Inhibition of amino acid transporter LAT1 in cancer cells suppresses G0/G1-S transition by downregulating cyclin D1 via p38 MAPK activation.

L-type amino acid transporter 1 (LAT1, SLC7A5) is upregulated in various cancers and associated with disease progression. Nanvuranlat (Nanv; JPH203, KYT-0353), a selective LAT1 inhibitor, suppresses the uptake of large neutral amino acids required for rapid growth and proliferation of cancer cells. Previous studies have suggested that the inhibition of LAT1 by Nanv induces the cell cycle arrest at G0/G1 phase, although the underlying mechanisms remain unclear. Using pancreatic cancer cells arrested at the restriction check point (R) by serum deprivation, we found that the Nanv drastically suppresses the G0/G1-S transition after release. This blockade of the cell cycle progression was accompanied by a sustained activation of p38 mitogen-activated protein kinase (MAPK) and subsequent phosphorylation-dependent proteasomal degradation of cyclin D1. Isoform-specific knockdown of p38 MAPK revealed the predominant contribution of p38α. Proteasome inhibitors restored the cyclin D1 amount and released the cell cycle arrest caused by Nanv. The increased phosphorylation of p38 MAPK and the decrease of cyclin D1 were recapitulated in xenograft tumor models treated with Nanv. This study contributes to delineating the pharmacological activities of LAT1 inhibitors as anti-cancer agents and provides significant insights into the molecular basis of the amino acid-dependent cell cycle checkpoint at G0/G1 phase.

Upregulation of ATF4 mediates the cellular adaptation to pharmacologic inhibition of amino acid transporter LAT1 in pancreatic ductal adenocarcinoma cells.

L-type amino acid transporter 1 (LAT1) is recognized as a promising target for cancer therapy; however, the cellular adaptive response to its pharmacological inhibition remains largely unexplored. This study examined the adaptive response to LAT1 inhibition using nanvuranlat, a high-affinity LAT1 inhibitor. Proteomic analysis revealed the activation of a stress-induced transcription factor ATF4 following LAT1 inhibition, aligning with the known cellular responses to amino acid deprivation. This activation was linked to the GCN2-eIF2α pathway which regulates translation initiation. Our results show that ATF4 upregulation counteracts the suppressive effect of nanvuranlat on cell proliferation in pancreatic ductal adenocarcinoma cell lines, suggesting a role for ATF4 in cellular adaptation to LAT1 inhibition. Importantly, dual targeting of LAT1 and ATF4 exhibited more substantial anti-proliferative effects in vitro than individual treatments. This study underscores the potential of combining LAT1 and ATF4 inhibition as a therapeutic strategy in cancer treatment.

Invariant NKT cells metabolically adapt to the acute myeloid leukaemia environment.

Acute myeloid leukaemia (AML) creates an immunosuppressive environment to conventional T cells through Arginase 2 (ARG2)-induced arginine depletion. We identify that AML blasts release the acute phase protein serum amyloid A (SAA), which acts in an autocrine manner to upregulate ARG2 expression and activity, and promote AML blast viability. Following in vitro cross-talk invariant natural killer T (iNKT) cells become activated, upregulate mitochondrial capacity, and release IFN-γ. iNKT retain their ability to proliferate and be activated despite the low arginine AML environment, due to the upregulation of Large Neutral Amino Acid Transporter-1 (LAT-1) and Argininosuccinate Synthetase 1 (ASS)-dependent amino acid pathways, resulting in AML cell death. T cell proliferation is restored in vitro and in vivo. The capacity of iNKT cells to restore antigen-specific T cell immunity was similarly demonstrated against myeloid-derived suppressor cells (MDSCs) in wild-type and Jα18-/- syngeneic lymphoma-bearing models in vivo. Thus, stimulation of iNKT cell activity has the potential as an immunotherapy against AML or as an adjunct to boost antigen-specific T cell immunotherapies in haematological or solid cancers.

LAT1 enables T cell activation under inflammatory conditions.

The aim of this study was to assess the L-type amino acid transporter-1 (LAT1) as a possible therapeutic target for rheumatoid arthritis (RA). Synovial LAT1 expression in RA was monitored by immunohistochemistry and transcriptomic datasets. The contribution of LAT1 to gene expression and immune synapse formation was assessed by RNA-sequencing and total internal reflection fluorescent (TIRF) microscopy, respectively. Mouse models of RA were used to assess the impact of therapeutic targeting of LAT1. LAT1 was strongly expressed by CD4+ T cells in the synovial membrane of people with active RA and the level of expression correlated with levels of ESR and CRP as well as DAS-28 scores. Deletion of LAT1 in murine CD4+ T cells inhibited the development of experimental arthritis and prevented the differentiation of CD4+ T cells expressing IFN-γ and TNF-α, without affecting regulatory T cells. LAT1 deficient CD4+ T cells demonstrated reduced transcription of genes associated with TCR/CD28 signalling, including Akt1, Akt2, Nfatc2, Nfkb1 and Nfkb2. Functional studies using TIRF microscopy revealed a significant impairment of immune synapse formation with reduced recruitment of CD3ζ and phospho-tyrosine signalling molecules in LAT1 deficient CD4+ T cells from the inflamed joints but not the draining lymph nodes of arthritic mice. Finally, it was shown that a small molecule LAT1 inhibitor, currently undergoing clinical trials in man, was highly effective in treating experimental arthritis in mice. It was concluded that LAT1 plays a critical role in activation of pathogenic T cell subsets under inflammatory conditions and represents a promising new therapeutic target for RA.

Combination effects of amino acid transporter LAT1 inhibitor nanvuranlat and cytotoxic anticancer drug gemcitabine on pancreatic and biliary tract cancer cells.

BACKGROUND: Cytotoxic anticancer drugs widely used in cancer chemotherapy have some limitations, such as the development of side effects and drug resistance. Furthermore, monotherapy is often less effective against heterogeneous cancer tissues. Combination therapies of cytotoxic anticancer drugs with molecularly targeted drugs have been pursued to solve such fundamental problems. Nanvuranlat (JPH203 or KYT-0353), an inhibitor for L-type amino acid transporter 1 (LAT1; SLC7A5), has novel mechanisms of action to suppress the cancer cell proliferation and tumor growth by inhibiting the transport of large neutral amino acids into cancer cells. This study investigated the potential of the combined use of nanvuranlat and cytotoxic anticancer drugs. METHODS: The combination effects of cytotoxic anticancer drugs and nanvuranlat on cell growth were examined by a water-soluble tetrazolium salt assay in two-dimensional cultures of pancreatic and biliary tract cancer cell lines. To elucidate the pharmacological mechanisms underlying the combination of gemcitabine and nanvuranlat, we investigated apoptotic cell death and cell cycle by flow cytometry. The phosphorylation levels of amino acid-related signaling pathways were analyzed by Western blot. Furthermore, growth inhibition was examined in cancer cell spheroids. RESULTS: All the tested seven types of cytotoxic anticancer drugs combined with nanvuranlat significantly inhibited the cell growth of pancreatic cancer MIA PaCa-2 cells compared to their single treatment. Among them, the combined effects of gemcitabine and nanvuranlat were relatively high and confirmed in multiple pancreatic and biliary tract cell lines in two-dimensional cultures. The growth inhibitory effects were suggested to be additive but not synergistic under the tested conditions. Gemcitabine generally induced cell cycle arrest at the S phase and apoptotic cell death, while nanvuranlat induced cell cycle arrest at the G0/G1 phase and affected amino acid-related mTORC1 and GAAC signaling pathways. In combination, each anticancer drug basically exerted its own pharmacological activities, although gemcitabine more strongly influenced the cell cycle than nanvuranlat. The combination effects of growth inhibition were also verified in cancer cell spheroids. CONCLUSIONS: Our study demonstrates the potential of first-in-class LAT1 inhibitor nanvuranlat as a concomitant drug with cytotoxic anticancer drugs, especially gemcitabine, on pancreatic and biliary tract cancers.

Retraction: Nuclear Morphometric Analysis of Leydig Cells of Male Pubertal Rats Exposed In Utero to Di(n-butyl) Phthalate.

[This retracts the article on p. 439 in vol. 26, PMID: 24526819.].

Pharmacologic inhibition of LAT1 predominantly suppresses transport of large neutral amino acids and downregulates global translation in cancer cells.

L-type amino acid transporter 1 (LAT1; SLC7A5), which preferentially transports large neutral amino acids, is highly upregulated in various cancers. LAT1 supplies cancer cells with amino acids as substrates for enhanced biosynthetic and bioenergetic reactions and stimulates signalling networks involved in the regulation of survival, growth and proliferation. LAT1 inhibitors show anti-cancer effects and a representative compound, JPH203, is under clinical evaluation. However, pharmacological impacts of LAT1 inhibition on the cellular amino acid transport and the translational activity in cancer cells that are conceptually pivotal for its anti-proliferative effect have not been elucidated yet. Here, we demonstrated that JPH203 drastically inhibits the transport of all the large neutral amino acids in pancreatic ductal adenocarcinoma cells. The inhibitory effects of JPH203 were observed even in competition with high concentrations of amino acids in a cell culture medium. The analyses of the nutrient-sensing mTORC1 and GAAC pathways and the protein synthesis activity revealed that JPH203 downregulates the global translation. This study demonstrates a predominant contribution of LAT1 to the transport of large neutral amino acids in cancer cells and the suppression of protein synthesis by JPH203 supposed to underly its broad anti-proliferative effects across various types of cancer cells.

Proteomics and phosphoproteomics reveal key regulators associated with cytostatic effect of amino acid transporter LAT1 inhibitor.

L-type amino acid transporter 1 (LAT1) is highly expressed in various cancers and plays important roles not only in the amino acid uptake necessary for cancer growth but also in cellular signaling. Recent research studies have reported anticancer effects of LAT1 inhibitors and demonstrated their potential for cancer therapy. Here, we characterized the proteome and phosphoproteome in LAT1-inhibited cancer cells. We used JPH203, a selective LAT1 inhibitor, and performed tandem mass tag-based quantitative proteomics and phosphoproteomics on four biliary tract cancer cell lines sensitive to JPH203. Our analysis identified hundreds to thousands of differentially expressed proteins and phosphorylated sites, demonstrating the broad influence of LAT1 inhibition. Our findings showed various functional pathways altered by LAT1 inhibition, and provided possible regulators and key kinases in LAT1-inhibited cells. Comparison of these changes among cell lines provides insights into general pathways and regulators associated with LAT1 inhibition and particularly suggests the importance of cell cycle-related pathways and kinases. Moreover, we evaluated the anticancer effects of the combinations of JPH203 with cell cycle-related kinase inhibitors and demonstrated their potential for cancer therapy. This is the first study providing the proteome-wide scope of both protein expression and phosphorylation signaling perturbed by LAT1 inhibition in cancer cells.

First-in-human phase I study of JPH203, an L-type amino acid transporter 1 inhibitor, in patients with advanced solid tumors.

This open-label first-in-human study evaluated JPH203, which is a novel selective L-type amino acid transporter 1 inhibitor. We also evaluated the association between the N-acetyltransferase 2 phenotype and outcomes. Japanese patients with advanced solid tumors received daily intravenous JPH203 treatment for 7 days, followed by a 21-day rest period, at escalating doses of 12-85 mg/m2. Dose-limiting toxicities were evaluated during the first cycle using a 3 + 3 design. The study enrolled 17 patients, although grade 3 liver dysfunction was detected in one of six patients receiving 60 mg/m2 and in the first patient to receive 85 mg/m2. Further enrollment was terminated and the maximum tolerated dose was defined as 60 mg/m2. The AUC∞ increased between 12 mg/m2 and 25 mg/m2, although no differences were observed at 25-40 mg/m2. Partial response was observed for one patient with biliary tract cancer (BTC) at the 12 mg/m2 dose, and disease control was achieved by 3 of 6 patients at the 12 mg/m2 and 25 mg/m2 dose levels. Based on these results, we recommend a phase II dose of 25 mg/m2. The disease control rate for BTC was 60%. Two patients with grade 3 liver dysfunction had the rapid N-acetyltransferase 2 phenotype, and disease control was more common for the non-rapid phenotype (50% vs. 12.5%). It appears that JPH203 was well-tolerated and provided promising activity against BTC. The N-acetyltransferase 2 phenotype might help predict the safety and efficacy of JPH203. Clinical trial registration: UMIN000016546.

Metabolic Acidosis Alters Expression of Slc22 Transporters in Mouse Kidney.

INTRODUCTION: The kidneys play a central role in eliminating metabolic waste products and drugs through transporter-mediated excretion along the proximal tubule. This task is mostly achieved through a variety of transporters from the solute carrier family 22 (SLC22) family of organic cation and anion transporters. Metabolic acidosis modulates metabolic and renal functions and also affects the clearance of metabolites and drugs from the body. We had previously shown that induction of metabolic acidosis in mice alters a large set of transcripts, among them also many transporters including transporters from the Slc22 family. OBJECTIVE: Here we further investigated the impact of acidosis on Slc22 family members. METHODS: Metabolic acidosis was induced for 2 or 7 days with NH4Cl, some animals also received the uricase inhibitor oxonic acid for comparison. Expression of transporters was studied by qPCR and immunoblotting. RESULTS: NH4Cl induced no significant changes in plasma or urine uric acid levels but caused downregulation of Slc22a1 (Oct1), Slc22a6 (Oat1), Slc22a19 (Oat5), and -Slc22a12 (Urat1) at mRNA level. In contrast, Slc22a4 mRNA (Octn1) was upregulated. On protein level, NH4Cl increased Octn1 (after 7 days) and Urat1 (after 2 days) abundance and decreased Oat1 (after 2 days) and Urat1 (after 7 days). Oxonic acid had no impact on protein abundance of any of the transporters tested. CONCLUSION: In summary, metabolic acidosis alters expression of several transporters involved in renal excretion of metabolic waste products and drugs. This may have implications for drug kinetics and clearance of waste metabolites.

Inhibition of the amino-acid transporter LAT1 demonstrates anti-neoplastic activity in medulloblastoma.

Most cases of medulloblastoma (MB) occur in young children. While the overall survival rate can be relatively high, current treatments combining surgery, chemo- and radiotherapy are very destructive for patient development and quality of life. Moreover, aggressive forms and recurrences of MB cannot be controlled by classical therapies. Therefore, new therapeutic approaches yielding good efficacy and low toxicity for healthy tissues are required to improve patient outcome. Cancer cells sustain their proliferation by optimizing their nutrient uptake capacities. The L-type amino acid transporter 1 (LAT1) is an essential amino acid carrier overexpressed in aggressive human cancers that was described as a potential therapeutic target. In this study, we investigated the therapeutic potential of JPH203, a LAT1-specific pharmacological inhibitor, on two independent MB cell lines belonging to subgroups 3 (HD-MB03) and Shh (DAOY). We show that while displaying low toxicity towards normal cerebral cells, JPH203 disrupts AA homeostasis, mTORC1 activity, proliferation and survival in MB cells. Moreover, we demonstrate that a long-term treatment with JPH203 does not lead to resistance in MB cells. Therefore, this study suggests that targeting LAT1 with JPH203 is a promising therapeutic approach for MB treatment.

The glutamine transporter ASCT2 (SLC1A5) promotes tumor growth independently of the amino acid transporter LAT1 (SLC7A5).

The transporters for glutamine and essential amino acids, ASCT2 (solute carrier family 1 member 5, SLC1A5) and LAT1 (solute carrier family 7 member 5, SLC7A5), respectively, are overexpressed in aggressive cancers and have been identified as cancer-promoting targets. Moreover, previous work has suggested that glutamine influx via ASCT2 triggers essential amino acids entry via the LAT1 exchanger, thus activating mechanistic target of rapamycin complex 1 (mTORC1) and stimulating growth. Here, to further investigate whether these two transporters are functionally coupled, we compared the respective knockout (KO) of either LAT1 or ASCT2 in colon (LS174T) and lung (A549) adenocarcinoma cell lines. Although ASCT2KO significantly reduced glutamine import (>60% reduction), no impact on leucine uptake was observed in both cell lines. Although an in vitro growth-reduction phenotype was observed in A549-ASCT2KO cells only, we found that genetic disruption of ASCT2 strongly decreased tumor growth in both cell lines. However, in sharp contrast to LAT1KO cells, ASCT2KO cells displayed no amino acid (AA) stress response (GCN2/EIF2a/ATF4) or altered mTORC1 activity (S6K1/S6). We therefore conclude that ASCT2KO reduces tumor growth by limiting AA import, but that this effect is independent of LAT1 activity. These data were further supported by in vitro cell proliferation experiments performed in the absence of glutamine. Together these results confirm and extend ASCT2's pro-tumoral role and indicate that the proposed functional coupling model of ASCT2 and LAT1 is not universal across different cancer types.

Inhibition of l-type amino acid transporter 1 activity as a new therapeutic target for cholangiocarcinoma treatment.

Unlike normal cells, cancer cells undergo unlimited growth and multiplication, causing them to require massive amounts of amino acid to support their continuous metabolism. Among the amino acid transporters expressed on the plasma membrane, l-type amino acid transporter-1, a Na+-independent neutral amino acid transporter, is highly expressed in many types of human cancer including cholangiocarcinoma. Our previous study reported that l-type amino acid transporter-1 and its co-functional protein CD98 were highly expressed and implicated in cholangiocarcinoma progression and carcinogenesis. Therefore, this study determined the effect of JPH203, a selective inhibitor of l-type amino acid transporter-1 activity, on cholangiocarcinoma cell inhibition both in vitro and in vivo. JPH203 dramatically suppressed [14C]l-leucine uptake as well as cell growth in cholangiocarcinoma cell lines along with altering the expression of l-type amino acid transporter-1 and CD98 in response to amino acid depletion. We also demonstrated that JPH203 induced both G2/M and G0/G1 cell cycle arrest, as well as reduced the S phase accompanied by altered expression of the proteins in cell cycle progression: cyclin D1, CDK4, and CDK6. There was also cell cycle arrest of the related proteins, P21 and P27, in KKU-055 and KKU-213 cholangiocarcinoma cells. Apoptosis induction, detected by an increase in trypan blue-stained cells along with a cleaved caspase-3/caspase-3 ratio, occurred in JPH203-treated cholangiocarcinoma cells at the highest concentration tested (100 µM). As expected, daily intravenous administration of JPH203 (12.5 and 25 mg/kg) significantly inhibited tumor growth in KKU-213 cholangiocarcinoma cell xenografts in the nude mice model in a dose-dependent manner with no statistically significant change in the animal's body weight and with no differences in the histology and appearance of the internal organs compared with the control group. Our study demonstrates that suppression of l-type amino acid transporter-1 activity using JPH203 might be used as a new therapeutic strategy for cholangiocarcinoma treatment.

JPH203, a selective L-type amino acid transporter 1 inhibitor, induces mitochondria-dependent apoptosis in Saos2 human osteosarcoma cells.

Most normal cells express L-type amino acid transporter 2 (LAT2). However, L-type amino acid transporter 1 (LAT1) is highly expressed in many tumor cells and presumed to support their increased growth and proliferation. This study examined the effects of JPH203, a selective LAT1 inhibitor, on cell growth and its mechanism for cell death in Saos2 human osteosarcoma cells. FOB human osteoblastic cells and Saos2 cells expressed LAT1 and LAT2 together with their associating protein 4F2 heavy chain, but the expression of LAT2 in the Saos2 cells was especially weak. JPH203 and BCH, a non-selective L-type amino acid transporter inhibitor, potently inhibited L-leucine uptake in Saos2 cells. As expected, the intrinsic ability of JPH203 to inhibit L-leucine uptake was far more efficient than that of BCH in Saos2 cells. Likewise, JPH203 and BCH inhibited Saos2 cell growth with JPH203 being superior to BCH in this regard. Furthermore, JPH203 increased apoptosis rates and formed DNA ladder in Saos2 cells. Moreover, JPH203 activated the mitochondria-dependent apoptotic signaling pathway by upregulating pro-apoptotic factors, such as Bad, Bax, and Bak, and the active form of caspase-9, and downregulating anti-apoptotic factors, such as Bcl-2 and Bcl-xL. These results suggest that the inhibition of LAT1 activity via JPH203, which may act as a potential novel anti-cancer agent, leads to apoptosis mediated by the mitochondria-dependent intrinsic apoptotic signaling pathway by inducing the intracellular depletion of neutral amino acids essential for cell growth in Saos2 human osteosarcoma cells.

HOXB9 acts as a negative regulator of activated human T cells in response to amino acid deficiency.

T-cell activation is an energy expenditure process and should be properly controlled in accordance with the availability of nutrients such as amino acids to eliminate wasteful energy consumption. However, the details of response to amino acids insufficiency in activated T cells remain largely unknown. Here we show that homeobox B9 (HOXB9), a member of the homeobox gene family that is known as a morphogenesis regulator, acts as a suppressor of activated human T cells to address amino acid starvation. The expression of HOXB9 was triggered by amino acid deprivation as well as functional inhibition of L-type amino acid transporter 1 (also known as SLC7A5) via activating transcription factor 4 in activated T cells. HOXB9 interfered the activities of NF-κB, nuclear factor of activated T-cells (NFAT) and AP-1 but not retinoic acid receptor-related orphan receptor, resulting in attenuation of the production of selective cytokines in activated T cells. Thus, the morphogenetic gene plays an unexpected role in the regulation of cellular metabolism with changes in the nutrition status in human T cells.

Metformin enhances anti-tumor effect of L-type amino acid transporter 1 (LAT1) inhibitor.

BACKGROUND: In many cancer cells, L-type amino acid transporter 1 (LAT1) transports neutral amino acids with bulky side chain, which activate mammalian target of rapamycin (mTOR) to cause cell proliferation. An anti-diabetic drug, metformin, has been shown to activate AMP-activated protein kinase (AMPK), which leads to inhibition of mTOR. LAT1 inhibition in combination with metformin could result in more prominent suppression of mTOR activity. PURPOSE: Anti-proliferative effect of a newly developed LAT1 specific inhibitor JPH203 in combination with metformin is evaluated in 2 head and neck cancer cell lines, Ca9-22 and HEp-2 cells and in nude mice inoculated with Ca9-22 cells. RESULTS AND DISCUSSION: By MTT assay, 0.5 mM metformin inhibited proliferation of Ca9-22 cells to 70% of control. In the presence of 100 µM JPH203, proliferation of Ca9-22 cells was inhibited to 60% of control. By combining these 2 drugs, proliferation of Ca9-22 was significantly inhibited to 40% of control. However, this regimen was not very effective against HEp-2 cells. This combination also suppressed in vivo growth of Ca9-22 cells in a xenotransplant model. A combination of anti-LAT1 drug with metformin may be an effective anti-proliferative therapy for certain subsets of cancers.

LAT1 acts as a crucial transporter of amino acids in human thymic carcinoma cells.

L-type amino acid transporter 1 (LAT1, SLC7A5) incorporates essential amino acids into cells. Recent studies have shown that LAT1 is a predominant transporter in various human cancers. However, the function of LAT1 in thymic carcinoma remains unknown. Here we demonstrate that LAT1 is a critical transporter for human thymic carcinoma cells. LAT1 was strongly expressed in human thymic carcinoma tissues. LAT1-specific inhibitor significantly suppressed leucine uptake and growth of Ty82 human thymic carcinoma cell lines, suggesting that thymic carcinoma takes advantage of LAT1 as a quality transporter and that LAT1-specific inhibitor might be clinically beneficial in therapy for thymic carcinoma.

LAT1 is a critical transporter of essential amino acids for immune reactions in activated human T cells.

Activation of T cells accompanies remarkable enhancement of metabolism. Sufficient and continuous nutrient supply is therefore important to support immune reaction in T cells. However, the mechanism of the promotion of nutrient incorporation in activated T cells has not been elucidated. In this study, we show that L-type amino acid transporter 1 (LAT1) is a major transporter for essential amino acids into activated human T cells. CD3/CD28 stimulation in primary human T cells triggered dramatic induction of LAT1 expression mediated by NF-κB and AP-1. Functional disturbance of LAT1 by a specific inhibitor and by small interfering RNA in human T cells suppressed essential amino acid uptake and induced a stress response mediated by DNA damage-inducible transcript 3 to attenuate cytokine production via inhibition of NF-κB and NFAT activities. These results uncover the previously unknown mechanism by which T cells accelerate essential amino acid uptake upon activation and adapt to essential amino acid starvation. Our results also raise the possibility for application of an LAT1 inhibitor as a new drug for therapy of disease caused by exaggerated immune response.