Vitamin B6 and cancer: a novel pyridoxal 5-phosphate conjugate in tumor cells and blood of cancer patients.

Studies on the metabolic transformations of labeled pyridoxine showed that its utilization by tumor animals and tumor cells differs greatly from that seen in control animals. When [3,4-14C] and/or tritium labeled pyridoxine at the 6th ring carbon is administered i.p. to tumor-bearing animals and its fate is subsequently determined at different time intervals (using HPLC separation of the labeled metabolites following acid extraction from tissues), in addition to other differences, synthesis of a novel labeled product occurs which begins with the onset of tumor growth. It is either absent or present only at minimal levels in normal animals and regenerating rat liver. It is present in all tumor sources examined to date, i.e. serum of tumor rats, a spectrum of rat hepatomas, solid human tumors, tumor cells in culture and plasma of cancer patients. The novel product is a conjugate of pyridoxal 5'-phosphate with the structure Adenosine-N6-Diethylthioether-N1- Pyridoximine-5'-phosphate. This communication reports on the occurrence and distribution of the novel product in different tumor tissues and cells as well as the blood of cancer patients with active disease and in remission, and in normal volunteers. The results show significantly higher levels of this product in the blood of patients with different malignancies and in the active state. The novel vitamin B6 compound may be a good candidate as a marker for tumor presence and/or metastasis.