Microtubule Targeting Agents in Disease: Classic Drugs, Novel Roles

SIMPLE SUMMARY: Microtubules (MTs) are highly conserved proteins present in all eukaryotic organisms. They form the cell cytoskeleton, and its function is essential for a large number of biological processes. Drugs against MTs (i.e., microtubule-targeting agents or MTAs) have been used for centuries to treat arthritis and gout. In the last 100 years, new MTAs either isolated from natural sources or synthesized in labs have been used to treat a great variety of human illnesses, from cancer and neurodegenerative diseases to the elimination of parasites. In this review, we analyze how MTAs bind to MTs, and the molecular mechanisms behind MTAs function, and we describe the last and novel roles of these drugs. ABSTRACT: Microtubule-targeting agents (MTAs) represent one of the most successful first-line therapies prescribed for cancer treatment. They interfere with microtubule (MT) dynamics by either stabilizing or destabilizing MTs, and in culture, they are believed to kill cells via apoptosis after eliciting mitotic arrest, among other mechanisms. This classical view of MTA therapies persisted for many years. However, the limited success of drugs specifically targeting mitotic proteins, and the slow growing rate of most human tumors forces a reevaluation of the mechanism of action of MTAs. Studies from the last decade suggest that the killing efficiency of MTAs arises from a combination of interphase and mitotic effects. Moreover, MTs have also been implicated in other therapeutically relevant activities, such as decreasing angiogenesis, blocking cell migration, reducing metastasis, and activating innate immunity to promote proinflammatory responses. Two key problems associated with MTA therapy are acquired drug resistance and systemic toxicity. Accordingly, novel and effective MTAs are being designed with an eye toward reducing toxicity without compromising efficacy or promoting resistance. Here, we will review the mechanism of action of MTAs, the signaling pathways they affect, their impact on cancer and other illnesses, and the promising new therapeutic applications of these classic drugs.