Pteridine and riboflavin in tumor tissue and the effect of chloramphenicol and isoxanthopterin.

Human squamous cell carcinoma has elevated levels of tetrahydrobiopterin. As the level of riboflavin is low, the ratio tetrahydrobiopterin/riboflavin shows values of 5 — 8.3. In contrast, in differentiated tissues with high metabolic activity but low mitotic rate, like submaxillary glands, elevated levels of tetrahydrobiopterin are accompanied by high content of riboflavin. Thus the ratio tetrahydrobiopterin/riboflavin in kept as low as about 0.5. Chloramphenicol and, in particular, isoxanthopterin reduce tumor growth in rats and prevent tetrahydrobiopterin accumulation as well.