Response of Photofrin-sensitised mesothelioma xenografts to photodynamic therapy with 514 nm light

Our plain-English summary of Response of Photofrin-sensitised mesothelioma xenografts to photodynamic therapy with 514 nm light, by T.H. Foster, S.L. Gibson, R.F. Raubertas (British Journal of Cancer, 1996).

The study

• Authors: T.H. Foster, S.L. Gibson, R.F. Raubertas
• Journal: British Journal of Cancer
• Published: 1996;73(8):933-6
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

We have studied the response of human mesothelioma xenografts in nude mice to Photofrin-sensitised photodynamic therapy with 514 nm light. Delays in tumour regrowth following four different 514 nm irradiation regimens were compared with results obtained with the more commonly used 630 nm light. One of these 514 nm regimens, which consisted of 1 h of irradiation at an incident fluence rate of 20 mW cm-2 and a second hour at a fluence rate of 28 mW cm-2, produced tumour volume doubling times that were statistically indistinguishable from results that were observed when tumours were irradiated for 2 h with 630 nm light at an incident fluence rate of 50 mW cm-2. The three other 514 nm light protocols tested were found to be less effective than the 630 nm regimen. The 514 nm treatment protocols were devised on the basis of attempts to equate the photodynamic dose and the dose rate at these two wavelengths, with photodynamic dose defined as the number of photons absorbed by the sensitiser. Photosensitiser extinction coefficients, photon energies and tissue optical properties were considered in these attempts. Our results indicate that, under certain conditions, photodynamic therapy performed with 514 nm light can provide tumour control that is similar to that achieved with 630 nm, with potential for diminished normal tissue damage.

In plain English

This animal experiment did not study asbestos exposure or patients. The authors grew human mesothelioma tumours under the skin of nude mice and gave them the light-sensitising drug Photofrin. A day later, green laser light (514 nm) was shone on the tumours for 2 hours using four intensity schedules. The authors measured days until each tumour doubled in size and compared results with red light (630 nm), partly from earlier published data. All treatments delayed regrowth compared with untreated tumours. A stepped schedule (20 mW/cm2 for one hour, then 28 mW/cm2) gave a median doubling time of 72 days in 11 tumours (95% confidence interval 27 days to no upper limit). This could not be distinguished statistically from red light (median 100 days, interval 54 days to no upper limit, 16 tumours). The other three green schedules did significantly worse than red light: medians of 18 days (14 to 70), 25 days (18 to 36) and 20 days (16 to 38). The authors concluded that, under certain conditions, green light can give tumour control similar to red light.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Animal experiment (human tumour xenografts in mice) comparing photodynamic therapy light regimens
• Who was studied: Athymic nude mice carrying transplanted human mesothelioma tumours grown from H-MESO-1 cells, University of Rochester, USA. Tumour counts: untreated controls 21; red light 630 nm 16; green light 514 nm at 20 mW/cm2 19, at 28 mW/cm2 11, stepped 20 then 28 mW/cm2 11, stepped 20 then 40 mW/cm2 10.
• Exposure: No asbestos exposure was studied. The treatment was Photofrin 5 mg/kg given into the abdomen. Twenty-four hours later the tumours received 2 hours of 514 nm argon-ion laser light at 20 or 28 mW/cm2 continuously, or 20 mW/cm2 for 1 hour followed by 28 or 40 mW/cm2 for 1 hour. The comparison was 630 nm light at 50 mW/cm2 for 2 hours.
• Main results:
  • All treatment regimens delayed tumour volume doubling compared with untreated controls (P<0.001). Untreated controls had a median doubling time of 3 days (95% CI 2 to 4).
  • Among the green-light schedules, the stepped 20:28 schedule had the longest median doubling time: 72 days (95% CI 27 days to no upper limit), with 7 of 11 tumours doubling. The other schedules were 20 mW/cm2 at 18 days (95% CI 14 to 70; 14 of 19 doubled), 28 mW/cm2 at 25 days (95% CI 18 to 36; 11 of 11 doubled), and 20:40 at 20 days (95% CI 16 to 38; 10 of 10 doubled).
  • The 20:28 schedule was significantly more effective than the 28 mW/cm2 schedule and the 20:40 schedule. The text gives P of 0.01 for both; Table II gives 0.012 and 0.015.
  • The 20:28 schedule was not significantly different from the 20 mW/cm2 schedule (Table II P = 0.161), despite medians of 72 vs 18 days. The authors attributed this to several long-term cures in the 20 mW/cm2 group.
  • The response to the 20:28 green-light schedule could not be distinguished statistically from the 630 nm red-light group (Table II P = 0.297). The red-light group had a median doubling time of 100 days (95% CI 54 days to no upper limit), and 4 of 16 tumours doubled.
  • Red light delayed regrowth significantly longer than the 20 mW/cm2, 28 mW/cm2 and 20:40 green-light schedules. The text gives P-values below 0.006; Table II lists 0.006, below 0.001 and below 0.001.
  • The 2-hour red-light treatment delivered a total fluence of 360 J/cm2. The 20:28 green-light treatment delivered 173 J/cm2.
• The authors' conclusion: The authors concluded that they had shown a 514 nm regimen producing long-term tumour control in this mouse model that was statistically indistinguishable from 630 nm light. They suggested about 20 mW/cm2 or less at 514 nm for carcinoma in situ and for lesions 2 mm or less thick. For thicker lesions, they suggested that stepped protocols be explored further. Their stated 'potential for diminished normal tissue damage' was not measured in this study.
• Limitations the authors state:
  • The authors had no measured optical absorption and scattering values for this tumour at these wavelengths.
  • The authors said the stepped schedules were designed somewhat empirically and that more work is needed based on real knowledge of tumour optical properties.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma.

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