Biodistribution studies were carried out on 14C-labeled benzoporphyrin derivative monoacid ring A (BPD), which had been formulated as a unilamellar liposome or taken from a stock solution in dimethyl sulfoxide diluted into phosphate-buffered saline immediately before intravenous injection into DBA/2 mice. By and large the general distribution of BPD to various organs and tissues was comparable for both formulations. It was noted, however, that liposomal material appeared to enter tissues more rapidly and to be cleared more rapidly, as demonstrated by shorter half-lives for a number of tissues including skin, lung and fat, and generally lower levels in most tissues 24 h following administration. Accumulation in tumor tissue was slightly higher with liposomal BPD, and clearance rates for this tissue were equivalent (half-lives 16.1 h for liposomal BPD and 16.9 h for aqueous BPD). When the two preparations were tested in a bioassay in tumor-bearing mice, photodynamic therapy (PDT) with liposomal BPD proved to be superior to the aqueous preparation when PDT was administered 3 h following intravenous administration of BPD. Plasma distribution studies in vitro demonstrated that 91.1 +/- 0.3% of the liposomal BPD distributed to the lipoprotein fraction within the first hour of mixing, whereas only 49.1 +/- 2.6% of nonliposomal BPD was associated with lipoprotein under the same conditions. Furthermore, while lipoprotein-associated liposomal BPD distributed evenly between all three types of lipoprotein (high, low and very low density), a majority of nonliposomal BPD associated with the high-density lipoprotein fraction.

Benzoporphyrin derivative monoacid ring A (BPD), a hydrophobic chlorin-like porphyrin derivative, which fluoresces strongly at 690 nm, may have potential for both oncologic and nononcologic applications in photodynamic therapy (PDT). To study the influence of cellular characteristics on the uptake of BPD, the murine tumor cell line (P815), and in vitro and in vivo concanavalin A (Con A) -stimulated and unstimulated murine splenic lymphocytes were incubated with 2 micrograms/mL BPD at 37 degrees C for 0-60 min. At various times, cells were lysed and the amount of BPD taken up by cells was quantified by fluorescence measurements. The subsets of cells taking up BPD were analyzed using a panel of monoclonal antibodies and the Coulter XL fluorescence-activated cell sorter. Furthermore, Con A-stimulated and unstimulated spleen cells were incubated with 0-50 ng/mliter of BPD for 1 h prior to exposure to red light (7.2 J/cm2). Cell survival 24 h post-PDT was measured by the MTT assay. We found that the rapidly dividing tumor cell line and mitogen-stimulated murine T cells (mainly CD4+/IL-2R+) took up significantly more BPD (5-10-fold) than do unstimulated splenic lymphocytes. Increased BPD uptake correlated with greater photoinactivation when these cells were exposed to light at a wavelength of 690 nm. These findings suggest that activated cells of the immune system may be a target for photoinactivation by BPD.

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In vitro experiments with benzoporphyrin derivative monoacid ring A (BPD) confirmed earlier studies that it was taken up rapidly (within 30 min) to maximum concentrations by all cells tested. It was also confirmed that rapidly dividing tumor cell lines and mitogen-activated murine T lymphocytes took up significantly more (5-10-fold) BPD than did normal splenic lymphocytes. Further experiments were undertaken to determine whether BPD could be activated by whole-body irradiation with red light in the blood of animals, shortly after intravenous (i.v.) administration, in the absence of skin photosensitivity. It was found that shaved and depilated mice injected i.v. 60 min earlier with BPD at between 0.5 and 1.0 mg/kg could tolerate 160 J/cm2 of broad-band red light (560-900 nm) delivered, at a relatively low rate, over a 90 min time interval without developing skin photosensitivity or general phototoxicity. During the treatment time, plasma levels of BPD were between 0.7 and 1.0 micrograms/mL. The light treatment resulted in between 70 and 80% photoinactivation of circulating BPD. When L1210 tumor cells were preincubated with BPD and injected i.v. into mice immediately before total-body light treatment (160 J/cm2 of 590-900 nm light delivered over 90 min), significant reductions in circulating clonogenic tumor cells were observed in blood samples taken immediately following treatment. This indicated that sufficient light was being delivered to BPD in the blood flowing in the peripheral vasculature to effect cytotoxicity to cells containing the photosensitizer without causing either vascular or skin photosensitivity.(ABSTRACT TRUNCATED AT 250 WORDS)

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