Amino Acid Transporters as Potential Therapeutic Targets in Thyroid Cancer

Taurine and Creatine Transporters as Potential Drug Targets in Cancer Therapy

Cancer cells are characterized by uncontrolled growth, proliferation, and impaired apoptosis. Tumour progression could be related to poor prognosis and due to this fact, researchers have been working on novel therapeutic strategies and antineoplastic agents. It is known that altered expression and function of solute carrier proteins from the SLC6 family could be associated with severe diseases, including cancers. These proteins were noticed to play important physiological roles through transferring nutrient amino acids, osmolytes, neurotransmitters, and ions, and many of them are necessary for survival of the cells. Herein, we present the potential role of taurine (SLC6A6) and creatine (SLC6A8) transporters in cancer development as well as therapeutic potential of their inhibitors. Experimental data indicate that overexpression of analyzed proteins could be connected with colon or breast cancers, which are the most common types of cancers. The pool of known inhibitors of these transporters is limited; however, one ligand of SLC6A8 protein is currently tested in the first phase of clinical trials. Therefore, we also highlight structural aspects useful for ligand development. In this review, we discuss SLC6A6 and SLC6A8 transporters as potential biological targets for anticancer agents.

SLC6A14 Depletion Contributes to Amino Acid Starvation to Suppress EMT-Induced Metastasis in Gastric Cancer by Perturbing the PI3K/AKT/mTORC1 Pathway

Metastasis is the main obstacle for the treatment of gastric cancer (GC), leading to low survival rate and adverse outcomes in CG patients. SLC6A14, a general amino acid transporter, can import all the essential amino acids in a manner dependent on the NaCl-generated osmotic gradients. Herein, we constructed GC cell sublines with high (SGC7901-M and MKN28-M) and low (MKN28-NM and SGC7901-NM) metastatic ability. Putative functional genes advancing GC metastasis were identified using mRNA microarray analysis and High-Content Screening. In particular, most significant change with a dampening trend in the migration potentiality of GC cells emerged after SLC6A14 gene was silenced. SLC6A14 expression was positively correlated with the migrated capability of different GC cell lines, and SLC6A14 was also constitutively expressed in GC patients with venous or lymphatic invasion, lymph node, or distant metastasis and poor prognosis, thus prompting SLC6A14 as a nonnegligible presence in supporting GC migration and invasion. Consistently, SLC6A14 depletion drastically depressed GC metastasis in vitro and in vivo. Most importantly, pharmacological blockade and gene silence of SLC6A14 both restricted epithelial-mesenchymal transition- (EMT-) driven GC metastasis, in which attenuated activation of the PI3K/AKT/mTORC1 pathway caused by amino acid starvation was involved. In summary, it is conceivable that targeting SLC6A14 has a tremendous promising for the treatment of metastatic GC.

Excellent physicochemical and sensing characteristics of a Re x O y based pH sensor at low post-deposition annealing temperature

pH monitoring in clinical assessment is pivotal as pH imbalance significantly influences the physiological and extracellular functions of the human body. Metal oxide based pH sensors, a promising alternative to bulky pH electrodes, mostly require complex fabrication, high-temperature post-deposition treatment, and high expenses that inhibit their practical applicability. So, there is still room to develop a straightforward and cost-effective metal oxide based pH sensor comprising high sensitivity and reliability. In this report, a novel solution-processed and low-temperature annealed (220 °C) mixed-valence (vii/vi) oxide of rhenium (Re x O y ) was applied in an electrolyte-insulator-semiconductor (EIS) structure. The annealing effect on morphological, structural, and compositional properties was scrutinized by physical and chemical characterizations. The post-annealed Re x O y exhibited a high pH sensitivity (57.3 mV pH-1, R 2 = 0.99), a lower hysteresis (4.7 mV), and a reduced drift rate (1.7 mV h-1) compared to the as-prepared sample for an analytically acceptable pH range (2-12) along with good stability and reproducibility. The magnified sensing performance originated due to the valence state of Re from Re6+ to Re7+ attributed to each electron transfer for a single H+ ion. The device showed high selectivity for H+ ions, which was confirmed by the interference study with other relevant ions. The feasibility of the sensor was verified by measuring the device in real samples. Hence, the ease-of-fabrication and notable sensing performance of the proposed sensor endorsed its implementation for diagnosing pH-related diseases.

GLUT1 and ASCT2 Protein Expression in Papillary Thyroid Carcinoma Patients and Relation to Hepatitis C Virus: A Propensity-Score Matched Analysis

Purpose

Recently, glucose and amino acid transporters have gradually become a hot topic in thyroid gland biology and cancer research. We aimed to investigate the expressions of glucose transporter 1 (GLUT1) and glutamine transporter 2 (ASCT2) in papillary thyroid carcinoma (PTC) and their clinical significance and relation to HCV-related hepatitis.

Patients and Methods

Screening 202 TC tissue samples against the selection criteria using a propensity-score matched analysis to adjust for age, sex, side of tumor, histopathological variants, TNM staging system, and the positivity for HCV yielded 51 matched (17 HCV positive and 34 HCV negative) PTC samples. The expressions of GLUT1 and ASCT2 expressions were detected by immunohistochemical staining. Kaplan–Meier survival curves were generated for disease-free and overall survival, and multivariate Cox regression analysis was applied to identify predictors for mortality.

Results

Of 51 thyroid cancer tissues, 85% showed positive GLUT1 cytoplasmic staining, and 26% had a high expression score. All thyroid cancer specimens demonstrated ASCT2 cytoplasmic staining with membranous accentuation. Of these, 78% showed a high expression score, and 22% showed weak staining. On stratifying the study cohort based on the HCV status, HCV negative cohort showed a significantly higher immunoreactivity score for GLUT1 (p = 0.004) but not ASCT2 (p = 0.94) than HCV positive group. The expressions of the studied transporters showed no significant associations with the prognostic features of PTC nor the disease-free/overall survival.

Conclusion

GLUT1 and ASCT2 immunohistochemical staining showed positive expression with variable intensity in nearly 85% and 100% of PTC tissue samples compared to normal ones, respectively. Furthermore, GLUT1 protein expression, not ASCT2, showed a higher immunoreactivity score in PTC patients who are negative for HCV than cancer patients with positive HCV. Meanwhile, the expression of both protein markers was not associated with the clinicopathological characteristics of the studied PTC patients. Further large-scale multicenter studies are recommended to validate the present findings.

Applications of spatially resolved omics in the field of endocrine tumors

Endocrine tumors derive from endocrine cells with high heterogeneity in function, structure and embryology, and are characteristic of a marked diversity and tissue heterogeneity. There are still challenges in analyzing the molecular alternations within the heterogeneous microenvironment for endocrine tumors. Recently, several proteomic, lipidomic and metabolomic platforms have been applied to the analysis of endocrine tumors to explore the cellular and molecular mechanisms of tumor genesis, progression and metastasis. In this review, we provide a comprehensive overview of spatially resolved proteomics, lipidomics and metabolomics guided by mass spectrometry imaging and spatially resolved microproteomics directed by microextraction and tandem mass spectrometry. In this regard, we will discuss different mass spectrometry imaging techniques, including secondary ion mass spectrometry, matrix-assisted laser desorption/ionization and desorption electrospray ionization. Additionally, we will highlight microextraction approaches such as laser capture microdissection and liquid microjunction extraction. With these methods, proteins can be extracted precisely from specific regions of the endocrine tumor. Finally, we compare applications of proteomic, lipidomic and metabolomic platforms in the field of endocrine tumors and outline their potentials in elucidating cellular and molecular processes involved in endocrine tumors.

Evaluation of 3-l- and 3-d-[18F]Fluorophenylalanines as PET Tracers for Tumor Imaging

Simple Summary

The early detection and treatment of malignant brain tumors can significantly improve the survival time and life quality of affected patients. Whereas positron emission tomography (PET) with O-(2-[¹⁸F]fluoroethyl)tyrosine ([¹⁸F]FET) offers improved diagnostic accuracy compared to other imaging methods, there is still a need for PET tracers with better tumor-specificity. A higher protein incorporation rate, as well as a higher affinity for the amino acid transporter LAT1, could provide probes with superior image quality compared to [¹⁸F]FET. The aim of the present study was a preclinical evaluation of the two enantiomeric phenylalanine (Phe) analogues, 3-l- and 3-d-[¹⁸F]fluorophenylalanine ([¹⁸F]FPhes), as possible alternatives to [¹⁸F]FET. Based on promising in vitro evaluation results, the radiolabeled amino acids were studied in vivo in two subcutaneous and one orthotopic rodent tumor xenograft models using µPET. The results show that 3-l- and 3-d-[¹⁸F]FPhe enable high-quality visualization of tumors with certain advantages over [¹⁸F]FET, making them promising candidates for further preclinical and clinical evaluations.

Abstract

Purpose: The preclinical evaluation of 3-l- and 3-d-[¹⁸F]FPhe in comparison to [¹⁸F]FET, an established tracer for tumor imaging. Methods: In vitro studies were conducted with MCF-7, PC-3, and U87 MG human tumor cell lines. In vivo µPET studies were conducted in healthy rats with/without the inhibition of peripheral aromatic l-amino acid decarboxylase by benserazide pretreatment (n = 3 each), in mice bearing subcutaneous MCF-7 or PC-3 tumor xenografts (n = 10), and in rats bearing orthotopic U87 MG tumor xenografts (n = 14). Tracer accumulation was quantified by SUV_max, SUV_mean and tumor-to-brain ratios (TBrR). Results: The uptake of 3-l-[¹⁸F]FPhe in MCF-7 and PC-3 cells was significantly higher relative to [¹⁸F]FET. The uptake of all three tracers was significantly reduced by the suppression of amino acid transport systems L or ASC. 3-l-[¹⁸F]FPhe but not 3-d-[¹⁸F]FPhe exhibited protein incorporation. In benserazide-treated healthy rats, brain uptake after 42–120 min was significantly higher for 3-d-[¹⁸F]FPhe vs. 3-l-[¹⁸F]FPhe. [¹⁸F]FET showed significantly higher uptake into subcutaneous MCF-7 tumors (52–60 min p.i.), while early uptake into orthotopic U87 MG tumors was significantly higher for 3-l-[¹⁸F]FPhe (SUV_max: 3-l-[¹⁸F]FPhe, 107.6 ± 11.3; 3-d-[¹⁸F]FPhe, 86.0 ± 4.3; [¹⁸F]FET, 90.2 ± 7.7). Increased tumoral expression of LAT1 and ASCT2 was confirmed immunohistologically. Conclusion: Both novel tracers enable accurate tumor delineation with an imaging quality comparable to [¹⁸F]FET.

Next-Generation Molecular Imaging of Thyroid Cancer

An essential aspect of thyroid cancer (TC) management is personalized and precision medicine. Functional imaging of TC with radioiodine and [18F]FDG has been frequently used in disease evaluation for several decades now. Recently, advances in molecular imaging have led to the development of novel tracers based on aptamer, peptide, antibody, nanobody, antibody fragment, and nanoparticle platforms. The emerging targets-including HER2, CD54, SHP2, CD33, and more-are promising targets for clinical translation soon. The significance of these tracers may be realized by outlining the way they support the management of TC. The provided examples focus on where preclinical investigations can be translated. Furthermore, advances in the molecular imaging of TC may inspire the development of novel therapeutic or theranostic tracers. In this review, we summarize TC-targeting probes which include transporter-based and immuno-based imaging moieties. We summarize the most recent evidence in this field and outline how these emerging strategies may potentially optimize clinical practice.

Genetic Engineering in Combination with Semi-Synthesis Leads to a New Route for Gram-Scale Production of the Immunosuppressive Natural Product Brasilicardin A

Brasilicardin A (1) consists of an unusual anti/syn/anti-perhydrophenanthrene skeleton with a carbohydrate side chain and an amino acid moiety. It exhibits potent immunosuppressive activity, yet its mode of action differs from standard drugs that are currently in use. Further pre-clinical evaluation of this promising, biologically active natural product is hampered by restricted access to the ready material, as its synthesis requires both a low-yielding fermentation process using a pathogenic organism and an elaborate, multi-step total synthesis. Our semi-synthetic approach included a) the heterologous expression of the brasilicardin A gene cluster in different non-pathogenic bacterial strains producing brasilicardin A aglycone (5) in excellent yield and b) the chemical transformation of the aglycone 5 into the trifluoroacetic acid salt of brasilicardin A (1 a) via a short and straightforward five-steps synthetic route. Additionally, we report the first preclinical data for brasilicardin A.