Optimization of multifiber light delivery for the photodynamic therapy of localized prostate cancer

Microfluidic system with light intensity filters facilitating the application of photodynamic therapy for high-throughput drug screening

BACKGROUND

Photodynamic therapy utilizes light energy with a photosensitizer (a light-sensitive drug) to kill cancer cells through light activation. When a photosensitizer is injected into the bloodstream and exposed to a specific wavelength of light, it generates oxygen to destroy or damage nearby cancer cells, while minimizing side effects on normal cells. Although photodynamic therapy is effective for treating cancer, various parameters, such as the optimum light intensity and photosensitizer dose, are currently poorly understood due to the complexity of conventional experimental schemes.

METHODS

To effectively perform a simultaneous single parallel test for several different light irradiation conditions on each cell, a microfluidic device was developed to generate eight different intensities from a single light-emitting diode source, through eight different color dye concentrations functioning as light intensity filters. To show that this novel high-throughput microfluidic system can analyze the effects of various light intensities during photodynamic therapy, the optimum light intensities and photosensitizer doses were determined for two different cancer cell lines.

RESULTS

Optimum light intensities and photosensitizer were determined for all cell lines. The photodynamic therapy effects in response to different irradiated light intensities were characterized by analyzing cell viability after photosensitizer treatment CONCLUSIONS: : The developed platform is capable of being used as a photodynamic therapy screening tool. The proposed platform provides a simple and robust way to optimize the combined parameters of light intensity and dosage for diverse types of cancer cells.

Clinical Trials and Basic Research in Photodynamic Diagnostics and Therapies from the Center for Laser Diagnostics and Therapy in Poland

The purpose of this review is to present an overview of the development of photodiagnostic and photodynamic therapy (PDD and PDT) techniques in Poland. The paper discusses the principles of PDD, including fluorescent techniques in determining precancerous conditions and cancers of the skin, digestive tract, bladder and respiratory tract. Methods of PDT of cancer will be discussed and the current state of knowledge as well as future trends in the development of photodynamic techniques will be presented, including the possibility of using photodynamic antimicrobial therapy. Research pioneers in photodynamic medicine such as Thomas Dougherty are an inspiration for the development of methods of PDD and PDT in our Clinic. The Center for Laser Diagnostics and Therapy in Bytom, Poland, promotes the propagation of PDD and PDT through the training of clinicians and raising awareness among students in training and the general public. Physicians at the Center are engaged in photomedical research aimed at clinical implementation and exploration of new avenues in photomedicine while optimizing existing modalities. The Center promotes dissemination of clinical results from a wide range of topics in PDD and PDT and serving as representative authorities of photodynamic medicine in Poland and Europe.

A fast heterogeneous algorithm for light fluence rate for prostate photodynamic therapy

To accurately calculate light fluence rate distribution in prostate photodynamic therapy (PDT), optical heterogeneity has to be taken into account. Previous study has shown that a kernel based on analytic solution of the diffusion equation can perform the calculation with accuracy comparable to Finite-element method. An assumption is made that light fluence rate detected at a point in the medium is affected primarily by the optical properties of points (or elements) on the line between the source and the point. The exponential decay term of the light fluence rate is expressed as an integral of effective attenuation coefficient of each point along the line. The kernel method is first developed for a point source and then extended for a linear source. A linear source is considered being composed of multiple point sources and light fluence rate is summation of the fluence rates generated by the point sources. In this study, we have implemented a fast ray-trace algorithm to substantially speed up the calculation. The kernel calculation is compared with FEM calculation and is examined with light fluence rate measurements. The examination with clinical measurement data shows that calculated fluence rates present similar features in distribution as the measurement, with errors of 30%-70% for the peak fluence rates. We concluded that our heterogeneous algorithm is potentially valuable for light fluence rate optimization during interstitial PDT.

Determination of in vivo light fluence distribution in a heterogeneous prostate during photodynamic therapy

Light fluence delivered to the tumor volume is an important dosimetry quantity in photodynamic therapy (PDT). The in vivo measurements in four patients showed that light fluence rates varied significantly in a prostate during PDT. The maximum and the mean fluence rates in a quadrant varied from 74 to 777 mW cm(-2) and from 45 to 385 mW cm(-2), respectively, among 13 quadrants of four patients' prostates. To determine three-dimensional (3D) light fluence rate distribution in a heterogeneous prostate, a kernel model was developed. The accuracy of the model was examined with a finite-element-method (FEM) model calculation, a phantom measurement, and the in vivo measurements. The kernel model calculations showed good agreements with the FEM model calculation and the measurements. The maximum and the mean deviations of the kernel model calculation from the in vivo measurements in the four patients were 23% and 4%, respectively. The kernel model, which is based on an analytic expression of a point source in a spherically symmetrical heterogeneity, has the advantage of fast calculation and is suitable for real-time PDT treatment planning.

In vivo optical characterization of human prostate tissue using near-infrared time-resolved spectroscopy

The development of photodynamic therapy into a modality for treatment of prostate cancer calls for reliable optical dosimetry. We employ, for the first time, interstitial time-resolved spectroscopy to determine in vivo optical properties of human prostate tissue. Nine patients are included in the study, and measurements are conducted prior to primary brachytherapy treatment of prostate cancer. Intrasubject variability is examined by measuring across three tissue volumes within each prostate. The time-resolved instrumentation proves its usefulness by producing good signal levels in all measurements. We are able to present consistent values on reduced scattering coefficients (mu(s)'), absorption coefficients (mu(a)), and effective attenuation (mu(eff)) at the wavelengths 660, 786, and 916 nm. At 660 nm, mu(s)' is found to be 9+/-2 cm(-1), and mu(a) is 0.5+/-0.1 cm(-1). Derived values of mu(eff) are in the range of 3 to 4 cm(-1) at 660 nm, a result in good agreement with previously published steady state data. Total hemoglobin concentration (THC) and oxygen saturation are spectroscopically determined using derived absorption coefficients. Derived THC values are fairly variable (215+/-65 microM), while derived values of oxygen saturation are gathered around 75% (76+/-4%). Intrasubject variations in derived parameters correlate (qualitatively) with the heterogeneity exhibited in acquired ultrasound images.

Magnetic resonance imaging correlated with the histopathological effect of Pd-bacteriopheophorbide (Tookad) photodynamic therapy on the normal canine prostate gland

BACKGROUND AND OBJECTIVE

To determine the optimal magnetic resonance imaging (MRI) methodology to assess photodynamic therapy (PDT)-induced histopathological responses in the prostate.

STUDY DESIGN/MATERIALS AND METHODS

Laparotomy was performed in five healthy dogs. Cylindrical diffuser was placed in the prostates to deliver light of 50-300 J/cm at 150 mW/cm and 763 nm to activate IV-injected Tookad (1 mg/kg b.w.). Fast spin echo (FSE) T2-weighted, post-contrast-enhanced T1-(CE-T1) and diffusion weighted images (DWI) were obtained pre- and 2 days, 7 days, and 1 month post-PDT. Radiological-histopathological correlation was performed at 7 days (n = 4) and 1 month (n = 1) after PDT. A qualitative assessment of signal changes and apparent diffusion coefficient (ADC) mapping was performed.

RESULTS

At 2 or 7 days post-PDT, there was good spatial correlation between PDT-induced hemorrhagic necrosis and unenhanced regions on CE-T1 images. There was a rapidly and persistently enhancing rim corresponding to edema and inflammation. FSE T2 and DWI showed altered signal but did not clearly define necrosis in all cases. At 1 month, it was hard to correlate MR images to histopathologic changes as they represented a mixture of necrosis and developing fibrosis, which led to a mixed signal intensity and less demarcated contrast enhancement.

CONCLUSIONS

At 7 days after PDT, gadolinium DTPA contrast-enhanced MRI is superior to DWI and T2 imaging in assessing the boundary of Tookad PDT-induced tissue necrosis in the normal canine prostate.

A review of progress in clinical photodynamic therapy

Photodynamic therapy (PDT) has received increased attention since the regulatory approvals have been granted to several photosensitizing drugs and light applicators worldwide. Much progress has been seen in basic sciences and clinical photodynamics in recent years. This review will focus on new developments of clinical investigation and discuss the usefulness of various forms of PDT techniques for curative or palliative treatment of malignant and non-malignant diseases.

Photodynamic therapy with Pd-Bacteriopheophorbide (TOOKAD): successful in vivo treatment of human prostatic small cell carcinoma xenografts

Small cell carcinoma of the prostate (SCCP), although relatively rare, is the most aggressive variant of prostate cancer, currently with no successful treatment. It was therefore tempting to evaluate the response of this violent malignancy and its bone lesions to Pd-Bacteriopheophorbide (TOOKAD)-based photodynamic therapy (PDT), already proven by us to efficiently eradicate other aggressive non-epithelial solid tumors. TOOKAD is a novel bacteriochlorophyll-derived, second-generation photosensitizer recently, developed by us for the treatment of bulky tumors. This photosensitizer is endowed with strong light absorbance (epsilon(0) approximately 10(5) mol(-1) cm(-1)) in the near infrared region (lambda=763nm), allowing deep tissue penetration. The TOOKAD-PDT protocol targets the tumor vasculature leading to inflammation, hypoxia, necrosis and tumor eradication. The sensitizer clears rapidly from the circulation within a few hours and does not accumulate in tissues, which is compatible with the treatment of localized tumor and isolated metastases. Briefly, male CD1-nude mice were grafted with the human SCCP (WISH-PC2) in 3 relevant anatomic locations: subcutaneous (representing tumor mass), intraosseous (representing bone metastases) and orthotopically within the murine prostate microenvironment. The PDT protocol consisted of i.v. administration of TOOKAD (4 mg/kg), followed by immediate illumination (650-800 nm) from a xenon light source or a diode laser emitting at 770 nm. Controls included untreated animals or animals treated with light or TOOKAD alone. Tumor volume, human plasma chromogranin A levels, animal well being and survival were used as end points. In addition, histopathology and immunohistochemistry were used to define the tumor response. Subcutaneous tumors exhibited complete healing within 28-40 days, reaching an overall long-term cure rate of 69%, followed for 90 days after PDT. Intratibial WISH-PC2 lesions responded with complete tumor elimination in 50% of the treated mice at 70-90 days after PDT as documented histologically. The response of the orthotopic model was also analyzed histologically with similar results. The study with this model suggests that TOOKAD-based PDT can reach large tumors and is a feasible, efficient and well-tolerated approach for minimally invasive treatment of local and disseminated SCCP.

Light penetration in bladder tissue: implications for the intravesical photodynamic therapy of bladder tumours

OBJECTIVES

To assess (i) the optical properties and depth of penetration of varying wavelengths of light in ex-vivo human bladder tissue, using specimens of normal bladder wall, transitional cell carcinoma (TCC) and bladder tissue after exposure to ionizing radiation; and (ii) to estimate the depth of bladder wall containing cancer that could potentially be treated with intravesical photodynamic therapy (PDT), assuming satisfactory tissue levels of photosensitizer. Materials and methods The study included 11 cystectomy specimens containing invasive TCC (five from patients who had previously received external-beam bladder radiotherapy, but with recurrent TCC) and three 'normal' bladders removed from patients treated by exenteration surgery for extravesical pelvic cancer. Full-thickness bladder wall and tumour samples were taken from these specimens and using an 'intravesical' and a previously validated interstitial model, the optical penetration depths (i.e. the tissue depth at which the light fluence is 37% of incident) were calculated at wavelengths of 633, 673 and 693 nm.

RESULTS

There were no significant differences in light penetration between normal and tumour-affected bladder tissue at each wavelength. There were significant differences in light penetration among wavelengths; light at 693 nm penetrated approximately 40% further than light at 633 nm (P < 0.002). The light currently used in bladder PDT (633 nm) has a mean (SEM) optical penetration depth of 4.0 (0.1) mm within TCC. In addition, at this wavelength, there was 29% greater light penetration in previously irradiated than in unirradiated bladder wall (P = 0.001). This did not occur in the tumour-affected bladder.

CONCLUSIONS

Bladder tissue is relatively more translucent than other human tissues and there is therefore great potential for PDT in the treatment of bladder cancer. As there is no difference in light penetration between TCC and normal bladder tissue, a tumour-specific response with diffuse illumination of the bladder will depend on drug localization within the tumour. The currently used wavelength of 633 nm can be expected to exert a PDT effect within bladder tumour up to a depth of 20 mm. Increasing the wavelength will allow deeper pathology to be treated.

Laser dosimetry studies in the prostate

OBJECTIVE

To review the currently available data of photodynamic therapy (PDT) optical dosimetry for possible prostatic applications.

SUMMARY BACKGROUND DATA

PDT is a new cancer treatment modality often used as an alternative tumor treatment method. Recently, PDT has been suggested as an alternative therapy for prostatic carcinoma and BPH.

METHODS

PDT: utilizes light and a preadministered photosensitizer drug to achieve localized tumor control. This article reviews currently available data on optical dosimetry of PDT in both human and canine prostates.

RESULTS

At 630 nm, a common wavelength used for Photofrin PDT, results indicate that light penetration is similar in cancerous and normal prostatic tissue. Because of limited light penetration, multiple fiber irradiation is necessary if eradicating the entire prostate glad is the ultimate goal. The available data also show that dynamic changes occur in light fluence rate distribution during PDT irradiation.

CONCLUSIONS

PDT can be used to destroy prostatic tissue. Real-time optical dosimetry is necessary if accurate lesion volume control is desired.

Interstitial photodynamic therapy in the canine prostate with disulfonated aluminum phthalocyanine and 5-aminolevulinic acid-induced protoporphyrin IX

BACKGROUND

Photodynamic therapy (PDT) is an experimental approach for treating prostate cancer localized to the gland that does not involve surgery or irradiation. Second-generation photosensitizers 5-aminolevulinic acid (ALA) and aluminum disulfonated phthalocyanine (AlS2Pc) were studied in the normal canine prostate.

METHODS

Tissue biodistribution of photosensitizers on serial biopsies was examined using fluorescence microscopy. Photodynamic therapy was done by delivering red light interstitially at 100 mW through fibers placed under transrectal ultrasound guidance.

RESULTS

Peak levels of AlS2Pc appeared at 5-24 hr and at 3 hr for ALA. Macroscopic PDT lesions were up to 12 mm in diameter using AlS2Pc, but only 1-2 mm with ALA. Light at 300 mW caused thermal lesions. At 28 days, damaged glands remained atrophic, but the interlobular supporting stroma was well-preserved. Urethral lesions healed by 28 days without functional impairment.

CONCLUSIONS

Although the results with ALA were disappointing, PDT using AlS2Pc looks like a promising modality for treatment of localized prostate cancer.

In situ comparison of 665 nm and 633 nm wavelength light penetration in the human prostate gland

The depth of treatment in photodynamic therapy (PDT) of tumors varies with the wavelength of light activating the photosensitizer. New generation photosensitizers that are excited at longer wavelengths have the potential for increasing treatment depths. Tin ethyl etiopurpurin (SnET2), a promising second-generation photosensitizer is maximally activated at 665 nm, which may be significantly more penetrating than 633 nm light currently used with porphyrins in PDT. The penetration of 665 nm and 633 nm wavelength red light in the prostate gland was compared in 11 patients undergoing prostatic biopsies for suspected prostatic cancer. Interstitial optical fibers determined the light attenuation within the prostate gland. Of the 11 patients, 7 had dual wavelength and 4 had single wavelength studies. The mean attenuation coefficients, mueff, for 665 nm and 633 nm wavelength light were 0.32 +/- 0.05 mm-1 and 0.39 +/- 0.05 mm-1, respectively, showing a statistically significant difference (P = 0.0003). This represented a 22% increase in the mean penetration depth and at 10 mm from the delivery fiber there was 1.8 times as much 665 nm light fluence than 633 nm. The mean mueff at 665 nm for benign and malignant prostate tissue were similar (P = 0.42), however, there was significant interpatient variation (mueff ranging from 0.24 to 0.42 mm-1) reflecting biological differences of therapeutic importance. The enhanced light fluence and penetration depth with 665 nm light should allow significantly larger volumes of prostatic tissue to be treated with SnET2-mediated PDT.

In vivo laser light distribution in human prostatic carcinoma

The extent of laser light diffusion within prostatic tumor is of major importance in the treatment of localized prostatic cancer with photodynamic therapy (PDT). The penetration of 633 nm. wavelength red light was studied in eleven patients with suspected prostatic cancer using a novel method suitable for in situ measurements. Light delivery and detector fiber, placed interstitially within the gland, determined light attenuation at different interfiber separations. Of 11 patients, 10 had bilateral and 1 had single lobe studies. The mean +/- the standard error of the mean attenuation coefficients (sigma eff) for benign and malignant prostate tissue were 0.35 +/- 0.02 mm-1 and 0.36 +/- 0.02 mm-1, respectively, indicating similar optical densities (p = .58). Patients with bilateral lobe involvement showed little intraglandular variation in sigma eff (p = 0.23). However, there was interpatient variation (sigma eff = 0.28 to 0.48 mm-1) reflecting biological differences which, though therapeutically important, were not statistically significant (p = 0.057). This study showed that treatment requires individualization and predicted that 4 cylindrical diffusers are expected to destroy 25 ml. of prostatic tumor with PDT.