The photochemotherapeutic properties of a novel
benzophenothiazine, 5-ethylamino-9-diethylaminobenzo[a]phenothiazinium
chloride, were assessed in vitro and in vivo against two murine mammary
sarcoma models (EMT-6 and RIF).
Photodynamic therapy (
PDT) of EMT-6 and RIF cells following a 30-min incubation with
dye (0.4 microgram/ml) and a light dose of 3.3 J/cm2 killed 87.0 and 99.6% of the cells, respectively. Over this same time period, RIF cells accumulate more than twice the amount of
dye than the EMT-6 cell line [7.54 +/- 0.17 (SD) versus 3.11 +/- 0.15 nmol/10(6) cells] which probably accounts for their increased sensitivity to
PDT. Conversely, in vivo, the EMT-6
tumor accumulates 3 times more
dye (34.66 +/- 2.16 micrograms/g dry weight) than the RIF
tumor (12.28 +/- 1.27 micrograms of
dye/g) 3 h post-s.c. injection of
dye (15 mg/kg). A study of the concentration dependent uptake of
dye (following s.c. injection) in the
tumor and plasma of mice bearing the EMT-6
tumor indicated a nonlinear relationship for both compartments. Maximum tissue uptake of
dye and discrimination between
tumor and skin or muscle occur 3-8 h following s.c. injection of
dye. The ratios of
dye in the
tumor to the
dye in surrounding skin and gastrocnemius muscle 8 h following
dye injection were 4:1 and 8:1, respectively. At 24 h after
dye injection, the
dye was not detectable by absorption spectroscopy in the
tumor, skin, or muscle. Decreasing the fluence rate from 200 to 50 mW/cm2 at a total light dose of 100 J/cm2 optimized the
PDT effect. At 3 h following s.c. administration of
dye,
PDT of EMT-6 (7.5 mg of
dye/kg; 50 mW/cm2; 100 J/cm2) and RIF
tumors (15 mg
dye/kg; 50 mW/cm2; 150 J/cm2) resulted in 100 and 70% cures, respectively. Histology at 24 and 72 h post-
PDT showed minimal or no damage to the surrounding tissue (skin) while 70-90% of the
tumor cells were destroyed or damaged. Moreover, 50-60% of the
tumor cells isolated and cultured immediately following
PDT were found to be nonviable. Similarly, the administration of 60 mg 5-ethylamino-9-diethylaminobenzo[a]phenothiazinium
chloride/kg also resulted in no damage to the skin 24 h following
PDT. It is suggested that the redox properties of the
dye coupled with the differing metabolic states of the
tumor and skin, which increase the amount of photoactive, oxidized
dye present in the
tumor and decrease it in the skin, are responsible for this unique differential
PDT effect.(ABSTRACT TRUNCATED AT 400 WORDS)