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Positron emission tomography (PET) using 2-deoxy-2-[18 F]fluoro-d-glucose ([18 F]FDG), a marker of energy metabolism and cell proliferation, is routinely used in the clinic to assess patient response to chemotherapy and to monitor tumor growth. Treatment with some tyrosine kinase inhibitors (TKIs) causes changes in blood glucose levels in both nondiabetic and diabetic patients. We evaluated the interaction of several classes of TKIs with human glucose transporter-1 (hGLUT-1) in FaDu and GIST-1 cells by measuring [3 H]2-deoxy-d-glucose ([3 H]2-DG) and [3 H]FDG uptake. Uptake of both was inhibited to varying extents by the TKIs, and representative TKIs from each class showed competitive inhibition of [3 H]2-DG uptake. In GIST-1 cells, [3 H]FDG uptake inhibition by temsirolimus and nilotinib was irreversible, whereas inhibition by imatinib, gefitinib, and pazopanib was reversible. Molecular modeling studies showed that TKIs form multiple hydrogen bonds with polar residues of the sugar binding site (i.e., Q161, Q282, Q283, N288, N317, and W388), and van der Waals interactions with the H-pocket site. Our results showed interaction of TKIs with amino acid residues at the glucose binding site to inhibit glucose uptake by hGLUT-1. We hypothesize that inhibition of hGLUT-1 by TKIs could alter glucose levels in patients treated with TKIs, leading to hypoglycemia and fatigue, although further studies are required to evaluate roles of other SLC2 and SLC5 members. In addition, TKIs could affect tumor [18 F]FDG uptake, increasingly used as a marker of tumor response. The hGLUT-1 inhibition by TKIs may have implications for routine [18 F]FDG-PET monitoring of tumor response in patients.

Tubulin is an electrostatically negative protein that forms cylindrical polymers termed microtubules, which are crucial for a variety of intracellular roles. Exploiting the electrostatic behavior of tubulin and microtubules within functional microfluidic and optoelectronic devices is limited due to the lack of understanding of tubulin behavior as a function of solvent composition. This work displays the tunability of tubulin surface charge using dimethyl sulfoxide (DMSO) for the first time. Increasing the DMSO volume fractions leads to the lowering of tubulin's negative surface charge, eventually causing it to become positive in solutions >80% DMSO. As determined by electrophoretic mobility measurements, this change in surface charge is directionally reversible, i.e., permitting control between -1.5 and + 0.2 cm2 (V s)-1 . When usually negative microtubules are exposed to these conditions, the positively charged tubulin forms tubulin sheets and aggregates, as revealed by an electrophoretic transport assay. Fluorescence-based experiments also indicate that tubulin sheets and aggregates colocalize with negatively charged g-C3 N4 sheets while microtubules do not, further verifying the presence of a positive surface charge. This study illustrates that tubulin and its polymers, in addition to being mechanically robust, are also electrically tunable.

The binding free energies on human tubulin of selected colchicine and thiocolchicine compounds were determined. Two methods were used for the determination of binding free energies: one is based on theoretical prediction simulating the dissociation of the compound from tubulin using a series of molecular dynamics simulations, and the other method involves a series of experiments that measured the affinity of the compound on a synthetically expressed and purified tubulin protein using a spectrofluorometric technique.

Microtubules are the primary target for many anti-cancer drugs, the majority of which bind specifically to beta-tubulin. The existence of several beta-tubulin isotypes, coupled with their varied expression in normal and cancerous cells provides a platform upon which to construct selective chemotherapeutic agents. We have examined five prevalent human beta-tubulin isotypes and identified the colchicine-binding site as the most promising for drug design based on specificity. Using this binding site as a template, we have designed several colchicine derivatives and computationally probed them for affinity to the beta-tubulin isotypes. These compounds were synthesized and subjected to cytotoxicity assays to determine their effectiveness against several cancerous cell lines. We observed a correlation between computational-binding predictions and experimentally determined IC(50) values, demonstrating the utility of computational screening in the design of more effective colchicine derivatives. The most promising derivative exhibited an IC(50) approximately threefold lower than values previously reported for either colchicine or paclitaxel, demonstrating the utility of computational design and assessment of binding to tubulin.