Enhanced anti-tumor efficacy with multi-transgene armed mesenchymal stem cells for treating peritoneal carcinomatosis

BACKGROUND

Mesenchymal stem cells (MSCs) have garnered significant interest for their tumor-tropic property, making them potential therapeutic delivery vehicles for cancer treatment. We have previously shown the significant anti-tumour activity in mice preclinical models and companion animals with naturally occurring cancers using non-virally engineered MSCs with a therapeutic transgene encoding cytosine deaminase and uracil phosphoribosyl transferase (CDUPRT) and green fluorescent protein (GFP). Clinical studies have shown improved response rate with combinatorial treatment of 5-fluorouracil and Interferon-beta (IFNb) in peritoneal carcinomatosis (PC). However, high systemic toxicities have limited the clinical use of such a regime.

METHODS

In this study, we evaluated the feasibility of intraperitoneal administration of non-virally engineered MSCs to co-deliver CDUPRT/5-Flucytosine prodrug system and IFNb to potentially enhance the cGAS-STING signalling axis. Here, MSCs were engineered to express CDUPRT or CDUPRT-IFNb. Expression of CDUPRT and IFNb was confirmed by flow cytometry and ELISA, respectively. The anti-cancer efficacy of the engineered MSCs was evaluated in both in vitro and in vivo model. ES2, HT-29 and Colo-205 were cocultured with engineered MSCs at various ratio. The cell viability with or without 5-flucytosine was measured with MTS assay. To further compare the anti-cancer efficacy of the engineered MSCs, peritoneal carcinomatosis mouse model was established by intraperitoneal injection of luciferase expressing ES2 stable cells. The tumour burden was measured through bioluminescence tracking.

RESULTS

Firstly, there was no changes in phenotypes of MSCs despite high expression of the transgene encoding CDUPRT and IFNb (CDUPRT-IFNb). Transwell migration assays and in-vivo tracking suggested the co-expression of multiple transgenes did not impact migratory capability of the MSCs. The superiority of CDUPRT-IFNb over CDUPRT expressing MSCs was demonstrated in ES2, HT-29 and Colo-205 in-vitro. Similar observations were observed in an intraperitoneal ES2 ovarian cancer xenograft model. The growth of tumor mass was inhibited by ~ 90% and 46% in the mice treated with MSCs expressing CDUPRT-IFNb or CDUPRT, respectively.

CONCLUSIONS

Taken together, these results established the effectiveness of MSCs co-expressing CDUPRT and IFNb in controlling and targeting PC growth. This study lay the foundation for the development of clinical trial using multigene-armed MSCs for PC.

Pushing the Frontiers of Cancer Research: Highlights from the Frontiers in Cancer Science Conference 2023

The 15th annual Frontiers in Cancer Science (FCS) conference gathered scientific experts who shared the latest research converging upon several themes of cancer biology. These themes included the dysregulation of metabolism, cell death, and other signaling processes in cancer cells; using patient "omics" datasets and single-cell and spatial approaches to investigate heterogeneity, understand therapy resistance, and identify targets; innovative strategies for inhibiting tumors, including rational drug combinations and improved drug delivery mechanisms; and advances in models that can facilitate screening for cancer vulnerabilities and drug testing. We hope the insights from this meeting will stimulate further progress in the field.

Biology of Cancer-Testis Antigens and Their Therapeutic Implications in Cancer

Tumour-specific antigens have been an area of interest in cancer therapy since their discovery in the middle of the 20th century. In the era of immune-based cancer therapeutics, redirecting our immune cells to target these tumour-specific antigens has become even more relevant. Cancer-testis antigens (CTAs) are a class of antigens with an expression specific to the testis and cancer cells. CTAs have also been demonstrated to be expressed in a wide variety of cancers. Due to their frequency and specificity of expression in a multitude of cancers, CTAs have been particularly attractive as cancer-specific therapeutic targets. There is now a rapid expansion of CTAs being identified and many studies have been conducted to correlate CTA expression with cancer and therapy-resistant phenotypes. Furthermore, there is an increasing number of clinical trials involving using some of these CTAs as molecular targets in pharmacological and immune-targeted therapeutics for various cancers. This review will summarise the current knowledge of the biology of known CTAs in tumorigenesis and the regulation of CTA genes. CTAs as molecular targets and the therapeutic implications of these CTA-targeted anticancer strategies will also be discussed.

MLL5 is involved in retinal photoreceptor maturation through facilitating CRX-mediated photoreceptor gene transactivation

Histone methylation, particularly at the H3K4 position, is thought to contribute to the specification of photoreceptor cell fate; however, the mechanisms linking histone methylation with transcription factor transactivation and photoreceptor gene expression have not yet been determined. Here, we demonstrate that MLL5 is abundantly expressed in the mouse retina. Mll5 deficiency impaired electroretinogram responses, alongside attenuated expression of a number of retina genes. Mechanistic studies revealed that MLL5 interacts with the retina-specific transcription factor, CRX, contributing to its binding to photoreceptor-specific gene promoters. Moreover, depletion of MLL5 impairs H3K4 methylation and H3K79 methylation, which subsequently compromises CRX-CBP assembly and H3 acetylation on photoreceptor promoters. Our data support a scenario in which recognition of H3K4 methylation by MLL5 is required for photoreceptor-specific gene transcription through maintaining a permissive chromatin state and proper CRX-CBP recruitment at promoter sites.

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MLL5 is essential for the expression of critical photoreceptor genes

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MLL5 depletion reduces H3K4/K79 methylation at photoreceptor gene promoters

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MLL5 interacts with CRX via its CD4 domain

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Recognition of H3K4me2/3 by MLL5 is a prerequisite for CRX recruitment to chromatin

Redox-sensitive cyclophilin A elicits chemoresistance through realigning cellular oxidative status in colorectal cancer

Cancer cells utilize rapidly elevated cellular antioxidant programs to accommodate chemotherapy-induced oxidative stress; however, the underlying mechanism remains largely unexplored. Here we screen redox-sensitive effectors as potential therapeutic targets for colorectal cancer (CRC) treatment and find that cyclophilin A (CypA) is a compelling candidate. Our results show that CypA forms an intramolecular disulfide bond between Cys115 and Cys161 upon oxidative stress and the oxidized cysteines in CypA are recycled to a reduced state by peroxiredoxin-2 (PRDX2). Furthermore, CypA reduces cellular reactive oxygen species levels and increases CRC cell survival under insults of H₂O₂ and chemotherapeutics through a CypA-PRDX2-mediated antioxidant apparatus. Notably, CypA is upregulated in chemoresistant CRC samples, which predicts poor prognosis. Moreover, targeting CypA by cyclosporine A exhibits promising efficacy against chemoresistant CRC when combined with chemotherapeutics. Collectively, our findings highlight CypA as a component of cellular noncanonical antioxidant defense and as a potential druggable therapeutic target to ameliorate CRC chemoresistance.

Fatty acid oxidation is a druggable gateway regulating cellular plasticity for driving metastasis in breast cancer

Cell state transitions control the functional behavior of cancer cells. Epithelial-to-mesenchymal transition (EMT) confers cancer stem cell-like properties, enhanced tumorigenicity and drug resistance to tumor cells, while mesenchymal-epithelial transition (MET) reverses these phenotypes. Using high-throughput chemical library screens, retinoids are found to be potent promoters of MET that inhibit tumorigenicity in basal-like breast cancer. Cell state transitions are defined by reprogramming of lipid metabolism. Retinoids bind cognate nuclear receptors, which target lipid metabolism genes, thereby redirecting fatty acids for β-oxidation in the mesenchymal cell state towards lipid storage in the epithelial cell state. Disruptions of key metabolic enzymes mediating this flux inhibit MET. Conversely, perturbations to fatty acid oxidation (FAO) rechannel fatty acid flux and promote a more epithelial cell phenotype, blocking EMT-driven breast cancer metastasis in animal models. FAO impinges on the epigenetic control of EMT through acetyl-CoA-dependent regulation of histone acetylation on EMT genes, thus determining cell states.

GAGE mediates radio resistance in cervical cancers via the regulation of chromatin accessibility

Radiotherapy (RT) resistance is a major cause of treatment failure in cancers that use definitive RT as their primary treatment modality. This study identifies the cancer/testis (CT) antigen G antigen (GAGE) as a mediator of radio resistance in cervical cancers. Elevated GAGE expression positively associates with de novo RT resistance in clinical samples. GAGE, specifically the GAGE12 protein variant, confers RT resistance through synemin-dependent chromatin localization, promoting the association of histone deacetylase 1/2 (HDAC1/2) to its inhibitor actin. This cumulates to elevated histone 3 lysine 56 acetylation (H3K56Ac) levels, increased chromatin accessibility, and improved DNA repair efficiency. Molecular or pharmacological disruption of the GAGE-associated complex restores radiosensitivity. Molecularly, this study demonstrates the role of GAGE in the regulation of chromatin dynamics. Clinically, this study puts forward the utility of GAGE as a pre-screening biomarker to identify poor responders at initial diagnosis and the therapeutic potential of agents that target GAGE and its associated complex in combination with radiotherapy to improve outcomes.

Automated synthesis of prexasertib and derivatives enabled by continuous-flow solid-phase synthesis

Recent advances in end-to-end continuous-flow synthesis are rapidly expanding the capabilities of automated customized syntheses of small-molecule pharmacophores, resulting in considerable industrial and societal impacts; however, many hurdles persist that limit the number of sequential steps that can be achieved in such systems, including solvent and reagent incompatibility between individual steps, cumulated by-product formation, risk of clogging and mismatch of timescales between steps in a processing chain. To address these limitations, herein we report a strategy that merges solid-phase synthesis and continuous-flow operation, enabling push-button automated multistep syntheses of active pharmaceutical ingredients. We demonstrate our platform with a six-step synthesis of prexasertib in 65% isolated yield after 32 h of continuous execution. As there are no interactions between individual synthetic steps in the sequence, the established chemical recipe file was directly adopted or slightly modified for the synthesis of twenty-three prexasertib derivatives, enabling both automated early and late-stage diversification.

Cysteine Deprivation Targets Ovarian Clear Cell Carcinoma Via Oxidative Stress and Iron-Sulfur Cluster Biogenesis Deficit

Aims: Current treatment options for ovarian clear cell carcinoma (OCCC) are limited to combination of platinum-based and other cytotoxic agents to which patients respond poorly due to intrinsic chemoresistance. There is therefore an urgent need to develop alternative therapeutic strategies for OCCC. Results: Cysteine deprivation suppresses OCCC growth in vitro and in vivo with no apparent toxicity. Modes of cell death induced by cysteine deprivation in OCCC are determined by their innate metabolic profiles. Cysteine-deprived glycolytic OCCC is abolished primarily by oxidative stress-dependent necrosis and ferroptosis, which can otherwise be prevented by pretreatment with antioxidative agents. Meanwhile, OCCC that relies on mitochondria respiration for its bioenergetics is suppressed through apoptosis, which can otherwise be averted by pretreatment with cysteine precursor alone, but not with antioxidative agents. Cysteine deprivation induces apoptosis in respiring OCCC by limiting iron-sulfur (Fe-S) cluster synthesis in the mitochondria, without which electron transport chain may be disrupted. Respiring OCCC responds to Fe-S cluster deficit by increasing iron influx into the mitochondria, which leads to iron overload, mitochondria damage, and eventual cell death. Innovation/Conclusion: This study demonstrates the importance of cysteine availability in OCCC that is for its antioxidative property and its less appreciated role in mitochondria respiration. Regardless of OCCC metabolic profiles, cysteine deprivation abolishes both glycolytic and respiring OCCC growth in vitro and in vivo. Conclusion: This study highlights the therapeutic potential of cysteine deprivation for OCCC.

Biological Effects of Morpholin-4-Ium 4 Methoxyphenyl (Morpholino) Phosphinodithioate and Other Phosphorothioate-Based Hydrogen Sulfide Donors

Significance: Hydrogen sulfide (H₂S) is regarded as the third gasotransmitter along with nitric oxide and carbon monoxide. Extensive studies have demonstrated a variety of biological roles for H₂S in neurophysiology, cardiovascular disease, endocrine regulation, and other physiological and pathological processes. Recent Advances: Novel H₂S donors have proved useful in understanding the biological functions of H₂S, with morpholin-4-ium 4 methoxyphenyl (morpholino) phosphinodithioate (GYY4137) being one of the most common pharmacological tools used. One advantage of GYY4137 over sulfide salts is its ability to release H₂S in a slow and sustained manner akin to endogenous H₂S production, rather than the delivery of H₂S as a single concentrated burst. Critical Issues: Here, we summarize recent progress made in the characterization of the biological activities and pharmacological effects of GYY4137 in a range of in vitro and in vivo systems. Recent developments in the structural modification of GYY4137 to generate new compounds and their biological effects are also discussed. Future Directions: Slow-releasing H₂S donor, GYY4137, and other phosphorothioate-based H₂S donors are potent tools to study the biological functions of H₂S. Despite recent progress, more work needs to be performed on these new compounds to unravel the mechanisms behind H₂S release and pace of its discharge, as well as to define the effects of by-products of donors after H₂S liberation. This will not only lead to better in-depth understanding of the biological effects of H₂S but will also shed light on the future development of a new class of therapeutic agents with potential to treat a wide range of human diseases.

Intracellular Hyper-Acidification Potentiated by Hydrogen Sulfide Mediates Invasive and Therapy Resistant Cancer Cell Death

Slow and continuous release of H₂S by GYY4137 has previously been demonstrated to kill cancer cells by increasing glycolysis and impairing anion exchanger and sodium/proton exchanger activity. This action is specific for cancer cells. The resulting lactate overproduction and defective pH homeostasis bring about intracellular acidification-induced cancer cell death. The present study investigated the potency of H₂S released by GYY4137 against invasive and radio- as well as chemo-resistant cancers, known to be glycolytically active. We characterized and utilized cancer cell line pairs of various organ origins, based on their aggressive behaviors, and assessed their response to GYY4137. We compared glycolytic activity, via lactate production, and intracellular pH of each cancer cell line pair after exposure to H₂S. Invasive and therapy resistant cancers, collectively termed aggressive cancers, are receptive to H₂S-mediated cytotoxicity, albeit at a higher concentration of GYY4137 donor. While lactate production was enhanced, intracellular pH of aggressive cancers was only modestly decreased. Inherently, the magnitude of intracellular pH decrease is a key determinant for cancer cell sensitivity to H₂S. We demonstrated the utility of coupling GYY4137 with either simvastatin, known to inhibit monocarboxylate transporter 4 (MCT4), or metformin, to further boost glycolysis, in bringing about cell death for aggressive cancers. Simvastatin inhibiting lactate extrusion thence contained excess lactate induced by GYY4137 within intracellular compartment. In contrast, the combined exposure to both GYY4137 and metformin overwhelms cancer cells with lactate over-production exceeding its expulsion rate. Together, GYY4137 and simvastatin or metformin synergize to induce intracellular hyper-acidification-mediated cancer cell death.

MLL5 (KMT2E): structure, function, and clinical relevance

The mixed lineage leukemia (MLL) family of genes, also known as the lysine N-methyltransferase 2 (KMT2) family, are homologous to the evolutionarily conserved trithorax group that plays critical roles in the regulation of homeotic gene (HOX) expression and embryonic development. MLL5, assigned as KMT2E on the basis of its SET domain homology, was initially categorized under MLL (KMT2) family together with other six SET methyltransferase domain proteins (KMT2A-2D and 2F-2G). However, emerging evidence suggests that MLL5 is distinct from the other MLL (KMT2) family members, and the protein it encodes appears to lack intrinsic histone methyltransferase (HMT) activity towards histone substrates. MLL5 has been reported to play key roles in diverse biological processes, including cell cycle progression, genomic stability maintenance, adult hematopoiesis, and spermatogenesis. Recent studies of MLL5 variants and isoforms and putative MLL5 homologs in other species have enriched our understanding of the role of MLL5 in gene expression regulation, although the mechanism of action and physiological function of MLL5 remains poorly understood. In this review, we summarize recent research characterizing the structural features and biological roles of MLL5, and we highlight the potential implications of MLL5 dysfunction in human disease.

MLL5 maintains spindle bipolarity by preventing aberrant cytosolic aggregation of PLK1

Faithful chromosome segregation with bipolar spindle formation is critical for the maintenance of genomic stability. Perturbation of this process often leads to severe mitotic failure, contributing to tumorigenesis. MLL5 has been demonstrated to play vital roles in cell cycle progression and the maintenance of genomic stability. Here, we identify a novel interaction between MLL5 and PLK1 in the cytosol that is crucial for sustaining spindle bipolarity during mitosis. Knockdown of MLL5 caused aberrant PLK1 aggregation that led to acentrosomal microtubule-organizing center (aMTOC) formation and subsequent spindle multipolarity. Further molecular studies revealed that the polo-box domain (PBD) of PLK1 interacted with a binding motif on MLL5 (Thr887-Ser888-Thr889), and this interaction was essential for spindle bipolarity. Overexpression of wild-type MLL5 was able to rescue PLK1 mislocalization and aMTOC formation in MLL5-KD cells, whereas MLL5 mutants incapable of interacting with the PBD failed to do so. We thus propose that MLL5 preserves spindle bipolarity through maintaining cytosolic PLK1 in a nonaggregated form.

Highly selective and sensitive near-infrared-fluorescent probes for the detection of cellular hydrogen sulfide and the imaging of H2S in mice

Herein, we report the development of two fluorescent probes for the highly selective and sensitive detection of H2S. The probes take advantage of a Cu(II)-cyclen complex, which acts as a reaction center for H2S and as a quencher of BODIPY (boron-dipyrromethene)-based fluorophores with emissions at 765 and 680 nm, respectively. These non-fluorescent probes could only be turned on by the addition of H2 S, and not by other potentially interfering biomolecules, including reactive oxygen species, cysteine, and glutathione. In a chemical system, both probes detected H2S with a detection limit of 80 nM. The probes were successfully used for the endogenous detection of H2S in HEK 293 cells, for measuring the H2S-release activity of dietary organosulfides in MCF-7 cells, and for the in vivo imaging of H2S in mice.

Targeted silencing of MLL5β inhibits tumor growth and promotes gamma-irradiation sensitization in HPV16/18-associated cervical cancers

We previously identified a novel MLL5 isoform, MLL5β, which was essential for E6 and E7 transcriptional activation in HPV16/18-associated cervical cancers. In this report, we investigated the potential of RNAi-mediated silencing of MLL5β through the use of MLL5β-siRNA as a novel therapeutic strategy for HPV16/18-positive cervical cancer. We observed concurrent downregulation of E6 and E7 after MLL5β silencing, leading to growth inhibition via the activation of apoptosis and senescence in the HeLa cell model. This corresponded with the enhanced antitumor effects of MLL5β-siRNA compared with E6- or E7-siRNA single treatments. Significant reduction in tumor size after MLLβ-siRNA treatment in the HeLa xenograft tumor model further emphasized the importance of MLL5β in HPV16/18-associated tumor growth and the potential of RNAi therapeutics that target MLL5β. We also identified MLL5β as a modulator of gamma-irradiation (IR) sensitization properties of cisplatin. We observed that while MLL5β silencing alone was enough to evoke cisplatin-like IR sensitization in tumor cells in vitro, overexpression of MLL5β inhibited the ability of cisplatin to sensitize HeLa cells to IR-induced cytotoxicity. MLL5β-siRNA-IR cotreatment was also observed to enhance tumor growth inhibition in vivo. Taken together, our findings highlight the potential of targeted silencing of MLL5β via the use of MLL5β-siRNA as a novel therapeutic strategy and propose that MLL5β-siRNA could be a viable alternative for cisplatin in the current cisplatin-based chemotherapeutics for HPV16/18-associated cervical cancers.

Hydrogen sulfide donors in research and drug development

This review summarized most of the H₂S donors such as inorganic compounds, natural products, anethole trithione derivatives and synthetic compounds used in research and drug development. These special bioactivities provided us some effective strategies for antiphlogosis, cancer therapy, cardiovascular protection and so on.

Nickel(II) dithiocarbamate complexes containing sulforhodamine B as fluorescent probes for selective detection of nitrogen dioxide

We synthesized complexes of Ni(II) with dithiocarbamate ligands derived from the ortho and para isomers of sulforhodamine B fluorophores and demonstrated they are highly selective in reactions with nitrogen dioxide (NO2). Compared with the para isomer, the ortho isomer showed a much greater fluorescence increase upon reaction with NO2, which led to oxidation and decomplexation of the dithiocarbamate ligand from Ni(II). We applied this probe for visual detection of 1 ppm NO2 in the gas phase and fluorescence imaging of NO2 in macrophage cells treated with a nitrogen dioxide donor.

The Chemistry and Biology of Nakiterpiosin - C-nor-D-Homosteroids

Isolated from the sponge Terpios hoshinota that causes coral black disease, nakiterpiosin was the first C-nor-D-homosteroid discovered from a marine source. We provide in this account an overview of the chemistry and biology of this natural product. We also include a short history of the synthesis of C-nor-D-homosteroids and the results of some unpublished biological studies of nakiterpiosin.

MLL5 maintains genomic integrity by regulating the stability of the chromosomal passenger complex through a functional interaction with Borealin

Mixed lineage leukemia 5 (MLL5) is a versatile nuclear protein associated with many cellular events. We have shown previously that phosphorylation of MLL5 by Cdk1 is required for mitotic entry. In this paper, the function of MLL5 in mitotic regulation is further explored. SiRNA-mediated downregulation of MLL5 caused improper chromosome alignment at metaphase and resulted in failure of DNA segregation and cytokinesis. Mechanistic studies revealed that the chromosomal passenger complex (CPC), which plays a key role in chromosomal bi-orientation, was delocalized from the inner centromere region because of proteasome-mediated degradation in MLL5-depleted cells. Biochemical analyses further demonstrated that the central domain of MLL5 interacted with the C-terminus of Borealin, and the interaction is essential to maintain the stability of Borealin. Moreover, the mitotic defects in MLL5-depleted cells were rescued by overexpression of FLAG-MLL5, but not by a FLAG-MLL5 mutant that did not contain the central domain. Collectively, our results suggest that MLL5 functionally interacts with Borealin, facilitates the expression of CPC, and hence contributes to mitotic fidelity and genomic integrity.

HURP regulates chromosome congression by modulating kinesin Kif18A function

Chromosome biorientation and congression during mitosis require precise control of microtubule dynamics [1-4]. The dynamics of kinetochore microtubules (K-MTs) are regulated by a variety of microtubule-associated proteins (MAPs) [4-9]. Recently, a MAP known as HURP (hepatoma upregulated protein) was identified [10-12]. During mitosis, Ran-guanosine 5'-triphosphate (RanGTP) releases HURP from the importin β inhibitory complex and allows it to localize to the kinetochore fiber (k-fiber) [12, 13]. HURP stabilizes k-fibers and promotes chromosome congression [12, 14, 15]. However, the molecular mechanism underlying the role of HURP in regulating chromosome congression remains elusive. Here, we show that overexpression of the N-terminal microtubule binding domain (1-278 aa, HURP(278)) of HURP induces a series of mitotic defects that mimic the effects of Kif18A depletion. In addition, coimmunoprecipitation and bimolecular fluorescence complementation assays identify Kif18A as a novel interaction partner of HURP. Furthermore, quantitative results from live-cell imaging analyses illustrate that HURP regulates Kif18A localization and dynamics at the plus end of K-MTs. Lastly, misaligned chromosomes in HURP(278)-overexpressing cells can be partially rescued by the overexpression of Kif18A. Our results demonstrate in part the regulatory mechanism for Kif18A during chromosome congression and provide new insights into the mechanism of chromosome movement at the metaphase plate.

A novel MLL5 isoform that is essential to activate E6 and E7 transcription in HPV16/18-associated cervical cancers

Human papillomavirus (HPV) is the primary cause of human cervical cancer. The viral proteins E6 and E7 are essential to transform noncancerous epithelial cells into cancerous carcinomas by targeting key tumor suppressors p53 and retinoblastoma (Rb) proteins, respectively, but the cellular factors involved in E6 and E7 transcription themselves are incompletely understood. In this study, we defined a novel isoform of the mixed lineage leukemia 5 gene (MLL5β) as a specific and critical regulator of E6 and E7 transcription in cervical carcinoma cells. MLL5β is present in HPV16/18-positive cells including human primary cervical carcinoma specimens. Interaction of MLL5β with the AP-1-binding site at the distal region of the HPV18 long control region led to activation of E6/E7 transcription. Conversely, RNA interference-mediated knockdown of MLL5β downregulated both E6 and E7 expression. MLL5β downregulation was sufficient to restore p53 protein levels and reduce Rb phosphorylation, thereby reactivating apoptosis and cell-cycle checkpoints. By defining this novel MLL5β isoform and its specific critical role in activating E6/E7 gene transcription in HPV16/18-induced cervical cancers, our work highlights the potential of MLL5β as a biomarker and new therapeutic target in primary HPV-induced cervical cancers.

The slow-releasing hydrogen sulfide donor, GYY4137, exhibits novel anti-cancer effects in vitro and in vivo

The slow-releasing hydrogen sulfide (H₂S) donor, GYY4137, caused concentration-dependent killing of seven different human cancer cell lines (HeLa, HCT-116, Hep G2, HL-60, MCF-7, MV4-11 and U2OS) but did not affect survival of normal human lung fibroblasts (IMR90, WI-38) as determined by trypan blue exclusion. Sodium hydrosulfide (NaHS) was less potent and not active in all cell lines. A structural analogue of GYY4137 (ZYJ1122) lacking sulfur and thence not able to release H₂S was inactive. Similar results were obtained using a clonogenic assay. Incubation of GYY4137 (400 µM) in culture medium led to the generation of low (<20 µM) concentrations of H₂S sustained over 7 days. In contrast, incubation of NaHS (400 µM) in the same way led to much higher (up to 400 µM) concentrations of H₂S which persisted for only 1 hour. Mechanistic studies revealed that GYY4137 (400 µM) incubated for 5 days with MCF-7 but not IMR90 cells caused the generation of cleaved PARP and cleaved caspase 9, indicative of a pro-apoptotic effect. GYY4137 (but not ZYJ1122) also caused partial G₂/M arrest of these cells. Mice xenograft studies using HL-60 and MV4-11 cells showed that GYY4137 (100–300 mg/kg/day for 14 days) significantly reduced tumor growth. We conclude that GYY4137 exhibits anti-cancer activity by releasing H₂S over a period of days. We also propose that a combination of apoptosis and cell cycle arrest contributes to this effect and that H₂S donors should be investigated further as potential anti-cancer agents.

Regulation of heart function by endogenous gaseous mediators-crosstalk between nitric oxide and hydrogen sulfide

Both nitric oxide (NO) and hydrogen sulfide (H(2)S) are two important gaseous mediators regulating heart function. The present study examined the interaction between these two biological gases and its role in the heart. We found that l-arginine, a substrate of NO synthase, decreased the amplitudes of myocyte contraction and electrically induced calcium transients. Sodium hydrogen sulfide (an H(2)S donor), which alone had minor effect, reversed the negative inotropic effects of l-arginine. The effect of l-arginine + sodium hydrogen sulfide was abolished by three thiols (l-cysteine, N-acetyl-cysteine, and glutathione), suggesting that the effect of H(2)S + NO is thiol sensitive. The stimulatory effect on heart contractility was also induced by GYY4137, a slow-releasing H(2)S donor, when used together with sodium nitroprusside, an NO-releasing donor. More importantly, enzymatic generation of H(2)S from recombinant cystathionine-γ-lyase protein also interacted with endogenous NO generated from l-arginine to stimulate heart contraction. In summary, our data suggest that endogenous NO may interact with H(2)S to produce a new biological mediator that produces positive inotropic effect. The crosstalk between H(2)S and NO also suggests an intriguing potential for the endogenous formation of a thiol-sensitive molecule, which may be of physiological significance in the heart.

Phosphorylation of mixed lineage leukemia 5 by CDC2 affects its cellular distribution and is required for mitotic entry

The human mixed lineage leukemia-5 (MLL5) gene is frequently deleted in myeloid malignancies. Emerging evidence suggests that MLL5 has important functions in adult hematopoiesis and the chromatin regulatory network, and it participates in regulating the cell cycle machinery. Here, we demonstrate that MLL5 is tightly regulated through phosphorylation on its central domain at the G(2)/M phase of the cell cycle. Upon entry into mitosis, the phosphorylated MLL5 delocalizes from condensed chromosomes, whereas after mitotic exit, MLL5 becomes dephosphorylated and re-associates with the relaxed chromatin. We further identify that the mitotic phosphorylation and subcellular localization of MLL5 are dependent on Cdc2 kinase activity, and Thr-912 is the Cdc2-targeting site. Overexpression of the Cdc2-targeting MLL5 fragment obstructs mitotic entry by competitive inhibition of the phosphorylation of endogenous MLL5. In addition, G(2) phase arrest caused by depletion of endogenous MLL5 can be compensated by exogenously overexpressed full-length MLL5 but not the phosphodomain deletion or MLL5-T912A mutant. Our data provide evidence that MLL5 is a novel cellular target of Cdc2, and the phosphorylation of MLL5 may have an indispensable role in the mitotic progression.

Structural basis for the inhibition mechanism of human cystathionine gamma-lyase, an enzyme responsible for the production of H(2)S

Impairment of the formation or action of hydrogen sulfide (H(2)S), an endogenous gasotransmitter, is associated with various diseases, such as hypertension, diabetes mellitus, septic and hemorrhagic shock, and pancreatitis. Cystathionine beta-synthase and cystathionine gamma-lyase (CSE) are two pyridoxal-5'-phosphate (PLP)-dependent enzymes largely responsible for the production of H(2)S in mammals. Inhibition of CSE by DL-propargylglycine (PAG) has been shown to alleviate disease symptoms. Here we report crystal structures of human CSE (hCSE), in apo form, and in complex with PLP and PLP.PAG. Structural characterization, combined with biophysical and biochemical studies, provides new insights into the inhibition mechanism of hCSE-mediated production of H(2)S. Transition from the open form of apo-hCSE to the closed PLP-bound form reveals large conformational changes hitherto not reported. In addition, PAG binds hCSE via a unique binding mode, not observed in PAG-enzyme complexes previously. The interaction of PAG-hCSE was not predicted based on existing information from known PAG complexes. The structure of hCSE.PLP.PAG complex highlights the particular importance of Tyr(114) in hCSE and the mechanism of PAG-dependent inhibition of hCSE. These results provide significant insights, which will facilitate the structure-based design of novel inhibitors of hCSE to aid in the development of therapies for diseases involving disorders of sulfur metabolism.

RNA interference against mixed lineage leukemia 5 resulted in cell cycle arrest

Mixed lineage leukemia 5 (MLL5) encodes a mammalian trithorax group (TrxG) protein located within chromosome band 7q22, which is a frequently deleted region found in acute myeloid malignancies. Trithorax and polycomb (PcG) group proteins are evolutionarily conserved transcriptional regulators that maintain the expression of Homeobox (HOX) genes at the epigenetic level during development. Recently, the emerging roles of TrxG and PcG group proteins in cell cycle regulation have begun to be elucidated. In this study, we demonstrated that the mammalian trxG protein MLL5 is involved in multiple cell cycle regulation. Knockdown of MLL5 by small interfering RNA resulted in the retarded cell growth and attenuated intake of BrdU in multiple tumor and normal diploid cells. The cell cycle arrest induced by knockdown of MLL5 took place at both the G1 and G2/M phases. This growth-inhibitory effect and dual-phase arrest were also found in p53-knockout cell lines, suggesting that the transactivation activity of p53 was dispensable for the MLL5-knockdown-mediated cell cycle arrest. In addition, up-regulation of cyclin-dependent kinase inhibitor p21 and de-phosphorylation of retinoblastoma protein were observed in all cell lines tested regardless of their p53 status. Taken together, our data suggest that silencing of MLL5 leads to up-regulation of p21 and dephosphorylation of pRb, which at least partially contributes to the G1 phase and G2/M phase arrest. These findings provide evidence that MLL5 might be an important cell cycle regulator, participating in cell cycle regulatory network machinery at multiple cell cycle stages.

MLL 5 protein forms intranuclear foci, and overexpression inhibits cell cycle progression

MLL5 is a mammalian trithorax group (trx-G) gene identified within chromosome band 7q22, a frequently deleted element found in cytogenetic aberrations of acute myeloid malignancies. MLL5 cDNA was linked with the FLAG and V5 tags at the N and C terminus, respectively, and transfected into 293T cells. Immunofluoresence staining of the expressed tagged MLL5 protein showed localization to the nucleus and exclusion from nucleoli, and no surface staining was detected. Both ectopically introduced and endogenous MLL5 protein displayed a speckled nuclear distribution. By using a series of MLL5-truncated mutants fused with enhanced GFP, a domain (residues 945-1,156) required for foci accumulation was identified, and regions containing functional nuclear localization signals were mapped. Ectopic overexpression of GFP-MLL5 induced cell cycle arrest in G(1) phase. This inhibition of cell cycle progression was indicated by delayed progression into nocodazole-induced mitotic arrest and was confirmed by a lack of BrdUrd incorporation. These findings suggest that MLL5 forms intranuclear protein complexes that may play an important role in chromatin remodeling and cellular growth suppression.

Uniquely conformed peptide-containing beta 2-microglobulin-free heavy chains of HLA-B2705 on the cell surface

The human class I MHC molecules are known to generally exist on the cell surface either as peptide-containing complexes of H chain (alpha-chain) and beta(2)-microglobulin (beta(2)m) or as beta(2)m-free H chains incapable of binding peptides. In this study, a uniquely conformed peptide-containing beta(2)m-free HLA-B2705 H chain has been isolated using the recently described highly efficient perfusion-affinity chromatography system for purification of class I MHC protein molecules. This form recognized by the mAb MARB4 is very closely associated with the remainder of the peptide containing HLA-B2705/beta(2)m complex reactive with mAb ME1 and is present to approximately 1-10% of mAb ME1 reactive forms on the cell surface. Also, HLA-B2705 purified using the mAb ME1 affinity column includes this unique mAb MARB4-reactive, unusually stable peptide-containing beta(2)m-free form. A peptide nonamer GRWRGWYTY was isolated and identified from this beta(2)m-free HLA-B2705 H chain and was used to assemble the mAb MARB4 reactive form efficiently on the surface of cells expressing HLA-B2705. The discovery of this form opens new avenues for further investigation of the role of HLA-B27 in spondyloarthropathies.

Delineating the site of interaction on the pIII protein of filamentous bacteriophage fd with the F-pilus of Escherichia coli

The minor coat protein pIII at one end of the filamentous bacteriophage fd, mediates the infection of Escherichia coli cells displaying an F-pilus. pIII has three domains (D1, D2 and D3), terminating with a short hydrophobic segment at the C-terminal end. Domain D2 binds to the tip of F-pilus, which is followed by retraction of the pilus and penetration of the E. coli cell membrane, the latter involving an interaction between domain D1 and the TolA protein in the membrane. Surface residues on the D2 domain of pIII were replaced systematically with alanine. Mutant virions were screened for D2-pilus interaction in vivo by measuring the release of infectious virions from E. coli F(+) cells infected with the mutants. A competitive ELISA was developed to measure in vitro the ability of mutant phages to bind to purified pili. This allowed the identification of amino acid residues involved in binding to F and to EDP208 pili. These residues were found to cluster on the outer rim of the 3D structure of the D2 domain, unexpectedly identifying this as the F-pilus binding region on the pIII protein.

[A nasopharyngeal carcinoma negatively related EST on 7q32]

To isolate and clone the tumor suppressor gene on chromosomal region 7q32 that corelated with the occurrence of human NPC, we detected the genotype of polymorphic microsatellite markers on 7q32 in 24 nasopharyngeal carcinoma biopsies and matched normal lymphocyte DNA. LOH was found in 30% biopsies. Using differential RT-PCR and Northern hybridization we compared the expression level of 20 EST on 7q32 between NPC cell line HNE1 and primary culture of normal nasopharyngeal epithelial cell, and found AA070437 EST expressed high in primary culture of normal nasopharyngeal epithelial cell, but very low in HNE1. Differential RT-PCR (dRT-PCR) analysis showed that the expression level of AA070437 was lower in 30.7% NPC biopses than in normal cell. Differential PCR (dPCR) showed that allelic loss of AA070437 was observed in 29.1% NPC biopses. This EST is a part of sequence of a new gene compared with GeneBank database. Our results showed that AA070437 EST negatively related with the occurrence of human NPC is a candidate of tumor suppressor gene of NPC on 7q32.

Interaction of the globular domains of pIII protein of filamentous bacteriophage fd with the F-pilus of Escherichia coli

Gene 3 protein (pIII), a minor coat protein at one end of the filamentous bacteriophage fd, is involved in initiating the infection by the virus of Escherichia coli cells that display an F-pilus. Infection is thought to start with the adsorption of the D2 domain of pIII to the tip of the pilus, retraction of the pilus, and penetration of the E. coli cell membrane mediated by an interaction between the D1 domain of pIII and the Tol protein complex in the membrane. A subgene encoding the pIII-D1D2 di-domain was created, and the subgene was successfully overexpressed in E. coli cells. Domains D1 and D2 were separated after limited proteolysis of a modified pIII-D1D2 (designated pIII-D1D2.trp) into which two tryptic cleavage sites were introduced at appropriate points. The purified pIII-D1D2 di-domain and pIII-D2 domain were able to bind to the F-pilus, competing with the wild-type pIII and delaying infection by the intact filamentous phage. The pIII-D1 domain was unable to bind to the F-pilus by this criterion. This provides conclusive evidence that the pIII-D2 domain is responsible for the adsorption to the tip of the F-pilus and can achieve this in the absence of domain D1, opening the way to identifying the molecular basis of the interaction of pIII-D2 with the pilus.