Folinic acid is used to counteract methotrexate toxicity in cancer patients. But why exactly doesn't it counteract methotrexate's therapeutic effects? Why doesn't this "leucovorin rescue" make tumors grow?
I found this explanation:
because the cancer cells have decreased function of the Reduced folate carrier, LEUCOVORIN can be used to rescue the normal cells following administration of the extremely high doses of methotrexate needed to kill the resistant cancer/bacterial cells.
Basically, folinic acid gets more into healthy cells, which have RFC on them, while it does not get as much into cancerous cells, which have less RFC on them, according to this webpage. Subsequently, cancerous cells die off.
I did not manage to find a corroboration of this explanation in Google Books or in scientific reviews though. Is this explanation correct and up-to-date? If so, I would be grateful for references. If not, I would be interested to know the current state of understanding of this issue.
(I was reading about Cerebral folate deficiency and decided to investigate the mechanisms of folate metabolism and treatment).