Potent and selective inhibition of the human Na+/H+ exchanger isoform NHE1 by a novel aminoguanidine derivative T-162559

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.

Structure and mechanism of the human NHE1-CHP1 complex

Sodium/proton exchanger 1 (NHE1) is an electroneutral secondary active transporter present on the plasma membrane of most mammalian cells and plays critical roles in regulating intracellular pH and volume homeostasis. Calcineurin B-homologous protein 1 (CHP1) is an obligate binding partner that promotes NHE1 biosynthetic maturation, cell surface expression and pH-sensitivity. Dysfunctions of either protein are associated with neurological disorders. Here, we elucidate structures of the human NHE1-CHP1 complex in both inward- and inhibitor (cariporide)-bound outward-facing conformations. We find that NHE1 assembles as a symmetrical homodimer, with each subunit undergoing an elevator-like conformational change during cation exchange. The cryo-EM map reveals the binding site for the NHE1 inhibitor cariporide, illustrating how inhibitors block transport activity. The CHP1 molecule differentially associates with these two conformational states of each NHE1 monomer, and this association difference probably underlies the regulation of NHE1 pH-sensitivity by CHP1.

Pyrazine ring-based Na+/H+ exchanger (NHE) inhibitors potently inhibit cancer cell growth in 3D culture, independent of NHE1

The Na+/H+ exchanger-1 (NHE1) supports tumour growth, making NHE1 inhibitors of interest in anticancer therapy, yet their molecular effects are incompletely characterized. Here, we demonstrate that widely used pyrazinoylguanidine-type NHE1 inhibitors potently inhibit growth and survival of cancer cell spheroids, in a manner unrelated to NHE1 inhibition. Cancer and non-cancer cells were grown as 3-dimensional (3D) spheroids and treated with pyrazinoylguanidine-type (amiloride, 5-(N-ethyl-N-isopropyl)-amiloride (EIPA), 5-(N,N-dimethyl)-amiloride (DMA), and 5-(N,N-hexamethylene)-amiloride (HMA)) or benzoylguanidine-type (eniporide, cariporide) NHE1 inhibitors for 2-7 days, followed by analyses of viability, compound accumulation, and stress- and death-associated signalling. EIPA, DMA and HMA dose-dependently reduced breast cancer spheroid viability while cariporide and eniporide had no effect. Although both compound types inhibited NHE1, the toxic effects were NHE1-independent, as inhibitor-induced viability loss was unaffected by NHE1 CRISPR/Cas9 knockout. EIPA and HMA accumulated extensively in spheroids, and this was associated with marked vacuolization, apparent autophagic arrest, ER stress, mitochondrial- and DNA damage and poly-ADP-ribose-polymerase (PARP) cleavage, indicative of severe stress and paraptosis-like cell death. Pyrazinoylguanidine-induced cell death was partially additive to that induced by conventional anticancer therapies and strongly additive to extracellular-signal-regulated-kinase (ERK) pathway inhibition. Thus, in addition to inhibiting NHE1, pyrazinoylguanidines exert potent, NHE1-independent cancer cell death, pointing to a novel relevance for these compounds in anticancer therapy.

Benzimidazol-2-yl or benzimidazol-2-ylthiomethyl benzoylguanidines as novel Na+/H+ exchanger inhibitors, synthesis and protection against ischemic-reperfusion injury

A novel series of benzimidazol-2-yl or benzimidazol-2-ylthiomethyl benzoylguanidines were designed and synthesized as Na(+)/H(+)exchanger inhibitors. Most of them were found to inhibit NHE1-mediated platelet swelling in a concentration-dependent manner, and to have significant cardioprotective effect against myocardial ischemic-reperfusion injury, among which compounds 10a and 34 were more potent than cariporide in both in vivo and in vitro tests.

Amiloride peptide conjugates: prodrugs for sodium-proton exchange inhibition

Inhibition of the sodium-proton exchanger (NHE) plays an important role in reducing tissue damage during ischemic reperfusion injury; however, pharmacological inhibitors of NHE have restricted access to acutely ischemic tissues because of severely compromised tissue perfusion. We describe the syntheses, characterization, and NHE inhibitory activities of a novel class of amiloride derivatives where peptides are conjugated to the amiloride C(5) amino group. These new peptide-C(5)-amiloride conjugates are inactive; however, peptide residues were chosen such that selective cleavage by neutral endopeptidase 24.11 (enkephalinase) liberates an amino acid-C(5)-amiloride conjugate that inhibits NHE in a glial cell line. These results confirm the feasibility of using peptide-amiloride conjugates as NHE inhibitor prodrugs. We envision the design of analogous peptide-amiloride prodrugs that can be administered prior to ischemic events and subsequently activated by endopeptidases selectively expressed by ischemic tissues.

Activation of Na+-H+ exchange and stretch-activated channels underlies the slow inotropic response to stretch in myocytes and muscle from the rat heart

We present the first direct comparison of the major candidates proposed to underlie the slow phase of the force increase seen following myocardial stretch: (i) the Na(+)-H(+) exchanger (NHE) (ii) nitric oxide (NO) and the ryanodine receptor (RyR) and (iii) the stretch-activated channel (SAC) in both single myocytes and multicellular muscle preparations from the rat heart. Ventricular myocytes were stretched by approximately 7% using carbon fibres. Papillary muscles were stretched from 88 to 98% of the length at which maximum tension is generated (L(max)). Inhibition of NHE with HOE 642 (5 microm) significantly reduced (P < 0.05) the magnitude of the slow force response in both muscle and myocytes. Neither inhibition of phosphatidylinositol-3-OH kinase (PtdIns-3-OH kinase) with LY294002 (10 microm) nor NO synthase with L-NAME (1 mm) reduced the slow force response in muscle or myocytes (P > 0.05), and the slow response was still present in the single myocyte when the sarcoplasmic reticulum was rigorously inhibited with 1 microm ryanodine and 1 microm thapsigargin. We saw a significant reduction (P < 0.05) in the slow force response in the presence of the SAC blocker streptomycin in both muscle (80 microm) and myocytes (40 microm). In fura 2-loaded myocytes, HOE 642 and streptomycin, but not L-NAME, ablated the stretch-induced increase in [Ca(2+)](i) transient amplitude. Our data suggest that in the rat, under our experimental conditions, there are two mechanisms that underlie the slow inotropic response to stretch: activation of NHE; and of activation of SACs. Both these mechanisms are intrinsic to the myocyte.

Mice with a null mutation in the NHE1 Na+-H+ exchanger are resistant to cardiac ischemia-reperfusion injury

Pharmacological studies indicate that Na+-H+ exchanger isoform 1 (NHE1) plays a central role in myocardial ischemia-reperfusion injury; however, confirmation by alternative methods is lacking. To address this issue, we examined the role of NHE1 in ischemia-reperfusion injury using gene-targeted NHE1-null mutant (Nhe1-/-) mice. Nhe1-/- and wild-type hearts were perfused in a Langendorff apparatus in both the absence and presence of the NHE1 inhibitor eniporide, subjected to 40 minutes of ischemia and 30 minutes of reperfusion, and the effects of genetic ablation or inhibition of NHE1 on hemodynamic, biochemical, and pathological changes were assessed. In the absence of eniporide, left ventricular developed pressure, end-diastolic pressure, and coronary flow were significantly less impaired in Nhe1-/- hearts relative to wild-type hearts, and release of lactate dehydrogenase, morphological damage, and ATP depletion were also significantly less. In the presence of eniporide, however, wild-type hearts were significantly protected and there were no significant differences between the two genotypes with respect to cardiac performance, lactate dehydrogenase release, or morphological damage. Furthermore, the presence or absence of eniporide had no apparent effect on the degree of cardioprotection observed in Nhe1-/- hearts. These data demonstrate that genetic ablation of NHE1 protects the heart against ischemia-reperfusion injury. In addition to providing direct evidence that confirms previous pharmacological studies indicating a role for NHE1 in ischemia-reperfusion injury, these results suggest that the long-term absence of NHE1 does not elicit major compensatory changes that might negate the cardioprotective effects of blocking its activity over the short-term.

Novel, non-acylguanidine-type Na(+)/H(+) exchanger inhibitors: synthesis and pharmacology of 5-tetrahydroquinolinylidene aminoguanidine derivatives

In the course of our research into new types of non-acylguanidine Na(+)/H(+) exchanger (NHE) inhibitors, we designed and synthesized aryl-fused tetrahydropyranylidene and cyclohexylidene aminoguanidine derivatives I (X = O, CH(2)), which were tested for their inhibitory effects on rat platelet NHEs. After optimization, we found that the S isomer of tetrahydroquinoline derivatives that possess a methyl group in the 4-position and a halogen or methyl group in the o-position of Ar(2) exhibited high inhibitory activity. In these compounds, (5E,7S)-[[7-(5-fluoro-2-methylphenyl)-4-methyl-7,8-dihydro-5(6H)-quinolinylidene]amino]guanidine dimethanesulfonate (18, T-162559) was found to be a potent inhibitor of both rat and human platelet NHEs, with IC(50) values of 14 and 13 nM, respectively. Furthermore, in a rat myocardial infarction model in vivo (1 h ischemia-24 h reperfusion), 18 (0.1 mg/kg, intravenously administered 5 min or 2 h before coronary occlusion) showed significant activity (33% or 23% inhibition, respectively). These results suggested that 18 may exhibit a potent and long-lasting protective activity against cardiac injuries induced by ischemia-reperfusion.

In vitro and in vivo pharmacology of a structurally novel Na+-H+ exchange inhibitor, T-162559

1. We investigated the inhibitory effects of a non-acylguanidine Na(+)-H(+) exchange (NHE) inhibitor, T-162559 ((5E,7S)-[7-(5-fluoro-2-methylphenyl)-4-methyl-7,8-dihydro-5(6H)-quinolinylideneamino] guanidine dimethanesulphonate), on NHE-1, and its cardioprotective effect against ischaemia and reperfusion injury in rats and rabbits. 2. T-162559 inhibited human platelet NHE-1 in a concentration-dependent manner, with an IC(50) value of 13+/-3 nmol l(-1), making it 16 and three times more potent than cariporide IC(50): 209+/-75 nmol l(-1), P<0.01) and eniporide (IC(50): 40+/-11 nmol l(-1), P=0.066), respectively. T-162559 also inhibited rat NHE-1 with an IC(50) value of 14+/-2 nmol l(-1), which was five and three times lower than that of cariporide (IC(50): 75+/-7 nmol l(-1), P<0.01) and eniporide (IC(50): 44+/-2 nmol l(-1), P<0.01), respectively. 3. T-162559 inhibited, in a concentration-dependent manner, the reduction in cardiac contractility, progression of cardiac contracture, and increase in lactate dehydrogenase release after global ischaemia and reperfusion in perfused rat hearts. The inhibitory effects of T-162559 were observed at a lower concentration range (10 - 100 nmol l(-1)) than with cariporide and eniporide. T-162559 did not alter basal cardiac contractility or coronary flow after reperfusion, suggesting that it exerts direct cardioprotective effects on the heart. 4. Intravenous administration of T-162559 (0.03 and 0.1 mg kg(-1)) significantly inhibited the progression of myocardial infarction induced by left coronary artery occlusion and reperfusion in rabbits; the infarct size normalized by area at risk was 74+/-6% in the vehicle group, and 47+/-5% and 51+/-7% in the T-162559-0.03 mg kg(-1) and T-162559-0.1 mg kg(-1) groups (both P<0.05), respectively. 5. These results indicate that the new structural NHE-1 inhibitor T-162559 is more potent than cariporide and eniporide and possesses a cardioprotective effect against ischaemia and reperfusion injury in rat and rabbit models.