Necrosis response to photodynamic therapy using light pulses in the femtosecond regime

J, M.D.P. DE. C, RAJENDRAM S. Photodynamic Therapy : An Overview and Insights into a Prospective Mainstream Anticancer Therapy

Photodynamic therapy (PDT) procedure has minimum invasiveness in contrast to conventional anticancer surgical procedures. Although clinically approved a few decades ago, it is not commonly used due to its poor efficacy, mainly due to poor light penetration into deeper tissues. PDT uses a photosensitizer (PS), which is photoactivated on illumination by light of appropriate wavelength and oxygen in the tissue, leading to a series of photochemical reactions producing reactive oxygen species (ROS) triggering various mechanisms resulting in lethal effects on tumor cells. This review looks into the fundamental aspects of PDT, such as photochemistry, photobiological effects, and the current clinical applications in the light of improving PDT to become a mainstream therapeutic procedure against a broad spectrum of cancers and malignant lesions. The side effects of PDT, both early and late-onset, are elaborated on in detail to highlight the available options to minimize side effects without compromising therapeutic efficacy. This paper summarizes the benefits, drawbacks, and limitations of photodynamic therapy along with the recent attempts to achieve improved therapeutic efficacy via monitoring various cellular and molecular processes through fluorescent imagery aided by suitable biomarkers, prospective nanotechnology-based targeted delivery methods, the use of scintillating nanoparticles to deliver light to remote locations and also combining PDT with conventional anticancer therapies have opened up new dimensions for PDT in treating cancers. This review inquires and critically analyses prospective avenues in which a breakthrough would finally enable PDT to be integrated into mainstream anticancer therapy.

PDT with genetically encoded photosensitizer miniSOG on a tumor spheroid model: A comparative study of continuous-wave and pulsed irradiation

BACKGROUND

Therapeutic effects of PDT depend on many factors, including the amount of singlet oxygen, localization of photosensitizer and irradiation protocol. The present study was aimed to compare the cytotoxic mechanisms of PDT under continuous-wave (CW) and pulsed irradiation using a tumor spheroid model and a genetically encoded photosensitizer miniSOG.

METHODS

1O2 detection in miniSOG and flavin mononucleotide (FMN) solutions was performed. Photobleaching of miniSOG in solution and in HeLa tumor spheroids was analyzed. Tumor spheroid morphology and growth and the cell death mechanisms after PDT in CW and pulsed modes were assessed.

RESULTS

We found a more rapid 1O2 generation and a higher photobleaching rate in miniSOG solution upon irradiation in pulsed mode compared to CW mode. Photobleaching of miniSOG in tumor spheroids was also higher after irradiation in the pulsed mode. PDT of spheroids in CW mode resulted in a moderate expansion of the necrotic core of tumor spheroids and a slight inhibition of spheroid growth. The pulsed mode was more effective in induction of cell death, including apoptosis, and suppression of spheroid growth.

CONCLUSIONS

Comparison of CW and pulsed irradiation modes in PDT with miniSOG showed more pronounced cytotoxic effects of the pulsed mode. Our results suggest that the pulsed irradiation regimen enables enhanced 1O2 production by photosensitizer and stimulates apoptosis.

GENERAL SIGNIFICANCE

Our results provide more insights into the cellular mechanisms of anti-cancer PDT and open the way to improvement of light irradiation protocols.

Light Technology for Efficient and Effective Photodynamic Therapy: A Critical Review

Photodynamic therapy (PDT) is a cancer treatment with strong potential over well-established standard therapies in certain cases. Non-ionising radiation, localisation, possible repeated treatments, and stimulation of immunological response are some of the main beneficial features of PDT. Despite the great potential, its application remains challenging. Limited light penetration depth, non-ideal photosensitisers, complex dosimetry, and complicated implementations in the clinic are some limiting factors hindering the extended use of PDT. To surpass actual technological paradigms, radically new sources, light-based devices, advanced photosensitisers, measurement devices, and innovative application strategies are under extensive investigation. The main aim of this review is to highlight the advantages/pitfalls, technical challenges and opportunities of PDT, with a focus on technologies for light activation of photosensitisers, such as light sources, delivery devices, and systems. In this vein, a broad overview of the current status of superficial, interstitial, and deep PDT modalities-and a critical review of light sources and their effects on the PDT process-are presented. Insight into the technical advancements and remaining challenges of optical sources and light devices is provided from a physical and bioengineering perspective.

Photodynamic and Sonodynamic Therapy with Protoporphyrin IX: In Vitro and In Vivo Studies

Sono-photodynamic therapy is a promising anticancer technique based on the combination of sonodynamic and photodynamic therapy to improve the cancer treatment effectiveness. This study was aimed at analyzing the effects of the sono-photodynamic (SPD) activity on protoporphyrin IX (PpIX) solution and PpIX-loaded rat liver. In vitro, PpIX 5 μM solutions were irradiated with light (635 nm, 30-50 mW/cm²), ultrasound (1 MHz, 1-2 W/cm²) and both. The PpIX absorption spectra recorded over exposure time revealed that the PpIX decay rate induced by SPD activity (combined irradiation) was approximately the sum of those induced by photodynamic and sonodynamic activity. In vivo, rats were intraperitoneally injected with 5-aminolevulinic acid at the dose of 500 mg/kg weight. After 3 h of injection, the PpIX-loaded livers were irradiated with light (635 nm, 180 ± 9 J/cm²), ultrasound (1.0 MHz, 770 ± 40 J/cm²) and both using a single probe capable of illuminating and sonicating the liver simultaneously. After 30 h, the liver damage induced by each protocol was analyzed histologically. It was found that a greater necrosis depth was induced by the SPD activity. These results suggest that the SPD activity could improve the PpIX decay rate and have greater scope than photodynamic or sonodynamic activity. Further studies should be performed to gain a better understanding of this protocol.

Light-driven photosensitizer uptake increases Candida albicans photodynamic inactivation

Photodynamic Inactivation (PDI) is based on the use of a photosensitizer (PS) and light that results mainly in the production of reactive oxygen species, aiming to produce microorganism cell death. PS incubation time and light dose are key protocol parameters that influence PDI response; the correct choice of them can increase the efficiency of inactivation. The results of this study show that a minor change in the PDI protocol, namely light-driven incubation leads to a higher photosensitizer and more uniform cell uptake inside the irradiated zone. Furthermore, as the uptake increases, the damage caused by PDI also increases. The proposed light-driven incubation prior to the inactivation illumination dose has advantages when compared to the traditional PDI treatments since it can be more selective and effective. Using a violet light as pre-illumination (light-driven incubation) source and a red-light system as PDI source, it was possible to demonstrate that when compared to the traditional protocol of dark incubation, the pre-illuminated cell culture showed an inactivation increase of 7 log units. These in vitro results performed in Candida albicans cells may result in the introduction of a new protocol for PDI.

Beyond the Barriers of Light Penetration: Strategies, Perspectives and Possibilities for Photodynamic Therapy

Photodynamic therapy (PDT) is a photochemistry based treatment modality that involves the generation of cytotoxic species through the interactions of a photosensitizer molecule with light irradiation of an appropriate wavelength. PDT is an approved therapeutic modality for several cancers globally and in several cases has proved to be effective where traditional treatments have failed. The key parameters that determine PDT efficacy are 1. the photosensitizer (nature of the molecules, selectivity, and macroscopic and microscopic localization etc.), 2. light application (wavelength, fluence, fluence rate, irradiation regimes etc.) and 3. the microenvironment (vascularity, hypoxic regions, stromal tissue density, molecular heterogeneity etc.). Over the years, several groups aimed to monitor and manipulate the components of these critical parameters to improve the effectiveness of PDT treatments. However, PDT is still misconstrued to be a surface treatment primarily due to the limited depths of light penetration. In this review, we present the recent advances, strategies and perspectives in PDT approaches, particularly in cancer treatment, that focus on increasing the 'damage zone' beyond the reach of light in the body. This is enabled by a spectrum of approaches that range from innovative photosensitizer excitation strategies, increased specificity of phototoxicity, and biomodulatory approaches that amplify the biotherapeutic effects induced by photodynamic action. Along with the increasing depth of understanding of the underlying physical, chemical and physiological mechanisms, it is anticipated that with the convergence of these strategies, the clinical utility of PDT will be expanded to a powerful modality in the armamentarium for the management of cancer.

Towards PDT with Genetically Encoded Photosensitizer KillerRed: A Comparison of Continuous and Pulsed Laser Regimens in an Animal Tumor Model

The strong phototoxicity of the red fluorescent protein KillerRed allows it to be considered as a potential genetically encoded photosensitizer for the photodynamic therapy (PDT) of cancer. The advantages of KillerRed over chemical photosensitizers are its expression in tumor cells transduced with the appropriate gene and direct killing of cells through precise damage to any desired cell compartment. The ability of KillerRed to affect cell division and to induce cell death has already been demonstrated in cancer cell lines in vitro and HeLa tumor xenografts in vivo. However, the further development of this approach for PDT requires optimization of the method of treatment. In this study we tested the continuous wave (593 nm) and pulsed laser (584 nm, 10 Hz, 18 ns) modes to achieve an antitumor effect. The research was implemented on CT26 subcutaneous mouse tumors expressing KillerRed in fusion with histone H2B. The results showed that the pulsed mode provided a higher rate of photobleaching of KillerRed without any temperature increase on the tumor surface. PDT with the continuous wave laser was ineffective against CT26 tumors in mice, whereas the pulsed laser induced pronounced histopathological changes and inhibition of tumor growth. Therefore, we selected an effective regimen for PDT when using the genetically encoded photosensitizer KillerRed and pulsed laser irradiation.

Assessment of ALA-induced PpIX production in porcine skin pretreated with microneedles

Photodynamic therapy (PDT) is used for skin treatments of premalignant and cancer lesions and recognized as a non-invasive technique that combines tissue photosensitization and subsequent exposure to light to induce cell death. However, it is limited to the treatment of superficial lesions, mainly due to the low cream penetration. Therefore, the improvement of transdermal distribution of aminolevulinic acid (ALA) is needed. In this study, the kinetics and homogeneity of production of ALA-induced PpIX after the skin pre-treatment with microneedles rollers of 0.5, 1.0 and 1.5 mm length were investigated. An improvement in homogeneity and production of PpIX was shown in a porcine model. Widefield fluorescence imaging three hours after the topical application of ALA-cream in the combined treatment with microeedles rollers.

Polymeric microbubbles as delivery vehicles for sensitizers in sonodynamic therapy

Microbubbles (MBs) have recently emerged as promising delivery vehicles for sensitizer drugs in sonodynamic therapy (SDT). The ability to selectively destroy the MB and activate the sensitizer using an external ultrasound trigger could provide a minimally invasive and highly targeted therapy. While lipid MBs have been approved for use as contrast agents in diagnostic ultrasound, the attachment of sensitizer drugs to their surface results in a significant reduction in particle stability. In this Article, we prepare both lipid and polymer (PLGA) MBs with rose bengal attached to their surface and demonstrate that PLGA MB conjugates are significantly more stable than their lipid counterparts. In addition, the improved stability offered by the PLGA shell does not hinder their selective destruction using therapeutically acceptable ultrasound intensities. Furthermore, we demonstrate that treatment of ectopic human tumors (BxPC-3) in mice with the PLGA MB-rose bengal conjugate and ultrasound reduced tumor volume by 34% 4 days after treatment while tumors treated with the conjugate alone increased in volume by 48% over the same time period. Therefore, PLGA MBs may offer a more stable alternative to lipid MBs for the site specific delivery of sensitizers in SDT.

Evaluation of one- and two-photon activated photodynamic therapy with pyropheophorbide-a methyl ester in human cervical, lung and ovarian cancer cells

Two-photon activated photodynamic therapy (2-γ PDT) has the potential of treating deeper tumors and/or improving tumor targeting. Here, we evaluated the one- and two-photon activated PDT efficacy of pyropheophorbide-a methyl ester (MPPa), a second-generation photosensitizer derived from chlorophyll a. We show that MPPa, when activated by femtosecond (fs) laser pulses at 674 nm, has high one-photon (1-γ) PDT efficacy against cisplatin-sensitive human cervical (HeLa) and cisplatin-resistant human lung (A549) and ovarian (NIH:OVCAR-3) cancer cells. At a low light dose of 0.06 J cm(-2), the IC50 (the MPPa concentration required to kill 50% of the cells) was determined to be 5.3 ± 0.3, 3.4 ± 0.3 and 3.6 ± 0.4 μM for HeLa, A549 and NIH:OVCAR-3 cells, respectively. More significantly, we also show that MPPa can be effectively activated by an 800 nm, 120 fs laser through 2-γ excitation; at a light dose causing no measurable photocytotoxicity in the absence of photosensitizer, the corresponding IC50 values were measured to be 4.1 ± 0.3, 9.6 ± 1.0 and 1.6 ± 0.3 μM, respectively. These results indicate that MPPa is a potent photosensitizer for both 1- and 2-γ activated PDT with potential applications for difficult-to-treat tumors by conventional therapies.