Peter Lenz

Correlation between meta(tetrahydroxyphenyl)chlorin (m-THPC) biodistribution and photodynamic effects in mice

Analysis of sensitizer kinetics is essential for the performance of light irradiation when tumour concentration and tumour-to-normal tissue ratios are optimal. In this study nude mice were grafted with human adenocarcinoma 15 days before meta(tetrahydroxyphenyl)chlorin (m-THPC) intra-peritoneal (IP) injection. Fluorescence was recorded through an optic fibre spectrofluorometer at 650 (the most intense) and 714 nm, with intensity being proportional to injected dose. In tumour, skin and muscle the maximum fluorescence was obtained with 1.6 mg kg-1 72 h after injection (44 counts per second). Tumour-to-skin and tumour-to-muscle ratios obtained by high performance liquid chromatography (HPLC) analysis and spectrofluorometric measurements decreased between 12 and 72 h (from 15 to 1.5), indicating that tumour selectivity decreases with time. This contrast between selectivity and fluorescence levels was also observed with photodynamic therapy (PDT) results, for which no differences were observed when 10 J cm-2 were delivered at 100 or 200 mW. PDT results were better 24 h after drug administration than at 72 h. Tumour growth decrease (-40%) was found when 1.6 mg kg-1 were injected 24 h before irradiation. For other groups a slower increase (12% vs. 23%) was noted in the first few days after PDT. The paradoxal correlation between fluorometric or HPLC measurements and PDT effects suggests that m-THPC localizes differently with time in tumour components.

Influence of water conductivity on the efficiency and the reproducibility of electrohydraulic shock wave generation

In an electrohydraulic generator, two underwater metal electrodes are connected with a capacitor charged to a high voltage. When the circuit is switched on, a plasma is generated reaching temperatures of thousands of K, resulting in a compressive pressure pulse. The formation of the plasma is a nonreproducible phenomenon inducing great variations of the pressure pulse. When the electrodes are immersed in an electrolyte instead of degassed water, the conditions of electrical discharge are dramatically modified. The latency time and the amplitude of the oscillations of the discharge current decrease as the conductivity of the electrolyte increases. For a conductivity of 7 omega.cm, there is no latency, and the critically damped discharge is achieved. The expanding pressure wave is increased by 10%, and the mean peak pressure value over 120 shocks at the second focus after focalization is increased by 50%. The relative standard deviation of the pressure value at the second focus is only 5%, while it is about 30% in ordinary water. The fragmentation efficiency is considerably increased because total fragmentation is obtained in 220 shocks instead of 450 shocks in ordinary water when standard stones are used, and in 131 shocks instead of 304 shocks when gallstones are used. Last, we show that the wear of the electrodes is reduced by a factor 8 when electrolyte is used. The improvement is supposed to have two causes: First, the energy is delivered into the medium in a shorter time, and, second, the center of the shock wave is always located at the same place. The decreased wear should make it possible to treat a much greater number of patients without changing electrodes, and the enhancement of the pressure should increase the efficiency of the fragmentation of the gallstones without aggravating the patients pain.

In vitro and in vivo spectrofluorornetry of a water-soluble meta-(tetrahydroxyphenyl) chlorin (m-T PC) derivative

The pharmacokinetics of a water-soluble derivative obtained from meta-(tetrahydroxyphenyl)chlorin (m-THPC) was evaluated in in vitro and in vivo studies. Cytoplasm fluorescence was measured in two cell models (L1210 and HT29) using a flow cytometer and a confocal microspectrofluorometer. Cells were incubated with the compound at several doses (0-150 micrograms ml-1 for flow cytometry) and for several time periods (0-6 h for microspectrofluorometry). For in vivo studies, nude mice were grafted with human adenocarcinoma 15 days before intraperitoneal injection of polyethylene glycol-m-THPC (PEG-m-THPC). Fluorescence was recorded through an optical fibre spectrofluorometer using the 660 nm peak for detection. In in vitro studies, the fluorescence was found to be proportional to the dose. Maximum fluorescence was recorded in L1210 cells earlier and more intensely than in HT29 cells (3 h at 202 +/- 14 counts s-1 and 5 h at 43 +/- 2.15 counts s-1 respectively). Concerning in vivo studies, maximum tumour fluorescence was observed 24 h after injection (3568 +/- 178 counts s-1). Selectivity was expressed by the calculated tumour-to-skin and tumour-to-muscle ratios. The time taken to observe the maximum ratios (2.95 +/- 0.16 for tumour-to-skin and 6.61 +/- 0.3 for tumour-to-muscle) was almost the same as the time taken to observe the maximum fluorescence in the tumour. Studies are in progress to correlate these results with photodynamic effects.

Enhancement of Delta aminolevulinic acid-photodynamic therapy in vivo by decreasing tumor pH with glucose and amiloride

Objectives/Hypothesis Delta aminolevulinic acid (ALA)–induced protoporphyrin IX (PpIX) is a fluorescent sensitizer that permits detection and treatment of squamous cell carcinoma of the oral cavity. An exogenously induced decrease in tissue pH was evaluated for its effect in enhancing cellular uptake of ALA and facilitating its transformation into PpIX.

Fluorescence measurement in thick tissue layers by linear or nonlinear long-wavelength excitation

Samples of different animal tissues containing, at variable depth, a thin fluorescent sheet are irradiated with continuous violet or red light or with nonlinearly absorbed pulsed infrared light. The fluorescence intensity measured at the tissue surface as a function of the location of the fluorescent sheet exhibits, after a transition zone close to the tissue surface, an exponential decrease, the slope of which depends on the optical penetration depths of the exciting and the fluorescent light. From these results the total fluorescence output is determined for specific fluorophor distributions. It is seen that considerably deeper tissue layers are explored by use of excitation with red instead of violet light. Nonlinear excitation by infrared light can provide a further improvement, especially in liver tissue.

Light distributor for endoscopic photochemotherapy of tumors

This device is fixed to the extremity of an optical fiber and permits light to spread over tumors situated inside hollow organs accessible by endoscopes. Compared to currently used diffusing tips, light distributors have several advantages, in particular precise matching of the irradiated area to the target area, high transmission efficiency, high power density favoring therapeutically relevant hyperthermia, and great mechanical resistance. The clinical usefulness of light distributors has been demonstrated.

Determination of the acoustic pressure at and the reflection coefficient of a target through measurements of the absorbed power and the emitter voltage

A harmonic acoustic wave, fed back by a reflecting target, modifies the electric impedance of the emitter. This effect is studied using a tightly focused beam and various flat targets with known reflection coefficients, which are placed at pressure maxima or minima of the standing wave in the focal zone. It is possible to establish relationships that allow one to determine, for flat targets with unknown acoustic properties, the acoustic impedance and reflection coefficient of the target as well as the acoustic pressure present at the target, only from measurements of the absorbed power and the emitter voltage.

Clinically occult bladder cancer diagnosis. Trial using ultraviolet cystoscopy

Ultraviolet cystoscopy was used to demonstrate flat cancerous and precancerous bladder lesions by two techniques based on different principles: the loss of epithelium blood group antigenic expression using immunofluorescence reaction, and submucosa neoangiogenesis after fluorescein intravenous injection. The results obtained with these two techniques were disappointing, but do not preclude the use of ultraviolet cystoscopy in this type of study.

Ex vivo clinical measurement of the optical penetration depth in digestive tissues.

Abstract.The optical penetration depth of 120 biopsy samples taken from normal or neoplastic digestive tissues is measured by means of a device which can be used in a clinical environment, is easy to handle and delivers results quickly. It is seen that, at 655u2009nm, values of the penetration depth are centred around 1.1u2009mm and that they can vary by roughly a factor of 2 between samples of a given kind of tissue. This latter result suggests performing individual measurements immediately before carrying out photodynamic therapy.

Photochemically-induced tissue injury observed very shortly after sensitizer injection

In clinical photochemotherapy, irradiation is delayed by a few days with respect to sensitizer injection in order to enhance the specificity of action. However, there are animal experiments which, above all, require a strong response; this is expected to occur if the delay time is much shorter. To assess the influence of the delay time, lesions were produced in rat ears using haematoporphyrin derivative and green light, and characterized by a scoring system. It was found that, starting from the shortest experimentally accessible value (8 min), the intensity of lesions decreases with increasing delay time (by a factor of 2 in 90 min). This result suggests that the lesions are induced by circulating sensitizer. Dose fractionation, performed 97 min after injection, enhances the response (p<0.005).