Imaging the pharmacodynamics of HER2 degradation in response to Hsp90 inhibitors

Molecular imaging for monitoring treatment response in breast cancer patients

Currently, tumour response following drug treatment is based on measurement of anatomical size changes. This is often done according to Response Evaluation Criteria in Solid Tumours (RECIST) and is generally performed every 2-3 cycles. Bone metastases, being the most common site of distant metastases in breast cancer, are not measurable by RECIST. The standard response measurement provides no insight in changes of molecular characteristics. In the era of targeted medicine, knowledge of specific molecular tumour characteristics becomes more important. A potential way to assess this is by means of molecular imaging. Molecular imaging can visualise general tumour processes, such as glucose metabolism with (18)F-fluorodeoxyglucose ((18)F-FDG) and DNA synthesis with (18)F-fluorodeoxythymidine ((18)F-FLT). In addition, an increasing number of more specific targets, such as hormone receptors, growth factor receptors, and growth factors can be visualised. In the future molecular imaging may thus be of value for personalised treatment-selection by providing insight in the expression of these drug targets. Additionally, when molecular changes can be detected early during therapy, this may serve as early predictor of response. However, in order to define clinical utility of this approach results from (ongoing) clinical trials is required. In this review we summarise the potential role of molecular imaging of general tumour processes as well as hormone receptors, growth factor receptors, and tumour micro-environment for predicting and monitoring treatment response in breast cancer patients.

Recent advances in optical cancer imaging of EGF receptors

Epidermal growth factor (EGF) receptors are commonly expressed on the cell membrane of cancer cells and activity of these receptors results in accelerated cell growth and carcinogenesis. A variety of targeted molecules have been developed to block ligand binding and/or inhibit the function of these receptor tyrosine kinases, and several have proven therapeutic benefits. Along with the advent of new therapeutic agents comes a need for non-invasive tools to diagnose, characterize, and monitor tumor responsiveness to therapy. Imaging EGF receptors with radionuclides has been performed for decades. However, recently this area has advanced considerably with the development of EGF receptor-targeted optical imaging probes. Herein, we review recent advances in molecular imaging of the EGF receptor family, focusing specifically on optical imaging. Such agents provide the opportunity for earlier diagnosis, improved tumor characterization, and the ability to measure and monitor tumor responsiveness to anti-EGF receptor treatment strategies.

Combined MR, fluorescence and histology imaging strategy in a human breast tumor xenograft model

Applications of molecular imaging in cancer and other diseases frequently require the combination of in vivo imaging modalities, such as MR and optical imaging, with ex vivo optical, fluorescence, histology and immunohistochemical imaging to investigate and relate molecular and biological processes to imaging parameters within the same region of interest. We have developed a multimodal image reconstruction and fusion framework that accurately combines in vivo MRI and MRSI, ex vivo brightfield and fluorescence microscopic imaging and ex vivo histology imaging. Ex vivo brightfield microscopic imaging was used as an intermediate modality to facilitate the ultimate link between ex vivo histology and in vivo MRI/MRSI. Tissue sectioning necessary for optical and histology imaging required the generation of a three-dimensional reconstruction module for two-dimensional ex vivo optical and histology imaging data. We developed an external fiducial marker-based three-dimensional reconstruction method, which was able to fuse optical brightfield and fluorescence with histology imaging data. The registration of the three-dimensional tumor shape was pursued to combine in vivo MRI/MRSI and ex vivo optical brightfield and fluorescence imaging data. This registration strategy was applied to in vivo MRI/MRSI, ex vivo optical brightfield/fluorescence and histology imaging datasets obtained from human breast tumor models. Three-dimensional human breast tumor datasets were successfully reconstructed and fused with this platform.

Molecular imaging probes for diagnosis and therapy evaluation of breast cancer

Breast cancer is a major cause of cancer death in women where early detection and accurate assessment of therapy response can improve clinical outcomes. Molecular imaging, which includes PET, SPECT, MRI, and optical modalities, provides noninvasive means of detecting biological processes and molecular events in vivo. Molecular imaging has the potential to enhance our understanding of breast cancer biology and effects of drug action during both preclinical and clinical phases of drug development. This has led to the identification of many molecular imaging probes for key processes in breast cancer. Hormone receptors, growth factor receptor, and angiogenic factors, such as ER, PR, HER2, and VEGFR, have been adopted as imaging targets to detect and stage the breast cancer and to monitor the treatment efficacy. Receptor imaging probes are usually composed of targeting moiety attached to a signaling component such as a radionuclide that can be detected using dedicated instruments. Current molecular imaging probes involved in breast cancer diagnosis and therapy evaluation are reviewed, and future of molecular imaging for the preclinical and clinical is explained.

The diversity of (68)Ga-based imaging agents

Development of new radiopharmaceuticals and their availability are crucial factors influencing the expansion of clinical nuclear medicine. The number of new (68)Ga-based imaging agents for positron emission tomography (PET) is increasing greatly. (68)Ga has been used for labeling of a broad range of molecules (small organic molecules, peptides, proteins, and oligonucleotides) as well as particles, thus demonstrating its potential to become a PET analog of the legendary generator-produced gamma-emitting (99m)Tc but with added value of higher sensitivity and resolution as well as quantitation and dynamic scanning. Further, the availability of technology for GMP-compliant automated tracer production can facilitate the introduction of new radiopharmaceuticals and enable standardized, harmonized multicenter studies to be conducted for regulatory approval. This chapter presents some examples of tracers for targeted, pretargeted, and nontargeted imaging with emphasis on the potential of (68)Ga to facilitate clinically practical PET development and to promote the PET technique worldwide for earlier and better diagnostics, and personalized medicine with the ultimate objective of improved therapeutic outcome.

Imaging a functional tumorigenic biomarker in the transformed epithelium

Proteases responsible for the increased peritumoral proteolysis associated with cancer represent functional biomarkers for monitoring tumorigenesis. One attractive extracellular biomarker is the transmembrane serine protease matriptase. Found on the surface of epithelial cells, the activity of matriptase is regulated by its cognate inhibitor hepatocyte growth factor activator inhibitor-1 (HAI-1). Quantitative mass spectrometry allowed us to show that, in selected cancers, HAI-1 expression decreases, leading to active matriptase. A preclinical probe specific for the measurement of emergent active matriptase was developed. Using an active-site-specific, recombinant human antibody for matriptase, we found that the selective targeting of active matriptase can be used to visualize the tumorigenic epithelium. Live-cell fluorescence imaging validated the selectivity of the antibody in vitro by showing that the probe localized only to cancer cell lines with active matriptase on the surface. Immunofluorescence with the antibody documented significant levels of active matriptase in 68% of primary and metastatic colon cancer sections from tissue microarrays. Labeling of the active form of matriptase in vivo was measured in human colon cancer xenografts and in a patient-derived xenograft model using near-infrared and single-photon emission computed tomography imaging. Tumor uptake of the radiolabeled antibody, (111)In-A11, by active matriptase was high in xenografts (28% injected dose per gram) and was blocked in vivo by the addition of a matriptase-specific variant of ecotin. These findings suggest, through a HAI-1-dependent mechanism, that emergent active matriptase is a functional biomarker of the transformed epithelium and that its proteolytic activity can be exploited to noninvasively evaluate tumorigenesis in vivo.

Advances in immuno-positron emission tomography: antibodies for molecular imaging in oncology

Identification of cancer cell-surface biomarkers and advances in antibody engineering have led to a sharp increase in the development of therapeutic antibodies. These same advances have led to a new generation of radiolabeled antibodies and antibody fragments that can be used as cancer-specific imaging agents, allowing quantitative imaging of cell-surface protein expression in vivo. Immuno-positron emission tomography (immunoPET) imaging with intact antibodies has shown success clinically in diagnosing and staging cancer. Engineered antibody fragments, such as diabodies, minibodies, and single-chain Fv (scFv) -Fc, have been successfully employed for immunoPET imaging of cancer cell-surface biomarkers in preclinical models and are poised to bring same-day imaging into clinical development. ImmunoPET can potentially provide a noninvasive approach for obtaining target-specific information useful for titrating doses for radioimmunotherapy, for patient risk stratification and selection of targeted therapies, for evaluating response to therapy, and for predicting adverse effects, thus contributing to the ongoing development of personalized cancer treatment.

Lapatinib and 17AAG reduce 89Zr-trastuzumab-F(ab')2 uptake in SKBR3 tumor xenografts

Human epidermal growth factor receptor-2 (HER2) directed therapy potentially can be improved by insight in drug effects on HER2 expression. This study evaluates the effects of the EGFR/HER2 tyrosine kinase inhibitor lapatinib, the heat shock protein-90 inhibitor 17AAG, and their combination, on HER2 expression with in vivo HER2-PET imaging. Lapatinib and 17AAG effects on EGFR and HER2 membrane expression were determined in vitro using flow cytometry of human SKBR3 tumor cells. Effect of lapatinib on HER2 internalization was studied in vitro by (89)Zr-trastuzumab-F(ab')(2) internalization. For in vivo evaluation, (89)Zr-trastuzumab-F(ab')(2) μPET imaging was performed two times with a 7 day interval. Lapatinib was administered for 6 days, starting 1 day after the baseline scan. 17AAG was given 1 day before the second (89)Zr-trastuzumab-F(ab')(2) injection. Imaging data were compared with ex vivo biodistribution analysis and HER2 immunohistochemical staining. 17AAG treatment lowered EGFR expression by 41% (P = 0.016) and HER2 by 76% (P = 0.022). EGFR/HER2 downregulation by 17AAG was inhibited by lapatinib pretreatment. Lapatinib reduced internalization of (89)Zr-trastuzumab-F(ab')(2) with 25% (P = 0.0022). (89)Zr-trastuzumab-F(ab')(2) tumor to blood ratio was lowered 32% by lapatinib (P = 0.00004), 34% by 17AAG (P = 0.0022) and even 53% by the combination (P = 0.011). Lapatinib inhibits HER2 internalization and 17AAG lowers HER2 membrane expression. Both drugs reduce (89)Zr-trastuzumab-F(ab')(2) tumor uptake. Based on our findings, supported by previous preclinical data indicating the antitumor potency of lapatinib in combination with HSP90 inhibition, combination of these drugs deserves further investigation.

Measuring oncogenic signaling pathways in cancer with PET: an emerging paradigm from studies in castration-resistant prostate cancer

As parallel advances in cancer biology and drug development continue to elevate the role of targeted therapies in oncology, the need for imaging biomarkers that systematically measure the biology associated with therapeutic intervention has become more urgent. Although the molecular imaging community has a commitment to develop technologies to this end, few investigational radiotracers directly measure the biology of common oncogenic signaling pathways often addressed by targeted therapies. Visible progress has been achieved with a handful of radiotracers rationally designed to intercalate the pathobiology of prostate cancer, a molecularly heterogeneous disease nevertheless broadly defined by a fairly small repertoire of recurrent oncogenic lesions.

SIGNIFICANCE

That variable treatment responses or emergent resistance phenotypes are often documented in humans argues strongly for diagnostic technologies that can be realistically applied posttherapy to capture the dynamic patterns of disease response. The purpose of this review is to describe a collection of radiotracers developed to measure the pathobiology of prostate cancer for improved treatment monitoring, placing particular emphasis on the biologic rationale for their preparation. A chronologic description of radiotracer development programs is outlined, primarily to stress how an ongoing dialectic between earlier and more contemporary imaging technologies has accelerated discovery.

Use of pharmacokinetic/pharmacodynamic biomarkers to support rational cancer drug development

The process of drug development in oncology has struggled to alter at a pace in keeping with the rapid discovery and testing of agents that act on a wide variety of molecular targets. The rational development of such agents requires an understanding of drug effect(s) on their purported target. It is likely that testing these drugs in a framework designed to examine cytotoxic agents will fail to establish their full potential. We discuss how data gained from biomarker investigation might impact on drug development and provide examples that highlight the development, validation and use of pharmacokinetic, and especially pharmacodynamic biomarkers as drug development moves from the laboratory into clinical testing. The challenges of performing assays to satisfy regulatory requirements have been the subject of much debate. We recommend the implementation of appropriate, fit-for-purpose biomarkers in clinical trials of all new cancer drugs.

Discovery and validation of small-molecule heat-shock protein 90 inhibitors through multimodality molecular imaging in living subjects

Up-regulation of the folding machinery of the heat-shock protein 90 (Hsp90) chaperone protein is crucial for cancer progression. The two Hsp90 isoforms (α and β) play different roles in response to chemotherapy. To identify isoform-selective inhibitors of Hsp90(α/β)/cochaperone p23 interactions, we developed a dual-luciferase (Renilla and Firefly) reporter system for high-throughput screening (HTS) and monitoring the efficacy of Hsp90 inhibitors in cell culture and live mice. HTS of a 30,176 small-molecule chemical library in cell culture identified a compound, N-(5-methylisoxazol-3-yl)-2-[4-(thiophen-2-yl)-6-(trifluoromethyl)pyrimidin-2-ylthio]acetamide (CP9), that binds to Hsp90(α/β) and displays characteristics of Hsp90 inhibitors, i.e., degradation of Hsp90 client proteins and inhibition of cell proliferation, glucose metabolism, and thymidine kinase activity, in multiple cancer cell lines. The efficacy of CP9 in disrupting Hsp90(α/β)/p23 interactions and cell proliferation in tumor xenografts was evaluated by non-invasive, repetitive Renilla luciferase and Firefly luciferase imaging, respectively. At 38 h posttreatment (80 mg/kg × 3, i.p.), CP9 led to selective disruption of Hsp90α/p23 as compared with Hsp90β/p23 interactions. Small-animal PET/CT in the same cohort of mice showed that CP9 treatment (43 h) led to a 40% decrease in (18)F-fluorodeoxyglucose uptake in tumors relative to carrier control-treated mice. However, CP9 did not lead to significant degradation of Hsp90 client proteins in tumors. We performed a structural activity relationship study with 62 analogs of CP9 and identified A17 as the lead compound that outperformed CP9 in inhibiting Hsp90(α/β)/p23 interactions in cell culture. Our efforts demonstrated the power of coupling of HTS with multimodality molecular imaging and led to identification of Hsp90 inhibitors.

PET of signal transduction pathways in cancer

In this era of systems biology, the tide of information derived from "omic" technologies (genomics, proteomics, etc.) has sparked a revolution in drug design, with many industrial and academic programs now embracing the concepts of molecular medicine (i.e., targeting changes in specific proteins or pathways) as measures of treatment efficacy and outcome. This approach has yielded a plethora of new preclinical therapeutics directed at novel targets within oncology. In many ways, the evolution of molecular imaging agents as diagnostic probes mirrors that of chemotherapeutics; yet despite an increasing number of PET and SPECT radiotracers being evaluated in human trials, relatively few agents have found widespread use in clinical oncology. In light of this observation, is it time to reevaluate our strategies for radiopharmaceutical design and use? In this article, we argue that PET has enormous potential to deliver clinically relevant information on disease dynamics that extends beyond mapping the density and spatial distribution of a target. Recent developments in targeting pharmacodynamic biomarkers aim to exploit better the advantages of functional PET by detecting changes in signal transduction pathways, particularly in response to disease progression or treatment in cancer.

In vivo targeting of HER2-positive tumor using 2-helix affibody molecules

Molecular imaging of human epidermal growth factor receptor type 2 (HER2) expression has drawn significant attention because of the unique role of the HER2 gene in diagnosis, therapy and prognosis of human breast cancer. In our previous research, a novel cyclic 2-helix small protein, MUT-DS, was discovered as an anti-HER2 Affibody analog with high affinity through rational protein design and engineering. MUT-DS was then evaluated for positron emission tomography (PET) of HER2-positive tumor by labeling with two radionuclides, 68Ga and 18F, with relatively short half-life (t1/2<2 h). In order to fully study the in vivo behavior of 2-helix small protein and demonstrate that it could be a robust platform for labeling with a variety of radionuclides for different applications, in this study, MUT-DS was further radiolabeled with 64Cu or 111In and evaluated for in vivo targeting of HER2-positive tumor in mice. Design 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) conjugated MUT-DS (DOTA-MUT-DS) was chemically synthesized using solid phase peptide synthesizer and I2 oxidation. DOTA-MUT-DS was then radiolabeled with 64Cu or 111In to prepare the HER2 imaging probe (64Cu/111In-DOTA-MUT-DS). Both biodistribution and microPET imaging of the probe were evaluated in nude mice bearing subcutaneous HER2-positive SKOV3 tumors. DOTA-MUT-DS could be successfully synthesized and radiolabeled with 64Cu or 111In. Biodistribution study showed that tumor uptake value of 64Cu or 111In-labeled DOTA-MUT-DS was 4.66±0.38 or 2.17±0.15%ID/g, respectively, in nude mice bearing SKOV3 xenografts (n=3) at 1 h post-injection (p.i.). Tumor-to-blood and tumor-to-muscle ratios for 64Cu-DOTA-MUT-DS were attained to be 3.05 and 3.48 at 1 h p.i., respectively, while for 111In-DOTA-MUT-DS, they were 2.04 and 3.19, respectively. Co-injection of the cold Affibody molecule ZHER2:342 with 64Cu-DOTA-MUT-DS specifically reduced the SKOV3 tumor uptake of the probe by 48%. 111In-DOTA-MUT-DS displayed lower liver uptake at all the time points investigated and higher tumor to blood ratios at 4 and 20 h p.i., when compared with 64Cu-DOTA-MUT-DS. This study demonstrates that the 2-helix protein based probes, 64Cu/111In DOTA-MUT-DS, are promising molecular probes for imaging HER2-positive tumor. Two-helix small protein scaffold holds great promise as a novel and robust platform for imaging and therapy applications.

Imaging: strategies, controversies, and opportunities

At a Clinical and Translational Cancer Research Think Tank meeting sponsored by the American Association for Cancer Research in 2010, one of the breakout groups focused on new technologies and imaging. The discussions emphasized new opportunities in translational imaging and its role in the future, rather than established techniques that are currently in clinical practice. New imaging methods under development are changing the approach of imaging science from a focus on the anatomic description of disease to a focus on the molecular basis of disease. Broadly referred to as molecular imaging, these new strategies directly embrace the incorporation of cell and molecular biology concepts and techniques into image generation and can involve the introduction of genes into cells with the explicit intent to image the end products of gene expression with external imaging devices. These new methods hold the promise of providing clinicians with (i) robust linkages between cell and animal models and clinical trials, (ii) in vivo biomarkers that can be measured repeatedly and sequentially over time to observe dynamic disease processes and responses to treatment, and (iii) tools for preselection and patient population enrichment in phase II and III trials to improve outcomes and better direct treatment. These strategies provide real-time pharmacodynamic parameters and can be powerful tools to monitor therapeutic effects in a spatially and tissue-specific manner, which may reduce cost during drug development, because pharmacodynamic studies in animals can inform clinical trials and accelerate the translation process. The Imaging Response Assessment Team (IRAT) program serves as an example of how imaging techniques can be incorporated into clinical trials. IRATs work to advance the role of imaging in assessment of response to therapy and to increase the application of quantitative anatomic, functional, and molecular imaging endpoints in clinical trials, and imaging strategies that will lead to individualized patient care.

Molecular targeting of CEACAM6 using antibody probes of different sizes

Carcinocinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6) is overexpressed in a number of human malignancies, especially in pancreatic cancer. It has been demonstrated that CEACAM6 is a potential target for monoclonal antibody (mAb) therapy with a safe therapeutic index. Here, we labeled three anti-CEACAM6 antibodies of different sizes, including a single-domain antibody 2A3 (16 kDa), a heavy chain antibody 2A3-mFc (80 kDa) and a full length antibody 9A6 (150 kDa), with ⁶⁴Cu to image CEACAM6 expression in a xenografted pancreatic tumor model. For positron emission tomography (PET) imaging, the tumor mice were intravenously injected with ⁶⁴Cu-DOTA-antibodies and static scans were obtained at 5 min, 0.5, 1, 2, 4, 8 and 24h post-injection (p.i.). All three antibodies showed strong CEACAM6 binding. Ex vivo immunostaining on tumor sections at 24 h after Ab injection demonstrated specific tumor targeting of both 2A3-mFc and 9A6. ⁶⁴Cu-DOTA-2A3 showed fast BxPC3 tumor uptake and rapid whole-body clearance. At 24 h p.i., the tumor uptakes were 98.2±6.12%ID/g for ⁶⁴Cu-DOTA-2A3-mFc and 57.8±3.73%ID/g for ⁶⁴Cu-DOTA-9A6, respectively. Compared with the full length antibody 9A6, the heavy chain antibody 2A3-mFc showed higher tumor uptake, lower liver uptake and shorter circulation half-life. All the data supported that the heavy chain antibody 2A3-mFc is superior to the single domain antibody and the full-length antibody with regard to tumor detection and pharmacokinetics, which has great potential to be developed for CEACAM6-targeted pancreatic cancer imaging and therapy.

Standardized uptake value by positron emission tomography/computed tomography as a prognostic variable in metastatic breast cancer

BACKGROUND

In this retrospective, single-institution study, the authors examine the maximum standardized uptake value (SUVmax) on positron emission tomography/computed tomography (PET/CT) images as a prognostic variable in patients with newly diagnosed metastatic breast cancer (MBC).

METHODS

Patients with ≥1 metastatic lesion on PET/CT images that were obtained within 60 days of their MBC diagnosis between January 1, 2001 and December 31, 2008 were included. Patients were excluded if they had received chemotherapy ≤30 days before the PET/CT images were obtained. Electronic medical reports were reviewed to determine the SUVmax and overall survival. Because of intraindividual variation in the SUV by body site, separate analyses were conducted by metastatic site. Relationships between site-specific PET/CT variable tertiles and overall survival were assessed using Cox regression; hazard ratios for the highest tertile versus the lowest tertile were reported.

RESULTS

In total, 253 patients were identified, and their median age was 57 years (range, 27-90 years). Of these, 152 patients (60%) died, and the median follow-up was 40 months. On univariate analysis, SUVmax tertile was strongly associated with overall survival in patients who had bone metastases (N = 141; hazard ratio, 3.13; 95% confidence interval, 1.79-5.48; P < .001). This effect was maintained on multivariate analysis (HR = 3.19; 95% confidence interval, 1.64-6.20, P = .002) after correcting for known prognostic variables. A greater risk of death was associated with SUVmax tertile in patients who had metastases to the liver (N = 46; hazard ratio, 2.07; 95% confidence interval, 0.90-4.76), lymph nodes (N = 149; hazard ratio, 1.1; 95% confidence interval, 0.69-1.88), and lung (N = 62; hazard ratio, 2.2; 95% confidence interval, 0.97-4.95), although these results were not significant (P = .18, P = .31, and P = .095, respectively).

CONCLUSIONS

The current results indicate that PET/CT has value as a prognostic tool in patients with newly diagnosed MBC to bone.

Molecular imaging for personalized cancer care

Molecular imaging is rapidly gaining recognition as a tool with the capacity to improve every facet of cancer care. Molecular imaging in oncology can be defined as in vivo characterization and measurement of the key biomolecules and molecularly based events that are fundamental to the malignant state. This article outlines the basic principles of molecular imaging as applied in oncology with both established and emerging techniques. It provides examples of the advantages that current molecular imaging techniques offer for improving clinical cancer care as well as drug development. It also discusses the importance of molecular imaging for the emerging field of theranostics and offers a vision of how molecular imaging may one day be integrated with other diagnostic techniques to dramatically increase the efficiency and effectiveness of cancer care.

86Y based PET radiopharmaceuticals: radiochemistry and biological applications

Development of targeted radionuclide therapy with (90)Y labeled antibodies and peptides has gained momentum in the past decade due to the successes of (90)Y-ibritumomab tiuxetan and (90)Y-DOTA-Phe(1)-Tyr(3)-octreotide in treatment of cancer. (90)Y is a pure β(-)-emitter and cannot be imaged for patient-specific dosimetry which is essential for pre-therapeutic treatment planning and accurate absorbed dose estimation in individual patients to mitigate radiation related risks. This review article describes the utility of (86)Y, a positron emitter (33%) with a 14.7-h half-life that can be imaged by positron emission tomography and used as an isotopically matched surrogate radionuclide for (90)Y radiation doses estimations. This review discusses various aspects involved in the development of (86)Y labeled radiopharmaceuticals with the specific emphasis on the radiochemistry and biological applications with antibodies and peptides.

Comparative analysis of novel and conventional Hsp90 inhibitors on HIF activity and angiogenic potential in clear cell renal cell carcinoma: implications for clinical evaluation

BACKGROUND

Perturbing Hsp90 chaperone function targets hypoxia inducible factor (HIF) function in a von Hippel-Lindau (VHL) independent manner, and represents an approach to combat the contribution of HIF to cell renal carcinoma (CCRCC) progression. However, clinical trials with the prototypic Hsp90 inhibitor 17-AAG have been unsuccessful in halting the progression of advanced CCRCC.

METHODS

Here we evaluated a novel next generation small molecule Hsp90 inhibitor, EC154, against HIF isoforms and HIF-driven molecular and functional endpoints. The effects of EC154 were compared to those of the prototypic Hsp90 inhibitor 17-AAG and the histone deacetylase (HDAC) inhibitor LBH589.

RESULTS

The findings indicate that EC154 is a potent inhibitor of HIF, effective at doses 10-fold lower than 17-AAG. While EC154, 17-AAG and the histone deacetylase (HDAC) inhibitor LBH589 impaired HIF transcriptional activity, CCRCC cell motility, and angiogenesis; these effects did not correlate with their ability to diminish HIF protein expression. Further, our results illustrate the complexity of HIF targeting, in that although these agents suppressed HIF transcripts with differential dynamics, these effects were not predictive of drug efficacy in other relevant assays.

CONCLUSIONS

We provide evidence for EC154 targeting of HIF in CCRCC and for LBH589 acting as a suppressor of both HIF-1 and HIF-2 activity. We also demonstrate that 17-AAG and EC154, but not LBH589, can restore endothelial barrier function, highlighting a potentially new clinical application for Hsp90 inhibitors. Finally, given the discordance between HIF activity and protein expression, we conclude that HIF expression is not a reliable surrogate for HIF activity. Taken together, our findings emphasize the need to incorporate an integrated approach in evaluating Hsp90 inhibitors within the context of HIF suppression.

Concomitant inhibition of HSP90, its mitochondrial localized homologue TRAP1 and HSP27 by green tea in pancreatic cancer HPAF-II cells

Pancreatic cancer is a deadly disease characterized by poor prognosis and patient survival. Green tea polyphenols have been shown to exhibit multiple antitumor activities in various cancers, but studies on the pancreatic cancer are very limited. To identify the cellular targets of green tea action, we exposed a green tea extract (GTE) to human pancreatic ductal adenocarcinoma HPAF-II cells and performed two-dimensional gel electrophoresis of the cell lysates. We identified 32 proteins with significantly altered expression levels. These proteins are involved in drug resistance, gene regulation, motility, detoxification and metabolism of cancer cells. In particular, we found GTE inhibited molecular chaperones heat-shock protein 90 (Hsp90), its mitochondrial localized homologue Hsp75 (tumor necrosis factor receptor-associated protein 1, or Trap1) and heat-shock protein 27 (Hsp27) concomitantly. Western blot analysis confirmed the inhibition of Hsp90, Hsp75 and Hsp27 by GTE, but increased phosphorylation of Ser78 of Hsp27. Furthermore, we showed that GTE inhibited Akt activation and the levels of mutant p53 protein, and induced apoptosis and growth suppression of the cells. Our study has identified multiple new molecular targets of GTE and provided further evidence on the anticancer activity of green tea in pancreatic cancer.

68Ga-DOTA-affibody molecule for in vivo assessment of HER2/neu expression with PET

PURPOSE

Overexpression of HER2/neu in breast cancer is correlated with a poor prognosis. It may vary between primary tumors and metastatic lesions and change during the treatment. Therefore, there is a need for a new means to assess HER2/neu expression in vivo. In this work, we used (68)Ga-labeled DOTA-Z(HER2:2891)-Affibody to monitor HER2/neu expression in a panel of breast cancer xenografts.

METHODS

DOTA-Z(HER2:2891)-Affibody molecules were labeled with (68)Ga. 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.

RESULTS

The (68)Ga-DOTA-Z(HER2:2891)-Affibody probe showed high binding affinity to MDA-MB-361 cells (K (D) = 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 concentration of radioactivity in normal tissue was seen in the kidneys (227 ± 14%ID/g). High-contrast PET images of HER2/neu-overexpressing tumors were recorded as soon as 1 h after tracer injection. A good correlation was observed between PET imaging, biodistribution estimates of tumor tracer concentration, and the receptor expression.

CONCLUSION

These results suggest that PET imaging using (68)Ga-DOTA-Z(HER2:2891)-Affibody is sensitive enough to detect different levels of HER2/neu expression in vivo.

Quantitating antibody uptake in vivo: conditional dependence on antigen expression levels

PURPOSE

Antibodies form an important class of cancer therapeutics, and there is intense interest in using them for imaging applications in diagnosis and monitoring of cancer treatment. Despite the expanding body of knowledge describing pharmacokinetic and pharmacodynamic interactions of antibodies in vivo, discrepancies remain over the effect of antigen expression level on tumoral uptake with some reports indicating a relationship between uptake and expression and others showing no correlation.

PROCEDURES

Using a cell line with high epithelial cell adhesion molecule expression and moderate epidermal growth factor receptor expression, fluorescent antibodies with similar plasma clearance were imaged in vivo. A mathematical model and mouse xenograft experiments were used to describe the effect of antigen expression on uptake of these high-affinity antibodies.

RESULTS

As predicted by the theoretical model, under subsaturating conditions, uptake of the antibodies in such tumors is similar because localization of both probes is limited by delivery from the vasculature. In a separate experiment, when the tumor is saturated, the uptake becomes dependent on the number of available binding sites. In addition, targeting of small micrometastases is shown to be higher than larger vascularized tumors.

CONCLUSIONS

These results are consistent with the prediction that high affinity antibody uptake is dependent on antigen expression levels for saturating doses and delivery for subsaturating doses. It is imperative for any probe to understand whether quantitative uptake is a measure of biomarker expression or transport to the region of interest. The data provide support for a predictive theoretical model of antibody uptake, enabling it to be used as a starting point for the design of more efficacious therapies and timely quantitative imaging probes.

Recent trends in antibody-based oncologic imaging

Antibodies, with their unmatched ability for selective binding to any target, are considered as potentially the most specific probes for imaging. Their clinical utility, however, has been limited chiefly due to their slow clearance from the circulation, longer retention in non-targeted tissues and the extensive optimization required for each antibody-tracer. The development of newer contrast agents, combined with improved conjugation strategies and novel engineered forms of antibodies (diabodies, minibodies, single chain variable fragments, and nanobodies), have triggered a new wave of antibody-based imaging approaches. Apart from their conventional use with nuclear imaging probes, antibodies and their modified forms are increasingly being employed with non-radioisotopic contrast agents (MRI and ultrasound) as well as newer imaging modalities, such as quantum dots, near infra red (NIR) probes, nanoshells and surface enhanced Raman spectroscopy (SERS). The review article discusses new developments in the usage of antibodies and their modified forms in conjunction with probes of various imaging modalities such as nuclear imaging, optical imaging, ultrasound, MRI, SERS and nanoshells in preclinical and clinical studies on the diagnosis, prognosis and therapeutic responses of cancer.

A comparison of 111In- or 64Cu-DOTA-trastuzumab Fab fragments for imaging subcutaneous HER2-positive tumor xenografts in athymic mice using microSPECT/CT or microPET/CT

Background

Our objective was to compare ¹¹¹In- or ⁶⁴Cu-DOTA-trastuzumab Fab fragments for imaging small or large s.c. tumor xenografts in athymic mice that display a wide range of human epidermal growth factor receptor-2 (HER2) expression using microSPECT/CT or microPET/CT.

Methods

Trastuzumab Fab were labeled with ¹¹¹In or ⁶⁴Cu by conjugation to 1,4,7,10-tetraazacyclododecane N, N', N'', N'''-tetraacetic acid (DOTA). The purity of ¹¹¹In- and ⁶⁴Cu-DOTA-trastuzumab Fab was measured by SDS-PAGE and HPLC. HER2 binding affinity was determined in saturation radioligand binding assays using SKBR-3 cells (1.3 × 10⁶ HER2/cell). MicroSPECT/CT and microPET/CT were performed in athymic mice bearing s.c. BT-20 and MDA-MB-231 xenografts with low (0.5 to 1.6 × 10⁵ receptors/cell), MDA-MB-361 tumors with intermediate (5.1 × 10⁵ receptors/cell) or SKOV-3 xenografts with high HER2 expression (1.2 × 10⁶ receptors/cell) at 24 h p.i. of 70 MBq (10 μg) of ¹¹¹In-DOTA-trastuzumab Fab or 22 MBq (10 μg) of ⁶⁴Cu-DOTA-trastuzumab Fab or irrelevant ¹¹¹In- or ⁶⁴Cu-DOTA-rituximab Fab. Tumor and normal tissue uptake were quantified in biodistribution studies.

Results

¹¹¹In- and ⁶⁴Cu-DOTA-trastuzumab were > 98% radiochemically pure and bound HER2 with high affinity (K_d = 20.4 ± 2.5 nM and 40.8 ± 3.5 nM, respectively). MDA-MB-361 and SKOV-3 tumors were most clearly imaged using ¹¹¹In- and ⁶⁴Cu-DOTA-trastuzumab Fab. Significantly higher tumor/blood (T/B) ratios were found for ¹¹¹In-DOTA-trastuzumab Fab than ¹¹¹In-DOTA-rituximab Fab for BT-20, MDA-MB-231 and MDA-MB-361 xenografts, and there was a direct association between T/B ratios and HER2 expression. In contrast, tumor uptake of ⁶⁴Cu-DOTA-trastuzumab Fab was significantly higher than ⁶⁴Cu-DOTA-rituximab Fab in MDA-MB-361 tumors but no direct association with HER2 expression was found. Both ¹¹¹In- and ⁶⁴Cu-DOTA-trastuzumab Fab imaged small (5 to 10 mm) or larger (10 to 15 mm) MDA-MB-361 tumors. Higher blood, liver, and spleen radioactivity were observed for ⁶⁴Cu-DOTA-trastuzumab Fab than ¹¹¹In-DOTA-trastuzumab Fab.

Conclusions

We conclude that ¹¹¹In-DOTA-trastuzumab Fab was more specific than ⁶⁴Cu-DOTA-trastuzumab Fab for imaging HER2-positive tumors, especially those with low receptor density. This was due to higher levels of circulating radioactivity for ⁶⁴Cu-DOTA-trastuzumab Fab which disrupted the relationship between HER2 density and T/B ratios. Use of alternative chelators that more stably bind ⁶⁴Cu may improve the association between T/B ratios and HER2 density for ⁶⁴Cu-labeled trastuzumab Fab.

Metallic radionuclides in the development of diagnostic and therapeutic radiopharmaceuticals

Metallic radionuclides are the mainstay of both diagnostic and therapeutic radiopharmaceuticals. Therapeutic nuclear medicine is less advanced but has tremendous potential if the radionuclide is accurately targeted. Great interest exists in the field of inorganic chemistry for developing target specific radiopharmaceuticals based on radiometals for non-invasive disease detection and cancer radiotherapy. This perspective will focus on the nuclear properties of a few important radiometals and their recent applications to developing radiopharmaceuticals for imaging and therapy. Other topics for discussion will include imaging techniques, radiotherapy, analytical techniques, and radiation safety. The ultimate goal of this perspective is to introduce inorganic chemists to the field of nuclear medicine and radiopharmaceutical development, where many applications of fundamental inorganic chemistry can be found.

A practical guide to the construction of radiometallated bioconjugates for positron emission tomography

Positron emission tomography (PET) has become a vital imaging modality in the diagnosis and treatment of disease, most notably cancer. A wide array of small molecule PET radiotracers have been developed that employ the short half-life radionuclides (11)C, (13)N, (15)O, and (18)F. However, PET radiopharmaceuticals based on biomolecular targeting vectors have been the subject of dramatically increased research in both the laboratory and the clinic. Typically based on antibodies, oligopeptides, or oligonucleotides, these tracers have longer biological half-lives than their small molecule counterparts and thus require labeling with radionuclides with longer, complementary radioactive half-lives, such as the metallic isotopes (64)Cu, (68)Ga, (86)Y, and (89)Zr. Each bioconjugate radiopharmaceutical has four component parts: biomolecular vector, radiometal, chelator, and covalent link between chelator and biomolecule. With the exception of the radiometal, a tremendous variety of choices exists for each of these pieces, and a plethora of different chelation, conjugation, and radiometallation strategies have been utilized to create agents ranging from (68)Ga-labeled pentapeptides to (89)Zr-labeled monoclonal antibodies. Herein, the authors present a practical guide to the construction of radiometal-based PET bioconjugates, in which the design choices and synthetic details of a wide range of biomolecular tracers from the literature are collected in a single reference. In assembling this information, the authors hope both to illuminate the diverse methods employed in the synthesis of these agents and also to create a useful reference for molecular imaging researchers both experienced and new to the field.

The challenges of integrating molecular imaging into the optimization of cancer therapy

We review novel, in vivo and tissue-based imaging technologies that monitor and optimize cancer therapeutics. Recent advances in cancer treatment centre around the development of targeted therapies and personalisation of treatment regimes to individual tumour characteristics. However, clinical outcomes have not improved as expected. Further development of the use of molecular imaging to predict or assess treatment response must address spatial heterogeneity of cancer within the body. A combination of different imaging modalities should be used to relate the effect of the drug to dosing regimen or effective drug concentration at the local site of action. Molecular imaging provides a functional and dynamic read-out of cancer therapeutics, from nanometre to whole body scale. At the whole body scale, an increase in the sensitivity and specificity of the imaging probe is required to localise (micro)metastatic foci and/or residual disease that are currently below the limit of detection. The use of image-guided endoscopic biopsy can produce tumour cells or tissues for nanoscopic analysis in a relatively patient-compliant manner, thereby linking clinical imaging to a more precise assessment of molecular mechanisms. This multimodality imaging approach (in combination with genetics/genomic information) could be used to bridge the gap between our knowledge of mechanisms underlying the processes of metastasis, tumour dormancy and routine clinical practice. Treatment regimes could therefore be individually tailored both at diagnosis and throughout treatment, through monitoring of drug pharmacodynamics providing an early read-out of response or resistance.

The evolution of imaging in cancer: current state and future challenges

Molecular imaging allows for the remote, noninvasive sensing and measurement of cellular and molecular processes in living subjects. Drawing upon a variety of modalities, molecular imaging provides a window into the biology of cancer from the subcellular level to the patient undergoing a new, experimental therapy. As signal transduction cascades and protein interaction networks become clarified, an increasing number of relevant targets for cancer therapy--and imaging--become available. Although conventional imaging is already critical to the management of patients with cancer, molecular imaging will provide even more relevant information, such as early detection of changes with therapy, identification of patient-specific cellular and metabolic abnormalities, and the disposition of therapeutic, gene-tagged cells throughout the body--all of which will have a considerable impact on morbidity and mortality. This overview discusses molecular imaging in oncology, providing examples from a variety of modalities, with an emphasis on emerging techniques for translational imaging.

Molecular Imaging in Breast Cancer - Potential Future Aspects

SUMMARY: Molecular imaging aims to visualize and quantify biological, physiological, and pathological processes at cellular and molecular levels. Recently, molecular imaging has been introduced into breast cancer imaging. In this review, we will present a survey of the molecular imaging techniques that are either clinically available or are being introduced into clinical imaging. We will discuss nuclear imaging and multiparametric magnetic resonance imaging as well as the combined application of molecular imaging in the assessment of breast lesions. In addition, we will briefly discuss other evolving molecular imaging techniques, such as phosphorus magnetic resonance spectroscopic imaging and sodium imaging.

PET/CT in cancer research: from preclinical to clinical applications

The identification of genetic and biochemical mechanisms underlying tumor growth and progression along with the unraveling of human genoma provided a plethora of new targets for cancer detection, treatment and monitoring. Simultaneously, the extraordinary development of a number of imaging technologies, including hybrid systems, allowed the visualization of biochemical, molecular and physiological aberrations linked to underlying mutations in a given tumor. In vivo evaluation of complex biological processes such as proliferation, apoptosis, angiogenesis, metastasis, gene expression, receptor-ligand interactions, transport of substrates and metabolism of nutrients in human cancers is feasible using PET/CT and radiolabeled molecular probes. Some of these compounds are in preclinical phases of evaluation whereas others have been already applied in clinical settings. Here we provide prominent examples on how some biological processes and target expression can be visualized by PET/CT in animal tumor models and cancer patients for the noninvasive detection of well-known markers of tumor aggressiveness, invasiveness and resistance to treatment and for the evaluation of tumor response to therapy.

Assessing antibody pharmacokinetics in mice with in vivo imaging

Recent advances in small-animal molecular imaging instrumentation combined with well characterized antibody-labeling chemistry have enabled detailed in vivo measurements of antibody distribution in mouse models. This article reviews the strengths and limitations of in vivo antibody imaging methods with a focus on positron emission tomography and single-photon emission computed tomography and a brief discussion of the role of optical imaging in this application. A description of the basic principles behind the imaging techniques is provided along with a discussion of radiolabeling methods relevant to antibodies. Practical considerations of study design and execution are presented through a discussion of sensitivity and resolution tradeoffs for these techniques as defined by modality, signaling probe (isotope or fluorophore) selection, labeling method, and radiation dosimetry. Images and analysis results from a case study are presented with a discussion of output data content and relevant informatics gained with this approach to studying antibody pharmacokinetics.

Radiolabeled affibody-albumin bioconjugates for HER2-positive cancer targeting

Affibody molecules have received significant attention in the fields of molecular imaging and drug development. However, Affibody scaffolds display an extremely high renal uptake, especially when modified with chelators and then labeled with radiometals. This unfavorable property may impact their use as radiotherapeutic agents in general and as imaging probes for the detection of tumors adjacent to kidneys in particular. Herein, we present a simple and generalizable strategy for reducing the renal uptake of Affibody molecules while maintaining their tumor uptake. Human serum albumin (HSA) was consecutively modified by 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid mono-N-hydroxysuccinimide ester (DOTA-NHS ester) and the bifunctional cross-linker sulfosuccinimidyl 4-[N-maleimidomethyl]cyclohexane-1-carboxylate (Sulfo-SMCC). The HER2 Affibody analogue, Ac-Cys-Z(HER2:342), was covalently conjugated with HSA, and the resulting bioconjugate DOTA-HSA-Z(HER2:342) was further radiolabeled with ⁶⁴Cu and ¹¹¹In and evaluated in vitro and in vivo. Radiolabeled DOTA-HSA-Z(HER2:342) conjugates displayed a significant and specific cell uptake into SKOV3 cell cultures. Positron emission tomography (PET) investigations using ⁶⁴Cu-DOTA-HSA-Z(HER2:342) were performed in SKOV3 tumor-bearing nude mice. High tumor uptake values (>14% ID/g at 24 and 48 h) and high liver accumulations but low kidney accumulations were observed. Biodistribution studies and single-photon emission computed tomography (SPECT) investigations using ¹¹¹In-DOTA-HSA-Z(HER2:342) validated these results. At 24 h post injection, the biodistribution data revealed high tumor (16.26% ID/g) and liver (14.11% ID/g) uptake but relatively low kidney uptake (6.06% ID/g). Blocking studies with coinjected, nonlabeled Ac-Cys-Z(HER2:342) confirmed the in vivo specificity of HER2. Radiolabeled DOTA-HSA-Z(HER2:342) Affibody conjugates are promising SPECT and PET-type probes for the imaging of HER2 positive cancer. More importantly, DOTA-HSA-Z(HER2:342) is suitable for labeling with therapeutic radionuclides (e.g., ⁹⁰Y or ¹⁷⁷Lu) for treatment studies. The approach of using HSA to optimize the pharmacokinetics and biodistribution profile of Affibodies may be extended to the design of many other targeting molecules.

Preparation and quality control of 166Ho-DTPA-antiCD20 for radioimmunotherapy

In this work, anti-CD20 was successively labeled with beta-particle emitting radionuclide, Ho-166, for ultimate radioimmunotherapy applications. Ho-166 chloride was obtained by thermal neutron flux (1×1013 n cm−2 s−1) of natural Ho2(NO3)3 sample, dissolved in acidic media. 166Ho-holmium chloride (185 MBq) was added to the conjugated antibody after ccDTPA residulation at room temperature. Radiochemical purity of 95% (ITLC) and 98% (HPLC) were obtained for final radioimmunoconjugate (specific activity =3–3.5 GBq/mg). The final isotonic 166Ho-rituximab complex was checked by gel electrophoresis for protein integrity retention. Biodistribution studies of Ho-166 chloride and radioimmunoconjugate were performed in wild-type rats to determine the biodistribution. The accumulation of the radiolabeled antibody in lungs, liver and spleen demonstrates a similar pattern to the other radiolabeled anti-CD20 immunoconjugates.

Breast cancer

Diagnostic imaging modalities utilized in the care of cancer patients must fulfill several requirements: they must diagnose and characterize tumors with high accuracy, must reliably stage and restage the disease, and should allow for monitoring the effects of therapeutic interventions on the course of the disease. They should impact management by guiding treating physicians to appropriate individualized treatment strategies. There is ample evidence that positron emission tomography (PET) and PET-computed tomography (CT) imaging can meet these requirements. This chapter discusses the role and contributions of PET and PET-CT imaging using (18)F-fluorodeoxyglucose in diagnosing, staging, restaging, and treatment monitoring of breast cancer. Novel molecular imaging probes and devices that have been developed and translated into early clinical research protocols are also introduced.

Evaluation of the anti-HER2 C6.5 diabody as a PET radiotracer to monitor HER2 status and predict response to trastuzumab treatment

PURPOSE

The rapid tumor targeting and pharmacokinetic properties of engineered antibodies make them potentially suitable for use in imaging strategies to predict and monitor response to targeted therapies. This study aims to evaluate C6.5 diabody (C6.5 db), a noncovalent anti-HER2 single-chain Fv dimer, as a radiotracer for predicting response to HER2-targeted therapies such as trastuzumab.

EXPERIMENTAL DESIGN

Immunodeficient mice bearing established HER2-positive tumor xenografts were injected with radioiodinated C6.5 db and imaged by PET/CT. Radiotracer biodistribution was quantified by biopsied tumor and normal tissues. Potential competition between trastuzumab and C6.5 db was examined in vitro by flow cytometry and coimmunoprecipitations.

RESULTS

Biodistribution analysis of mice bearing xenografts with varying HER2 density revealed that the tumor uptake of (125)I-C6.5 db correlates with HER2 tumor density. In vitro competition experiments suggest that the C6.5 db targets an epitope on HER2 that is distinct from that bound by trastuzumab. Treatment of mice affected with SK-OV-3 tumor with trastuzumab for 3 days caused a 42% (P = 0.002) decrease in tumor uptake of (125)I-C6.5 db. This is consistent with a dramatic decrease in the tumor PET signal of (124)I-C6.5 db after trastuzumab treatment. Furthermore, mice affected with BT-474 tumor showed an approximately 60% decrease (P = 0.0026) in C6.5 db uptake after 6 days of trastuzumab treatment. Immunohistochemistry of excised xenograft sections and in vitro flow cytometry revealed that the decreased C6.5 db uptake on trastuzumab treatment is not associated with HER2 downregulation.

CONCLUSIONS

These studies suggest that (124)I-C6.5 db-based imaging can be used to evaluate HER2 levels as a predictor of response to HER2-directed therapies.

Hsp90 (heat shock protein 90) inhibitor occupancy is a direct determinant of client protein degradation and tumor growth arrest in vivo

Several Hsp90 (heat shock protein 90) inhibitors are currently under clinical evaluation as anticancer agents. However, the correlation between the duration and magnitude of Hsp90 inhibition and the downstream effects on client protein degradation and cancer cell growth inhibition has not been thoroughly investigated. To investigate the relationship between Hsp90 inhibition and cellular effects, we developed a method that measures drug occupancy on Hsp90 after treatment with the Hsp90 inhibitor IPI-504 in living cells and in tumor xenografts. In cells, we find the level of Hsp90 occupancy to be directly correlated with cell growth inhibition. At the molecular level, the relationship between Hsp90 occupancy and Hsp90 client protein degradation was examined for different client proteins. For sensitive Hsp90 clients (e.g. HER2 (human epidermal growth factor receptor 2), client protein levels directly mirror Hsp90 occupancy at all time points after IPI-504 administration. For insensitive client proteins, we find that protein abundance matches Hsp90 occupancy only after prolonged incubation with drug. Additionally, we investigate the correlation between plasma pharmacokinetics (PK), tumor PK, pharmacodynamics (PD) (client protein degradation), tumor growth inhibition, and Hsp90 occupancy in a xenograft model of human cancer. Our results indicate Hsp90 occupancy to be a better predictor of PD than either plasma PK or tumor PK. In the nonsmall cell lung cancer xenograft model studied, a linear correlation between Hsp90 occupancy and tumor growth inhibition was found. This novel binding assay was evaluated both in vitro and in vivo and could be used as a pharmacodynamic readout in the clinic.

Detection of Cancer Metastases with a Dual-labeled Near-Infrared/Positron Emission Tomography Imaging Agent

By dual labeling a targeting moiety with both nuclear and optical probes, the ability for noninvasive imaging and intraoperative guidance may be possible. Herein, the ability to detect metastasis in an immunocompetent animal model of human epidermal growth factor receptor 2 (HER-2)-positive cancer metastases using positron emission tomography (PET) and near-infrared (NIR) fluorescence imaging is demonstrated.

METHODS

((64)Cu-DOTA)(n)-trastuzumab-(IRDye800)(m) was synthesized, characterized, and administered to female Balb/c mice subcutaneously inoculated with highly metastatic 4T1.2neu/R breast cancer cells. ((64)Cu-DOTA)(n)-trastuzumab-(IRDye800)(m) (150 µg, 150 µCi, m = 2, n = 2) was administered through the tail vein at weeks 2 and 6 after implantation, and PET/computed tomography and NIR fluorescence imaging were performed 24 hours later. Results were compared with the detection capabilities of F-18 fluorodeoxyglucose ((18)FDG-PET).

RESULTS

Primary tumors were visualized with (18)FDG and ((64)Cu-DOTA)(n)-trastuzumab-(IRDye800)(m), but resulting metastases were identified only with the dual-labeled imaging agent. (64)Cu-PET imaging detected lung metastases, whereas ex vivo NIR fluorescence showed uptake in regions of lung, skin, skeletal muscle, and lymph nodes, which corresponded with the presence of cancer cells as confirmed by histologic hematoxylin and eosin stains. In addition to detecting the agent in lymph nodes, the high signal-to-noise ratio from NIR fluorescence imaging enabled visualization of channels between the primary tumor and the axillary lymph nodes, suggesting a lymphatic route for trafficking cancer cells. Because antibody clearance occurs through the liver, we could not distinguish between nonspecific uptake and liver metastases.

CONCLUSION

((64)Cu-DOTA)(n)-trastuzumab-(IRDye800)(m) may be an effective diagnostic imaging agent for staging HER-2-positive breast cancer patients and intraoperative resection.

Targeting HER2: a report on the in vitro and in vivo pre-clinical data supporting trastuzumab as a radioimmunoconjugate for clinical trials

The potential of the HER2-targeting antibody trastuzumab as a radioimmunoconjugate useful for both imaging and therapy was investigated. Conjugation of trastuzumab with the acyclic bifunctional chelator CHX-A"-DTPA yielded a chelate:protein ratio of 3.4 ± 0.3; the immunoreactivity of the antibody unaffected. Radiolabeling was efficient, routinely yielding a product with high specific activity. Tumor targeting was evaluated in mice bearing subcutaneous (s.c.) xenografts of colorectal, pancreatic, ovarian, and prostate carcinomas. High uptake of the radioimmunoconjugate, injected intravenously (i.v.), was observed in each of the models, and the highest tumor %ID/g (51.18 ± 13.58) was obtained with the ovarian (SKOV-3) tumor xenograft. Specificity was demonstrated by the absence of uptake of 111In-trastuzumab by melanoma (A375) s.c. xenografts and 111In-HuIgG by s.c. LS-174T xenografts. Minimal uptake of i.v. injected 111In-trastuzumab in normal organs was confirmed in non-tumor-bearing mice. The in vivo behavior of 111In-trastuzumab in mice bearing intraperitoneal (i.p.) LS-174T tumors resulted in a tumor %ID/g of 130.85 ± 273.34 at 24 h. Visualization of tumor, s.c. and i.p. xenografts, was achieved by γ-scintigraphy and PET imaging. Blood pool was evident as expected, but cleared over time. The blood pharmacokinetics of i.v. and i.p. injected 111In-trastuzumab was determined in mice with and without tumors. The data from these in vitro and in vivo studies supported advancement of radiolabeled trastuzumab into two clinical studies, a Phase 0 imaging study in the Molecular Imaging Program of the National Cancer Institute and a Phase 1 radioimmunotherapy study at the University of Alabama.