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Novel photodynamic effects of a benzophenothiazine on two different murine sarcomas
L Cincotta1, J W Foley, T MacEachern
1Rowland Institute for Science, Cambridge, Massachusetts 02142.
Abstract:
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)
Insights
This study shows a novel benzophenothiazine dye effectively kills cancer cells using photodynamic therapy (PDT). The dye demonstrates selective tumor targeting and minimal damage to surrounding tissues, suggesting its potential for cancer treatment.
Area of Science:
- Biochemistry
- Oncology
- Photomedicine
Background:
- Benzophenothiazine derivatives are investigated for photochemotherapeutic applications.
- Photodynamic therapy (PDT) utilizes photosensitizing agents and light to induce cell death.
Purpose of the Study:
- To evaluate the in vitro and in vivo efficacy of a novel benzophenothiazine, 5-ethylamino-9-diethylaminobenzo[a]phenothiazinium chloride, as a photosensitizer for PDT.
- To assess the dye's tumor-targeting capabilities and its differential effects on tumor versus normal tissues.
Main Methods:
- In vitro PDT assays on murine mammary sarcoma cell lines (EMT-6 and RIF).
- In vivo studies using EMT-6 and RIF tumor models in mice, assessing dye uptake, biodistribution, and therapeutic outcomes.
- Histological analysis of tumor and surrounding tissues post-PDT.
Main Results:
- PDT with the benzophenothiazine dye achieved significant cancer cell killing in vitro (87.0% for EMT-6, 99.6% for RIF).
- In vivo, the dye exhibited preferential accumulation in EMT-6 tumors compared to RIF tumors and surrounding tissues (skin, muscle).
- Optimized PDT parameters (fluence rate, light dose) led to complete tumor cures (100% for EMT-6, 70% for RIF) with minimal damage to normal tissues.
Conclusions:
- The novel benzophenothiazine derivative shows potent photodynamic activity against murine mammary sarcomas.
- The dye's differential uptake and retention in tumors, coupled with its redox properties, contribute to a selective anti-tumor effect.
- This compound holds promise as a photosensitizer for targeted cancer therapy with reduced side effects.