Wikipedia
Photostatins are inhibitors that can be switched on and off in vivo by visible light, to optically control microtubule dynamics. Photostatins are a form of photodynamic therapy.
As a cell prepares to divide, its microtubules, arrange themselves into a spindle that permits its chromosomes to split into two bundles. These bundles become the nuclei of the daughter cells, Out-of-control cell replication is the underlying cause of cancer, developing drugs that interfere with microtubule activity offers one potential therapeutic approach. They can operate microtubule dynamics with a subsecond response time and control mitosis in living organisms with single-cell spatial precision.
Most microtubule inhibitors affect both cancerous and healthy cells, requiring lower doses to avoid severe side effects. Because photostatins are inactive in the absence of light, they only affect cells that are illuminated. Focusing light on tumors directs their activities to appropriate targets with fewer side effects.