By taking into account that Gch1 is a rate-limiting enzyme in BH4 production by Spr gene-encoded enzyme, that is, sepiapetrin reductase (45), it can be concluded that Gch1-Spr gene expression axis might be targeted in 96 h-SPS–treated tumor, but not in RPMI group, when the expression of Gch1 and Spr genes in these groups was compared with normal saline reference group. Here, GCH1 is linked to neoplasm.