Biosynthesis and photodynamic efficacy of protoporphyrin IX (PpIX) generated by 5-aminolevulinic acid (ALA) or its hexylester (hALA) in rat bladder carcinoma cells

Nanoparticles drug delivery for 5-aminolevulinic acid (5-ALA) in photodynamic therapy (PDT) for multiple cancer treatment: a critical review on biosynthesis, detection, and therapeutic applications

Photodynamic therapy (PDT) is a promising cancer treatment that kills cancer cells selectively by stimulating reactive oxygen species generation with photosensitizers exposed to specific light wavelengths. 5-aminolevulinic acid (5-ALA) is a widely used photosensitizer. However, its limited tumour penetration and targeting reduce its therapeutic efficacy. Scholars have investigated nano-delivery techniques to improve 5-ALA administration and efficacy in PDT. This review summarises recent advances in biological host biosynthetic pathways and regulatory mechanisms for 5-ALA production. The review also highlights the potential therapeutic efficacy of various 5-ALA nano-delivery modalities, such as nanoparticles, liposomes, and gels, in treating various cancers. Although promising, 5-ALA nano-delivery methods face challenges that could impair targeting and efficacy. To determine their safety and biocompatibility, extensive preclinical and clinical studies are required. This study highlights the potential of 5-ALA-NDSs to improve PDT for cancer treatment, as well as the need for additional research to overcome barriers and improve medical outcomes.

A Trojan horse approach for efficient drug delivery in photodynamic therapy: focus on taxanes

Photodynamic therapy is an effective method for the treatment of several types of cancerous and noncancerous diseases. The key to the success of this treatment method is effective drug delivery to the site of action, for instance, a tumor. This ensures not only the high effectiveness of the therapy but also the suppression of side effects. But how to achieve effective targeted delivery? Lately, much attention has been paid to systems based on the so-called Trojan horse model, which is gaining increasing popularity. The principle of this model is that the effective drug is hidden in the internal structure of a nanoparticle, liposome, or nanoemulsion and is released only at the site of action. In this review article, we focus on drugs from the group of mitotic poisons, taxanes, and their use with photosensitizers in combined therapy. Here, we discuss the possibilities of how to improve the paclitaxel and docetaxel bioavailability, as well as their specific targeting for use in combined photo- and chemotherapy. Moreover, we also present the state of the art multifunctional drugs based on cabazitaxel which, owing to a suitable combination with photosensitizers, can be used besides photodynamic therapy and also in photoacoustic imaging or sonodynamic therapy.

In vivo photobleaching kinetics and epithelial biodistribution of hexylaminolevulinate-induced protoporphyrin IX in rat bladder cancer

In a previous paper, we showed that rat bladder instillations with 8 or 16 mM of hexyl aminolevulinate (hALA) result in diametrically opposed photodynamic therapy efficiency. Although the same fluorescent intensities were detected spectroscopically and by fluorescent microscopy in both conditions, while a given light dose resulted in tumor necrosis with an intact bladder wall after 8 mM hALA, bladders instilled with 16 mM showed total wall necrosis without impact on the tumor. The current study investigated the photobleaching and localization pattern of protoporphyrin IX (PpIX) after both hALA intravesical instillations in tumor-bearing rat bladders. The total PpIX content was evaluated by the extraction of postmortem whole bladders. Photobleaching was evaluated in vivo by fluorescent spectroscopy. Cryosections of bladders were subjected to fluorescent microscopy for cellular localization of the photosensitizer. PpIX extraction showed identical amounts of photosensitizer in tumor-bearing bladders at both concentrations. Photobleaching experiments revealed mono-exponential decay curves in both situations but with a two times faster decay constant in 16 mM bladders. Fluorescent microscopy showed an identical fluorescent pattern for normal bladders at both concentrations and tumor bladders at 8 mM with bright spots. Tumor bladders at 16 mM exhibited a more diffuse cytoplasmatic fluorescent distribution. The different response to photodynamic therapy with regard to the initial pro-drug concentration can thus be attributed to the different cellular localizations.

Prodrug strategies for targeted therapy triggered by reactive oxygen species

Increased levels of reactive oxygen species (ROS) have been associated with numerous pathophysiological conditions including cancer and inflammation and the ROS stimulus constitutes a potential trigger for drug delivery strategies. Over the past decade, a number of ROS-sensitive functionalities have been identified with the purpose of introducing disease-targeting properties into small molecule drugs - a prodrug strategy that offers a promising approach for increasing the selectivity and efficacy of treatments. This review will provide an overview of the ROS-responsive prodrugs developed to date. A discussion on the current progress and limitations is provided along with a reflection on the unanswered questions that need to be addressed in order to advance this novel approach to the clinic.

Photodynamic diagnosis with methyl-5-aminolevulinate in squamous intraepithelial lesions of the vulva: Experimental research

The incidence of the High-grade Squamous Intraepithelial Lesion of the vulva, formerly vulvar intra-epithelial neoplasia is progressively increasing. Today, an early detection and a precise localization of vulvar lesions are still problematic issues, due to the lack of accuracy of the available diagnostic tool. A new approach is the photodynamic diagnosis based on the fluorescence detection of protoporphyrin IX (PpIX) in cancer cells after topical application of a cream of methyl amino-levulinic acid. This study aimed to evaluate the effectiveness of photodiagnosis in order to discriminate the intensity of PpIX fluorescence between vulvar tumor and healthy skin. After topical application of the cream, the fluorescence on xenografted A431 tumor and adjacent skin was non-invasively measured with optical fiber. The tumor to skin fluorescence ratios were 1.38 and 1.41 at respectively 3h and 6h after application, which were significantly higher compared to those observed before application. PpIX accumulation at different depths of the tumor was investigated by spectrofluorimetry after PpIX chemical extraction from tumor sections at 3h and 6h post-application. It was noticed at both application times that the concentration of PpIX within the tumor progressively decreased. However PpIX fluorescence was always detectable up to 2.5 mm, a depth equivalent to more than three quarters of the tumor. The tumor to exposed skin ratios of PpIX fluorescence showed a good selectivity up to1mm depth at 3h post-application and up to 1.5mm at 6h post-m-ALA. Thus, the photodynamic diagnosis using in vivo topical methyl amino-levulinic acid appears to be a promising way to detect the intraepithelial lesions of the vulva. Our results open the possibility for implementation of topical methyl amino-levulinic acid in clinical settings for recognition of vulvar high-grade squamous intraepithelial lesions.

Transcriptional activation of HIF-1 by a ROS-ERK axis underlies the resistance to photodynamic therapy

Photodynamic therapy (PDT), a promising treatment option for cancer, involves the activation of a photosensitizer (PS) by local irradiation with visible light. Excitation of the PS leads to a series of photochemical reactions and consequently the local generation of harmful reactive oxygen species (ROS) causing limited or none systemic defects. However, the development of resistance to this promising therapy has slowed down its translation into the clinical practice. Thus, there is an increase need in understanding of the molecular mechanism underlying resistance to PDT. Here, we aimed to examine whether a relationship exists between PDT outcome and ROS-involvement in the resistance mechanism in photosensitized cancer cells. In order to recapitulate tumor architecture of the respective original tumor, we developed a multicellular three-dimensional spheroid system comprising a normoxic periphery, surrounding a hypoxic core. Using Me-ALA, a prodrug of the PS PpIX, in human colorectal spheroids we demonstrate that HIF-1 transcriptional activity was strongly up-regulated and mediates PDT resistant phenotype. RNAi knockdown of HIF-1 impairs resistance to PDT. Oxidative stress-mediated activation of ERK1/2 followed PDT was involved on positive modulation of HIF-1 transcriptional activity after photodynamic treatment. ROS scavenging and MEK/ERK pathway inhibition abrogated the PDT-mediated HIF-1 upregulation. Together our data demonstrate that resistance to PDT is in part mediated by the activation of a ROS-ERK1/2-HIF-1 axis, thus, identifying novel therapeutic targets that could be used in combination with PDT.

Efficient activation of a visible light-activatable CA4 prodrug through intermolecular photo-unclick chemistry in mitochondria

Mitochondria-targeted and visible light-activatable CA4 prodrug was efficiently activated through intermolecular photo-unclick chemistry in mitochondria for the combination therapy.

Clearance mechanism of protoporphyrin IX from mouse skin after application of 5-aminolevulinic acid

BACKGROUND

5-Aminolevulinic acid (ALA) or its esters mediated photodynamic therapy (PDT) is the most widely practiced form of PDT in dermatology. One of its advantages is that undesirable photosensitization lasts only for 24-48 h. In order to optimize ALA-PDT it is necessary to understand the mechanisms of intracellular production and clearance of PpIX (efflux from cells into blood stream and/or its conversion into haem). The aim of this study is to investigate the factors controlling the clearance of intracellular PpIX from healthy skin of mice.

METHODS

PpIX was induced in mouse skin by topical or systemic application of ALA or by topical application of the iron chelator ethylenediaminetetraacetic acid (EDTA). Fluorescence spectroscopy was used to study PpIX kinetics in alive and dead skin.

RESULTS

Topical application of ALA or EDTA leads to porphyrin production in living skin, but not in excised skin. The clearance rates of PpIX from alive and dead skin were the same in the absence of an intracellular ALA pool. The clearance half-life of EDTA-induced PpIX was 4-7 times longer than that of PpIX after application of ALA.

CONCLUSIONS

Skin temperature and intracellular iron availability strongly affect PpIX clearance, while ALA application mode (topical versus systemic) and skin viability (dead versus alive) have no influence on PpIX decay. These results demonstrate that the clearance kinetics of PpIX from skin are determined mostly by the conversion of PpIX into haem, while the cellular efflux of PpIX into blood plays a minor role.

Accumulation of protoporphyrin-IX in rat Leydig cells following induction by 5-aminolevulinic acid and tramadol

OBJECTIVES

This study aimed to monitor the accumulation of endogenous protoporphyrin-IX (PpIX) in rat Leydig cells (R(2)C) under the effect of 5-aminolevulinic acid (ALA) and various concentrations of tramadol, an analgesic drug.

BACKGROUND DATA

Pain during photodynamic treatment with ALA is one of the adverse effects of this new treatment to eradicate tumor cells. ALA is utilized in photodynamic diagnosis and therapy (PDT) as a compound capable of augmenting the intracellular pool of PpIX, which exhibits properties of a photosensitizer.

METHODS

Cellular content of PpIX was determined following incubation of the cells for 1 and 2 h in culture medium that contained ALA and different concentrations of tramadol. The amount of PpIX was determined using fluorescent technique under a confocal microscope (laser wavelength 458 nm and filter LP 585 nm), and evaluated using CytFlu 1.2 software.

RESULTS

After 1 h of incubation, no significant alterations were noted in the cellular PpIX concentration. However, 2 h of incubation resulted in a significant increase (p < 0.05) in PpIX fluorescence inside the cells, when the medium contained ALA and tramadol in concentrations ranging from 1-2 mg/1 mL.

CONCLUSIONS

The results suggested that in R(2)C cells, exogenous ALA and tramadol induced protoporphyrin accumulation. This information is useful for two reasons. First, it may help to diminish pain after ALA-PDT treatment; and second, it allows the use of lower concentrations of ALA during therapy.

Enhanced porphyrin accumulation using dendritic derivatives of 5-aminolaevulinic acid for photodynamic therapy: An in vitro study

Intracellular porphyrin generation following administration of 5-aminolaevulinic acid has been widely used in photodynamic therapy for a range of malignant and certain non-malignant lesions. However, cellular uptake of 5-aminolaevulinic acid is limited by its hydrophilic nature and improved means of delivery are therefore being sought. Highly branched polymeric drug carriers known as dendrimers are a promising new approach to drug delivery. The aim of this study was to investigate the efficacy of dendrimers conjugated with 5-aminolaevulinic acid for porphyrin production in the transformed PAM 212 keratinocyte cell line and skin explants. Each dendritic derivative incorporated three 5-aminolaevulinic acid residues which were conjugated as esters via methyl or propyl linkers to a central tertiary carbon whose remaining terminal bore an amino, aminobenzyloxycarbonyl or nitro group. In the cell line, all compounds were more efficient at low concentrations compared to equimolar 5-aminolaevulinic acid for porphyrin production, with the most efficient incorporating the longer propyl linker. This compound was also the most lipophilic according to partition coefficient measurements. The intracellular porphyrin fluorescence levels showed good correlation with cellular phototoxicity following light exposure for all the compounds, together with minimal dark toxicity. Our findings indicate that the key factors influencing the efficacy of the dendritic derivatives are lipophilicity and steric hindrance within the dendritic structure which could restrict access to intracellular esterases for liberation of 5-aminolaevulinic acid. These findings should be taken into account in the design of larger dendrimers of 5-aminolaevulinic acid.

Delivery of hypericin for photodynamic applications

Early cancer detection is critical in improving disease management outcomes. Cancer diagnosis presents unique difficulties mainly due to its pathological presentation and poor accessibility that could limit the usefulness of conventional white light endoscopy in early cancer detection. Fluorescence endoscopy has been proven to improve the sensitivity and specificity of early cancer detection. Hypericin (HY) has been found to be superior to 5-aminolevulinic acid (5-ALA) and its ester derivative hexaminolevulinate (HA) as a fluorescence diagnostic agent, hence its development for delivery in vitro and in vivo, is the subject of this review.

KINETICS, BIODISTRIBUTION AND THERAPEUTIC EFFICACY OF HEXYLESTER 5-AMINOLEVULINATE INDUCED PHOTODYNAMIC THERAPY IN AN ORTHOTOPIC RAT BLADDER TUMOR MODEL

PURPOSE

To optimize photodynamic therapy (PDT) we investigated the kinetics and biodistribution of hexylester 5-aminolevulinate (hALA) induced protoporphyrin IX (PpIX) and the therapeutic efficacy of PDT at different drug and light doses in an orthotopic rat bladder tumor model.

MATERIALS AND METHODS

Healthy and tumor bearing rats were instilled intravesically with hALA (4, 8 and 16 mM) for 1 hour. Fluorescence was recorded spectroscopically in situ. PpIX fluorescence distribution and quantification across the bladders was visualized with fluorescence microscopy. PDT efficacy at different fluences (15 to 80 J/cm2) was histologically assessed 48 hours and 1 week after treatment.

RESULTS

Spectroscopic analysis in normal or tumor bearing rats showed the highest tumor-to-normal ratios 2 or 3 hours after the end of the 8 or 16 mM hALA instillation (5.4 and 5.7, respectively). Within the same tumor bearing animal the same fluorescence levels were observed in normal epithelium and transitional cell carcinoma, whereas the tumor-to-muscle ratio was 3. Tumor necrosis with an intact normal bladder wall was observed with a fluence of 20 J/cm2 for 8 mM hALA, while 15 J/cm2 was ineffective and 25 J/cm2 induced total wall necrosis. Although it induced comparable PpIX fluorescence, 16 mM hALA did not result in tumor eradication at any fluence.

CONCLUSIONS

An optimal PDT effect was obtained with 8 mM hALA and a fluence of 20 J/cm2. While different hALA concentrations ind uce identical PpIX fluorescence intensities, the PDT outcome was considerably different. Thus, fluorescence does not necessarily predict the therapeutic efficacy of PDT.

Comparative in vitro percutaneous penetration of 5-aminolevulinic acid and two of its esters through excised hairless mouse skin

BACKGROUND AND OBJECTIVES

ALA esters have been developed to improve PpIX production in ALA-PDT, but they do not perform as well in skin as they do in cells and the bladder.

STUDY DESIGN/MATERIALS AND METHODS

The in vitro penetration across normal mouse skin of ALA and its methyl and hexyl ester was determined for different application concentrations. ALA and the esters were also applied to tape stripped skin to determine the effect of the stratum corneum.

RESULTS

The penetration of ALA and the esters was higher through tape stripped skin than through normal skin (P < 0.01), showing that the stratum corneum is an important barrier. The experiments with different application concentrations indicated that the skin penetration through normal skin and tape stripped skin is highest for ALA and lowest for the hexyl ester.

CONCLUSIONS

The differences in skin penetration properties could be (co-)responsible for the finding that ALA esters do not induce substantially higher PpIX levels in in vivo skin.

A comparison of protoporphyrin IX and protoporphyrin IX dimethyl ester as a photosensitizer in poorly differentiated human nasopharyngeal carcinoma cells

Protoporphyrin IX dimethyl ester (PME), a dimethyl esterification of protoporphyrin IX (PpIX), exhibits higher intracellular uptake into NPC/CNE2 cells, a poorly differentiated human nasopharyngeal carcinoma, than does PpIX. Phototoxicity studies reveal PME to be a more potent photosensitizer than is PpIX, at the early and late incubation time points. Correlating phototoxicity with subcellular localization indicates that PME is a more potent photosensitizer when its primary target of photodamage is mitochondria. Also, additional targeting of lysosome enhances phototoxicity.

Fluorescence detection of bladder cancer: a review

An effective therapeutic outcome in the treatment of bladder cancer is largely defined by its early detection. In this context, big expectations have been placed on the fluorescence-guided diagnosis of bladder cancer. This paper reviews the applications of endo- and exogenous fluorescence for early diagnosis of in situ carcinoma of the bladder. Despite certain advantages of autofluorescence, exogenous fluorescence, based on the intravesical instillation of fluorophores with the following visible light excitation, has been shown to be more effective in terms of sensitivity and specificity for detecting carcinoma in situ. The equipment consists of a slightly modified light source in order to choose between white (conventional endoscopy) or blue light (fluorescence endoscopy) excitation, and specific lenses, in order to enhance maximally the contrast between normal (blue) autofluorescence and red fluorescence from malignancies. Among exogenous fluorophores, a particular emphasis will be put on the 5-aminolevulinic acid (ALA), its ester derivative (h-ALA) and hypericin. These dyes demonstrated an excellent sensitivity above 90% and specificity ranging from 70% to 90%.

ALA and ALA hexyl ester in free and liposomal formulations for the photosensitisation of tumour organ cultures

In spite of the wide range of tumours successfully treated with 5-aminolevulinic acid mediated photodynamic therapy, the fact that 5-aminolevulinic acid has low lipid solubility, limits its clinical application. More lipophilic 5-aminolevulinic acid prodrugs and the use of liposomal carriers are two approaches aimed at improving 5-aminolevulinic acid transmembrane access. In this study we used both 5-aminolevulinic acid and its hexyl ester in their free and encapsulated formulations to compare their corresponding endogenous synthesis of porphyrins. Employing murine tumour cultures, we found that neither the use of hexyl ester nor the entrapment of either 5-aminolevulinic acid or hexyl ester into liposomes increase the rate of tumour porphyrin synthesis. By light and electronic microscopy it was demonstrated that exposure of tumour explants to either free or liposomal 5-aminolevulinic acid and subsequent illumination induces the same type of subcellular damage. Mitochondria, endoplasmic reticulum and plasma membrane are the structures mostly injured in the early steps of photodynamic treatment. In a later stage, cytoplasmic and nuclear disintegration are observed. By electronic microscopy the involvement of the endocytic pathway in the incorporation of liposomal 5-aminolevulinic acid into the cells was shown.