Monocarboxylate Transporter Inhibitor Research Articles

The Role of Astrocyte-Neuron Lactate Shuttle in Neuropathic Orofacial Pain.

Inhibition of astrocytic energy metabolism alleviates neuropathic pain. To explore whether astrocyte-neuron lactate shuttle (ANLS) played any role in neuropathic orofacial pain. Rats with partial transection of the right infraorbital nerve (p-IONX) or sham operation were intrathecally injected with acetazolamide (a carbonic anhydrase inhibitor), bithionol (a soluble adenylyl cyclase inhibitor), α-cyano-4-hydroxycinnamic acid [α-CHCA, a monocarboxylate transporter (MCT) inhibitor] or vehicle once a day from postoperative day 1-14. The facial mechanical thresholds were tested on preoperative day 1 and 2 and postoperative days 1, 3, 5, 7, 10 and 14, expression of glucose transporters (GLUTs) and MCTs in the trigeminal subnucleus caudalis (Vc) were examined on the postoperative day 3 and neuronal activities in the Vc were examined in the p-IONX rats on postoperative days 3-5. Compared with the sham group, the mechanical thresholds in the p-IONX group were significantly reduced at postoperative days 1-7, and the number of astrocytes expressing GLUT1 and MCT1/4, and neurons expressing MCT2 was significantly increased on postoperative day 3. In the p-IONX groups, neurons in the Vc were sensitised, and acetazolamide, bithionol and α-CHCA reversed the central sensitisation, significantly increased the mechanical thresholds at postoperative days 1-7 and decreased the number of astrocytes expressing GLUT1 and MCT1/4, and neurons expressing MCT2 at postoperative day 3 compared with those in the vehicle-treated rats. Inhibition of ANLS alleviates p-IONX-related neuronal, behavioural and immunohistochemical changes, which suggests that ANLS plays an important role in trigeminal neuropathic pain.

Enhanced glycolysis causes extracellular acidification and activates acid-sensing ion channel 1a in hypoxic pulmonary hypertension.

In pulmonary hypertension (PHTN), a metabolic shift to aerobic glycolysis promotes a hyperproliferative, apoptosis-resistant phenotype in pulmonary arterial smooth muscle cells (PASMCs). Enhanced glycolysis induces extracellular acidosis, which can activate proton-sensing membrane receptors and ion channels. We previously reported that activation of the proton-gated cation channel acid-sensing ion channel 1a (ASIC1a) contributes to the development of hypoxic PHTN. Therefore, we hypothesize that enhanced glycolysis and subsequent acidification of the PASMC extracellular microenvironment activate ASIC1a in hypoxic PHTN. We observed decreased oxygen consumption rate and increased extracellular acidification rate in PASMCs from chronic hypoxia (CH)-induced PHTN rats, indicating a shift to aerobic glycolysis. In addition, we found that intracellular alkalization and extracellular acidification occur in PASMCs following CH and in vitro hypoxia, which were prevented by the inhibition of glycolysis with 2-deoxy-d-glucose (2-DG). Inhibiting H+ transport/secretion through carbonic anhydrases, Na+/H+ exchanger 1, or vacuolar-type H+-ATPase did not prevent this pH shift following hypoxia. Although the putative monocarboxylate transporter 1 (MCT1) and -4 (MCT4) inhibitor syrosingopine prevented the pH shift, the specific MCT1 inhibitor AZD3965 and/or the MCT4 inhibitor VB124 were without effect, suggesting that syrosingopine targets the glycolytic pathway independent of H+ export. Furthermore, 2-DG and syrosingopine prevented enhanced ASIC1a-mediated store-operated Ca2+ entry in PASMCs from CH rats. These data suggest that multiple H+ transport mechanisms contribute to extracellular acidosis and that inhibiting glycolysis-rather than specific H+ transporters-more effectively prevents extracellular acidification and ASIC1a activation. Together, these data reveal a novel pathological relationship between glycolysis and ASIC1a activation in hypoxic PHTN.NEW & NOTEWORTHY In pulmonary hypertension, a metabolic shift to aerobic glycolysis drives a hyperproliferative, apoptosis-resistant phenotype in pulmonary arterial smooth muscle cells. We demonstrate that this enhanced glycolysis induces extracellular acidosis and activates the proton-gated ion channel, acid-sensing ion channel 1a (ASIC1a). Although multiple H+ transport/secretion mechanisms are upregulated in PHTN and likely contribute to extracellular acidosis, inhibiting glycolysis with 2-deoxy-d-glucose or syrosingopine effectively prevents extracellular acidification and ASIC1a activation, revealing a promising therapeutic avenue.

Poly-L-Lactic Acid Reduces the Volume of Dermal Adipose Tissue Through its Metabolite Lactate.

Poly-L-lactic acid (PLLA), a well-established biostimulator that induces collagenases, is widely used among clinical practice to treat skin aging. However, the precise regulatory effect of PLLA on different dermal cell subsets beyond fibroblast has not been fully elucidated. In this study, we constructed in vivo PLLA injection and in vitro PLLA-adipocyte co-culture models to analyze the regulatory effects of PLLA on the volume, differentiation, lipolysis, and thermogenic capacity of dermal adipocyte. We found that PLLA injection significantly reduced the thickness of dermal fat in mice. In co-culture assay, PLLA showed no effect on adipogenesis, but stimulated the lipolysis activity. Interestingly, PLLA also enhanced the differentiation of fat cells into beige fat cells, which possess higher thermogenic capacity. In mechanical study, we blocked adipocyte lactate uptake with a monocarboxylate transporter (MCT1/4) inhibitor and found that the regulatory effect of PLLA on dermal adipocyte relies on its metabolite lactate. In summary, our results suggest that PLLA has complex regulatory effects on the dermal cells, and its ability to improve skin aging is not fully attributed to stimulating collagen synthesis, but also partially involves adipocytes.No Level Assigned This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

LPS-induced monocarboxylate transporter-1 inhibition facilitates lactate accumulation triggering epithelial-mesenchymal transformation and pulmonary fibrosis

The epithelial-mesenchymal transformation (EMT) process of alveolar epithelial cells is recognized as involved in the development of pulmonary fibrosis. Recent evidence has shown that lipopolysaccharide (LPS)-induced aerobic glycolysis of lung tissue and elevated lactate concentration are associated with the pathogenesis of sepsis-associated pulmonary fibrosis. However, it is uncertain whether LPS promotes the development of sepsis-associated pulmonary fibrosis by promoting lactate accumulation in lung tissue, thereby initiating EMT process. We hypothesized that monocarboxylate transporter-1 (MCT1), as the main protein for lactate transport, may be crucial in the pathogenic process of sepsis-associated pulmonary fibrosis. We found that high concentrations of lactate induced EMT while moderate concentrations did not. Besides, we demonstrated that MCT1 inhibition enhanced EMT process in MLE-12 cells, while MCT1 upregulation could reverse lactate-induced EMT. LPS could promote EMT in MLE-12 cells through MCT1 inhibition and lactate accumulation, while this could be alleviated by upregulating the expression of MCT1. In addition, the overexpression of MCT1 prevented LPS-induced EMT and pulmonary fibrosis in vivo. Altogether, this study revealed that LPS could inhibit the expression of MCT1 in mouse alveolar epithelial cells and cause lactate transport disorder, which leads to lactate accumulation, and ultimately promotes the process of EMT and lung fibrosis.

Role of monocarboxylate transporters in AMPK-mediated protection against excitotoxic injury in the rat retina

Activation of adenosine monophosphate (AMP)-activated protein kinase (AMPK) pathway protects against N-methyl-D-aspartic acid (NMDA)-induced excitotoxic retinal injury. AMPK activation enhances fatty acid metabolism and ketone body synthesis. Ketone bodies are transported into neurons by monocarboxylate transporters (MCTs) and exert neuroprotective effects. In this study, we examined the distribution and expression levels of MCT1 and MCT2 in the retina and analyzed the effects of pharmacological inhibition of MCTs on the protective effects of metformin and 5-aminoimidazole-4-carboxamide (AICAR), activators of AMPK, against NMDA-induced retinal injury in rats. MCT1 was expressed in the blood vessels, processes of astrocytes and Müller cells, and inner segments of photoreceptors in the rat retina, whereas MCT2 was expressed in neuronal cells in the ganglion cell layer (GCL) and in astrocyte processes. The expression levels of MCT2, but not MCT1, decreased one day after intravitreal injection of NMDA (200 nmol). Intravitreal injection of NMDA decreased the number of cells in the GCL compared to the vehicle seven days after injection. Simultaneous injection of metformin (20 nmol) or AICAR (50 nmol) with NMDA attenuated NMDA-induced cell loss in the GCL, and these protective effects were attenuated by AR-C155858 (1 pmol), an inhibitor of MCTs. AR-C155858 alone had no significant effect on the retinal structure. These results suggest that AMPK-activating compounds protect against NMDA-induced excitotoxic retinal injury via mechanisms involving MCTs in rats. NMDA-induced neurotoxicity may be associated with retinal neurodegenerative changes in glaucoma and diabetic retinopathy. Therefore, AMPK-activating compounds may be effective in managing these retinal diseases.

Monocarboxylate transporter-1 (MCT-1) inhibitors screened from autodisplayed FV-antibody library

Monocarboxylate transporter-1 (MCT-1) inhibitors were screened from the Fv-antibody library, which contained complementary determining region 3 with randomized amino acid sequences (11 residues) through site-directed mutagenesis. Fv-antibodies against MCT-1 were screened from the autodisplayed Fv-antibody library. Two clones were screened, and the binding affinity (KD) against MCT-1 was estimated using flow cytometry. The screened Fv-antibodies were expressed as soluble fusion proteins (Fv-1 and Fv-2) and the KD for MCT-1 was estimated using the SPR biosensor. The inhibitory activity of the expressed Fv-antibodies was observed in HEK293T and Jurkat cell lines by measuring intracellular pH and lactate accumulation. The level of cell viability in HEK293T and Jurkat cell lines was decreased by the inhibitory activity of the expressed Fv-antibodies. The binding properties of the Fv-antibodies to MCT-1 were analyzed using molecular docking simulations. Overall, the results showed that the screened Fv-antibodies against MCT-1 from the Fv-antibody library had high binding affinity and inhibitory activity against MCT-1, which could be used as potential therapeutic drug candidates for the MCT-1 inhibitor.

Severely polarized extracellular acidity around tumour cells.

Extracellular pH impacts many molecular, cellular and physiological processes, and hence is tightly regulated. Yet, in tumours, dysregulated cancer cell metabolism and poor vascular perfusion cause the tumour microenvironment to become acidic. Here by leveraging fluorescent pH nanoprobes with a transistor-like activation profile at a pH of 5.3, we show that, in cancer cells, hydronium ions are excreted into a small extracellular region. Such severely polarized acidity (pH <5.3) is primarily caused by the directional co-export of protons and lactate, as we show for a diverse panel of cancer cell types via the genetic knockout or inhibition of monocarboxylate transporters, and also via nanoprobe activation in multiple tumour models in mice. We also observed that such spot acidification in ex vivo stained snap-frozen human squamous cell carcinoma tissue correlated with the expression of monocarboxylate transporters and with the exclusion of cytotoxic T cells. Severely spatially polarized tumour acidity could be leveraged for cancer diagnosis and therapy.

Exploring monocarboxylate transporter inhibition for cancer treatment.

Cells are separated from the environment by a lipid bilayer membrane that is relatively impermeable to solutes. The transport of ions and small molecules across this membrane is an essential process in cell biology and metabolism. Monocarboxylate transporters (MCTs) belong to a vast family of solute carriers (SLCs) that facilitate the transport of certain hydrophylic small compounds through the bilipid cell membrane. The existence of 446 genes that code for SLCs is the best evidence of their importance. In-depth research on MCTs is quite recent and probably promoted by their role in cancer development and progression. Importantly, it has recently been realized that these transporters represent an interesting target for cancer treatment. The search for clinically useful monocarboxylate inhibitors is an even more recent field. There is limited pre-clinical and clinical experience with new inhibitors and their precise mechanism of action is still under investigation. What is common to all of them is the inhibition of lactate transport. This review discusses the structure and function of MCTs, their participation in cancer, and old and newly developed inhibitors. Some suggestions on how to improve their anticancer effects are also discussed.

Sex and Cross-Sex Testosterone Treatment Alters Gamma-Hydroxybutyrate Acid Toxicokinetics and Toxicodynamics in Rats.

Γ-hydroxybutyric acid (GHB) is widely abused due to its sedative/hypnotic and euphoric effects. In recent years, GHB use has witnessed a notable rise within the LGBTQ+ community. GHB is a substrate of monocarboxylate transporters (MCTs) and exhibits nonlinear toxicokinetics, characterized by saturable metabolism, absorption, and renal reabsorption. This study investigates the impact of exogenous testosterone administration on GHB toxicokinetics and toxicodynamics, exploring the potential of MCT1 inhibition as a strategy to counteract toxicity. Ovariectomized (OVX) females and castrated (CST) male Sprague Dawley rats were treated with testosterone or placebo for 21 days. GHB was administered at two doses (1000 mg/kg or 1500 mg/kg i.v.), and the MCT1 inhibitor AR-C 155858 (1 mg/kg i.v.) was administered 5 min after GHB (1500 mg/kg i.v.) administration. Plasma and urine were collected up to 8 h post-dose, and GHB concentrations were quantified via a validated LC/MS/MS assay. Sleep time (sedative/hypnotic effect) was utilized as the toxicodynamic endpoint. Testosterone treatment significantly affected GHB toxicokinetics and toxicodynamics. Testosterone-treated CST rats exhibited significantly lower renal clearance, higher AUC, and increased sedative effect, while testosterone-treated OVX rats demonstrated higher metabolic clearance. AR-C 155858 treatment led to an increase in GHB renal and total clearance together with an improvement in sedative/hypnotic effect. In conclusion, exogenous testosterone treatment induces significant alterations in GHB toxicokinetics and toxicodynamics, and MCT inhibition can serve as a potential therapeutic strategy for GHB overdose in both cisgender and transgender male populations.

ATP-mediated increase in H+ efflux from retinal Müller cells of the axolotl.

Previous work has shown that activation of tiger salamander retinal radial glial cells by extracellular ATP induces a pronounced extracellular acidification, which has been proposed to be a potent modulator of neurotransmitter release. This study demonstrates that low micromolar concentrations of extracellular ATP similarly induce significant H+ effluxes from Müller cells isolated from the axolotl retina. Müller cells were enzymatically isolated from axolotl retina and H+ fluxes were measured from individual cells using self-referencing H+-selective microelectrodes. The increased H+ efflux from axolotl Müller cells induced by extracellular ATP required activation of metabotropic purinergic receptors and was dependent upon calcium released from internal stores. We further found that the ATP-evoked increase in H+ efflux from Müller cells of both tiger salamander and axolotl were sensitive to pharmacological agents known to interrupt calmodulin and protein kinase C (PKC) activity: chlorpromazine (CLP), trifluoperazine (TFP), and W-7 (all calmodulin inhibitors) and chelerythrine, a PKC inhibitor, all attenuated ATP-elicited increases in H+ efflux. ATP-initiated H+ fluxes of axolotl Müller cells were also significantly reduced by amiloride, suggesting a significant contribution by sodium-hydrogen exchangers (NHEs). In addition, α-cyano-4-hydroxycinnamate (4-cin), a monocarboxylate transport (MCT) inhibitor, also reduced the ATP-induced increase in H+ efflux in both axolotl and tiger salamander Müller cells, and when combined with amiloride, abolished ATP-evoked increase in H+ efflux. These data suggest that axolotl Müller cells are likely to be an excellent model system to understand the cell-signaling pathways regulating H+ release from glia and the role this may play in modulating neuronal signaling.NEW & NOTEWORTHY Glial cells are a key structural part of the tripartite synapse and have been suggested to regulate synaptic transmission, but the regulatory mechanisms remain unclear. We show that extracellular ATP, a potent glial cell activator, induces H+ efflux from axolotl retinal Müller (glial) cells through a calcium-dependent pathway that is likely to involve calmodulin, PKC, Na+/H+ exchange, and monocarboxylate transport, and suggest that such H+ release may play a key role in modulating neuronal transmission.

Abstract LB_A13: Phase 1 dose expansion results of CYT-0851, a monocarboxylate transporter (MCT) inhibitor, in combination with capecitabine (cape) in platinum-resistant ovarian cancer

Abstract Background: The MCT inhibitor CYT-0851 potently inhibits MCT1, has activity against MCT4, and blocks lactate transport resulting in cell death in glycolytic cancer cells. In an in vitro CRISPR screen, thymidylate synthetase was a significant hit in 2 resistant cell models, sensitizing them to CYT-0851. Follow-up in vitro combination studies showed that CYT-0851 synergized with 5-FU to inhibit cancer cell growth. Monotherapy clinical activity of CYT-0851 has been reported previously in lymphoma and solid tumors. In the phase 1 dose escalation trial of CYT-0851 plus cape, 400 mg was identified as the recommended phase 2 dose. In three phase 2 trials, cape had a RECIST response rate of 5-8% in ovarian cancer. Methods: An expansion cohort of 10 patients (pts) with platinum resistant advanced ovarian cancer were treated with CYT-0851, 400 mg QD in combination with cape, 1000 mg/m2 PO BID x 14 days every 21 days and were evaluable. One additional pt treated at the 300 mg dose level was evaluable and added to the analysis. The primary objective was safety, and secondary objectives were pharmacokinetics and preliminary anti-tumor activity by RECIST. Results: As of Aug 21, 2023, 11 pts were treated and evaluable, 9 white, 1 African American black, and 1 American Indian or Alaskan native, with a median age of 64 (range 52-76). Median prior therapies were 6 (range 2-14). All but one had 3 or more prior therapies. Median CYT-0851 dose compliance with continuous daily dosing was 99% (range 91– 100%). There were no treatment discontinuations or CYT-0851 dose reductions for treatment related adverse events. 7 pts (64%) experienced a treatment-related adverse event, all were Grade 1-2. There were no grade 3+ treatment related adverse events. The most common related AEs were fatigue reported in 5 pts (46%), and decreased appetite, diarrhea, nausea, palmar-plantar erythrodysaesthesia syndrome and vomiting, each reported in 2 patients (18%). Exposure of CYT-0851 in combination with capecitabine exhibits dose proportional behavior and was similar between combination therapy and monotherapy. One pt had a confirmed PR with progression on day 294, and 2 additional pts achieved a PR that has not been confirmed yet, with treatment ongoing on day 113 and 41. 7 pts had SD, and one patient PD as best response. The disease control rate was 91%. 5 Pts discontinued for progressive disease with a median of 133 days of treatment (range 43-300), and 2 withdrew consent on days 131-134. 4 patients continue therapy on days 42,47,106, and 113. Median PFS was 170 days (95% CI 79-NA). Conclusions: The oral outpatient combination of CYT-0851 and cape has demonstrated an acceptable safety and tolerability profile without any unanticipated toxicities at clinically active doses. The disease control rate of 91% and unconfirmed response rate of 27% in refractory platinum resistant ovarian cancer is promising and warrants further exploration. Furthermore, this regimen should be evaluated in other tumor types commonly treated with 5-FU, including breast and colorectal cancer. Citation Format: Elizabeth Swisher, Gerald Steven Falchook, Pamela N. Munster, Nina Beri, Kathleen N. Moore, Timothy A. Yap, David R. Spigel, Susan Doleman, William D. Bradley, Thomas J. O'Shea, Markus F. Renschler, Ryan C. Lynch. Phase 1 dose expansion results of CYT-0851, a monocarboxylate transporter (MCT) inhibitor, in combination with capecitabine (cape) in platinum-resistant ovarian cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr LB_A13.

Role of monocarboxylate transporter I/lactate dehydrogenase B-mediated lactate recycling in tamoxifen-resistant breast cancer cells.

Although tamoxifen (TAM) is widely used in patients with estrogen receptor-positive breast cancer, the development of tamoxifen resistance is common. The previous finding suggests that the development of tamoxifen resistance is driven by epiregulin or hypoxia-inducible factor-1α-dependent glycolysis activation. Nonetheless, the mechanisms responsible for cancer cell survival and growth in a lactic acid-rich environment remain elusive. We found that the growth and survival of tamoxifen-resistant MCF-7 cells (TAMR-MCF-7) depend on glycolysis rather than oxidative phosphorylation. The levels of the glycolytic enzymes were higher in TAMR-MCF-7 cells than in parental MCF-7 cells, whereas the mitochondrial number and complex I level were decreased. Importantly, TAMR-MCF-7 cells were more resistant to low glucose and high lactate growth conditions. Isotope tracing analysis using 13C-lactate confirmed that lactate conversion to pyruvate was enhanced in TAMR-MCF-7 cells. We identified monocarboxylate transporter1 (MCT1) and lactate dehydrogenase B (LDHB) as important mediators of lactate influx and its conversion to pyruvate, respectively. Consistently, AR-C155858 (MCT1 inhibitor) inhibited the proliferation, migration, spheroid formation, and in vivo tumor growth of TAMR-MCF-7 cells. Our findings suggest that TAMR-MCF-7 cells depend on glycolysis and glutaminolysis for energy and support that targeting MCT1- and LDHB-dependent lactate recycling may be a promising strategy to treat patients with TAM-resistant breast cancer.

Abstract 13712: Imaging Short-Chain Fatty Acid Metabolism and Transport in the Failing Heart by PET

Introduction: Heart failure compromises the transport and oxidation of long chain fatty acids. Cardiomyocytes can compensate by using short-chain fatty acids (SCFA) which rely on other transport mechanisms. Based on this principle, we used 2-[ 18 F]fluoropropionic acid ([ 18 F]FPA), a radiolabeled SCFA analog, to assess these metabolic changes and image them by positron emission tomography (PET) in a doxorubicin-induced mouse model of cardiotoxicity. Hypothesis: We hypothesize that the increased demand for SCFA by the failing heart promotes cardiac accumulation of [ 18 F]FPA which can be imaged by PET. Methods: [ 18 F]FPA was injected intravenously into male C57BL/6J mice 10 weeks following intraperitoneal injections of 8 x 3 mg/kg doxorubicin (DOX). Dynamic PET acquisitions were performed from 60-120 min post injection of 9.25-11 MBq [ 18 F]FPA. These images were acquired in the presence or absence of 5 mg/kg AZD3965, an inhibitor of monocarboxylate transporters. Heart uptake of [ 18 F]FPA was determined by image-based quantitation and confirmed by a biodistribution study. Mechanistic [ 18 F]FPA uptake studies were also conducted in primary human cardiomyocyte (HCM) cultures. Results: Mice experiencing DOX-induced cardiotoxicity exhibited statistically significant increases in cardiac [ 18 F]FPA. AZD3965 did not significantly alter cardiac uptake but reduced uptake in all other tissues except the kidneys, the route of excretion. Additionally, [ 18 F]FPA uptake is lost in HCM for which mitochondrial acyl-CoA synthetase (ACSS) 1, but not cytosolic ACSS2, is inhibited. Conclusions: Our findings present both mechanistic and translational applications for [ 18 F]FPA. AZD3965 effectively reduced [ 18 F]FPA uptake in other tissues except for the heart and can therefore be co-administered to enhance the heart-to-background ratio. Altogether, our results indicate that [ 18 F]FPA may enter cardiac tissues by diffusion and become metabolically trapped in mitochondria.

Small molecule anion carriers facilitate lactate transport in model liposomes and cells

An excessive production of lactate by cancer cells fosters tumor growth and metastasis. Therefore, targeting lactate metabolism and transport offers a new therapeutic strategy against cancer, based on dependency of some cancer cells for lactate as energy fuel or as oncogenic signal. Herein we present a family of anionophores based on the structure of click-tambjamines that have proved to be extremely active lactate carriers across phospholipid membranes. Compound 1, the most potent lactate transmembrane carrier, was studied in HeLa cells. The use of a monocarboxylate transporters (MCTs) inhibitor proved that 1 is an active lactate transporter in living cells, confirming the results obtained in phospholipid vesicles. Moreover, an additive effect of compound 1 with cisplatin was observed in HeLa cells. Identification of active lactate anionophores working in living cells opens up ways to exploit this class of compounds as molecular tools and drugs addressing dysregulated lactate metabolism.

Heterocyclic and non-heterocyclic arena of monocarboxylate transporter inhibitors to battle tumorigenesis.

Monocarboxylate transporters (MCTs) have gained significant attention in cancer research due to their critical role in tumour metabolism. MCTs are legends for transporting lactate molecules in cancer cells, an oncometabolite and waste product of glycolysis, acting as an indispensable factor of tumour proliferation. Targeting MCTs with inhibitors has emerged as a promising strategy to combat tumorigenesis. This article summarizes the most recent research on MCT inhibitors in preventing carcinogenesis, covering both heterocyclic and non-heterocyclic compounds. Heterocyclic and non-heterocyclic compounds such as pteridine, pyrazole, indole, flavonoids, coumarin derivatives and cyanoacetic acid derivatives have been reported as potent MCT inhibitors. We examine the molecular underpinnings of MCTs in cancer metabolism, the design and synthesis of heterocyclic and non-heterocyclic MCT inhibitors, their impact on tumour cells and the microenvironment and their potential as therapeutic agents. Moreover, we explore the challenges associated with MCT inhibitor development and propose future directions for advancing this field. This write-up aims to provide researchers, scientists and clinicians with a comprehensive understanding of the heterocyclic and non-heterocyclic MCT inhibitors and their potential in combating tumorigenesis.

P02.04.B TARGETING METABOLIC VULNERABILITIES IN GLIOBLASTOMA

Abstract BACKGROUND Glioblastoma is the most common and aggressive primary brain cancer, with a median survival of 16 months. A subset of cells within these tumours, termed glioblastoma stem cells (GSCs), displays high tumourigenic capacity and resistance to conventional therapies, and are responsible for tumour recurrence. Glioblastomas have been initially shown to mainly rely on glycolysis as a source of energy. However, a growing body of literature reports that GSCs are less glycolytic than their differentiated progeny and can thrive on oxidative phosphorylation (OXPHOS) to survive, sustain stemness and fuel tumourigenic potential. Thus, targeting OXPHOS could be a promising strategy to halt energy production and starve GSCs to death. However, under metabolic stress, GSCs can also switch to a more glycolytic phenotype, suggesting a metabolic plasticity in GSCs, and thus adding a layer of complexity to target GSC metabolism. In the current study, we have investigated the impact of compound X (CX), recently shown to impair mitochondrial respiration, on the fate and tumourigenesis of GSCs. MATERIAL AND METHODS Multiple patient-derived and murine GSC models were used to test the impact of CX on GSCs in vitro. The effect of CX on glioblastoma tumors was evaluated using patient-derived xenografts and syngeneic mouse models. RESULTS We have established that CX inhibits GSC proliferation and impairs stemness-related pathways in vitro. CX delays glioblastoma tumourigenesis in vivo. While a drastic decrease in cell proliferation was observed, cell death assays revealed that CX does not induce cell death. This suggests that GSCs gain a slow-cycling phenotype to resist energy depletion. Mechanistically, we have established that CX targets complex I of the mitochondrial respiratory chain, leading to an impairment of OXPHOS. Interestingly, inhibition of OXPHOS by CX was associated with an extensive production of extracellular lactate, indicating that at least, a subset of GSCs gain metabolic adaptability by co-opting glycolysis to survive. Thus, to tackle this metabolic plasticity in GSCs, we adopted a new strategy that involves sequestration of the lactic acid intracellularly via disruption of lactate transporters. Treatment of GSCs with monocarboxylate transporter inhibitors, AZD3965 and syrosingopine, alone did not significantly impact GSC growth and viability. Strikingly, combined CX treatment with either AZD3965 or syrosingopine resulted in high intracellular lactate buildup, increased reactive oxygen species, and led to drastic cell lethality in multiple GSC models. CONCLUSION This study highlights that re-routing the OXPHOS-dependent GSCs to glycolysis offers a vulnerability to sensitize GSCs to cell death. Dual inhibition of OXPHOS and lactate export could be a promising therapeutic approach to deplete malignant GSCs and suppress glioblastoma tumourigenesis.

Alpha-cyano-4-hydroxycinnamic acid alleviates renal fibrosis and inflammation in chronic kidney disease

Renal fibrosis is a crucial pathological phenomenon of chronic kidney disease (CKD) that contributes to the progressive loss of renal function. Monocarboxylate transporter 1 (MCT1) plays an important role in clear cell renal cell carcinoma; however, the role of the MCT1 inhibitor alpha-cyano-4-hydroxycinnamic acid (α-CHCA) in renal fibrosis remains unclear. In this study, we evaluated the role of α-CHCA, an MCT1 inhibitor, in treating renal fibrosis associated with CKD. We used α-CHCA in a CKD mouse model of unilateral ureteral obstruction (UUO), and mouse proximal tubular epithelial cells (mPTCs) stimulated by transforming growth factor-β1 (TGF-β1). In vivo, administration of α-CHCA improved tubulointerstitial fibrosis, which was consistent with the reduced expression of collagen I/III, fibronectin (FN1), and α-smooth muscle actin (α-SMA) in the kidneys of UUO mice. Similarly, the overexpression of inflammatory factors in UUO kidneys decreased in response to α-CHCA treatment. In vitro, α-CHCA pretreatment inhibited the induction of collagen I/III, FN1, and α-SMA production in mPTCs treated with TGF-β1. Collectively, these findings indicate that α-CHCA may play a therapeutic role in renal fibrosis associated with CKD by inhibiting collagen deposition and subsequent fibrosis and inflammation. Highlights Chronic kidney disease (CKD) mice have increased MCT1 expression. α-CHCA, a MCT1 inhibitor, alleviates renal fibrosis in CKD mice. α-CHCA improves the inflammation in CKD mice. α-CHCA inhibits TGF-β1-induced extracellular matrix secretion of proximal tubular epithelial cells.

MCT-Dependent Cryptosporidium parvum-Induced Bovine Monocyte Extracellular Traps (METs) under Physioxia.

The apicomplexan protozoan parasite Cryptosporidium parvum is responsible for cryptosporidiosis, which is a zoonotic intestinal illness that affects newborn cattle, wild animals, and people all over the world. Mammalian monocytes are bone marrow-derived myeloid leukocytes with important defense effector functions in early host innate immunity due to their ATP purinergic-, CD14- and CD16-receptors, adhesion, migration and phagocytosis capacities, inflammatory, and anti-parasitic properties. The formation of monocyte extracellular traps (METs) has recently been reported as an additional effector mechanism against apicomplexan parasites. Nonetheless, nothing is known in the literature on METs extrusion neither towards C. parvum-oocysts nor sporozoites. Herein, ATP purinergic receptor P2X1, glycolysis, Notch signaling, and lactate monocarboxylate transporters (MCT) were investigated in C. parvum-exposed bovine monocytes under intestinal physioxia (5% O2) and hyperoxia (21% O2; most commonly used hyperoxic laboratory conditions). C. parvum-triggered suicidal METs were confirmed by complete rupture of exposed monocytes, co-localization of extracellular DNA with myeloperoxidase (MPO) and histones (H1-H4) via immunofluorescence- and confocal microscopy analyses. C. parvum-induced suicidal METs resulted not only in oocyst entrapment but also in hindered sporozoite mobility from oocysts according to scanning electron microscopy (SEM) analyses. Early parasite-induced bovine monocyte activation, accompanied by membrane protrusions toward C. parvum-oocysts/sporozoites, was unveiled using live cell 3D-holotomographic microscopy analysis. The administration of NF449, an inhibitor of the ATP purinergic receptor P2X1, to monocytes subjected to varying oxygen concentrations did not yield a noteworthy decrease in C. parvum-induced METosis. This suggests that the cell death process is not dependent on P2X1. Additionally, blockage of glycolysis in monocyte through 2-deoxy glucose (2-DG) inhibition reduced C. parvum-induced METosis but not significantly. According to monocyte energetic state measurements, C. parvum-exposed cells neither increased extracellular acidification rates (ECAR) nor oxygen consumption rates (OCR). Lactate monocarboxylate transporters (MCT) inhibitor (i.e., AR-C 141990) treatments significantly diminished C. parvum-mediated METs extrusion under physioxic (5% O2) condition. Similarly, treatment with either DAPT or compound E, two selective Notch inhibitors, exhibited no significant suppressive effects on bovine MET production. Overall, for the first time, we demonstrate C. parvum-mediated METosis as P2X1-independent but as an MCT-dependent defense mechanism under intestinal physioxia (5% CO2) conditions. METs findings suggest anti-cryptosporidial effects through parasite entrapment and inhibition of sporozoite excystation.

An acid test for metformin†.

Lactic acid export from highly glycolytic cancer cells is critical to maintain cellular homeostasis. The identification of syrosingopine as an inhibitor of the lactate transporters monocarboxylate transporter (MCT) 1 and the tumor-induced isoform MCT4 suggests a potential therapeutic intervention. In a recent issue of this journal, Van der Vreken, Oudaert I and colleagues showed that syrosingopine, together with another drug metformin, had a synergistic effect in killing cultured multiple myeloma (MM) cell lines, primary MM blasts from patients, and in a mouse MM model. The antidiabetic drug metformin is currently also being investigated for anticancer efficacy. The synthetic lethality of these two drugs, which have good safety records and are approved for noncancer indications, raises the possibility of their combination for clinical anticancer therapy. © 2023 The Author. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Phase 1 results of CYT-0851, a monocarboxylate transporter (MCT) inhibitor, in combination with capecitabine (cape) or gemcitabine (gem) in advanced solid tumors.

3099 Background: The MCT inhibitor CYT-0851 blocks lactate transport resulting in glycolytic cancer cell death. Monotherapy clinical activity has been previously reported in lymphoma and solid tumors. Preclinical studies assessing CYT-0851 with chemotherapy identified enhanced growth inhibition when combined with 5-FU or gem supporting clinical evaluation. Methods: Patients (pts) with solid tumors were treated with CYT-0851 + standard dosing of cape or gem in 21- and 28-day cycles, respectively, following a 3+3 design. The primary objective was to determine the MTD. Secondary objectives included: safety, PK, and anti-tumor activity by RECIST. Results: As of Feb 1, 2023, 14 pts (pancreatic n=9; ovarian n=5) were treated in 4 cohorts (100 - 400 mg QD) with cape. No DLTs occurred, and 400 mg QD was selected as the RP2D. 8 pts (57%) experienced a treatment-related adverse event (TRAE), including 2 (14%) with a G3/4 AE. The most common related AEs were primarily G1/2 and included fatigue (21%), nausea, decreased appetite, dry skin, mucosal inflammation and maculopapular rash (all 14%). 10 pts (sarcoma n=6; HNSCC n=1; ovarian n=1; pancreatic n=2) were treated in 2 cohorts (100, 200 mg QD) with gem. No DLTs occurred. Escalation is ongoing with up to 2 further cohorts. 9 pts (90%) experienced a TRAE, including 5 (50%) with a G3/4 AE which were primarily cytopenias. The most common TRAEs were fatigue (50%), anemia (50%), neutropenia (40%), thrombocytopenia (30%), nausea, pruritus, ALT/AST increased, neutrophil decreased and WBC decreased (all 20%). CYT-0851 exposure was similar between combination therapy and monotherapy. 8 pts in the cape cohorts were response-evaluable, including 3 with ovarian cancer. 1 pt with platinum-resistant ovarian cancer had a confirmed PR with treatment ongoing at 174 days. 7 pts had SD. 6 pts in the gem cohorts were response-evaluable. 1 pt with sarcoma had a confirmed PR, 4 pts had SD and 1 had PD. Conclusions: 400 mg QD was selected as the RP2D in combination with cape as no MTD was identified. Escalation of gem + CYT-0851 is ongoing to identify the MTD. Both combinations have demonstrated an acceptable safety and tolerability profile with no unanticipated toxicities at clinically active doses. Encouraging antitumor activity has been observed in heavily pre-treated pts with both regimens including pts with ovarian cancer in the cape combo. The cape cohort is being expanded with additional pts with ovarian cancer and will be presented. Clinical trial information: NCT03997968 .