Response of a rodent fibrosarcoma to photodynamic therapy using 5-aminolaevulinic acid or polyhaematoporphyrin

The effects of 5-aminolaevulinic acid (ALA)-based photodynamic therapy (PDT) on the growth of an intradermal rat fibrosarcoma have been determined following topical, intravenous, or intratumour application of ALA. The pattern of tumour growth was identical following each type of therapy and we conclude that the efficacy of ALA-PDT is independent of the route of drug administration, at least in this tumour system. We have also compared the efficacy of interstitial ALA-based PDT with similar therapy using a conventional photosensitizer, polyhaematoporphyrin (PHP). ALA-PDT was less effective than PHP-based therapy at inhibiting the growth of a subcutaneous rat fibrosarcoma at light doses over 300 J. It is suggested that protoporphyrin IX photo-bleaching may limit the effectiveness of treatment, whilst the more bleach-resistant PHP may continue to be effective at higher light doses.

The response of a rodent fibrosarcoma to combined treatment with photodynamic therapy and radiotherapy

The response of a rodent fibrosarcoma to photodynamic therapy (PDT), radiotherapy (RT) or combined PDT and RT was examined. PDT used intravenous polyhaematoporphyrin (PHP) and interstitial illumination with 630 nm light (300 or 400J). RT was given as an external beam of gamma-rays (15, 20 or 25 Gy). Both PDT and RT induced a significant delay in tumour growth when applied alone. PHP given alone, without subsequent illumination, did not alter the response of the tumour to RT. The effect of combining PDT and RT was dependent on the dose of light administered, but not, in most cases, on either the radiation dose or the sequence in which the two treatments were given. Using 300J of light, all combined treatments produced additive tumour growth delays. In contrast, sub-additive tumour responses were observed following most combined treatments using 400J of light.

Prostatic sequestration of Cryptococcus neoformans in immunocompromised persons treated for cryptococcal meningoencephalitis

We report a case of a patient with acquired immune deficiency syndrome who was successfully treated for cryptococcal meningoencephalitis with amphotericin B and 5-flucytosine. He died from other sequelae of acquired immune deficiency syndrome two years later. An autopsy revealed prominent cryptococcal prostatitis. Cryptococci were neither found in the central nervous system nor in other anatomic sites. The autopsy files yielded seven other cases of men with a history of cryptococcal meningoencephalitis. The possibility that the prostate sequesters Cryptococcus neoformans thereby contributing to systemic relapse is explored. The qualify as a sequestration, cyptococci must be cultured from the prostate, or from a midstream voided specimen after prostatic massage, and the prostate must be the only focus of infection.

On the photodynamic therapy action spectrum of zinc phthalocyanine tetrasulphonic acid in vivo

The photodynamic therapy (PDT) activity of zinc phthalocyanine tetrasulphonic acid in a rodent tumour model was shown to be critically dependent on the wavelength of the excitation laser light over a relatively small wavelength range. Thus the sensitizer showed a doubling of the PDT activity with fibrosarcoma LSBD1 in BDIX rats when the wavelength of the illuminant was displaced from 680 to 692 nm. Under these conditions, the sensitizer is approximately three times more effective than polyhaematoporphyrin, whereas previously it has been considered to be of low PDT activity. This wavelength effect is attributed to a red shift of the absorption spectrum of the sensitizer in cells compared with that in solution. Fluorescence excitation studies with sensitizer absorbed in mouse 3T3 fibroblast cells are consistent with such a red shift.