Mechanism of dentin hardness measurements using a dentin hardness measuring device with a light-emitting diode.

Significance: Managing caries is imperative in a rapidly aging society. Current diagnoses use qualitative indices. However, a quantitative evaluation of hardness in a clinical setting may lead to more accurate diagnoses. Previously, hardness meter using indenter with light for tooth monitoring (HAMILTOM) was developed to quantitatively measure tooth hardness. Herein, the physical interpretation of dentin hardness measured using HAMILTOM and the dentin hardness measurement mechanism are discussed. Aim: This study evaluates the mechanism of dentin hardness measurements using HAMILTOM physically and compare the invasiveness to dentin by HAMILTOM with those using a dental probe for palpation. Approach: Eleven bovine dentin samples were used to create caries models. HAMILTOM measured the dark areas, and its indentations were observed using scanning electron microscopy. Also, its invasiveness was evaluated by comparing the results with those from dental probe palpation. Results: The indentation areas were smaller than the dark areas in HAMILTOM, which may be due to exuded water from the dentin sample and the elastic recovery of dentin sample. Additionally, the dental probe indentation was deeper than the HAMILTOM indentations. Conclusions: The results demonstrate that the indentation areas were smaller than the dark areas measured by HAMILTOM, which might contain the influence of exuded water and the deformation of dentin sample. Also, HAMILTOM is less invasive than dental probe palpation. In the future, HAMILTOM may become a standard hardness measuring method to diagnose root caries.

Increased fluorescence observation intensity during the photodynamic diagnosis of deeply located tumors by fluorescence photoswitching of protoporphyrin IX.

Significance: Photobleaching of the photosensitizer reduces fluorescence observation time and the intensity of fluorescence emitted for tumor detection during 5-aminolevulinic acid-based photodynamic diagnosis. Aim: This study aims to utilize the concept of fluorescence photoswitching, which uses the fluorescence emission from photosensitizer excitation followed by the simultaneous excitation of the photosensitizer and its photoproduct to increase the fluorescence detection intensity during PDD of deeply located tumors. Approach: The fluorescence photobleaching of protoporphyrin IX (PpIX) and the formation of its photoproduct, photoprotoporhyrin (Ppp), caused by exposure to 505 nm light were investigated in solution, ex vivo, and in vivo, and the fluorescence photoswitching was analyzed. The fluorescence observations of PpIX and Ppp were performed with 505 and 450 or 455 nm excitation, respectively, which is the suited wavelength for the primary excitation of each fluorophore. Results: Fluorescence photoswitching was observed in all forms of PpIX investigated, and the fluorescence photoswitching time, fluorescence intensity relative to the initial PpIX and Ppp intensity, and fluorescence intensity relative to PpIX after photobleaching were obtained. The dependence of the fluorescence photoswitching time and intensity on the irradiation power density was noted. A fluorescence intensity increase between 1.6 and 3.9 times was achieved with simultaneous excitation of PpIX and Ppp after fluorescence photoswitching, compared with the excitation of PpIX alone. Conclusions: We have demonstrated the potential of fluorescence photoswitching for the improvement of the fluorescence observation intensity for the PDD of deeply located tumors.

Demonstration of an optical dentin hardness measuring device using bovine dentin with different demineralization times.

Significance: The increase in root caries is a serious problem as society ages. Root caries is diagnosed by inspection and palpation, which are qualitative. A method to objectively and quantitatively evaluate the progress of root caries in a clinical setting is strongly desired. The root caries could be diagnosed by measuring hardness because dentin becomes softer as the caries progresses. Vickers hardness has been customarily used as an indicator of tooth hardness. However, this method cannot be used to in vivo teeth because the teeth must be dried prior to measurement to make the indentation. A hardness meter using an indenter with light for tooth monitoring (HAMILTOM) is proposed as an optical device. HAMILTOM could measure hardness of teeth in wet condition as a dark area while applying a load to dentins without drying. Therefore, HAMILTOM may realize hardness measurements of in vivo teeth in a clinical setting quantitatively. Aim: The aim of our study is to demonstrate the optical dentin hardness measuring device HAMILTOM using bovine dentin with different demineralization times and to evaluate the correlation between the dark areas measured by HAMILTOM and the Vickers hardness measured by the Vickers hardness tester. Approach: The samples were 20 bovine dentins. They were demineralized by a lactic acid solution with different times and divided into groups 1 and 2 of 10 samples each. In both groups, the dark areas and Vickers hardness were measured for each sample. Group 1 was used to obtain a calibration curve to calculate Vickers hardness from the dark area. Group 2 was used to validate the calibration curve obtained from the dentin samples of group 1. Results: The areas appearing black without a total internal reflection of the indenter measured by HAMILTOM increased as the demineralization time increased. Additionally, the Vickers hardness of group 2 calculated by the dark areas of group 2 and the calibration curve obtained in group 1 and the Vickers hardness of group 2 measured by the Vickers hardness tester were strongly correlated with a determination coefficient of 0.99. Conclusions: The results demonstrate that HAMILTOM may be a suitable alternative to the conventional method. Unlike the conventional method, which cannot be used for in vivo teeth, HAMILTOM holds potential to quantitatively evaluate the progress of caries in in vivo teeth.

Effect of Q-switched Er:YAG laser irradiation on bonding performance to dentin surface.

The use of Q-switched erbium:yttrium-aluminum-garnet laser (Er:YAG laser), which have much less thermal effects than conventional Er:YAG lasers, has been proposed mainly in the medical field. The purpose of this study was to evaluate the bonding ability of dentin after Q-switched Er:YAG laser irradiation.The effects of dentin irradiation with Q-switched and conventional lasers were evaluated in terms of dentin morphology, roughness, hardness, elemental content, and resin bonding strength. Q-switched Er:YAG laser at average power densities of 20, 40, and 60 W/cm2 and conventional Er:YAG laser at 909 W/cm2 were used, and their performance was compared with that of the untreated group. Significant differences (p<0.05) were observed between 20 W/cm2 and the other groups in term of surface roughness and surface hardness. The resin adhesion of the 20 W/cm2 group was significantly higher than that of the other groups (p<0.05).

Mass Spectrometric Analysis of the Photobleaching of Protoporphyrin IX Used in Photodynamic Diagnosis and Therapy of Cancer.

Photobleaching and photoproduct formations are considered essential phenomena in improving the efficacy of photodynamic diagnosis and therapy (PDD and PDT). We investigated the photobleaching of protoporphyrin IX (PpIX) by measuring its concentration with mass spectrometry (MS). The reduction in the concentration of PpIX dissolved in dimethyl sulfoxide was measured during PDD and PDT conditions using lasers with wavelengths of 405 and 635 nm, respectively, at a power density of 10, 50 or 100 mW/cm2 . The obtained results were compared with the results of conventional fluorescence spectroscopy and previously reported results. Our results demonstrate the variation in the MS-based photobleaching coefficient of PpIX with the power density, while the fluorescence-based photobleaching coefficient was independent of the power density. The results of MS also show faster photobleaching of PpIX in comparison with that obtained from fluorescence. The difference may be attributed to the change in the fluorescence quantum yield of PpIX with its concentration and the effect of fluorescence emission from the PpIX photoproducts. Thus, an MS-based investigation of the photobleaching poses to be a more stable investigation form. Our finding highlights the importance of recognizing the potential significance of these discoveries in the PDD and PDT dosimetry and efficacy.

Incident Fluence Analysis for 755-nm Picosecond Laser Treatment of Pigmented Skin Lesions Based on Threshold Fluences for Melanosome Disruption.

BACKGROUND AND OBJECTIVES: In this study, the threshold fluences for disrupting the melanosomes for pigmented skin lesion treatment were determined using a 755-nm picosecond laser for clinical use. Based on the melanosome disruption thresholds, incident fluences corresponding to the target lesion depths were evaluated in silico for different laser spot sizes. STUDY DESIGN/MATERIALS AND METHODS: Melanosome samples were isolated from porcine eyes as alternative samples for human cutaneous melanosomes. The isolated melanosomes were exposed to 755-nm picosecond laser pulses to measure the mean particle sizes by dynamic light scattering and confirm their disruption by scanning electron microscopy. The threshold fluences were statistically determined from the relationships between the irradiated fluences and the mean particle sizes. Incident fluences of picosecond laser pulses for the disruption of melanosomes located at different depths in skin tissue were calculated through a light transport simulation using the obtained thresholds. RESULTS: The threshold fluences of 550- and 750-picosecond laser pulses were determined to be 2.19 and 2.49 J/cm2 , respectively. The numerical simulation indicated that appropriate incident fluences of picosecond laser pulses differ depending on the depth distribution of the melanosomes in the skin tissue, and large spot sizes are desirable for disrupting the melanosomes more deeply located within the skin tissue. CONCLUSION: The threshold fluences of picosecond laser pulses for melanosome disruption were determined. The incident fluence analysis based on the thresholds for melanosome disruption provides valuable information for the selection of irradiation endpoints for picosecond laser treatment of pigmented skin lesions. Lasers Surg. Med. © 2021 The Authors. Lasers in Surgery and Medicine published by Wiley Periodicals LLC.

Measurement of absorption and reduced scattering coefficients in Asian human epidermis, dermis, and subcutaneous fat tissues in the 400- to 1100-nm wavelength range for optical penetration depth and energy deposition analysis (Errata).

The errata correct errors that appeared in Table 2 of the published article.

Improvement in Ionization Efficiency Using Metal Oxide Nanoparticles in Laser Desorption/Ionization Mass Spectrometry of a Cancer Drug.

Mass spectrometry imaging (MSI) without labeling has the potential for faster screening in drug development. Matrix-assisted laser desorption/ionization (MALDI) is typically used, but it has a large matrix size and uneven drug distribution. Surface-assisted laser desorption/ionization (SALDI) using nanoparticles (NPs) may overcome these issues. Here, the influence of NPs, solvent ratio, and order of dropping of NPs on SALDI-MSI of protoporphyrin IX (PpIX), a cancer drug, are reported. A solution of PpIX in a 50% aqueous solution of 50% acetonitrile at a concentration of 10 µM was used. The NPs include ZnO, Fe3O4, and four types of TiO2. The NPs were fabricated by dissolving them on an aqueous 90% acetonitrile solution. Mass spectra were obtained with a time-of-flight mass spectrometer using a Nd:YAG laser at a 355-nm wavelength. The signal intensity using TiO2 at a 0.5 mg/mL concentration in 50% acetonitrile was increased by 1.6-fold compared to that without TiO2. Changing the solvent to 90% acetonitrile gave a uniform TiO2 distribution and a 9-fold increase in the signal intensity for PpIX. Among the four types of TiO2 with different particle sizes and crystal structures, TiO2 with a smaller particle size and a rutile crystal structure produced the highest signal intensity. Forming a layer on top of the PpIX also resulted in an increased signal intensity. Hence, SALDI using TiO2 provides effective ionization of the drug. In the future, we plan to investigate a spray method for the ionization of PpIX using TiO2 for the MSI of various drugs.

Efficient photodynamic therapy against drug-resistant prostate cancer using replication-deficient virus particles and talaporfin sodium.

To enhance the potency of photosensitizer, we developed a novel photosensitizer, Laserphyrin®-HVJ-E (L-HVJ-E), by incorporating talaporfin sodium (Laserphyrin®, Meiji Seika Pharma) into hemagglutinating virus of Japan envelope (HVJ-E). In this study, we examined the optimal Laserphyrin® concentration for preparation of Laserphyrin®-HVJ-E which had photocytotoxicity and maintained direct cytotoxicity derived from HVJ-E. Then, potency of Laserphyrin®-HVJ-E and Laserphyrin® were compared in vitro using castration-resistant prostate cancer cell line (PC-3). A laser diode (L660P120, Thorlabs, USA) with a wavelength of 664 nm was used for light activation of Laserphyrin®, which corresponds to an absorption peak of Laserphyrin® and provides a high therapeutic efficiency. The photocytotoxicity and direct cytotoxicity of Laserphyrin®-HVJ-E prepared using various Laserphyrin® concentrations were evaluated using PC-3 cell in vitro. We categorized the treatment groups as Group 1: 50 µL of D-MEM treatment group, Group 2: HVJ-E treatment group, Group 3: Laserphyrin®-HVJ-E treatment group, and Group 4: Laserphyrin® treatment group. Group 3 was subjected to different concentrations of Laserphyrin®-HVJ-E suspension, and all groups were subjected to different incubation periods (24, 48 h), (30 min, 1 h, or 3 h,) respectively, without and after PDT. Laserphyrin®-HVJ-E prepared using 15 mM Laserphyrin® had high photocytotoxicity and maintained HVJ-E's ability to induce direct cytotoxicity. Therapeutic effect of Laserphyrin®-HVJ-E was substantially equivalent to that of Laserphyrin® alone even at half Laserphyrin® concentration. By utilizing Laserphyrin®-HVJ-E, PDT could be performed with lower Laserphyrin® concentration. In addition, Laserphyrin®-HVJ-E showed higher potency than Laserphyrin® by combining cytotoxicities of HVJ-E and PDT.

Enhancement of Ionization Efficiency Using Zeolite in Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry of Multiple Drugs in Cancer Cells (Mass Spectrometry of Multiple Drugs in Cells Using Zeolite).

Combined therapy using photodynamic therapy (PDT) and chemotherapy has been proposed for anticancer-drug-resistant cancer cells. To evaluate the efficacy of such a combined therapy, the uptakes of an anticancer drug and a photosensitizer in cancer cells must be assessed. Mass spectrometry using matrix-assisted laser desorption/ionization can detect multiple drugs simultaneously. Human prostate cancer cells PC-3 or docetaxel-resistant cancer cells PC-3-DR were incubated in a serum-free medium containing a photosensitizer, protoporphyrin IX (PpIX), and an anticancer drug, docetaxel. A zeolite matrix was created by mixing 6-aza-2-thiothymine and NaY5.6 zeolite, and dissolving in water with 50% acetone. Ions were obtained with a time-of-flight mass spectrometer using a Nd:YAG laser at a wavelength of 355 nm. The cell morphology was preserved by washing the cells with ammonium acetate and drying in a vacuum after drug administration. Protonated PpIX (m/z 563.3) and the sodium adduct ion of docetaxel (m/z 829.9) were obtained from PC-3 cells simultaneously using the zeolite matrix. On the other hand, PpIX was detected but ions originating from docetaxel were not detected from PC-3-DR cells. The result indicated the efficacy of PDT for docetaxel-resistant cancer cells.

Measurement of absorption and reduced scattering coefficients in Asian human epidermis, dermis, and subcutaneous fat tissues in the 400- to 1100-nm wavelength range for optical penetration depth and energy deposition analysis.

SIGNIFICANCE: In laser therapy and diagnosis of skin diseases, the irradiated light distribution, which is determined by the absorption coefficient µa and reduced scattering coefficient µs' of the epidermis, dermis, and subcutaneous fat, affects the treatment outcome and diagnosis accuracy. Although values for µa and µs' have been reported, detailed analysis for Asian skin tissues is still lacking. AIM: We present µa and µs' measurements of Asian skin tissues in the 400- to 1100-nm wavelength range for evaluating optical penetration depth and energy deposition. APPROACH: The measurements with Asian human skin samples are performed employing a double integrating sphere spectrometric system and an inverse Monte Carlo technique. Using the measured parameters, the optical penetration depth and energy deposition are quantitatively analyzed. RESULTS: The µa of the epidermis layer varies among different ethnic groups, while the µa of the other layers and the µs' of all of the layers exhibit almost no differences. The analysis reveals that the optical penetration depth and the energy deposition affect the photodynamic therapy treatment depth and the heat production in skin tissue, respectively. CONCLUSIONS: The experimentally measured values of µa and µs' for Asian skin tissues are presented, and the light behavior in Asian skin tissues is analyzed using a layered tissue model.

Fluorescence detection of deep intramucosal cancer excited by green light for photodynamic diagnosis using protoporphyrin IX induced by 5-aminolevulinic acid: an ex vivo study.

SIGNIFICANCE: The diagnostic depth of photodynamic diagnosis (PDD) for gastric cancer with protoporphyrin IX (PpIX) is limited, which leads to missing intramucosal cancers in screening and surgery. AIM: The reason is that the excitation light, whose wavelength is determined by the highest absorption peak of PpIX (∼405 nm), is strongly attenuated by mucosal tissues. We investigated an excitation wavelength that can extend the diagnostic depth of PpIX fluorescence at the mucosal subsurface. APPROACH: By calculating the depth-dependent intensity of the excitation light in porcine gastric mucosa for each wavelength, relationships among the wavelength, fluorophore depth, and fluorescence intensity were assessed and fluorescence images of PpIX pellets located at different fluorophore depths were compared experimentally by changing the excitation wavelength. RESULTS: The numerical calculation showed that a 505-nm excitation light provided the highest fluorescence intensities at a fluorophore depth deeper than 1.1 mm. In the fluorescence observation, the fluorescence intensities at fluorophore depths of 0 and 1.0 mm at 405 nm were 5.4 × 103 and 1.0 × 103 arb. units, whereas those at 505 nm were 5.3 × 101 and 1.9 × 102 arb. units, respectively. CONCLUSION: The experimental results suggest that the diagnosis depth of PDD with PpIX for intramucosal cancer can be extended by 505-nm excitation light.

Enhancement of the safety and efficacy of colorectal endoscopic submucosal dissection using a CO2 laser.

Endoscopic submucosal dissection (ESD) has been at the forefront of international attention as a less invasive treatment for early gastrointestinal cancer. Currently, ESD involves the use of an electrosurgical knife for mucosal incision and subsequent submucosal dissection. However, it has been reported that perforation occurs in approximately 5% of cases. To enhance tissue selectivity with this modality, we focused on applying a laser to ESD (laser ESD). A CO2 laser was chosen as the surgical knife because the saline or sodium hyaluronate solution injected into the submucosal layer during the current ESD procedure has a high absorption coefficient at the wavelength of the CO2 laser. Thus, the purpose of this study is to quantitatively clarify the safety and efficacy of laser ESD for the colon. First, we validated a porcine colon as a model of the human colon in terms of optical and thermal properties. Next, ex vivo experiments on the safety and efficacy of laser ESD were performed. In ex vivo experiments using extracted porcine colon tissue, an incision depth of 0.5-1.0 mm was obtained without thermal damage to the muscle layer when the power density was set at 17, 22, or 28 W/mm2. In addition, less thermal damage was observed in tissue incised with this method compared with electrosurgical knives. These results might be explained by the strong absorption of the CO2 laser by the saline injected into the submucosa. Therefore, laser ESD is expected to be a safer method for the treatment of early colon cancer.

Determination and analysis of singlet oxygen quantum yields of talaporfin sodium, protoporphyrin IX, and lipidated protoporphyrin IX using near-infrared luminescence spectroscopy.

In photodynamic therapy (PDT), singlet oxygen ([Formula: see text]) is the main species responsible for promoting tumor cell death. The determination of the quantum yield (ΦΔ) of a photosensitizer (PS) is important for dosimetry. The purpose of this paper is to quantify the [Formula: see text] generated by the PS by near-infrared spectroscopy (NIRS). The ΦΔ of different PS species were measured by the detection of near-infrared [Formula: see text] luminescence. From the measurement results, the ΦΔ of talaporfin sodium, protoporphyrin IX (PpIX), and lipidated PpIX (PpIX lipid) were measured as 0.53, 0.77, and 0.87, respectively. In addition, the ΦΔ values of PpIX in a hypoxic and oxic solution were evaluated, since tumors are associated with regions of hypoxia. The measured ΦΔ indicated a same value at high (DO: 20%) and low (DO: 1%) oxygen concentrations. Using the measured ΦΔ, the amount of [Formula: see text] generated by the PSs was estimated using [[Formula: see text]] = D*ΦΔ, where D* is the total excited PS concentration. The generated [Formula: see text] amounts were little different at the high and the low oxygen concentrations, and the generated [Formula: see text] amount for each PS was different depending on each ΦΔ. The NIRS measurement determined the ΦΔ of talaporfin sodium, PpIX, and PpIX lipid. The quantitative evaluation based on the measured ΦΔ will support the development of PDT treatment monitoring and design.

Singlet oxygen model evaluation of interstitial photodynamic therapy with 5-aminolevulinic acid for malignant brain tumor.

Interstitial photodynamic therapy (iPDT) with 5-aminolevulinic acid (ALA) is a possible alternative treatment for malignant brain tumors. Further evaluation is, however, required before it can be clinically applied. Computational simulation of the photophysical process in ALA-iPDT can offer a quantitative tool for understanding treatment outcomes, which depend on various variables related to clinical treatment conditions. We propose a clinical simulation method of ALA-iPDT for malignant brain tumors using a singlet oxygen (O12) model and O12 threshold to induce cell death. In this method, the amount of O12 generated is calculated using a photosensitizer photobleaching coefficient and O12 quantum yield, which have been measured in several previous studies. Results of the simulation using clinical magnetic resonance imaging data show the need to specify the insertion positions of cylindrical light diffusers and the level of light fluence. Detailed analysis with a numerical brain tumor model demonstrates that ALA-iPDT treatment outcomes depend on combinations of photobleaching and threshold values. These results indicate that individual medical procedures, including pretreatment planning and treatment monitoring, will greatly benefit from simulation of ALA-iPDT outcomes.

New Development for Safer Endoscopic Submucosal Dissection using the Carbon Dioxide (CO2) Laser (Secondary publication).

Endoscopic Submucosal Dissection (ESD) has been increasingly accepted as a minimally invasive treatment for the patients with early gastrointestinal cancers. However, reliable ESD technique demands high maneuverability, and the success of the operation is dependent on each operator's skill. We have developed a novel laser endoscopic system for ESD to overcome such technique-related difficulties. Compared to conventional ESD using electrosurgical knives, an ESD method using the CO2 laser offers the advantages of less risk of perforation and the prevention of extensive thermal damage, because the CO2 laser is strongly absorbed by water. Furthermore, due to the non-contact technique associated with the CO2 laser and adequate visualization of the treatment area, the laser system may provide every endoscopist with more precise and safer treatment.

Photodynamic therapy by lysosomal-targeted drug delivery using talaporfin sodium incorporated into inactivated virus particles.

BACKGROUND: Photodynamic therapy (PDT), a minimally invasive cancer treatment involving the activation of photosensitizer by a specific wavelength of light, is considered to be a promising treatment option for drug-resistant prostate cancer. Hemagglutinating virus of Japan envelope (HVJ-E) has the potential to serve as a highly effective cancer therapy through selective drug delivery and enhancement of the anti-tumor immune response. OBJECTIVES: To improve therapeutic efficacy and selective accumulation of photosensitizer into tumor cells, we developed a novel photosensitizer, Laserphyrin®-HVJ-E (L-HVJ-E), by incorporating talaporfin sodium (Laserphyrin®, Meiji Seika Pharma) into HVJ-E. MATERIALS AND METHODS: The therapeutic effect of PDT with Laserphyrin® or L-HVJ-E was evaluated in the human prostate cancer cell line PC-3 in vitro. The subcellular localizations of Laserphyrin® and L-HVJ-E were observed by confocal microscopy. Apoptosis or necrosis following PDT was detected by annexin V-fluorescein/propidium iodide double staining. RESULTS: The cytotoxic effect of Laserphyrin®- and L-HVJ-E-mediated PDT were determined by evaluating cell survival rate and production of reactive oxygen species. The cytotoxicity of L-HVJ-E-mediated PDT was dependent on drug concentration and light dose. Laserphyrin® and L-HVJ-E gradually entered cells as incubation time increased, and both agents tended to be distributed in lysosomes rather than mitochondria. Time and dose dependent increase in ROS production was observed, and induction of both apoptotic and necrotic cell death was confirmed. CONCLUSIONS: Laserphyrin® and L-HVJ-E were distributed mainly in lysosomes and induced cell death by both apoptosis and necrosis. Furthermore, L-HVJ-E-mediated PDT effectively killed cultured PC-3 cells and exerted higher photocytotoxicity than Laserphyrin®-mediated PDT.

Matrix-Assisted Laser Desorption Ionization Imaging Mass Spectrometry of Drug Distribution in Mouse Brain Tissue by High-Resolution Time-of-Flight Mass Spectrometry.

Matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry provides the opportunity to visualize the distributions of drugs and metabolites in tissue specimens without requiring radioisotopes, as are used for whole-body autoradiography. However, the analysis of low-molecular-weight compounds is often difficult using the common reflectron-type MALDI time-of-flight mass spectrometers. Insufficient mass resolving power causes overlapping of the target drug peak with matrix compound or surface contaminant peaks. To solve this issue, we describe the procedure for imaging mass spectrometry using a high-mass-resolution mass spectrometer that can separate isobaric peaks.

Photodynamic therapy using a cytotoxic photosensitizer porphyrus envelope that targets the cell membrane.

BACKGROUND: Subcellular localization of a photosensitizer is known to determine the therapeutic efficacy of photodynamic therapy (PDT). Cell membrane is an optimal target that promises an effective treatment outcome. OBJECTIVES: We previously developed a novel photosensitizer named porphyrus envelope (PE) by combining hemagglutinating virus of Japan envelope (HVJ-E) with lipidated protoporphyrin IX (PpIX lipid). In the current study, the cellular localization of PE and its ability to induce multiple anti-tumor effect were characterized. MATERIALS AND METHODS: The localization and uptake of PpIX lipid in cells were evaluated with confocal laser scanning microscopy and a cell-based fluorescent assay, respectively. The ability of PE to suppress the migration and proliferation of cancer cells was assessed using a scratch-wound assay. The synergistic effect of PDT and HVJ-E treatment was evaluated using an in vitro experiment with PC-3 cells. RESULTS: PE localized along the cell membrane and PpIX lipid accumulated selectively in the prostate cancer cells within 10min. Also, PE maintained the ability to undergo fusion and induce cancer cell death even after light irradiation at the dose for PDT. Incubation with PE resulted in delayed migratory and proliferative activity of PC-3 cells. PE-mediated PDT was twice as effective when cells were further incubated with PE following PDT. CONCLUSIONS: PE allows rapid drug delivery targeting the cell membrane. Because the cytotoxicity of HVJ-E was maintained, synergistic effect of HVJ-E and the photochemical reactions resulted in highly effective killing of prostate cancer cells in vitro and thus represents a promising treatment for prostate cancer.