5-Aminolaevulinic acid peptide prodrugs enhance photosensitization for photodynamic therapy

Comparative study of topical 5-aminolevulinic acid photodynamic therapy and surgery for the treatment of vulvar squamous intraepithelial lesion

BACKGROUND

Vulvar squamous intraepithelial lesion (SIL) is a precursor lesion of vulvar squamous cell carcinoma. The current clinical treatments for vulvar SIL cause damage to the vulvar structure, chronic pain and psychological distress. Topical 5-aminolevulinic acid photodynamic therapy (ALA-PDT) is a novel, non-invasive therapy for intraepithelial lesions. The objective of this study was to compare the clinical efficacy and safety of ALA-PDT with local surgical resection for vulvar SIL.

METHODS

A total of 56 patients with vulvar SIL were enrolled in this retrospective study. Among them, 16 patients received local resection and 40 patients received ALA-PDT. HPV genotyping and ThinPrep cytologic test (TCT) were used to evaluate treatment efficacy. In addition, colposcopy-directed biopsy was performed in all patients at 3-month follow-up and in patients with positive high-risk human papillomavirus (HR-HPV) and/or abnormal TCT results during the follow-up.

RESULTS

At 3-month follow-up and in HSIL group the complete remission (CR) rate of the ALA-PDT group and surgery group was 90.6% (29/32) and 87.5% (14/16) (P = 1.000), respectively. The HPV clearance rate of the ALA-PDT group and surgery group was 45.2% (14/31) and 43.8% (7/16) (P = 0.927), respectively. The average numbers of ALA-PDT treatments were 5.34 for HSIL patients and 4.88 for LSIL patients, respectively. The CR rate of HSIL patients and LSIL patients was 90.6% (29/32) and 75.0% (6/8) (P = 0.550), respectively. The HPV clearance rate of HSIL patients and LSIL patients was 45.2% (14/31) and 37.5% (3/8) (P = 1.000), respectively. The ALA-PDT group showed similar clinical efficacy and milder adverse effects compared with the surgical group.

CONCLUSION

ALA-PDT showed similar clinical efficacy as surgery in the treatment of vulvar SIL, but with milder adverse effects and maintaining the integrity of the vulvar structure.

Hexyl-Aminolevulinate Ethosomes: a Novel Antibiofilm Agent Targeting Zinc Homeostasis in Candida albicans

Substantial drug resistance afforded by Candida albicans biofilms results in ineffective treatment with conventional drugs and persistent infection. Our previous study showed that hexyl-aminolevulinate ethosomes (HAL-ES) act against C. albicans biofilms and weaken their drug resistance and pathogenicity; however, the mechanism involved remains unclear. Here, we systematically evaluated the effects and mechanisms of HAL-ES on biofilm formation and drug resistance. We found that, in addition to mediating antifungal photodynamic therapy, HAL-ES inhibited the early, developmental, and mature stages of biofilm formation compared with fluconazole, HAL, or ES. Notably, adhesion and hyphal formation were significantly inhibited by postdrug effects even after brief exposure (2 h) to HAL-ES. Its therapeutic effect in vivo also has been demonstrated in cutaneous candidiasis. RNA sequencing and quantitative PCR showed that HAL-ES inhibited ribosome biogenesis by disrupting zinc homeostasis in C. albicans, thereby reducing the translation process during protein synthesis. Furthermore, HAL-ES downregulated the expression of multidrug resistance genes and increased fluconazole susceptibility in C. albicans. Our findings provide a novel and efficient method for the treatment of biofilm resistance in C. albicans infection as well as a basis for the application of HAL-ES. We also describe a new strategy for the treatment of biofilm-related infections via zinc restriction. IMPORTANCE Candida albicans is the most prevalent fungal species of the human microbiota. The medical impact of C. albicans on its human host depends on its ability to form biofilms. The intrinsic resistance conferred by biofilms to conventional antifungal drugs makes biofilm-based infections a significant clinical challenge. In this study, we demonstrate the attenuating effect of HAL-ES on C. albicans biofilm formation and drug resistance. Furthermore, we propose that HAL-ES inhibits protein translation by disrupting zinc homeostasis in C. albicans. This study not only provides a novel and effective therapeutic strategy against C. albicans biofilm but also proposes a new strategy to resolve C. albicans biofilm infection by disrupting zinc homeostasis.

A Thiosemicarbazone Derivative as a Booster in Photodynamic Therapy-A Way to Improve the Therapeutic Effect

Photodynamic therapy is one of the most patient friendly and promising anticancer therapies. The active ingredient is irradiated protoporphyrin IX, which is produced in the body that transfers energy to the oxygen-triggering phototoxic reaction. This effect could be enhanced by using iron chelators, which inhibit the final step of heme biosynthesis, thereby increasing the protoporphyrin IX concentration. In the presented work, we studied thiosemicarbazone derivative, which is a universal enhancer of the phototoxic effect. We examined several genes that are involved in the transport of the heme substrates and heme itself. The results indicate that despite an elevated level of ABCG2, which is responsible for the PpIX efflux, its concentration in a cell is sufficient to trigger a photodynamic reaction. This effect was not observed for 5-ALA alone. The analyzed cell lines differed in the scale of the effect and a correlation with the PpIX accumulation was observed. Additionally, an increased activation of the iron transporter MFNR1 was also detected, which indicated that the regulation of iron transport is essential in PDT.

Enlarging the Scope of 5-Aminolevulinic Acid-Mediated Photodiagnosis towards Breast Cancers

Today, most research on treating cancers targets one single cancer, often because of the very specific operation principle of the therapy. For instance, immunotherapies require the expression of a particular antigen, which might not be expressed in all cancers or in all patients. What about metastases? Combination therapies are promising but require treatment personalization and are an expensive approach that many health systems are not willing to pay for. Resection of cancerous tissues may be conducted beforehand. However, the precise location and removal of tumors are in most cases, hurdles that require margins to prevent recurrence. Herein, we further demonstrate the wide application of aminolevulinate-based photodynamic diagnosis and therapy toward breast cancers. By selecting four breast cancer cell lines that represent the main breast tumor subtypes, we investigated their ability to accumulate the fluorescent protoporphyrin IX upon treatment with the marketed 5-aminolevulinic acid hexyl ester (ALA-Hex) or our new and more stable derivative PSI-ALA-Hex. We found that all cell lines were able to accumulate PpIX under a few hours independent of their hormonal status with both treatments. Additionally, this accumulation was less dose-dependent with PSI-ALA-Hex and induced similar or higher fluorescence intensity than ALA-Hex in three out of four cell lines. The toxicity of the two molecules was not different up to 0.33 mM. However, PSI-ALA-Hex was more toxic at 1 mM, even though lower concentrations of PSI-ALA-Hex led to the same PpIX accumulation level. Additional illumination with blue light to induce cell death by generating reactive oxygen species was also considered. The treatments led to a dramatic death of the BT-474 cells under all conditions. In SK-BR-3 and MCF-7, ALA-Hex was also very efficient at all concentrations. However, increasing doses of PSI-ALA-Hex (0.33 and 1 mM) surprisingly led to a higher viability rate. In contrast, the triple-negative breast cancer cells MDA-MB-231 showed a higher death induction with higher concentrations of ALA-Hex or PSI-ALA-Hex. Derivatives of ALA seem promising as fluorescence-guided resection tools and may enable subsequent completion of cancer cell destruction by blue light irradiation.

Current Status of Photodynamic Technology for Urothelial Cancer

5‐Aminolevulinic acid is a new‐generation photosensitizer with high tumor specificity. It has been used successfully in the diagnosis, treatment, and screening of urological cancers including bladder cancer; specifically, it has been used in photodynamic diagnosis to detect tumors by illuminating the lesion with a specific wavelength of light to produce fluorescence in the lesion after administration of 5‐aminolevulinic acid, in photodynamic therapy, which induces tumor cell death via production of cytotoxic reactive oxygen species, and in photodynamic screening, in which porphyrin excretion in the blood and urine is used as a tumor biomarker after administration of 5‐aminolevulinic acid. In addition to these applications in urological cancers, 5‐aminolevulinic acid–based photodynamic technology is expected to be used as a novel strategy for a large number of cancer types because it is based on a property of cancer cells known as the Warburg effect, which is a basic biological property that is common across all cancers.

Recent Advancements in Stimuli Responsive Drug Delivery Platforms for Active and Passive Cancer Targeting

The tumor-specific targeting of chemotherapeutic agents for specific necrosis of cancer cells without affecting the normal cells poses a great challenge for researchers and scientists. Though extensive research has been carried out to investigate chemotherapy-based targeted drug delivery, the identification of the most promising strategy capable of bypassing non-specific cytotoxicity is still a major concern. Recent advancements in the arena of onco-targeted therapies have enabled safe and effective tumor-specific localization through stimuli-responsive drug delivery systems. Owing to their promising characteristic features, stimuli-responsive drug delivery platforms have revolutionized the chemotherapy-based treatments with added benefits of enhanced bioavailability and selective cytotoxicity of cancer cells compared to the conventional modalities. The insensitivity of stimuli-responsive drug delivery platforms when exposed to normal cells prevents the release of cytotoxic drugs into the normal cells and therefore alleviates the off-target events associated with chemotherapy. Contrastingly, they showed amplified sensitivity and triggered release of chemotherapeutic payload when internalized into the tumor microenvironment causing maximum cytotoxic responses and the induction of cancer cell necrosis. This review focuses on the physical stimuli-responsive drug delivery systems and chemical stimuli-responsive drug delivery systems for triggered cancer chemotherapy through active and/or passive targeting. Moreover, the review also provided a brief insight into the molecular dynamic simulations associated with stimuli-based tumor targeting.

Peptide-targeted dendrimeric prodrugs of 5-aminolevulinic acid: A novel approach towards enhanced accumulation of protoporphyrin IX for photodynamic therapy

Photodynamic therapy (PDT) is a promising approach for the targeted treatment of cancer and various other human disorders. An effective, clinically approved approach in PDT involves the administration of 5-aminolevulinic acid (ALA) to generate elevated levels of the natural photosensitiser protoporphyrin IX (PpIX). The development of prodrugs of ALA is of considerable interest as a means to enhance the efficiency and cell selectivity of PpIX accumulation for PDT applications. In this work a novel peptide-targeted dendrimeric prodrug of 5-aminolevulinic acid (ALA) 13 was synthesised which displays nine copies of ALA on a core structure that is linked to a homing peptide for targeted delivery to a specific cancer cell type. The synthesis was accomplished effectively via a flexible, modular solid phase and solution phase route, using a combination of solid phase peptide synthesis and copper-catalysed azide-alkyne cycloaddition chemistry. The prodrug system shows a sustained and enhanced production of protoporphyrin IX (PpIX) in the MDA-MB-231 cell line that over-expresses the epidernal growth factor receptor (EGFR+) in comparison to equimolar ALA and the corresponding non-targeted ALA dendrimer (nine copies of ALA). This study provides a proof of concept for the development of a new generation of prodrugs for ALA-based photodynamic therapy that can deliver an enhanced ALA payload to specific tissue types.

Recent advances in innovative strategies for enhanced cancer photodynamic therapy

Photodynamic therapy (PDT), a non-invasive therapeutic modality, has received increasing attention owing to its high selectivity and limited side effects. Although significant clinical research progress has been made in PDT, the breadth and depth of its clinical application have not been fully realized due to the limitations such as inadequate light penetration depth, non-targeting photosensitizers (PSs), and tumor hypoxia. Consequently, numerous investigations put their emphasis on innovative strategies to overcome the aforementioned limitations and enhance the therapeutic effect of PDT. Herein, up-to-date advances in these innovative methods for PDT are summarized by introducing the design of PS systems, their working mechanisms and application examples. In addition, current challenges of these innovative strategies for clinical application, and future perspectives on further improvement of PDT are also discussed.

Advances in nanomaterials for photodynamic therapy applications: Status and challenges

Photodynamic therapy (PDT), as a non-invasive therapeutic modality that is alternative to radiotherapy and chemotherapy, is extensively investigated for cancer treatments. Although conventional organic photosensitizers (PSs) are still widely used and have achieved great progresses in PDT, the disadvantages such as hydrophobicity, poor stability within PDT environment and low cell/tissue specificity largely limit their clinical applications. Consequently, nano-agents with promising physicochemical and optical properties have emerged as an attractive alternative to overcome these drawbacks of traditional PSs. Herein, the up-to-date advances in the fabrication and fascinating applications of various nanomaterials in PDT have been summarized, including various types of nanoparticles, carbon-based nanomaterials, and two-dimensional nanomaterials, etc. In addition, the current challenges for the clinical use of PDT, and the corresponding strategies to address these issues, as well as future perspectives on further improvement of PDT have also been discussed.

Chemical approaches for the enhancement of 5-aminolevulinic acid-based photodynamic therapy and photodiagnosis

The development of photodynamic therapy and photodiagnosis with 5-aminolevulinic acid presents a number of challenges that can be addressed by applying chemical insight and a range of novel prodrug strategies.

Synthesis and evaluation of new 5-aminolevulinic acid derivatives as prodrugs of protoporphyrin for photodynamic therapy

Upon light activation, 13a can induce the production of PpIX in vivo which produces ROS and other reactive oxygen species to lead to the apoptosis of S180 cell tumors.

Improved photodynamic activity of a dual phthalocyanine–ALA photosensitiser

The higher efficiency of the dual photosensitiser is a consequence of the generation of two photosensitisers inside the cell, which are activated concomitantly.

Synthesis of chemically diverse esters of 5-aminolevulinic acid for photodynamic therapy via the multicomponent Passerini reaction

A chemically diverse set of 5-aminolevulinic acid prodrugs were obtained via a Passerini reaction and studied as photodinamic agents in vitro.

Expression of Genes Involved in Porphyrin Biosynthesis Pathway in the Human Renal Cell Carcinoma

Renal cell carcinoma (RCC) remains one of the greatest challenges of urological oncology and is the third leading cause of death in genitourinary cancers. Surgery may be curative when patients present with localized disease. Our previous results demonstrated the autofluorescence of blood PpIX in primary RCC mouse model and an increase in fluorescence intensity as a function of growth of the subcutaneous tumor mass. In another work, a nice correlation between the growth of the tumor mass and tissue fluorescence intensity was found. The aim of this study was to evaluate the expression profile of porphyrin biosynthesis pathway-related genes of human kidney cells. We used two kidney cell lines, one normal (HK2) and another malignant (Caki-1). Endogenous and 5-aminolevolinic acid (ALA) induced protoporphyrin IX (PpIX) HK2 and Caki-1 cells were analyzed by fluorescence spectroscopy. Real-time quantitative polymerase chain reaction (qRT-PCR) was used to measure mRNA of those genes. Emission spectra were obtained by exciting the samples at 405 nm. For ALA untreated cells the maximum fluorescence intensity was detected at 635 nm. The mean peak area of emission spectra in both cells types increased linearly in function of cell number. Besides, basal levels of PpIX autofluorescence of each cell concentration of HK2 samples were significantly lower than those of Caki-1 samples. For ALA-treated cells the mean PpIX spectra shows PpIX emission peak at 635 nm with a shoulder at 700 nm. Analysis of PpIX fluorescence intensity ratio between tumor cells and HK2 cells showed that fluorescence intensity was, on average, 26 times greater in tumor cells than in healthy cells. qRT-PCR revealed that in Caki-1 ALA-treated cells, PEPT gene was significantly up-regulated and FECH and HO-1 genes were significantly down regulated in comparison with HK2 ALA-treated cells. In conclusion, our results demonstrate the preferential accumulation of ALA-induced PpIX in human RCC and also indicate that PEPT1, FECH and HO-1 genes are major contributors to this accumulation.

Increased expression of ABCB6 enhances protoporphyrin IX accumulation and photodynamic effect in human glioma

BACKGROUND

Glioma recurrence usually occurs close to the tumor resection margins as a result of residual infiltrating glioma cells. 5-aminolevulinic acid (ALA) fluorescence-guided resection of gliomas has been demonstrated to enhance discrimination of tumor tissue and to improve survival. ALA-based photodynamic therapy is an effective albeit still experimental adjuvant treatment option for gliomas. However, insufficient protoporphyrin IX (PpIX) accumulation may limit the benefits of fluorescence-guided resection and photodynamic therapy.

METHODS

We investigated the expression of the ATP-binding cassette transporter ABCB6, which regulates porphyrin synthesis, in surgical specimens from human gliomas and manipulated ABCB6 in human glioma cell lines.

RESULTS

Our findings demonstrated that expression levels of ABCB6 were greatly elevated in human gliomas compared with normal brain tissues and correlated with World Health Organization histologic grade. A previously undescribed finding was that ABCB6 mRNA expression in solidly fluorescing tumor tissues was higher than that in vaguely fluorescing tumors, suggesting that ABCB6 may be at least in part responsible for PpIX accumulation in glioma cells. Accordingly, ABCB6 overexpression in glioma cell lines caused a marked increase in intracellular levels of PpIX, and was more sensitive to ALA-induced photodynamic therapy-events that could be prevented by silencing ABCB6 via siRNA treatment.

CONCLUSIONS

Our findings indicate a crucial role of ABCB6 in ALA metabolism and accumulation of PpIX in glioma. ABCB6 overexpression is a potential approach to enhance accumulation of PpIX for optimizing the subjective discrimination of vague fluorescence and improving the efficacy of ALA-based photodynamic therapy.

Poly(L-histidine)-tagged 5-aminolevulinic acid prodrugs: new photosensitizing precursors of protoporphyrin IX for photodynamic colon cancer therapy

Background

5-Aminolevulinic acid (ALA) and its derivatives have been widely used in photodynamic therapy. The main drawback associated with ALA-based photodynamic therapy (ALA-PDT) and ALA fluorescence diagnosis results from the hydrophilic nature of ALA and lack of selectivity for tumor versus nontumor cells. The application of certain triggers, such as pH, into conventional sensitizers for controllable ¹O₂ release is a promising strategy for tumor-targeted treatment.

Methods

A series of pH-sensitive ALA-poly(L-histidine) [p(L-His)_n] prodrugs were synthesized via ring opening polymerization of 1-benzyl-N-carboxy-L-histidine anhydride initiated by the amine hydrochloride group of ALA itself. As an alternative to ALA for PDT, the synthesized prodrugs were used to treat a cultured human colon cancer HCT116 cell line under different pH conditions. The effect of ALA-p(L-His)_n derivatives was evaluated by monitoring the fluorescence intensity of protoporphyrin IX, and measuring the cell survival rate after suitable light irradiation.

Results

The cytotoxicity and dark toxicity of ALA and synthesized ALA-p(L-His) derivatives in HEK293T and HCT116 cells in the absence of light at pH 7.4 and 6.8 shows that the cell viability was relatively higher than 100%. ALA-p(L-His)_n showed high phototoxicity and selectivity in different pH conditions compared with ALA alone. Because the length of the histidine chain increases in the ALA-p(L-His)_n prodrugs, the PDT effect was found to be more powerful. In particular, high phototoxicity was observed when the cells were treated with ALA-p(L-His)¹⁵, compared with treatment using ALA alone.

Conclusion

The newly synthesized ALA-p(L-His)_n derivatives are an effective alternative to ALA for enhancing protoporphyrin IX production and the selectivity of the phototoxic effect in tumor cells.

Synthesis and anti-HIV activities of glutamate and peptide conjugates of nucleoside reverse transcriptase inhibitors

Mono-, di-, and trinucleoside conjugates of glutamate or peptide scaffolds containing nucleoside reverse transcriptase inhibitors were synthesized. Among dinucleoside glutamate ester derivatives, N-myristoylated derivatives showed significantly higher anti-HIV activity than the corresponding N-acetylated conjugates against cell-free virus. Myristoyl-Glu(3TC)-FLT (46, EC(50) = 0.3-0.6 μM) and myristoyl-Glu(FTC)-FLT (47, EC(50) = 0.1-0.4 μM) derivatives were the most active glutamate-dinucleoside conjugates. A trinucleoside glutamate derivative containing AZT, FLT, and 3TC (34, EC(50) = 0.9-1.4 μM) exhibited higher anti-HIV activity than AZT and 3TC against cell-free virus. Compound 34 also exhibited higher anti-HIV activity against multidrug (IC(50) = 5.9 nM) and NNRTI (IC(50) = 12.9 nM) resistant viruses than parent nucleosides. The physical mixture containing FLT-succinate, AZT, 3TC, and glutamic acid exhibited 115-fold less activity against cell associated virus (EC(50) = 91.9 μM) when compared to 34 (EC(50) = 0.8 μM). Other conjugates showed less or comparable potency to that of the corresponding physical mixtures.

Effect of surfactant on 5-aminolevulinic acid uptake and PpIX generation in human cholangiocarcinoma cell

Photodynamic therapy (PDT) is a palliative therapy and has been used to cure cholangiocarcinoma (CC), which has a poor prognosis and limited available curative therapy. PDT was shown to improve the median survival time of advanced-stage patients. Recently, 5-aminolevulinic acid (ALA) has been used as a pro-photosensitizer, which can be transferred to intercellular protoporphyrin IX (PpIX), which is a strong photosensitizer, via the heme pathway. The main limitation of using ALA in PDT is the hydrophilic properties of ALA, which results in low cellular uptake. In this study, non-ionic surfactants, pluronic F68 (PF68) and Tween 80 (TW80), were used to address this limitation. The human CC cell line, HuCC-T1, was cotreated with ALA and different concentrations of surfactants for 4h. The effect of surfactants was evaluated by monitoring the uptake of ALA, the fluorescence intensity of PpIX, and the cell survival rate after suitable light irradiation. Cotreatment with the surfactant resulted in an increased intracellular ALA level, PpIX formation, and phototoxicity.

Nanoparticles and microparticles for skin drug delivery

Skin is a widely used route of delivery for local and systemic drugs and is potentially a route for their delivery as nanoparticles. The skin provides a natural physical barrier against particle penetration, but there are opportunities to deliver therapeutic nanoparticles, especially in diseased skin and to the openings of hair follicles. Whilst nanoparticle drug delivery has been touted as an enabling technology, its potential in treating local skin and systemic diseases has yet to be realised. Most drug delivery particle technologies are based on lipid carriers, i.e. solid lipid nanoparticles and nanoemulsions of around 300 nm in diameter, which are now considered microparticles. Metal nanoparticles are now recognized for seemingly small drug-like characteristics, i.e. antimicrobial activity and skin cancer prevention. We present our unpublished clinical data on nanoparticle penetration and previously published reports that support the hypothesis that nanoparticles >10nm in diameter are unlikely to penetrate through the stratum corneum into viable human skin but will accumulate in the hair follicle openings, especially after massage. However, significant uptake does occur after damage and in certain diseased skin. Current chemistry limits both atom by atom construction of complex particulates and delineating their molecular interactions within biological systems. In this review we discuss the skin as a nanoparticle barrier, recent work in the field of nanoparticle drug delivery to the skin, and future directions currently being explored.

Protoporphyrin IX enhancement by 5-aminolaevulinic acid peptide derivatives and the effect of RNA silencing on intracellular metabolism

Intracellular generation of the photosensitiser, protoporphyrin IX, from a series of dipeptide derivatives of the haem precursor, 5-aminolaevulinic acid (ALA), was investigated in transformed PAM212 murine keratinocytes, together with studies of their intracellular metabolism. Porphyrin production was substantially increased compared with equimolar ALA using N-acetyl terminated phenylalanyl, leucinyl and methionyl ALA methyl ester derivatives in the following order: Ac-L-phenylalanyl-ALA-Me, Ac-L-methionyl-ALA-Me and Ac-L-leucinyl-ALA-Me. The enhanced porphyrin production was in good correlation with improved photocytotoxicity, with no intrinsic dark toxicity apparent. However, phenylalanyl derivatives without the acetyl/acyl group at the N terminus induced significantly less porphyrin, and the replacement of the acetyl group by a benzyloxycarbonyl group resulted in no porphyrin production. Porphyrin production was reduced in the presence of class-specific protease inhibitors, namely serine protease inhibitors. Using siRNA knockdown of acylpeptide hydrolase (ACPH) protein expression, we showed the involvement of ACPH, a member of the prolyl oligopeptidase family of serine peptidases, in the hydrolytic cleavage of ALA from the peptide derivatives. In conclusion, ALA peptide derivatives are capable of delivering ALA efficiently to cells and enhancing porphyrin synthesis and photocytotoxicity; however, the N-terminus state, whether free or substituted, plays an important role in determining the biological efficacy of ALA peptide derivatives.