Functional and histological bladder damage in mice after photodynamic therapy: the influence of sensitiser dose and time of administration

In vivo photodynamic characteristics of the near-infrared photosensitizer 5,10,15,20-tetrakis(M-hydroxyphenyl) bacteriochlorin

This paper describes the photodynamic characteristics of the new near-infrared photosensitizer 5,10,15,20-tetrakis(m-hydroxyphenyl)bacteriochlorin (mTHPBC or SQN400) in normal rat and mouse tissues. A rat liver model of photodynamic tissue necrosis was used to determine the in vivo action spectrum and the dose-response relationships of tissue destruction with drug and light doses. The effect of varying the light irradiance and the time interval between drug administration and light irradiation on the biological response was also measured in the rat liver model. Photobleaching of mTHPBC was measured and compared with that of its chlorine analog (mTHPC) in normal mouse skin and an implanted mouse colorectal tumor. The optimum wavelength for biological activation of mTHPBC in rat liver was 739 nm. mTHPBC was found to have a marked drug-dose threshold of around 0.6 mg kg-1 when liver tissue was irradiated 48 h after drug administration. Below this administered drug dose, irradiation, even at very high light doses, did not cause liver necrosis. At administered doses above the photodynamic threshold the effect of mTHPBC-PDT was directly proportional to the product of the drug and light doses. No difference in the extent of liver necrosis produced by mTHPBC was found on varying the light irradiance from 10 to 100 mW cm-2. The extent of liver necrosis was greatest when tissue was irradiated shortly after mTHPBC administration and necrosis was absent when irradiation was performed 72 h or later after drug administration, suggesting that the drug was rapidly cleared from the liver. In vivo photobleaching experiments in mice showed that the rate of bleaching of mTHPBC was approximately 20 times greater than that of mTHPC. It is argued that this greater rate of bleaching accounts for the higher photodynamic threshold and this could be exploited to enhance selective destruction of tissues which accumulate the photosensitizer.

Endobronchial photodynamic therapy: comparison of mTHPC and polyethylene glycol-derived mTHPC on human tumor xenografts and tumor-free bronchi of minipigs

BACKGROUND AND OBJECTIVE

Photodynamic therapy (PDT) with mTHPC and polyethylene glycol-derived mTHPC (pegylated mTHPC) was compared on nude mice bearing human squamous cell carcinoma and adenocarcinoma xenografts. The same treatment regimens were applied to the bronchi of tumor-free minipigs to assess injury to normal tissue.

STUDY DESIGN/MATERIALS AND METHODS

Laser light (652 nm, 20 J/cm2) was delivered as surface radiation to the xenografts 4 days after intraperitoneal administration of 0.1 mg/kg mTHPC or an equimolar dose of pegylated mTHPC, respectively. The extent of tumor necrosis was assessed by histomorphometry. Endobronchial PDT was performed on the bronchi of minipigs with the same drug and light doses at drug-light intervals ranging from 12-96 hr.

RESULTS

Both sensitizers produced larger necrosis of squamous cell carcinoma and adenocarcinoma xenografts than was observed in untreated controls (P < 0.005). Pegylated mTHPC led to larger tumor necrosis than mTHPC in squamous cell carcinoma (P < 0.001), but not in adenocarcinoma xenografts. mTHPC-PDT resulted in ulceration and necrosis of bronchial mucosa in minipigs at drug-light intervals ranging from 12-48 hr, which was not observed after use of pegylated mTHPC.

CONCLUSIONS

In this setting, pegylated mTHPC had advantages as a photosensitiser compared to mTHPC.

Photodynamic therapy of rat bladder and urethra: evaluation of urinary and reproductive function after inducing protoporphyrin IX with 5-aminolaevulinic acid

OBJECTIVE

To assess the urinary and reproductive function of rats after inducing protoporphyrin IX with 5-aminolaevulinic acid (ALA) and subsequent intraurethral photodynamic therapy (PDT). Materials and methods Twelve female Wistar rats were given ALA orally or intravesically (four each), followed by intraurethral PDT through a 10-mm cylindrical fibre at 100 mW for 500 s (argon laser, 632 nm). Urinary frequency, the number of gestations and histological changes were then evaluated and compared with a group of eight control rats.

RESULTS

There was only a slight increase in urinary frequency during the first 2 weeks after PDT in the group given oral ALA, while the same degree of urinary frequency was evident for up to 4 weeks in those given intravesical ALA. Despite the occurrence of urinary incontinence from undefined causes in two rats, reproductive function remained unchanged. There was no histological evidence of damage to the reproductive system adjacent to the bladder.

CONCLUSIONS

PDT of the urethra with ALA is relatively safe and carries few risks of inducing permanent urological complications.

Photodynamic therapy with mTHPC and polyethylene glycol-derived mTHPC: a comparative study on human tumour xenografts

The photosensitizing properties of m-tetrahydroxyphenylchlorin (mTHPC) and polyethylene glycol-derivatized mTHPC (pegylated mTHPC) were compared in nude mice bearing human malignant mesothelioma, squamous cell carcinoma and adenocarcinoma xenografts. Laser light (20 J/cm2) at 652 nm was delivered to the tumour (surface irradiance) and to an equal-sized area of the hind leg of the animals after i.p. administration of 0.1 mg/kg body weight mTHPC and an equimolar dose of pegylated mTHPC, respectively. The extent of tumour necrosis and normal tissue injury was assessed by histology. Both mTHPC and pegylated mTHPC catalyse photosensitized necrosis in mesothelioma xenografts at drug-light intervals of 1-4 days. The onset of action of pegylated mTHPC seemed slower but significantly exceeds that of mTHPC by days 3 and 4 with the greatest difference being noted at day 4. Pegylated mTHPC also induced significantly larger photonecrosis than mTHPC in squamous cell xenografts but not in adenocarcinoma at day 4, where mTHPC showed greatest activity. The degree of necrosis induced by pegylated mTHPC was the same for all three xenografts. mTHPC led to necrosis of skin and underlying muscle at a drug-light interval of 1 day but minor histological changes only at drug-light intervals from 2-4 days. In contrast, pegylated mTHPC did not result in histologically detectable changes in normal tissues under the same treatment conditions at any drug-light interval assessed. In this study, pegylated mTHPC had advantages as a photosensitizer compared to mTHPC. Tissue concentrations of mTHPC and pegylated mTHPC were measured by high-performance liquid chromatography in non-irradiated animals 4 days after administration. There was no significant difference in tumour uptake between the two sensitizers in mesothelioma, adenocarcinoma and squamous cell carcinoma xenografts. Tissue concentration measurements were of limited use for predicting photosensitization in this model.

A comparison of functional bladder damage after intravesical photodynamic therapy with three different photosensitizers

The influence of type of photosensitizer, drug and light dose, and time interval between photosensitizer and illumination on the extent of photodynamic therapy (PDT)-induced bladder damage and recovery was investigated using a mouse model. The three photosensitizers studied were Photofrin, meso-tetrahydroxyphenylchlorin (m-THPC) and bacteriochlorin a (BCA). Functional bladder damage was quantitatively assessed from increases in urination frequency index (FI) at 1-35 weeks after illumination and histological damage was qualitatively assessed at 1 day, 1, 2 and 12 weeks. Photofrin-mediated PDT caused an acute increase in FI at 1 week, with recovery within 2-8 weeks after light doses of 2.7-8.2 J/cm2. After higher light doses there was only partial recovery. Previous results indicated that the acute response and rate of recovery was the same whether Photofrin was given at 1 day or up to 7 days before illumination. The m-THPC-mediated PDT at drug doses of > or = 0.3 mg/kg also resulted in a marked acute response with good recovery, even after 10.8 J/cm2. Lower drug doses in combination with 5.4 J/cm2 did not result in acute or late damage. There was no significant difference in acute response when m-THPC was given 1, 3 or 7 days before illumination, although recovery was faster for the longer illumination intervals (3 or 7 days). Illumination at 1 h after 20 mg/kg BCA induced an acute response within 2 days after illumination, with recovery within 4-8 weeks. Lower drug doses did not result in damage. The most prominent histological changes during the acute period with all three photosensitizers were submucosal edema and vessel dilation, with epithelial denudation (depending on drug/light dose). We conclude that BCA and m-THPC are both potent new photosensitizers. They can induce a moderate to severe acute bladder response with complete healing over a period of a few weeks. The photosensitizer m-THPC is very effective with low doses of photosensitizer and light, whereas relatively high doses of BCA and light are required to obtain equivalent functional bladder damage in our mouse model.

The influence of intravesical photodynamic therapy on subsequent bladder irradiation tolerance

The aim of this project was to measure the irradiation tolerance of normal (non tumour bearing) mouse bladder after previous intravesical photodynamic therapy (PDT). Illumination with a range of light doses at 24 h after Photofrin was used as the initial PDT treatment and irradiation with a range of X-ray doses was given at 12 or 24 weeks after the initial therapy. Functional bladder damage was assessed from changes in micturition frequency (tested regularly for a follow-up period of 53 weeks after irradiation) and from cystometry measurements of the bladder at 53-56 weeks. PDT alone caused a marked increase in micturition frequency, with (partial) recovery by the time of irradiation. Irradiation alone caused a modest, transient acute response within 5 weeks and a progressive, permanent late response starting from about 25 weeks depending on X-ray dose. A reduced bladder capacity was also evident at 53-56 weeks after 20 Gy X-rays and after PDT alone. Irradiation after previous intravesical PDT caused an acute reaction similar to X-rays alone, but there was a much earlier expression of late functional bladder damage. The final level of damage prior to sacrifice at 53-56 weeks, was not significantly greater than after X-rays alone. These results suggest that irradiation after previous whole bladder PDT, for refractory bladder tumours, may lead to an increased risk of persistent increases in micturition frequency and reduced bladder capacity, beginning at very early times after irradiation.