Design and interpretation of cell trajectory assays

Targeting cholesterol transport in circulating melanoma cells to inhibit metastasis

Despite recent breakthroughs in targeted- and immune-based therapies, rapid development of drug resistance remains a hurdle for the long-term treatment of patients with melanoma. Targeting metastatically spreading circulating tumor cells (CTCs) may provide an additional approach to manage melanoma. This study investigates whether targeting cholesterol transport in melanoma CTCs can retard metastasis development. Nanolipolee-007, the liposomal form of leelamine, reduced melanoma metastasis in both a novel in vitro flow system mimicking the circulating system and in experimental as well as spontaneous animal metastasis models, irrespective of the BRAF mutational status of the CTCs. Leelamine led to cholesterol trapping in lysosomes, which subsequently shut down receptor-mediated endocytosis, endosome trafficking, and inhibited the major oncogenic signaling cascades important for survival such as the AKT pathway. As pAKT is important in CTC survival, inhibition by targeting cholesterol metabolism led to apoptosis, suggesting this approach might be particularly effective for those CTCs having high levels of pAKT to aid survival in the circulation system.

Calculating the Fickian diffusivity for a lattice-based random walk with agents and obstacles of different shapes and sizes

Random walk models are often used to interpret experimental observations of the motion of biological cells and molecules. A key aim in applying a random walk model to mimic an in vitro experiment is to estimate the Fickian diffusivity (or Fickian diffusion coefficient), D. However, many in vivo experiments are complicated by the fact that the motion of cells and molecules is hindered by the presence of obstacles. Crowded transport processes have been modeled using repeated stochastic simulations in which a motile agent undergoes a random walk on a lattice that is populated by immobile obstacles. Early studies considered the most straightforward case in which the motile agent and the obstacles are the same size. More recent studies considered stochastic random walk simulations describing the motion of an agent through an environment populated by obstacles of different shapes and sizes. Here, we build on previous simulation studies by analyzing a general class of lattice-based random walk models with agents and obstacles of various shapes and sizes. Our analysis provides exact calculations of the Fickian diffusivity, allowing us to draw conclusions about the role of the size, shape and density of the obstacles, as well as examining the role of the size and shape of the motile agent. Since our analysis is exact, we calculate D directly without the need for random walk simulations. In summary, we find that the shape, size and density of obstacles has a major influence on the exact Fickian diffusivity. Furthermore, our results indicate that the difference in diffusivity for symmetric and asymmetric obstacles is significant.