Qun Chen

Fast photoacoustic imaging system based on 320-element linear transducer array

A fast photoacoustic (PA) imaging system, based on a 320-transducer linear array, was developed and tested on a tissue phantom. To reconstruct a test tomographic image, 64 time-domain PA signals were acquired from a tissue phantom with embedded light-absorption targets. A signal acquisition was accomplished by utilizing 11 phase-controlled sub-arrays, each consisting of four transducers. The results show that the system can rapidly map the optical absorption of a tissue phantom and effectively detect the embedded light-absorbing target. By utilizing the multi-element linear transducer array and phase-controlled imaging algorithm, we thus can acquire PA tomography more efficiently, compared to other existing technology and algorithms. The methodology and equipment thus provide a rapid and reliable approach to PA imaging that may have potential applications in noninvasive imaging and clinic diagnosis.

Photoacoustic imaging with deconvolution algorithm

The impulse response of the ultrasonic transducer used for detection is crucial for photoacoustic imaging with high resolution. We demonstrate a reconstruction method that allows the optical absorption distribution of a sample to be reconstructed without knowing the impulse response of the ultrasonic transducer. A convolution relationship between photoacoustic signals measured by an ultrasound transducer and optical absorption distribution is developed. Based on this theory, the projection of the optical absorption distribution of a sample can be obtained directly by deconvolving the recorded PA signal originating from a point source out of that from the sample. And a modified filtered back projection algorithm is used to reconstruct the optical absorption distribution. We constructed a photoacoustic imaging system to validate the reconstruction method and the experimental results demonstrated that the reconstructed images agreed well with the original phantom samples. The spatial resolution of the system reaches 0.3 mm.

Pyropheophorbide A and c(RGDyK) Comodified Chitosan-Wrapped Upconversion Nanoparticle for Targeted Near-Infrared Photodynamic Therapy

Near-infrared (NIR)-to-visible upconversion nanoparticle (UCNP) has shown promising prospects in photodynamic therapy (PDT) as a drug carrier or energy donor. In this work, a photosensitizer pyropheophorbide a (Ppa) and RGD peptide c(RGDyK) comodified chitosan-wrapped NaYF(4):Yb/Er upconversion nanoparticle UCNP-Ppa-RGD was developed for targeted near-infrared photodynamic therapy. The properties of UCNP-Ppa-RGD, such as morphology, stability, optical spectroscopy and singlet oxygen generation efficiency, were investigated. The results show that covalently linked pyropheophorbide a molecule not only is stable but also retains its spectroscopic and functional properties. In vitro studies confirm a stronger targeting specificity of UCNP-Ppa-RGD to integrin α(v)β(3)-positive U87-MG cells compared with that in the corresponding negative group. The photosensitizer-attached nanostructure exhibited low dark toxicity and high phototoxicity against cancer cells upon 980 nm laser irradiation at an appropriate dosage. These results represent the first demonstration of a highly stable and efficient photosensitizer modified upconversion nanostructure for targeted near-infrared photodynamic therapy of cancer cells. The novel UCNP-Ppa-RGD nanoparticle may provide a powerful alternative for near-infrared photodynamic therapy with an improved tumor targeting specificity.

Photoacoustic and ultrasonic coimage with a linear transducer array

A technique is developed to simultaneously acquire ultrasound and photoacoustic (PA) images based on a linear transducer array. The system uses conventional ultrasound for rapid identification of potential targets. After a target is identified, the ultrasound echo and PA signals can be simultaneously obtained with optimized excitation and a signal collection sequence. The corresponding ultrasound impedance and optical absorption images are reconstructed with a phase-controlled algorithm. The approach can effectively reduce the artifacts associated with a conventional filter backprojection algorithm used in PA imaging by linear scanning. The technique provides a new approach for practical applications.

Mitochondrial autophagy protects against heat shock-induced apoptosis through reducing cytosolic cytochrome c release and downstream caspase-3 activation

Autophagy is an evolutionarily conserved process for bulk degradation of cytoplasmic components, including large molecules and organelles. It can either help to enhance or to resist apoptosis, depending on the circumstances. The mechanism of how autophagy impacts apoptosis and the subsequent cellular events upon heat shock remains unclear. In this study, we demonstrate for the first time that mitochondrial membrane permeability transition (MPT)-sensitive mitochondrial autophagy can protect against heat-induced apoptosis through reduction of cytosolic cytochrome c release and downstream caspase-3 activation. With confocal microscopy, it was revealed that as autophagosomes increased, mitochondrial content was mass decreased after heat shock. Detailed analysis shows that a single swelling mitochondrion could be entrapped into autophagosome. The depolarization of mitochondria preceded the mitochondrial loss, and both could be abolished by MPT inhibitor cyclosporine (CsA). In addition, along with the decrease of mitochondrial content, the level of total cytochrome c was also reduced, resulting in a reduction of its release to cytoplasm. When heat shock was combined with 3-methyladenine (3-MA), an inhibitor of autophagy, the mitochondrial loss and the reduction of total cytochrome c were both inhibited, and then caspase-3 activation and cell apoptosis were increased. Thus, it is reasonable to believe that, heat shock-induced cellular events can be modulated by controlling autophagy, and this may represent a novel approach to enhance the efficacy of hyperthermia.

Dihydroartemisinin and transferrin dual-dressed nano-graphene oxide for a pH-triggered chemotherapy.

Dihydroartemisinin (DHA) is a unique anti-malarial drug isolated from the plant Artemisia annua. Recently, it has been studied as an alternative modality for cancer therapy, utilizing its reactive oxygen species (ROS) yielding mechanism from interacting with Ferrous ion (Fe (II)). In this work, a novel nanodrug (DHA-GO-Tf) is constructed based on nanoscale Graphene oxide (GO) dual-dressed with DHA and Transferrin (Tf). Tf dually functions as a pilot for the nanoparticle to target tumor cell with over expressed Transferrin receptor (TfR) and a ferric ion carrier. Upon tumor cellular endocytosis, Ferric ion (Fe(III)) is released from the Tf, triggered by the low pH in the lysosomes of the tumor cell. The intracellular Fe (III) is reduced to Fe (II) and interacts with DHA to increase its cytotoxicity. The potential of this alternative anti-tumor modality is demonstrated both in vitro and in vivo. Comparing with DHA alone, the nanodrug DHA-GO-Tf resulted in a significantly enhanced tumor delivery specificity and cytotoxicity, and achieved a complete tumor cure in mice with minimal side-effects.

Bid Is Required in NPe6-PDT-induced Apoptosis

Photodynamic therapy (PDT) employing photosensiter N‐aspartyl chlorin e6 (NPe6) can induce lysosome disruption and initiate the intrinsic apoptotic pathway. Yet the precise signal transduction pathway remains poorly understood. In this study, we have investigated the molecular mechanism in NPe6‐PDT‐induced apoptosis in human lung adenocarcinoma cells (ASTC‐a‐1). A recombinant fluorescence resonance energy transfer (FRET) Bid probe was utilized to determine the kinetics of Bid cleavage. The results show that cleavage of the Bid‐FRET probe occurred 150 ± 5 min after NPe6‐PDT treatment, and this process lasted for 45 ± 5 min. The Bid cleavage coincided with a translocation of tBid from cytoplasm to mitochondria. Remarkably, a significant protection against cell death was observed by using small interfering RNA for Bid. Therefore, our study clearly showed the dynamics of Bid activation and redistribution during NPe6‐PDT‐induced apoptosis by using real‐time analysis in living cells, and the inhibition of cell death by silencing Bid with interference strongly suggested that activation of Bid is required for inducing apoptosis in this experimental model.

Cancer Phototherapy via Selective Photoinactivation of Respiratory Chain Oxidase to Trigger a Fatal Superoxide Anion Burst

AIMS Here, we develop a novel cancer treatment modality using mitochondria-targeting, high-fluence, low-power laser irradiation (HF-LPLI) in mouse tumor models and explore the mechanism of mitochondrial injury by HF-LPLI. RESULTS We demonstrated that the initial reaction after photon absorption was photosensitization of cytochrome c oxidase (COX), to inhibit enzymatic activity of COX in situ and cause respiratory chain superoxide anion (O2(-•)) burst. We also found that HF-LPLI exerted its main tumor killing effect through mitochondrial O2(-•) burst via electron transport chain (ETC). These phenomena were completely absent in the respiration-deficient cells and COX knockdown cells. With a carefully selected irradiation protocol, HF-LPLI could efficaciously destroy tumors. The inhibition of enzymatic activity of COX and generation of O2(-•) by HF-LPLI in vivo were also detected. INNOVATION It is the first time that the mechanism involved in the interaction between light and its photoacceptor under HF-LPLI treatment is clarified. Our results clearly indicate that HF-LPLI initiates its effects via targeted COX photoinactivation and that the tumor-killing efficacy is dependent of the subsequent mitochondrial O2(-•) burst via ETC. CONCLUSION Based on both in vitro and in vivo results, we conclude that HF-LPLI can selectively photoinactivate respiratory chain oxidase to trigger a fatal mitochondrial O2(-•) burst, producing oxidative damage on cancer cells. This study opens up the possibilities of applications of HF-LPLI as a mitochondria-targeting cancer phototherapy.

Increasing the efficiency of photodynamic therapy by improved light delivery and oxygen supply using an anticoagulant in a solid tumor model

The main factors in photodynamic therapy (PDT) are: photosensitizer retention, photon absorption, and oxygen supply. Each factor has its unique set of problems that poses limitation to the treatment. Both light delivery and oxygen supply are significant bottlenecks in PDT. Vascular closure during PDT reduces oxygen supply to the targeted tissue. On the other hand, with the changes in blood perfusion, the tissue optical properties change, and result in variation in irradiation light transmission. For these reasons, it becomes very important to avoid blood coagulation and vascular closure during PDT.

New insights of mitochondria reactive oxygen species generation and cell apoptosis induced by low dose photodynamic therapy

Photodynamic therapy (PDT) is an approved therapeutic procedure that exerts cytotoxic activity towards tumour cells by irradiating photosensitisers with light exposure to produce reactive oxygen species (ROS). In the current study, we have observed that there is an additional production of intracellular ROS during low dose PDT. A mitochondrial respiration-deficient cell line (ρ(0) cells) was investigated to determine the involvement of electron transfer chain (ETC). The production of ROS was significantly different between ASTC-a-1 and ρ(0)ASTC-a-1 cells after an identical PDT treatment. Yet, with an increasing Photofrin dose, the difference gradually diminished. Pretreatment of the ASTC-a-1 cells with the ETC inhibitor rotenone lead the corresponding ROS production to a similar level from ρ(0)ASTC-a-1 cells subjected to identical PDT protocols. Moreover, we found that the difference in intracellular ROS productions between ASTC-a-1 and ρ(0)ASTC-a-1 cells started during a PDT treatment, while the irradiation was still being delivered. A cytotoxicity assay showed that, the ASTC-a-1 cells were more sensitive to PDT than ρ(0)ASTC-a-1 cells. ROS scavenger n-acetyl-l-cysteine (NAC) attenuated the toxicity of PDT in both cell lines. Altogether, these results indicate that low dose PDT can induce an endogenous ROS production via the ETC. This additional endogenous ROS, on top of that from PDT photochemical reactions, contributes to an increased cell apoptosis. Thus, mitochondria are not only targets but also can be a source of ROS during low dose PDT. These results may provide a novel approach to improve PDT applications by maximising the efficiency of currently available photosensitisers.