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

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.

Pulmonary pleomorphic carcinoma: a clinicopathological study including EGFR mutation analysis

BACKGROUND

Pulmonary pleomorphic carcinoma is a rare epithelial tumor and has an aggressive clinical course. As few studies of pulmonary pleomorphic carcinoma have been described, the clinicopathological characteristics of the disease remain unclear. Especially, the information on the epidermal growth factor receptor (EGFR) mutation status of pulmonary pleomorphic carcinoma is sparse.

METHODS

We retrospectively examined 17 patients with pulmonary pleomorphic carcinoma. EGFR mutation and Ki-67 labeling index were investigated in these patients.

RESULTS

The median age of the patients was 72 years (range, 47-84 years). Thirteen patients were men and four were women. EGFR mutation was observed in 3 (18%) of 17 patients. The median value of Ki-67 labeling index was 62% (range, 20-87%). Positron emission tomography with 18-fluorodeoxy-glucose was performed in 16 patients, and the standardized uptake value tended to be high (median 19.3). The survival of patients without surgery demonstrated a significantly poor prognosis compared with those with surgery (P = 0.0096). Palliative chemotherapy was almost poor response in advanced pulmonary pleomorphic carcinoma. The response to gefitinib in a patient with EGFR mutation was small and transient.

CONCLUSION

EGFR mutation was recognized in approximately 20% of patients with pulmonary pleomorphic carcinoma. It is necessary to investigate whether the use of a molecular targeting drug improves outcome for pulmonary pleomorphic carcinoma.

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.

Overexpression of the mammalian target of rapamycin: a novel biomarker for poor survival in resected early stage non-small cell lung cancer

INTRODUCTION

The best hope of cure for patients with non-small cell lung cancer (NSCLC) is surgical resection. However, even in stage IA patients, 30% die within 5 years. Further improvements in survival require a biomarker(s), which defines the subset of these patients destined to do badly so that they could be targeted for additional therapies. Here, we investigate whether the immunohistochemical expression of a key kinase implicated in lung cancer biology, the mammalian target of rapamycin (mTOR) can predict survival outcome in patients with early stage resected NSCLC.

MATERIALS AND METHODS

One hundred thirty-four patients with resected early stage (IA-IIB) NSCLC were pathologically reviewed centrally before staining for mTOR. Multiple variables including age, sex, stage, angioinvasion, lymph node status, and mTOR staining were assessed by univariate and multivariate analyses.

RESULTS

Stage (p = 0.044), lymph node status (p = 0.049), angioinvasion (p = 0.017), and mTOR staining (p = 0.007) were significant univariate predictors of poor survival. However, only angioinvasion (p = 0.016) and mTOR staining (p = 0.046) remained significant after multivariate analysis. Moreover, mTOR staining was the only variable to predict poor outcome in patients who either had negative lymph nodes (p = 0.016) or were stage IA (p = 0.0016).

CONCLUSIONS

The mTOR staining provides a new biomarker for poor outcome in early stage NSCLC and could enable resected stage IA patients to be selected for novel therapies possibly with an mTOR inhibitor.

L-type amino acid transporter 1 inhibitors inhibit tumor cell growth

Most tumor cell membranes overexpress L-type amino acid transporter 1, while normal cell membranes contain l-type amino acid transporter 2; both are Na(+)-independent amino acid transporters. Therefore, compounds that selectively inhibit L-type amino acid transporter 1 offer researchers with a novel cancer molecular target. Synthetic chemistry efforts and in vitro screening have produced a variety of novel compounds possessing high in vitrol-type amino acid transporter 1 selectivity; KYT-0353 was one such compound. The present studies illustrate that KYT-0353 inhibited (14)C-leucine uptake and cell growth in human colon cancer-derived HT-29 cells; IC(50)s were 0.06 microm and 4.1 microm, respectively. KYT-0353 also inhibited (14)C-leucine uptake in mouse renal proximal tubule cells expressing l-type amino acid transporter 1, and inhibited cell growth; IC(50)s were 0.14 microm and 16.4 microm, respectively. Compared to control animals, intravenously administered KYT-0353 (12.5 mg/kg and 25.0 mg/kg) showed statistically significant growth inhibition against HT-29 tumors transplanted to nude mice with maximal inhibition ratios of 65.9% and 77.2%, respectively. Body weight increase with time--a safety indicator--was slightly depressed at 12.5 mg/kg and 25.0 mg/kg with maximal ratios of 3.7% (day 2) and 6.3% (day 11), respectively. Thus, KYT-0353 showed significant growth inhibitory effects on HT-29 cells both in vitro and in vivo, whereas it only caused a slight body weight depression. Therefore, KYT-0353 appears to have potential as a novel anti-tumor agent, presumably via selective in vivol-type amino acid transporter 1 inhibition.

CD98 expression is associated with poor prognosis in resected non-small-cell lung cancer with lymph node metastases

BACKGROUND

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 resectable non-small-cell lung cancer (NSCLC) patients with N1 and N2 nodal involvement.

METHODS

A total of 220 consecutive patients were retrospectively reviewed. Immunohistochemical expression of LAT1, CD98, Ki-67 labeling index, vascular endothelial growth factor (VEGF), and microvessel density (MVD) was correlated with clinical features and prognosis of patients after complete resection of the tumor.

RESULTS

Positive expression of LAT1 and CD98 was recognized in 60% (132/220) and 47% (103/220), respectively (P = 0.021). A positive rate of LAT1 expression was significantly higher in squamous cell carcinoma (SQC) (91%; 65/71) and large cell carcinoma (LCC) (82%; 9/11) than in adenocarcinoma (AC) (42%; 58/138). Moreover, a positive rate of CD98 expression was also significantly higher in SQC (76%; 54/71) and LCC (73%; 8/11) than in AC (30%; 42/138). LAT1 expression was significantly correlated with CD98, Ki-67 labeling index, VEGF, and MVD. The 5-year survival rates of LAT1-positive and LAT1-negative patients and CD98-positive and CD98-negative patients, were 43% and 48% (P = 0.1043), respectively and 39% and 50% (P = 0.0239), respectively. Multivariate analysis confirmed that positive expression of CD98 was an independent factor for predicting a poor prognosis.

CONCLUSIONS

In our limited series, CD98 is a pathological factor that predicts prognosis in resectable adenocarcinoma patients with N2 disease.

A novel five-antibody immunohistochemical test for subclassification of lung carcinoma

Malignant epithelial lung carcinoma can be subclassified by histology into several tumor types, including adenocarcinoma and squamous cell carcinoma. The need for a uniform method of classifying lung carcinomas is growing as clinical trials reveal treatment and side effect differences associated with histological subtypes. Diagnosis is primarily performed by morphological assessment. However, the increased use of needle biopsy has diminished the amount of tissue available for interpretation. These changes in how lung carcinomas are diagnosed and treated suggest that the development of improved molecular-based classification tools could improve patient management. We used a 551-patient surgical specimen lung carcinoma retrospective cohort from a regional hospital to assess the association of a large number of proteins with histological type by immunohistochemistry. Five of these antibodies, targeting the proteins TRIM29, CEACAM5, SLC7A5, MUC1, and CK5/6, were combined into one test using a weighted algorithm trained to discriminate adenocarcinoma from squamous cell carcinoma. Antibody-based classification on 600 muM tissue array cores with the five-antibody test was compared to standard histological evaluation on surgical specimens in three independent lung carcinoma cohorts (combined population of 1111 patients). In addition, the five-antibody test was tested against the two-marker panel thyroid transcription factor-1 (TTF-1) and TP63. Both the five-antibody test and TTF-1/TP63 panel had similarly low misclassification rates on the validation cohorts compared to morphological-based diagnosis (4.1 vs 3.5%). However the percentage of patients remaining unclassifiable by TTF-1/TP63 (22%, 95% CI: 20-25%) was twice that of the five-antibody test (11%, 95% CI: 8-13%). The results of this study suggest the five-antibody test may have an immediate function in the clinic for helping pathologists distinguish lung carcinoma histological types. The results also suggest that if validated in prospectively defined clinical trials this classifier might identify candidates for targeted therapy that are overlooked with current diagnostic approaches.

LAT1 expression in non-small-cell lung carcinomas: analyses by semiquantitative reverse transcription-PCR (237 cases) and immunohistochemistry (295 cases)

OBJECTIVE

System l-amino acid transport mediates the uptake of aromatic neutral amino acids and nutritionally essential amino acids from extracellular fluids. Little is known about the role of l-amino acid transporter 1 (LAT1), a member of the system l-amino acid transporter family, in non-small-cell lung carcinomas (NSCLCs).

PATIENTS AND METHODS

We examined (i) LAT1 mRNA levels in 40 normal lung tissues (NLTs) and 237 NSCLCs using semiquantitative RT-PCR, (ii) LAT1 protein expression in 295 NSCLCs using immunohistochemistry, and (iii) whether LAT1 mRNA and protein expressions were related to clinicopathologic findings and outcome.

RESULTS

The LAT1 mRNA level was significantly higher in all NSCLCs (6.81+/-1.13) than in NLT (1.00+/-0.18). The LAT1 mRNA level showed no association with clinicopathologic findings or outcome. LAT1 protein was detected with a diffuse or granular appearance within the cytoplasm and/or on the plasma membrane of tumor cells. When tumors were graded as positive if staining indicating a plasma membrane expression of LAT1 protein made up more than 10% of the tumor, the frequency of this membrane expression was found to be associated with tumor histology, differentiation grade, pathologic stage, T classification, pleural invasion, lymph-vessel invasion, and overall survival rate.

CONCLUSION

Detection of a plasma membrane expression of LAT1 protein would appear to be of value in informing the prognosis in NSCLC cases.

Significance of system L amino acid transporter 1 (LAT-1) and 4F2 heavy chain (4F2hc) expression in human developing intestines

To clarify the significance of expression of system L amino acid transporter 1 (LAT1) and 4F2 heavy chain (4F2hc) in the developing intestine, immunohistochemical investigation and molecular analysis were performed in the human embryonic and/or fetal intestines, ranging from 28–30 days to 34–35 weeks gestation. The molecular analysis for the expression of LAT1 and 4F2hc mRNAs was done in the pure epithelial cell samples prepared after laser assisted microdissection. The immunoreactivities against LAT1 and 4F2hc were detected along the basolateral cell membrane of the primitive gut epithelium at 28–30 days gestation. According to advance in gestational age of up to 24–25 weeks gestation, the immunoreactivity of LAT1 was predominantly observed in the supranuclear cytplasmic localization with a granular or dot-like staining pattern. Up to 8–9 weeks gestation, the immunoreactivity of 4F2hc showed almost the same as that of LAT1. However, after the age of 12–13 weeks gestation, the immunoreactivity of 4F2hc was predominantly localized along the cell membrane of apical surface of the epithelial cells. No apical and linear membranous localization of LAT1 was observed until nearly 20 weeks gestation. In the late gestational stage, both the immunoreactivities against LAT1 and 4F2hc were localized along the apical surface of the epithelial cells. In conclusion, the expression of LAT1 and 4F2hc in early developing intestine suggests they have a more important role in cell proliferation rather than functional differentiation. The predominant cytoplasmic localization of LAT1 during mid-fetal life seems to be largely inactive as amino acid transporter. On the other hand, the apical and linear membranous co-localization of LAT1 and 4F2hc in the late fetal life suggests that these molecules may play a role as a functional amino acid transporter in the fetal intestinal epithelium.

L-type amino acid transporter 1 (LAT1) is frequently expressed in thymic carcinomas but is absent in thymomas

BACKGROUND

L-type amino acid transporter 1 (LAT1) has been associated with tumor growth and is highly expressed in the primary human neoplasms. We investigated the significance of LAT1 expression to evaluate malignant potential in thymic epithelial tumors.

MATERIALS AND METHODS

Immunohistochemical studies of 45 surgically resected thymic epithelial tumors [15 noninvasive thymomas (NT), 22 invasive thymomas (IT), and 8 thymic carcinomas (TC)] were conducted. LAT1, Ki-67 labeling index (LI), vascular endothelial growth factor (VEGF), and microvessel density of the thymic epithelial tumors were analyzed.

RESULTS

LAT1 expression for thymomas and thymic carcinomas were 0 (0%) of 37 and 6 (75%) of eight patients, respectively. Ki-67 LI for NT, IT, and TC were 7.9 +/- 2.8%, 16.1 +/- 8.5%, and 50.6 +/- 24.4%, respectively. VEGF expression in groups NT, IT, and TC was 0 (0%) of 15, 9 (41%) of 22, and 6 (75%) of eight patients, respectively. VEGF expression was statistically associated with microvessel count. The LAT1 expression was statistically associated with Ki-67 LI, VEGF, and microvessel density in thymic carcinomas.

CONCLUSION

LAT1 is frequently expressed in thymic carcinomas but is absent in thymomas. Our results suggest that LAT1 expression might be an immunohistochemical marker for carcinomas, and could distinguish between thymomas and thymic carcinomas.

L-type amino-acid transporter 1 as a novel biomarker for high-grade malignancy in prostate cancer

To find reliable biomarkers for high-grade malignancy, the relationship between immunohistochemical L-type amino-acid transporter 1 (LAT1) expression of biopsy samples, determined with the newly developed monoclonal antibody against human LAT1, and prognosis of patients with prostate cancer, was investigated. The intensity and score of immunohistochemical LAT1 expression of first biopsy samples were assessed using the modified Sinicrope et al. method and were found to be correlated with poor survival for the study group of 114 surgically treated patients as a whole (P = 0.0002 and 0.0270, respectively). LAT1 intensity further had a significant relationship (P = 0.0057) with prognosis in pathological T3 + T4 groups. Multivariate analysis indicated that the LAT1 intensity and score were more reliable prognostic markers, compared with the Gleason score and the Ki-67 labeling index. A relationship of the LAT1 intensity and score with prognosis could also be confirmed in 63 patients with inoperable cancer (P = 0.0070 and <0.0001, respectively). Similarly, significant differences in prognosis were confirmed in clinical T3 + T4 groups (P = 0.0091 and 0.0244, respectively). Moreover, the combination of LAT1 expression and Gleason score was found to have a more reliable correlation with prognosis. Thus, elevated LAT1 expression in prostate cancers is a novel independent biomarker of high-grade malignancy, which can be utilized together with the Gleason score, which is mainly dependent on cellular and structural atypia, to assess prognosis.

Quantification of tryptophan transport and metabolism in lung tumors using PET

Abnormal tryptophan metabolism catalyzed by indoleamine 2,3-dioxygenase may play a prominent role in tumor immunoresistance in many tumor types, including lung tumors. The goal of this study was to evaluate the in vivo kinetics of alpha-(11)C-methyl-l-tryptophan (AMT), a PET tracer for tryptophan metabolism, in human lung tumors.

METHODS

Tracer transport and metabolic rates were evaluated in 18 lesions of 10 patients using dynamic PET/CT with AMT. The kinetic values were compared between tumors and unaffected lung tissue, tested against a simplified analytic approach requiring no arterial blood sampling, and correlated with standardized uptake values (SUVs) obtained from (18)F-FDG PET/CT scans.

RESULTS

Most non-small cell lung cancers (NSCLCs) showed prolonged retention of AMT, but 3 other lesions (2 benign lesions and a rectal cancer metastasis) and unaffected lung tissue showed no such retention. Transport and metabolic rates of AMT were substantially higher in NSCLCs than in the other tumors and unaffected lung tissue. A simplified analytic approach provided an excellent estimate of transport rates but only suboptimal approximation of tryptophan metabolic rates. (18)F-FDG SUVs showed a positive correlation with AMT uptake, suggesting higher tryptophan transport and metabolism in tumors with higher proliferation rates.

CONCLUSION

Prolonged retention of AMT in NSCLCs suggests high metabolic rates of tryptophan in these tumors. AMT PET/CT may be a clinically useful molecular imaging method for personalized cancer treatment by identifying and monitoring patients who have increased tumor tryptophan metabolism and are potentially sensitive to immunopharmacotherapy with indoleamine 2,3-dioxygenase inhibitors.

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.

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.

Establishment and characterization of mammalian cell lines stably expressing human L-type amino acid transporters

System L (SL), a basolateral amino acid transporter, transports large neutral amino acids (LNAAs) in a Na(+)-independent manner. Previously, we identified two isoforms of transporters: L-type amino acid transporter 1 (LAT1) and 2 (LAT2) and revealed their distinct substrate selectivity and transport properties. In this study, to establish more stable human LAT1 (hLAT1) and LAT2 (hLAT2) in vitro assay systems, we established mouse cell lines stably expressing hLAT1 (S2-LAT1) and hLAT2 (S2-LAT2). Real-time quantitative RT-PCR analysis revealed that S2-LAT1 and S2-LAT2 cells express hLAT1 and hLAT2 mRNAs at 20 - 1000-fold higher levels than those of endogenous mouse Lat1 and Lat2. S2-LAT1 and S2-LAT2 mediated [(14)C]L-leucine transport properties were measured and corresponded to results observed via Xenopus oocytes. Using these cells, the data demonstrate that hLAT1 and hLAT2 exhibit different characters in the acceptance of alpha-methyl amino acids and amino acid-related compounds with bulky side chains such as thyroid hormones and melphalan. S2-LAT1 and S2-LAT2 cells are expected to facilitate hLAT1 and hLAT2 substrate recognition research and contribute to drug development by providing an efficient assay system to screen for chemical compounds that interact with hLAT1 and hLAT2.

System L amino acid transporter inhibitor enhances anti-tumor activity of cisplatin in a head and neck squamous cell carcinoma cell line

LAT1, a subunit of heterodimeric system L transporter responsible for transporting neutral amino acids into cells, has been investigated in several cancers because of its onco-fetal nature. Based on the studies of its functional inhibition, LAT1 has been proposed to be a new molecular target of a cancer therapy. We have shown here that human head and neck cancer cell line, Hep-2, expresses both LAT1 and 4F2hc, another subunit of system L transporter. An inhibitor of system L, 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid (BCH), inhibited leucine uptake by the cells. BCH administration or restriction of essential amino acid leucine decreased viability of Hep-2 cells. Co-administration of cisplatin with BCH reduced the viability of the cells more than either agent alone. When BCH treatment preceded cisplatin administration, reduction in Hep-2 cell viability was additive. In contrast, when BCH was given after cisplatin treatment, synergistic effect in decreasing the number of viable cells was obtained. BCH treatment decreased the phosphorylation of mTOR, p70S6K and 4EBP1, suggesting that BCH enhanced anti-tumor action of cisplatin by inhibiting mTOR pathway. This potentiation may be used to reduce cisplatin exposure to alleviate many unwanted toxicity of the drug.

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.