Browsing by Author "Lewis, John"
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Item Revealing and attenuating the electrostatic properties of tubulin and microtubules(2020) Kalra, Aarat P.; Patel, Sahil D.; Winter, Philip; Wang, Hui; Carlson, Kris W.; Rezania, Vahid; Lewis, John; Meldrum, Al; Shankar, Karthik; Tuszynski, Jack A.Cancer treatment modalities such as chemotherapy and radiation therapy involve several side effects including an increased risk of getting cancer a second time. TTField (Tumour-treating field) therapy is a novel cancer-treatment modality that has attained U.S FDA approval for treatment of Glioblastoma Multiforme. TTFields are low intensity (1-2 V/cm), intermediate frequency (100-300 kHz) electric fields that have been shown to drastically lower tumor growth. While the only side-effects of TTField exposure are mild skin rashes, the exact mechanism of how TTFields act is not well understood. Models of TTFields posit that they target α, β- tubulin, a highly negatively charged (−50e), high dipole moment (∼1750 D) protein. Tubulin forms hollow cylindrical polymers termed microtubules, which form bundles that are crucial for mitosis and macromolecular transport. When exposed to TTFields, tubulin is expected to re-align and spatially relocate in response, inhibiting microtubule growth and interfering with mitosis. Using photolithography for microelectrode fabrication, we exposed unpolymerized tubulin containing solutions to AC electric fields and measured solution conductance. Interestingly, while we found that the presence of microtubules increased solution ionic conductance with a peak at TTField-like frequencies, the presence of unpolymerized tubulin reduced ionic conductance. Next, we used a parallel-plate electrode setup to compare the capacitance of solutions containing unpolymerized tubulin to those containing microtubules at identical physiological tubulin concentrations and ionic strengths. We found that while the presence of microtubules increased solution capacitance appreciably, the presence of unpolymerized tubulin did not. We are presently quantifying the chemical nature of the counterionic cloud around tubulin using a pH-sensitive fluorophore and Dynamic Light Scattering. Our results, in addition to displaying the significance of the tubulin polymerization state on the solution’ dielectric properties, also indicate that TTFields may target ion-tubulin interactions to inhibit tumour growth.Item Tubulin and microtubules as molecular targets for ttfield therapy(2019) Kalra, Aarat P.; Patel, Sahil D.; Bhuiyan, Asadullah; Rezania, Vahid; Lewis, John; Shankar, Karthik; Tuszynski, Jack A.TTField (Tumor-treating field) therapy utilizes low intensity intermediate frequency AC electric fields to reduce the spread of cancer. While it has attained FDA approval for the treatment of recurrent glioblastoma multiforme, the exact molecular targets of TTField therapy are not well understood. Microtubules are pipe-like polymers of the highly charged (–31 e) and strongly dipolar (dipole moment 1666 D) protein, α, β- tubulin. Studies on the electrical properties of microtubules have recently gained interest, with them being modelled as molecular targets of TTFields. Here, we experimentally show that while tubulin polymerized into microtubules leads to an increase in solution capacitance, unpolymerized tubulin has no appreciable effect. To the best of our knowledge, we present the first experimental quantification of the capacitance of a 20 μm-long microtubule. Using these results, we calculate the resonant frequency of a microtubule meshwork in a cell-like environment to be in the TTField regime. Our results utilize high ionic strength solutions and cell-like concentrations of tubulin to show the potential of microtubules as the targets of TTField action and as intracellular charge-storage devices. We conclude with a hypothesis of an electrically-tunable cell, where the dielectric properties of the cytoskeleton alter local and global charge storage and transport.