Increased plasma proteasome chymotrypsin-like activity in patients with advanced solid tumors

The chymotrypsin-like (ChT-L) activity is one of the key regulators of intracellular protein degradation. Elevated proteasome ChT-L activity has recently been reported in plasma of patients with leukemia and myelodysplastic syndrome and suggested to have a prognostic significance. The aim of the present study was to evaluate plasma proteasome ChT-L activity in patients with newly diagnosed solid tumors at early and advanced stages of the disease. The activity was assayed using the fluorogenic peptide substrate, Suc-Leu-Leu-Val-Tyr-AMC, in a cohort of 155 patients with early/advanced rectal ( n = 43/29), gastric ( n = 6/13), and breast ( n = 37/27) cancer and compared with that in normal individuals ( n = 55). The median plasma proteasome ChT-L activity was elevated by 20–32% in patients with advanced stage of rectal, gastric, and breast cancer compared with healthy donors. The difference turned out to be statistically significant ( P