Interstitial photodynamic therapy in subcutaneously implanted urologic tumors in rats after intravenous administration of 5-aminolevulinic acid

Subcutaneous Xenograft Models for Studying PDT In Vivo

The most facile, reproducible, and robust in vivo models for evaluating the anticancer efficacy of photodynamic therapy (PDT) are subcutaneous xenograft models of human tumors. The accessibility and practicality of light irradiation protocols for treating subcutaneous xenograft models also increase their value as relatively rapid tools to expedite the testing of novel photosensitizers, respective formulations, and treatment regimens for PDT. This chapter summarizes the methods used in the literature to prepare various types of subcutaneous xenograft models of human cancers and syngeneic models to explore the role of PDT in immuno-oncology. This chapter also summarizes the PDT treatment protocols tested on the subcutaneous models, and the procedures used to evaluate the efficacy at the molecular, macromolecular, and host organism levels.

Aminolevulinic acid (ALA): photodynamic detection and potential therapeutic applications

Aminolevulinic acid (ALA) is a heme precursor that may have potential applications for photodynamic detection and photodynamic therapy-based treatment of solid tumors in a variety of malignancies. ALA may have a role in other applications in surgical oncology based on its ability to discriminate neoplastic tissue from adjacent normal tissue. In this review, we provide a comprehensive summary of the published studies of ALA in noncutaneous solid malignancies.

Efficiency of 5-ALA mediated photodynamic therapy on hypoxic prostate cancer: a preclinical study on the Dunning R3327-AT2 rat tumor model

OBJECTIVES

To evaluate photodynamic therapy (PDT) using 5-ALA-induced protoporphyrin IX (PPIX) in an in vivo hypoxic tumor model and its monitoring using MRI.

MATERIAL AND METHODS

Dunning R3327-AT2 tumors were grafted in the neck of Copenhagen rats. PDT using 150 mg 5-ALA/kg i.v. was performed by focal interstitial illumination of the photosensitized tumor (λ=633 nm; fluence=100 J/cm(2)). MRI at baseline and 2 days after treatment (T1, T2 and dynamic gadolinium enhanced sequences) were performed. Necrosis volumes were determined on post-procedure MRI. Tumors were resected 2 days post-PDT and obtained necrosis was determined histopathologically. Intra-tumoral PPIX distribution was evaluated using confocal microscopy and tissue porphyrin quantification.

RESULTS

Twenty rats were treated divided into three groups: continuous (n=7), fractionated illumination (n=7), and a control group receiving only light or only ALA or neither (n=6). Baseline MRI confirmed the hypoxic character of tumors. Necrosis volumes determined on posttreatment MRI were not reproducible and presented with important geometric and volumetric variability. Average necrosis volumes of 0.39 cc (0-0.874 cc) in the continuous group, 0.24 cc (0.107-0.436 cc) in the fractionated group and 0.012 cc (0-0.071 cc) in the control group were observed. Intra-tumoral PPIX distribution was heterogeneous and PPIX quantification revealed low intra-tumoral concentration.

CONCLUSION

Necrosis volumes induced by 5-ALA-mediated PDT were highly variable and non reproducible, probably because of lack of intra-tissular oxygen. Photosensitizer was poorly represented inside the tumor and its distribution was heterogeneous. Our study suggests that 5-ALA-mediated PDT might not be the best management option for hypoxic prostatic adenocarcinoma.

Diffusion-weighted imaging of the prostate and rectal wall: comparison of biexponential and monoexponential modelled diffusion and associated perfusion coefficients

This study compares parameters from monoexponential and biexponential modelling of diffusion-weighted imaging of normal and malignant prostate tissue and normal rectal wall tissues. Fifty men with Stage Ic prostate cancer were studied using endorectal T(2)-weighted imaging and diffusion-weighted imaging with 11 diffusion-sensitive values (b-values = 0, 1, 2, 4, 10, 20, 50, 100, 200, 400, 800 s/mm(2)). Regions of interest were drawn within non-malignant central gland and peripheral zone, malignant prostate tissue and normal rectal wall tissue. Both a monoexponential and biexponential model was fitted over various b-value ranges, giving an apparent diffusion coefficient (ADC) from the monoexponential model and a diffusion coefficient, perfusion coefficient and perfusion fraction from the biexponential model. In all tissues, over the full range of b-values, the ADC from the monoexponential model was significantly higher than the corresponding diffusion coefficient from the biexponential model. As the minimum b-value increased, the ADC decreased and was equal to the diffusion coefficient for some b-value ranges. The biexponential model best described the data when low b-values were included, suggesting that there is a fast perfusion component. Neither model could distinguish between benign prostate tissues on the basis of diffusion coefficients, but the rectal wall tissue and malignant prostate tissue had significantly lower diffusion coefficients than normal prostate tissues. Perfusion coefficients and fractions were highly variable within the population, so their clinical utility may be limited, but removal of this variable perfusion component from reported diffusion coefficients is important when attributing clinical differences to diffusion within tissues.

Protoporphyrin IX nanoparticle carrier: preparation, optical properties, and singlet oxygen generation

The present study is focused on developing a nanoparticle carrier for the photosensitizer protoporphyrin IX for use in photodynamic therapy. The entrapment of protoporphyrin IX (Pp IX) in silica spheres was achieved by modification of Pp IX molecules with an organosilane reagent. The immobilized drug preserved its optical properties and the capacity to generate singlet oxygen, which was detected by a direct method from its characteristic phosphorescence decay curve at near-infrared and by a chemical method using 1,3-diphenylisobenzofuran to trap singlet oxygen. The lifetime of singlet oxygen when a suspension of Pp IX-loaded particles in acetonitrile was excited at 532 nm was determined as 52 micros, which is in good agreement with the value determined for methylene blue in acetonitrile solution under the same conditions. The Pp IX-loaded silica particles have an efficiency of singlet oxygen generation (eta Delta) higher than the quantum yield of free porphyrins. This high efficiency of singlet oxygen generation was attributed to changes on the monomer-dimer equilibrium after photosentisizer immobilization.

High-field magnetic resonance imaging of the response of human prostate cancer to Pc 4-based photodynamic therapy in an animal model

INTRODUCTION

High-field magnetic resonance imaging (MRI) is an emerging technique that provides a powerful, non-invasive tool for in vivo studies of cancer therapy in animal models. Photodynamic therapy (PDT) is a relatively new treatment modality for prostate cancer, the second leading cause of cancer mortality in American males. The goal of this study was to evaluate the response of human prostate tumor cells growing as xenografts in athymic nude mice to Pc 4-sensitized PDT.

MATERIALS AND METHODS

PC-3, a cell line derived from a human prostate malignant tumor, was injected intradermally on the back flanks of athymic nude mice. Two tumors were initiated on each mouse. One was treated and the other served as the control. A second-generation photosensitizing drug Pc 4 (0.6 mg/kg body weight) was delivered to each animal by tail vein injection 48 hours before laser illumination (672 nm, 100 mW/cm(2), 150 J/cm(2)). A dedicated high-field (9.4 T) small-animal MR scanner was used for image acquisitions. A multi-slice multi-echo (MSME) technique, permitting noninvasive in vivo assessment of potential therapeutic effects, was used to measure the T2 values and tumor volumes. Animals were scanned immediately before and after PDT and 24 hours after PDT. T2 values were computed and analyzed for the tumor regions.

RESULTS

For the treated tumors, the T2 values significantly increased (P<0.002) 24 hours after PDT (68.2+/- 8.5 milliseconds), compared to the pre-PDT values (55.8+/-6.6 milliseconds). For the control tumors, there was no significant difference (P = 0.53) between the pre-PDT (52.5+/-6.1 milliseconds) and 24-hour post-PDT (54.3+/-6.4 milliseconds) values. Histologic analysis showed that PDT-treated tumors demonstrated necrosis and inflammation that was not seen in the control.

DISCUSSION

Changes in tumor T2 values measured by multi-slice multi-echo MR imaging provide an assay that could be useful for clinical monitoring of photodynamic therapy of prostate tumors.

Photodynamic therapy of the canine prostate: intra-arterial drug delivery

PURPOSE

Interstitial photodynamic therapy (PDT) selectively destroys tissue targeted with a photosensitizer and then exposed to light of a specific wavelength. We report a novel delivery method--intra-arterial drug delivery for PDT of the prostate--in a canine model.

METHODS

To evaluate drug distribution, the prostatovesical artery was selectively cannulated and photosensitizers alone or in conjunction with 99m-technetium-labeled macro-aggregated albumin ((99m)Tc-MAA) were injected via a 3 Fr microcatheter in 8 animals. One dog was followed for 3 months to determine tolerance and toxicity. The remaining animals were euthanized and imaged with whole-body single photon emission CT and gamma counting for radioactivity distribution. Photosensitizer distribution was further analyzed by fluorescence confocal microscopy and tissue chemical extraction. To evaluate PDT, the photosensitizer QLT0074 was infused in 3 animals followed by interstitial illumination with 690 nm laser light.

RESULTS

Intra-arterial infusion selectively delivered drugs to the prostate, with both radioactivity and photosensitizer levels significantly higher (up to 18 times) than in the surrounding organs (i.e., rectum). With unilateral injection of (99m)Tc-MAA, only the injected half of the prostate showed activity whereas bilateral administration resulted in drug delivery to the entire prostate. PDT resulted in comprehensive damage to the prostate without severe complications or systemic toxicity.

CONCLUSION

Injection of radiolabeled MAA into the prostatovesical artery results in distribution within the prostate with negligible amounts reaching the adjacent organs. PDT also demonstrates selective damage to the prostate, which warrants clinical application in targeted prostate therapies.

Interstitial photodynamic therapy of the canine prostate using intra-arterial administration of photosensitizer and computerized pulsed light delivery

PURPOSE

We determined the feasibility of complete treatment of the canine prostate and long-term effectiveness of interstitial photodynamic therapy using the intra-arterial photosensitizer QLT0074 (benzoporphyrin derivative 1,3-diene C,D-diethylene glycol ester A ring) (QLT, Vancouver, British Columbia, Canada) administration and pulsed light delivery.

MATERIALS AND METHODS

The prostate gland of 11 dogs were infused with QLT0074 via the prostatovesical arteries (2 mg drug per artery bilaterally) under fluoroscopic guidance. Immediately following infusion the prostate was surgically exposed and 7 optical fibers with 1.5 cm cylindrical diffusers in after loading sheaths were inserted into the prostate through a template. Light was delivered sequentially to the optic fibers via a computer driven switch system. One dog was sacrificed 6 days after photodynamic therapy to assess acute tissue effects. The other 10 dogs were monitored for clinical tolerance and urinary function, and sacrificed at between 3 and 11 months. Prostate specimens were examined microscopically to evaluate long-term tissue reactions.

RESULTS

Comprehensive destruction of the prostate was noted in the acute dog. Except for urinary retention and mild hematuria no other perioperative complications were observed in the chronic dogs. Urodynamic examination did not reveal deleterious bladder and urethral function. Average prostate volume decreased 71% at 3 months and 56% after 6 months (p=0.007 and 0.014, respectively). Microscopic evaluation revealed prostate glandular epithelial atrophy, stromal fibrosis and mononuclear cell infiltration.

CONCLUSIONS

Interstitial photodynamic therapy using intra-arterial QLT0074 and pulsed light delivery is safe and feasible for comprehensive destruction of the canine prostate. Clinical trials are required to confirm it for managing prostate diseases.

Combined Use of Diffusion-Weighted MRI and 1H MR Spectroscopy to Increase Accuracy in Prostate Cancer Detection

OBJECTIVE

The objective of our study was to establish the sensitivity and specificity for prostate cancer detection using a combined 1H MR spectroscopy and diffusion-weighted MRI approach.

SUBJECTS AND METHODS

Forty-two men (mean age +/- SD, 69.3 +/- 4.7 years) with prostate cancer were studied using endorectal T2-weighted imaging, 2D chemical shift imaging (CSI), and isotropic apparent diffusion coefficient (ADC) maps. Regions of interest (ROIs) were drawn around the entire gland, central gland, and peripheral zone tumor, diagnostically defined as low signal intensity on T2-weighted images within a sextant that was biopsy-positive for tumor. Lack of susceptibility artifact on a gradient-echo B0 map through the slice selected for CSI and no high signal intensity on external array T1-weighted images confirmed the absence of significant hemorrhage after biopsy. CSI voxels were classified as nonmalignant or as tumor (ROI included > or = 30% or > or = 70% tumor). Choline-citrate (Cho/Cit) ratios and average ADCs were calculated for every voxel. A plot of Cho/Cit ratios versus ADCs yielded a line of best separation of tumor voxels from nonmalignant voxels. Receiver operating characteristic (ROC) curves were plotted for Cho/Cit ratios alone, ADCs alone, and a combination of the two.

RESULTS

The Cho/Cit ratios were significantly higher (p < 0.001) and the ADCs were significantly lower (p < 0.006) in tumor-containing voxels than in non-tumor-containing voxels. When voxels containing 30% or more tumor were considered positive, the area under the ROC curves using combined MR spectroscopy and ADC (0.81) was similar to that of Cho/Cit alone (0.79) and better than ADC alone (0.66). When voxels containing 70% or more tumor were considered positive and cutoffs to achieve a 90%-or-greater sensitivity chosen, a combination of Cho/Cit and ADC achieved a significant improvement in specificity compared with Cho/Cit alone (p < 0.0001) or ADC alone (p < 0.0001).

CONCLUSION

When voxels containing > or = 70% tumor are considered positive, the combined use of MR spectroscopy and diffusion-weighted MRI increases the specificity for prostate cancer detection while retaining the sensitivity compared with MR spectroscopy alone or diffusion-weighted MRI alone.

In vivo measurement of parameters of dosimetric importance during interstitial photodynamic therapy of thick skin tumors

A system for interstitial photodynamic therapy is used in the treatment of thick skin tumors. The system allows simultaneous measurements of light fluence rate, sensitizer fluorescence, and tissue oxygen saturation by using the same fibers as for therapeutic light delivery. Results from ten tumor treatments using delta-aminolevulinic acid (ALA)-induced protoporphyrin IX show a significant, treatment-induced increase in tissue absorption at the therapeutic wavelength, and rapid sensitizer photobleaching. The changes in oxy- and deoxyhemoglobin content are monitored by means of near-infrared spectroscopy, revealing a varying tissue oxygenation and significant changes in blood volume during treatment. These changes are consistent with the temporal profiles of the light fluence rate at the therapeutic wavelength actually measured. We therefore propose the observed absorption increase to be due to treatment-induced deoxygenation in combination with changes in blood concentration within the treated volume. A higher rate of initial photobleaching is found to correlate with a less pronounced increase in tissue absorption. Based on the measured signals, we propose how real-time treatment supervision and feedback can be implemented. Simultaneous study of the fluence rate, sensitizer fluorescence, and local tissue oxygen saturation level may contribute to the understanding of the threshold dose for photodynamic therapy.

Effect of Tumor Host Microenvironment on Photodynamic Therapy in a Rat Prostate Tumor Model

Purpose: Tumor host microenvironment plays an important role in tumor growth, metastasis, and response to cancer therapy. In this study, the influence of tumor host environment on tumor pathophysiology, photosensitizer distribution, and photodynamic therapy (PDT) treatment effect was examined in the metastatic at lymph node and lung (MatLyLu) rat prostate tumor.

Experimental Design: MatLyLu tumors implanted in different host environment [i.e., orthotopically (in the prostate) or s.c.] were compared for difference in vessel density, average vessel size, vascular permeability, tumor vascular endothelial growth factor production, and tumor oxygenation. Uptake of photosensitizer verteporfin in tumors in both sites was determined by fluorescence microscopy. To compare tumor response to PDT, both orthotopic and s.c. MatLyLu tumors were given the same doses of verteporfin and laser light treatment, and PDT-induced tumor necrotic area was measured histologically.

Results: Orthotopic MatLyLu tumors were found to grow faster, have higher vessel density and more permeable vasculature, have higher vascular endothelial growth factor protein levels, and have lower tumor hypoxic fraction than the s.c. tumors. Uptake of photosensitizer verteporfin in the orthotopic tumor was higher than in the s.c. tumors at 15 minutes after injection (1 mg/kg, i.v.), and became similar at 3 hours after injection. For the vascular targeting PDT treatment (0.25 mg/kg verteporfin, 50 J/cm2 at 50 mW/cm2, 15 minutes drug-light interval), there was no significant difference in PDT-induced tumor necrotic area between the orthotopic and s.c. tumors, with 85% to 90% necrosis in both types of tumors. However, tumor necrosis induced by the cellular targeting PDT (1 mg/kg verteporfin, 50 J/cm2 at 50 mW/cm2, 3 hours drug-light interval) was significantly different in the orthotopic (64%) versus the s.c. (29%) tumors.

Conclusions: Tumor host environment can significantly affect photosensitizer verteporfin distribution and PDT treatment effect. Verteporfin-PDT regimen targeting tumor cells is more sensitive to such influence than the vascular targeting PDT. Our study showed the importance of tumor host environment in determining tumor physiologic properties and tumor response to PDT. To obtain clinically relevant information, orthotopic tumor model should be used in the experimental studies.

OPTICAL CHARACTERISTICS OF THE CANINE PROSTATE AT 665 NM SENSITIZED WITH TIN ETIOPURPURIN DICHLORIDE: NEED FOR REAL-TIME MONITORING OF PHOTODYNAMIC THERAPY

PURPOSE

Photodynamic therapy (PDT) is an emerging, minimally invasive therapy for prostate cancer that depends on the sequestration of a photosensitizing drug within targeted tissue. The photosensitizer is subsequently activated by light of a specific wavelength, resulting in destruction of the targeted tissue. Successful treatment requires knowledge of the optical properties of the target tissue, a critical element for therapy.

MATERIALS AND METHODS

Adult canines were injected with tin etiopurpurin dichloride (1.0 mg/kg) as a liposome emulsion vehicle in saline 24 hours prior to light treatment. Laser light was delivered to the prostate via a 400 microm optical fiber fitted with a 2.0 cm cylindrical diffuser and optical properties of the prostate were measured.

RESULTS

In this study we determined the attenuation coefficient and critical fluence in the canine prostate. Our studies shown that the attenuation coefficient is not uniform but higher at the base (average for all animals 2.59 to 2.79 cm-1) than in the mid section or apex of the prostate (1.71 to 1.90 cm-1). Significant differences among dogs (0.11 to 12.70 cm-1) were found. In some cases we observed a fluctuation of the attenuation coefficient during treatment. We also established experimentally the minimum energy (1449 mJ/cm2) needed (critical fluence) to produce necrosis. Experimentally establishing the values of effective attenuation and critical fluence is necessary to predict the area of ablation during PDT and protect surrounding organs from over treatment.

CONCLUSIONS

Based on our results it is evident that for PDT of the prostate to be successful the optical parameters of the prostate must be measured and monitored during treatment. We suggest that the optimum way of doing this is real-time computerized monitoring combined with simulation PDT.

Effects of Pd-bacteriopheophorbide (TOOKAD)-mediated photodynamic therapy on canine prostate pretreated with ionizing radiation

The aim of this study was to evaluate the effects of photodynamic therapy (PDT) using a novel palladium bacteriopherophorbide photosensitizer TOOKAD (WST09) on canine prostate that had been pretreated with ionizing radiation. To produce a physiological and anatomical environment in canine prostate similar to that in patients for whom radiotherapy has failed, canine prostates (n = 4) were exposed to ionizing radiation (54 Gy) 5 to 6 months prior to interstitial TOOKAD-mediated PDT. Light irradiation (763 nm, 50-200 J/cm at 150 mW/cm from a 1-cm cylindrical diffusing fiber) was delivered during intravenous infusion of TOOKAD at 2 mg/kg over 10 min. Interstitial measurements of tissue oxygen profile (pO(2)) and of local light fluence rate were also measured. The prostates were harvested for histological examination 1 week after PDT. The baseline pO(2) of preirradiated prostate was in the range 10-44 mmHg. The changes in relative light fluence rate during PDT ranged from 12 to 43%. The acute lesions were characterized by hemorrhagic necrosis, clearly distinguishable from the radiotherapy-induced pre-existing fibrosis. The lesion size was correlated with light fluence and comparable to that in unirradiated prostate treated with a similar TOOKAD-PDT protocol. There was no noticeable damage to the urethra, bladder or adjacent colon. The preliminary results obtained from a small number of animals indicate that TOOKAD-PDT can effectively ablate prostate pretreated with ionizing radiation, and so it may provide an alternative modality for those prostate cancer patients for whom radiotherapy has failed.