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

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.

Association of High LAT1 Expression with Poor Prognosis and Recurrence in Colorectal Cancer Patients Treated with Oxaliplatin-Based Adjuvant Chemotherapy

The mammalian target of rapamycin (mTOR) is often activated in several cancers. We focused on two mTOR regulatory mechanisms: oxaliplatin-induced mTOR signaling and L-type amino acid transporter 1 (LAT1)-induced mTOR activation. High LAT1 expression in several cancers is associated with mTOR activation and resistance to chemotherapy. However, the significance of LAT1 has not yet been elucidated in colorectal cancer (CRC) patients treated with post-operative adjuvant chemotherapy. Immunohistochemistry was conducted to examine the significance of membrane LAT1 expression in 98 CRC patients who received adjuvant chemotherapy, including oxaliplatin. In vitro analysis was performed using CRC cell lines to determine the effects of LAT1 suppression on proliferation, oxaliplatin sensitivity, and mTOR signaling. LAT1 expression was associated with cancer aggressiveness and poor prognosis in 98 CRC patients treated with adjuvant chemotherapy. We found that positive LAT1 expression correlated with shorter survival in 43 patients treated with the capecitabine-plus-oxaliplatin (CAPOX) regimen. LAT1 suppression in CRC cells inhibited the proliferation potency and oxaliplatin-induced activation of mTOR signaling, and improved oxaliplatin sensitivity. LAT1 evaluation before adjuvant treatment may therefore be a sensitive marker for oxaliplatin-based regimens. Moreover, LAT1 may be a promising target for patients with refractory CRC.

Monitoring of Current Cancer Therapy by Positron Emission Tomography and Possible Role of Radiomics Assessment

Evaluation of cancer therapy with imaging is crucial as a surrogate marker of effectiveness and survival. The unique response patterns to therapy with immune-checkpoint inhibitors have facilitated the revision of response evaluation criteria using FDG-PET, because the immune response recalls reactive cells such as activated T-cells and macrophages, which show increased glucose metabolism and apparent progression on morphological imaging. Cellular metabolism and function are critical determinants of the viability of active cells in the tumor microenvironment, which would be novel targets of therapies, such as tumor immunity, metabolism, and genetic mutation. Considering tumor heterogeneity and variation in therapy response specific to the mechanisms of therapy, appropriate response evaluation is required. Radiomics approaches, which combine objective image features with a machine learning algorithm as well as pathologic and genetic data, have remarkably progressed over the past decade, and PET radiomics has increased quality and reliability based on the prosperous publications and standardization initiatives. PET and multimodal imaging will play a definitive role in personalized therapeutic strategies by the precise monitoring in future cancer therapy.

Positron Emission Tomography for Response Evaluation in Microenvironment-Targeted Anti-Cancer Therapy

Therapeutic response is evaluated using the diameter of tumors and quantitative parameters of 2-[¹⁸F] fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET). Tumor response to molecular-targeted drugs and immune checkpoint inhibitors is different from conventional chemotherapy in terms of temporal metabolic alteration and morphological change after the therapy. Cancer stem cells, immunologically competent cells, and metabolism of cancer are considered targets of novel therapy. Accumulation of FDG reflects the glucose metabolism of cancer cells as well as immune cells in the tumor microenvironment, which differs among patients according to the individual immune function; however, FDG-PET could evaluate the viability of the tumor as a whole. On the other hand, specific imaging and cell tracking of cancer cell or immunological cell subsets does not elucidate tumor response in a complexed interaction in the tumor microenvironment. Considering tumor heterogeneity and individual variation in therapeutic response, a radiomics approach with quantitative features of multimodal images and deep learning algorithm with reference to pathologic and genetic data has the potential to improve response assessment for emerging cancer therapy.

Uptake of positron emission tomography tracers reflects the tumor immune status in esophageal squamous cell carcinoma

The relationship between the local immune status and cancer metabolism regarding ¹⁸F‐FDG and ¹⁸F‐FAMT uptake in esophageal squamous cell carcinoma (ESCC) remains unknown. The present study examined the correlations between tumor immune status, clinicopathological factors, and positron emission tomography (PET) tracer uptake in ESCC. Forty‐one ESCC patients who underwent ¹⁸F‐FDG PET and ¹⁸F‐FAMT PET before surgery were enrolled in the study. Immunohistochemistry was conducted for programmed death 1 (PD‐1), CD8, Ki‐67, CD34, GLUT1 (¹⁸F‐FDG transporter) and LAT1 (¹⁸F‐FAMT transporter). ESCC specimens with high tumoral PD‐L1 and high CD8‐positive lymphocytes were considered to have “hot tumor immune status.” High PD‐L1 expression (53.7%) was significantly associated with tumor/lymphatic/venous invasion (P = 0.028, 0.032 and 0.018), stage (P = 0.041), CD8‐positive lymphocytes (P < 0.001), GLUT1 (P < 0.001), LAT1 expression (P = 0.006), Ki‐67 labelling index (P = 0.009) and CD34‐positive vessel counts (P < 0.001). SUVmax of ¹⁸F‐FDG was significantly higher in high PD‐L1 cases than in low PD‐L1 cases (P = 0.009). SUVmax of ¹⁸F‐FAMT was significantly higher in high PD‐L1 (P < 0.001), high CD8 (P = 0.012) and hot tumor groups (P = 0.028) than in other groups. High SUVmax of ¹⁸F‐FAMT (≥4.15) was identified as the only predictor of hot tumor immune status. High PET tracer uptake was significantly associated with cancer aggressiveness and hot tumor immune status in ESCC. PET imaging may be an effective tool to predict tumor immune status in ESCC with respect to immune checkpoint inhibitor sensitivity.

A convenient and reproducible method for the synthesis of astatinated 4-[211At]astato-l-phenylalanine via electrophilic desilylation

The 211At-labeled compound, 4-[211At]astato-l-phenylalanine, is one of the most promising amino acid derivatives for use in targeted alpha therapy (TAT) for various cancers. Electrophilic demetallation of a stannyl precursor is the most widely used approach for labeling biomolecules with 211At. However, the low acid-resistance of the stannyl precursor necessitates the use of an N- and C-terminus-protected precursor, which results in a low overall radiochemical yield (RCY) due to the multiple synthetic steps involved. In this study, a deprotected organosilyl compound, 4-triethylsilyl-l-phenylalanine, was employed for the direct synthesis of astatinated phenylalanines. 211At was separately recovered from the irradiated 209Bi target using chloroform (CHCl3) and N-chlorosuccinimide-methanol (NCS-MeOH) solution. The RCYs of 4-[211At]astato-l-phenylalanine obtained from the triethylsilyl precursor with the use of 211At, isolated in CHCl3 and NCS-MeOH solution, were 75% and 64% respectively. In both cases, the retention time of the 4-[211At]astato-l-phenylalanine was found to be about 20 min, which showed reasonable correlation with the retention time of non-radioactive 4-halo-l-phenylalanines (4-chloro-, 4-bromo-, and 4-iodo-l-phenylalanine). The one-step reaction examined in this study involved mild reaction conditions (70 °C) and a short time (10 min) compared to the other currently reported procedures for astatination. Electrophilic desilylation was found to be very effective for the labeling of aromatic amino acids with 211At.

Prognostic value of metabolic tumor volume of pretreatment 18F-FAMT PET/CT in non-small cell lung Cancer

Background

This study aimed to determine the prognostic value of positron emission tomography (PET) metabolic parameters—namely metabolic tumor volume (MTV), total lesion glycolysis (TLG), and total lesion retention (TLR)—on fluorine-18 (¹⁸F) fluorodeoxyglucose (FDG) and L- [3-¹⁸F]-α-methyltyrosine (¹⁸F-FAMT) PET/CT in patients with non-small-cell lung cancer (NSCLC).

Methods

The study group comprised 112 NSCLC patients who underwent ¹⁸F-FDG and ¹⁸F-FAMT PET/CT prior to any therapy. The MTV, TLG, TLR, and maximum standardized uptake value (SUV_max) of the primary tumors were determined. Automatic MTV measurement was performed using PET volume computer assisted reading software. (GE Healthcare). Cox proportional hazards models were built to assess the prognostic value of MTV, TLG (for ¹⁸F-FDG), TLR (for ¹⁸F-FAMT), SUV_max, T stage, N stage, M stage, clinical stage, age, sex, tumor histological subtype, and treatment method (surgery or other therapy) on overall survival (OS).

Results

Higher TNM, higher clinical stage, inoperable status, and higher values for all PET parameters (both ¹⁸F-FAMT and ¹⁸F-FDG PET) were significantly associated (P < 0.05) with shorter OS. Multivariate analysis revealed that a higher MTV of ¹⁸F-FAMT (hazard ratio [HR]: 2.88, CI: 1.63–5.09, P < 0.01) and advanced clinical stage (HR: 5.36, CI: 1.88–15.34, P < 0.01) were significant predictors of shorter OS.

Conclusions

MTV of ¹⁸F-FAMT is of prognostic value for OS in NSCLC cases and can help guide decision-making during patient management.

Synthesis and physical chemical properties of 2-amino-4-(trifluoromethoxy)butanoic acid - a CF3O-containing analogue of natural lipophilic amino acids

2-Amino-2-(trifluoromethoxy)butanoic acid (O-trifluoromethyl homoserine) was synthesized as a racemate and in both enantiomeric forms. The measured pK_a and log D values establish the compound as a promising analogue of natural aliphatic amino acids.

Clinical value of fluorine-18α-methyltyrosine PET in patients with gliomas: comparison with fluorine-18 fluorodeoxyglucose PET

Background

We investigated the relationship between metabolic activity and histological features of gliomas using fluorine-18α-methyltyrosine (¹⁸F-FAMT) positron emission tomography (PET) compared with fluorine-18 fluorodeoxyglucose (¹⁸F-FDG) PET in 38 consecutive glioma patients. The tumor to normal brain ratios (T/N ratios) were calculated, and the relationships between T/N ratio and World Health Organization tumor grade or MIB-1 labeling index were evaluated. The diagnostic values of T/N ratios were assessed using receiver operating characteristic (ROC) curve analyses to differentiate between high-grade gliomas (HGGs) and low-grade gliomas (LGGs).

Results

Median T/N ratio of ¹⁸F-FAMT PET was 2.85, 4.65, and 4.09 for grade II, III, and IV gliomas, respectively, with significant differences between HGGs and LGGs (p = 0.006). Both T/N ratio (p = 0.016) and maximum standardized uptake value (p = 0.033) of ¹⁸F-FDG PET showed significant differences between HGGs and LGGs. ROC analysis yielded an optimal cut-off of 3.37 for the T/N ratio of ¹⁸F-FAMT PET to differentiate between HGGs and LGGs (sensitivity 81%, specificity 67%, accuracy 76%, area under the ROC curve 0.776). Positive predictive value was 84%, and negative predictive value was 62%. T/N ratio of ¹⁸F-FAMT PET was not correlated with MIB-1 labeling index in all gliomas, whereas T/N ratio of ¹⁸F-FDG PET was positively correlated (r_s = 0.400, p = 0.013). Significant positive correlation was observed between T/N ratios of ¹⁸F-FDG and ¹⁸F-FAMT (r_s = 0.454, p = 0.004), but median T/N ratio of ¹⁸F-FAMT PET was significantly higher than that of ¹⁸F-FDG PET in all grades of glioma.

Conclusions

The T/N ratio of ¹⁸F-FAMT uptake has high positive predictive value for detection of HGGs. ¹⁸F-FAMT PET had higher T/N ratio, with better tumor-normal brain contrast, compared to ¹⁸F-FDG PET in both LGGs and HGGs. Therefore, ¹⁸F-FAMT is a useful radiotracer for the preoperative visualization of gliomas.

Efficacy of system l amino acid transporter 1 inhibition as a therapeutic target in esophageal squamous cell carcinoma

System l amino acid transporter 1 (LAT1) is highly expressed in various types of human cancer, and contributes to cancer growth and survival. Recently, we have shown that LAT1 expression is closely related to the growth and aggressiveness of esophageal cancer, and is an independent marker of poor prognosis. However, it remains unclear whether LAT1 inhibition could suppress esophageal cancer growth. In this study, we investigated the tumor‐suppressive effects of the inhibition of LAT1. Both LAT1 and CD98, which covalently associates to LAT1 on the membrane, were expressed in human esophageal cancer cell lines KYSE30 and KYSE150. Quantitative PCR analysis showed that the expression of LAT1 was much higher than other subtypes of LAT. A selective inhibitor of LAT, 2‐aminobicyclo‐(2,2,1)‐heptane‐2‐carboxylic acid (BCH), suppressed cellular uptake of l‐¹⁴C‐leucine and cell proliferation in a dose‐dependent manner. It also suppressed phosphorylation of mammalian target of rapamycin, 4E‐BP1, and p70S6K protein, and induced cell cycle arrest at G₁ phase. These results suggest that suppression of both mammalian target of rapamycin signaling and cell cycle progression is involved in BCH‐induced growth inhibition. In tumor‐bearing mice, daily treatment with BCH significantly delayed tumor growth and decreased glucose metabolism, indicating that LAT1 inhibition potentially suppresses esophageal cancer growth in vivo. Thus, our results suggest that LAT1 inhibition could be a promising molecular target for the esophageal cancer therapy.

A Continuously Infused Microfluidic Radioassay System for the Characterization of Cellular Pharmacokinetics

Measurement of cellular tracer uptake is widely applied to learn the physiologic status of cells and their interactions with imaging agents and pharmaceuticals. In-culture measurements have the advantage of less stress to cells. However, the tracer solution still needs to be loaded, unloaded, and purged from the cell culture during the measurements. Here, we propose a continuously infused microfluidic radioassay (CIMR) system for continuous in-culture measurement of cellular uptake. The system was tested to investigate the influence of the glucose concentration in cell culture media on ¹⁸F-FDG uptake kinetics.

METHODS

The CIMR system consists of a microfluidic chip integrated with a flow-control unit and a positron camera. Medium diluted with radioactive tracer flows through a cell chamber continuously at low speed. Positrons emitted from the cells and from tracer in the medium are measured with the positron camera. The human cell lines SkBr3 and Capan-1 were incubated with media of 3 different glucose concentrations and then measured with ¹⁸F-FDG on the CIMR system. In addition, a conventional uptake experiment was performed. The relative uptake ratios between different medium conditions were compared. A cellular 2-compartment model was applied to estimate the cellular pharmacokinetics on CIMR data. The estimated pharmacokinetic parameters were compared with expressions of glucose transporter-1 (GLUT1) and hexokinase-2 measured by quantitative real-time polymerase chain reaction.

RESULTS

The relative uptake ratios obtained from CIMR measurements correlated significantly with those from the conventional uptake experiments. The relative SDs of the relative uptake ratios obtained from the CIMR uptake experiments were significantly lower than those from the conventional uptake experiments. The fit of the cellular 2-compartment model to the ¹⁸F-FDG CIMR measurements was of high quality. For SkBr3, the estimated pharmacokinetic parameters k₁ and k₃ were consistent with the messenger RNA expression of GLUT1 and hexokinase-2: culturing with low glucose concentrations led to higher GLUT1 and hexokinase-2 expression as well as higher estimated k₁ and k₃ For Capan-1, the estimated k₁ and k₃ increased as the glucose concentration in the culture medium decreased, and this finding did not match the corresponding messenger RNA expression.

CONCLUSION

The CIMR system captures dynamic uptake within the cell culture and enables estimation of the cellular pharmacokinetics.

Prognostic significance of L-type amino acid transporter 1 (LAT1) expression in cutaneous melanoma

Amino acid transporters play a crucial role in the development and invasiveness of cancer cells. However, it remains unclear whether or not the expression of L-type amino acid transporter 1 (LAT1) has prognostic significance in patients with cutaneous melanoma. A total of 128 patients with cutaneous melanoma were evaluated. Tumor sections were stained by immunohistochemistry for LAT1, CD98, Ki-67, and microvessel density determined by CD34 and p53. We also analyzed 30 specimens of patients with melanocytic nevi as negative controls. LAT1 and CD98 were highly expressed in 58% (75/128) and 75% (97/128), respectively. The rates of positivity for LAT1 in the melanocytic nevi were 0% (0/30). The expression of LAT1 was associated significantly with tumor thickness, T factor, CD98 expression, cell proliferation (Ki-67), and microvessel density (CD34). By Spearman's rank test, LAT1 expression was correlated with CD98, Ki-67, and CD34. By univariate analysis, tumor thickness, ulceration, disease staging, LAT1, and CD34 showed a significant relationship with overall survival and disease-free survival. Furthermore, a multivariate analysis confirmed that LAT1 was an independent prognostic factor for predicting a poor prognosis. This study had a small sample size. LAT1 can serve as a significant prognostic factor to predict a poor outcome and it may therefore play an important role in the aggressiveness of cutaneous melanoma.

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.

Correlation between the Uptake of 18F-Fluorodeoxyglucose (18F-FDG) and the Expression of Proliferation-Associated Antigen Ki-67 in Cancer Patients: A Meta-Analysis

Objective

To study the correlation between ¹⁸F-FDG uptake and cell proliferation in cancer patients by meta-analysis of published articles.

Methods

We searched PubMed (MEDLINE included), EMBASE, and Cochrane Database of Systematic Review, and selected research articles on the relationship between ¹⁸F-FDG uptake and Ki-67 expression (published between August 1, 1994-August 1, 2014), according to the literature inclusion and exclusion criteria. The publishing language was limited to English. The quality of included articles was evaluated according to the Quality Assessment of Diagnosis Accuracy Studies-2 (QUADAS-2). The correlation coefficient (r) was extracted from the included articles and processed by Fisher's r-to-z transformation. The combined correlation coefficient (r) and the 95% confidence interval (CI) were calculated with STATA 11.0 software under a random-effects model. Begg's test was used to analyze the existence of publication bias and draw funnel plot, and the sources of heterogeneity were explored by sensitivity and subgroup analyses.

Results

According to the inclusion and exclusion criteria, 79 articles were finally included, including 81 studies involving a total of 3242 patients. All the studies had a combined r of 0.44 (95% CI, 0.41-0.46), but with a significant heterogeneity (I² = 80.9%, P<0.01). Subgroup analysis for different tumor types indicated that most subgroups showed a reduced heterogeneity. Malignant melanoma (n = 1) had the minimum correlation coefficient (-0.22) between ¹⁸F-FDG uptake and Ki-67 expression, while the thymic epithelial tumors (TETs; n = 2) showed the maximum correlation coefficient of 0.81. The analytical results confirmed that correlation between ¹⁸F-FDG uptake and Ki-67 expression was extremely significant in TETs, significant in gastrointestinal stromal tumors (GISTs), moderate in patients with lung, breast, bone and soft tissue, pancreatic, oral, thoracic, and uterine and ovarian cancers, average in brain, esophageal and colorectal cancers, and poor in head and neck, thyroid, gastric and malignant melanoma tumors. Subgroup analysis indicated that positron emission tomography (PET) or PET/CT imaging technology or Ki-67 and standardized uptake value (SUV) measurement technology did not significantly affect the results of r values, and Begg's test showed no significant publication bias.

Conclusion

In cancer patients, ¹⁸F-FDG uptake showed a moderate positive correlation with tumor cell proliferation. Different tumor types exhibited varied degree of correlation, and the correlation was significant in TETs and GSTs. However, our results need further validation by clinical trials with a large sample of different tumor types.