Multifaceted effects of LRP6 in cancer: exploring tumor development, immune modulation and targeted therapies.

Low-density lipoprotein receptor (LDLR)-related protein 6 (LRP6), a member of the LDLR superfamily of cell surface receptors, is most widely known as a crucial co-receptor in the activation of canonical Wnt/ß-catenin signaling. This signaling pathway is implicated in multiple biological processes, such as lipoprotein metabolism, protease regulation, cell differentiation, and migration. LRP6 is frequently overexpressed in a variety of tumors, including liver cancer, colorectal cancer, and prostate cancer, and is generally considered an oncogene that promotes tumor proliferation, migration, and invasion. However, there are exceptions; some studies have reported that LRP6 inhibits lung metastasis of breast cancer through its ectodomain (LRP6N), and patients with low LRP6 expression tend to have a poor prognosis. Thus, the role of LRP6 in tumors remains controversial. Although limited studies have shown that LRP6 is associated with the expression and roles of a variety of immune cells in tumors, the interaction of LRP6 with the tumor microenvironment (TME) is not fully understood. Furthermore, it is crucial to acknowledge that LRP6 can engage with alternative pathways, including the mTORC1, CXCL12/CXCR4, and KRAS signaling pathways mentioned earlier, resulting in the regulation of biological functions independent of canonical Wnt/ß-catenin signaling. Due to the potential of LRP6 as a molecular target for cancer therapy, various treatment modalities have been developed to directly or indirectly inhibit LRP6 function, demonstrating promising anti-cancer effects across multiple cancer types. This review will concentrate on exploring the expression, function, and potential therapeutic applications of LRP6 in different cancer types, along with its influence on the TME.

MP-13, a novel chimeric peptide of morphiceptin and pepcan-9, produces potent antinociception with limited side effects.

Pharmacological investigations have substantiated the potential of bifunctional opioid/cannabinoid agonists in delivering potent analgesia while minimizing adverse reactions. Peptide modulators of cannabinoid receptors, known as pepcans, have been investigated before. In this study, we designed a series of chimeric peptides based on pepcans and morphiceptin (YPFP-NH2). Here, we combined injections of pepcans and morphiceptin to investigate the combination treatment of opioids and cannabis and compared the analgesic effect with chimeric compounds. Subsequently, we employed computational docking to screen the compounds against opioid and cannabinoid receptors, along with an acute pain model, to identify the most promising peptide. Among these peptides, MP-13, a morphiceptin and pepcan-9 (PVNFKLLSH) construct, exhibited superior supraspinal analgesic efficacy in the tail-flick test, with an ED50 value at 1.43 nmol/mouse, outperforming its parent peptides and other chimeric analogs. Additionally, MP-13 displayed potent analgesic activity mediated by mu-opioid receptor (MOR), delta-opioid receptor (DOR), and cannabinoid type 1 (CB1) receptor pathways. Furthermore, MP-13 did not induce psychological dependence and gastrointestinal motility inhibition at the effective analgesic doses, and it maintained non-tolerance-forming antinociception throughout a 7-day treatment regimen, with an unaltered count of microglial cells in the periaqueductal gray region, supporting this observation. Moreover, intracerebroventricular administration of MP-13 demonstrated dose-dependent antinociception in murine models of neuropathic, inflammatory, and visceral pain. Our findings provide promising insights for the development of opioid/cannabinoid peptide agonists, addressing a crucial gap in the field and holding significant potential for future research and development. PERSPECTIVE: This article offers insights into the combination treatment of pepcans with morphiceptin. Among the chimeric peptides, MP-13 exhibited potent analgesic effects in a series of preclinical pain models with a favorable side-effect profile.

Rhein exerts anti-multidrug resistance in acute myeloid leukemia via targeting FTO to inhibit AKT/mTOR.

Chemotherapy failure and resistance are the leading causes of mortality in patients with acute myeloid leukemia (AML). However, the role of m6A demethylase FTO and its inhibitor rhein in AML and AML drug resistance is unclear. Therefore, this study aimed to investigate the antileukemic effect of rhein on AML and explore its potential mechanisms underlying drug resistance. Bone marrow fluid was collected to assess FTO expression in AML. The Cell Counting Kit 8 reagent was used to assess cell viability. Migration assays were conducted to assess the cell migration capacity. Flow cytometry was used to determine the apoptotic effects of rhein and western blot analysis was used to detect protein expression. Online SynergyFinder software was used to calculate the drug synergy scores. The in-vivo antileukemic effect of rhein was assessed in an AML xenograft mouse model. We analyzed different types of AML bone marrow specimens to confirm that FTO is overexpressed in AML, particularly in cases of multidrug resistance. Subsequently, we conducted in-vivo and in-vitro investigations to explore the pharmacological activity and mechanism of rhein in AML and AML with multidrug resistance. The findings demonstrated that rhein effectively suppressed the proliferation and migration of AML cells in a time- and dose-dependent manner and induced apoptosis. Rhein targets FTO, inhibits the AKT/mTOR pathway, and exhibits synergistic antitumor effects when combined with azacitidine. This study elucidates the significant role of FTO and its inhibitor rhein in AML and AML with multidrug resistance, providing new insights for overcoming multidrug resistance in AML.

The m6A modulator-mediated cytarabine sensitivity and immune cell infiltration signature in acute myeloid leukemia.

PURPOSE: The study aims to investigate the impact of m6A modulators on drug resistance and the immune microenvironment in acute myeloid leukemia (AML). The emergence of drug resistance is a significant factor that contributes to relapse and refractory AML, leading to a poor prognosis. METHODS: The AML transcriptome data were retrieved from the TCGA database. The "oncoPredict" R package was utilized to assess the sensitivity of each sample to cytarabine (Ara-C) and classify them into distinct groups. Differential expression analysis was performed to identify m6A modulators differentially expressed between the two groups. Select Random Forest (RF) to build a predictive model. Model performance was evaluated using calibration curve, clinical decision curve, and clinical impact curve. The impacts of METTL3 on Ara-C sensitivity and immune microenvironment in AML were examined using GO, KEGG, CIBERSORT, and GSEA analyses. RESULTS: Seventeen out of 26 m6A modulators exhibited differential expression between the Ara-C-sensitive and resistant groups, with a high degree of correlation. We selected the 5 genes with the highest scores in the RF model to build a reliable and accurate prediction model. METTL3 plays a vital role in m6A modification, and further analysis shows its impact on the sensitivity of AML cells to Ara-C through its interaction with 7 types of immune-infiltrating cells and autophagy. CONCLUSION: This study utilizes m6A modulators to develop a prediction model for the sensitivity of AML patients to Ara-C, which can assist in treating AML drug resistance by targeting mRNA methylation.

Salinomycin sodium exerts anti diffuse large B-cell lymphoma activity through inhibition of LRP6-mediated Wnt/ß-catenin and mTORC1 signaling.

Low-density lipoprotein receptor-related protein-6 (LRP6) is overexpressed in various cancers. The small molecule salinomycin sodium inhibits LRP6. We observed a higher proportion of subjects with non-germinal center B (non-GCB) subtypes having high LRP6 expression than those with GCB subtypes by immunohistochemistry. The PCR and Western blot assays demonstrated increased LRP6 expression in non-GCB subtype cells. In addition, CCK-8 assays and transwell cell migration assays revealed that salinomycin sodium exhibited dose- and time-dependent inhibition of proliferation and migration in non-GCB subtype cells. Furthermore, Western blot assays showed that salinomycin sodium decreased the expression of Bcl2, while increasing the expression of Bax. Additionally, salinomycin sodium suppressed LRP6 expression, blocked LRP6 phosphorylation, and inhibited the Wnt/ß-catenin and mTORC1 signaling pathways. Our results suggest that LRP6 is highly expressed in non-GCB subtype. Furthermore, salinomycin sodium inhibited LRP6 expression and the Wnt/ß-catenin and mTORC1 signaling in non-GCB subtype cells, and displayed potent anticancer activity.

Immune scoring model based on immune cell infiltration to predict prognosis in diffuse large B-cell lymphoma.

BACKGROUND: Diffuse large B-cell lymphoma (DLBCL) is genetically heterogeneous in both pathogenesis and clinical symptoms. Most studies on tumor prognosis have not fully considered the role of tumor-infiltrating immune cells. This study focused on the role of tumor-infiltrating immune cells in the prognosis of DLBCL. METHODS: The GSE10846 data set from the National Center for Biotechnology Information's Gene Expression Omnibus was used as the training set, and the GSE53786 data set was used as the validation set. The proportion of immune cells in each sample was calculated with the CIBERSORT algorithm using R software. After 10 immune cells were screened out (activated memory CD4 positive T cells, follicular helper T cells, regulatory T cells, gamma-delta T cells, activated natural killer cells, M0 macrophages, M2 macrophages, resting dendritic cells, and eosinophils) by univariate Cox analysis, Lasso regression and random forest sampling analyses were performed, the intersecting immune cells were selected for multifactor Cox analysis, and a predictive model was constructed combined with clinical information. Predictive performance was assessed using survival analysis and time-dependent receiver operating characteristic curve analysis. RESULTS: In total, 539 samples were included in this study, and samples with p < .05 were retained using CIBERSORT. Univariate Cox analysis yielded 10 cell types that were associated with overall survival. Two kinds of immune cells were obtained by Lasso regression combined with the random forest method and were used to construct a prognostic model combined with clinical information. The reliability of the model was validated in two data sets. CONCLUSIONS: The immune cell-based prediction model constructed by the authors can effectively predict the prognostic outcome of patients with DLBCL, whereas nomogram plots can help clinicians assess the probability of long-term survival.

MCRT, a multifunctional ligand of opioid and neuropeptide FF receptors, attenuates neuropathic pain in spared nerve injury model.

Chimeric peptide MCRT (YPFPFRTic-NH2 ) was a multifunctional ligand of opioid and neuropeptide FF (NPFF) receptors and reported to be potentially antalgic in acute tail-flick test. Here, we developed spared nerve injury (SNI) model to explore its efficacy in chronic neuropathic pain. Analgesic tolerance, opioid-induced hyperalgesia and gastrointestinal transit were measured for safety evaluation. Intracerebroventricular (i.c.v.) and intraplantar (i.pl.) injections were conducted as central and peripheral routes, respectively. Results demonstrated that MCRT alleviated neuropathic pain effectively and efficiently, with the ED50 values of 4.93 nmol/kg at the central level and 3.11 nmol/kg at the peripheral level. The antagonist blocking study verified the involvement of mu-, delta-opioid and NPFF receptors in MCRT produced anti-allodynia. Moreover, the separation of analgesia from unwanted effects was preliminarily achieved and that MCRT caused neither analgesic tolerance nor hyperalgesia after chronic i.c.v. administration, nor constipation after i.pl. administration. Notably, the local efficacy of MCRT in SNI mice was about one thousandfold higher than morphine and ten thousandfold higher than pregabalin, indicating a great promise in the future treatment of neuropathic pain.

[Research Status of New Targets MRD Detection in Acute Myeloid Leukemia Recurrence--Review].

Although most acute myeloid leukemia (AML) patients can achieve complete remission (CR) induced by standardized chemotherapy, but the relapse rate after remission remains high. The key reason is its high heterogeneity in cytogenetics and molecular biology. There are evidences show that minimal residual disease (MRD) is closely associated with disease recurrence, so that, finding specific genetic and molecular biological changes as new targets for MRD detection has become a research hotspot in recent years. In this review the intrinsic relationship between relapse of AML and MRD detection of specific molecular events, the application of these new targets in MRD detection and their targeted therapies according to the latest guidelines, so as to achieve the optimal treatment in CR phase.

Studies on the changes of uPA system in a co-culture model of bone marrow stromal cells-leukemia cells.

The core of the tumor microenvironment in the hematological system is formed by bone marrow stromal cells (BMSCs). In the present study, we explored the interaction between the urokinase plasminogen activator (uPA) system and the leukemia bone marrow microenvironment (BMM). We established BMSCs-HL60 and HS-5-K562 co-culture models in direct contact mode to simulate the BMM in leukemia. In BMSCs-HL60 co-culture model, the expression levels of uPA, uPA receptor (uPAR), plasminogen activator inhibitor 1 (PAI-1) and vascular endothelial growth factor (VEGF) in BMSCs were higher than those in mono-cultured BMSCs. Matrix metalloproteinase (MMP)-9 (MMP-9) was up-regulated in co-cultured HL60 cells. In HS-5-K562 co-culture model, only uPA, PAI-1, and VEGF-A were up-regulated in HS-5 cells. The levels of the uPA protein in the co-culture supernatant were significantly higher than that of mono-cultured BMSCs or HS-5 cells. Our findings demonstrate that the co-culture stimulates the production of uPA, uPAR, PAI-1, MMP-9, and VEGF-A by BMSCs. It could further explain how the uPA system in leukemia cells is involved in the growth, development, and prognosis of leukemia.

AML­derived mesenchymal stem cells upregulate CTGF expression through the BMP pathway and induce K562­ADM fusiform transformation and chemoresistance.

Bone marrow­derived mesenchymal stem cells (MSCs), are the basic cellular components that make up the bone marrow microenvironment (BMM). In acute myeloid leukemia (AML), the morphology and function of MSCs changes in accordance with the transformation of the BMM. Moreover, the transformation of MSCs into osteoblasts is determined through the bone morphogenetic protein (BMP) pathway, ultimately leading to an altered expression of the downstream adhesion molecule, connective tissue growth factor (CTGF). In this study, we aimed to explore the interaction of possible pathways in AML­derived mesenchymal stem cells (AML­MSCs) co­cultured with the K562 and K562­ADM cell lines. AML­MSCs were co­cultured with K562/K562­ADM cells, and the interactions between the cells were verified by morphological detection, peroxidase staining (POX), reverse transcription­quantitative polymerase chain reaction (RT­qPCR) and fluorescence in situ hybridization (FISH). The proliferation of K562/K562­ADM cells under co­culture conditions was detected by flow cytometry. The expression levels of BMP4 and CTGF were examined by RT­qPCR and western blot (WB) analysis. The detection of interleukin (IL)­6 and IL­32 was also determined by enzyme linked immunosorbent assay (ELISA). In the co­culture system, the K562­ADM cells underwent fusiform transformation. The occurrence of this transformation was associated with an increased expression of CTGF due to the dysregulation of the BMP pathway. The AML­MSCs promoted the proliferation of the K562­ADM cell, but inhibited that of the K562 cells. These findings were confirmed by changes in the expression of the soluble cytokines, IL­6 and IL­32. On the whole, the findings of this study demonstrate that AML­MSCs regulate the expression of CTGF through the BMP pathway. In addition, they affect cytokine production, induce spindle­shaped transformation, and increase drug resistance in the K562­ADM cells. Thus, the morphological transformation through the BMP pathway provides us with a novel target with which to circumvent tumor occurrence, development, drug resistance, invasion and metastasis.

In vitro and in vivo characterization of the bifunctional µ- and δ- opioid receptors ligand MCRT on mouse gastrointestinal motility.

BACKGROUND: Chimeric opioid MCRT was a novel multi-target ligand based on morphiceptin and PFRTic-NH2, and produced potent analgesia (ED50 = 0.03 nmol/mouse) with less upper gastrointestinal dysmotility. In this study, we sought to perform the tests to evaluate the pharmacological effects of MCRT on distal colon motility and defecation function. Moreover, opioid receptor antagonists and neuropeptide FF (NPFF) receptor antagonists were utilized to explore the mechanisms. METHODS: Isolated mouse colon bioassay and colonic bead expulsion were to characterize MCRT-induced inhibition of colonic motility in vitro and in vivo, respectively. Fecal pellet output was to evaluate the defecation function. RESULTS: (1) In vitro, MCRT increased colonic contraction via µ- and δ- opioid receptors (MOR and DOR). (2) In vivo, MCRT delayed colonic bead expulsion (ED50 = 1.1 nmol/mouse) independent of opioid and NPFF receptors. (3) In vivo, MCRT inhibited fecal number (ED50 = 1.43 nmol/mouse) and dry weight (ED50 = 1.63 nmol/mouse), which was mediated by DOR partially but not MOR. CONCLUSIONS: (1) Data indicated that MCRT was less prone to induce gastrointestinal dysmotility at analgesic doses, and provided a possibility for safer opioid analgesic. (2) Based on the mechanism explorations, we speculated on the existence of such an opioid receptor subtype or MOR/DOR heterodimer, which was involved in the central analgesia and the in vitro colonic contractions but not the central colonic dysmotility.

Association of cytotoxic T-lymphocyte antigen 4 gene with immune thrombocytopenia in Chinese Han children.

OBJECTIVES: To investigate the association of cytotoxic T lymphocyte-associated antigen 4 (CTLA4) with immune thrombocytopenia (ITP). METHODS: A case-control association analysis of 277 Chinese Han children was performed. The tagging variants rs11571315 and rs3087243 in the CTLA4 gene were detected using polymerase chain reaction-restriction fragment length polymorphism method. The expression quantitative trait loci (eQTL) analysis and quantitative real-time polymerase chain reaction were performed to determine the relationship of CTLA4 with ITP. RESULTS: Neither SNP was significantly different between case and control groups in either the genotypic or allelic distribution. The eQTL analysis results indicated that in the spleen, the rs3087243 was significant with the expression of CTLA4. The rs11571315 has similar results. Interestingly, the transcript level of CTLA4 was found to significantly decrease in patients with ITP. DISCUSSION: The autoimmune and gene etiology is implicated in the pathogen of ITP. The CTLA4 is important for negative regulation of T-cell activation, and CTLA-4 gene has been identified as a risk factor for some autoimmune diseases. However, association studies of ITP and CTLA4 gene have obtained conflicting results. This is the first study to systematically investigate the association of CTLA4 with ITP in Chinese Han children. CONCLUSIONS: The CTLA4 gene is suggested to correlate with ITP through its abnormal expression level instead of gene site mutation.

Arminin 1a-C, a novel antimicrobial peptide from ancient metazoan Hydra, shows potent antileukemia activity against drug-sensitive and drug-resistant leukemia cells.

PURPOSE: Due to the emergence of multidrug resistance (MDR), traditional antileukemia drugs no longer meet the treatment needs. Therefore, new antileukemia drugs with different action mechanisms are urgently needed to cope with this situation. MATERIALS AND METHODS: Arminin 1a-C is an antimicrobial peptide (AMP) developed from the ancient metazoan marine Hydra. In this study, we first explored its antileukemia activity. RESULTS: Our results showed that Arminin 1a-C formed an α-helical structure and efficaciously suppressed the viability of leukemia cell lines whether or not they were multidrug resistant or sensitive, and there were no obvious differences between these cell lines. Arminin 1a-C exhibited distinct selectivity between noncancerous and cancerous cell lines. Arminin 1a-C interfered with K562/adriamycin (ADM) cell (a kind of multidrug-resistant leukemia cell line) proliferation in a very rapid manner and formed pores in its cell membrane, making it difficult to develop resistance against Arminin 1a-C. CONCLUSION: Our data show that Arminin 1a-C possesses great potential as a therapeutic candidate for the treatment of multidrug-resistant leukemia.

NK-18, a promising antimicrobial peptide: anti-multidrug resistant leukemia cells and LPS neutralizing properties.

With the increase of multidrug resistance, novel anti-leukemia agents with diverse mechanisms of action are required to address this challenge. NK-18, the core region of mammalian derived protein NK-lysin, effectively inhibited the viability of both multidrug resistant and sensitive leukemia cell lines. Meanwhile, this proliferation inhibition effect was not distinct between sensitive and multidrug resistant leukemia cell line. NK-18 showed selectivity between non-tumorigenic and tumorigenic cells. It preferentially bound to tumor cells whose outer leaflet with high phosphatidylserine content. NK-18 acted on the multidrug resistant leukemia cell line by a rapid pore formation on the cell membrane, it is not easy for K562/ADM cells developing resistance against NK-18. Furthermore, NK-18 could neutralize lipopolysaccharides by electrostatic attraction and reduce NO production. These research data demonstrated NK-18 possesses great advantage in the multidrug resistant leukemia treatment compared with conventional chemotherapies and it could be a potential candidate for further research.

Influence of Proline Substitution on the Bioactivity of Mammalian-Derived Antimicrobial Peptide NK-2.

Multidrug-resistant bacteria are emerging as a global threat, making the search for alternative compounds urgent. Antimicrobial peptides (AMPs) became a promising hotspot due to their distinct action mechanism and possibility to be used as an alternative or complement to traditional antibiotics. However, gaining a better understanding about the relationship between antimicrobial peptides structure and its bioactivity is crucial for the development of next generation of antimicrobial agents. NK-2, derived from mammalian protein NK-lysin, has potent antitumor and bactericidal abilities. As proline was considered to be an effective α-helix breaker due to its restricted conformation, to better comprehend the effects of proline in the structure-activity relationship of NK-2, we constructed two NK-2 analogs. We examined the biological activities of NK-2 and its proline substitution analogs and analyzed the resulting conformational changes. Our results showed that introducing proline into the primary sequence of NK-2 significantly decreased the antitumor, antibacterial, and cytotoxic effects, as well as DNA binding activity by changing the α-helix content. However, α-helical content was not the only determining factor, the position of proline inserted was also critical. This study will allow for clearer insight into the role of proline in structure and bioactivity of NK-2 and provide a foundation for future studies.

Soluble urokinase-type plasminogen activator receptor and urokinase-type plasminogen activator receptor contribute to chemoresistance in leukemia.

The soluble urokinase-type plasminogen activator receptor (suPAR) and the urokinase-type plasminogen activator receptor (uPAR) have been proposed as useful biomarkers of tumor progression. Recently, suPAR was associated with chemoresistance in lung cancer. However, its clinical significance in leukemia has not previously been investigated. The present study examined the plasma levels of suPAR and the expression of the uPAR on bone marrow (BM) cells in 86 patients with leukemia at diagnosis prior to chemotherapy and 26 normal subjects (control group). The plasma suPAR levels were measured using ELISA, whilst uPAR expression was assayed by flow cytometry analysis. In addition, cell surface uPAR expression on K562 and multidrug-resistant K562/ADM cell lines was studied by western blotting. On admission and follow-up, the levels of suPAR in patients with leukemia were significantly increased compared with controls. Systemic levels of suPAR were strongly associated with the numbers of white blood cells. A case was defined as uPAR-positive (uPAR+) if >20% of the gated cells expressed uPAR. In comparison with 26 healthy BM samples that were negative for uPAR expression, 48 (55.8%) of the 86 leukemia patients were uPAR+. uPAR expression on the cell surface of multidrug-resistant K562/ADM cells was increased compared with that on K562 cells. In conclusion, plasma suPAR expression may be a useful marker for subtype classification of patients with leukemia and cell surface uPAR may be associated with resistance to chemotherapy or disease progression.

Supraspinal inhibitory effects of chimeric peptide MCRT on gastrointestinal motility in mice.

OBJECTIVES: Chimeric peptide MCRT, based on morphiceptin and PFRTic-NH2 , was a bifunctional ligand of µ- and δ-opioid receptors (MOR-DOR) and produced potent analgesia in tail-withdrawal test. The study focused on the supraspinal effects of morphiceptin, PFRTic-NH2 and MCRT on gastrointestinal motility. Moreover, opioid receptor antagonists, naloxone (non-selective), cyprodime (MOR selective) and naltrindole (DOR selective) were utilized to explore the mechanisms. METHODS: Intracerebroventricular administration was achieved via the implanted cannula. Gastric emptying and intestinal transit were measured to evaluate gastrointestinal motility. KEY FINDINGS: (1) At supraspinal level, morphiceptin, PFRTic-NH2 and MCRT significantly decreased gastric emptying and intestinal transit; (2) MCRT at 1 nmol/mouse, far higher than its analgesic dose (ED50  = 29.8 pmol/mouse), failed to regulate the gastrointestinal motility; (3) MCRT-induced gastrointestinal dysfunction could be completely blocked by naloxone and naltrindole, but not affected by cyprodime. CONCLUSIONS: (1) Morphiceptin and PFRTic-NH2 played important roles in the regulation of gastrointestinal motility; (2) MCRT possessed higher bioactivity of pain relief than gastrointestinal regulation, suggesting its promising analgesic property; (3) MCRT-induced motility disorders were sensitive to DOR but not to MOR blockade, indicating the pain-relieving specificity of speculated MOR subtype or splice variant or MOR-DOR heterodimer.

MCRT, a chimeric peptide based on morphiceptin and PFRTic-NH2, regulates the depressor effects induced by endokinin A/B.

The interactions of the chimeric peptide MCRT (YPFPFRTic-NH2), based on morphiceptin and neuropeptide FF derivative PFRTic-NH2, on the effects of endokinin A/B (EKA/B) on mean arterial blood pressure of the urethane-anaesthetized rat have been investigated in the absence and presence of tachykinin receptor antagonists, naloxone and NO synthase inhibitors. While MCRT produced dose dependent decreases in mean arterial pressure, in its presence only a small but statistically insignificant decreases in the magnitude and the time course of the depressor effect of EKA/B (10nmol/kg) were observed. MCRT had little influence on the depressor effect of EKA/B (1 nmol/kg), but strongly potentiated that of EKA/B (100nmol/kg). The tachykinin NK1 receptor antagonist SR140333B (1mg/kg) and the NK3 antagonist SR142891 (2.79mg/kg) both reduced the hypotensive effects of EKA/B and MCRT alone and blocked those of the two peptides in combination. The NK2 antagonist GR159897 (4mg/kg) partially blocked the depressor effects of EKA/B and MCRT alone. Naloxone (2mg/kg) completely blocked the depressor effect of MCTR, but partially blocked that of EKA/B. The NO synthase inhibitor l-NAME (50mg/kg) partially blocked the depressor effects of EKA/B, MCRT, and EKA/B + MCRT. These results could help to better understand the role of tachykinin receptors, opioid receptors and neuropeptide FF receptors in cardiovascular system.

Pain regulation of endokinin A/B or endokinin C/D on chimeric peptide MCRT in mice.

The present study focused on the interactive pain regulation of endokinin A/B (EKA/B, the common C-terminal decapeptide in EKA and EKB) or endokinin C/D (EKC/D, the common C-terminal duodecapeptide in EKC and EKD) on chimeric peptide MCRT (YPFPFRTic-NH2, based on YPFP-NH2 and PFRTic-NH2) at the supraspinal level in mice. Results demonstrated that the co-injection of nanomolar EKA/B and MCRT showed moderate regulation, whereas 30 pmol EKA/B had no effect on MCRT. The combination of EKC/D and MCRT produced enhanced antinociception, which was nearly equal to the sum of the mathematical values of single EKC/D and MCRT. Mechanism studies revealed that pre-injected naloxone attenuated the combination significantly compared with the equivalent analgesic effects of EKC/D alone, suggesting that EKC/D and MCRT might act on two totally independent pathways. Moreover, based on the above results and previous reports, we made two reasonable hypotheses to explain the cocktail-induced analgesia, which may potentially pave the way to explore the respective regulatory mechanisms of EKA/B, EKC/D, and MCRT and to better understand the complicated pain regulation of NK1 and µ opioid receptors, as follows: (1) MCRT and endomorphin-1 possibly activated different µ subtypes; and (2) picomolar EKA/B might motivate the endogenous NPFF system after NK1 activation.

Tetrazine-Containing Amino Acid for Peptide Modification and Live Cell Labeling.

A novel amino acid derivative 3-(4-(1, 2, 4, 5-tetrazine-3-yl) phenyl)-2-aminopropanoic acid was synthesized in this study. The compound possessed better water-solubility and was synthesized more easily compared with the well-known and commercially available 3-(p-benzylamino)-1, 2, 4, 5-tetrazine. Tetrazine-containing amino acid showed excellent stability in biological media and might be used for cancer cell labeling. Moreover, the compound remained relatively stable in 50% TFA/DCM with little decomposition after prolonged exposure at room temperature. The compound could be utilized as phenylalanine or tyrosine analogue in peptide modification, and the tetrazine-containing peptide demonstrated more significant biological activity than that of the parent peptide. The combination of tetrazine group and amino acid offered broad development prospects of the bioorthogonal labeling and peptide synthesis.