SILICON PHTHALOCYANINE PC-4 AND RED-LIGHT CAUSES APOPTOSIS IN HIV-INFECTED CELLS

The silicon phthalocyanine HOSiPcOSi(CH3)(2)(CH2)(3) N(CH3)(2) (Pc 4), is being studied as a photosensitizer for virus inactivation in red b lood cell concentrates (RBCC), The RBCC spiked with cell-free human im munodeficiency virus (HIV) or with HIV actively replicating in the T-l ymphocytic cell line CEM can be successfully inactivated (greater than or equal to 6 log(10)) when exposed to 2 mu M Pc 4 and 90 J/cm(2) red light (600-800 nm), Inactivation of greater than or equal to 6 log(10 ) inducible HIV in the latently infected promonocytic cell line U1 occ urred at 22.5 J/cm(2) (H. Margolis-Nunno et al., Transfusion 36, 743-7 50, 1996), In order to understand the reason for the increased suscept ibility of U1 to photosensitized inactivation we looked for induction of apoptosis by photodynamic treatment (PDT), Agarose gel electrophore sis was used to observe the appearance of a characteristic 180-200 bas e pair DNA ladder, which can indicate apoptosis, Using this assay it i s shown that Pc 4 treatment induced apoptosis in U1 cells in a light d ose-dependent manner, starting 30 min after light exposure, Using the ApopTag(TM) Plus kit (which attaches a fluorescent label to the 3'-OH ends of the degraded DNA) and flow cytometry, the percentage of cells undergoing apoptosis was quantitated, At 10.5 J/cm(2), 3 h after light exposure, about 92.5% of the cells were apoptotic, Under these condit ions 99% of the cells eventually die, The CEM cells similarly treated underwent apoptosis at slower kinetics and required higher light doses , Other cell lines latently infected with HIV (ACH-2 and OM 10.1) were as sensitive as U1 to HIV inactivation by Pc 4-PDT (H. Margolis-Nunno et al., Transfusion 36, 743-750, 1996) and underwent apoptosis at a s imilar kinetic, These results suggest that the enhanced inactivation o f HIV in latently infected cells compared to CEM cells by Pc 4-PDT may be due, at least in part, to apoptosis in the former.