GROWTH-PHASE-DEPENDENT BINDING OF HEMATOPORPHYRIN DERIVATIVE TO HUMANGLIOBLASTOMA (U-87MG) CELLS

Studies on the binding of hematoporphyrin derivative (HpD) to asynchro nous and synchronized human glioblastoma (U-87MG) cells were performed using fluorescence spectroscopy. Cell-bound HpD exhibited three fluor escence bands. The intensity distribution of fluorescence spectrum was found to be dependent on the growth phase of cells. The relative inte nsity of 636 nm band increased as the cells progressed through the gro wth curve. A more distinct change was observed when the fluorescence s pectrum of Hpd bound to M-phase cells was compared with G1-phase cells . M-phase cells exhibited maximum fluorescence emission at 615 nm, wit h a small shoulder at 636 nm whereas in G1-phase cells the 636 nm fluo rescence band showed enhancement. HpD binding to synchronized cells wa s also studied during the cell division cycle. A clear variation in th e intensity ratio of 636 to 615 nm fluorescence bands was observed alo ng the cell division cycle. This intensity ratio was maximum in mid G1 and early G2 phases of growth, whereas a minimum was observed in mid S phase. The photosensitivity of asynchronous as well as synchronized cells was determined under above-mentioned experimental conditions. Th e photosensitivity also varied with the growth phase of the cells. A g ood correlation was found between the photosensitivity and the fluores cence intensity distribution of cell-bound HpD.