Targeting amino acids transporters (SLCs) to starve cancer cells to death

Development of a Genetically Encoded Sensor for Arginine

The amino acid l-arginine (Arg) plays important roles in multiple metabolic and physiological processes, and changes in its concentration have been implicated in pathological processes. While it is important to measure Arg levels in biological systems directly and in real-time, existing Arg sensors respond to l-ornithine or l-lysine. Here we report ArgS1, a new Arg sensor. It showed a concentration-dependent increase in the ratio Ex488/405 for Arg with an apparent affinity of ∼64 μM and with a dynamic range (ΔR/R0) of 3. ArgS1 responds to Arg in both the cytoplasm and the subcellular organelles. ArgS1 monitored Arg levels in MDA-MB-231 cells, a breast cancer cell line deficient in a key enzyme for Arg synthesis (arginino-succinate synthetase1, ASS1) and amenable to Arg depletion therapy. We found that Arg levels in MDA-MB-231 cells decreased after depletion of extracellular Arg with a concomitant decline in cell viability. When ASS1 was overexpressed in the cells, Arg levels increased and cell viability was also enhanced. Thus, ArgS1 is an effective tool for real-time monitoring of Arg in human cells over a dynamic range of physiological and pathological relevance.

A Carbonic Anhydrase IX/SLC1A5 Axis Regulates Glutamine Metabolism Dependent Ferroptosis in Hypoxic Tumor Cells

The ability of tumor cells to alter their metabolism to support survival and growth presents a challenge to effectively treat cancers. Carbonic anhydrase IX (CAIX) is a hypoxia-induced, metabolic enzyme that plays a crucial role in pH regulation in tumor cells. Recently, through a synthetic lethal screen, we identified CAIX to play an important role in redox homeostasis. In this study, we show that CAIX interacts with the glutamine (Gln) transporter, solute carrier family 1 member 5 (SLC1A5), and coordinately functions to maintain redox homeostasis through the glutathione/glutathione peroxidase 4 (GSH/GPX4) axis. Inhibition of CAIX increases Gln uptake by SLC1A5 and concomitantly increases GSH levels. The combined inhibition of CAIX activity and Gln metabolism or the GSH/GPX4 axis results in an increase in lipid peroxidation and induces ferroptosis, both in vitro and in vivo. Thus, this study demonstrates cotargeting of CAIX and Gln metabolism as a potential strategy to induce ferroptosis in tumor cells.

Blockade of the amino acid transporter SLC6A14 suppresses tumor growth in colorectal Cancer

Background

The amino acid transporter SLC6A14, which transports 18 of the 20 proteinogenic amino acids, is too low to be detected in healthy normal tissues but is significantly increased in some solid cancers. However, little is known about the roles of SLC6A14 in colorectal cancer (CRC).

Methods

The mRNA and protein levels of SLC6A14 were detected using TCGA database, real-time polymerase chain reaction, western blot, and tissue microarrays, respectively. Amino acids concentration was determined by LC-MS/MS. Cell proliferation and apoptosis were determined using MTT assay and flow cytometry. Transwell invasion assay and wound healing assay were employed to analyze cell migration and invasion. The protein levels of Akt-mTOR signaling pathway and MMPs proteins were detected by western blot.

Results

Both of the mRNA and protein levels of SLC6A14 were upregulated in CRC tissues, and the protein levels of SLC6A14 were closely related to the tumor cells differentiation: the higher the expression of SLC6A14 was, the poorer the differentiation of the tumor cells was. Further knockdown SLC6A14 with siRNA or treatment with α-MT in CRC cell lines reduced cell proliferation and migration in vitro and inhibited xenograft tumor growth in vivo. Mechanistically, SLC6A14 was demonstrated to regulate the expression and phosphorylation of Akt-mTOR, which mediates the promoting tumor growth function of SLC6A14. Blockade of SLC6A14 with α-MT inhibited the activation of mTOR signaling.

Conclusion

SLC6A14 was upregulated in CRC and could promote tumor progression by activating the Akt-mTOR signaling pathway, which may serve as an effective molecular target for the treatment of CRC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09935-0.

Research Progress on Improving the Efficiency of CDT by Exacerbating Tumor Acidification

In recent years, chemodynamic therapy (CDT) has received extensive attention as a novel means of cancer treatment. The CDT agents can exert Fenton and Fenton-like reactions in the acidic tumor microenvironment (TME), converting hydrogen peroxide (H₂O₂) into highly toxic hydroxyl radicals (·OH). However, the pH of TME, as an essential factor in the Fenton reaction, does not catalyze the reaction effectively, hindering its efficiency, which poses a significant challenge for the future clinical application of CDT. Therefore, this paper reviews various strategies to enhance the antitumor properties of nanomaterials by modulating tumor acidity. Ultimately, the performance of CDT can be further improved by inducing strong oxidative stress to produce sufficient ·OH. In this paper, the various acidification pathways and proton pumps with potential acidification functions are mainly discussed, such as catalytic enzymes, exogenous acids, CAIX, MCT, NHE, NBCn1, etc. The problems, opportunities, and challenges of CDT in the cancer field are also discussed, thereby providing new insights for the design of nanomaterials and laying the foundation for their future clinical applications.

The Interleukin-6/Signal Transducer and Activator of Transcription-3/Cystathionine γ-Lyase Axis Deciphers the Transformation Between the Sensitive and Resistant Phenotypes of Breast Cancer Cells

Drug resistance of cancer cells is associated with redox homeostasis. The mechanism of acquired resistance of cancer cells to antitumor drugs is not well understood. Our previous studies revealed that drug resistance and highly expressed P-glycoprotein (P-gp) of MCF-7 breast cancer cells was dependent on intracellular redox homeostasis and declined capacity for scavenging reactive oxygen species (ROS). Recently, we observed that, unlike nontumorigenic cells MCF-10A, three tumorigenic breast cancer cells (MCF-7S, BT474, MDA-MB-231) reprogrammed their metabolism, highly expressed cystathionine-γ-lyase (CTH), and acquired a particular specialty to use methionine (Met) to synthesize glutathione (GSH) through the transsulfuration pathway. Interestingly, doxorubicin (adriamycin) further reprogrammed metabolism of MCF-7 cells sensitive to adriamycin (MCF-7S) and induced them to be another MCF-7 cell line resistant to adriamycin (MCF-7R) with dramatically downregulated CTH. The two MCF-7 cell lines showed distinctly different phenotypes in terms of intracellular GSH, ROS levels, expression and activity of P-gp and CTH, and drug resistance. We showed that CTH modulation or the methionine supply brought about the interconversion between MCF-7S and MCF-7R. Methionine deprivation or CTH silencing induced a resistant MCF-7R and lowered paclitaxel activity, yet methionine supplementation or CTH overexpression reversed the above effects, induced a sensitive phenotype of MCF-7S, and significantly increased the cytotoxicity of paclitaxel both in vitro and in vivo. Interleukin-6 (IL-6)/signal transducer and activator of transcription-3 (STAT3) initiated CTH expression and activity, and the effect on the resistant phenotype was exclusively dependent on CTH and ROS. This study suggests that the IL-6/STAT3/CTH axis plays a key role in the transformation between sensitive and resistant MCF-7 cells. SIGNIFICANCE STATEMENT: Cystathionine γ-lyase (CTH) plays a key role in transformation between the sensitive and resistant phenotypes of MCF-7 cells and is dependent on the interleukin-6 (IL-6)/signal transducer and activator of transcription-3 (STAT3) signaling axis. Modulation of the transsulfuration pathway on CTH or IL-6/STAT3 or methionine supplementation is beneficial for reversing the resistance of MCF-7 cells, which indicates a clinical translation potential.

YAP Accelerates Notch-Driven Cholangiocarcinogenesis via mTORC1 in Mice

Intrahepatic cholangiocarcinoma (iCCA) is a lethal malignant neoplasm with limited therapeutic options. Previous studies have found that Notch1 overexpression alone suffices to induce iCCA in the mouse, albeit after long latency. The current study found that activation of the Yes-associated protein (Yap) proto-oncogene occurs during Notch1-driven iCCA progression. After co-expressing activated Notch1 intracellular domain (Nicd) and Yap (YapS127A) in the mouse liver, rapid iCCA formation and progression occurred in Nicd/Yap mice. Mechanistically, an increased expression of amino acid transporters and activation of the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway was detected in Nicd/Yap mouse liver tumors. Significantly, the genetic deletion of Raptor, the major mTORC1 component, completely suppressed iCCA development in Nicd/Yap mice. Elevated expression of Notch1, YAP, amino acid transporters, and members of the mTORC1 pathway was also detected ubiquitously in a collection of human iCCA specimens. Their levels were associated with a poor patient outcome. This study demonstrates that Notch and YAP concomitant activation is frequent in human cholangiocarcinogenesis. Notch and YAP synergize to promote iCCA formation by activating the mTORC1 pathway.

Amino Acid Transporters Are a Vital Focal Point in the Control of mTORC1 Signaling and Cancer

The mechanistic target of rapamycin complex 1 (mTORC1) integrates signals from growth factors and nutrients to control biosynthetic processes, including protein, lipid, and nucleic acid synthesis. Dysregulation in the mTORC1 network underlies a wide array of pathological states, including metabolic diseases, neurological disorders, and cancer. Tumor cells are characterized by uncontrolled growth and proliferation due to a reduced dependency on exogenous growth factors. The genetic events underlying this property, such as mutations in the PI3K-Akt and Ras-Erk signaling networks, lead to constitutive activation of mTORC1 in nearly all human cancer lineages. Aberrant activation of mTORC1 has been shown to play a key role for both anabolic tumor growth and resistance to targeted therapeutics. While displaying a growth factor-independent mTORC1 activity and proliferation, tumors cells remain dependent on exogenous nutrients such as amino acids (AAs). AAs are an essential class of nutrients that are obligatory for the survival of any cell. Known as the building blocks of proteins, AAs also act as essential metabolites for numerous biosynthetic processes such as fatty acids, membrane lipids and nucleotides synthesis, as well as for maintaining redox homeostasis. In most tumor types, mTORC1 activity is particularly sensitive to intracellular AA levels. This dependency, therefore, creates a targetable vulnerability point as cancer cells become dependent on AA transporters to sustain their homeostasis. The following review will discuss the role of AA transporters for mTORC1 signaling in cancer cells and their potential as therapeutic drug targets.