Abstract
Propolis has been known to include couples of bioactive substances that inhibit growth of tumor cells. Among them, a plant flavonoid quercetin (QU) specifically antagonized proliferating rat C6 Glioma cells at a micoromolar concentration range, while QU left C6 cells intact when arrested at the G0/G1 phase of the cell cycle. Thus, QU seems to be a promising candidate for cancer chemotherapy. However, QU has been known to bind with serum albumin after being absorbed from digestive tract. This interaction with albumin makes effects of QU less predictable and may modulate biological actions of other drugs. To clarify binding property of QU with albumin, we have set off kinetic analysis of quercetin-albumin interaction with a BIACORE instrument, that is based on a surface plasmon resonance. It was found that QU binds to bovine serum albumin (BSA) with two different kinetics; fast and slow association mechanisms were recognized. The maximum binding of the slow component was highly dependent on temperature, being largest at a body temperature. The dissociation constant for a quercetin-albumin interaction is in submicoromolar range. Thus, almost all of QU in blood stream is likely bound to serum albumin, For an efficient and predictable chemotherapy, QU must be modified to avoid any interaction with serum albumin. [J Physiol Sci. 2007;57 Suppl:S178]
