PNP and cancer: Among the recently used drugs, we can mention pralatrexate (folate analogue) which has a greater activity than methotrexate thanks to its greater affinity for reduced folate carrier 1, which allows a greater accumulation in cancer cells, and forodesine which is a potent inhibitor of purine nucleoside phosphorylases (PNP) that causes apoptosis in neoplastic T cells and normal T lymphocytes, sparing other lymphocyte populations [81] (Table 4).