Biomedical subjects

H van den Bergh

Publications and source records attributed to H van den Bergh.

At least 19 recordsLinked to original sources

PubMed2006

Combination therapy using aspirin-enhanced photodynamic selective drug delivery.

In photodynamic therapy (PDT), excitation of a drug by light leads to a cascade of biochemical processes that can cause closure of blood vessels. It has been observed clinically that significant short-term leakage from the irradiated vasculature can occur prior to vessel closure and blood flow stasis. In this paper we demonstrate in a chicken embryo model that this leakage can be significantly enhanced by the presence of the cyclo-oxygenase inhibitor, aspirin. We also observe that following this aspirin-enhanced leakage, blood vessels close as effectively as after PDT in the absence of aspirin. Consequently we propose that this PDT-induced aspirin-enhanced leakage can be used to locally deliver a drug for combination therapy. This is then demonstrated in the chicken embryo using Visudyne as a PDT agent in combination with aspirin and fluorescein isothiocyanate dextran 10 kDa as leakage indicator. The latter represents a hypothetical drug to be delivered in various kinds of combination therapy. Two examples of this procedure would be the photodynamic treatment of choroidal neovasculature associated with exudative age-related macular degeneracy (AMD) where local delivery of an anti-angiogenic or an anti-inflammatory drug has been shown to be effective, or PDT of cancer where local dosing of a chemotherapeutic drug may well increase the treatment efficacy.

Animals↗

PubMed2006

Photothrombic activity of m-THPC-loaded liposomal formulations: pre-clinical assessment on chick chorioallantoic membrane model.

The objective of this study was to evaluate the ability of meso-tetra(hydroxyphenyl)chlorin (m-THPC) encapsulated into liposomal formulations to occlude neovascularization. Two m-THPC formulations including conventional or plain liposomes (Foslip) based on dipalmitoylphosphatidylcholine (DPPC) and the corresponding long-circulating poly(ethylene glycol) (PEG)-modified liposomes (PEGylated liposomes: Fospeg) were evaluated as delivery systems. Using the chick chorioallantoic membrane (CAM) as in vivo model, the fluorescence pharmacokinetic behaviour of encapsulated m-THPC reflecting the rate of the extravasation of the dye from the CAM vasculature and its photothrombic effectiveness were determined. This study was focused on the influence of the drug and/or light doses on the mean retention time of m-THPC within the CAM blood vessels after intravenous injection, and its photothrombic efficacy. Irrespective of the formulations tested and the drug doses injected, similar fluorescence pharmacokinetic profiles were obtained. The fluorescence contrast reached a steady state 30 s after injection. Constant positive values of the fluorescence contrast suggest that m-THPC is confined into the intravascular compartment during the experimental time (500 s). However, the photodynamic therapy assays showed that Foslip appears to be less potent than Fospeg in terms of photothrombic activities on the CAM model. For instance, the light dose necessary to induce the desired vascular damage with Foslip was twice (100 J/cm2) higher than with Fospeg (50 J/cm2). It can be inferred that this pre-clinical study showed that the formulation based on PEGylated liposomes technology offers a suitable delivery system for the treatment of choroidal neovascularization associated with age-related macular degeneration.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2006

Open path atmospheric spectroscopy using room temperature operated pulsed quantum cascade laser.

We report the application of a distributed feedback quantum cascade laser for 5.8 km long open path spectroscopic monitoring of ozone, water vapor and CO(2). The thermal chirp during a 140 or 200 ns long excitation pulse is used for fast wavelength scanning. The fast wavelength scanning has the advantage of the measured spectra not being affected by atmospheric turbulence, which is essential for long open path measurements. An almost linear tuning of about 0.6 and 1.2 cm(-1) is achieved, respectively. Lines from the nu(3) vibrational band of the ozone spectra centered at 1,031 and 1,049 cm(-1) is used for ozone detection by differential absorption. The lowest column densities (LCD) for ozone of the order of 0.3 ppmm retrieved from the absorption spectra for averaging times less than 20s are better then the LCD value of 2 ppmm measured with UV DOAS systems. The intrinsic haze immunity of mid-IR laser sources is an additional important advantage of mid-IR open path spectroscopy, compared with standard UV-vis DOAS. The third major advantage of the method is the possibility to measure more inorganic and organic atmospheric species compared to the UV-vis DOAS.

Carbon Dioxide↗

PubMed2004

On the selectivity of photodynamic therapy of choroidal neovascularization associated with age-related macular degeneration.

PURPOSE: This paper discusses the lack of complete selectivity in the photodynamic closure of choroidal neovasculature (CNV) associated with age-related macular degeneration. The arguments presented are supported by examples of clinical observations and may be useful for the design of the next generation of photosensitizers. RESULTS AND CONCLUSION: Based on worldwide patient follow-up, it can be concluded that a substantial number of the more than 200000 treatments that have been dispensed so far could have resulted in stabilization of the disease for at least a number of years. Clinical observations also indicate that, in addition to the effective closure of the CNV observed 1 week after PDT, a significant closure (or at least reduced leakage) of normal choriocapillaries is observed in the treated area. Some of the concepts associated with the selectivity of Visudyne photodynamic therapy of choroidal neovascularization in age-related macular degeneration are also discussed. DISCUSSION: Novel approaches to improving selectivity could include attaching a photosensitizer to a targeting moiety such as a monoclonal antibody or a peptide. The undesirable closure of normal choriocapillaries in the treated area is one area of possible improvement to be sought for the next generation of drugs.

Capillaries↗

PubMed2004

[Visudyne photodynamic therapy and feeder vessel occlusion: rationale of a synergistic association and clinical options].

PURPOSE: Visudyne photodynamic therapy (PDT) has provided considerable improvement in patient care of subfoveal choroidal neovascularization (CNV). Patients tend to loose vision for a few months after the initial treatment, but the 4-year proven stability in vision most often provides an acceptable quality of life, sometimes with additional low vision rehabilitation. The initial visual acuity loss, borderline cost-effectiveness, and subgroups of patients not responding to PDT warrant improving the symptomatic treatment of subfoveal CNV. Today, the most tempting solution would be to combine PDT with an occlusion of the feeder vessel (FV). METHODS: Two patients are described in whom the feeder vessel was occluded using modifications of the classic PDT treatment method. The FV was identified in both patients using fluorescein and indocyanine green angiographies at a recorded video rate using a modified scanning laser ophthalmoscope (Rodenstock SLO). The feeder vessel of the first patient was occluded by minimal photocoagulation immediately after a Visudyne PDT treatment in order to take advantage of the reduced blood flow within the feeder vessel. The second patient presenting a subfoveal FV was treated using a modified PDT treatment called feeder-vessel PDT. The photosensitizing agent was activated by a first classic spot covering the lesion, followed immediately by a small spot focused on the feeder vessel. RESULTS: Both subfoveal CNVs were successfully and selectively occluded and some visual acuity was gained following the treatment. CONCLUSION: Occlusion of the feeder vessel is an appealing clinical option that is complementary to Visudyne PDT. Both treatment methods presented here could provide additional options to close subfoveal CNV with an optimal efficacy-risk ratio.

Angiography↗

PubMed2003

Selectivity of the photosensitiser Tookad for photodynamic therapy evaluated in the Syrian golden hamster cheek pouch tumour model.

The response to photodynamic therapy (PDT) with the photosensitiser (PS) Tookad was measured in the Syrian hamster cheek pouch model on normal mucosae and chemically induced squamous cell carcinoma. This PS is a palladium-bacteriopheophorbide presenting absorption peaks at 538 and 762 nm. The light dose, drug dose and drug injection-light irradiation times (DLI), ranging between 100 and 300 J cm(-2), 1-5 mg kg(-1) and 10-240 min respectively, were varied and the response to PDT was analysed by staging the macroscopic response and by the histological examination of the sections of the irradiated cheek pouch. A fast time decay of the tissular response with drug dose of 1-5 mg kg(-1) was observed for DLI ranging from 10 to 240 min and for light doses of 100-300 J cm(-2) delivered at a light dose rate of 150 mW cm(-2). A significantly higher level of tissular response was observed for squamous cell carcinoma compared to normal tissue. Nevertheless, the threshold level of the drug-light dose for a detectable response was not significantly different in the tumoral vs normal tissue. The highest response at the shortest DLIs and the absence of measurable response at DLI larger than 240 min at light dose of 300 J cm(-2) and drug dose of 5 mg kg(-1) reveals the predominantly vascular effect of Tookad. This observation suggests that Tookad could be effective in PDT of vascularised lesions.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed2003

Endoscopic fluorescence detection of intraepithelial neoplasia in Barrett's esophagus after oral administration of aminolevulinic acid.

BACKGROUND AND STUDY AIMS: Barrett's esophagus is strongly associated with adenocarcinoma. Early malignant transformation of the Barrett's mucosa is often not visible endoscopically and may remain undetected until the invasive adenocarcinoma stage. Endoscopic surveillance is currently carried out on random four-quadrant biopsies at 1-2 cm intervals. Endoscopic fluorescence detection of protoporphyrin IX induced by 5-aminolevulinic acid can identify premalignant lesions. This study evaluates endoscopic fluorescence detection in patients having Barrett's esophagus and compares the results to those of standard endoscopy with random four-quadrant biopsies. PATIENTS AND METHODS: The study included 30 examinations in 28 patients (22 men, 6 women; age range 37-78 years, mean age 60 years,), with five patients having known intraepithelial neoplasia. A dose of 20 mg/kg of 5-aminolevulinic acid was given orally 5 hours before examination. Random four-quadrant biopsies were performed 4-6 weeks before endoscopic fluorescence detection. RESULTS: Of the biopsies taken during the endoscopic fluorescence detection procedure, 28 % (23/81) were true positives. More than one-third of the false-positive results were due to inflammation. None of the 97 control biopsies taken on nonfluorescing areas during endoscopic fluorescence detection were dysplastic. Endoscopic fluorescence detection showed low-grade intraepithelial neoplasia in five patients which was not diagnosed with random four-quadrant biopsies, while random four-quadrant biopsies alone showed three low-grade intraepithelial neoplasias that were invisible during endoscopic fluorescence detection. All high-grade intraepithelial neoplasias or adenocarcinomas (2/2) were detected with both methods. CONCLUSIONS: Fluorescence detection achieved a similar performance when compared with four-quadrant random biopsy, but resulted in fewer biopsies (81 for endoscopic fluorescence detection vs 531 for random four-quadrant biopsies).

Administration, Oral↗

PubMed2003

High efficacy of photodynamic therapy on rat endometrium after systemic administration of benzoporphyrin derivative monoacid ring A.

BACKGROUND: The aim of this study was to evaluate the effect of the benzoporphyrin derivative monoacid ring A (verteporfin)-mediated photodynamic therapy (PDT) on rat endometrium and to determine the optimal drug concentration for endometrial ablation. METHODS: Five minutes after i.v. injection of different concentrations of verteporfin into 24 female Sprague-Dawley rats, 630 nm light treatment was delivered for 500 s (120 J/cm2) to the left horn of the uterus. The 24 rats were divided into six groups according to the drug dose injected, four rats per group: group I (2 mg/kg), group II (1 mg/kg), and groups III, IV, V and VI with 0.5, 0.25, 0.125 and 0.0625 mg/kg respectively. Four days later, the rat uteri were analysed by light microscopy. RESULTS: Endometrial destruction was seen in all six groups, with the most significant result in group I (P<0.008). Conservation of the myometrium was most significant in groups III, IV, V and VI. Acute inflammatory cells in the stromal endometrium were recorded mainly in groups I and II. However, the drug dosage that was most significant in destroying the glands with conservation of the myometrium and not causing severe inflammation was between 0.5 and 0.125 mg/kg. CONCLUSIONS: Verteporfin was effective in endometrial ablation in all our animal groups, and the dose range of 0.5-0.125 mg/kg appeared to be adequate. This observation will have to be scaled for clinical application.

Animals↗

PubMed2002

Uptake and localisation of mTHPC (Foscan) and its 14C-labelled form in normal and tumour tissues of the hamster squamous cell carcinoma model: a comparative study.

The aim of this study was to evaluate the pharmacokinetics of meta(tetrahydroxyphenyl)chlorin (mTHPC) on different tissues of interest in a hamster tumour model and to confirm our earlier animal studies on semi-quantitative fluorescence microscopy. The results obtained by three different evaluation methods were compared: in vivo spectrofluorometry, ex vivo fluorescence microscopy and chemical extraction of (14)C-labelled mTHPC. Following intracardiac injection of 0.5 mg kg(-1) mTHPC, groups of five tumour-bearing animals were used for in situ light-induced fluorescence spectroscopy. Afterwards, the biopsies were taken and snap frozen for fluorescence microscopy. The presence of radioactivity in serum and tissues was determined after chemical digestion in scintillation fluid using a scintillation counter. For each analysed tissue, a good correlation was observed between the three evaluation methods. The highest fluorescence intensity and quantities of mTHPC were observed between 12 and 24 h in liver, kidney, serum, vascular endothelium and advanced neoplasia. The majority of mTHPC was found at around 48 h in smooth muscle and at 96 h in healthy cheek pouch mucosa and early malignant lesions. The lowest level of mTHPC was noted in striated muscle at all times. No selectivity in dye localisation was observed between early squamous cell carcinoma and healthy mucosa. Soon after the injection, a significant selectivity was noted for advanced squamous cell carcinoma as compared to healthy cheek pouch mucosa or striated muscle. A significant difference in mTHPC localisation and quantity was also observed between striated and smooth muscle during the first 48 h following the injection. Finally, this study demonstrated the usefulness of non-invasive in situ spectroscopic measurements to be performed systematically prior to photodynamic therapy as a real-time monitoring for each treated patient in order to individualise and adapt the light dosimetry and avoid over or under treatments.

Animals↗

PubMed2002

Optimization of the diameter of a radial irradiation device for photodynamic therapy in the esophagus.

BACKGROUND AND STUDY AIMS: Photodynamic therapy (PDT) is a local therapeutic technique based on the photosensitization of lesions using a dye prior to light-induced tissue destruction. PDT of intraepithelial neoplasia in Barrett's esophagus, or of early squamous-cell carcinoma of the esophagus, requires light application devices that allow homogeneous and well-defined illumination of the tissue surface. Such devices must be large enough to induce complete unfolding of the esophagus in spite of esophageal motility and elasticity. The aim of this study was therefore to determine the optimal diameter of a cylindrical illumination device for PDT in this organ. PATIENTS AND METHODS: The study included nine patients (aged 49-72 years) who underwent panendoscopy. Flexible transparent hollow tubes with diameters ranging from 13 to 19 mm were successively introduced into the esophagus, and the esophageal wall was viewed from the inside through the tube using a flexible small-diameter endoscope. The number of folds was counted. Observations of the upper, middle, and lower thirds of the esophagus were recorded. The radial location of the folds was also recorded, and defined as follows: anterior wall (up), posterior wall (down), side walls (right, left). RESULTS: No significant difference in the number of folds between the lower and middle parts of the esophagus was noticed. However, the upper third had significantly fewer folds (about 30 %) than the other two parts. For diameters above 17 mm, this difference was less dramatic. The number of such folds was shown to decrease with the increasing diameter of the device. CONCLUSIONS: It appears that 18 mm or more is the optimal diameter for a fixed-geometry cylindrical photodynamic therapy irradiating device for the patient category considered in this study. It was also observed that most folds were located on the side walls of the esophagus.

Aged↗

PubMed2001

Localization of tetra(m-hydroxyphenyl)chlorin (Foscan) in human healthy tissues and squamous cell carcinomas of the upper aero-digestive tract, the esophagus and the bronchi: a fluorescence microscopy study.

To date, little is known about precise time-dependent distribution and histological localization of tetra(m-hydroxyphenyl)chlorin (mTHPC) in human healthy tissues and squamous cell malignancies in the upper aero-digestive tract. A fluorescence microscopy study was performed on 50 healthy tissue biopsies and on 13 tumors (graded from Tis to T1 SCC) from 30 patients. Tissue samples were taken between 4 h and 11 days following injection of 0.15 mg/kg mTHPC. A fairly comparable distribution pattern in various tissues was observed over time in different patients. Vascular localization of mTHPC fluorescence predominates at a short delay, whereas the dye is essentially located in the tumoral and healthy mucosa after longer delays. A much lower uptake and retention of mTHPC fluorescence was noted in striated muscle and cartilage as compared to neoplastic lesions. No significant selectivity was found between healthy and tumoral mucosa. The obtained data are important to confirm drug-light interval that have been selected for effective PDT for early SCC malignancies while minimizing the risks of over- or under-treatment. The low fluorescence level in striated muscle provides the opportunity to develop interstitial PDT as a treatment modality for invasive SCC of unfavorable locations in the oral cavity or pharynx, such as the base of the tongue.

Aged↗

PubMed2001

Photodynamic therapy of age-related macular degeneration: History and principles.

We briefly review the history and principles of photodynamic therapy (PDT), especially as it is applied to choroidal neovascularization (CNV) in age-related macular degeneration (AMD). After a brief general history of PDT, we discuss the relationship between the physicochemical structure and photodynamic activity of the second-generation photosensitizers, such as those in current clinical use. We then discuss the basic photophysics of photosensitizer molecules, and describe the initial chemical reactions induced by activated sensitizers. We outline a novel method for screening photosensitizers to be used in treating CNV, as well as the complex biomolecular pathways modulated by PDT-induced oxidative stress and the vascular effects of PDT in solid tumors. The paper closes with a discussion of how all this information might be used to improve the selectivity and efficacy of clinically useful photosensitizers.

Clinical Trials as Topic↗

PubMed2001

In vivo autofluorescence spectroscopy of human bronchial tissue to optimize the detection and imaging of early cancers.

We are developing an imaging system to detect pre-/early cancers in the tracheo-bronchial tree. Autofluorescence might be useful but many features remain suboptimal. We have studied the autofluorescence of human healthy, metaplastic and dysplastic/CIS bronchial tissue, covering excitation wavelengths from 350 to 480 nm. These measurements are performed with a spectrofluorometer whose distal end is designed to simulate the spectroscopic response of an imaging system using routine bronchoscopes. Our data provide information about the excitation and emission spectral ranges to be used in a dual range detection imaging system to maximize the tumor vs healthy and the tumor vs. inflammatory/metaplastic contrast in detecting pre-/early malignant lesions. We find that the excitation wavelengths yielding the highest contrasts are between 400 and 480 nm with a peak at 405 nm. We also find that the shape of the spectra of healthy tissue is similar to that of its inflammatory/metaplastic counterpart. Finally we find that, when the spectra are normalized, the region of divergence between the tumor and the nontumor spectra is consistently between 600 and 800 nm and that the transition wavelength between the two spectral regions is around 590 nm for all the spectra regardless of the excitation wavelength, thus suggesting that there might be one absorber or one fluorophore. The use of backscattered red light enhances the autofluorescence contrast.

Bronchi↗

PubMed2001

A new drug-screening procedure for photosensitizing agents used in photodynamic therapy for CNV.

PURPOSE: Because vascular occlusion has been observed as a consequence of photodynamic therapy (PDT), this method has been successfully used for the treatment of choroidal neovascularization (CNV) in age-related macular degeneration (AMD). However, most conventional photosensitizers, primarily developed for tumor PDT, lack selectivity for the targeting of neovascularization. An experimental model has been developed for drug screening of new photosensitizers for the treatment of CNV associated with AMD. It consists of intravenous (IV) injection of photosensitizers and fluorescent dyes into the chick's chorioallantoic membrane (CAM), followed by measurement of fluorescence pharmacokinetics, leakage from the vascular system, and photothrombic efficacy. METHODS: Fertilized chicken eggs were placed under a fluorescence microscope. After intravenous injection of different dyes, time-dependent fluorescence angiography was performed. The effect of PDT parameters was assessed by fluorescence angiography 24 hours after PDT. RESULTS: Although fluorescence of lipophilic benzoporphyrin derivative monoacid ring A (BPD-MA) remained intravascular during 2 hours, hydrophilic dyes tended to leak through the fenestrated neovascularization. By variation of PDT parameters, vascular damage could be directed toward closure of vessels with a diameter smaller than 10 microm, as measured 24 hours after PDT. High photosensitizer concentrations and high light doses resulted in blood flow stasis within 60 minutes, confirmed by fluorescence angiography. CONCLUSIONS: Fluorescence angiography and PDT after IV injection into the CAM showed strong similarities to results obtained in clinical tests of PDT in CNV associated with AMD. Thus, this model can provide valuable information about PDT mechanisms and can be used for drug-screening purposes in development of improved sensitizers for the PDT of CNV.

Allantois↗

PubMed2000

A preliminary study of photodynamic therapy using verteporfin for choroidal neovascularization in pathologic myopia, ocular histoplasmosis syndrome, angioid streaks, and idiopathic causes.

OBJECTIVE: To evaluate short-term safety and the effects on visual acuity and fluorescein angiography of single or multiple sessions of photodynamic therapy with verteporfin for choroidal neovascularization (CNV) not related to age-related macular degeneration (AMD), including pathologic myopia, the ocular histoplasmosis syndrome, angioid streaks, and idiopathic causes. DESIGN: A nonrandomized, multicenter, open-label, dose-escalation phase 1 and 2 clinical trial. SETTING: Four ophthalmic centers in Europe and North America providing retinal care. PARTICIPANTS: Thirteen patients with subfoveal CNV due to pathologic myopia, the ocular histoplasmosis syndrome, angioid streaks, or idiopathic causes. METHODS: Standardized protocol refraction, visual acuity testing, ophthalmic examinations, color photographs, and fluorescein angiograms were used to evaluate the results of photodynamic therapy treatments with verteporfin. Follow-up ranged from 12 weeks for patients who were treated once to 43 weeks for patients who were treated up to 4 times. RESULTS: Verteporfin therapy was well tolerated in patients with CNV not related to AMD. No deterioration in visual acuity was observed; most patients gained at least 1 line of vision. Reduction in the size of leakage area from classic CNV was noted in all patients as early as 1 week after verteporfin therapy, with complete absence of leakage from classic CNV in almost half of the patients. Improvement in visual acuity after verteporfin therapy was greatest (+6, +8, and +9 lines) in 3 patients with relatively poor initial visual acuity (between 20/200 and 20/800). Up to 4 treatments were found to have short-term safety even with retreatment intervals as short as 4 weeks. CONCLUSIONS: Treatment of CNV not related to AMD with verteporfin therapy achieves short-term cessation of fluorescein leakage from CNV in a small number of patients without loss of vision. Further randomized clinical trials including a larger number of patients are under way to confirm whether verteporfin therapy is beneficial for subfoveal CNV not related to AMD.

Adult↗

PubMed2000

Fluorescence pharmacokinetics of Lutetium Texaphyrin (PCI-0123, Lu-Tex) in the skin and in healthy and tumoral hamster cheek-pouch mucosa.

We have investigated the pharmacokinetics (PK) of Lutetium Texaphyrin (Lu-Tex), a second-generation photosensitizer, in the Syrian hamster cheek pouch early cancer model. Ten male hamsters, five with chemically induced early squamous cell cancer of the left cheek pouch, received an intracardiac injection of a 10 mg/ml Lu-Tex solution, resulting in a dose of 12 mg Lu-Tex per kg of bodyweight. The PK of the dye have been measured during the 24 h following the injection with an optical-fiber-based spectrofluorometer on the ventral skin, the healthy and the tumoral cheek-pouch mucosa. The Lu-Tex fluorescence is excited at 460 nm and detected around 740 nm. All the measurements yield very similar pharmacokinetic curves. The fluorescence intensity reaches a maximum between two and three hours after the injection and, at its maximum, it is consistently higher (up to 1.5 times) on the tumor than on the healthy mucosa. It remains smaller on the skin than on cheek-pouch mucosa. After 24 h, the Lu-Tex fluorescence is no longer detectable either on the skin, on the lesion or on the healthy mucosa. Moreover, Lu-Tex clearly displays a significant fluorescence selectivity between early carcinoma and healthy mucosa in this model. Furthermore, the inter-animal fluctuations of the fluorescence signal are small (+/-16% on the tumor-bearing mucosa). Eight-minute-long skin-irradiation tests have been performed 24 h after the injection of the Lu-Tex on the ventral skin of 16 additional animals with a solar simulator. No reaction is observed, either macroscopically or microscopically, which further demonstrates, as suggested by the fluorescence measurements, that this photosensitizer is significantly cleared from the skin after 24 h.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed2000

Pharmacokinetics and pharmacodynamics of tetra(m-hydroxyphenyl)chlorin in the hamster cheek pouch tumor model: comparison with clinical measurements.

The pharmacokinetics (PK) of the photosensitizer tetra(m-hydroxyphenyl)chlorin (mTHPC) was measured by optical fiber-based light-induced fluorescence spectroscopy (LIFS) in the normal and tumoral cheek pouch mucosa of 29 Golden Syrian hamsters with chemically induced squamous cell carcinoma. Similar measurements were carried out on the normal oral cavity mucosa of five patients up to 30 days after injection. The drug doses were between 0.15 and 0.3 mg per kg of body weight (mg/kg), and the mTHPC fluorescence in the tissue was excited at 420 nm. The PK in both human and hamster exhibited similar behavior although the PK in the hamster mucosa was slightly delayed in comparison with that of its human counterpart. The mTHPC fluorescence signal of the hamster mucosa was smaller than that of the human mucosa by a factor of about 3 for the same injected drug dose. A linear correlation was found between the fluorescence signal and the mTHPC dose in the range from 0.075 to 0.5 mg/kg at times between 8 and 96 h after injection. No significant selectivity in mTHPC fluorescence between the tumoral and normal mucosa of the hamsters was found at any of the applied conditions. The sensitivity of the normal and tumoral hamster cheek pouch mucosa to mTHPC photodynamic therapy as a function of the light dose was determined by light irradiation at 650 nm and 150 mW/cm2, 4 days after the injection of a drug dose of 0.15 mg/kg. These results were compared with irradiations of the normal oral and normal and tumoral bronchial mucosa of 37 patients under the same conditions. The reaction to PDT of both types of human mucosae was considerably stronger than that of the hamster cheek pouch mucosa. The sensitivity to PDT became comparable between hamster and human mucosa when the drug dose for the hamster was increased to 0.5 mg/kg. A significant therapeutic selectivity between the normal and neoplastic hamster cheek pouch was observed. Less selectivity was found following irradiations of normal mucosa and early carcinomas in the human bronchi. The pharmacodynamic behavior of mTHPC was determined by test irradiations of the normal mucosa of hamsters and patients between 6 h and 8 days after injection of 0.5 and 0.15 mg/kg in the hamsters and the patients, respectively. The normal hamster cheek pouch showed a maximum response to irradiation 6 h after injection and then decreased continuously to no observable reaction at 8 days after injection. The reaction of the normal human oral mucosa, however, showed an increasing sensitivity to the applied light between 6 h and 4 days after mTHPC injection and then decreased again at 8 days. The hamster model with the chemically induced early squamous cell cancer in the cheek pouch thus showed some similarity to the early squamous cell cancer of the human oral mucosa considering the PK. However, a quantitative difference in fluorescence signal for identical mTHPC doses as well as a significant difference in pharmacodynamic behavior were also observed. The suitability of this animal model for the optimization of PDT parameters in the clinic is therefore limited. Hence great care must be taken in screening new dyes for PDT of early squamous cell cancer of the upper aerodigestive tract based upon observables in the hamster cheek pouch model.

Animals↗

PubMed2000

5-Aminolevulinic acid and its derivatives: physical chemical properties and protoporphyrin IX formation in cultured cells.

Protoporphyrin IX (PpIX) is used as a fluorescence marker and photosensitizing agent in photodynamic therapy (PDT). A temporary increase of PpIX in tissues can be obtained by administration of 5-aminolevulinic acid (ALA). Lipophilicity is one of the key parameters defining the bioavailability of a topically applied drug. In the present work, octanol-water partition coefficients of ALA and several of its esters have been determined to obtain a parameter related to their lipophilicity. The influence of parameters such as lipophilicity, concentration, time, and pH value on PpIX formation induced by ALA and its esters is then investigated in human cell lines originating from the lung and bladder. ALA esters are found to be more lipophilic than the free acid. The optimal concentration (c(opt), precursor concentration at which maximal PpIX accumulation is observed) is then measured for each precursor. Long-chained ALA esters are found to decrease the c(opt) value by up to two orders of magnitude as compared to ALA. The reduction of PpIX formation observed at higher concentrations than c(opt) is correlated to reduced cell viability as determined by measuring the mitochondrial activity. Under optimal conditions, the PpIX formation rate induced by the longer-chained esters is higher than that of ALA or the shorter-chained esters. A biphasic pH dependence on PpIX generation is observed for ALA and its derivatives. Maximal PpIX formation is measured under physiological conditions (pH 7.0-7.6), indicating that further enhancement of intracellular PpIX content may be achieved by adjusting the pharmaceutical formulation of ALA or its derivatives to these pH levels.

Aminolevulinic Acid↗