, GLUT5 shows a 5-fold and 17-fold higher protein expression in MCF7 and MDA-MB-231 breast cancer cell lines, respectively, than in the 184B5 non-cancerous breast cell line [74]. However, the lack of specific binders to these transporters has hindered the development of therapeutics that can utilize these proteins [74]. For the case of GLUT5, fluorescently labeled glycoconjugates (2,5-anhydro-D-mannitol-coumarines) have shown high affinity and specificity of binding [75,76].…”

“…These prodrugs showed selective uptake into the GLUT5-expressing MCF7 breast cancer cell line compared to the 184B5 non-cancerous mammary tissue cell line, which competed with the uptake of previously used fluorescent probes, showing a GLUT5-dependent uptake mechanism. All but one of the synthesized prodrugs also showed a cytotoxic effect [74].…”

“…The high or specific expression of other glucose transporters such as GLUT2/SLC2A2, GLUT3/SLC2A3, GLUT12/SLC2A12 or the fructose transporter GLUT5/SLC2A5 has also been associated with various cancer types and stages [70][71][72][73]. For example, GLUT5 shows a 5-fold and 17-fold higher protein expression in MCF7 and MDA-MB-231 breast cancer cell lines, respectively, than in the 184B5 non-cancerous breast cell line [74]. However, the lack of specific binders to these transporters has hindered the development of therapeutics that can utilize these proteins [74].…”

“…For the case of GLUT5, fluorescently labeled glycoconjugates (2,5-anhydro-D-mannitol-coumarines) have shown high affinity and specificity of binding [75,76]. Based on these results, either mannitol directly, or mannitol-coumarin were chemically conjugated with chlorambucil, an anticancer agent [74]. These prodrugs showed selective uptake into the GLUT5-expressing MCF7 breast cancer cell line compared to the 184B5 non-cancerous mammary tissue cell line, which competed with the uptake of previously used fluorescent probes, showing a GLUT5-dependent uptake mechanism.…”