Diagnostic usefulness of ¹⁸F-FAMT PET and L-type amino acid transporter 1 (LAT1) expression in oral squamous cell carcinoma

SLC7A5 correlated with malignancies and immunotherapy response in bladder cancer

BACKGROUND

Metabolic reprogramming contributes to bladder cancer development. This study aimed to understand the role of SLC7A5 in bladder cancer.

METHODS

We systematically analyzed the correlation between SLC7A5 and bladder cancer through various approaches, including bioinformatics, western blotting, cell cycle analysis, cell proliferation assays, and invasion experiments. We also investigated the immunological features within the tumor microenvironment (TME), encompassing cancer immune cycles, immune modulators, immune checkpoints, tumor-infiltrating immune cells (TIIC), T cell inflammation scores, and treatment responses. Additionally, for a comprehensive assessment of the expression patterns and immunological roles of SLC7A5, pan-cancer analysis was performed using cancer genomics datasets.

RESULTS

SLC7A5 was associated with adverse prognosis in bladder cancer patients, activating the Wnt pathway and promoting bladder cancer cell cycle progression, proliferation, migration, and invasion. Based on the evidence that SLC7A5 positively correlated with immunomodulators, TIIC, the cancer immune cycle, immune checkpoint and T cell inflammation scores, we also found that SLC7A5 was associated with the inflammatory tumor immune microenvironment. EGFR-targeted therapy, cancer immunotherapy, and radiation therapy were effective for patients with high SLC7A5 expression in bladder cancer. Low SLC7A5 patients were, however, sensitive to targeted therapies and anti-angiogenic therapy, such as blocking β-catenin network, PPAR-γ and FGFR3 signaling. Anti-SLC7A5 combined with cancer immunotherapy may have greater effectiveness than either therapy alone. Furthermore, we observed specific overexpression of SLC7A5 in TME of various cancers.

CONCLUSION

SLC7A5 can predict therapeutic response to immunotherapy, radiotherapy and chemotherapy in bladder cancer patients. Targeting SLC7A5 in combination with immunotherapy may be a potentially appropriate treatment option.

Structure-activity characteristics of phenylalanine analogs selectively transported by L-type amino acid transporter 1 (LAT1)

L-type amino acid transporter 1 (LAT1) is a transmembrane protein responsible for transporting large neutral amino acids. While numerous LAT1-targeted compound delivery for the brain and tumors have been investigated, their LAT1 selectivity often remains ambiguous despite high LAT1 affinity. This study assessed the LAT1 selectivity of phenylalanine (Phe) analogs, focusing on their structure-activity characteristics. We discovered that 2-iodo-L-phenylalanine (2-I-Phe), with an iodine substituent at position 2 in the benzene ring, markedly improves LAT1 affinity and selectivity compared to parent amino acid Phe, albeit at the cost of reduced transport velocity. L-Phenylglycine (Phg), one carbon shorter than Phe, was found to be a substrate for LAT1 with a lower affinity, exhibiting a low level of selectivity for LAT1 equivalent to Phe. Notably, (R)-2-amino-1,2,3,4-tetrahydro-2-naphthoic acid (bicyclic-Phe), with an α-methylene moiety akin to the α-methyl group in α-methyl-L-phenylalanine (α-methyl-Phe), a known LAT1-selective compound, showed similar LAT1 transport maximal velocity to α-methyl-Phe, but with higher LAT1 affinity and selectivity. In vivo studies revealed tumor-specific accumulation of bicyclic-Phe, underscoring the importance of LAT1-selectivity in targeted delivery. These findings emphasize the potential of bicyclic-Phe as a promising LAT1-selective component, providing a basis for the development of LAT1-targeting compounds based on its structural framework.

Exploring Amino Acid Transporters as Therapeutic Targets for Cancer: An Examination of Inhibitor Structures, Selectivity Issues, and Discovery Approaches

Amino acid transporters are abundant amongst the solute carrier family and have an important role in facilitating the transfer of amino acids across cell membranes. Because of their impact on cell nutrient distribution, they also appear to have an important role in the growth and development of cancer. Naturally, this has made amino acid transporters a novel target of interest for the development of new anticancer drugs. Many attempts have been made to develop inhibitors of amino acid transporters to slow down cancer cell growth, and some have even reached clinical trials. The purpose of this review is to help organize the available information on the efforts to discover amino acid transporter inhibitors by focusing on the amino acid transporters ASCT2 (SLC1A5), LAT1 (SLC7A5), xCT (SLC7A11), SNAT1 (SLC38A1), SNAT2 (SLC38A2), and PAT1 (SLC36A1). We discuss the function of the transporters, their implication in cancer, their known inhibitors, issues regarding selective inhibitors, and the efforts and strategies of discovering inhibitors. The goal is to encourage researchers to continue the search and development within the field of cancer treatment research targeting amino acid transporters.

Evaluation of (2S,4S)-4-[18F]FEBGln as a Positron Emission Tomography Tracer for Tumor Imaging

Glutamine metabolism-related tracers have the potential to visualize numerous tumors because glutamine is the second largest source of energy for tumors. (2S,4S)-4-[18F]FEBGln was designed by introducing [18F]fluoroethoxy benzyl on carbon-4 of glutamine. The aim of this study was to investigate the pharmacokinetic properties and tumor positron emission tomography (PET) imaging characteristics of (2S,4S)-4-[18F]FEBGln in detail. The biodistribution results of nude mice bearing MCF-7 tumor showed that (2S,4S)-4-[18F]FEBGln had high initial tumor uptake, and a fast clearance rate, resulting in a high tumor-to-muscle ratio at 30 min postinjection. There was no obvious defluorination in vivo. The micro-PET-CT imaging results of (2S,4S)-4-[18F]FEBGln orthotopic MCF-7 tumor-bearing nude mice were consistent with the biological distribution results. Compared with (2S,4R)-4-[18F]FGln, (2S,4S)-4-[18F]FEBGln showed poor tumor retention, but its clearance in normal tissues was also fast, so it had better PET image contrast than the former. Unlike poor retention in MCF-7-bearing nude mice, (2S,4S)-4-[18F]FEBGln has good retention in NCI-h1975 and 22Rv1 tumor models. Since (2S,4S)-4-[18F]FEBGln has low uptake in normal lungs and high uptake in the bladder, it is expected to be used in the accurate diagnosis of lung cancer but cannot accurately determine prostate cancer. Consistent with the advantages of radiolabeled amino acids in the application of brain tumors, (2S,4S)-4-[18F]FEBGln accurately diagnoses U87MG glioma with higher contrast than [18F]FET and [18F]FDG, and there is a correlation between (2S,4S)-4-[18F]FEBGln uptake and tumor growth cycle. Further kinetic model analysis showed that (2S,4S)-4-[18F]FEBGln was similar to (2S,4R)-4-[18F]FGln, conforming to the one-compartment model and the Logan graphical model, and was expected to assess the size of the glutamine pool of the tumor. Therefore, (2S,4S)-4-[18F]FEBGln is expected to provide a strong imaging basis for the diagnosis, formulation of personalized plans, and efficacy evaluation of glioma, lung cancer, and breast cancer.

Rethinking glutamine metabolism and the regulation of glutamine addiction by oncogenes in cancer

Glutamine, the most abundant non-essential amino acid in human blood, is crucial for cancer cell growth and cancer progression. Glutamine mainly functions as a carbon and nitrogen source for biosynthesis, energy metabolism, and redox homeostasis maintenance in cancer cells. Dysregulated glutamine metabolism is a notable metabolic characteristic of cancer cells. Some carcinogen-driven cancers exhibit a marked dependence on glutamine, also known as glutamine addiction, which has rendered the glutamine metabolic pathway a breakpoint in cancer therapeutics. However, some cancer cells can adapt to the glutamine unavailability by reprogramming metabolism, thus limiting the success of this therapeutic approach. Given the complexity of metabolic networks and the limited impact of inhibiting glutamine metabolism alone, the combination of glutamine metabolism inhibition and other therapeutic methods may outperform corresponding monotherapies in the treatment of cancers. This review summarizes the uptake, transport, and metabolic characteristics of glutamine, as well as the regulation of glutamine dependence by some important oncogenes in various cancers to emphasize the therapeutic potential of targeting glutamine metabolism. Furthermore, we discuss a glutamine metabolic pathway, the glutaminase II pathway, that has been substantially overlooked. Finally, we discuss the applicability of polytherapeutic strategies targeting glutamine metabolism to provide a new perspective on cancer therapeutics.

Tryptophan and its metabolites in normal physiology and cancer etiology

Within the growing field of amino acid metabolism, tryptophan (Trp) catabolism is an area of increasing interest. Trp is essential for protein synthesis, and its metabolism gives rise to biologically active catabolites including serotonin and numerous metabolites in the kynurenine (Kyn) pathway. In normal tissues, the production of Trp metabolites is directly regulated by the tissue-specific expression of Trp-metabolizing enzymes. Alterations of these enzymes in cancers can shift the balance and lead to an increased production of specific byproducts that can function as oncometabolites. For example, increased expression of the enzyme indoleamine 2,3-dioxygenase, which converts Trp into Kyn, leads to an increase in Kyn levels in numerous cancers. Kyn functions as an oncometabolite in cancer cells by promoting the activity of the transcription factor aryl hydrocarbon receptor, which regulates progrowth genes. Moreover, Kyn also inhibits T-cell activity and thus allows cancer cells to evade clearance by the immune system. Therefore, targeting the Kyn pathway has become a therapeutic focus as a novel means to abrogate tumor growth and immune resistance. This review summarizes the biological role and regulation of Trp metabolism and its catabolites with an emphasis on tumor cell growth and immune evasion and outlines areas for future research focus.

Analyzing spatial distribution between 18F-fluorodeoxyglucose and 18F-boronophenylalanine positron emission tomography to investigate selection indicators for boron neutron capture therapy

BACKGROUND

¹⁸F-FDG PET is often utilized to determine BNCT selection due to the limited availability of ¹⁸F-BPA PET, which is performed by synthesizing ¹⁸F into the boron drug used for BNCT, although the uptake mechanisms between those are different. Additionally, only a few non-spatial point parameters, such as maximum SUV (SUV_max), have reported a correlation between those in previous studies. This study aimed to investigate the spatial accumulation pattern between those PET images in tumors, which would be expected to either show higher uptake on ¹⁸F-BPA PET or be utilized in clinical, to verify whether ¹⁸F-FDG PET could be used as a selection indicator for BNCT.

METHODS

A total of 27 patients with 30 lesions (11 squamous cell carcinoma, 9 melanoma, and 10 rhabdomyosarcoma) who received ¹⁸F-FDG and ¹⁸F-BPA PET within 2 weeks were enrolled in this study. The ratio of metabolic tumor volumes (MTVs) to GTV, histogram indices (skewness/kurtosis), and the correlation of total lesion activity (TLA) and non-spatial point parameters (SUV_max, SUV_peak, SUV_min, maximum tumor-to-normal tissue ratio (T_max/N), and T_min/N) were evaluated. After local rigid registration between those images, distances of locations at SUV_max and the center of mass with MTVs on each image and similarity indices were also assessed along its coordinate.

RESULTS

In addition to SUV_max, SUV_peak, and T_max/N, significant correlations were found in TLA. The mean distance in SUV_max was [Formula: see text] and significantly longer than that in the center of mass with MTVs. The ratio of MTVs to GTV, skewness, and kurtosis were not significantly different. However, the similarities of MTVs were considerably low. The similarity indices of Dice similarity coefficient, Jaccard coefficient, and mean distance to agreement for MTV40 were [Formula: see text], [Formula: see text], and [Formula: see text] cm, respectively. Furthermore, it was worse in MTV50. In addition, spatial accumulation patterns varied in cancer types.

CONCLUSIONS

Spatial accumulation patterns in tumors showed low similarity between ¹⁸F-FDG and ¹⁸F-BPA PET, although the various non-spatial point parameters were correlated. In addition, the spatial accumulation patterns were considerably different in cancer types. Therefore, the selection for BNCT using ¹⁸F-FDG PET should be compared carefully with using ¹⁸F-FBPA PET.

Amino acid transporter LAT1 (SLC7A5) as a molecular target for cancer diagnosis and therapeutics

Cancer cells require a massive supply of nutrients, including sugars and amino acids-the upregulation of transporters for each nutrient contributes to meet the demand. Distinct from glucose transporters, amino acid transporters include ones whose expression is specific to cancer cells. For example, LAT1 (SLC7A5) displays protein expression mostly limited to the plasma membrane of cancer cells. The exceptions are the placental barrier and the blood-brain barrier, where immunohistochemical and mass spectrometric studies have shown LAT1 expression, although their levels are supposed to be lower than those in cancers. The expression of LAT1 has been reported in cancers from various tissue origins, where high LAT1 expression is related to the poor prognosis of patients. LAT1 is essential for cancer cell growth because the pharmacologic inhibition and knockdown/knockout of LAT1 suppress the proliferation of cancer cells and the growth of xenograft tumors. The inhibition of LAT1 suppresses protein synthesis by downregulating the mTORC1 signaling pathway and mobilizing the general amino acid control (GAAC) pathway in cancer cells. LAT1 is, thus, a candidate molecular target for the diagnosis and therapeutics of cancers. ¹⁸F-labeled 3-fluoro-l-α-methyl-tyrosine (FAMT) is used as a LAT1-specific PET probe for cancer detection due to the LAT1 specificity of α-methyl aromatic amino acids. FAMT accumulation is cancer-specific and avoids non-cancer lesions, including inflammation, confirming the cancer-specific expression of LAT1 in humans. Due to the cancer-specific nature, LAT1 can also be used for cancer-specific delivery of anti-tumor agents such as l-para-boronophenylalanine used for boron neutron capture therapy and α-emitting nuclide-labeled LAT1 substrates developed for nuclear medicine treatment. Based on the importance of LAT1 in cancer progression, high-affinity LAT1-specific inhibitors have been developed for anti-tumor drugs. JPH203 (KYT0353) is such a compound designed based on the structure-activity relationship of LAT1 ligands. It is one of the highest-affinity inhibitors with less affecting other transporters. It suppresses tumor growth in vivo without significant toxicity in preclinical studies at doses enough to suppress tumor growth. In the phase-I clinical trial, JPH203 appeared to provide promising activity. Because the mechanisms of action of LAT1 inhibitors are novel, with or without combination with other anti-tumor drugs, they could contribute to the treatment of cancers that do not respond to current therapy. The LAT1-specific PET probe could also be used as companion diagnostics of the LAT1-targeting therapies to select patients to whom therapeutic benefits could be expected. Recently, the cryo-EM structure of LAT1 has been solved, which would facilitate the understanding of the mechanisms of the dynamic interaction of ligands and the binding site, and further designing new compounds with higher activity.

α-Emitting cancer therapy using 211 At-AAMT targeting LAT1

α-Methyl-l-tyrosine (AMT) has a high affinity for the cancer-specific l-type amino acid transporter 1 (LAT1). Therefore, we established an anti-cancer therapy, with ²¹¹ At-labeled α-methyl-l-tyrosine (²¹¹ At-AAMT) as a carrier of ²¹¹ At into tumors. ²¹¹ At-AAMT had high affinity for LAT1, inhibited tumor cell growth, and induced DNA double-stranded breaks in vitro. We evaluated the accumulation of ²¹¹ At-AAMT in vivo and the role of LAT1. Treatment with 0.4 MBq/mouse ²¹¹ At-AAMT inhibited tumor growth in the PANC-1 tumor model and 1 MBq/mouse ²¹¹ At-AAMT inhibited metastasis in the lung of the B16F10 metastasis model. Our results suggested that ²¹¹ At would be useful for anti-cancer therapy and that LAT1 is suitable as a target for radionuclide therapy.

Review of the Correlation of LAT1 With Diseases: Mechanism and Treatment

LAT1 is a member of the system L transporter family. The main role of the LAT1 is to transport specific amino acids through cell membranes to provide nutrients to cells and participate in several metabolic pathways. It also contributes to the transport of hormones and some drugs, which are essential for the development and treatment of some diseases. In recent years, many studies have shown that LAT1 is related to cancer, obesity, diabetes, and other diseases. However, the specific mechanism underlying the influence of LAT1 on such conditions remains unclear. Through the increasing number of studies on LAT1, we have obtained a preliminary understanding on the function of LAT1 in diseases. These studies also provide a theoretical basis for finding treatments for LAT1-related diseases, such as cancer. This review summarizes the function and mechanism of LAT1 in different diseases and the treatment of LAT1-related diseases. It also provides support for the development of novel and reliable disease treatments.

L-Type amino acid transporter 1 as a target for drug delivery

Our growing understanding of membrane transporters and their substrate specificity has opened a new avenue in the field of targeted drug delivery. The L-type amino acid transporter 1 (LAT1) has been one of the most extensively investigated transporters for delivering drugs across biological barriers. The transporter is predominantly expressed in cerebral cortex, blood-brain barrier, blood-retina barrier, testis, placenta, bone marrow and several types of cancer. Its physiological function is to mediate Na⁺ and pH independent exchange of essential amino acids: leucine, phenylalanine, etc. Several drugs and prodrugs designed as LAT1 substrates have been developed to improve targeted delivery into the brain and cancer cells. Thus, the anti-parkinsonian drug, L-Dopa, the anti-cancer drug, melphalan and the anti-epileptic drug gabapentin, all used in clinical practice, utilize LAT1 to reach their target site. These examples provide supporting evidence for the utility of the LAT1-mediated targeted delivery of the (pro)drug. This review comprehensively summarizes recent advances in LAT1-mediated targeted drug delivery. In addition, the use of LAT1 is critically evaluated and limitations of the approach are discussed.

Image screening for maxillo-mandibular actinomycosis with CT, 18F-FDG-PET/CT, and 18F-α-methyl tyrosine PET/CT

OBJECTIVES

Clinical features and imaging findings of maxillo-mandibular actinomycosis are similar to those of intraosseous carcinoma. The purpose of this study is to clarify the characteristics of the imaging findings for screening of maxillo-mandibular actinomycosis using CT and PET.

METHODS

Reports on maxillo-mandibular actinomycosis published between 1997 and 2016 were searched in PubMed using "actinomycosis," "maxilla," and "mandibular" as keywords. Ten cases suspected to have malignant tumors on diagnostic imaging findings were selected. In addition, three patients who visited Gunma University Hospital were also included. The 13 total cases were subjected to a pooled analysis of diagnostic screening of maxillo-mandibular actinomycosis using CT, ¹⁸F-FDG-PET/CT (FDG-PET/CT) and ¹⁸F-α-methyl tyrosine PET/CT (FAMT-PET/CT). Additionally, cases of intraosseous carcinoma were analyzed as comparative controls to investigate the difference between maxillo-mandibular actinomycosis and intraosseous carcinoma on CT imaging.

RESULTS

CT images of the 13 cases with maxillo-mandibular actinomycosis were investigated; spotty-type bone resorption was observed in 66.7% (8/12). Moreover, FDG-PET/CT showed abnormal accumulation, but FAMT-PET/CT showed no apparent abnormal accumulation.

CONCLUSIONS

Clinical and imaging findings of maxillo-mandibular actinomycosis are similar to those of intraosseous carcinoma. Differential diagnostic screening can confirm spotty-type bone resorption in cortical bone with CT and specific accumulation in malignant tumors with FAMT-PET/CT. This screening facilitates the rapid implementation of therapeutic interventions.

Targeting Cellular Metabolism Modulates Head and Neck Oncogenesis

Considering the great energy and biomass demand for cell survival, cancer cells exhibit unique metabolic signatures compared to normal cells. Head and neck squamous cell carcinoma (HNSCC) is one of the most prevalent neoplasms worldwide. Recent findings have shown that environmental challenges, as well as intrinsic metabolic manipulations, could modulate HNSCC experimentally and serve as clinic prognostic indicators, suggesting that a better understanding of dynamic metabolic changes during HNSCC development could be of great benefit for developing adjuvant anti-cancer schemes other than conventional therapies. However, the following questions are still poorly understood: (i) how does metabolic reprogramming occur during HNSCC development? (ii) how does the tumorous milieu contribute to HNSCC tumourigenesis? and (iii) at the molecular level, how do various metabolic cues interact with each other to control the oncogenicity and therapeutic sensitivity of HNSCC? In this review article, the regulatory roles of different metabolic pathways in HNSCC and its microenvironment in controlling the malignancy are therefore discussed in the hope of providing a systemic overview regarding what we knew and how cancer metabolism could be translated for the development of anti-cancer therapeutic reagents.

The L-type amino acid transporter LAT1 inhibits osteoclastogenesis and maintains bone homeostasis through the mTORC1 pathway

L-type amino acid transporter 1 (LAT1), which is encoded by solute carrier transporter 7a5 (Slc7a5), plays a crucial role in amino acid sensing and signaling in specific cell types, contributing to the pathogenesis of cancer and neurological disorders. Amino acid substrates of LAT1 have a beneficial effect on bone health directly and indirectly, suggesting a potential role for LAT1 in bone homeostasis. Here, we identified LAT1 in osteoclasts as important for bone homeostasis. Slc7a5 expression was substantially reduced in osteoclasts in a mouse model of ovariectomy-induced osteoporosis. The osteoclast-specific deletion of Slc7a5 in mice led to osteoclast activation and bone loss in vivo, and Slc7a5 deficiency increased osteoclastogenesis in vitro. Loss of Slc7a5 impaired activation of the mechanistic target of rapamycin complex 1 (mTORC1) pathway in osteoclasts, whereas genetic activation of mTORC1 corrected the enhanced osteoclastogenesis and bone loss in Slc7a5-deficient mice. Last, Slc7a5 deficiency increased the expression of nuclear factor of activated T cells, cytoplasmic 1 (Nfatc1) and the nuclear accumulation of NFATc1, a master regulator of osteoclast function, possibly through the canonical nuclear factor κB pathway and the Akt-glycogen synthase kinase 3β signaling axis, respectively. These findings suggest that the LAT1-mTORC1 axis plays a pivotal role in bone resorption and bone homeostasis by modulating NFATc1 in osteoclasts, thereby providing a molecular connection between amino acid intake and skeletal integrity.

18F-FDG and 18F-FAMT PET-derived metabolic parameters predict outcome of oral squamous cell carcinoma

Objectives

L-3-[¹⁸F]-Fluoro-α-methyl tyrosine (FAMT), an amino acid positron emission tomography (PET) tracer, complements [¹⁸F]-fluorodeoxyglucose (FDG) in the diagnosis of malignancies. We compared the predictive ability of FAMT PET versus FDG PET regarding metastatic oral squamous cell carcinoma (OSCC) outcomes for distant metastasis, including lymph node metastasis, and identified the relevant metabolic parameters for each.

Methods

We enrolled 160 patients with OSCC who underwent PET/computed tomography using FDG and FAMT before treatment. Outcomes were assessed using clinicopathological characteristics such as the standardized uptake value (SUV_max, SUV_peak), metabolic tumor volume (MTV), and total lesion glycolysis or total lesion retention. Univariate and multivariate Cox proportional hazards models were used to identify the independent predictors of disease-free survival (DFS) and overall survival (OS) during an average follow-up time of 1401.7 and 1646.0 days, respectively. Areas under the receiver operating characteristic curves were analyzed for the accuracy and predictive value of imaging parameters.

Results

Clinical parameters (excluding age) and PET metabolic parameters were significantly associated with OS. Multivariate analysis showed that an infiltrative growth pattern [p = 0.034, hazard ratio (HR) = 2.30], and the FDG-measured SUV_peak (p = 0.045, HR = 2.45) were independent risk factors for DFS and that lymph node metastasis (p = 0.03, HR = 2.57) and the FAMT-measured MTV (p = 0.004, HR = 3.65) were independent risk factors for OS.

Conclusions

In patients with OSCC, FDG PET predicted DFS, whereas FAMT predicted OS. The two PET tracers, combined with clinical parameters, provide complementary, outcome-related diagnostic information in OSCC.

Amino acid transporters revisited: New views in health and disease

Amino acid transporters (AATs) are membrane-bound transport proteins that mediate transfer of amino acids into and out of cells or cellular organelles. AATs have diverse functional roles ranging from neurotransmission to acid-base balance, intracellular energy metabolism, and anabolic and catabolic reactions. In cancer cells and diabetes, dysregulation of AATs leads to metabolic reprogramming, which changes intracellular amino acid levels, contributing to the pathogenesis of cancer, obesity and diabetes. Indeed, the neutral amino acid transporters (NATs) SLC7A5/LAT1 and SLC1A5/ASCT2 are likely involved in several human malignancies. However, a clinical therapy that directly targets AATs has not yet been developed. The purpose of this review is to highlight the structural and functional diversity of AATs, their diverse physiological roles in different tissues and organs, their wide-ranging implications in human diseases and the emerging strategies and tools that will be necessary to target AATs therapeutically.

Combining laser-assisted microdissection (LAM) and RNA-seq allows to perform a comprehensive transcriptomic analysis of epidermal cells of Arabidopsis embryo

BACKGROUND

Genome-wide characterization of tissue- or cell-specific gene expression is a recurrent bottleneck in biology. We have developed a sensitive approach based on ultra-low RNA sequencing coupled to laser assisted microdissection for analyzing different tissues of the small Arabidopsis embryo.

METHODS AND RESULTS

We first characterized the number of genes detected according to the quantity of tissue yield and total RNA extracted. Our results revealed that as low as 0.02 mm² of tissue and 50 pg of total RNA can be used without compromising the number of genes detected. The optimised protocol was used to compare the epidermal versus mesophyll cell transcriptomes of cotyledons at the torpedo-shaped stage of embryo development. The approach was validated by the recovery of well-known epidermal genes such AtML1 or AtPDF2 and genes involved in flavonoid and cuticular waxes pathways. Moreover, the interest and sensitivity of this approach were highlighted by the characterization of several transcription factors preferentially expressed in epidermal cells.

CONCLUSION

This technical advance unlocks some current limitations of transcriptomic analyses and allows to investigate further and efficiently new biological questions for which only a very small amounts of cells need to be isolated. For instance, it paves the way to increasing the spatial accuracy of regulatory networks in developing small embryo of Arabidopsis or other plant tissues.

Characterization of 5-(2- 18F-fluoroethoxy)-L-tryptophan for PET imaging of the pancreas

Purpose: In diabetes, pancreatic beta cell mass declines significantly prior to onset of fasting hyperglycemia. This decline may be due to endoplasmic reticulum (ER) stress, and the system L amino acid transporter LAT1 may be a biomarker of this process. In this study, we used 5-(2- ¹⁸F-fluoroethoxy)-L-tryptophan ( ¹⁸F-L-FEHTP) to target LAT1 as a potential biomarker of beta cell function in diabetes.

Procedures: Uptake of ¹⁸F-L-FEHTP was determined in wild-type C57BL/6 mice by ex vivo biodistribution. Both dynamic and static positron emission tomography (PET) images were acquired in wild-type and Akita mice, a model of ER stress-induced diabetes, as well as in mice treated with streptozotocin (STZ). LAT1 expression in both groups of mice was evaluated by immunofluorescence microscopy.

Results: Uptake of ¹⁸F-L-FEHTP was highest in the pancreas, and static PET images showed highly specific pancreatic signal. Time-activity curves showed significantly reduced ¹⁸F-L-FEHTP uptake in Akita mice, and LAT1 expression was also reduced. However, mice treated with STZ, in which beta cell mass was reduced by 62%, showed no differences in ¹⁸F-L-FEHTP uptake in the pancreas, and there was no significant correlation of ¹⁸F-L-FEHTP uptake with beta cell mass.

Conclusions: ¹⁸F-L-FEHTP is highly specific for the pancreas with little background uptake in kidney or liver. We were able to detect changes in LAT1 in a mouse model of diabetes, but these changes did not correlate with beta cell function or mass. Therefore, ¹⁸F-L-FEHTP PET is not a suitable method for the noninvasive imaging of changes in beta cell function during the progression of diabetes.

Characterization of 5-(2- 18F-fluoroethoxy)-L-tryptophan for PET imaging of the pancreas

Purpose: In diabetes, pancreatic beta cell mass declines significantly prior to onset of fasting hyperglycemia. This decline may be due to endoplasmic reticulum (ER) stress, and the system L amino acid transporter LAT1 may be a biomarker of this process. In this study, we used 5-(2- 18F-fluoroethoxy)-L-tryptophan ( 18F-L-FEHTP) to target LAT1 as a potential biomarker of beta cell function in diabetes. Procedures: Uptake of 18F-L-FEHTP was determined in wild-type C57BL/6 mice by ex vivo biodistribution. Both dynamic and static positron emission tomography (PET) images were acquired in wild-type and Akita mice, a model of ER stress-induced diabetes, as well as in mice treated with streptozotocin (STZ). LAT1 expression in both groups of mice was evaluated by immunofluorescence microscopy. Results: Uptake of 18F-L-FEHTP was highest in the pancreas, and static PET images showed highly specific pancreatic signal. Time-activity curves showed significantly reduced 18F-L-FEHTP uptake in Akita mice, and LAT1 expression was also reduced. However, mice treated with STZ, in which beta cell mass was reduced by 62%, showed no differences in 18F-L-FEHTP uptake in the pancreas, and there was no significant correlation of 18F-L-FEHTP uptake with beta cell mass. Conclusions:18F-L-FEHTP is highly specific for the pancreas with little background uptake in kidney or liver. We were able to detect changes in LAT1 in a mouse model of diabetes, but these changes did not correlate with beta cell function or mass. Therefore, 18F-L-FEHTP PET is not a suitable method for the noninvasive imaging of changes in beta cell function during the progression of diabetes.

Specific transport of 3-fluoro-l-α-methyl-tyrosine by LAT1 explains its specificity to malignant tumors in imaging

3‐¹⁸F‐l‐α‐methyl‐tyrosine ([¹⁸F]FAMT), a PET probe for tumor imaging, has advantages of high cancer‐specificity and lower physiologic background. FAMT‐PET has been proved useful in clinical studies for the prediction of prognosis, the assessment of therapy response and the differentiation of malignant tumors from inflammation and benign lesions. The tumor uptake of [¹⁸F]FAMT in PET is strongly correlated with the expression of L‐type amino acid transporter 1 (LAT1), an isoform of system L upregulated in cancers. In this study, to assess the transporter‐mediated mechanisms in FAMT uptake by tumors, we examined amino acid transporters for FAMT transport. We synthesized [¹⁴C]FAMT and measured its transport by human amino acid transporters expressed in Xenopus oocytes. The transport of FAMT was compared with that of l‐methionine, a well‐studied amino acid PET probe. The significance of LAT1 in FAMT uptake by tumor cells was confirmed by siRNA knockdown. Among amino acid transporters, [¹⁴C]FAMT was specifically transported by LAT1, whereas l‐[¹⁴C]methionine was taken up by most of the transporters. K_m of LAT1‐mediated [¹⁴C]FAMT transport was 72.7 μM, similar to that for endogenous substrates. Knockdown of LAT1 resulted in the marked reduction of [¹⁴C]FAMT transport in HeLa S3 cells, confirming the contribution of LAT1 in FAMT uptake by tumor cells. FAMT is highly specific to cancer‐type amino acid transporter LAT1, which explains the cancer‐specific accumulation of [¹⁸F]FAMT in PET. This, vice versa, further supports the cancer‐specific expression of LAT1. This study has established FAMT as a LAT1‐specific molecular probe to monitor the expression of a potential tumor biomarker LAT1.

Increase in L-type amino acid transporter 1 expression during cholangiocarcinogenesis caused by liver fluke infection and its prognostic significance

L-type amino acid transporter 1 (LAT1) is highly expressed in various human cancers, including cholangiocarcinoma (CCA), the most common cancer in Northeast Thailand. Chronic inflammation and oxidative stress induced by liver fluke, Opisthorchis viverrini, infection has been recognized as the major cause of CCA in this area. We show here that an increased expression of LAT1 and its co-functional protein CD98 are found during carcinogenesis induced by Ov in hamster CCA tissues. We also demonstrate that oxidative stress induced by H₂O₂ is time-dependent and dramatically activates LAT1 and CD98 expression in immortal cholangiocytes (MMNK1). In addition, H₂O₂ treatment increased LAT1 and CD98 expression, as well as an activated form of AKT and mTOR in MMNK1 and CCA cell lines (KKU-M055 and KKU-M213). We also show that suppression of PI3K/AKT pathway activity with a dual PI3K/mTOR inhibitor, BEZ235, causes a reduction in LAT1 and CD98 expression in KKU-M055 and KKU-M213 in parallel with a reduction of activated AKT and mTOR. Interestingly, high expression of LAT1 in human CCA tissues is a significant prognostic factor for shorter survival. Taken together, our data show that LAT1 expression is significantly associated with CCA progression and cholangiocarcinogenesis induced by oxidative stress. Moreover, the expression of LAT1 and CD98 in CCA is possibly regulated by the PI3K/AKT signaling pathway.

The role of L-type amino acid transporter 1 in human tumors

L-type amino acid transporter 1 (LAT1) is an L-type amino acid transporter and transports large neutral amino acids such as leucine, isoleucine, valine, phenylalanine, tyrosine, tryptophan, methionine, and histidine. LAT1 was found to be highly expressed especially in human cancer tissues, and up-regulated LAT1 can lead to dysfunction in human tumor cells. These findings suggest that LAT1 plays an important role in human tumors. This review provides an overview of the current understanding of LAT1 expression and its clinical significance and function in tumors.

L-type amino acid transporter-1 and CD98 expression in bone and soft tissue tumors

L-type amino acid transporter-1 (LAT1) is expressed in many cancers. We examined LAT1 and CD98 expression immunohistochemically in surgically resected specimens of various bone and soft tissue tumors. Out of 226 cases, 79 (35%) were LAT1(+) and 95 (42%) were CD98(+) . In bone tumors, LAT1 was highly expressed in osteoblastoma (89%), chondrosarcoma (50%), and osteosarcoma (60%); in soft tissue tumors, LAT1 was highly expressed in rhabdomyosarcoma (80%), synovial sarcoma (63%), Ewing's sarcoma (60%), epithelioid sarcoma (100%) and angiosarcoma (100%). In malignant soft tissue tumors, LAT1 expression was associated with higher histological grade. High CD98 expression was seen in many bone tumors of intermediate and high malignancy. Among soft tissue tumors, CD98 was expressed in tendon sheath giant cell tumor and malignant peripheral nerve sheath tumor (57%), Ewing's sarcoma (50%) and undifferentiated sarcoma (64%). Some of the malignant soft tissue tumors expressed both LAT1 and CD98. This study showed that LAT1 and CD98 was expressed in many malignant and intermediate bone tumors, and some malignant soft tissue tumors.

(18)F-FDG uptake on PET correlates with biological potential in early oral squamous cell carcinoma

CONCLUSION

The maximum standardized uptake value (SUVmax) of early oral squamous cell carcinoma (OSCC) may have a role as an imaging biomarker for assessment of malignant potential, including cell metabolism and angiogenesis.

OBJECTIVE

The usefulness of (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) has been proven in various cancers, including OSCC. Moreover, in several carcinomas, the SUVmax of the tumor has been shown to correlate with the histological type, tumor stage, differentiation, and prognosis. Here, we investigated whether the SUVmax of early OSCC was associated with the biological features.

METHODS

Twenty-seven patients with newly diagnosed early OSCC who underwent preoperative FDG-PET and curative surgical resection were included in this study. Tumor sections were stained by immunohistochemistry for glucose transporter 1 (GLUT1), L-type amino acid transporter 1 (LAT1), CD98, microvessels (CD34), cell proliferation marker (Ki-67), and cell cycle regulator (p53). The correlation between SUVmax and clinicopathological findings or the expression level of these molecules was analyzed.

RESULTS

SUVmax of primary OSCC was significantly higher in patients with T2 stage. Moreover, patients whose tumors showed vascular invasion had a tendency to show higher SUVmax. A significant correlation was observed between SUVmax and the expression of LAT1 or microvessel density.

State-of-the-art molecular imaging in esophageal cancer management: implications for diagnosis, prognosis, and treatment

Molecular imaging techniques are increasingly being used in addition to standard imaging methods such as endoscopic ultrasound (EUS) and computed tomography (CT) for many cancers including those of the esophagus. In this review, we will discuss the utility of the most widely used molecular imaging technique, (18)F-fluorodeoxyglucose ((18)F-FDG) positron emission tomography (PET). (18)F-FDG PET has a variety of potential applications ranging from improving staging accuracy at the time of initial diagnosis to assisting in radiation target volume delineation. Furthermore, (18)F-FDG PET can be used to evaluate treatment response after completion of neoadjuvant therapy or potentially during neoadjuvant therapy. Finally, we will also discuss other novel molecular imaging techniques that have potential to further improve cancer care.

Effects of intratumoral inflammatory process on 18F-FDG uptake: pathologic and comparative study with 18F-fluoro-α-methyltyrosine PET/CT in oral squamous cell carcinoma

The accurate depiction of both biologic and anatomic profiles of tumors has long been a challenge in PET imaging. An inflammation, which is innate in the carcinogenesis of oral squamous cell carcinoma (OSCC), frequently complicates the image analysis because of the limitations of (18)F-FDG and maximum standardized uptake values (SUV(max)). New PET parameters, metabolic tumor volume (MTV) and total lesion glycolysis (TLG), as well as (18)F-fluoro-α-methyltyrosine ((18)F-FAMT), a malignancy-specific amino acid-based PET radiotracer, are considered more comprehensive in tumor image analysis. Here, we showed the substantial effects of the intratumoral inflammatory process on (18)F-FDG uptake and further study the possibility of MTV and TLG to predict both tumor biology (proliferation activity) and anatomy (pathologic tumor volume).

METHODS

(18)F-FDG and (18)F-FAMT PET images from 25 OSCC patients were analyzed. SUV(max) on the tumor site was obtained. PET volume computerized-assisted reporting was used to generate a volume of interest to obtain MTV and TLG for (18)F-FDG and total lesion retention (TLR) for (18)F-FAMT. The whole tumor dissected from surgery was measured and sectioned for pathologic analysis of tumor inflammation grade and Ki-67 labeling index.

RESULTS

The high SUV(max) of (18)F-FDG was related to the high inflammation grade. The SUV(max )ratio of (18)F-FDG to (18)F-FAMT was higher in inflammatory tumors (P < 0.05) whereas the corresponding value in tumors with a low inflammation grade was kept low. All (18)F-FAMT parameters were correlated with Ki-67 labeling index (P < 0.01). Pathologic tumor volume predicted from MTV of (18)F-FAMT was more accurate (R = 0.90, bias = 3.4 ± 6.42 cm(3), 95% confidence interval = 0.77-6.09 cm(3)) than that of (18)F-FDG (R = 0.77, bias = 8.1 ± 11.17 cm(3), 95% confidence interval = 3.45-12.67 cm(3)).

CONCLUSION

(18)F-FDG uptake was overestimated by additional uptake related to the intratumoral inflammatory process, whereas (18)F-FAMT simply accumulated in tumors according to tumor activity as evaluated by Ki-67 labeling index in OSCC.

Expression of L-type amino acid transporter 1 (LAT1) as a prognostic and therapeutic indicator in multiple myeloma

L-type amino-acid transporter 1 (LAT1) plays a key role in cell growth and survival. To determine the prognostic significance of LAT1 in multiple myeloma (MM), we investigated the expression of LAT1 and its functional subunit, 4Fc heavy chain (CD98), on myeloma cells by immunohistochemistry in 100 newly diagnosed MM patients. High expression (moderate or strong staining intensity) of LAT1 and CD98 was detected in 56% and 45% of patients, respectively. The LAT1 expression score was positively correlated with Ki-67 index (r = 0.631, P < 0.001), and there was a statistically significant difference in Durie-Salmon stage between patients with high and low LAT1 expression (P = 0.03). In 43 patients treated with melphalan and prednisolone, the overall response rate was significantly higher in the high LAT1 expression group (60.0%) than in the low LAT1 expression group (17.6%) (P = 0.03). Multivariate analysis confirmed that high expression of LAT1 was a significant prognostic factor for predicting poor overall survival independently from the International Staging System (both P = 0.01). Here, we show that the overexpression of LAT1 is significantly associated with high proliferation and poor prognosis in newly diagnosed MM patients. Thus, LAT1 may be a promising pathological marker for identifying high-risk MM.

miR-34a is an intracellular and exosomal predictive biomarker for response to docetaxel with clinical relevance to prostate cancer progression

BACKGROUND

Docetaxel-resistance limits successful treatment of castration resistant prostate cancer. We previously demonstrated that extracellular vesicles (exosomes) may play a role in regulating docetaxel resistance. Here, we investigated intracellular and extracellular (exosomal) miRNAs related to docetaxel resistance.

METHODS

Following global miRNA profiling of cell line models of docetaxel-resistance and their corresponding exosomes, we investigated the clinical relevance of four selected miRNAs (miR-598, miR-34a, miR-146a, miR-148a) in four publically available clinical cohorts representing both primary and advanced disease in tissue and urine specimens. One of these miRNAs, miR-34a was selected for functional evaluation by miRNA inhibition and over-expression in vitro. We further assessed the panel of miRNAs for their combined clinical relevance as a biomarker signature by examining their common predicted targets.

RESULTS

A strong correlation was found between the detection of miRNAs in exosomes and their corresponding cells of origin. Of the miRNAs chosen for further validation and clinical assessment, decreased miR-34a levels showed substantial clinical relevance and so was chosen for further analysis. Manipulating miR-34a in prostate cancer cells confirms that this miRNA regulates BCL-2 and may, in part, regulate response to docetaxel. When combined, these miRNAs are predicted to regulate a range of common mRNA targets, two of which (e.g., SNCA, SCL7A5) demonstrate a strong relationship with prostate cancer progression and poor prognosis.

CONCLUSIONS

This study supports the extracellular environment as an important source of minimally invasive predictive biomarkers representing their cellular origin. Using miR-34a as example, we showed that biomarkers identified in this manner may also hold functional relevance.

Prognostic significance of amino-acid transporter expression (LAT1, ASCT2, and xCT) in surgically resected tongue cancer

BACKGROUND

Amino-acid transporters are necessary for the tumour cell growth and survival, and have a crucial role in the development and invasiveness of cancer cells. But, it remains unclear about the prognostic significance of L-type amino-acid transporter 1 (LAT1), system ASC amino-acid transporter-2 (ASCT2), and xCT expression in patients with tongue cancer. We conducted the clinicopathological study to investigate the protein expression of these amino-acid transporters in tongue cancer.

METHODS

Eighty-five patients with surgically resected tongue cancer were evaluated. Tumour sections were stained by immunohistochemistry for LAT1, ASCT2, xCT, 4F2hc/CD98hc (4F2hc), Ki-67, and microvessel density (MVD) determined by CD34, and p53.

RESULTS

L-type amino-acid transporter 1 and 4F2hc were highly expressed in 61% (52 out of 85) and 45% (38 out of 47), respectively. ASC amino-acid transporter-2 and xCT were positively expressed in 59% (50 out of 85) and 21% (18 out of 85), respectively. The expression of both LAT1 and ASCT2 was significantly associated with disease staging, lymph-node metastasis, lymphatic permeation, 4F2hc expression and cell proliferation (Ki-67). xCT expression indicated a significant association with advanced stage and tumour factor. By univariate analysis, disease staging, lymphatic permeation, vascular invasion, LAT1, ASCT2, 4F2hc, and Ki-67 had a significant relationship with overall survival. Multivariate analysis confirmed that LAT1 was an independent prognostic factor for predicting poor prognosis.

CONCLUSIONS

L-type amino-acid transporter 1 and ASCT2 can serve as a significant prognostic factor for predicting worse outcome after surgical treatment and may have an important role in the development and aggressiveness of tongue cancer.

Biological significance of fluorine-18-α-methyltyrosine (FAMT) uptake on PET in patients with oesophageal cancer

PURPOSE

(18)F-FAMT as an amino-acid tracer for positron emission tomography (PET) is useful for detecting human neoplasms. (18)F-FAMT is accumulated in tumour cells solely via L-type amino-acid transporter 1 (LAT1). This study was conducted to investigate the biological significance of (18)F-FAMT uptake in patients with oesophageal cancer.

METHODS

From April 2008 to December 2011, 42 patients with oesophageal cancer underwent both (18)F-FAMT PET/CT and (18)F-FDG PET/CT before surgical treatment. The immunohistochemical analysis of LAT1, CD98, Ki-67, CD34, p53, p-Akt and p-mTOR was performed on the primary lesions. In vitro experiments were performed to examine the mechanism of (18)F-FAMT uptake.

RESULTS

High uptake of (18)F-FAMT was significantly associated with advanced stage, lymph node metastasis and the expression of LAT1, CD98, Ki-67 and CD34. LAT1 expression yielded a statistically significant correlation with CD98 expression, cell proliferation, angiogenesis and glucose metabolism. In vitro experiments revealed that (18)F-FAMT was specifically transported by LAT1.

CONCLUSIONS

The uptake of (18)F-FAMT within tumour cells is determined by the LAT1 expression and correlated with cell proliferation and angiogenesis in oesophageal cancer. The present experiments also confirmed the presence of LAT1 as an underlying mechanism of (18)F-FAMT accumulation.