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

PURPOSE

L-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.

METHODS

LAT1 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-[(18)F]fluorocyclobutane-1-carboxylic acid (anti-[(18)F]FACBC) PET was assessed for its diagnostic biomarker potential.

RESULTS

Normal 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-[(18)F]FACBC, has been demonstrated to be an excellent PET tracer for the non-invasive imaging of malignant breast cancer using an orthotopic animal model.

CONCLUSIONS

The overexpression of LAT1 is required for the progression of breast cancer. LAT1 represents a potential biomarker for therapy and diagnosis of breast cancer. Anti-[(18)F]FACBC that correlates with LAT1 function is a potential PET tracer for malignant breast tumor imaging.

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

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.

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.

Antitumor effect of 2-methoxyestradiol in a rat orthotopic brain tumor model

Grade 4 malignant glioma (GBM) is a fatal disease despite aggressive surgical and adjuvant therapies. The hallmark of GBM tumors is the presence of pseudopalisading necrosis and microvascular proliferation. These tumor cells are hypoxic and express hypoxia-inducible factor-1 (HIF-1), a prosurvival transcription factor that promotes formation of neovasculature through activation of target genes, such as vascular endothelial growth factor. Here, we evaluated whether 2-methoxyestradiol, a microtubule and HIF-1 inhibitor, would have therapeutic potential for this disease in a 9L rat orthotopic gliosarcoma model using a combination of noninvasive imaging methods: magnetic resonance imaging to measure the tumor volume and bioluminescence imaging for HIF-1 activity. After imaging, histologic data were subsequently evaluated to elucidate the drug action mechanism in vivo. Treatment with 2-methoxyestradiol (60-600 mg/kg/d) resulted in a dose-dependent inhibition of tumor growth. This effect was also associated with improved tumor oxygenation as assessed by pimonidazole staining, decreased HIF-1alpha protein levels, and microtubule destabilization as assessed by deacetylation. Our results indicate that 2-methoxyestradiol may be a promising chemotherapeutic agent for the treatment of malignant gliomas, with significant growth inhibition. Further studies are needed to assess the effect of low or intermediate doses of 2-methoxyestradiol in combination with chemotherapeutic agents in clinical studies focused on malignant gliomas. In addition to showing tumor growth inhibition, we identified three potential surrogate biomarkers to determine the efficacy of 2-methoxyestradiol therapy: decreased HIF-1alpha levels, alpha-tubulin acetylation, and degree of hypoxia as determined by pimonidazole staining.

Lower expression of CXCR4 in lymph node metastases than in primary breast cancers: potential regulation by ligand-dependent degradation and HIF-1alpha

Stromal-derived factor-1 (SDF-1) is a unique ligand of the CXC chemokine receptor 4 (CXCR4), which is critically involved in the metastasis of breast cancer. High levels of SDF-1 in the common destination organs of metastasis, such as the lymph nodes, lungs, liver, and bones, attract CXCR4-positive tumor cells. The interaction between SDF-1 and CXCR4 leads to the activation of specific signaling pathways, allowing for homing and metastatic progression. However, regulation of CXCR4 expression at the metastatic organ site is not well-documented. We detected the expression of CXCR4 and hypoxia inducible factor (HIF)-1alpha in breast tumor tissues by immunohistochemical staining and analyzed SDF-1 in primary tumors and lymph nodes using real-time RT-PCR. Compared to the corresponding metastasized tumors in the lymph nodes, primary invasive carcinomas showed more intense staining for CXCR4, particularly on the cellular membrane. Both primary tumors and lymph node metastases exhibited higher levels of CXCR4 expression compared to non-neoplastic breast tissues. Therefore, we hypothesized that the tumor environment in the lymph nodes may cause the reduction of CXCR4 levels in the metastatic tumor cells because of: (1) high SDF-1 levels and (2) lower levels of HIF-1alpha. Our in vitro data demonstrated that high levels of SDF-1 can induce the internalization and degradation of CXCR4 through the lysosome pathway. In addition, lower levels of HIF-1alpha in the lymph node metastases, probably induced by the less hypoxic environment, further lowered CXCR4 levels. These results indicate that ligand-dependent degradation and lower HIF-1alpha levels may be potential causes of lowered levels of CXCR4 in the lymph nodes compared to the primary tumors. Our study suggests that CXCR4 levels in tumor cells are regulated by its microenvironment. These findings may enhance our ability to understand the biological behavior of breast cancers.

Mitotic regulation of protein 4.1R involves phosphorylation by cdc2 kinase

The nonerythrocyte isoform of the cytoskeletal protein 4.1R (4.1R) is associated with morphologically dynamic structures during cell division and has been implicated in mitotic spindle function. In this study, we define important 4.1R isoforms expressed in interphase and mitotic cells by RT-PCR and mini-cDNA library construction. Moreover, we show that 4.1R is phosphorylated by p34cdc2 kinase on residues Thr60 and Ser679 in a mitosis-specific manner. Phosphorylated 4.1R135 isoform(s) associate with tubulin and Nuclear Mitotic Apparatus protein (NuMA) in intact HeLa cells in vivo as well as with the microtubule-associated proteins in mitotic asters assembled in vitro. Recombinant 4.1R135 is readily phosphorylated in mitotic extracts and reconstitutes mitotic aster assemblies in 4.1R-immunodepleted extracts in vitro. Furthermore, phosphorylation of these residues appears to be essential for the targeting of 4.1R to the spindle poles and for mitotic microtubule aster assembly in vitro. Phosphorylation of 4.1R also enhances its association with NuMA and tubulin. Finally, we used siRNA inhibition to deplete 4.1R from HeLa cells and provide the first direct genetic evidence that 4.1R is required to efficiently focus mitotic spindle poles. Thus, we suggest that 4.1R is a member of the suite of direct cdc2 substrates that are required for the establishment of a bipolar spindle.

Alpha-expansins in the semiaquatic ferns Marsilea quadrifolia and Regnellidium diphyllum: evolutionary aspects and physiological role in rachis elongation

To investigate the evolutionary history of expansins and their role in cell elongation in early land plants, we isolated two alpha-expansin genes, Mq-EXP1 and Rd-EXP1, respectively, from the semiaquatic ferns Marsilea quacdrifolia L. and Regnellidium diphyllum Lindm. The deduced amino acid sequences of the fern expansins exhibit a high degree of identity to those of seed plants, showing that expansin genes were conserved during the evolution of vascular plants. Gel-blot analysis of M. quadrifolia and R. diphyllum genomic DNA indicated that, in both ferns, alpha-expansins are encoded by multigene families. Expression of alpha-expansin genes probed with Mq-EXP1 was confined to the elongating region of the Marsilea rachis. Cell-wall proteins of M. quadrifolia induced in-vitro extension of acidified cucumber cell walls. In R. diphyllum, expression of Rd-EXP1 increased when elongation of the rachis was enhanced by submergence or ethylene. These results indicate that alpha-expansins act as wall-loosening proteins in ferns, as has been proposed for angiosperms. In addition, Rd-EXP1 may play a role in mediating elongation of the rachis in submerged plants.

Altered expression of expansin modulates leaf growth and pedicel abscission in Arabidopsis thaliana

Expansins are cell-wall-loosening proteins that induce stress relaxation and extension of plant cell walls. To evaluate their hypothesized role in cell growth, we genetically manipulated expansin gene expression in Arabidopsis thaliana and assessed the consequent changes in growth and cell-wall properties. Various combinations of promoters were used to drive antisense and sense sequences of AtEXP10, which is maximally expressed in the growing leaf and at the base of the pedicel. Compared with controls, antisense lines had smaller rosettes because of shorter petioles and leaf blades and often acquired a twisted leaf morphology. Petiole cells from antisense plants were smaller than controls and their cell walls were significantly less extensible in vitro. Sense plants had slightly longer petioles, larger leaf blades, and larger cells than controls. Abscission at the base of the pedicel, where AtEXP10 is endogenously expressed, was enhanced in sense plants but reduced in antisense lines. These results support the concept that expansins function endogenously as cell-wall-loosening agents and indicate that expansins have versatile developmental roles that include control of organ size, morphology, and abscission.

Tissue localization of expansins in deepwater rice

Expansins are a family of proteins capable of inducing stress relaxation of isolated cell walls. In earlier studies, we showed that the expression of expansin genes in deepwater rice (Oryza sativa L.) is regulated by developmental, hormonal and environmental stimuli. Here, we describe the spatial distribution pattern of expansin transcripts and proteins in tissues and organs of deepwater rice using in situ mRNA hybridization and immunohistochemical analysis. Expansin transcripts and proteins are present at high levels in the growing internodal epidermis, which has thick cell walls and acts, therefore, as a growth-limiting cell layer. Expansins are also concentrated in the differentiating vascular bundles of internodes. In the primary root, expansins are predominantly expressed in the tip region, particularly in the epidermis, differentiating vascular cylinder, and around the pericyle. Developing adventitious roots and lateral root primordia also contain high levels of expansin mRNA. In the shoot apex, expansin transcripts are abundant in the emerging leaf primordia. Our results indicate that expansins play an important role in the expansion and differentiation of plant tissues and organs.

Expression of expansin genes is correlated with growth in deepwater rice

Expansins are a family of proteins that catalyze long-term extension of isolated cell walls. Previously, two expansin proteins have been isolated from internodes of deepwater rice, and three rice expansin genes, Os-EXP1, Os-EXP2, and Os-EXP3, have been identified. We report here on the identification of a fourth rice expansin gene, Os-EXP4, and on the expression pattern of the rice expansin gene family in deepwater rice. Rice expansin genes show organ-specific differential expression in the coleoptile, root, leaf, and internode. In these organs, there is increased expression of Os-EXP1, Os-EXP3, and Os-EXP4 in developmental regions where elongation occurs. This pattern of gene expression is also correlated with acid-induced in vitro cell wall extensibility. Submergence and treatment with gibberellin, both of which promote rapid internodal elongation, induced accumulation of Os-EXP4 mRNA before the rate of growth started to increase. Our results indicate that the expression of expansin genes in deepwater rice is differentially regulated by developmental, hormonal, and environmental signals and is correlated with cell elongation.

Expansins in deepwater rice internodes

Cell walls of deepwater rice (Oryza sativa L.) internodes undergo long-term extension (creep) when placed under tension in acidic buffers. This is indicative of the action of the cell wall-loosening protein expansin. Wall extension had a pH optimum of around 4.0 and was abolished by boiling. Acid-induced extension of boiled cell walls could be reconstituted by addition of salt-extracted rice or cucumber cell wall proteins. Cucumber expansin antibody recognized a single protein band of 24.5-kD apparent molecular mass on immunoblots of rice cell wall proteins. Expansins were partially purified by concanavalin A affinity chromatography and sulfopropyl (SP) cation-exchange chromatography. The latter yielded two peaks with extension activity (SP20 and SP29), and immunoblot analysis showed that both of these active fractions contained expansin of 24.5-kD molecular mass. The N-terminal amino acid sequence of SP20 expansin is identical to that deduced from the rice expansin cDNA Os-EXP1. The N-terminal amino acid sequence of SP29 expansin matches that deduced from the rice expansin cDNA Os-EXP2 in six of eight amino acids. Our results show that two expansins occur in the cell walls of rice internodes and that they may mediate acid-induced wall extension.

Localization of interleukin-1 in human squamous carcinomas of the head and neck

Recent investigations revealed that interleukin-1 can promote bone resorption by activating osteoclasts. The authors' immunocytochemical studies with monoclonal antibody against human interleukin-1 localized interleukin-1 at the bone resorption site of the squamous carcinomas as well as within the squamous carcinomas. In addition, Western blotting and dot blotting methods were used to isolate interleukin-1 from the extracts of the squamous carcinomas in the head and neck. Finding interleukin-1, a potent bone resorption-stimulating factor, in squamous carcinomas suggests that interleukin-1 might play an important role in the extensive local bone destruction seen in the head and neck patients with squamous carcinomas.

Squamous cell carcinoma of the thyroid: a diagnostic dilemma

Four cases of primary squamous cell carcinoma of the thyroid gland are reported. Thorough evaluation confirmed these lesions to be of primary thyroid origin rather than from metastasis or direct invasion from contiguous structures. These cases illustrate the aggressive nature of the disease and the propensity for local and distant metastases. The clinicopathologic data presented here underscore the challenge in diagnosis and treatment of this rare entity.

The role of needle aspiration biopsy in the selection of patients for thyroidectomy

Fine needle aspiration (FNA) biopsy is gaining in popularity among all diagnostic tests used in the evaluation of patients for thyroidectomy. Its safety and accuracy have been well documented, but criteria regarding when FNA is appropriate are lacking. We retrospectively reviewed our experience with 408 consecutive patients evaluated for thyroid surgery. Two hundred seventy-three ultimately underwent thyroidectomy; 100 of these had preoperative FNA. An additional 135 patients underwent FNA without surgery. Patients who benefited from FNA were those in whom cytologic findings led to surgery for otherwise unsuspected malignancy (15), and those with asymptomatic benign nodules who avoided unnecessary thyroidectomy on the basis of FNA findings (96). FNA is superfluous when clinical conditions mandate surgery. These include nodules that arouse clinical suspicion of malignancy, massive nodules that cause aerodigestive tract compression or cosmetic disfigurement, and nodules extending into the mediastinum. All patients with asymptomatic, clinically benign thyroid nodules should undergo FNA biopsy, as approximately 50% can anticipate significant benefit from the procedure.

Management of substernal and intrathoracic goiters

Goiters that descend into the mediastinum can cause respiratory embarrassment, dysphagia, vascular compression, vocal cord paralysis, and sudden death. Although many such goiters remain clinically silent, their ability to produce sudden and unpredictable respiratory distress is well known. The condition was not considered uncommon in the first half of the twentieth century; some authors reported series of hundreds of thyroidectomies for intrathoracic goiter. Though seen less frequently today, the only effective treatment for mediastinal goiter is surgical removal. We report our experience with the management of 70 consecutive patients with substernal or intrathoracic goiters. The clinical presentation, preoperative evaluation, operative technique, and results and complications of therapy are discussed. Consideration is also given to the pathogenesis of intrathoracic extension. The transcervical approach for resection is emphasized--even goiters extending to the aortic arch were safely removed without requiring sternotomy. A multidisciplinary team approach, including the surgeon, anesthesiologist, and endocrinologist, is essential. Because of more conservative trends in the selection of patients for thyroidectomy, the incidence of mediastinal goiter may be increasing.

Delayed failure of myocutaneous flaps in head and neck reconstruction

Since the concept of myocutaneous flap reconstruction of the head and neck region was introduced it has opened a new approach to surgical management in this area. This flap not only reduced the number of operations as compared to "staged procedure", but also reduced the costs of medical care. We are, however, experiencing significant failures as the applications of this flap are extended. This paper reviews our experience with myocutaneous flaps in 15 partial and total failures. An evaluation of these failures reveals that most occurred 1 1/2 to 3 weeks after reconstruction. The factors predisposing to failure seem related more to technical errors rather than to general factors. Diabetes, peripheral vascular disease, malnutrition and low hemoglobin, and low blood pressure were not major contributors to the failures in our series. Local factors predisposing to failure of myocutaneous flaps can be divided into two large categories--arterial failure and venous failure. In our series of unsuccessful myocutaneous flaps, the major factors appeared to be venous stasis leading to arterial insufficiency. All failures had developed after the initial critical period of flap survival (7-10 days). The following techniques showed an especially high rate of failure: 1. SCM--myocutaneous flap to resurface floor of mouth. 2. Tubed pectoralis myocutaneous flap to reconstruct pharynx and esophagus. 3. Flaps developed with very narrow vascular pedicles. Individual cases representing delayed failure are presented.

Parotid space tumors of non-salivary origin

A review of 700 parotidectomies showed that 98 procedures were performed for parotid space tumors of non-salivary origin. The clinical presentation in this group of patients did not differ significantly from the larger group of salivary tumors except for a higher incidence (12%) of the former in the younger age group. Of the 98 cases, 54 proved to be lymph node tumors, both neoplastic and inflammatory and 44 were tumors of various somatic origins. Among the latter group, bone and joint tumors, vascular lesions and some connective tissue tumors may be recognized preoperatively. Generally, however, the entire group of non-salivary tumors can be distinguished only intra-operatively, if at all. Correct recognition may lead to variations in operative techniques and extent of resection.