Aizhi Zhu

CXC Chemokine Receptor-4 Antagonist Blocks Both Growth of Primary Tumor and Metastasis of Head and Neck Cancer in Xenograft Mouse Models

Squamous cell carcinoma of the head and neck (SCCHN) metastasizes to the lymph nodes and lungs. We have generated previously an orthotopic mouse model for head and neck metastasis and did in vivo selection of SCCHN cells through four rounds of serial metastases. A subpopulation of 686LN cells with high metastatic potential (686LN-Ms) was isolated. When the highly metastatic cells were compared with their low metastatic parental cells (686LN-Ps), we found that CXC chemokine receptor-4 (CXCR4) mRNA levels were significantly higher in the 686LN-Ms cells than the 686LN-Ps cells. Interestingly, the metastatic subclones had lost epithelial morphology and acquired mesenchymal features, which were maintained during cell expansion in vitro. This was featured by decreased E-cadherin and involucrin and increased vimentin and integrin beta(1). These results imply that CXCR4 and epithelial-mesenchymal transition markers can be potential biomarkers to identify the subpopulation of cells with high metastatic potential. Using the orthotopic SCCHN animal model, we showed that anti-CXCR4 treatment suppressed primary tumor growth by inhibiting tumor angiogenesis and prevented lung metastasis. Because the reduction of metastasis seen in the treated group could have resulted from 2-fold reduction in primary tumor size compared with that in the control group, we examined the effects of the CXCR4 antagonist in an experimental metastatic animal model in which 686LN-Ms cells were i.v. injected. 686LN-Ms cells failed to metastasize in the CXCR4 antagonist-treated group, whereas they metastasized to the lungs in the control group. Our data indicate that CXCR4 is an important target to inhibit tumor progression in SCCHN.

Metabolic positron emission tomography imaging in cancer detection and therapy response.

Positron emission tomography (PET) is a noninvasive imaging technique that provides a functional or metabolic assessment of normal tissue or disease conditions. Fluorine 18-fluorodeoxyglucose PET imaging (FDG-PET) is widely used clinically for tumor imaging due to increased glucose metabolism in most types of tumors, and has been shown to improve the diagnosis and subsequent treatment of cancers. We review its use in cancer diagnosis, staging, restaging, and assessment of response to treatment. In addition, other metabolic PET imaging agents in pre-clinical research or clinical trial stages of development are discussed, including amino acid analogs based on increased protein synthesis, and choline, which is based on increased membrane lipid synthesis. Amino acid analogs and choline are more specific to tumor cells than FDG, so they play an important role in differentiating cancers from benign conditions and in the diagnosis of cancers with low FDG uptake or high background FDG uptake. For decades, researchers have shown that tumors display altered metabolic profiles with elevated uptake of glucose, amino acids, and lipids. This can be used for cancer diagnosis and monitoring of the therapeutic response with excellent signal-to-noise ratios.

Development of a unique small molecule modulator of CXCR4.

Background Metastasis, the spread and growth of tumor cells to distant organ sites, represents the most devastating attribute and plays a major role in the morbidity and mortality of cancer. Inflammation is crucial for malignant tumor transformation and survival. Thus, blocking inflammation is expected to serve as an effective cancer treatment. Among anti-inflammation therapies, chemokine modulation is now beginning to emerge from the pipeline. CXC chemokine receptor-4 (CXCR4) and its ligand stromal cell-derived factor-1 (CXCL12) interaction and the resulting cell signaling cascade have emerged as highly relevant targets since they play pleiotropic roles in metastatic progression. The unique function of CXCR4 is to promote the homing of tumor cells to their microenvironment at the distant organ sites. Methodology/Principal Findings We describe the actions of N,N′-(1,4-phenylenebis(methylene))dipyrimidin-2-amine (designated MSX-122), a novel small molecule and partial CXCR4 antagonist with properties quite unlike that of any other reported CXCR4 antagonists, which was prepared in a single chemical step using a reductive amination reaction. Its specificity toward CXCR4 was tested in a binding affinity assay and a ligand competition assay using 18F-labeled MSX-122. The potency of the compound was determined in two functional assays, Matrigel invasion assay and cAMP modulation. The therapeutic potential of MSX-122 was evaluated in three different murine models for inflammation including an experimental colitis, carrageenan induced paw edema, and bleomycin induced lung fibrosis and three different animal models for metastasis including breast cancer micrometastasis in lung, head and neck cancer metastasis in lung, and uveal melanoma micrometastasis in liver in which CXCR4 was reported to play crucial roles. Conclusions/Significance We developed a novel small molecule, MSX-122, that is a partial CXCR4 antagonist without mobilizing stem cells, which can be safer for long-term blockade of metastasis than other reported CXCR4 antagonists.

Current molecular imaging positron emitting radiotracers in oncology.

Molecular imaging is one of the fastest growing areas of medical imaging. Positron emission tomography (PET) has been widely used in the clinical management of patients with cancer. Nuclear imaging provides biological information at the cellular, subcellular, and molecular level in living subjects with non-invasive procedures. In particular, PET imaging takes advantage of traditional diagnostic imaging techniques and introduces positron-emitting probes to determine the expression of indicative molecular targets at different stages of cancer. 18F-fluorodeoxyglucose (18F-FDG), the only FDA approved oncological PET tracer, has been widely utilized in cancer diagnosis, staging, restaging, and even monitoring response to therapy; however, 18F-FDG is not a tumor-specific PET tracer. Over the last decade, many promising tumor-specific PET tracers have been developed and evaluated in preclinical and clinical studies. This review provides an overview of the current non-18F-FDG PET tracers in oncology that have been developed based on tumor characteristics such as increased metabolism, hyperproliferation, angiogenesis, hypoxia, apoptosis, and tumor-specific antigens and surface receptors.

Potential Biomarker of L-type Amino Acid Transporter 1 in Breast Cancer Progression

PurposeL-type amino acid transporter 1 (LAT1) is essential for the transport of large neutral amino acids. However, its role in breast cancer growth remains largely unknown. The purpose of the study is to investigate whether LAT1 is a potential biomarker for the diagnosis and treatment of breast cancer.MethodsLAT1 mRNA and protein levels in breast cancer cell lines and tissues were analyzed. In addition, the effects of targeting LAT1 for the inhibition of breast cancer cell tumorigenesis were assessed with soft agar assay. The imaging of xenograft with anti-1-amino-3-[18F]fluorocyclobutane-1-carboxylic acid (anti-[18F]FACBC) PET was assessed for its diagnostic biomarker potential.ResultsNormal breast tissue or low malignant cell lines expressed low levels of LAT1 mRNA and protein, while highly malignant cancer cell lines and high-grade breast cancer tissue expressed high levels of LAT1. In addition, higher expression levels of LAT1 in breast cancer tissues were consistent with advanced-stage breast cancer. Furthermore, the blockade of LAT1 with its inhibitor, 2-amino-bicyclo[2.2.1]heptane-2-carboxylic acid (BCH), or the knockdown of LAT1 with siRNA, inhibited proliferation and tumorigenesis of breast cancer cells. A leucine analog, anti-[18F]FACBC, has been demonstrated to be an excellent PET tracer for the non-invasive imaging of malignant breast cancer using an orthotopic animal model.ConclusionsThe overexpression of LAT1 is required for the progression of breast cancer. LAT1 represents a potential biomarker for therapy and diagnosis of breast cancer. Anti-[18F]FACBC that correlates with LAT1 function is a potential PET tracer for malignant breast tumor imaging.

Application of Metabolic PET Imaging in Radiation Oncology

Positron emission tomography (PET) is a noninvasive imaging technique that provides functional or metabolic assessment of normal tissue or disease conditions and is playing an increasing role in cancer radiotherapy planning. 18F-Fluorodeoxyglucose PET imaging (FDG-PET) is widely used in the clinic for tumor imaging due to increased glucose metabolism in most types of tumors; its role in radiotherapy management of various cancers is reviewed. In addition, other metabolic PET imaging agents at various stages of preclinical and clinical development are reviewed. These agents include radiolabeled amino acids such as methionine for detecting increased protein synthesis, radiolabeled choline for detecting increased membrane lipid synthesis, and radiolabeled acetate for detecting increased cytoplasmic lipid synthesis. The amino acid analogs choline and acetate are often more specific to tumor cells than FDG, so they may play an important role in differentiating cancers from benign conditions and in the diagnosis of cancers with either low FDG uptake or high background FDG uptake. PET imaging with FDG and other metabolic PET imaging agents is playing an increasing role in complementary radiotherapy planning.

Abstract 5227: Detection of metastatic potential by a novel small molecule F-18 PET imaging agent

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Squamous cell carcinoma (SCC), a malignant tumor of epithelial origin, represents more than 90% of all head and neck cancers. While lymph node metastases are more common in SCCHN patients (∼60%), approximately 20 to 25% of patients with SCCHN develop distant metastases, primarily in the lungs, liver, and bone. We established metastatic SCCHN subclones from a poorly metastatic parental cell line by in vivo selection. These metastatic subclones expressed high levels of CXCR4 chemokine receptor while non-metastatic parental cells did not, which suggests that CXCR4 is required for metastatic progression. CXCR4 plays a key role as a homing receptor to the lymph nodes, lung, liver, and bone. Homing, the mechanism that allows foreign tissue-origin cells to reside and proliferate, is believed to be the rate-limiting step of the multi-step metastatic process. Therefore, CXCR4 overexpression can be a predictor of the metastatic potential and the lethality of tumor cells. Here, we developed a novel small molecule CXCR4-reporting PET tracer. We have identified a novel small molecule CXCR4 antagonist, N, N′-(1,4-phenylenebis(methylene)) dipyrimidin-2-amines (M508F), through rational design by analysis of emerging structural and functional data. Its binding potency (EC50) is <10 nM in a binding affinity assay, with a great inhibitory efficacy against CXCR4/CXCL12-mediated Matrigel invasion and cAMP reduction. [18F]M508F was generated from M508Cl by a one-step chloride substitution. This reaction yield was reproducibly 30%. Biodistribution in mice was studied, and mouse tumor models with primary tumor or lung metastasis were imaged in microPET. Competition assays against cold form [19F]M508F and CXCL12 showed that [19F]M508F or CXCL12 blocked [18F]M508F binding to CXCR4 in a dose-dependent manner. In 30 minute post-injection microPET imaging, [18F]M508F-PET images of an orthotopic SCCHN animal model and an experimental animal model for lung metastasis of SCCHN exhibited fast blood clearance and significant uptake of [18F]M508F in the primary tumor as well as in the lung metastases. To date, several CXCR4 antagonists have been developed. Fujiis group at Kyoto University pioneered development of a series of peptide analogs that exhibited excellent potency against CXCR4. An attempt to label a peptidic antagonist for single photon emission computed tomography (SPECT) with In-111 showed that the blood clearance was too slow for 18F-PET. Currently, [64Cu]AMD3100, a metal-chelating bicyclam, is the only reported PET tracer for CXCR4 imaging. [18F]M508F reported here has a CXCR4 binding affinity over 50 times better than [64Cu]AMD3100. So far, we have finished toxicity studies in macaque monkeys and we are in a process of eIND filing for clinical translation. As the first CXCR4-detecting [18F]PET tracer, [18F]M508F has a great potential to become a clinical imaging agent for prediction and early detection of SCCHN metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5227. doi:10.1158/1538-7445.AM2011-5227

Abstract 2736: Overexpression of L-type amino acid transporter-1 in breast cancer cells and tissues: potential association with growth and progression of tumors

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC For a tumor to constantly proliferate, malignant cells require nutrients, especially glucose and amino acids. There is abundant evidence that tumor growth depends heavily on glucose uptake. The L-type amino acid transporter 1 (LAT1) is a major nutrient transport system responsible for the transport of large neutral essential amino acids. In the present study, we analyzed expression levels of LAT1 mRNA and protein with RT-PCR, Western blot and immunohistochemical staining. The results showed that normal breast tissues or low malignant cell lines expressed low levels of LAT1 mRNA and protein, while LAT1 was overexpressed in highly malignant cancer cell lines and high grade breast cancer tissues. In addition, we found higher expression levels of LAT1 in breast cancer tissues were consistent with high stages of breast cancer. Furthermore, we demonstrated that blockade of LAT1 with its inhibitor, 2-amino-bicyclo[2.2.1]heptane-2-carboxylic acid (BCH), or knockdown of LAT1 with transfection of specific siRNA inhibited proliferation of breast cancer cells. A variety of 11C- and 18F-labeled amino acids have been studied for potential use in positron emission tomography (PET) oncology. A non-natural, not-metabolizable leucine analog, anti-1-amino-3-[18F]fluorocyclobutane-1-carboxylic acid ([18F]FACBC), has shown superior tumor/normal brain ratio. We tested whether [18F]FACBC would also be an excellent PET tracer for malignant breast cancer imaging using an orthotopic breast cancer animal model and an experimental animal model of breast cancer metastasis. Our results support that [18F]FACBC could be a useful PET tracer for non-invasive imaging of breast cancer. These findings suggest that overexpression of LAT1 is necessary for proliferation of breast cancer cells and may contribute to progression of tumors. LAT1 may represent a potential target for diagnosis of breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2736.