In Situ Fabrication of Silver Nanoparticle-Decorated Polymeric Vesicles for Antibacterial Applications.

Silver/polymeric vesicle composite nanoparticles with good antibacterial properties were fabricated in this study. Silver nanoparticles (AgNPs) were prepared in situ on cross-linked vesicle membranes through the reduction of silver nitrate (AgNO3) using polyvinylpyrrolidone (PVP) via coordination bonding between the Ag+ ions and the nitrogen atoms on the vesicles. X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-vis), and transmission electron microscopy (TEM) analyses confirmed the formation of AgNPs on the vesicles. The antibacterial test demonstrated good antibacterial activity against both Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus) for the produced AgNP-decorated vesicles. The minimum inhibitory concentration (MIC) values of the AgNP-decorated vesicles for E. coli and S. aureus were 8.4 and 9.6 µg/mL, respectively. Cell viability analysis on the A549 cells indicated that the toxicity was low when the AgNP concentrations did not exceed the MIC values, and the wound healing test confirmed the good antibacterial properties of the AgNP-decorated vesicles.

CLDN18.2 and 4-1BB bispecific antibody givastomig exerts antitumor activity through CLDN18.2-expressing tumor-directed T-cell activation.

BACKGROUND: Claudin18.2 (CLDN18.2) is a tight junction protein that has been identified as a clinically proven target in gastric cancer. Stimulation of 4-1BB with agonistic antibodies is also a promising strategy for immunotherapy and 4-1BB+ T cells were reported to be present within the tumor microenvironment of patients with gastric cancer. However, hepatotoxicity-mediated by 4-1BB activation was observed in clinical trials of agonistic anti-4-1BB monoclonal antibodies. METHODS: To specifically activate the 4-1BB+ T cells in tumor and avoid the on-target liver toxicity, we developed a novel CLDN18.2×4-1BB bispecific antibody (termed 'givastomig' or 'ABL111'; also known as TJ-CD4B or TJ033721) that was designed to activate 4-1BB signaling in a CLDN18.2 engagement-dependent manner. RESULTS: 4-1BB+ T cells were observed to be coexisted with CLDN18.2+ tumor cells in proximity by multiplex immunohistochemical staining of tumor tissues from patients with gastric cancer (n=60). Givastomig/ABL111 could bind to cell lines expressing various levels of CLDN18.2 with a high affinity and induce 4-1BB activation in vitro only in the context of CLDN18.2 binding. The magnitude of T-cell activation by givastomig/ABL111 treatment was closely correlated with the CLDN18.2 expression level of tumor cells from gastric cancer patient-derived xenograft model. Mechanistically, givastomig/ABL111 treatment could upregulate the expression of a panel of pro-inflammatory and interferon-γ-responsive genes in human peripheral blood mononuclear cells when co-cultured with CLDN18.2+ tumor cells. Furthermore, in humanized 4-1BB transgenic mice inoculated with human CLDN18.2-expressing tumor cells, givastomig/ABL111 induced a localized immune activation in tumor as evident by the increased ratio of CD8+/regulatory T cell, leading to the superior antitumor activity and long-lasting memory response against tumor rechallenge. Givastomig/ABL111 was well tolerated, with no systemic immune response and hepatotoxicity in monkeys. CONCLUSIONS: Givastomig/ABL111 is a novel CLDN18.2×4-1BB bispecific antibody which has the potential to treat patients with gastric cancer with a wide range of CLDN18.2 expression level through the restricted activation of 4-1BB+ T cells in tumor microenvironment to avoid the risk of liver toxicity and systemic immune response.

Association of KMT2C/D loss-of-function variants with response to immune checkpoint blockades in colorectal cancer.

Immune checkpoint inhibitors (ICIs) have become important treatment strategies, yet responses vary among patients and predictive biomarkers are urgently needed. Mutations in KMT2C and KMT2D lead to increased levels of genomic instability. Therefore, we aimed to examine whether KMT2C/D mutations might be a predictor of immunotherapeutic efficacy. Here, we investigated the associations of KMT2C/D loss-of-function (LOF) variants with tumor mutation burden (TMB), MSI-H, PD-L1 expression, the levels of tumor-infiltrating leukocytes (TILs), and clinical response to ICIs. It was found that KMT2C/D LOF variants were associated with higher TMB. Compared with the non-LOF group, the proportion of patients with MSI-H tumors was larger in the LOF group. PD-L1 expression was higher in the LOF group only for colorectal cancer in both the Chinese and The Cancer Genome Atlas cohorts. Importantly, KMT2C/D LOF variants were associated with decreased regulatory T cells and increased levels of CD8+ T cells, activated NK cells, M1 macrophages, and M2 macrophages in colorectal cancer. However, there was no significant association between KMT2C/D LOF and TILs levels in other cancer types. Consistently, the results showed that KMT2C/D LOF variants were associated with prolonged overall survival only in colorectal cancer (p = 0.0485). We also presented that patients with KMT2C/D LOF mutations exhibited a better clinical response to anti-PD-1 therapy in a Chinese colorectal cancer cohort (p = 0.002). Taken together, these results suggested that KMT2C/D LOF variants could be a useful predictor for ICIs efficacy in colorectal cancer. In addition, the predictive value of KMT2C/D LOF variants was consistent with their association with TILs levels.

Molecular and clinical characteristics of IDH mutations in Chinese NSCLC patients and potential treatment strategies.

BACKGROUND: Isocitrate dehydrogenase (IDH) is an appealing target for anticancer therapy, and IDH (IDH1/2) inhibitors have been approved for targeted therapy of acute myeloid leukemia (AML) and Cholangiocarcinoma. The therapeutic potential of IDH inhibitors for non-small-cell lung cancer (NSCLC) patients is under active clinical investigation. Thus, it would be necessary and meaningful to study the molecular and clinical characteristics of IDH mutation in NSCLC patients, especially in the Chinese population. METHODS: A total of 17,978 Chinese patients with NSCLC who underwent next -generation sequencing (NGS) testing were retrospectively reviewed. RESULTS: We identified 161 unique IDH mutations in 361 of 17,978 patients (2.01%). Common active-site mutations, including IDH1R100 , IDH1R132 , IDH2R140 , and IDH2R172 , were detected in 154 patients (0.86%) and were associated with male sex (p = 0.004) and older age (p = 0.02). The IDH mutation spectra observed in NSCLC were quite different from those in glioma or AML. Patients with IDH active-site mutations exhibited significantly higher coalterations in KRAS (p. G12/13/61, 22.1% vs. 8.2%, p < 0.001) or BRAF (p. V600E, 6.5% vs. 1.0%, p < 0.001), but significantly lower coalterations in activating EGFR (e18-e20, 22.7 vs. 37.9%, p < 0.001) than IDH wild-type patients. Furthermore, we found that active-site IDH mutations were correlated with a short PFS (2-5.6 months) and short OS (2-9.5 months), which may arise as a resistance mechanism against common targeted drugs. In vitro, we experimentally observed that the combination of an IDH inhibitor and EGFR TKI could better inhibit lung cancer cell proliferation than an EGFR TKI alone. CONCLUSIONS: Taken together, this study reveals the molecular and clinical characteristics of IDH mutations in Chinese NSCLC patients and provides a theoretical basis for IDH-directed treatment. The potential of IDH mutations as response markers for targeted therapy warrants further investigation.

Targeting BCAT1 Combined with α-Ketoglutarate Triggers Metabolic Synthetic Lethality in Glioblastoma.

Branched-chain amino acid transaminase 1 (BCAT1) is upregulated selectively in human isocitrate dehydrogenase (IDH) wildtype (WT) but not mutant glioblastoma multiforme (GBM) and promotes IDHWT GBM growth. Through a metabolic synthetic lethal screen, we report here that α-ketoglutarate (AKG) kills IDHWT GBM cells when BCAT1 protein is lost, which is reversed by reexpression of BCAT1 or supplementation with branched-chain α-ketoacids (BCKA), downstream metabolic products of BCAT1. In patient-derived IDHWT GBM tumors in vitro and in vivo, cotreatment of BCAT1 inhibitor gabapentin and AKG resulted in synthetic lethality. However, AKG failed to evoke a synthetic lethal effect with loss of BCAT2, BCKDHA, or GPT2 in IDHWT GBM cells. Mechanistically, loss of BCAT1 increased the NAD+/NADH ratio but impaired oxidative phosphorylation, mTORC1 activity, and nucleotide biosynthesis. These metabolic alterations were synergistically augmented by AKG treatment, thereby causing mitochondrial dysfunction and depletion of cellular building blocks, including ATP, nucleotides, and proteins. Partial restoration of ATP, nucleotides, proteins, and mTORC1 activity by BCKA supplementation prevented IDHWT GBM cell death conferred by the combination of BCAT1 loss and AKG. These findings define a targetable metabolic vulnerability in the most common subset of GBM that is currently incurable. SIGNIFICANCE: Metabolic synthetic lethal screening in IDHWT glioblastoma defines a vulnerability to ΑΚG following BCAT1 loss, uncovering a therapeutic strategy to improve glioblastoma treatment. See related commentary by Meurs and Nagrath, p. 2354.

Genomic and Transcriptional Profiling of Chinese Melanoma Patients Enhanced Potentially Druggable Targets: A Multicenter Study.

BACKGROUND: In contrast to Caucasian melanoma, which has been extensively studied, there are few studies on melanoma in Asian populations. Sporadic studies reported that only 40% of Asian melanoma patients could be druggable, which was much lower than that in Caucasians. More studies are required to refine this conclusion. METHODS: Chinese melanoma patients (n = 469) were sequentially sequenced by DNA-NGS and RNA-NGS. The genomic alterations were determined, and potentially actionable targets were investigated. RESULTS: Patients with potential druggable targets were identified in 75% of Chinese melanoma patients by DNA-NGS based on OncoKB, which was much higher than in a previous Asian study. NRG1 fusions were first identified in melanoma. In addition, up to 11.7% (7/60) of patients in the undruggable group could be recognized as actionable by including RNA-NGS analysis. By comparing the fusion detection rate between DNA-NGS and RNA-NGS, all available samples after DNA-NGS detection were further verified by RNA-NGS. The use of RNA-NGS enhanced the proportion of druggable fusions from 2.56% to 17.27%. In total, the use of RNA-NGS increased the druggable proportion from 75% to 78%. CONCLUSIONS: In this study, we systemically analyzed the actionable landscape of melanoma in the largest Asian cohort. In addition, we first demonstrated how DNA and RNA sequential sequencing is essential in bringing clinical benefits to more patients with melanoma.

Prior Therapy With Pegylated-Interferon Alfa-2b Improves the Efficacy of Adjuvant Pembrolizumab in Resectable Advanced Melanoma.

Combination immunotherapy can overcome the limited objective response rates of PD-1 blockade. Interferon alpha (IFN-α) has been proven to be effective in modulating immune responses and may enhance the clinical responses to PD-1 blockade. According to clinical practice guidelines, IFN-α was recommended as adjuvant therapy for stage IIB/C melanoma patients. However, the impact of prior IFN-α therapy on the efficacy of subsequent PD-1 blockade in melanoma has not been previously reported. Therefore, we performed a retrospective analysis for melanoma patients and addressed whether prior IFN-α therapy enhanced adjuvant pembrolizumab as later-line treatment. Fifty-six patients with resectable stage III/IV melanoma who received adjuvant therapy with pembrolizumab were retrospectively enrolled in this study. Notably, 25 patients received adjuvant pegylated IFN-α (PEG-IFN-α) in the prior line of treatment while 31 patients did not receive prior PEG-IFN-α therapy. Cox regression analysis showed that prior PEG-IFN-α therapy was associated with the efficacy of later-line adjuvant pembrolizumab (hazard ratio=0.37, 95% CI 0.16-0.89; P = 0.026). The recurrence rates after treatment with adjuvant pembrolizumab were significantly reduced in the prior PEG-IFN-α group (P < 0.001). The Kaplan-Meier analysis also showed that recurrence-free survival (RFS) after adjuvant pembrolizumab therapy was prolonged by prior PEG-IFN-α treatment (median RFSPem 8.5 months vs. 4.5 months; P = 0.0372). These findings indicated that prior PEG-IFN-α could enhance the efficacy of adjuvant pembrolizumab. The long-lasting effects of PEG-IFN-α provide a new rationale for designing combination or sequential immunotherapy.

LncIHAT Is Induced by Hypoxia-Inducible Factor 1 and Promotes Breast Cancer Progression.

Hypoxia induces thousands of mRNAs and miRNAs to mediate tumor malignancy. However, hypoxia-induced long noncoding RNA (lncRNA) transcriptome and their role in triple-negative breast cancer (TNBC) have not been defined. Here we identified hypoxia-induced lncRNA transcriptome in two human TNBC cell lines by whole transcriptome sequencing. AC093818.1 was one of 26 validated lncRNAs and abundantly expressed in TNBC in vitro and in vivo. 5'- and 3'-rapid amplification of cDNA ends assays revealed that the isoform 2 was a dominant AC093818.1 transcript in TNBC cells and thus referred to as lncIHAT (lncRNA induced by hypoxia and abundant in TNBC). Hypoxia-inducible factor 1 (HIF1) but not HIF2 bound to the hypoxia response element at the promoter of lncIHAT to activate its transcription in hypoxic TNBC cells. LncIHAT promoted TNBC cell survival in vitro and tumor growth and lung metastasis in mice. Mechanistically, lncIHAT was required for the expression of its proximal neighboring oncogenic genes PDK1 and ITGA6 in TNBC cells and tumors. Reexpression of PDK1 and ITGA6 rescued survival and growth of lncIHAT knockdown TNBC cells in vitro. Collectively, these findings uncovered lncIHAT as a new hypoxia-induced oncogenic cis-acting lncRNA in TNBC. IMPLICATIONS: This study systematically identified hypoxia-induced lncRNA transcriptome in TNBC and sheds light on multiple layers of regulatory mechanisms of gene expression under hypoxia.

Fabrication and characterization of structurally stable pH-responsive polymeric vesicles by polymerization-induced self-assembly.

Smart polymeric vesicles with both tertiary amine and epoxy functional groups were fabricated for the first time via a reversible addition-fragmentation chain transfer dispersion polymerization approach, using (2-(diisopropylamino)ethyl methacrylate (DIPEMA) and glycidyl methacrylate (GlyMA) in an ethanol-water mixture. Monitoring of the in situ polymerization revealed the low molecular weight distributions and the intermediate structures of spheres and worms, indicating an evolution in particle morphology. A phase diagram was constructed for reproducible fabrication of the vesicles, and copolymer composition was found to be more related to particle morphology. The vesicles exhibited superior structural stability for the cross-linking of the core through epoxydiamine chemistry, and intelligent pH responsibility due to the presence of the tertiary amine groups. The cross-linked vesicles showed good stability and reversibility during the swelling and shrinking cycles by switching the pH values, which endowed them with potential cell-like transmission functions. This research thus provides a method for producing structurally stable pH-responsive polymeric vesicles, and the reported vesicles are based on commercially available starting materials for possible industrial scale-up.

Romance of the three kingdoms in hypoxia: HIFs, epigenetic regulators, and chromatin reprogramming.

Hypoxia is a hallmark of cancer. To cope with hypoxic conditions, tumor cells alter their transcriptional profiles mainly through hypoxia-inducible factors (HIFs) and epigenetic reprogramming. Hypoxia, in part through HIF-dependent mechanisms, influences the expression or activity of epigenetic regulators to control epigenetic reprogramming, including DNA methylation and histone modifications, which regulate hypoxia-responsive gene expression in cells. Conversely, epigenetic regulators and chromatin architecture can modulate the expression, stability, or transcriptional activity of HIF. Understanding the complex networks between HIFs, epigenetic regulators, and chromatin reprogramming in response to hypoxia will provide insight into the fundamental mechanism of transcriptional adaptation to hypoxia, and may help identify novel targets for future therapies. In this review, we will discuss the comprehensive relationship between HIFs, epigenetic regulators, and chromatin reprogramming under hypoxic conditions.

HIF2-Induced Long Noncoding RNA RAB11B-AS1 Promotes Hypoxia-Mediated Angiogenesis and Breast Cancer Metastasis.

Hypoxia induces a vast array of long noncoding RNAs (lncRNA) in breast cancer cells, but their biological functions remain largely unknown. Here, we identified a hitherto uncharacterized hypoxia-induced lncRNA RAB11B-AS1 in breast cancer cells. RAB11B-AS1 is a natural lncRNA upregulated in human breast cancer and its expression is induced by hypoxia-inducible factor 2 (HIF2), but not HIF1, in response to hypoxia. RAB11B-AS1 enhanced the expression of angiogenic factors including VEGFA and ANGPTL4 in hypoxic breast cancer cells by increasing recruitment of RNA polymerase II. In line with increased angiogenic factors, conditioned media from RAB11B-AS1-overexpressing breast cancer cells promoted tube formation of human umbilical vein endothelial cells in vitro. Gain- and loss-of-function studies revealed that RAB11B-AS1 increased breast cancer cell migration and invasion in vitro and promoted tumor angiogenesis and breast cancer distant metastasis without affecting primary tumor growth in mice. Taken together, these findings uncover a fundamental mechanism of hypoxia-induced tumor angiogenesis and breast cancer metastasis. SIGNIFICANCE: This study reveals the molecular mechanism by which the lncRNA RAB11B-AS1 regulates hypoxia-induced angiogenesis and breast cancer metastasis, and provides new insights into the functional interaction between a lncRNA and tumor microenvironment. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/5/964/F1.large.jpg.

Mck1 defines a key S-phase checkpoint effector in response to various degrees of replication threats.

The S-phase checkpoint plays an essential role in regulation of the ribonucleotide reductase (RNR) activity to maintain the dNTP pools. How eukaryotic cells respond appropriately to different levels of replication threats remains elusive. Here, we have identified that a conserved GSK-3 kinase Mck1 cooperates with Dun1 in regulating this process. Deleting MCK1 sensitizes dun1Δ to hydroxyurea (HU) reminiscent of mec1Δ or rad53Δ. While Mck1 is downstream of Rad53, it does not participate in the post-translational regulation of RNR as Dun1 does. Mck1 phosphorylates and releases the Crt1 repressor from the promoters of DNA damage-inducible genes as RNR2-4 and HUG1. Hug1, an Rnr2 inhibitor normally silenced, is induced as a counterweight to excessive RNR. When cells suffer a more severe threat, Mck1 inhibits HUG1 transcription. Consistently, only a combined deletion of HUG1 and CRT1, confers a dramatic boost of dNTP levels and the survival of mck1Δdun1Δ or mec1Δ cells assaulted by a lethal dose of HU. These findings reveal the division-of-labor between Mck1 and Dun1 at the S-phase checkpoint pathway to fine-tune dNTP homeostasis.

The Helicase Activity of Hyperthermophilic Archaeal MCM is Enhanced at High Temperatures by Lysine Methylation.

Lysine methylation and methyltransferases are widespread in the third domain of life, archaea. Nevertheless, the effects of methylation on archaeal proteins wait to be defined. Here, we report that recombinant sisMCM, an archaeal homolog of Mcm2-7 eukaryotic replicative helicase, is methylated by aKMT4 in vitro. Mono-methylation of these lysine residues occurs coincidently in the endogenous sisMCM protein purified from the hyperthermophilic Sulfolobus islandicus cells as indicated by mass spectra. The helicase activity of mini-chromosome maintenance (MCM) is stimulated by methylation, particularly at temperatures over 70°C. The methylated MCM shows optimal DNA unwinding activity after heat-treatment between 76 and 82°C, which correlates well with the typical growth temperatures of hyperthermophilic Sulfolobus. After methylation, the half life of MCM helicase is dramatically extended at 80°C. The methylated sites are located on the accessible protein surface, which might modulate the intra- and inter- molecular interactions through changing the hydrophobicity and surface charge. Furthermore, the methylation-mimic mutants of MCM show heat resistance helicase activity comparable to the methylated MCM. These data provide the biochemical evidence that posttranslational modifications such as methylation may enhance kinetic stability of proteins under the elevated growth temperatures of hyperthermophilic archaea.

Balancing acts of SRI and an auto-inhibitory domain specify Set2 function at transcribed chromatin.

Set2-mediated H3K36 methylation ubiquitously functions in coding regions in all eukaryotes. It has been linked to the regulation of acetylation states, histone exchange, alternative splicing, DNA repair and recombination. Set2 is recruited to transcribed chromatin through its SRI domain's direct association with phosphorylated Pol II. However, regulatory mechanisms for histone modifying enzymes like Set2 that travel with elongating Pol II remain largely unknown beyond their initial recruitment events. Here, by fusing Set2 to RNA Pol II, we found that the SRI domain can also recognize linker DNA of chromatin, thereby controlling Set2 substrate specificity. We also discovered that an auto-inhibitory domain (AID) of Set2 primarily restricts Set2 activity to transcribed chromatin and fine-tunes several functions of SRI. Finally, we demonstrated that AID mutations caused hyperactive Set2 in vivo and displayed a synthetic interaction with the histone chaperone FACT. Our data suggest that Set2 is intrinsically regulated through multiple mechanisms and emphasize the importance of a precise temporal control of H3K36 methylation during the dynamic transcription elongation process.

Role for Protein Kinase A in the Neurospora Circadian Clock by Regulating White Collar-Independent frequency Transcription through Phosphorylation of RCM-1.

Rhythmic activation and repression of clock gene expression is essential for the eukaryotic circadian clock functions. In the Neurospora circadian oscillator, the transcription of the frequency (frq) gene is periodically activated by the White Collar (WC) complex and suppressed by the FRQ-FRH complex. We previously showed that there is WC-independent frq transcription and its repression is required for circadian gene expression. How WC-independent frq transcription is regulated is not known. We show here that elevated protein kinase A (PKA) activity results in WC-independent frq transcription and the loss of clock function. We identified RCM-1 as the protein partner of RCO-1 and an essential component of the clock through its role in suppressing WC-independent frq transcription. RCM-1 is a phosphoprotein and is a substrate of PKA in vivo and in vitro. Mutation of the PKA-dependent phosphorylation sites on RCM-1 results in WC-independent transcription of frq and impaired clock function. Furthermore, we showed that RCM-1 is associated with the chromatin at the frq locus, a process that is inhibited by PKA. Together, our results demonstrate that PKA regulates frq transcription by inhibiting RCM-1 activity through RCM-1 phosphorylation.

A prototypic lysine methyltransferase 4 from archaea with degenerate sequence specificity methylates chromatin proteins Sul7d and Cren7 in different patterns.

BACKGROUND: The origin of eukaryotic histone modification enzymes still remains obscure. RESULTS: Prototypic KMT4/Dot1 from Archaea targets chromatin proteins (Sul7d and Cren7) and shows increased activity on Sul7d, but not Cren7, in the presence of DNA. CONCLUSION: Promiscuous aKMT4 could be regulated by chromatin environment. SIGNIFICANCE: This study supports the prokaryotic origin model of eukaryotic histone methyltransferases and sheds light on chromatin dynamics in Archaea. Histone methylation is one of the major epigenetic modifications even in early diverging unicellular eukaryotes. We show that a widespread lysine methyltransferase from Archaea (aKMT4), bears striking structural and functional resemblance to the core of distantly related eukaryotic KMT4/Dot1. aKMT4 methylates a set of various proteins, including the chromatin proteins Sul7d and Cren7, and RNA exosome components. Csl4- and Rrp4-exosome complexes are methylated in different patterns. aKMT4 can self-methylate intramolecularly and compete with other proteins for the methyl group. Automethylation is inhibited by suitable substrates or DNA in a concentration-dependent manner. The automethylated enzyme shows relatively compromised activity. aKMT4-8A mutant with abrogated automethylation shows a more than 150% increase in methylation of substrates, suggesting a possible mechanism to regulate methyltransferase activity. More interestingly, methylation of Sul7d, but not Cren7, by aKMT4 is significantly enhanced by DNA. MS/MS and kinetic analysis further suggest that aKMT4 methylates Sul7d in the chromatin context. These data provide a clue to the possible regulation of aKMT4 activity by the local chromatin environment, albeit as a promiscuous enzyme required for extensive and variegated lysine methylation in Sulfolobus. This study supports the prokaryotic origin model of eukaryotic histone modification enzymes and sheds light on regulation of archaeal chromatin.

Characterization of electrospray ionization mass spectrometry for N-diisopropyloxyphosphoryl dipeptide methyl esters.

A systematic study of the fragmentation pattern of N-diisopropyloxyphosphoryl (DIPP) dipeptide methyl esters in an electrospray ionization (ESI) tandem mass spectrometry (MS/MS) was presented. A combination of accurate mass measurement and tandem mass spectrometry had been used to characterize the major fragment ions observed in the ESI mass spectrum. It was found that the alkali metal ions acted as a fixed charge site and expelled the DIPP group after transferring a proton to the amide nitrogen. For all the N-phosphoryl dipeptide methyl esters, under the activation of a metal ion, the rearrangement product ion at m/z 163 was observed and confirmed to be the sodium adduct of phosphoric acid mono-isopropyl esters (PAIE), via a specific five-membered penta-co-ordinated phosphorus intermediate. However, no rearrangement ion was observed when a beta-amino acid was at the N-terminal. This could be used to develop a novel method for differentiating isomeric compounds when either alpha- or beta-amino acid are at the N-terminus of peptides. From the [M+Na]+ ESI-MS/MS spectra of N-phosphoryl dipeptide methyl esters (DIPP Xaa1 Xaa2 OMe), the peaks corresponding to the [M+Na Xaa1 C3H6]+ were observed and explained. The [M+Na]+ ESI-MS/MS spectra of N-phosphoryl dipeptide methyl esters with Phe located in the C-terminal, such as DIPPValPheOMe, DIPPLeuPheOMe, DIPPIlePheOMe, DIPPAlaPheOMe and DIPPPhePheOMe, had characteristic fragmentation. Two unusual gas-phase intramolecular rearrangement mechanisms were first proposed for this fragmentation. These rearrangements were not observed in dipeptide methyl ester analogs which did not contain the DIPP at the N-terminal, suggesting that this moiety was critical for the rearrangement.

[Apoptosis of K562 cell induced by N-phosphoryl dipeptide methyl ester].

BACKGROUND & OBJECTIVE: Phosphorus plays a crucial role in metabolism. Some N-phosphoryl amino acids and N-phosphopeptides have important biological activities and medicinal value. The current study was designed to investigate the apoptosis of K562 cells induced by N-phosphoryl dipeptide methyl ester. METHOD: Cell growth inhibition of K562 cells induced by 15 kinds of N-phosphoryl dipeptide methyl esters was analyzed by using MTT assay. The nuclei were stained by Hoechst 33,258 and the morphologic changes were observed. DNA agarose gel electrophoresis, double-staining, and flow cytomery were used to detect early apoptosis of K562 cells. RESULT: (DIPP-L-Leu)2-L-Lys-OCH3 was the compound screened with MTT method that had better growth inhibiting activity with the IC50 of 22.66 mumol/L. Chromatin condensation and nuclear fragmentation were seen under fluorescence microscope in the cells treated with Hoechst 33,258. DNA agarose gel electrophoresis showed nuclear fragmentation (DNA ladder). Early apoptotic cells were also detected by flow cytometry. CONCLUSION: These results suggest that(DIPP-L-Leu)2-L-Lys-OCH3 could induce the apoptosis of K562 cells.