A new type of monoclonal antibody (mAb)-based, highly specific phototherapy (photoimmunotherapy; PIT) that utilizes a near infrared (NIR) phthalocyanine dye, IRDye700DX (IR700) conjugated with a mAb, has recently been described. NIR light exposure leads to immediate, target-selective necrotic cell death in vitro. Detecting immediate in vivo cell death is more difficult because it takes at least 3 days for the tumor to begin to shrink in size. In this study, fluorescence lifetime (FLT) was evaluated before and after PIT for monitoring the immediate cytotoxic effects of NIR mediated mAb-IR700 PIT. Anti-EGFR panitumumab-IR700 was used for targeting EGFR-expressing A431 tumor cells. PIT with various doses of NIR light was performed in cell pellets in vitro and in subcutaneously xenografted tumors in mice in vivo. FLT measurements were obtained before and 0, 6, 24 and 48 h after PIT. In vitro, PIT at higher doses of NIR light immediately led to FLT shortening in A431 cells. In vivo PIT induced immediate shortening of FLT in treated tumors after a threshold NIR dose of 30J/cm2 or greater. In contrast, lower levels of NIR light (10J/cm2 or smaller) did not induce shortening of FLT. Prolongation of FLT in tissue surrounding the tumor site was noted 6 hours after PIT, likely reflecting phagocytosis by macrophages. In conclusion, FLT imaging can be used to monitor the acute cytotoxic effects of mAb-IR700-induced PIT even before morphological changes can be seen in the targeted tumors.
photoimmunotherapy; fluorescence lifetime imaging; necrotic cell death; molecular targeting; monoclonal antibody
Patient survival depends on the completeness of resection of peritoneal ovarian cancer metastases (POCM) and therefore, it is important to develop methods to enhance detection. Previous probe designs based on activatable galactosyl human serum albumin (hGSA)-fluorophore pairs, which target lectin receptors expressed on POCM, have used only visible range dyes conjugated to hGSA. However, imaging probes emitting fluorescence in the NIR range are advantageous because NIR photons have deeper in vivo tissue penetration and result in lower background autofluorescence than those emitting in the visible range. A NIR-activatable hGSA fluorophore was synthesized using a bacteriochlorin-based dye, NMP1. NMP1 has two unique absorption peaks, one in the green range and the other in the NIR range, but emits at a NIR peak of 780 nm. NMP1, thus, has two different Stokes shifts that have the potential to allow imaging of POCM both at the peritoneal surface and just below it.
hGSA was conjugated with 2 NMP1 molecules to create a self-quenching complex (hGSA-NMP1). The activation ratio of hGSA-NMP1 was measured by the fluorescence intensity before and after exposure to 10% SDS. The activation ratio of hGSA-NMP1 was ~100-fold in vitro. Flow cytometry, fluorescence microscopy, and in vivo spectral fluorescence imaging were carried out to compare hGSA-NMP1 with hGSA-IR800 and hGSA-ICG (two always-on control agents with similar emission to NMP1) in terms of comparative fluorescence signal and the ability to detect POCM in mice models. The sensitivity and specificity of hGSA-NMP1 for POCM implant detection were determined by co-localizing NMP1 emission spectra with red fluorescent protein (RFP) expressed constitutively in SHIN3 tumor implants at different depths below the peritoneal surface. In vitro, SHIN3 cells were easily detectable after 3 hours of incubation with hGSA-NMP1. In vivo submillimeter POCM foci were clearly detectable with spectral fluorescence imaging using hGSA-NMP1. Among 555 peritoneal lesions, hGSA-NMP, using NIR and green excitation light, respectively, detect 75% of all lesions and 91% of lesions ~0.8 mm or greater in diameter. Few false positives were encountered. Nodules located at a depth below the small bowel surface were only depicted with hGSA-NMP1.
We conclude that hGSA-NMP1 is useful in imaging peritoneal ovarian cancer metastases, located both superficially and deep in the abdominal cavity.
fluorescence imaging; activatable; near infrared; multiple excitations
We evaluated the kinetics of 18F-sodium fluoride (NaF) and reassessed the recommended dose, optimal uptake period, and reproducibility using a current-generation PET/CT scanner.
In this prospective study, 73 patients (31 patients with multiple myeloma or myeloma precursor disease and 42 with prostate cancer) were injected with a mean administered dose of 141 MBq of 18F-NaF. Sixty patients underwent 3 sequential sessions of 3-dimensional PET/CT of the torso beginning ~15 min after 18F-NaF injection, followed by a whole-body 3-dimensional PET/CT at 2 h. The remaining 13 prostate cancer patients were imaged only at 2 and 3 h after injection. Twenty-one prostate cancer patients underwent repeat baseline studies (mean interval, 5.9 d) to evaluate reproducibility.
The measured effective dose was 0.017 mSv/MBq, with the urinary bladder, osteogenic cells, and red marrow receiving the highest doses at 0.080, 0.077, and 0.028 mGy/MBq, respectively. Visual analysis showed that uptake in both normal and abnormal bone increased with time; however, the rate of increase decreased with time. A semiautomated workflow provided objective uptake parameters, including the mean standardized uptake value of all pixels within bone with SUVs greater than 10 and the average of the mean SUV of all malignant lesions identified by the algorithm. The values of these parameters for the images beginning at ~15 min and ~35 min were significantly different (0.3% change/minute). Differences between the later imaging time points were not significant (P < 0.01). Repeat baseline studies showed high intraclass correlations (>0.9) and relatively low critical percent change (the value above which a change can be considered real) for these parameters. The tumor-to-normal bone ratio, based on the SUVmax of identified malignant lesions, decreased with time; however, this difference was small, estimated at ~0.16%/min in the first hour.
18F-NaF PET/CT images obtained with modest radiation exposures can result in highly reproducible imaging parameters. Although the tumor-to-normal bone ratio decreases slightly with time, the high temporal dependence during uptake periods < 30 min may limit accurate quantitation. An uptake period of 60 ± 30 min has limited temporal dependence while maintaining high tumor-to-normal bone ratio.
bone scanning; oncology; pet/ct; prostate cancer; multiple myeloma
Patient management in oncology increasingly relies upon imaging for diagnosis, response assessment, and follow-up. The clinical availability of combined functional-anatomic imaging modalities, which integrate the benefits of visualizing tumor biology with those of high-resolution structural imaging, revolutionized clinical management of oncologic patients.[1–6] Conventional high resolution anatomic imaging modalities such as computed tomography (CT) and magnetic resonance imaging (MRI) excel at providing details regarding lesion location, size, morphology, and structural changes to adjacent tissues; however, these modalities provide little insight into tumor physiology. With the increasing focus on molecularly targeted therapies, imaging radiolabeled compounds with positron emission tomography (PET) and single photon emission tomography (SPECT) are often used to provide insight into a tumor's biologic functions and its surrounding microenvironment. Despite their high sensitivity and specificity, PET and SPECT alone are substantially limited by low spatial resolution and inability to provide anatomic detail. Integrating SPECT or PET with a modality capable of providing these (i.e. CT or MR) maximizes their separate strengths and provides anatomic localization of physiologic processes with detailed visualization of a tumor's structure. The availability of multi-modality (hybrid) imaging with PET/CT, SPECT/CT and PET/MR improves our ability to characterize lesions and to affect treatment decisions and patient management. We have just begun to exploit the truly synergistic capabilities of multi-modality imaging. Continued advances in instrumentation and imaging agent development will improve our ability to noninvasively characterize disease processes. This review will discuss the evolution of hybrid imaging technology and provide examples of its current and potential future clinical uses.
Multimodality imaging; PET/CT; SPECT/CT; MR/PET
Armed antibody-based targeted molecular therapies offer the possibility of effective tumor control with a minimum of side effects. Photoimmunotherapy (PIT) employs a monoclonal antibody-phototoxic phthalocyanine dye, IR700 conjugate that is activated by focal near infrared (NIR) light irradiation after antibody binding to the targeted tumor cell surface leading to rapid necrotic cell death. Therapy by single NIR light irradiation was effective without significant side-effects, however, recurrences were seen in most of treated mice probably because of inhomogeneous distribution of panitumumab-IR700 immuno-conjugate in the tumor, leading to ineffective PIT. We describe here an optimized regimen of effective PIT method for the same HER1-overexpressing tumor model (A431) with fractionated administration of panitumumab-IR700 conjugate followed by systematic repeated NIR light irradiation to the tumor based on timing of antibody redistribution into the remnant tumor under the guidance of IR700 fluorescence signal. Eighty percents of the A431 tumors were eradicated with repeated PIT without apparent side effects and survived with tumor free more than 120 days even after stoping therapy at the day 30. Therapeutic effects were monitored using IR700 fluorescent signal. PIT is a promising highly selective and clinically feasible theranostics for the treatment of MAb-binding tumors with minimal off target effects.
photoimmunotherapy; theranostics; epidermal growth factor receptor; molecular targeting; monoclonal antibody
Bladder Cancer (BCa) is the most common malignancy arising from the urinary tract. One of the mainstays of diagnosis, staging, and therapeutic decision-making for BCa is accurate and appropriate imaging. The ability to identify metastatic disease preoperatively is of utmost importance in determining treatment. Advances in standard cross sectional imaging techniques like Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) have improved imaging of bladder cancer. Over the last decade, 18F-fluorodeoxyglucose (FDG) Positron Emission Tomography (PET) in combination with CT (18F-FDG PET/CT) has become an important non-invasive imaging modality for the preoperative staging of various malignancies. 18F-FDG PET/CT is useful for detection of metastatic disease in BCa, but the ability to detect primary bladder wall lesions remains to be elucidated. To overcome the problem with urinary excretion of 18F-FDG, new PET tracers are being tested. MRI is an accurate technique for the local staging of BCa due to its superior spatial and contrast resolution. Anatomical MRI has a modest utility in NM-staging of BCa. However, incorporation of functional MR techniques, such as diffusion weighted MRI can improve the results for lesion detection and staging and multi-parametric MRI`s role is yet to be explored widely. The aim of this review is to present the recent advances in PET/CT and MRI in BCa, with particular focus on improvements in staging.
Positron Emission Tomography/Computed Tomography (PET/CT); Magnetic Resonance Imaging (MRI); Urothelial cancer; Bladder cancer
To identify, within the framework of a current Phase I trial, whether factors related to intraprostatic cancer lesions (IPLs) or individual patients predict the feasibility of high-dose intraprostatic irradiation.
Methods and Materials
Endorectal coil MRI scans of the prostate from 42 men were evaluated for dominant IPLs. The IPLs, prostate, and critical normal tissues were contoured. Intensity-modulated radiotherapy plans were generated with the goal of delivering 75.6 Gy in 1.8-Gy fractions to the prostate, with IPLs receiving a simultaneous integrated boost of 3.6 Gy per fraction to a total dose of 151.2 Gy, 200% of the prescribed dose and the highest dose cohort in our trial. Rectal and bladder dose constraints were consistent with those outlined in current Radiation Therapy Oncology Group protocols.
Dominant IPLs were identified in 24 patients (57.1%). Simultaneous integrated boosts (SIB) to 200% of the prescribed dose were achieved in 12 of the 24 patients without violating dose constraints. Both the distance between the IPL and rectum and the hip-to-hip patient width on planning CT scans were associated with the feasibility to plan an SIB (p = 0.002 and p = 0.0137, respectively).
On the basis of this small cohort, the distance between an intraprostatic lesion and the rectum most strongly predicted the ability to plan high-dose radiation to a dominant intraprostatic lesion. High-dose SIB planning seems possible for select intraprostatic lesions.
IMRT; Prostate cancer; Dose escalation; Radiotherapy; Treatment planning
prostate cancer; patient-specific mold; multiparametric MRI; registration; correlation
Tumors are characterized by a high degree of diversity and heterogeneity in receptor expression. Monoclonal antibodies (mAbs) are an established therapeutic method of targeting cell surface receptors. However, high affinity antibodies targeting highly expressed receptors are often prevented from distributing evenly throughout the tumor due to the “binding site barrier” whereby antibody is trapped peripherally before it can reach deeper into the tumor that leads inhomogeneous micro-distribution. When employing armed antibodies it is important that the toxin (in this case, phototoxin) be distributed evenly to more effectively treat the cancer. By adding an additional antibody conjugate, targeting a secondary, unsaturated receptor with lower expression, a more uniform distribution of the phototoxin can be achieved. In this study, panitumumab (Pan) and basiliximab (Bas) were conjugated with the phthalocyanine dye, IRDye700DX (IR700). Upon exposure to near infrared light, these armed antibodies produce rapid cell death only when bound to their respective receptors, a treatment termed photo-immunotherapy (PIT). ATAC4 cells which demonstrate high expression of human epidermal growth factor receptor (EGFR) and low expression of interleukin-2 receptor-alpha (CD25) were treated by PIT using a cocktail of Pan-IR700 and Bas-IR700. An in vivo study showed that the cocktail Pan-Bas-IR700 resulted in significantly reduced tumor growth and prolonged survival in ATAC4 tumor-bearing mice compared with either Pan-IR700 or Bas-IR700 alone. In conclusion, a cocktail injection of two different antibody-IR700 conjugates created a more homogeneous microdistribution of antibody-conjugates resulting in enhanced therapeutic effects after PIT, compared to the use of either antibody-IR700 conjugate.
photoimmunotherapy; monoclonal antibody; cocktail; micro-distribution; binding site barrier
Optical imaging is emerging as an important tool to visualize tumors. However, there are many potential choices among the available fluorophores. Optical imaging probes that emit in the visible range can image superficial tumors with high quantum yields, however, if deeper imaging is needed then near infrared (NIR) fluorophores are necessary. Most commercially available NIR fluorophores are cyanine based and are prone to non-specific binding and relatively limited photostability. Silica-containing rhodamine (SiR) fluorophores represent a new class of NIR fluorophores, which permit photoactivation via H-dimer formation as well as demonstrate improved photostability. This permits higher tumor-to-background ratios (TBRs) to be achieved over longer periods of time. Here, we compared an avidin conjugated with SiR700 (Av-SiR700) to similar compounds based on cyanine dyes (Av-Cy5.5 and Av-Alexa Fluor 680) in a mouse tumor model of ovarian cancer metastasis. We found that the Av-SiR700 probe demonstrated superior quenching enabling activation after binding-internalization to the target cell. As a result, Av-SiR700 had higher TBRs compared to Av-Cy5.5, and better biostability compared to Av-Alexa Fluor 680.
Near infrared; molecular imaging; cancer; activatable; cyanine; rhodamine
This work characterizes the uptake of 11C-Acetate in prostate cancer (PCa), benign prostate hyperplasia (BPH) and normal prostate tissue in comparison with multi-parametric MRI, whole mount histopathology and clinical markers, to evaluate its potential utility for delineating intra-prostatic tumors in a population of patients with localized PCa.
39 men with presumed localized PCa underwent dynamic/static abdomen-pelvic 11C-Acetate PET/CT for 30-minutes and 3T multi-parametric (MP) MRI prior to prostatectomy. PET/CT images were registered to MRI using pelvic bones for initial rotation-translation, followed by manual adjustments to account for prostate motion and deformation from the MRI endorectal coil. Whole-mount pathology specimens were sectioned using an MRI-based patient specific mold resulting in improved registration between the MRI, PET and pathology. 11C-Acetate PET standardized uptake values were compared with MP-MRI and pathology.
11C-Acetate uptake was rapid but reversible, peaking at 3–5 minutes post-injection and reaching a relative plateau at ~10 minutes. The average SUVmax(10–12min) of tumors was significantly higher than that of normal prostate tissue (4.4±2.05, range 1.8–9.2 vs. 2.1±0.94, range 0.7–3.4; p<0.001); however it was not significantly different from benign prostatic hyperplasia (4.8±2.01; range 1.8–8.8). A sector-based comparison with histopathology, including all tumors > 0.5 cm, revealed a sensitivity and specificity of 61.6 % and 80.0 % for 11C-Acetate PET/CT, and 82.3% and 95.1% for MRI, respectively. Considering only tumors >0.9 cm the 11C-Acetate accuracy was comparable to that of MRI. In a small cohort (n=9), 11C-Acetate uptake was independent of fatty acid synthase expression based on immunohistochemistry.
11C-Acetate PET/CT demonstrates higher uptake in tumor foci than normal prostate tissue; however 11C-Acetate uptake in tumors is similar to BPH nodules. While 11C-Acetate PET/CT is not likely to have utility as an independent modality for evaluation of localized PCa, the high uptake in tumors may make it useful for monitoring focal therapy, where tissue damage after therapy may limit anatomic imaging methods.
Prostate cancer; 11C-Acetate PET; Multi-parametric prostate MRI
Angiogenesis—the growth of new vessels—is both a normal physiologic response and a critical step in many pathologic processes, particularly cancer. Imaging has long relied on the different enhancement characteristics of cancer compared with normal tissue; the information generated is often primarily morphologic and qualitative. However, more quantitative methods based on functional and targeted imaging have recently emerged.
In this article, we review both functional and targeted imaging techniques for assessing tumor angiogenesis.
angiogenesis; functional imaging; targeted imaging; tumor angiogenesis
Prostate cancer is the most common noncutaneous malignancy among men in the Western world. Imaging has recently become more important in the diagnosis, local staging, and treatment follow-up of prostate cancer. In this article, we review conventional and functional imaging methods as well as targeted imaging approaches with novel tracers used in the diagnosis and staging of prostate cancer.
Although prostate cancer is the second leading cause of cancer death in men, imaging of localized prostate cancer remains limited. Recent developments in imaging technologies, particularly MRI and PET, may lead to significant improvements in lesion detection and staging.
MRI; PET; prostate cancer
The multifocal nature of prostate cancer has necessitated whole-gland therapy in the past; however, since the widespread use of PSA screening, patients frequently present with less-advanced disease. Many men with localized disease wish to avoid the adverse effects of whole-gland therapy; therefore, focal therapy for prostate cancer is being considered as a treatment option. For focal treatment to be viable, accurate imaging is required for diagnosis, staging, and monitoring of treatment. Developments in MRI and PET have brought more attention to prostate imaging and the possibility of improving the accuracy of focal therapy. In this Review, we discuss the advantages and disadvantages of conventional methods for imaging the prostate, new developments for targeted imaging, and the possible role of image-guided biopsy and therapy for localized prostate cancer.
Traditionally, the skeletal survey has been the standard modality for the detection of osteolytic bone disease in multiple myeloma. In addition to its poor sensitivity for the detection of osteolytic lesions, this modality is not able to identify extramedullary lesions and focal bone marrow involvement, nor measure response to therapy. The application of novel imaging techniques such as computed tomography (CT), magnetic resonance imaging (MRI), and molecular imaging such as fluorine-18 fluorodeoxyglucose positron emission tomography CT (18F-FDG PET/CT) and fluorine-18 sodium fluoride positron emission tomography CT (18F-NaF PET/CT) has the potential to overcome these limitations as well as provide prognostic information in precursor states and multiple myeloma. Also promising is the use of dynamic contrast enhanced magnetic resonance imaging (DCE MRI) to measure vascular permeability, an important feature of myelomagenesis. This review summarizes the current status and possible future role of novel imaging modalities in multiple myeloma and its precursor states.
Multiple myeloma; monoclonal gammopathy of undetermined significance; smoldering multiple myeloma; skeletal survey; PET/CT; DCE MRI
Angiogenesis is a key step in the pathophysiology of tumor growth and metastatic spread. Recently, dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has emerged as a method for assessing angiogenesis both during the initial diagnosis and for follow up of anti-angiogenic therapies. In this review, we discuss the technical aspects of implementing DCE-MRI in clinical practice with emphasis on acquisition methods and analytic techniques.
pathologic angiogenesis; angiogenic inhibitors; magnetic resonance imaging
Stimulating an immune response against cancer with the use of vaccines remains a challenge. We hypothesized that combining a melanoma vaccine with interleukin-2, an immune activating agent, could improve outcomes. In a previous phase 2 study, patients with metastatic melanoma receiving high-dose interleukin-2 plus the gp100:209–217(210M) peptide vaccine had a higher rate of response than the rate that is expected among patients who are treated with interleukin-2 alone.
We conducted a randomized, phase 3 trial involving 185 patients at 21 centers. Eligibility criteria included stage IV or locally advanced stage III cutaneous melanoma, expression of HLA⋆A0201, an absence of brain metastases, and suitability for high-dose interleukin-2 therapy. Patients were randomly assigned to receive interleukin-2 alone (720,000 IU per kilogram of body weight per dose) or gp100:209–217(210M) plus incomplete Freund’s adjuvant (Montanide ISA-51) once per cycle, followed by interleukin-2. The primary end point was clinical response. Secondary end points included toxic effects and progression-free survival.
The treatment groups were well balanced with respect to baseline characteristics and received a similar amount of interleukin-2 per cycle. The toxic effects were consistent with those expected with interleukin-2 therapy. The vaccine–interleukin-2 group, as compared with the interleukin-2–only group, had a significant improvement in centrally verified overall clinical response (16% vs. 6%, P = 0.03), as well as longer progression-free survival (2.2 months; 95% confidence interval [CI], 1.7 to 3.9 vs. 1.6 months; 95% CI, 1.5 to 1.8; P = 0.008). The median overall survival was also longer in the vaccine–interleukin-2 group than in the interleukin-2–only group (17.8 months; 95% CI, 11.9 to 25.8 vs. 11.1 months; 95% CI, 8.7 to 16.3; P = 0.06).
In patients with advanced melanoma, the response rate was higher and progression-free survival longer with vaccine and interleukin-2 than with interleukin-2 alone. (Funded by the National Cancer Institute and others; ClinicalTrials.gov number, NCT00019682.)
Polyethylene glycol (PEG)-surface modification can make nano-materials highly hydrophilic, reducing sequestration in the reticuloendothelial system. In this study, polyamidoamine (PAMAM) dendrimers bearing gadolinium chelates were PEGylated with different PEG-chain lengths and the effects on paramagnetic and pharmacokinetic properties were evaluated. Specifically, gadolinium chelate-bearing PAMAM dendrimers (G4 and G5) were conjugated with two different PEG chains (2k and 5k). Long PEG chains (5k) on the smaller (G4) dendrimer resulted in reduced relaxivity compared to unPEGylated dendrimer whereas short PEG (2k) and larger (G5) dendrimer produced comparable relaxivities to unPEGylated G4 dendrimer. The relaxivity of all PEGylated or lysine conjugated dendrimers increased at higher temperature, while that of intact G4 Gd-PAMAM-dendrimer decreased. All PEGylated dendrimers had minimal liver and kidney uptake and remained in circulation for at least 1 hour. Thus, surface-PEGylated Gd-PAMAM-Dendrimers showed decreased plasma clearance and prolonged retention in the blood pool. Shorter PEG, higher generation conjugates led higher relaxivity.
MRI; dendrimer; polyethylene glycol (PEG); relaxivity; pharmacokinetics
To develop and characterize the trafficking of a dual-modal agent that identifies primary draining or sentinel lymph node (LN).
Herein, a dual-reporting silica-coated iron oxide nanoparticle (SCION) is developed. Nude mice were imaged by magnetic resonance (MR) and optical imaging and axillary LNs were harvested for histological analysis. Trafficking through lymphatics was observed with intravital and ex vivo confocal microscopy of popliteal LNs in B6-albino, CD11c-EYFP, and lys-EGFP transgenic mice.
In vivo, SCION allows visualization of LNs. The particle’s size and surface functionality play a role in its passive migration from the intradermal injection site and its minimal uptake by CD11c+ dendritic cells and CD169+ and lys+ macrophages.
After injection, SCION passively migrates to LNs without macrophage uptake and then can be used to image LN(s) by MRI and fluorescence. Thus, SCION can potentially be developed for use in sentinel node resections or for intralymphatic drug delivery.
nanoparticle; molecular imaging; MRI; optical imaging; lymph node; superparamagnetic iron oxide
Imaging of the lymphatic system is critical in preoperative planning of resections of complex lymphatic malformations. However, safe, effective imaging methods with sufficient resolution to identify the lymphatics have been lacking. In this study, we demonstrate the use of gadolinium-labeled dendrimers to image the lymphatics in small and large animal models during magnetic resonance lymphangiography.
Polyamidoamine G6-Gd_1B4M_N-hydroxysuccinimide was synthesized and administered intradermally in the extremities of normal mice and pigs at several doses.
The lymphatics were well demonstrated in both animal models and there was rapid uptake in the deep lymphatic system, including the thoracic duct. A significant dose reduction was achieved (1 µmol Gd/kg) in the 35-kg pig compared with mice, while still producing excellent results. No toxicity was observed and only minor inflammatory changes were observed at the injection site 30 days later.
We demonstrate that a low dose of a macromolecular magnetic resonance contrast agent can provide rapid imaging of the deep lymphatic system in both small and large animals. This data provides a basis to consider a similar agent in clinical trials.
dendrimer; magnetic resonance lymphangiography; nanomaterials; pig; thoracic duct
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.
Molecular imaging; nanomaterial; quantum dot; dendrimer; iron oxide particle
Overexpression of HER2/neu in breast cancer is correlated with poor prognosis. It may vary between primary tumors and metastatic lesions and change during the treatment. Therefore, there is a need for new means to assess HER2/neu expression in vivo. In this work, we used 68Ga-labeled DOTA-ZHER2:2891-Affibody to monitor HER2/neu expression in a panel of breast cancer xenografts.
DOTA-ZHER2:2891-Affibody molecules were labeled with 68Ga. In vitro binding was characterized by a receptor saturation assay. Biodistribution and PET imaging studies were conducted in athymic nude mice bearing subcutaneous human breast cancer tumors with three different levels of HER2/neu expression. Nonspecific uptake was analyzed using non-HER2-specific Affibody molecules. Signal detected by PET was compared with ex vivo assessment of the tracer uptake and HER2/neu expression.
68Ga-DOTA-ZHER2:2891-Affibody probe showed high binding affinity to MDA-MB-361 cells (KD = 1.4±0.19 nM). In vivo biodistribution and PET imaging studies demonstrated high radioactivity uptake in HER2/neu-positive tumors. Tracer was eliminated quickly from the blood and normal tissues, resulting in high tumor-to-blood ratios. The highest normal tissue concentration of radioactivity was seen in the kidneys (227±14 %ID/g). High-contrast PET images of HER2/neu-overexpressing tumors were recorded as soon as 1 hour after tracer injection. Good correlation was observed between PET imaging, biodistribution estimates of tumor tracer concentration, and the receptor expression.
These results suggest that PET imaging using 68Ga-DOTA-ZHER2:2891-Affibody is sensitive enough to detect different levels of HER2/neu expression in vivo.
Affibody molecules; Molecular imaging; HER2/neu; PET; Ga-68
The key to improving the sensitivity of in vivo molecular imaging is to increase the target-to-background signal ratio (TBR). Optical imaging has a distinct advantage over other molecular imaging methods in that the fluorescent signal can be activated at the target thus reducing background signal. Previously, we found that H-dimer formation quenches fluorescence of xanthene fluorophores, and among these, TAMRA had the highest quenching ratio. Another approach to lowering background signal is to employ pH activation based on the photon-induced electron transfer (PeT) theory. We hypothesized that combining these two strategies could lead to greater quenching capacity than was possible with either probe alone. A pH-sensitive fluorophore, pHrodo or TAMRA was conjugated to the cancer targeting molecules, avidin (Av) and trastuzumab (Tra). As expected, both pHrodo and TAMRA formed H-dimers when conjugated to avidin or antibody and the dimerization resulted in efficient fluorescence quenching. In addition, pHrodo conjugated probes showed pH-dependent fluorescence activation. When the probes were used in an in vivo animal model, fluorescence endoscopy with Av-pHrodo depicted tumors with high TBR 1 h and 2 h after injection. Av-TAMRA also visualized tumors 1 h and 2 h after the injection, however, TBR was lower due to the background signal from non-specific binding 1 h after the injection as well as background fluorescence from the unbound agent. Thus, we demonstrate that a dual-controlled activatable optical probe based on the combination of H-dimer formation and pH activation can achieve high TBR at early time points during in vivo molecular imaging.
Clinical translation of novel optical probes requires testing of human specimens ex vivo to ensure efficacy. However, it may be difficult to remove human tissue from the operating room due to regulatory/privacy issues. Therefore, we designed a portable fluorescence camera to test targeted optical imaging probes on human specimens in the operating room.
A compact benchtop fluorescence camera was designed and built in-house. A mouse xenograft model of ovarian cancer with an activatable imaging probe based on rhodamine green was used to test the device. Comparison was made to commercially available imaging systems.
The prototype camera produced images comparable to images acquired with commercially available, non-portable imaging systems.
We demonstrate the feasibility of a specimen-based portable fluorescence camera for use in the operating room. Its small size ensures that tissue excised from patients can be tested promptly for fluorescence within the operating room environment, thus expediting the testing of novel imaging probes.
Fluorescence imaging; Surgery assistance; Portable camera; Surgical specimen