Detection of malignant tumors: whole-body PET with fluorine 18 alpha-methyl tyrosine versus FDG--preliminary study

The human LAT1-4F2hc (SLC7A5-SLC3A2) transporter complex: Physiological and pathophysiological implications

LAT1 and 4F2hc form a heterodimeric membrane protein complex, which functions as one of the best characterized amino acid transporters. Since LAT1-4F2hc is required for the efficient uptake of essential amino acids and hormones, it promotes cellular growth, in part, by stimulating mTORC1 (mechanistic target of rapamycin complex 1) signalling and by repressing the integrated stress response (ISR). Gain or loss of LAT1-4F2hc function is associated with cancer, diabetes, and immunological and neurological diseases. Hence, LAT1-4F2hc represents an attractive drug target for disease treatment. Specific targeting of LAT1-4F2hc will be facilitated by the increasingly detailed understanding of its molecular architecture, which provides important concepts for its function and regulation. Here, we summarize (i) structural insights that help to explain how LAT1 and 4F2hc assemble to transport amino acids across membranes, (ii) the role of LAT1-4F2hc in key metabolic signalling pathways, and (iii) how derailing these processes could contribute to diseases.

Exploration of the threshold SUV for diagnosis of malignancy using 18F-FBPA PET/CT

Background

The goal of the study was to evaluate the diagnostic ability of 18F-FBPA PET/CT for malignant tumors. Findings from 18F-FBPA and 18F-FDG PET/CT were compared with pathological diagnoses in patients with malignant tumors or benign lesions.

Methods

A total of 82 patients (45 males, 37 females; median age, 63 years; age range, 20–89 years) with various types of malignant tumors or benign lesions, such as inflammation and granulomas, were examined by 18F-FDG and 18F-FBPA PET/CT. Tumor uptake of FDG or FBPA was quantified using the maximum standardized uptake value (SUVmax). The final diagnosis was confirmed by cytopathology or histopathological findings of the specimen after biopsy or surgery. A ROC curve was constructed from the SUVmax values of each PET image, and the area under the curve (AUC) and cutoff values were calculated.

Results

The SUVmax for 18F-FDG PET/CT did not differ significantly for malignant tumors and benign lesions (10.9 ± 6.3 vs. 9.1 ± 2.7 P = 0.62), whereas SUVmax for 18F-FBPA PET/CT was significantly higher for malignant tumors (5.1 ± 3.0 vs. 2.9 ± 0.6, P < 0.001). The best SUVmax cutoffs for distinguishing malignant tumors from benign lesions were 11.16 for 18F-FDG PET/CT (sensitivity 0.909, specificity 0.390) and 3.24 for 18F-FBPA PET/CT (sensitivity 0.818, specificity 0.753). ROC analysis showed significantly different AUC values for 18F-FDG and 18F-FBPA PET/CT (0.547 vs. 0.834, p < 0.001).

Conclusion

18F-FBPA PET/CT showed superior diagnostic ability over 18F-FDG PET/CT in differential diagnosis of malignant tumors and benign lesions. The results of this study suggest that 18F-FBPA PET/CT diagnosis may reduce false-positive 18F-FDG PET/CT diagnoses.

SLC7A5 is a lung adenocarcinoma-specific prognostic biomarker and participates in forming immunosuppressive tumor microenvironment

Background

Amino acid metabolism participates in forming immunosuppressive tumor microenvironment. Amino acid transporters (AATs), as a gate for admission, remains to be studied.

Materials and methods

We identified LUAD-specific prognostic AATs, SLC7A5 by differential expression analysis, logistic regression, machine learning, Kaplan-Meier analysis, AUC value filtrating and Cox regression. Then differential expression and distribution of SLC7A5 were depicted. Copy number variation, DNA methylation, transcriptional factors and ceRNA network were investigated to explore potential mechanism causing differential expression. The prognostic and clinical relation were evaluated by Kaplan-Meier analysis, Cox regression analysis. GSEA and GSVA were used to analyze altered pathways between SLC7A5 high- and low-groups. The expression of HLA-related genes and immune checkpoint genes, and immune cells infiltration were detected. SLC7A5 expression in immune cells was evaluated by single-cell sequencing data. IPS and an independent immunotherapy cohort assessed response rates of patients with distinct SLC7A5 expression. Proliferation assay and wound healing assay validated the effects of SLC7A5 on proliferation and migration of LUAD cells. Western blotting and cell viability assays were performed to detect mTORC1 pathway activity and sensitivity to rapamycin.

Results

SLC7A5 was a LUAD-specific prognostic AAT and had significant differential expression in transcription and translation level. Methylation levels of cg00728300, cg00858400, cg12408911, cg08710629 were negative correlation with SLC7A5 expression. FOXP3 and TFAP2A were possible transcription factors and miR-30a-5p, miR-184, miR-195-5p may target SLC7A5 mRNA. SLC7A5 high-expression indicated poor prognosis and was an independent prognostic factor. mTORC1, cell cycle, DNA damage repair, response to reactive oxygen, angiogenesis, epithelial-mesenchymal transition (EMT) and various growth factors signaling pathways were activated in SLC7A5 high-expression group. Interestingly, SLC7A5 high-expression group had less immune-related genes expression and immune cells infiltration. Single-cell sequencing data also suggested SLC7A5 was downregulated in various T cells, especially effector T cells. Moreover, high SLC7A5 expression indicated poor immunotherapy efficacy and higher sensitivity to inhibitors of mTORC1 pathway, cell cycle and angiogenesis. SLC7A5 deficiency abrogated proliferation, migration and mTORC1 pathway activity.

Conclusions

In summary, as a LUAD-specific prognostic AAT, SLC7A5 is involved in activation of multiple oncogenic pathways and indicates poor prognosis. Moreover, SLC7A5 may participate in forming immunosuppressive TME and is associated with low response of immunotherapy. SLC7A5 is promising to be a new diagnostic and prognostic biomarker and therapeutic target in LUAD.

The Clinical Value of Breast Specific Gamma Imaging and Positron Imaging: An Update

In the management of patients with breast cancer (BC), a mammography contributed to screen an early-stage patient, to plan a therapy strategy, to evaluate a therapy outcome, to detect a recurrence, and to reduce a mortality. Currently, various imaging modalities, such as CT, MR, Ultrasound (US), SPECT/CT, PET/CT, PET/MR have been utilized for the management of BC patients. In order to overcome a limited spatial resolution and sensitivity of whole-body systems in nuclear medicine imaging, dedicated breast imaging modalities were developed. One is a gamma imaging system with single/dual head scintillation detectors or semiconductor detectors associated with light compression device for breast parenchyma. Radiopharmaceutical for the gamma imaging is ^99mTc-sestamibi. Another is a positron imaging system with opposite-type panel detectors and ring-shaped type detectors. Radiopharmaceutical for positron imaging is ¹⁸F-fluorodeoxyglucose. The breast-specific gamma and positron imaging systems were utilized mainly to detect small lesions less than 1 cm in diameter especially in patients with dense breast, to evaluate an effect of preoperative neo-adjuvant therapy, to plan surgical procedures (conservative-surgery vs mastectomy), and to detect a recurrence. By combining higher sensitivity and spatial resolution scanners with new radiopharmaceuticals, an information on molecular-level pathology of BC is increasingly available in an individual patient. This article reviewed clinical impact and future perspective of this field.

Enhancing the accumulation level of 3-[18F]fluoro-L-α-methyltyrosine in tumors by preloading probenecid

INTRODUCTION

3-[¹⁸F]fluoro-α-methyl-L-tyrosine ([¹⁸F]FAMT) is a promising amino acid tracer targeting L-type amino acid transporter 1 (LAT1). One concern regarding the diagnosis using [¹⁸F]FAMT is the possibility of false-negative findings because of its relatively low accumulation level even in malignant tumors. Moreover, preloading probenecid, an organic anion transporter inhibitor, markedly increased the tumor accumulation level of radioiodine-labeled α-methyltyrosine. In this study, we evaluated the usefulness of preloading probenecid in improving the tumor-imaging capability of [¹⁸F]FAMT.

METHODS

Three biodistribution studies of [¹⁸F]FAMT were conducted in normal mice to elucidate the usefulness of probenecid preloading. Later, a biodistribution study and positron emission tomography (PET) imaging of [¹⁸F]FAMT were conducted with or without probenecid injection in tumor-bearing mice.

RESULTS

Probenecid preloading significantly delayed blood clearance and consequently enhanced the accumulation of [¹⁸F]FAMT in the pancreas, a LAT1-positive organ. The effects of probenecid preloading were independent of the administration route. Tumor accumulation level in the biodistribution study and the maximum standardized uptake value in tumors on PET imaging of the probenecid preloading group were significantly higher than those of the control (without probenecid injection) group in tumor-bearing mice.

CONCLUSIONS

Preloading probenecid significantly delayed blood clearance and consequently enhanced the accumulation of [¹⁸F]FAMT in tumors. These results indicate that preloading probenecid could improve the diagnostic accuracy of [¹⁸F]FAMT.

Enhancing the Therapeutic Effect of 2-211At-astato-α-methyl-L-phenylalanine with Probenecid Loading

Simple Summary

To enhance the therapeutic effect of 2-²¹¹At-astato-α-methyl-L-phenylalanine (2-²¹¹At-AAMP), a radiopharmaceutical for targeted alpha therapy, we evaluated the effect of probenecid loading on its biodistribution and therapeutic effect in mice. Probenecid preloading significantly delayed the clearance of 2-²¹¹At-AAMP from the blood, increasing its accumulation in tumors. Consequently, the therapeutic effect of 2-²¹¹At-AAMP markedly improved. These results indicate that 2-²¹¹At-AAMP with probenecid loading is useful for the treatment of various types of cancers.

Abstract

L-type amino acid transporter 1 (LAT1) might be a useful target for tumor therapy since it is highly expressed in various types of cancers. We previously developed an astatine-211 (²¹¹At)-labeled amino acid derivative, 2-²¹¹At-astato-α-methyl-L-phenylalanine (2-²¹¹At-AAMP), and demonstrated its therapeutic potential for LAT1-positive cancers. However, the therapeutic effect of 2-²¹¹At-AAMP was insufficient, probably due to its low tumor retention. The preloading of probenecid, an organic anion transporter inhibitor, can delay the clearance of some amino acid tracers from the blood and consequently increase their accumulation in tumors. In this study, we evaluated the effect of probenecid preloading on the biodistribution and therapeutic effect of 2-²¹¹At-AAMP in mice. In biodistribution studies, the blood radioactivity of 2-²¹¹At-AAMP significantly increased with probenecid preloading. Consequently, the accumulation of 2-²¹¹At-AAMP in tumors was significantly higher with probenecid than without probenecid loading. In a therapeutic study, tumor growth was suppressed by 2-²¹¹At-AAMP with probenecid, and the tumor volume was significantly lower in the treatment group than in the untreated control group from day 2 to day 30 (end of the follow-up period) after treatment. These results indicate that probenecid loading could improve the therapeutic effect of 2-²¹¹At-AAMP by increasing its accumulation in tumors.

A Phase 0 Microdosing PET/CT Study Using O-[18F]Fluoromethyl-d-Tyrosine in Normal Human Brain and Brain Tumor

PURPOSE

The aim of the present study was to obtain information about distribution, radiation dosimetry, toxicity, and pharmacokinetics of O-[18F]fluoromethyl-d-tyrosine (d-18F-FMT), an amino acid PET tracer, in patients with brain tumors.

PATIENTS AND METHODS

A total of 6 healthy controls (age = 19-25 years, 3 males and 3 females) with brain PET images and radiation dosimetry and 12 patients (median age = 60 years, 6 males and 6 females) with primary (n = 5) or metastatic brain tumor (n = 7) were enrolled. We acquired 60-minute dynamic brain PET images after injecting 370 MBq of d-18F-FMT. Time-activity curves of d-18F-FMT uptake in normal brain versus brain tumors and tumor-to-background ratio were analyzed for each PET data set.

RESULTS

Normal cerebral uptake of d-18F-FMT decreased from 0 to 5 minutes after injection, but gradually increased from 10 to 60 minutes. Tumoral uptake of d-18F-FMT reached a peak before 30 minutes. Tumor-to-background ratio peaked at less than 15 minutes for 8 patients and more than 15 minutes for 4 patients. The mean effective dose was calculated to be 13.2 μSv/MBq.

CONCLUSIONS

Using d-18F-FMT as a PET radiotracer is safe. It can distinguish brain tumor from surrounding normal brain tissues with a high contrast. Early-time PET images of brain tumors should be acquired because the tumor-to-background ratio tended to reach a peak within 15 minutes after injection.

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.

[Drug Discovery Targeting an Amino Acid Transporter for Diagnosis and Therapy]

Nutrients are essential for all living organisms. Because growing cancer cells have strong metabolic demands, nutrient transporters are constitutively increased to facilitate the nutrient uptake. Among these nutrient transporters, L-type amino acid transporter 1 (LAT1), which transports large neutral amino acids including essential amino acids, is critical for cancer growth. Therefore, LAT1 has been considered as an attractive target for diagnosis and therapy of cancers. We have developed several lines of compounds for cancer diagnosis and therapy. To diagnose cancer by using positron emission tomography (PET) probes, we have created amino acid derivatives which are selectively transported by LAT1 and accumulated in cancer cells. In addition to amino acid derivatives as the LAT1 inhibitors, we also have made non-amino acid small compounds as anti-cancer drugs which inhibit LAT1 function and suppress tumor growth. The LAT1 targeting anti-cancer drug showed low toxicity but strong effects on various types of cancer cells in animal models. The novel PET probe is approved for clinical research and the new anti-cancer drug has been under clinical trial. Small compounds targeting the amino acid transporter bring us new tools for cancer diagnosis and therapy.

Imaging Assessment of Tumor Response in the Era of Immunotherapy

Assessment of tumor response during treatment is one of the most important purposes of imaging. Before the appearance of immunotherapy, response evaluation criteria in solid tumors (RECIST) and positron emission tomography response criteria in solid tumors (PERCIST) were, respectively, the established morphologic and metabolic response criteria, and cessation of treatment was recommended when progressive disease was detected according to these criteria. However, various types of immunotherapy have been developed over the past 20 years, which show novel false positive findings on images, as well as distinct response patterns from conventional therapies. Antitumor immune response itself causes 18F-fluorodeoxyglucose (FDG) uptake in tumor sites, known as "flare phenomenon", so that positron emission tomography using FDG can no longer accurately identify remaining tumors. Furthermore, tumors often initially increase, followed by stability or decrease resulting from immunotherapy, which is called "pseudoprogression", so that progressive disease cannot be confirmed by computed tomography or magnetic resonance imaging at a single time point. As a result, neither RECIST nor PERCIST can accurately predict the response to immunotherapy, and therefore several new response criteria fixed for immunotherapy have been proposed. However, these criteria are still controversial, and also require months for response confirmation. The establishment of optimal response criteria and the development of new imaging technologies other than FDG are therefore urgently needed. In this review, we summarize the false positive images and the revision of response criteria for each immunotherapy, in order to avoid discontinuation of a truly effective immunotherapy.

Preclinical evaluation of new α-radionuclide therapy targeting LAT1: 2-[211At]astato-α-methyl-L-phenylalanine in tumor-bearing model

INTRODUCTION

Targeted α-radionuclide therapy has attracted attention as a promising therapy for refractory cancers. However, the application is limited to certain types of cancer. Since L-type amino acid transporter 1 (LAT1) is highly expressed in various human cancers, we prepared an LAT1-selective α-radionuclide-labeled amino acid analog, 2-[²¹¹At]astato-α-methyl-L-phenylalanine (2-[²¹¹At]AAMP), and evaluated its potential as a therapeutic agent.

METHODS

2-[²¹¹At]AAMP was prepared from the stannyl precursor. Stability of 2-[²¹¹At]AAMP was evaluated both in vitro and in vivo. In vitro studies using an LAT1-expressing human ovarian cancer cell line, SKOV3, were performed to evaluate cellular uptake and cytotoxicity of 2-[²¹¹At]AAMP. Biodistribution and therapeutic studies in SKOV3-bearing mice were performed after intravenous injection of 2-[²¹¹At]AAMP.

RESULTS

2-[²¹¹At]AAMP was stable in murine plasma in vitro and excreted intact into urine. Cellular uptake of 2-[²¹¹At]AAMP was inhibited by treatment with an LAT1-selective inhibitor. After 24 h incubation, 2-[²¹¹At]AAMP suppressed clonogenic growth at 10 kBq/ml, and induced cell death and DNA double-strand breaks at 25 kBq/ml. When injected into mice, 2-[²¹¹At]AAMP exhibited peak accumulation in the tumor at 30 min postinjection, and radioactivity levels in the tumor were retained up to 60 min. The majority of the radioactivity was rapidly eliminated from the body into urine in an intact form immediately after injection. 2-[²¹¹At]AAMP significantly improved the survival of mice (P < 0.05) without serious side effects.

CONCLUSION

2-[²¹¹At]AAMP showed α-radiation-dependent cellular growth inhibition after it was taken up via LAT1. In addition, 2-[²¹¹At]AAMP had a beneficial effect on survival in vivo. These findings suggest that 2-[²¹¹At]AAMP would be useful for the treatment of LAT1-positive cancer.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

This is the first report of an LAT1-targeting radiopharmaceutical for α-radionuclide therapy; this agent would be applicable for the treatment of various types of cancer.

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.

Preoperative Evaluation of Sellar and Parasellar Macrolesions by [18F]Fluorodeoxyglucose Positron Emission Tomography

OBJECTIVE

Various diseases can occur in the sellar and suprasellar regions. The potential of [¹⁸F]fluorodeoxyglucose (FDG) positron emission tomography (PET) for the preoperative evaluation of sellar and parasellar lesions was investigated.

METHODS

A total of 49 patients aged 8-82 years with sellar and parasellar macroscopic lesions (≥10 mm) underwent FDG PET. Twenty-two patients had pituitary adenomas, including 14 nonfunctioning and 8 growth hormone-secreting adenomas. Eleven patients had craniopharyngiomas, including 5 adamantinomatous and 6 squamous-papillary types. Eight patients had chordoma, 4 had meningioma, and 4 had a Rathke cleft cyst. The maximum standardized uptake value (SUV_max), and the ratio of the SUV_max in the tumor to the mean standardized uptake value in the normal cortex (T/N ratio) or in the normal white matter (T/W ratio) were calculated. The relationships between SUV_max, T/N ratio, and T/W ratio, and lesion disease were evaluated.

RESULTS

Uptakes of FDG, including SUV_max, T/N ratio, and T/W ratio, were lower in chordoma and Rathke cleft cyst compared with pituitary adenoma. SUV_max, T/N ratio, and T/W ratio of nonfunctioning adenoma were significantly higher than those of growth hormone-secreting adenoma. SUV_max, T/N ratio, and T/W ratio of squamous-papillary type were significantly higher than those of the adamantinomatous type of craniopharyngioma.

CONCLUSIONS

FDG PET is useful for the preoperative diagnosis of sellar and parasellar macrolesions. High uptake in nonfunctioning pituitary adenoma, and low uptake in chordoma are significant. The difference in FDG uptake dependent on the histologic subtype may be related to the specific genetics of the craniopharyngioma subtype.

Advantages of L-3-[(18)F] fluoro-alpha-methyl tyrosine over 2-[(18)F]-fluoro-2-deoxyglucose in detecting liver metastasis during positron emission tomography scan

Purpose

We aimed to assess the usefulness of positron emission tomography (PET) using the amino acid tracer L-3-[18F] fluoro-alpha-methyl tyrosine (FAMT) in detecting metastatic liver lesions compared with 2-[18F]-fluoro-2-deoxyglucose (FDG).

Methods

We included 24 patients with liver metastases who underwent both FDG-PET/computed tomography (CT) and FAMT-PET/CT. Maximum standardized uptake value (SUVmax) and tumor-to-liver parenchymal (T/L) ratio were analyzed to evaluate the correlation between FDG and FAMT uptakes in metastatic liver lesions; adenocarcinoma (AC, n = 21), squamous cell carcinoma (SCC, n = 23), neuroendocrine tumor (NET, n = 9), and carcinoid tumor (CAR, n = 6).

Results

We detected 59 lesions on performing either FDG-PET or FAMT-PET. NETs had significantly lower T/L ratios for FAMT (median, 1.00; range, 0.86–1.34) compared with those for FDG (median 2.86; range 1.70–6.13, p < 0.01). CAR tumors tended to reveal lower T/L ratios for FDG (median 1.10; range 0.78–1.92) than those for FAMT (median 1.80; range 0.80–2.34). Comparison of T/L ratios of SCC and AC revealed that FAMT in the metastatic liver lesions of SCC was higher than those of AC (p < 0.05).

Conclusion

FAMT-PET could detect metastatic liver lesions from various cancers, except NET.

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.

Transparotid Approach for the Treatment of Condylar Osteochondroma and Ankylosis of the Temporomandibular Joint

Among the methods to treat temporomandibular joint (TMJ), preauricular, submandibular, retromandibular, and intraoral approaches have been described. These approaches, however, occasionally offer inadequate access, owing to the oblique course of the facial nerve, and access can be limited, especially to the medial and anterior part of the infratemporal fossa. The use of the transparotid approach can offer direct visualization of the facial nerves to prevent severe damage, and a wide work field can be achieved from the medial-anterior part of the infratemporal fossa to subcondylar region by retracting the mobilized facial nerves in either the superior or inferior direction. The 2 patients reported herein illustrate the addition of a transparotid approach to the standard procedures for the removal of an osteochondroma and condylectomy with displaced bone fragment for ankyloses of TMJ from the infratemporal fossa.

Differentiation of malignant tumours from granulomas by using dynamic [(18)F]-fluoro-L-α-methyltyrosine positron emission tomography

Background

Previous clinical studies have revealed the potential of [¹⁸F]-fluoro-L-α-methyltyrosine (¹⁸F-FAMT) for the differential diagnosis of malignant tumours from sarcoidosis. However, one concern regarding the differential diagnosis with ¹⁸F-FAMT is the possibility of false negatives given the small absolute uptake of ¹⁸F-FAMT that has been observed in some malignant tumours. The aim of this study was to evaluate a usefulness of dynamic ¹⁸F-FAMT positron emission tomography (PET) for differentiating malignant tumours from granulomas.

Methods

Rats bearing both granulomas (Mycobacterium bovis bacillus Calmette-Guérin (BCG)-induced) and tumours (C6 glioma cell-induced) underwent dynamic 2-deoxy-2-[¹⁸F]-fluoro-D-glucose (¹⁸F-FDG) PET and ¹⁸F-FAMT PET for 120 min on consecutive days. Time-activity curves, static images, mean standardized uptake values (SUVs) and the SUV ratios (SUVRs; calculated by dividing SUV at each time point by that of 2 min after injection) were assessed.

Results

In tumours, ¹⁸F-FAMT showed a shoulder peak immediately after the initial distribution followed by gradual clearance compared with granulomas. Although the mean SUV in the tumours (1.00 ± 0.10) was significantly higher than that in the granulomas (0.88 ± 0.12), a large overlap was observed. In contrast, the SUVR was markedly higher in tumours than in granulomas (50 min/2 min, 0.72 ± 0.06 and 0.56 ± 0.05, respectively) with no overlap. The dynamic patterns, SUVR, and mean SUV of ¹⁸F-FDG in the granulomas were comparable to those in the tumours.

Conclusions

Dynamic ¹⁸F-FAMT and SUVR analysis might compensate for the current limitations and help in improving the diagnostic accuracy of ¹⁸F-FAMT.

Development of a Widely Usable Amino Acid Tracer: ⁷⁶Br-α-Methyl-Phenylalanine for Tumor PET Imaging

Radiolabeled amino acids are superior PET tracers for the imaging of malignant tumors, and amino acids labeled with (76)Br, an attractive positron emitter because of its relatively long half-life (16.2 h), could potentially be a widely usable tumor imaging tracer. In this study, in consideration of its stability and tumor specificity, we designed two (76)Br-labeled amino acid derivatives, 2-(76)Br-bromo-α-methyl-l-phenylalanine (2-(76)Br-BAMP) and 4-(76)Br-bromo-α-methyl-l-phenylalanine (4-(76)Br-BAMP), and investigated their potential as tumor imaging agents.

METHODS

Both (76)Br- and (77)Br-labeled amino acid derivatives were prepared. We performed in vitro and in vivo stability studies and cellular uptake studies using the LS180 colon adenocarcinoma cell line. Biodistribution studies in normal mice and in LS180 tumor-bearing mice were performed, and the tumors were imaged with a small-animal PET scanner.

RESULTS

Both (77)Br-BAMPs were stable in the plasma and in the murine body. Although both (77)Br-BAMPs were taken up by LS180 cells and the uptake was inhibited by L-type amino acid transporter 1 inhibitors, 2-(77)Br-BAMP exhibited higher uptake than 4-(77)Br-BAMP. In the biodistribution studies, 2-(77)Br-BAMP showed more rapid blood clearance and lower renal accumulation than 4-(77)Br-BAMP. More than 90% of the injected radioactivity was excreted in the urine by 6 h after the injection of 2-(77)Br-BAMP. High tumor accumulation of 2-(77)Br-BAMP was observed in tumor-bearing mice, and PET imaging with 2-(76)Br-BAMP enabled clear visualization of the tumors.

CONCLUSION

2-(77)Br-BAMP exhibited preferred pharmacokinetics and high LS180 tumor accumulation, and 2-(76)Br-BAMP enabled clear visualization of the tumors by PET imaging. These findings suggest that 2-(76)Br-BAMP could constitute a potential new PET tracer for tumor imaging and may eventually enable the wider use of amino acid tracers.

Synthesis and biological evaluation of O-[3-18F-fluoropropyl]-α-methyl tyrosine in mesothelioma-bearing rodents

Radiolabeled tyrosine analogs enter cancer cells via upregulated amino acid transporter system and have been shown to be superior to ¹⁸F-fluoro-2-deoxy-D-glucose (¹⁸F-FDG) in differential diagnosis in cancers. In this study, we synthesized O-[3-¹⁹F-fluoropropyl]-α-methyl tyrosine (¹⁹F-FPAMT) and used manual and automated methods to synthesize O-[3-¹⁸F-fluoropropyl]-α-methyl tyrosine (¹⁸F-FPAMT) in three steps: nucleophilic substitution, deprotection of butoxycarbonyl, and deesterification. Manual and automated synthesis methods produced ¹⁸F-FPAMT with a radiochemical purity >96%. The decay-corrected yield of ¹⁸F-FPAMT by manual synthesis was 34% at end-of-synthesis (88 min). The decay-corrected yield of ¹⁸F-FPAMT by automated synthesis was 15% at end-of-synthesis (110 min). ¹⁸F-FDG and ¹⁸F-FPAMT were used for in vitro and in vivo studies to evaluate the feasibility of ¹⁸F-FPAMT for imaging rat mesothelioma (IL-45). In vitro studies comparing ¹⁸F-FPAMT with ¹⁸F-FDG revealed that ¹⁸F-FDG had higher uptake than that of ¹⁸F-FPAMT, and the uptake ratio of ¹⁸F-FPAMT reached the plateau after being incubated for 60 min. Biodistribution studies revealed that the accumulation of ¹⁸F-FPAMT in the heart, lungs, thyroid, spleen, and brain was significantly lower than that of ¹⁸F-FDG. There was poor bone uptake in ¹⁸F-FPAMT for up to 3 hrs suggesting its in vivo stability. The imaging studies showed good visualization of tumors with ¹⁸F-FPAMT. Together, these results suggest that ¹⁸F-FPAMT can be successfully synthesized and has great potential in mesothelioma imaging.

Biological evaluation of 3-[(18)F]fluoro-α-methyl-D-tyrosine (D-[(18)F]FAMT) as a novel amino acid tracer for positron emission tomography

OBJECTIVE

3-[(18)F]Fluoro-α-methyl-L-tyrosine (L-[(18)F]FAMT) is a useful amino acid tracer for positron emission tomography (PET) imaging of malignant tumors. Because D-amino acids are not well distributed in non-target organs and are rapidly excreted in urine, the D-isomer of [(18)F]FAMT could allow clear PET imaging of tumors early after administration. In this study, we prepared 3-[(18)F]fluoro-α-methyl-D-tyrosine (D-[(18)F]FAMT) and evaluated its usefulness.

METHODS

D-[(18)F]FAMT was synthesized according to the method for preparation of L-[(18)F]FAMT. The in vitro and in vivo stability of [(18)F]FAMT were evaluated by high-performance liquid chromatography. Cellular uptake of [(18)F]FAMT was evaluated using LS180 colon adenocarcinoma cells. Biodistribution studies were performed in LS180 tumor-bearing mice, and the tumors were imaged using a small-animal PET scanner.

RESULTS

The radiolabeling yield of D-[(18)F]FAMT was approximately 10 %, similar to that of L-[(18)F]FAMT. Over 95 % of D-[(18)F]FAMT remained intact in mice until 60 min after administration. D-[(18)F]FAMT was gradually taken up by the LS180 cells. Tumor uptake of D-[(18)F]FAMT was competitively inhibited by pretreatment with α-methyl-L-tyrosine, a selective substrate for the system L-amino acid transporter 1 (LAT1), suggesting the involvement of LAT1 in tumor uptake of D-[(18)F]FAMT. In biodistribution studies, D-[(18)F]FAMT showed rapid clearance from the blood, marked accumulation and retention in the tumor, and lower accumulation in non-target organs, especially kidney and pancreas, compared to L-[(18)F]FAMT. The amount of D-[(18)F]FAMT in the tumor was also reduced, and tumor-to-blood ratio and tumor-to-muscle ratio of D-[(18)F]FAMT were similar to those of L-[(18)F]FAMT at every time point. PET imaging with D-[(18)F]FAMT did not provide a clear image of the tumor early after administration. However, D-[(18)F]FAMT provided higher tumor-to-background contrast than L-[(18)F]FAMT.

CONCLUSIONS

D-[(18)F]FAMT showed rapid blood clearance, low accumulation in non-target organs, and tumor-selective imaging compared with L-[(18)F]FAMT. Thus, D-[(18)F]FAMT could potentially serve as a novel PET tracer for imaging malignant tumors.

¹⁸F-FAMT in patients with multiple myeloma: clinical utility compared to ¹⁸F-FDG

OBJECTIVE

L-[3-(18)F]-alpha-methyltyrosine ((18)F-FAMT) is an amino-acid tracer for positron emission tomography (PET), with uptake related to overexpression of L-type amino-acid transporter 1 and proliferative activity in tumour cells. This study evaluated the diagnostic performance of (18)F-FAMT PET compared with 2-[(18)F]-fluoro-2-deoxy-D-glucose ((18)F-FDG) PET in patients with multiple myeloma (MM).

METHODS

Eleven patients with MM (newly diagnosed, n = 3; relapsed after treatment, n = 8) underwent whole-body (18)F-FAMT and (18)F-FDG PET within a 2-week interval. Magnetic resonance imaging (MRI) of the spine was also performed to assess patterns of bone marrow infiltration. Tracer uptake was semi-quantitatively evaluated using maximal standardized uptake value (SUV(max)). Mean SUV was also determined for normal bone marrow and the aortic arch as mediastinal background SUV to calculate lesion-to-bone marrow (L/B) and lesion-to-mediastinum (L/M) ratios, respectively. Those values were statistically compared using Student's t test.

RESULTS

In 8 patients showing focal infiltration on MRI, 34 FDG-avid bone lesions were identified, with each showing increased FAMT uptake. Mean SUV(max) and L/B ratio of FDG (3.1 ± 1.2 and 3.3 ± 1.9, respectively) were significantly higher than those of FAMT (2.0 ± 1.0 and 2.6 ± 1.1, respectively; p < 0.05 each). In contrast, the L/M ratio of FDG showed no significant difference to that of FAMT (2.2 ± 1.0 and 2.4 ± 1.2, respectively; p = 0.3).

CONCLUSIONS

Clear (18)F-FAMT PET uptake was seen in most (18)F-FDG-avid lesions among patients with MM, and an equivalent semi-quantitative value was obtained using L/M ratio. Our preliminary data suggest that (18)F-FAMT PET provides a useful imaging modality for detecting active myelomatous lesions.

Transport of 3-fluoro-L-α-methyl-tyrosine by tumor-upregulated L-type amino acid transporter 1: a cause of the tumor uptake in PET

l-3-(18)F-α-methyl tyrosine ((18)F-FAMT) has been developed as a PET radiotracer for tumor imaging. Clinical studies have demonstrated the usefulness of (18)F-FAMT PET for the prediction of prognosis and the differentiation of malignant tumors and benign lesions. (18)F-FAMT exhibits higher cancer specificity in peripheral organs than other amino acid PET tracers and (18)F-FDG. The accumulation of (18)F-FAMT is strongly correlated with the expression of L-type amino acid transporter 1 (LAT1), an isoform of system L highly upregulated in cancers. In this study, we examined the interaction of 3-fluoro-l-α-methyl-tyrosine (FAMT) with amino acid transporters to assess the mechanisms of (18)F-FAMT uptake in PET.

METHODS

We applied in vitro assays using established mammalian cell lines stably expressing LAT1 or a non-cancer-type system L isoform LAT2. The inhibitory effect on l-(14)C-leucine uptake and the induction effect on efflux of preloaded l-(14)C-leucine were examined for FAMT and other amino acid tracers. FAMT transport was compared among cell lines with varied LAT1 expression level.

RESULTS

FAMT prominently inhibited LAT1-mediated l-(14)C-leucine uptake in a competitive manner but had less of an effect on LAT2. In the efflux experiments, FAMT induced the efflux of preloaded l-(14)C-leucine through LAT1, indicating that FAMT is transported by LAT1 and not by LAT2. Among amino acid-related compounds examined in this study, including those used for PET tracers, the compounds with an α-methyl group such as FAMT, 2-fluoro-l-α-methyl-tyrosine, 3-iodo-l-α-methyl-tyrosine, and l-α-methyl-tyrosine were well transported by LAT1 but not by LAT2. However, l-methionine, l-tyrosine, 3-fluoro-l-tyrosine, 2-fluoro-l-tyrosine, and O-(2-fluoroethyl)-l-tyrosine were transported by both LAT1 and LAT2, suggesting that the α-methyl moiety is responsible for the LAT1 selectivity of FAMT. FAMT transport rate and LAT1 protein level were well correlated, supporting the importance of LAT1 for the cellular uptake of FAMT.

CONCLUSION

Distinct from other amino acid PET tracers, because of its α-methyl moiety, FAMT is selective to LAT1 and not transported by LAT2. This property of FAMT is proposed to contribute to highly tumor-specific accumulation of (18)F-FAMT in PET.

Prognostic significance of L-type amino acid transporter 1 (LAT1) and 4F2 heavy chain (CD98) expression in early stage squamous cell carcinoma of the lung

The purpose of this study was to evaluate the prognostic value of L-type amino acid transporter 1 (LAT 1) and 4F2 heavy chain (CD98) in patients with stage I squamous cell carcinoma of the lung. A total of 84 consecutive patients with completely resected pathologic stage I squamous cell carcinoma of the lung were retrospectively reviewed. All patients underwent resection of the tumor and the immunohistochemical analysis was done to determine the expression of LAT 1, CD98, Ki-67 labeling index, vascular endothelial growth factor, and microvessel density. These pathological parameters were correlated with the prognosis of patients after complete resection of the tumor. A positive rate of LAT 1 expression (87%; 73/84) was significantly higher than that of CD98 expression (65%; 55/84) (P = 0.0018). Cooperative expression of LAT 1 and CD98 was recognized in 62% (52/84). LAT 1 expression was significantly correlated with CD98, Ki-67 labeling index, vascular endothelial growth factor, and microvessel density. The 5-year survival rates of the LAT 1-positive and LAT1-negative patients were 59% and 88%, respectively (P = 0.2186). Tumor cell proliferation and angiogenesis were not also (a) prognostic factor. However, the 5-year survival rate of patients with both LAT 1 and CD98-positivity (57%) was significantly worse than that of other patients (88%; P = 0.0136). Multivariate analysis confirmed that positive cooperative expression of LAT 1 and CD98 was an independent factor for predicting a poor prognosis. A cooperative expression of LAT 1 and CD98 is a significant pathological factor for predicting the poor prognosis in patients with resectable stage I squamous cell carcinoma of the lung.

Preparation and biological evaluation of 3-[(76)Br]bromo-α-methyl-L-tyrosine, a novel tyrosine analog for positron emission tomography imaging of tumors

INTRODUCTION

3-[(18)F]fluoro-α-methyl-l-tyrosine ([(18)F]FAMT) is a useful amino acid tracer for positron emission tomography (PET) imaging of malignant tumors. FAMT analogs labeled with (76)Br, a positron emitter with a long half-life (t(1/2)=16.1 h), could potentially be widely used as amino acid tracers for tumor imaging. In this study, 3-[(76)Br]bromo-α-methyl-l-tyrosine ([(76)Br]BAMT) was designed, and its usefulness was evaluated as a novel PET tracer for imaging malignant tumors.

METHODS

In this study, both [(76)Br]BAMT and [(77)Br]BAMT were prepared. The in vitro and in vivo stability of [(77)Br]BAMT was evaluated by HPLC analysis. Cellular uptake and retention of [(77)Br]BAMT and [(18)F]FAMT were evaluated using LS180 colon adenocarcinoma cells. Biodistribution studies were performed in normal mice and in LS180 tumor-bearing mice, and the tumors were imaged with a small-animal PET scanner.

RESULTS

[(77)Br]BAMT was stable in vitro but was catabolized after administration in mice. Cellular accumulation and retention of [(77)Br]BAMT were significantly higher than those of [(18)F]FAMT. In biodistribution studies, the tumor accumulation of [(77)Br]BAMT was higher than that of [(18)F]FAMT. However, some level of debromination was seen, which caused more retention of radioactivity in the blood and organs than was seen with [(18)F]FAMT. PET imaging with [(76)Br]BAMT enabled clear visualization of the tumor, and the whole-body image using [(76)Br]BAMT was similar to that using [(18)F]FAMT.

CONCLUSIONS

[(77)Br]BAMT showed high levels of tumor accumulation, and [(76)Br]BAMT enabled clear visualization of the tumor by PET imaging. Although an improvement in stability is still needed, (76)Br-labeled FAMT analogs could potentially serve as PET tracers for the imaging of malignant tumors.

Comparison of L-type amino acid transporter 1 expression and L-[3-18F]-α-methyl tyrosine uptake in outcome of non-small cell lung cancer

OBJECTIVE

L-Type amino acid transporter 1 (LAT1) has associated with tumor growth and poor outcome of patients with non-small cell lung cancer (NSCLC). L-[3-(18)F]-α-methyl tyrosine ((18)F-FAMT) is an amino acid tracer for positron emission tomography (PET) imaging, and (18)F-FAMT uptake is mediated by LAT1. The purpose of this study is to compare the prognostic significance of (18)F-FAMT uptake in the primary tumors with that of LAT1 expression in patients with NSCLC.

METHODS

Fifty-nine patients with NSCLC were enrolled in this study. All patients underwent (18)F-FAMT PET prior to resection of the tumor, and immunohistochemical staining of the resected tumors were performed to compare the (18)F-FAMT uptake and LAT1 expression. Uptake of (18)F-FAMT was evaluated using semiquantitative standardized uptake value (SUV(max)), and the cutoff value was determined to discriminate patients with high SUV(max) from those with low SUV(max). Expression of LAT1 was evaluated by the score of staining intensity through 1 to 4. SUV(max) and LAT1 expression were compared according to the clinicopathological variables.

RESULTS

The best discriminative cutoff value of (18)F-FAMT SUV(max) within the primary tumors was 1.6. The high SUV(max) (>1.6) in (18)F-FAMT PET was significantly associated with male, and positive LAT1 expression was significantly associated with male and nonadenocarcinoma. In the univariate analysis, high SUV(max) (>1.6) in (18)F-FAMT PET and positive LAT1 expression were significant predictor of the poor outcome. Multivariate analysis confirmed that positive LAT1 expression was an independent and significant factor for predicting poor prognosis in NSCLC (P=.035).

CONCLUSION

LAT1 expression is a stronger prognostic factor than (18)F-FAMT uptake in surgically resected NSCLC.

¹⁸F-FAMT uptake correlates with tumor proliferative activity in oral squamous cell carcinoma: comparative study with ¹⁸F-FDG PET and immunohistochemistry

OBJECTIVE

L-3-[¹⁸F]-fluoro-α-methyl tyrosine (FAMT) is transported into cancer cells by L: -type amino acid transporter 1 (LAT1). The purpose of the present study is to correlate the uptake of FAMT and FDG with the cellular proliferative activity measured by the Ki-67 labeling index (Ki-67 LI) in oral squamous cell carcinoma (OSCC).

METHODS

Twenty-five patients with OSCC were enrolled in this study. Both FAMT-PET and FDG-PET were performed within 4 weeks before surgery in all cases. The uptake of FAMT and FDG was compared by semiquantitative analysis with maximal standardized uptake values (SUVmax) of the primary tumors. Ki-67 LI of the tumors was analyzed by immunohistochemical staining and correlated with the clinicopathologic variables and the uptake of PET tracers.

RESULTS

For primary tumor detection, FAMT-PET exhibited a sensitivity of 84%, whereas that of FDG-PET was 88%. In all visible lesions, mean FDG uptake determined by average SUVmax was 9.7 (range 4.2-15.9) and mean FAMT uptake was 3.5 (range 1.3-8.5). The SUVmax of FAMT tended to show a better correlation with Ki-67 LI (r = 0.878) than that of FDG (r = 0.643).

CONCLUSIONS

Uptake of FAMT correlated with cellular proliferation of OSCC. FAMT-PET may be a useful procedure to evaluate tumor proliferation of OSCC.

Prognostic significance of L-type amino acid transporter 1 (LAT1) and 4F2 heavy chain (CD98) expression in surgically resectable stage III non-small cell lung cancer

The purpose of this study was to evaluate the prognostic value of L-type amino acid transporter 1 (LAT1) and 4F2 heavy chain (CD98) expression in patients with stage III non-small cell lung cancer (NSCLC). A total of 188 consecutive patients with pathologic stage III NSCLC were retrospectively reviewed. The expression of LAT1, CD98, Ki-67 labeling index, vascular endothelial growth factor (VEGF) as well as microvessel density (MVD) were evaluated immunohistochemically and correlated with the prognosis of patients after complete resection of the tumor. Positive expression of LAT1 and CD98 was noted in 58% (109/188) and 50% (94/188) of the cases, respectively (p=0.1473). A positive rate of LAT1 expression was significantly higher in squamous cell carcinoma (SQC) (90%, 48/53) and large-cell carcinoma (LCC) (100%, 12/12) than in adenocarcinoma (AC) (40%, 49/123). Moreover, a positive rate of LAT1 with CD98 expression was also significantly higher in SQC (74%, 39/53) and LCC (75%, 9/12) than AC (34%, 42/123). LAT1 expression was significantly higher in patients with mediastinal lymph node metastases than in patients without, and was significantly correlated with CD98, Ki-67 labeling index, VEGF and MVD. The 5-year survival rates of LAT1-positive and -negative patients and CD98-positive and -negative patients were 27.9 and 40.6% (p=0.0033), respectively, and 24.1 and 43.6% (p=0.0004), respectively. Multivariate analysis confirmed that positive expression of LAT1 and CD98 was an independent factor predicting a poor prognosis. In conclusion, the overexpression of LAT1 and CD98 is a pathological factor for predicting the prognosis of patients with surgically resectable stage III NSCLC.

Evaluation of thoracic tumors with (18)F-FMT and (18)F-FDG PET-CT: a clinicopathological study

L-[3-(18)F]-alpha-methyltyrosine ((18)F-FMT) is an aminoacid tracer for positron emission tomography (PET). The aim of this study was to determine whether PET-CT with (18)F-FMT provides additional information for the preoperative diagnostic workup as compared with (18)F-FDG PET. PET-CT studies with (18)F-FMT and (18)F-FDG were performed as a part of the preoperative workup in 36 patients with histologically confirmed bronchial carcinoma, 6 patients with benign lesions and a patient with atypical carcinoid. Expression of L-type amino acid transporter 1 (LAT1), CD98, Ki-67 labeling index, VEGF, CD31 and CD34 of the resected tumors were analyzed by immunohistochemical staining, and correlated with the uptake of PET tracers. For the detection of pulmonary malignant tumors, (18)F-FMT PET exhibited a sensitivity of 84% whereas the sensitivity for (18)F-FDG PET was 89% (p = 0.736). (18)F-FMT PET-CT and (18)F-FDG PET-CT agreed with pathological staging in 85 and 68%, respectively (p = 0.151). (18)F-FMT uptake was closely correlated with LAT1, CD98, cell proliferation and angiogenesis. The specificity of (18)F-FMT PET for diagnosing thoracic tumors was higher than that of (18)F-FDG PET. Our results suggest that coexpression of LAT1 and CD98 in addition to cell proliferation and angiogenesis is relavant for the progression and metastasis of lung cancer.

Correlation of angiogenesis with 18F-FMT and 18F-FDG uptake in non-small cell lung cancer

L-[3-18F]-alpha-methyltyrosine (18F-FMT) is an amino-acid tracer for positron-emission tomography (PET). We have conducted a clinicopathologic study to elucidate the correlation of angiogenesis with 18F-FMT and 2-[18F]-fluoro-2-deoxy-D-glucose (18F-FDG) uptake in patients with non-small cell lung cancer (NSCLC). Thirty-seven NSCLC patients were enrolled in this study, and two PET studies with 18F-FMT and 18F-FDG were performed. Uptake of PET tracers was evaluated with standardized uptake value. Vascular endothelial growth factor (VEGF), CD31, CD34, L-type amino acid transporter 1 (LAT1) and Ki-67 labeling index of the resected tumors were analyzed by immunohistochemical staining, and correlated with the clinicopathologic variables and the uptake of PET tracers. The median VEGF rate was 45% (range, 10-78%). High expression was seen in 30 patients (81%, 30/37). VEGF expression was statistically associated with progressively growing microvessel count. VEGF showed a correlation with LAT1 expression (P = 0.04) and Ki-67 labeling index (P = 0.01). However, it showed no correlation with age, gender, disease stage, tumor size, and histology. Microvessel density (MVD) showed no correlation with any parameters. 18F-FMT and 18F-FDG uptake correlated significantly with VEGF (P < 0.0001, P = 0.026, respectively), whereas the correlation of 18F-FMT and VEGF was more meaningful. The present study demonstrated that the metabolic activity of primary tumors as evaluated by PET study with 18F-FMT and 18F-FDG is related to tumor angiogenesis and the proliferative activity in NSCLC.

l-type amino acid transporter 1 and CD98 expression in primary and metastatic sites of human neoplasms

The significance of L-type amino acid transporter (LAT) 1 expression remains unclear in the metastatic process of human neoplasms, whereas experimental studies have demonstrated that LAT1 is associated with the metastatic process of cancer cells. We compared the immunohistochemical expression of LAT1 and CD98 between the primary site and a concordant pulmonary metastatic site in 93 cancer patients, all of whom had undergone thoracotomy. LAT1, CD98, Ki-67 labeling index, vascular endothelial growth factor (VEGF), CD31, and CD34 were analyzed by immunohistochemical staining in the resected tumors of 93 cancer patients: 45 colon cancers; nine breast cancers; eight head and neck cancers; 11 genital cancers; 14 soft-tissue sarcomas; and six other cancers. The expression of these markers was significantly higher in the metastatic sites than in the primary sites. In total, the positive rates of LAT1, CD98, Ki-67, VEGF, CD31, and CD34 were 40, 24, 56, 41, 45, and 39%, respectively, in the primary sites and 65, 45, 84, 67, 73, and 61%, respectively, in the metastatic sites. LAT1 expression was closely correlated with CD98 expression, angiogenesis, and cell proliferation. The association between LAT1 and CD98 expression was strongest in the primary and metastatic sites. The present study suggests that overexpression of LAT1 and CD98 has an important role to play in the metastatic process of variable human neoplasms. Moreover, LAT1 expression was significantly correlated with cell proliferation and angiogenesis.

Integrated FDG PET/CT: Utility and Applications in Clinical Oncology

Accurate diagnosis and staging are essential for an optimal management of cancer patients. Positron emision tomography with 2-deoxy-2-fluorine-18-fluoro-D-glucose (¹⁸FDG-PET) and, more recently, ¹⁸FDG-PET/computed tomography (¹⁸FDG-PET/CT) have emerged as powerful imaging tools in oncology, because of the valuable functional information they provide. The combined acquisition of PET and CT has synergistic advantages over its isolated constituents and minimizes their limitations. It decreases examination times by 25%–40%, leads to a higher patient throughput and unificates two imaging procedures in a single session. There is evidence that ¹⁸FDG-PET/CT is a more accurate test than either of its components for the evaluation of various tumors. It is a particularly valuable tool for detection of recurrence, especially in asymptomatic patients with rising tumor markers and those with negative or equivocal findings on conventional imaging tests. Yet, there are some limitations and areas of uncertainty, mainly regarding the lack of specificity of the ¹⁸FDG uptake and the variable ¹⁸FDG avidity of some cancers. This article reviews the advantages, limitations and main applications of ¹⁸FDG-PET/CT in oncology, with especial emphasis on lung cancer, colorectal cancer, lymphomas, melanoma and head and neck cancers.

Prospective comparison of FDG and FET PET/CT in patients with head and neck squamous cell carcinoma

AIM

The clinical usefulness of 2-deoxy-2-[F-18]fluoro-D-glucose-positron emission tomography (FDG-PET) in head and neck squamous cell carcinoma (HNSCC) is now well-documented. However, its sensitivity is greater than its specificity due to false-positive results in inflammatory or infectious lesions, which are frequent in this area, in particular after treatment by surgery and/or radiotherapy. O-2-fluoro-(18F)-ethyl-L-thyrosine (FET) has been reported not to be taken up by such lesions, and a preliminary study indicated that this may be clinically useful in HNSCC. We performed a prospective study to compare the diagnostic performances of FDG and FET PET/CT in the different settings of HNSCC.

MATERIALS AND METHODS

Twenty-seven patients (20 men and seven women, aged 48-76, among 30 patients included) and 69 suspected cancer sites are now evaluable on basis of postsurgical histology and/or follow-up greater than 6 months; 15 patients were referred for initial staging and 12 during posttherapy follow-up, a recurrence being suspected in eight of them. FDG and FET PET/CT were performed on two different days, the patient fasting for 6 h, 1 h after injection of 5 MBq/kg of body mass of each radiopharmaceutical. Both PET/CT examinations were blind read more than 6 months after the end of inclusions in a random order for each tracer and with a time interval greater than 1 month between FDG and FET PET/CT blind readings.

RESULTS

Overall diagnostic performances, derived from blind reading: FDG PET/CT on a per patient basis: sensitivity 100%, specificity 71%, accuracy 93%; FDG PET/CT on a per site basis: sensitivity 95%, specificity 63%, accuracy 83%; FET PET/CT on a per patient basis: sensitivity 70%, specificity 100%, accuracy 78%; FET PET/CT on a per site basis: sensitivity 64%, specificity 100%, accuracy 78%. At site level, sensitivity was significantly greater with FDG (p<0.02) and specificity with FET (p<0.01). The statistical level of significance was not reached at patient level.

CONCLUSION

Although its good specificity was confirmed, FET did not appear to be suited as a first-line PET tracer in HNSCC imaging and cannot replace FDG for staging due to insufficient sensitivity. However, it was useful in a few selected cases to favor a wait and see attitude when a FDG+ FET- focus was discovered in patients referred for systematic FDG PET during follow-up. In contrast, second primary cancers should not be ruled out if FDG was clearly positive in the lungs or the digestive tract.

Expression of L-type amino acid transporter 1 (LAT1) in neuroendocrine tumors of the lung

Amino acid transport systems play an important role in cellular proliferation. L-type amino acid transporter 1 (LAT1) has been associated with tumor growth, and is highly expressed in the established tumor cell lines and primary human neoplasms. In this study, we investigated the expression of LAT1 to evaluate the malignant potential and prognostic significance in neuroendocrine (NE) tumors of the lung. Twenty-one surgically resected, large cell neuroendocrine carcinomas (LCNEC), 13 small cell lung cancers (SCLC), five atypical carcinoids (AC), and 10 typical carcinoids (TC) were enrolled in the study. LAT1 expression and Ki-67 labeling index of the NE tumors were analyzed by immunohistochemical staining. LAT1 was overexpressed in 52.4% of the LCNEC, in 46.2% of the SCLC, and in 25% of the AC. LAT1 expression in LCNEC was significantly associated with lymph node metastasis and poor outcome. Moreover, a significant correlation was found between LAT1 expression and Ki-67 in both LCNEC and SCLC. Expression of LAT1 tended to increase from low-grade to high-grade NE tumors. The present results suggest that LAT1 may play a significant role in cellular proliferation, lymph node metastasis, and poor outcome in patients with NE tumors of the lung.

Prognostic significance of L-type amino acid transporter 1 expression in resectable stage I-III nonsmall cell lung cancer

The clinical significance of L-type amino acid transporter 1 (LAT1) expression remains unclear, whereas many experimental studies have demonstrated that LAT1 is associated with the proliferation of cancer cells. The purpose of this study was to evaluate the prognostic value of LAT1 in patients with nonsmall cell lung cancer (NSCLC). A total of 321 consecutive patients with completely resected pathologic stage I–III NSCLC were retrospectively reviewed. Expression of LAT1 and proliferative activity, as determined by the Ki-67 labelling index, was also evaluated immunohistochemically and correlated with the prognosis of patients who underwent complete resection of the tumour. Expression of LAT1 was positive in 163 patients (51%) (29% of adenocaricnoma (58 of 200 patients), 91% of squamous cell carcinoma (91 of 100 patients), and 67% of large cell carcinoma (14 of 21 patients)). The 5-year survival rate of LAT1-positive patients (51.8%) was significantly worse than that of LAT1-negative patients (87.8%; P<0.001). L-type amino acid transporter 1 expression was significantly associated with lymph node metastasis and disease stage. Multivariate analysis confirmed that positive expression of LAT1 was an independent factor for predicting a poor prognosis. There was a significant correlation between LAT1 expression and Ki-67 labelling index. LAT1 expression is a promising pathological factor to predict the prognosis in patients with resectable stage I–III NSCLC.

Fluorine-18-alpha-methyltyrosine positron emission tomography for diagnosis and staging of lung cancer: a clinicopathologic study

PURPOSE

L-[3-(18)F]-alpha-methyltyrosine ([(18)F]FMT) is an amino acid tracer for positron emission tomography (PET). We evaluated the diagnostic usefulness of [(18)F]FMT PET in non-small-cell lung cancer (NSCLC) patients. Tumor uptake of [(18)F]FMT was compared with that of 2-[(18)F]-fluoro-2-deoxy-D-glucose ([(18)F]FDG) and correlated with L-type amino acid transporter 1 (LAT1) expression.

EXPERIMENTAL DESIGN

Fifty NSCLC patients were enrolled in this study, and a pair of PET study with [(18)F]FMT and [(18)F]FDG was done. LAT1 expression and Ki-67 labeling index of the resected tumors were analyzed by immunohistochemical staining.

RESULTS

For the primary tumor detection, [(18)F]FMT PET exhibited a sensitivity of 90% whereas the sensitivity for [(18)F]FDG PET was 94%. For lymph node staging, the sensitivity and specificity of [(18)F]FMT PET were 57.8% and 100%, and those of [(18)F]FDG PET were 65.7% and 91%, respectively. The expression of LAT1 in squamous cell carcinoma and large cell carcinoma was significantly higher than that in adenocarcinoma. [(18)F]FMT uptake was also higher in squamous cell carcinoma and large cell carcinoma than in adenocarcinoma. Uptake of [(18)F]FMT in the tumor is closely correlated with LAT1 expression (rho = 0.890).

CONCLUSION

[(18)F]FMT PET had no false-positives in the detection of primary tumor and lymph node metastasis and could improve the diagnostic performance in NSCLC. Uptake of [(18)F]FMT correlated with the expression of LAT1 that showed a significant association with cellular proliferation.