Mechanical aspects of microtubule bundling in taxane-treated circulating tumor cells.

Microtubules play an important role in many cellular processes, including mitotic spindle formation and cell division. Taxane-based anticancer treatments lead to the stabilization of microtubules, thus preventing the uncontrolled proliferation of tumor cells. One of the striking physical features of taxane-treated cells is the localization of their microtubules, which can be observed via fluorescent microscopy as an intense fluorescent band and are referred to as a microtubule bundle. With the recent advances in capturing and analyzing tumor cells circulating in a patient's blood system, there is increasing interest in using these cells to examine a patient's response to treatment. This includes taxanes that are used routinely in clinics to treat prostate, breast, lung, and other cancers. Here, we have used a computational model of microtubule mechanics to investigate self-arrangement patterns of stabilized microtubules, which allowed for the identification of specific combinations of three physical parameters: microtubule stiffness, intracellular viscosity, and cell shape, that can prevent the formation of microtubule bundles in cells with stabilized microtubules, such as taxane-treated cells. We also developed a method to quantify bundling in the whole microtubule aster structure and a way to compare the simulated results to fluorescent images from experimental data. Moreover, we investigated microtubule rearrangement in both suspended and attached cells and showed that the observed final microtubule patterns depend on the experimental protocol. The results from our computational studies can explain the heterogeneous bundling phenomena observed via fluorescent immunostaining from a mechanical point of view without relying on heterogeneous cellular responses to the microtubule-stabilizing drug.