Abstract
BackgroundCancer cells require increased levels of nutrients such as amino acids to sustain their rapid growth. In particular, leucine and glutamine have been shown to be important for growth and proliferation of some breast cancers, and therefore targeting the primary cell-surface transporters that mediate their uptake, L-type amino acid transporter 1 (LAT1) and alanine, serine, cysteine-preferring transporter 2 (ASCT2), is a potential therapeutic strategy.MethodsThe ASCT2 inhibitor, benzylserine (BenSer), is also able to block LAT1 activity, thus inhibiting both leucine and glutamine uptake. We therefore aimed to investigate the effects of BenSer in breast cancer cell lines to determine whether combined LAT1 and ASCT2 inhibition could inhibit cell growth and proliferation.ResultsBenSer treatment significantly inhibited both leucine and glutamine uptake in MCF-7, HCC1806 and MDA-MB-231 breast cancer cells, causing decreased cell viability and cell cycle progression. These effects were not primarily leucine-mediated, as BenSer was more cytostatic than the LAT family inhibitor, BCH. Oocyte uptake assays with ectopically expressed amino acid transporters identified four additional targets of BenSer, and gas chromatography-mass spectrometry (GCMS) analysis of intracellular amino acid concentrations revealed that this BenSer-mediated inhibition of amino acid uptake was sufficient to disrupt multiple pathways of amino acid metabolism, causing reduced lactate production and activation of an amino acid response (AAR) through activating transcription factor 4 (ATF4).ConclusionsTogether these data showed that BenSer blockade inhibited breast cancer cell growth and viability through disruption of intracellular amino acid homeostasis and inhibition of downstream metabolic and growth pathways.
Highlights
Cancer cells require increased levels of nutrients such as amino acids to sustain their rapid growth
BenSer inhibits leucine and glutamine uptake in breast cancer cells Using three different breast cancer cell lines: estrogen-receptor (ER)-positive, Luminal A MCF-7 cells, triple-negative basal-like HCC1806 cells, and triple-negative claudin-low MDA-MB-231 cells, to represent a variety of breast cancer subtypes, we showed that treatment with BenSer reduced glutamine uptake to ~ 65% of control across all three cell lines (Fig. 1a), while leucine uptake was inhibited more strongly to ~ 45% (MCF-7 and MDA-MB-231) and 22% (HCC1806) of control (Fig. 1b)
BenSer directly inhibits other targets that are expressed in breast cancer cell lines and patient samples In light of these data, we examined the ability of BenSer to directly inhibit the uptake activity of other putative targets, such as additional L-type amino acid transporter (LAT) transporters (LAT2/ SLC7A8), glutamine transporters (SNATs; SLC38A1, SLC38A2) and other structurally similar amino acid transporters (ASCT1/SLC1A4), as well as confirming its known inhibition of ASCT2/SLC1A5
Summary
Cancer cells require increased levels of nutrients such as amino acids to sustain their rapid growth. Leucine and glutamine have been shown to be important for growth and proliferation of some breast cancers, and targeting the primary cell-surface transporters that mediate their uptake, L-type amino acid transporter 1 (LAT1) and alanine, serine, cysteine-preferring transporter 2 (ASCT2), is a potential therapeutic strategy. Glutamine transport is largely mediated by alanine, serine, cysteine-preferring transporter 2 (ASCT2; SLC1A5) in multiple cancers, including melanoma [8], non-small cell lung cancer [9, 10], prostate cancer [11], acute myeloid leukaemia [12], multiple myeloma [13], and breast cancer [14, 15]. Leucine and glutamine transporters are upregulated in a range of cancers, making them an appealing target for cancer therapy
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