Enhancement of meta-tetrahydroxyphenylchlorin-sensitized photodynamic treatment on human tumor xenografts using a water-soluble vitamin E analogue, Trolox.

Photodynamic therapy (PDT) using meta-tetrahydroxyphenylchlorin (mTHPC) performed on HT29 human colon adenocarcinoma xenografts in nude mice was shown to be enhanced by Trolox, a water-soluble vitamin E analogue. Trolox, injected i.p. at 250 mg/kg body weight 90 min before PDT, delayed tumor doubling time from 13 (PDT only) to 19 days. Enhancement of the tumoricidal effect of PDT by Trolox required the presence of the drug at the photochemical stage since its injection after irradiation is ineffective. HPLC measurements indicated that 1 hr after injection the Trolox concentration in plasma was as high as 0.8 mM. In vivo measurements of mTHPC fluorescence in mice treated by PDT with or without Trolox injection showed that Trolox did not protect mTHPC from photodegradation. Laser flash photolysis studies performed in solution demonstrated that Trolox reduces triplet mTHPC efficiently (reaction rate constant 2 x 10(7) M(-1) * sec(-1)) leading to the formation of radical products. Kinetic considerations suggest that the Trolox-mediated radical pathway can work in relay with singlet oxygen in hypoxic conditions, providing a possible explanation for the observed enhancement of mTHPC-sensitized PDT by Trolox.

Measurements by fluorescence microscopy of the time-dependent distribution of meso-tetra-hydroxyphenylchlorin in healthy tissues and chemically induced "early" squamous cell carcinoma of the Syrian hamster cheek pouch.

The influence of the time interval between dye administration and detection by fluorescence microscopy was assessed in "early" squamous cell carcinomas of the cheek pouch mucosa and different healthy tissues of the Syrian hamster. Following intracardiac injection of 0.15 mg (kg bodyweight)-1 of meso-tetra-hydroxyphenylchlorin (m-THPC), groups of three animals were sacrificed at different time intervals up to 30 days. A group of three non-injected animals was used to detect the endogene fluorescence of the corresponding normal tissues for autofluorescence subtraction. The following excised organs (oesophagus, trachea, liver, spleen, kidney, skin, striated muscle, healthy and tumoral cheek pouch mucosae) were fast frozen in liquid nitrogen and stored at -70 degrees C for fluorescence microscopy. The results show significant differences in the detectable m-THPC levels in different tissue layers (for instance, the epithelia and muscle of the oesophagus, trachea and cheek pouch) at different time intervals. These data indicate that pharmacokinetic studies may be useful for selecting the optimal time for the photodetection and phototherapy of cancer.

Photodynamic therapy using m-tetra(hydroxyphenyl) chlorin. An animal model.

OBJECTIVE: To evaluate the potent photosensitizer m-tetra (hydroxyphenyl) chlorin (m-THPC) by using rabbits with cottontail rabbit papillomavirus-induced tumors and the canine larynx as model systems. DESIGN: Nonrandomized control trial. SETTING: Division of ear, nose, and throat research at a tertiary care teaching hospital. MATERIALS: Rabbits were used for relative retention ratio studies and tissue tolerance tests. Studies on the swelling of normal tissues in the larynx after photoactivation were done with canines. INTERVENTION: Animals were injected with 0.3 mg/kg of m-THPC. At varying intervals, tissues were exposed to 652 nm of light. OUTCOME MEASURES: Outcome measures consisted of four elements: (1) decay of plasma concentration over time, (2) interval to and duration of maximal ratio between drug concentration in normal tissue and tumor, (3) maximal permissible light exposure to normal tissue (skin and laryngeal mucosa) at an optimal interval, and (4) efficacy--number of tumors with partial and complete response. RESULTS: The largest papilloma to skin ratio (10:1) occurred 4 to 8 days after drug injection. The rabbit skin damage threshold was 40 to 60 J/cm2 at 6 days. The canine laryngeal edema and erythema thresholds were 50 to 70 J. A 75% cure rate of papillomas was achieved with tumors that were less than 100 mm2 in area at light doses that ranged from 25 to 75 J/cm2. CONCLUSIONS: m-THPC shows efficacy in treating papilloma virus-induced tumors. We present a protocol for rapid optimization of the factors required for tumor destruction with minimal normal tissue damage, thus permitting determination of an optimal therapeutic protocol for any photosensitizer.