Imaging of specific activation of photodynamic molecular beacons in breast cancer vertebral metastases

Molecular Dynamics Simulations of RNA Motifs to Guide the Architectural Parameters and Design Principles of RNA Nanostructures

Molecular dynamics (MD) simulations can be used to investigate the stability and conformational characteristics of RNA nanostructures. However, MD simulations of an RNA nanostructure is computationally expensive due to the size of nanostructure and the number of atoms. Alternatively, MD simulations of RNA motifs can be used to estimate the conformational stability of constructed RNA nanostructure due to their small sizes. In this chapter, we introduce the preparation and MD simulations of two RNA kissing loop (KL) motifs, a linear KL complex and a bent KL complex, and an RNA nanoring. The initial solvated system and topology files of each system will be prepared by two major force fields, AMBER and CHARMM force fields. MD simulations will be performed by NAMD simulation package, which can accept both force fields. In addition, we will introduce the use of the AMBER cpptraj program and visual molecular dynamics (VMD) for data analysis. We will also discuss how MD simulations of two KL motifs can be used to estimate the conformation and stability of RNA nanoring as well as to explain the vibrational characteristics of RNA nanoring.

A Photosensitized Singlet Oxygen (1O2) Toolbox for Bio-Organic Applications: Tailoring 1O2 Generation for DNA and Protein Labelling, Targeting and Biosensing

Singlet oxygen (1O2) is the excited state of ground, triplet state, molecular oxygen (O2). Photosensitized 1O2 has been extensively studied as one of the reactive oxygen species (ROS), responsible for damage of cellular components (protein, DNA, lipids). On the other hand, its generation has been exploited in organic synthesis, as well as in photodynamic therapy for the treatment of various forms of cancer. The aim of this review is to highlight the versatility of 1O2, discussing the main bioorganic applications reported over the past decades, which rely on its production. After a brief introduction on the photosensitized production of 1O2, we will describe the main aspects involving the biologically relevant damage that can accompany an uncontrolled, aspecific generation of this ROS. We then discuss in more detail a series of biological applications featuring 1O2 generation, including protein and DNA labelling, cross-linking and biosensing. Finally, we will highlight the methodologies available to tailor 1O2 generation, in order to accomplish the proposed bioorganic transformations while avoiding, at the same time, collateral damage related to an untamed production of this reactive species.

Progress of Phototherapy Applications in the Treatment of Bone Cancer

Bone cancer including primary bone cancer and metastatic bone cancer, remains a challenge claiming millions of lives and affecting the life quality of survivors. Conventional treatments of bone cancer include wide surgical resection, radiotherapy, and chemotherapy. However, some bone cancer cells may remain or recur in the local area after resection, some are highly resistant to chemotherapy, and some are insensitive to radiotherapy. Phototherapy (PT) including photodynamic therapy (PDT) and photothermal therapy (PTT), is a clinically approved, minimally invasive, and highly selective treatment, and has been widely reported for cancer therapy. Under the irradiation of light of a specific wavelength, the photosensitizer (PS) in PDT can cause the increase of intracellular ROS and the photothermal agent (PTA) in PTT can induce photothermal conversion, leading to the tumoricidal effects. In this review, the progress of PT applications in the treatment of bone cancer has been outlined and summarized, and some envisioned challenges and future perspectives have been mentioned. This review provides the current state of the art regarding PDT and PTT in bone cancer and inspiration for future studies on PT.

Matrix Metalloproteinase Inspired Therapeutic Strategies for Bone Diseases

Matrix Metalloproteinases (MMPs), as a family of zinc-containing enzymes, show the function of decomposing Extracellular Matrix (ECM) and participate in the physiological processes of cell migration, growth, inflammation, and metabolism. Clinical and experimental studies have indicated that MMPs play an essential role in tissue injury and repair as well as tumor diagnosis, metastasis, and prognosis. An increasing number of researchers have paid attention to their functions and mechanisms in bone health and diseases. The present review focuses on MMPs-inspired therapeutic strategies for the treatment of bone-related diseases. We introduce the role of MMPs in bone diseases, highlight the MMPs-inspired therapeutic options, and posit MMPs as a trigger for smart cell/drug delivery.

Rational Design of Photosynthesis-Inspired Nanomedicines

The sun is the most abundant source of energy on earth. Phototrophs have discovered clever strategies to harvest this light energy and convert it to chemical energy for biomass production. This is achieved in light-harvesting complexes, or antennas, that funnel the exciton energy into the reaction centers. Antennas contain an array of chlorophylls, linear tetrapyrroles, and carotenoid pigments spatially controlled by neighboring proteins. This fine-tuned regulation of protein-pigment arrangements is crucial for survival in the conditions of both excess and extreme light deficit. Photomedicine and photodiagnosis have long been utilizing naturally derived and synthetic monomer dyes for imaging, photodynamic and photothermal therapy; however, the precise regulation of damage inflicted by these therapies requires more complex architectures. In this Account, we discuss how two mechanisms found in photosynthetic systems, photoprotection and light harvesting, have inspired scientists to create nanomedicines for more effective and precise phototherapies. Researchers have been recapitulating natural photoprotection mechanisms by utilizing carotenoids and other quencher molecules toward the design of photodynamic molecular beacons (PDT beacons) for disease-specific photoactivation. We highlight the seminal studies describing peptide-linked porphyrin-carotenoid PDT beacons, which are locally activated by a disease-specific enzyme. Examples of more advanced constructs include tumor-specific mRNA-activatable and polyionic cell-penetrating PDT beacons. An alternative approach toward harnessing photosynthetic processes for biomedical applications includes the design of various nanostructures. This Account will primarily focus on organic lipid-based micro- and nanoparticles. The phenomenon of nonphotochemical quenching, or excess energy release in the form of heat, has been widely explored in the context of porphyrin-containing nanomedicines. These quenched nanostructures can be implemented toward photoacoustic imaging and photothermal therapy. Upon nanostructure disruption, as a result of tissue accumulation and subsequent cell uptake, activatable fluorescence imaging and photodynamic therapy can be achieved. Alternatively, processes found in nature for light harvesting under dim conditions, such as in the deep sea, can be harnessed to maximize light absorption within the tissue. Specifically, high-ordered dye aggregation that results in a bathochromic shift and increased absorption has been exploited for the collection of more light with longer wavelengths, characterized by maximum tissue penetration. Overall, the profound understanding of photosynthetic systems combined with rapid development of nanotechnology has yielded a unique field of nature-inspired photomedicine, which holds promise toward more precise and effective phototherapies.

Disulfide-bridge dimeric porphyrin and their reference compounds for glutathione-based specific tumor-activation

The tumor micro-environment is rich in glutathione. To exploit this feature for tumor-activatable porphyrin-based photosensitizers, a dimeric disulfide-bridged porphyrin has been designed and prepared, together with two reference derivatives, a non-cleavable dimer and a monomer. The three compounds have been investigated from a photochemical and photophysical point of view. It appears that the disulfide-bridged derivative exhibited intramolecular aggregation, but to an insufficient extent to induce a satisfying self-quenching of its photoproperties. Unlike expected, the non-cleavable dimer behaved like the monomeric derivative, due to the superior flexibility of the alkyl bridge over the disulfide bridge.

Protease-Sensitive Nanomaterials for Cancer Therapeutics and Imaging

Many diseases can be characterized by the abnormal activity exhibited by various biomolecules, the targeting of which can provide therapeutic and diagnostic utility. Recent trends in medicine and nanotechnology have prompted the development of protease-sensitive nanomaterials systems for therapeutic, diagnostic, and theranostic applications. These systems can act specifically in response to the target enzyme and its associated disease conditions, thus enabling personalized treatment and improved prognosis. In this Review, we discuss recent advancements in the development of protease-responsive materials for imaging and drug delivery and analyze several representative systems to illustrate their key design principles.

Advancement of the Emerging Field of RNA Nanotechnology

The field of RNA nanotechnology has advanced rapidly during the past decade. A variety of programmable RNA nanoparticles with defined shape, size, and stoichiometry have been developed for diverse applications in nanobiotechnology. The rising popularity of RNA nanoparticles is due to a number of factors: (1) removing the concern of RNA degradation in vitro and in vivo by introducing chemical modification into nucleotides without significant alteration of the RNA property in folding and self-assembly; (2) confirming the concept that RNA displays very high thermodynamic stability and is suitable for in vivo trafficking and other applications; (3) obtaining the knowledge to tune the immunogenic properties of synthetic RNA constructs for in vivo applications; (4) increased understanding of the 4D structure and intermolecular interaction of RNA molecules; (5) developing methods to control shape, size, and stoichiometry of RNA nanoparticles; (6) increasing knowledge of regulation and processing functions of RNA in cells; (7) decreasing cost of RNA production by biological and chemical synthesis; and (8) proving the concept that RNA is a safe and specific therapeutic modality for cancer and other diseases with little or no accumulation in vital organs. Other applications of RNA nanotechnology, such as adapting them to construct 2D, 3D, and 4D structures for use in tissue engineering, biosensing, resistive biomemory, and potential computer logic gate modules, have stimulated the interest of the scientific community. This review aims to outline the current state of the art of RNA nanoparticles as programmable smart complexes and offers perspectives on the promising avenues of research in this fast-growing field.

Photosensitized singlet oxygen generation and detection: Recent advances and future perspectives in cancer photodynamic therapy

Photodynamic therapy (PDT) uses photosensitizers and visible light in combination with molecular oxygen to produce reactive oxygen species (ROS) that kill malignant cells by apoptosis and/or necrosis, shut down the tumor microvasculature and stimulate the host immune system. The excited singlet state of oxygen (¹ O₂ ) is recognized to be the main cytotoxic ROS generated during PDT for the majority of photosensitizers used clinically and for many investigational new agents, so that maximizing its production within tumor cells and tissues can improve the therapeutic response, and several emerging and novel approaches for this are summarized. Quantitative techniques for ¹ O₂ production measurement during photosensitization are also of immense importance of value for both preclinical research and future clinical practice. In this review, emerging strategies for enhanced photosensitized ¹ O₂ generation are introduced, while recent advances in direct detection and imaging of ¹ O₂ luminescence are summarized. In addition, the correlation between cumulative ¹ O₂ luminescence and PDT efficiency will be highlighted. Meanwhile, the validation of ¹ O₂ luminescence dosimetry for PDT application is also considered. This review concludes with a discussion on future demands of ¹ O₂ luminescence detection for PDT dosimetry, with particular emphasis on clinical translation. Eye-catching color image for graphical abstract.

Topical MMP beacon enabled fluorescence-guided resection of oral carcinoma

Each year almost 300,000 individuals worldwide are diagnosed with oral cancer, more than 90% of these being oral carcinoma [N. Engl. J. Med.328, 1841993]. Surgical resection is the standard of care, but accurate delineation of the tumor boundaries is challenging, resulting in either under-resection with risk of local recurrence or over-resection with increased functional loss and negative impact on quality of life. This study evaluates, in two pre-clinical in vivo tumor models, the potential of fluorescence-guided resection using molecular beacons activated by metalloproteinases, which are frequently upregulated in human oral cancer. In both models there was rapid (<15 min) beacon activation upon local application, allowing clear fluoresecence imaging in vivo and confirmed by ex vivo fluorescence microscopy and HPLC, with minimal activation in normal oral tissues. Although the tissue penetration was limited using topical application, these findings support further development of this approach towards translation to first-in-human trials.

Matrix metalloproteinase-based photodynamic molecular beacons for targeted destruction of bone metastases in vivo

The metastatic spread of cancer from the primary site or organ is one of its most devastating aspects, being responsible for up to 90% of cancer-associated mortality. Bone is one of the common sites of metastatic spread, including the vertebrae. Regardless of the treatment strategy, the clinical goals for patients with vertebral metastases are to improve the quality of life by preventing neurologic decline, to achieve durable pain relief and enhance local tumor control. However, in part due to the close proximity of the spinal cord, current treatment options are limited. We propose a novel therapeutic strategy with the use of photodynamic molecular beacons (PMBs) for targeted destruction of spinal metastases, particularly to de-bulk lesions as an adjuvant to vertebroplasty or kyphoplasty in order to mechanically stabilize weak or fractured vertebrae. The PDT efficacy of a matrix metalloproteinase-specific PMB is reported in a metstatic model that recapitulates the clinical features of tumor growth within the bone. We demonstrate that not only does tumor cell destruction occur but also the killing of bone stromal cells. The potential of PMB-PDT to destroy metastatic tumors, disrupt the osteolytic cycle and better preserve critical organs with an increased therapeutic window compared with conventional photosensitizers is demonstrated.

Synthesis and Evaluation of Cytosolic Phospholipase A(2) Activatable Fluorophores for Cancer Imaging

Activatable fluorophores selective to cytosolic phospholipase A2 (cPLA2) were synthesized and evaluated for their ability to image triple negative breast cancer cells. The activatable constructs were synthesized by esterification of a small molecule fluorophore with a fatty acid resulting in ablated fluorescence. Selectivity for cPLA2 was generated through the choice of fluorophore and fatty acid. Esterification with arachidonic acid was sufficient to impart specificity to cPLA2 when compared to esterification with palmitic acid. In vitro analysis of probes incorporated into phosphatidylcholine liposomes demonstrated that a nonselective phospholipase (sPLA2 group IB) was able to hydrolyze both arachidonate and palmitate coupled fluorophores resulting in the generation of fluorescence. Of the four fluorophores tested, DDAO (7-hydroxy-9H-(1,3-dichloro-9,9-dimethylacridin-2-one)) was observed to perform optimally in vitro and was analyzed further in 4175-Luc+ cells, a metastatic triple negative human breast cancer cell line expressing high levels of cPLA2. In contrast to the in vitro analysis, DDAO arachidonate was shown to activate selectively in 4175-Luc+ cells compared to the control DDAO palmitate as measured by fluorescence microscopy and quantitated with fluorescence spectroscopy. The addition of two agents known to activate cPLA2 enhanced DDAO arachidonate fluorescence without inducing any change to DDAO palmitate. Inhibition of cPLA2 resulted in reduced fluorescence of DDAO arachidonate but not DDAO palmitate. Together, we report the synthesis of a cPLA2 selective activatable fluorophore capable of detecting cPLA2 in triple negative breast cancer cells.

Bioresponsive probes for molecular imaging: concepts and in vivo applications

Molecular imaging is a powerful tool to visualize and characterize biological processes at the cellular and molecular level in vivo. In most molecular imaging approaches, probes are used to bind to disease-specific biomarkers highlighting disease target sites. In recent years, a new subset of molecular imaging probes, known as bioresponsive molecular probes, has been developed. These probes generally benefit from signal enhancement at the site of interaction with its target. There are mainly two classes of bioresponsive imaging probes. The first class consists of probes that show direct activation of the imaging label (from "off" to "on" state) and have been applied in optical imaging and magnetic resonance imaging (MRI). The other class consists of probes that show specific retention of the imaging label at the site of target interaction and these probes have found application in all different imaging modalities, including photoacoustic imaging and nuclear imaging. In this review, we present a comprehensive overview of bioresponsive imaging probes in order to discuss the various molecular imaging strategies. The focus of the present article is the rationale behind the design of bioresponsive molecular imaging probes and their potential in vivo application for the detection of endogenous molecular targets in pathologies such as cancer and cardiovascular disease.

Deep-red emissive BODIPY-chlorin arrays excitable with green and red wavelengths

We report here the synthesis and characterization of BODIPY-chlorin arrays containing a chlorin subunit, with tunable deep-red (641-685 nm) emission, and one or two BODIPY moieties, absorbing at 504 nm. Two types of arrays were examined: one where BODIPY moieties are attached through a phenylacetylene linker at the 13- or 3,13-positions of chlorin, and a second type where BODIPY is attached at the 10-position of chlorin through an amide linker. Each of the examined arrays exhibits an efficient (≥0.80) energy transfer from BODIPY to the chlorin moiety in both toluene and DMF and exhibits intense fluorescence of chlorin upon excitation of BODIPY at ∼500 nm. Therefore, the effective Stokes shift in such arrays is in the range of 140-180 nm. Dyads with BODIPY attached at the 10-position of chlorin exhibit a bright fluorescence in a range of solvents with different polarities (i.e., toluene, MeOH, DMF, and DMSO). In contrast to this, some of the arrays in which BODIPY is attached at the 3- or at both 3,13-positons of chlorin exhibit significant reduction of fluorescence in polar solvents. Overall, dyads where BODIPY is attached at the 10-position of chlorin exhibit ∼5-fold brighter fluorescence than corresponding chlorin monomers, upon excitation at 500 nm.

Targeting-triggered porphysome nanostructure disruption for activatable photodynamic therapy

Photodynamic therapy (PDT) and photothermal therapy (PTT) possess advantages over the conventional therapies with additional treatment selectivity achieved with local laser irradiation. Comparing to PTT that ablates target tissue via thermal necrosis, PDT induces target cell death via singlet oxygen without damaging the underling connective tissue, thus preserving its biological function. Activatable photosensitizers provide an additional level of treatment selectivity via the disease-associated activation mechanism. In this study, folate-conjugated porphysomes are introduced as targeting-triggered activatable nano-sized beacons for PDT. Porphysomes are reported previously as the most stable and efficient delivery system of porphyrin, but their nanostructure converts the singlet oxygen generation mechanism to thermal ablation mechanism. By folate-receptor-mediated endocytosis, folate-porphysomes are internalized into cells rapidly and resulted in efficient disruption of nanostructures, thus switching back on the photodynamic activity of the densely packed porphyrins for effective PDT. In both in vitro and in vivo studies, folate-porphysomes can achieve folate receptor-selective PDT efficacy, which proves the robustness of targeting-triggered PDT activation of porphysome nanostructure for highly selective tumor ablation. The formulation of porphysomes can be modified with other targeting ligands as activatable photosensitizers for personalized treatment in future.

Selective treatment and monitoring of disseminated cancer micrometastases in vivo using dual-function, activatable immunoconjugates

Drug-resistant micrometastases that escape standard therapies often go undetected until the emergence of lethal recurrent disease. Here, we show that it is possible to treat microscopic tumors selectively using an activatable immunoconjugate. The immunoconjugate is composed of self-quenching, near-infrared chromophores loaded onto a cancer cell-targeting antibody. Chromophore phototoxicity and fluorescence are activated by lysosomal proteolysis, and light, after cancer cell internalization, enabling tumor-confined photocytotoxicity and resolution of individual micrometastases. This unique approach not only introduces a therapeutic strategy to help destroy residual drug-resistant cells but also provides a sensitive imaging method to monitor micrometastatic disease in common sites of recurrence. Using fluorescence microendoscopy to monitor immunoconjugate activation and micrometastatic disease, we demonstrate these concepts of "tumor-targeted, activatable photoimmunotherapy" in a mouse model of peritoneal carcinomatosis. By introducing targeted activation to enhance tumor selectively in complex anatomical sites, this study offers prospects for catching early recurrent micrometastases and for treating occult disease.

Rational design of fluorophores for in vivo applications

Several classes of small organic molecules exhibit properties that make them suitable for fluorescence in vivo imaging. The most promising candidates are cyanines, squaraines, boron dipyrromethenes, porphyrin derivatives, hydroporphyrins, and phthalocyanines. The recent designing and synthetic efforts have been dedicated to improving their optical properties (shift the absorption and emission maxima toward longer wavelengths and increase the brightness) as well as increasing their stability and water solubility. The most notable advances include development of encapsulated cyanine dyes with increased stability and water solubility, squaraine rotaxanes with increased stability, long-wavelength-absorbing boron dipyrromethenes, long-wavelength-absorbing porphyrin and hydroporphyrin derivatives, and water-soluble phthalocyanines. Recent advances in luminescence and bioluminescence have made self-illuminating fluorophores available for in vivo applications. Development of new types of hydroporphyrin energy-transfer dyads gives the promise for further advances in in vivo multicolor imaging.

Near-IR emissive chlorin-bacteriochlorin energy-transfer dyads with a common donor and acceptors with tunable emission wavelength

Design, synthesis, and optical properties of a series of novel chlorin-bacteriochlorin energy transfer dyads are described. Each dyad is composed of a common red-absorbing (645-646 nm) chlorin, as an energy donor, and a different near-IR emitting bacteriochlorin, as an energy acceptor. Each bacteriochlorin acceptor is equipped with a different set of auxochromes, so that each of them emits at a different wavelength. Dyads exhibit an efficient energy transfer (≥0.77) even for chlorin-bacteriochlorin pairs with large (up to 122 nm) separation between donor emission and acceptor absorption. Excitation of the chlorin donor results in relatively strong emission of the bacteriochlorin acceptor, with a quantum yield Φf range of 0.155-0.23 in toluene and 0.12-0.185 in DMF. The narrow, tunable emission band of bacteriochlorins enables the selection of a series of three dyads with well-resolved emissions at 732, 760, and 788 nm, and common excitation at 645 nm. Selected dyads have been also converted into bioconjugatable N-succinamide ester derivatives. The optical properties of the described dyads make them promising candidates for development of a family of near-IR fluorophores for simultaneous imaging of multiple targets, where the whole set of fluorophores can be excited with the common wavelength, and fluorescence from each can be independently detected.

Inherently multimodal nanoparticle-driven tracking and real-time delineation of orthotopic prostate tumors and micrometastases

Prostate cancer is the most common cancer among men and the second cause of male cancer-related deaths. There are currently three critical needs in prostate cancer imaging to personalize cancer treatment: (1) accurate intraprostatic imaging for multiple foci and extra-capsular extent; (2) monitoring local and systemic treatment response and predicting recurrence; and (3) more sensitive imaging of occult prostate cancer bone metastases. Recently, our lab developed porphysomes, inherently multimodal, all-organic nanoparticles with flexible and robust radiochemistry. Herein, we validate the first in vivo application of (64)Cu-porphysomes in clinically relevant orthotopic prostate and bony metastatic cancer models. We demonstrate clear multimodal delineation of orthotopic tumors on both the macro- and the microscopic scales (using both PET and fluorescence) and sensitively detected small bony metastases (<2 mm). The unique and multifaceted properties of porphysomes offers a promising all-in-one prostate cancer imaging agent for tumor detection and treatment response/recurrence monitoring using both radionuclide- and photonic-based strategies.

A spinal cord window chamber model for in vivo longitudinal multimodal optical and acoustic imaging in a murine model

In vivo and direct imaging of the murine spinal cord and its vasculature using multimodal (optical and acoustic) imaging techniques could significantly advance preclinical studies of the spinal cord. Such intrinsically high resolution and complementary imaging technologies could provide a powerful means of quantitatively monitoring changes in anatomy, structure, physiology and function of the living cord over time after traumatic injury, onset of disease, or therapeutic intervention. However, longitudinal in vivo imaging of the intact spinal cord in rodent models has been challenging, requiring repeated surgeries to expose the cord for imaging or sacrifice of animals at various time points for ex vivo tissue analysis. To address these limitations, we have developed an implantable spinal cord window chamber (SCWC) device and procedures in mice for repeated multimodal intravital microscopic imaging of the cord and its vasculature in situ. We present methodology for using our SCWC to achieve spatially co-registered optical-acoustic imaging performed serially for up to four weeks, without damaging the cord or induction of locomotor deficits in implanted animals. To demonstrate the feasibility, we used the SCWC model to study the response of the normal spinal cord vasculature to ionizing radiation over time using white light and fluorescence microscopy combined with optical coherence tomography (OCT) in vivo. In vivo power Doppler ultrasound and photoacoustics were used to directly visualize the cord and vascular structures and to measure hemoglobin oxygen saturation through the complete spinal cord, respectively. The model was also used for intravital imaging of spinal micrometastases resulting from primary brain tumor using fluorescence and bioluminescence imaging. Our SCWC model overcomes previous in vivo imaging challenges, and our data provide evidence of the broader utility of hybridized optical-acoustic imaging methods for obtaining multiparametric and rich imaging data sets, including over extended periods, for preclinical in vivo spinal cord research.

Image guided therapy: the advent of theranostic agents

Theranostic agents represent a recently introduced class of imaging probes designed to offer to pharmacologists and physicians a robust tool for minimally invasive in vivo visualization of drug delivery/release and therapy monitoring. By means of these agents, novel strategies able to integrate diagnosis and therapy could be developed. This highly interdisciplinary research field is one of the more innovative products resulting from the synergism between molecular imaging and nanomedicine. Potential applications of theranosis include the in vivo assessment of drug biodistribution and accumulation at the target site, visualization of the drug release from a given nanocarrier, and real-time monitoring of the therapeutic outcome. The expected end-point of theranostic agents is to provide a fundamental support for the optimization of innovative diagnostic and therapeutic strategies that could contribute to emerging concepts in the field of the "personalized medicine". This perspective paper aims at providing the reader the basic principles of theranosis with a particular emphasis to the design of theranostic agents.