Cancer cell-selective in vivo near infrared photoimmunotherapy targeting specific membrane molecules.

Three major modes of cancer therapy (surgery, radiation and chemotherapy) are the mainstay of modern oncologic therapy. To minimize the side effects of these therapies, molecular-targeted cancer therapies, including armed antibody therapy, have been developed with limited success. In this study, we have developed a new type of molecular-targeted cancer therapy, photoimmunotherapy (PIT), that uses a target-specific photosensitizer based on a near-infrared (NIR) phthalocyanine dye, IR700, conjugated to monoclonal antibodies (mAbs) targeting epidermal growth factor receptors. Cell death was induced immediately after irradiating mAb-IR700-bound target cells with NIR light. We observed in vivo tumor shrinkage after irradiation with NIR light in target cells expressing the epidermal growth factor receptor. The mAb-IR700 conjugates were most effective when bound to the cell membrane and produced no phototoxicity when not bound, suggesting a different mechanism for PIT as compared to conventional photodynamic therapies. Target-selective PIT enables treatment of cancer based on mAb binding to the cell membrane.

Optimizing quantitative in vivo fluorescence imaging with near-infrared quantum dots.

Quantum dots (QDs) are fluorescent nanoparticles with broad excitation and narrow, wavelength-tunable emission spectra. They are used extensively for in vitro fluorescence imaging studies and more recently for in vivo small animal and pre-clinical studies. To date there has been little concern about the selection of QD size (and thus emission wavelength peak) and excitation wavelengths, as they have little relevance to the results of in vitro studies. In vivo imaging, however, poses additional constraints, such as the scattering and absorption by tissue, which may influence the signal intensity at the body surface. Here, we demonstrate that longer-wavelength excitation and emission yield less quantization error in measured relative fluorescence intensity, using three near-infrared QDs (QD655, QD705 and QD800) applied to in vivo lymphatic imaging, and a range of excitation wavelengths from the blue to the red. Statistically significant differences in quantization error were observed between nearly all pairs of excitation wavelengths (445-490, 503-555, 575-605, 615-665 and 671-705 nm). Similarly, quantization error decreased with longer emission wavelengths (655, 705 and 800 nm). Light absorbance and scattering were demonstrated to be more potent factors than absorbance efficiency of QDs in producing quantization error in the measured fluorescence intensity. As a result, while wavelengths can be adjusted for qualitative experiments, the longest possible wavelengths should be used if quantification is desired during QD imaging experiments.

Quantitative and specific molecular imaging of cancer with labeled engineered monoclonal antibody fragments.

The high target specificity of antibodies and related constructs makes them excellent scaffolds for molecular-imaging probes. Quantitative data on biodistribution and pharmacokinetics can be acquired by radiolabeling these agents. Such studies demonstrate prolonged circulation times and resulting nonspecific accumulation with high background signal using antibody-based agents. Antibody fragments demonstrate more rapid clearance, but lower tumor uptake. Optical labeling of antibodies provides a basis for developing activatable probes that can image antigens with very high specificity, potentially allowing for the simultaneous visualization of multiple targets. While radioimmunoimaging provides valuable whole-body, quantitative information, activatable optical antibody-based agents could generate real-time diagnostic and prognostic information about near-surface lesions at high-spatial and temporal resolution without requiring ionizing radiation.

In vivo molecular imaging using nanomaterials: general in vivo characteristics of nano-sized reagents and applications for cancer diagnosis.

Nanoparticles present a new collection of contrast agents for the field of in vivo molecular imaging. This review focuses on promising molecular imaging probes for optical and magnetic resonance imaging based on four representative nanomaterial(s) platforms: quantum dots, upconversion phosphors, superparamagnetic iron oxides, and dendrimer-based agents. Quantum dots are extremely efficient fluorescent nanoparticles with size-tunable emission properties, enabling high sensitivity and greater depth penetration. Their heavy metal composition and long retention in the body, however, pose concerns for clinical translational applications. Upconversion phosphors generate excellent signal-to-background contrast because they emit light with higher energy than the excitation photons and autofluorescence signals. For MRI, iron oxide particles also generate excellent signal and have been used in liver imaging and for cell tracking studies. As they are metabolized through endogenous iron salvage pathways, they have already been introduced as clinical contrast agents. Lastly, dendrimers, a 'soft' nanoparticle, can be used as a structural basis for the attachment of small molecule imaging agents and/or targeting groups. This array of nanoparticles should offer insights into the uses and potentials of nanoparticles for the molecular imaging.