- Joined
- Feb 20, 2021
This reminds me of something interesting. There's a family of chemotherapy drugs called multitargeted receptor tyrosine kinase inhibitors, which are designed to target specific genes expressed by some cancer cells. This class of medications is known for occasionally causing distinctive loss of pigmentation of the hair. Contrary to what people are taught in junior high biology class, hair color is really complicated. It's regulated by the complex interplay of the proteins encoded by multiple genes. One of these is c-KIT, which encodes a receptor tyrosine kinase protein called tyrosine-protein kinase KIT, or CD 117. This protein binds to another (called its ligand) called the stem cell factor, which is a cytokine that regulates cell growth. This is what makes c-KIT so attractive as a chemotherapy drug target. KIT is expressed in multiple cell types, including bone marrow progenitor cells, germ cells (the cells that become sperm or eggs), mast cells (a type of white blood cell), and melanoblasts (immature skin pigment cells). Stem cell factor is expressed in areas where the KIT-expressing cells need to go - basically, SCF is like a waypoint that helps certain types of cell to get to where they need to be.
So, you have a receptor tyrosine kinase protein that binds to another protein to make cells, including pigment cells, go to the right place. Remember how these drugs work? They inhibit receptor tyrosine kinases, preventing them from binding to their ligand. One result is that the pigmented cells never make it to the hair.
What's really neat is that there are reports of "periodic" hair depigmentation, which means that the hair shows a "striped" pattern of pigmentation loss which corresponds to the dosing schedule of the chemotherapy (usually 4 weeks on, 2 weeks off). Some papers describe the depigmentation as "greying", but having seen it in person, it is really distinctive and looks like complete color loss.
Here's a photo of the "periodic" pattern, taken from the NEJM paper linked previously. I personally think it looks bad ass:
Also interesting is that there are a handful of reports of people whose previously grey hair regains its pigmentation during treatment with one of these drugs.
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