PFK inhibition test for cancer detection: clinical applications and mechanisms of PFK inhibition.

A newly established cancer marker, the PFK inhibition test, has been further examined for its capacity to detect malignant neoplasms irrespective of the organs in which cancer cells start proliferating. We tested 1,160 sera from cancer patients and compared them with 756 normal sera, using histograms and normal paper for analysis of accumulated frequency. PFK activity through the influence of normal sera showed normal distribution, and cancerous sera shifted to the inhibitory site with an irregular shape. From these analyses, the patients were classified into the following types: normal range: PFK greater than SD (standard deviation of PFK activity in normal sera); suspicious range: SD greater than PFK greater than 2SD, must be given the PFK test again; and dangerous range: PFK less than 2SD, further examination must be carried out to detect cancer. Fifty percent of the sera from all the cancer patients inhibited PFK beyond 2 SD of normal sera. We also analyzed organ-associated PFK distribution, eg, gastric, colorectal, and mammary cancer. In gastric cancer, PFK inhibition was stronger in accordance with how far a particular stage of cancer had progressed. However, 50% of sera from stage I gastric cancer patients was positive beyond the cut-off line of 2 SD. We examined 104 sera from patients diagnosed as benign prostatic hypertrophy and found malignant cells in 10 patients whose sera tended to be positive in PFK inhibition. The PFK inhibitory factor in the body fluids of cancer patients was fractionated by Sephadex G-75 gel filtration and DEAE ion exchange chromatography. The approximate molecular weight of this factor was 13,000 daltons. The factor was resistant to heat and acid (0.1 N HCl and H2SO4) and was sensitive to 0.1 N NaOH and phosphate buffer. Diluted sulfuric acid and ammonium sulfate made an inactive NaOH-treated sample active when lyophilized following dialysis against distilled water. PFK inhibition by cancerous sera was eliminated by fructose-2,6-bisphosphate (the strongest activator of PFK) in a dose-dependent manner. PFK attached to agarose beads was found to be reversible even after being inhibited by cancerous body fluids and ATP water solution. Although PFK is apt to decay in a low pH range, the established procedure did not destroy PFK, but induced a direct inhibition of PFK by ATP through the ATP inhibition site on the PFK molecule. The PFK inhibitor may possibly function as a proton carrier and release protons to activate the ATP inhibition site.(ABSTRACT TRUNCATED AT 400 WORDS)