Sandhya Clement

X-ray induced singlet oxygen generation by nanoparticle-photosensitizer conjugates for photodynamic therapy: determination of singlet oxygen quantum yield.

Singlet oxygen is a primary cytotoxic agent in photodynamic therapy. We show that CeF3 nanoparticles, pure as well as conjugated through electrostatic interaction with the photosensitizer verteporfin, are able to generate singlet oxygen as a result of UV light and 8 keV X-ray irradiation. The X-ray stimulated singlet oxygen quantum yield was determined to be 0.79 ± 0.05 for the conjugate with 31 verteporfin molecules per CeF3 nanoparticle, the highest conjugation level used. From this result we estimate the singlet oxygen dose generated from CeF3-verteporfin conjugates for a therapeutic dose of 60 Gy of ionizing radiation at energies of 6 MeV and 30 keV to be (1.2 ± 0.7) × 108 and (2.0 ± 0.1) × 109 singlet oxygen molecules per cell, respectively. These are comparable with cytotoxic doses of 5 × 107–2 × 109 singlet oxygen molecules per cell reported in the literature for photodynamic therapy using light activation. We confirmed that the CeF3-VP conjugates enhanced cell killing with 6 MeV radiation. This work confirms the feasibility of using X- or γ- ray activated nanoparticle-photosensitizer conjugates, either to supplement the radiation treatment of cancer, or as an independent treatment modality.

Spectral and coherence signatures of threshold in random lasers

We investigated the spectral and coherence signatures of threshold in random lasers with incoherent feedback consisting of alumina colloidal nanoparticles suspended in rhodamine 6G methanol solution under nanosecond-pulsewidth pumping, based on measurement of temporal and spatial coherence properties and comparison with emission spectra. Feedback in this random laser was provided by multiple scattering from the alumina particles, and the effects of particle concentration and scattering length were studied for the weakly scattering and diffusive scattering regimes. At threshold, in each regime, the visibility of the interference fringes jumped abruptly, coinciding with a substantial increase in peak emission intensity and decrease in the linewidth of a single dominant emission peak.

Light-triggered liposomal cargo delivery platform incorporating photosensitizers and gold nanoparticles for enhanced singlet oxygen generation and increased cytotoxicity

We developed light-triggered liposomes incorporating 3–5 nm hydrophobic gold nanoparticles and Rose Bengal (RB), a well-known photosensitizer used for photodynamic therapy. Singlet oxygen generated by these liposomes with 532 nm light illumination was characterized for varying the molar ratio of lipids and gold nanoparticles while keeping the amount of RB constant. Gold nanoparticles were found to enhance the singlet oxygen generation rate, with a maximum enhancement factor of 1.75 obtained for the molar ratio of hydrogenated soy l-α-phosphatidylcholine:1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(hexanoylamine):gold of 57:5:17 compared with liposomes loaded with RB alone. The experimental results could be explained by the local electric field enhancement caused by gold nanoparticles. We further assessed cellular cytotoxicity of gold-loaded liposomes by encapsulating an antitumor drug, doxorubicin (Dox); such Dox-loaded liposomes were applied to human colorectal cancer cells (HCT116) and exposed to light. Gold-loaded liposomes containing RB and Dox where Dox release was triggered by light were found to exhibit higher cytotoxicity compared with the liposomes loaded with RB and Dox alone. Our results indicate that gold-loaded liposomes incorporating photosensitizers may serve as improved agents in photodynamic therapy and chemotherapy.

Controlled gene and drug release from a liposomal delivery platform triggered by X-ray radiation

Liposomes have been well established as an effective drug delivery system, due to simplicity of their preparation and unique characteristics. However conventional liposomes are unsuitable for the on-demand content release, which limits their therapeutic utility. Here we report X-ray-triggerable liposomes incorporating gold nanoparticles and photosensitizer verteporfin. The 6 MeV X-ray radiation induces verteporfin to produce singlet oxygen, which destabilises the liposomal membrane and causes the release of cargos from the liposomal cavity. This triggering strategy is demonstrated by the efficiency of gene silencing in vitro and increased effectiveness of chemotherapy in vivo. Our work indicates the feasibility of a combinatorial treatment and possible synergistic effects in the course of standard radiotherapy combined with chemotherapy delivered via X-ray-triggered liposomes. Importantly, our X-ray-mediated liposome release strategy offers prospects for deep tissue photodynamic therapy, by removing its depth limitation.X-ray radiation has excellent tissue penetration depth, making it a useful trigger for deep tissue cancer therapy. Here, the authors design X-ray triggered drug/gene-loaded liposomes by embedding photosensitizers and gold nanoparticles in the liposome bilayer, and demonstrate their efficacy in cancer and gene therapy.

Biodegradable nanoconstructs for targeted deep tumour therapy (Conference Presentation)

Photodynamic therapy (PDT) is a clinically approved method for the treatment of cancer by using singlet oxygen, a highly reactive oxygen generated from a photosensitizer drug upon photoactivation. Limited light penetration depth into the tissue means that PDT is unsuitable for deep tissue cancer treatments. To overcome this issue, we developed a dual PDT system where poly (D, L-lactide-co-glycolide) (PLGA) polymeric nanoparticles incorporating a photosensitizer, verteporfin, can be triggered to generate cytotoxic singlet oxygen by both red light at 690 nm and by 6 MeV X-ray radiation. The X-ray radiation used in this study allows this system to break through the PDT depth barrier, due to excellent penetration of 6 MeV X-ray radiation though biological tissue. In addition, the conjugation of the nanoparticles with folic acid moieties has enabled specific targeting of HCT116 cancer cells which overexpress the folate receptors. Physiochemical characterization of PLGA nanoparticles, such as size distribution, zeta potential, morphology and in-vitro release of verteporfin was also carried out. These studies indicate that improved tumour cell killing effects can be achieved with nanoparticles triggered by 690 nm as well as 6 MeV radiation, compared with nanoparticles alone. We attribute the X-ray induced singlet oxygen generation from the photosensitizer verteprofin to photoexcitation by Cerenkov radiation and/or chemical reaction facilitated by energetic secondary electrons produced in the tissue. This effect offers the possibility of enhancing the commonly prescribed radiation therapy by simultaneous PDT.

X-ray radiation-induced and targeted photodynamic therapy with folic acid-conjugated biodegradable nanoconstructs

Introduction The depth limitation of conventional photodynamic therapy (PDT) with visible electromagnetic radiation represents a challenge for the treatment of deep-seated tumors. Materials and methods To overcome this issue, we developed an X-ray-induced PDT system where poly(lactide-co-glycolide) (PLGA) polymeric nanoparticles (NPs) incorporating a photosensitizer (PS), verteporfin (VP), were triggered by 6 MeV X-ray radiation to generate cytotoxic singlet oxygen. The X-ray radiation used in this study allows this system to breakthrough the PDT depth barrier due to excellent penetration of 6 MeV X-ray radiation through biological tissue. In addition, the conjugation of our NPs with folic acid moieties enables specific targeting of HCT116 cancer cells that overexpress the folate receptors. We carried out physiochemical characterization of PLGA NPs, such as size distribution, zeta potential, morphology and in vitro release of VP. Cellular uptake activity and cell-killing effect of these NPs were also evaluated. Results and discussion Our results indicate that our nanoconstructs triggered by 6 MeV X-ray radiation yield enhanced PDT efficacy compared with the radiation alone. We attributed the X-ray-induced singlet oxygen generation from the PS, VP, to photoexcitation by Cherenkov radiation and/or reactive oxygen species generation facilitated by energetic secondary electrons produced in the tissue. Conclusion The cytotoxic effect caused by VP offers the possibility of enhancing the radiation therapy commonly prescribed for the treatment of cancer by simultaneous PDT.

Quantification of nanoparticle concentration in colloidal suspensions by a non-destructive optical method

The estimation of nanoparticle number concentration in colloidal suspensions is a prerequisite in many procedures, and in particular in multi-stage, low-yield reactions. Here, we describe a rapid, non-destructive method based on optical extinction and dynamic light scattering (DLS), which combines measurements using common bench-top instrumentation with a numerical algorithm to calculate the particle size distribution (PSD) and concentration. These quantities were derived from Mie theory applied to measurements of the optical extinction spectrum of homogeneous, non-absorbing nanoparticles, and the relative PSD of a colloidal suspension. The work presents an approach to account for PSDs achieved by DLS which, due to the underlying model, may not be representative of the true sample PSD. The presented approach estimates the absolute particle number concentration of samples with mono-, bi-modal and broad size distributions with <50% precision. This provides a convenient and practical solution for number concentration estimation required during many applications of colloidal nanomaterials.

Towards photodynamic therapy with ionizing radiation: nanoparticle-mediated singlet oxygen generation(Conference Presentation)

Photodynamic therapy (PDT) is a clinically approved method for the treatment of cancer by using singlet oxygen, a highly reactive oxygen generated from a photosensitizer drug upon photoactivation. Limited light penetration depth into to the tissue means that PDT is unsuitable for deep tissue cancer treatments. This can be overcome by using X-ray /gamma rays activated nanoparticles able to trigger the photosensitizer drug and generate singlet oxygen. Additionally, inorganic nanoparticles interact more strongly with X and/or gamma rays than the tissue, allowing to concentrate the effects of radiation near nanoparticle surface and they can also be molecularly targeted to cancer cells. In this work we synthesized and characterized CeF3 nanoparticles, a well-known scintillator material. The nanoparticles were conjugated with Verteporfin, a photosensitizer drug by electrostatic interaction. We assessed the performance of CeF3 and the conjugates to generate singlet oxygen exposed to X-ray radiation. The X-ray singlet oxygen quantum yield of the nanoparticle-photosensitizer system was accurately quantified for the first time. This provided realistic estimates of the singlet oxygen dose taking into consideration the dose partition of the radiation between CeF3 and the tissue. Furthermore, we investigated gold nanoparticle-photosensitizer systems. We confirmed that pure gold nanoparticles itself generate singlet oxygen which is attributed to plasmonic effects. We found enhanced singlet oxygen generation from gold-Rose Bengal conjugates and gold nanorod–verteporfin conjugates. These singlet-oxygen-generating nanomaterials add a new dimension to radiation-assisted PDT.