Reevaluating the Substrate Specificity of the L‑Type Amino Acid Transporter (LAT1)

The L-type amino acid transporter
1 (LAT1, SLC7A5) transports essential
amino acids across the blood–brain barrier (BBB) and into cancer
cells. To utilize LAT1 for drug delivery, potent amino acid promoieties
are desired, as prodrugs must compete with millimolar concentrations
of endogenous amino acids. To better understand ligand–transporter
interactions that could improve potency, we developed structural LAT1
models to guide the design of substituted analogues of phenylalanine
and histidine. Furthermore, we evaluated the structure–activity
relationship (SAR) for both enantiomers of naturally occurring LAT1
substrates. Analogues were tested in cis-inhibition
and trans-stimulation cell assays to determine potency
and uptake rate. Surprisingly, LAT1 can transport amino acid-like
substrates with wide-ranging polarities including those containing
ionizable substituents. Additionally, the rate of LAT1 transport was
generally nonstereoselective even though enantiomers likely exhibit
different binding modes. Our findings have broad implications to the
development of new treatments for brain disorders and cancer.

L型氨基酸转运蛋白1（L-type amino acid transporter 1, LAT1, SLC7A5）可介导必需氨基酸跨越血脑屏障（blood–brain barrier, BBB）并进入癌细胞。为利用LAT1实现药物递送，亟需研发强效的氨基酸类前体基团，因为前体药物必须与毫摩尔浓度的内源性氨基酸竞争结合位点。为深入解析可提升转运效能的配体-转运蛋白相互作用机制，我们构建了LAT1的结构模型，以此指导苯丙氨酸与组氨酸取代类似物的设计。此外，我们针对天然存在的LAT1底物的两种对映异构体，评估了其构效关系（structure–activity relationship, SAR）。通过顺式抑制（cis-inhibition）与反式刺激（trans-stimulation）细胞实验对合成类似物进行检测，以测定其效能与摄取速率。令人意外的是，LAT1可转运极性范围跨度极大的氨基酸类底物，其中包括带有可电离取代基的化合物。此外，尽管对映异构体可能呈现不同的结合模式，但LAT1的转运速率整体上无立体选择性。本研究结果为脑疾病与癌症的新型治疗方案开发具有广泛的指导意义。