Quenching-induced deactivation of photosensitizer by nanoencapsulation to improve phototherapy of cancer

Nanoformulations - Insights Towards Characterization Techniques

BACKGROUND

Drug-loaded novel nanoformulations are gaining importance due to their versatile properties compared to conventional pharmaceutical formulations. Nanomaterials, apart from their multifactorial benefits, have a wider scope in the prevention, treatment, and diagnosis of cancer. Understanding the chemistry of drug-loaded nano-formulations to elicit its behaviour both at molecular and systemic levels is critical in the present scenario. Drug-loaded nanoformulations are controlled by their size, shape, surface chemistry, and release behavior. The major pharmaceutical drug loaded nanocarriers reported for anticancer drug delivery for the treatment of various forms of cancers such as lung cancer, liver cancer, breast cancer, colon cancer, etc include nanoparticles, nanospheres, nanodispersions, nanocapsules, nanomicelles, cubosomes, nanoemulsions, liposomes and niosomes. The major objectives in designing anticancer drug-loaded nanoformulations are to manage the particle size/morphology correlating with the drug release to fulfil the specific objectives. Hence, nano characterizations are very critical both at in vitro and in vivo levels.

OBJECTIVE

The main objective of this review paper is to summarise the major characterization techniques used for the characterization of drug-loaded nanoformulations. Even though information on characterization techniques of various nano-formulations is available in the literature, it is scattered. The proposed review will provide a comprehensive understanding of nanocharacterization techniques.

CONCLUSION

To conclude, the proposed review will provide insights towards the different nano characterization techniques along with their recent updates, such as particle size, zeta potential, entrapment efficiency, in vitro release studies (chromatographic HPLC, HPTLC, and LC-MS/MS analysis), EPR analysis, X-ray diffraction analysis, thermal analysis, rheometric, morphological analysis etc. Additionally, the challenges encountered by the nano characterization techniques will also be discussed.

The Dark Side: Photosensitizer Prodrugs

Photodynamic therapy (PDT) and photodiagnosis (PD) are essential approaches in the field of biophotonics. Ideally, both modalities require the selective sensitization of the targeted disease in order to avoid undesired phenomena such as the destruction of healthy tissue, skin photosensitization, or mistaken diagnosis. To a large extent, the occurrence of these incidents can be attributed to “background” accumulation in non-target tissue. Therefore, an ideal photoactive compound should be optically silent in the absence of disease, but bright in its presence. Such requirements can be fulfilled using innovative prodrug strategies targeting disease-associated alterations. Here we will summarize the elaboration, characterization, and evaluation of approaches using polymeric photosensitizer prodrugs, nanoparticles, micelles, and porphysomes. Finally, we will discuss the use of 5-aminolevulinc acid and its derivatives that are selectively transformed in neoplastic cells into photoactive protoporphyrin IX.

Development of copolymeric nanoparticles of hypocrellin B: Enhanced phototoxic effect and ocular distribution

In the present work, we have developed a photosensitizer hypocrellin B (HB) and nano silver loaded PLGA-TPGS nanoparticles with improved singlet oxygen production for enhanced photodynamic effect for the efficient treatment of age related macular degeneration. Random copolymer (PLGA-TPGS) synthesized by ring opening and bulk polymerization was characterized by IR, ¹H NMR and TGA analysis. HBS-CP-NPs prepared by nanoprecipitation techniques were spherical shaped 89.6-753.6nm size particles with negative zeta potential. The average encapsulation efficiency was 84.06±11.43% and HB release from the HBS-CP-NPs was found to be biphasic with a slow release of 1.41% in the first 8h and 48.91% during 3days as measured by RP-HPLC. DSC thermograms indicate that HB was dispersed as amorphous form in HBS-CP-NPs. The ROS generation level of HBS-CP-NPs was significantly higher than that of HB/HB-CP-NPs. The production of ¹O₂ of HBS-CP-NPs has been assessed using EPR spectrometer. The ¹O₂ generating efficiency follows the order of nano silver>HB-CP-NPs>HBS-CP-NPs>pure HB drug solution. The superior phototoxic effect of HBS-CP-NPs (85.5% at 50μM) was attained at 2h irradiation in A549 cells. Significant anti angiogenic effect of HBS-CP-NPs was observed in treated CAM embryos. Following intravenous injection of HBS-CP-NPs to rabbits, the maximum amount of HB was found in retina (3h), iris (9h), aqueous humour (9h) and vitreous humour (9h).

Cyclopeptidic photosensitizer prodrugs as proteolytically triggered drug delivery systems of pheophorbide A: part I – self-quenched prodrugs

RAFTs bearing multiple copies of pheophorbide A allow perfectly defined photosensitizer prodrugs.

Hypocrellin B and nano silver loaded polymeric nanoparticles: Enhanced generation of singlet oxygen for improved photodynamic therapy

A nanoparticulate photodynamic approach was employed with an objective to achieve enhanced production of singlet oxygen (¹O₂), for the management of posterior segment eye diseases like age related macular degeneration. The hypocrellin B (HB) loaded poly lactide-co-glycolide nanoparticle formulations were incorporated with nano silver (HBS-NPs). The optimized HBS-NPs contained 2.60±0.06mg/mL of HB and showed (i) 135.6 to 828.2nm size range, and (ii) negative zeta potential with a narrow polydispersity index. The DSC thermograms suggested the amorphous nature of HB inside the HBS-NPs. With the average encapsulation efficiency of 92.9±1.79%, the drug release from the HBS-NPs followed a biphasic pattern with an initial burst of 3.50% during first 8h followed by a sustained release of 47.82% within 3days. The interaction between nano silver and HB as assessed by the increase in spectral intensity of Raman spectrum demonstrates that HB may be attached over the nano silver. Generation of reactive oxygen species (ROS) by HBS-NPs was significantly higher than that of HB/HB-NPs. The singlet oxygen generating efficiency assessed using EPR spectrometer follows the order of nano silver>HB-NPs>pure HB drug solution>HBS-NPs. The HBS-NPs had a concentration and time dependent phototoxicity on A549 (human adeno lung carcinoma) cells in the presence of light providing a superior phototoxic effect (82.2% at 50μM) at 2h irradiation. The CAM treated with HBS-NPs showed a significant anti-angiogenic effect compared to a blank formulation. In vivo biodistribution studies revealed that intravenous administration of HBS-NPs lead into significant exposure to the posterior segment of the eye. This proof of principle study demonstrates that HB based nanoparticles may be a valuable new tool for application in ocular photodynamic therapy for the treatment of AMD in future.

Redox-sensitive cross-linking enhances albumin nanoparticle function as delivery system for photodynamic cancer therapy

Photodynamic cancer therapy is still limited in its efficiency because of a lack of targeted methods avoiding non-specific toxicity. To overcome this we developed a system that is solely effective upon cellular uptake and intracellular activation by incorporating redox-sensitive chemistry. We used a nanoprecipitation method to obtain human serum albumin nanoparticles (HSA NP) with a diameter of 295 ± 5 nm and decorated them with the photosensitizer (PS) chlorin e6 (Ce6). The NP were stabilized using a redox-sensitive cross-linker to create a smart drug delivery system that is activated only upon NP disintegration in the reducing intracellular environment. Indeed, our drug delivery NP broke down in an environment emulating the reducing intracellular environment with 10 mM glutathione, but not under extracellular conditions. In contrast, the control cross-linked with glutaraldehyde did not break down in the reducing environment. Upon NP disintegration Ce6 fluorescence doubled as the result of diminished self-quenching. While the Ce6-HSA NP did not produce a significant amount of singlet oxygen upon irradiation, NP disintegration restored singlet oxygen production to about half of the value generated by the free Ce6. In vitro experiments with HeLa cells showed that the smart system was able to kill up to 81% of the cells while the glutaraldehyde cross-linked control only killed 56% of them at a drug concentration of 10 ng/ml. Also, Ce6 immobilization in HSA NP prevented dark toxicity in three different cell lines. For the first time, we demonstrate that it is possible to design a smart NP drug delivery system delivering a PS drug to cancer cells while avoiding toxicity prior to the uptake and irradiation. This finding may provide a means of designing more efficient PDT in cancer treatment.

In vivo cancer imaging by poly(ethylene glycol)-b-poly(ɛ-caprolactone) micelles containing a near-infrared probe

Noninvasive near-infrared (NIR) fluorescence imaging is a promising technique for the intraoperative assessment of solid tumor removal. We incorporated a lipophilic NIR probe, 1,1'-dioctadecyltetramethyl indotricarbocyanine iodide (DiR), in poly(ethylene glycol)-b-poly(ɛ-caprolactone) (PEG-b-PCL) micelles, resulting in DiR solubilization in water, occupying nanoscopic PEG-b-PCL micelles. DiR in a self-quenched or nonquenched state showed different kinetics of release from PEG-b-PCL micelles in vitro; however, both obtained high tumor delineation (tumor-to-muscle ratio of 30-43 from collected organs). These results suggest that PEG-b-PCL micelles with DiR are a promising nanosized imaging agent that will provide a basis for enhanced surgical guidance via NIR visualization of tumors.

FROM THE CLINICAL EDITOR

In this paper, noninvasive near-infrared fluorescence imaging coupled with specific lipophilic probes is discussed as a promising technique for intraoperative assessment of solid tumor removal, leading to optimized outcomes for in toto removal of tumors.