Identification of Novel Bisbenzimidazole Derivatives as Anticancer Vacuolar (H⁺)-ATPase Inhibitors

The vacuolar (H⁺)-ATPases (V-ATPases) are a family of ATP-driven proton pumps and they have been associated with cancer invasion, metastasis, and drug resistance. Despite the clear involvement of V-ATPases in cancer, the therapeutic use of V-ATPase-targeting small molecules has not reached human clinical trials to date. Thus, V-ATPases are emerging as important targets for the identification of potential novel therapeutic agents. We identified a bisbenzimidazole derivative (V) as an initial hit from a similarity search using four known V-ATPase inhibitors (I–IV). Based on the initial hit (V), we designed and synthesized a focused set of novel bisbenzimidazole analogs (2a–e). All newly prepared compounds have been screened for selected human breast cancer (MDA-MB-468, MDA-MB-231, and MCF7) and ovarian cancer (A2780, Cis-A2780, and PA-1) cell lines, along with the normal breast epithelial cell line, MCF10A. The bisbenzimidazole derivative (2e) is active against all cell lines tested. Remarkably, it demonstrated high cytotoxicity against the triple-negative breast cancer (TNBC) cell line, MDA-MB-468 (IC₅₀ = 0.04 ± 0.02 μM). Additionally, it has been shown to inhibit the V-ATPase pump that is mainly responsible for acidification. To the best of our knowledge the bisbenzimidazole pharmacophore has been identified as the first V-ATPase inhibitor in its class. These results strongly suggest that the compound 2e could be further developed as a potential anticancer V-ATPase inhibitor for breast cancer treatment.

Low-dose prednisone and immunoglobulin G treatment for woman at risk for neonatal alloimmune thrombocytopenia and T helper 1 immunity

PROBLEM

Fetal and neonatal alloimmune thrombocytopenia is an alloimmune disorder resulting from platelet opsonization by maternal antibodies that destroy fetal platelets. As there is no antenatal screening or immunization to prevent sensitization, selection of high-risk population or the prevention of antenatal sensitization is significantly limited.

METHOD OF STUDY

(i) A case report of ante- and postnatal management of a woman with paternal homozygosity for human platelet antigen-1(HPA) incompatibility. (ii) A retrospective case-control study of 11 confirmed FNAIT patients, 8 possible-FNAIT women, and 10 women with confirmed ITP.

RESULT

Antenatal screening, prevention of maternal sensitization by serial monitoring and immunosuppression with prednisone and intravenous immunoglobulin G (IVIG) infusion resulted in two successful pregnancies without sensitization.

CONCLUSION

Screening for couples at risk and prednisone and/or IVIG treatment is an option for women with paternal homozygosity for offending HPA antigen to prevent antenatal sensitization. HPA incompatibility is associated with increased Th1 immunity and NK cell cytotoxicity.

The enigma of the clandestine association between chloroquine and HIV-1 infection

OBJECTIVES

The antimalarial drug chloroquine (CQ) dampens the immune system and is used in the treatment of autoimmune disorders. CQ also shows antiviral activity against nonenveloped and enveloped viruses, including HIV-1. Persistent immune activation in chronic HIV-1infection leads to CD4 T-cell depletion. CQ is envisioned to attenuate immune activation and virus activity in HIV-1-infected patients. The role of CQ in immune activation and virus activity is discussed here.

METHODS

To elucidate the effect of CQ on immune activation, a retrospective review of published clinical trials, in vivo experimental studies in animals, and the most relevant in vitro observations in HIV-1-infected cells, together with observations from our own laboratory studies, was carried out and the findings discussed.

RESULTS

In a few clinical studies and animal experiments, CQ was ineffective in decreasing immune activation and HIV-1 infection. In vitro, CQ markedly increased HIV-1 infection in astrocytes and other non-CD4 cells.

CONCLUSIONS

The use of CQ in HIV-1-infected patients is questionable. The evidence for a dampening of immune activation by CQ is inconclusive.

Expression and role of a2 vacuolar-ATPase (a2V) in trafficking of human neutrophil granules and exocytosis

Neutrophils kill microorganisms by inducing exocytosis of granules with antibacterial properties. Four isoforms of the "a" subunit of V-ATPase-a1V, a2V, a3V, and a4V-have been identified. a2V is expressed in white blood cells, that is, on the surface of monocytes or activated lymphocytes. Neutrophil associated-a2V was found on membranes of primary (azurophilic) granules and less often on secondary (specific) granules, tertiary (gelatinase granules), and secretory vesicles. However, it was not found on the surface of resting neutrophils. Following stimulation of neutrophils, primary granules containing a2V as well as CD63 translocated to the surface of the cell because of exocytosis. a2V was also found on the cell surface when the neutrophils were incubated in ammonium chloride buffer (pH 7.4) a weak base. The intracellular pH (cytosol) became alkaline within 5 min after stimulation, and the pH increased from 7.2 to 7.8; this pH change correlated with intragranular acidification of the neutrophil granules. Upon translocation and exocytosis, a2V on the membrane of primary granules remained on the cell surface, but myeloperoxidase was secreted. V-ATPase may have a role in the fusion of the granule membrane with the cell surface membrane before exocytosis. These findings suggest that the granule-associated a2V isoform has a role in maintaining a pH gradient within the cell between the cytosol and granules in neutrophils and also in fusion between the surface and the granules before exocytosis. Because a2V is not found on the surface of resting neutrophils, surface a2V may be useful as a biomarker for activated neutrophils.

Sox9 drives columnar differentiation of esophageal squamous epithelium: a possible role in the pathogenesis of Barrett's esophagus

The molecular mechanism underlying the development of Barrett's esophagus (BE), the precursor to esophageal adenocarcinoma, remains unknown. Our previous work implicated sonic hedgehog (Shh) signaling as a possible driver of BE and suggested that bone morphogenetic protein 4 (Bmp4) and Sox9 were downstream mediators. We have utilized a novel in vivo tissue reconstitution model to investigate the relative roles of Bmp4 and Sox9 in driving metaplasia. Epithelia reconstituted from squamous epithelial cells or empty vector-transduced cells had a stratified squamous phenotype, reminiscent of normal esophagus. Expression of Bmp4 in the stromal compartment activated signaling in the epithelium but did not alter the squamous phenotype. In contrast, expression of Sox9 in squamous epithelial cells induced formation of columnar-like epithelium with expression of the columnar differentiation marker cytokeratin 8 and the intestinal-specific glycoprotein A33. In patient tissue, A33 protein was expressed specifically in BE, but not in normal esophagus. Expression of Cdx2, another putative driver of BE, alone had no effect on reconstitution of a squamous epithelium. Furthermore, epithelium coexpressing Cdx2 and Sox9 had a phenotype similar to epithelium expressing Sox9 alone. Our results demonstrate that Sox9 is sufficient to drive columnar differentiation of squamous epithelium and expression of an intestinal differentiation marker, reminiscent of BE. These data suggest that Shh-mediated expression of Sox9 may be an important early event in the development of BE and that the potential for inhibitors of the hedgehog pathway to be used in the treatment of BE and/or esophageal adenocarcinoma could be tested in the near future.

Physiological levels of Pik3ca(H1047R) mutation in the mouse mammary gland results in ductal hyperplasia and formation of ERα-positive tumors

PIK3CA, the gene coding for the p110α subunit of phosphoinositide 3-kinase, is frequently mutated in a variety of human tumors including breast cancers. To better understand the role of mutant PIK3CA in the initiation and/or progression of breast cancer, we have generated mice with a conditional knock-in of the common activating mutation, Pik3ca(H1047R), into one allele of the endogenous gene in the mammary gland. These mice developed a ductal anaplasia and hyperplasia by 6 weeks of age characterized by multi-layering of the epithelial lining of the mammary ducts and expansion of the luminal progenitor (Lin(-); CD29(lo); CD24(+); CD61(+)) cell population. The Pik3ca(H1047R) expressing mice eventually develop mammary tumors with 100% penetrance but with a long latency (>12 months). This is significantly longer than has been reported for transgenic models where expression of the mutant Pik3ca is driven by an exogenous promoter. Histological analysis of the tumors formed revealed predominantly ERα-positive fibroadenomas, carcinosarcomas and sarcomas. In vitro induction of Pik3ca(H1047R) in immortalized mammary epithelial cells also resulted in tumor formation when injected into the mammary fat pad of immunodeficient recipient mice. This novel model, which reproduces the scenario of a heterozygous somatic mutation occurring in the endogenous PIK3CA gene, will thus be a valuable tool for investigating the role of Pik3ca(H1047R) mutation in mammary tumorigenesis both in vivo and in vitro.

Abstract 3289: Tissue specific expression of the PI 3-kinase mutation Pik3caH1047R induces hyperplasia and tumorigenesis in a mouse model

Mutations in the p110α subunit of phosphoinositide 3-kinase (PI3K) (encoded by the gene PIK3CA) are frequent in human cancers. To better understand the role of mutant PIK3CA in the initiation or progression of tumorigenesis in vivo, we generated a conditional (Cre recombinase-inducible) knock-in mouse model of the common activating mutation, Pik3caH1047R, expressed from the endogenous locus. We have then targeted the mutation to specific tissues by crossing our mouse to mice expressing Cre under the control of tissue-specific promoters. The mouse mammary gland was targeted using a transgenic mouse expressing Cre under the control of the mouse mammary tumor virus promoter (MMTV-Cre). To target the gastrointestinal tract, we used the A33CrePR2 mouse, expressing Ru486-inducible version of Cre under the control of the gpa33 promoter. Tumors were formed in both these models but only following a long latency (>15 months) suggesting that a ‘second-hit’ may be necessary for tumor development. Similarly, activation of this mutation in the mouse ovary, by injection of an adenovirus expressing Cre into the ovarian bursa, revealed that Pik3caH1047R alone is a weak activator of AKT capable of inducing premalignant hyperplasia in ovarian surface epithelium. Interestingly, we found that combining Pik3caH1047R mutation with deletion of Pten in the mouse ovary resulted in robust epithelial AKT signaling and progression to ovarian serous adenocarcinomas and granulosa cell tumors within 6 months. Therapeutic inhibition of PI3K/mTOR in these mice delayed tumor growth and prolonged survival. This novel mouse is proving to be a fascinating model with which to explore the biological consequences and clinical significance of Pik3caH1047R mutation in diverse tissue types and a valuable tool for the preclinical evaluation of PI3K pathway inhibitors.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3289. doi:1538-7445.AM2012-3289

An activating Pik3ca mutation coupled with Pten loss is sufficient to initiate ovarian tumorigenesis in mice

Mutations in the gene encoding the p110α subunit of PI3K (PIK3CA) that result in enhanced PI3K activity are frequently observed in human cancers. To better understand the role of mutant PIK3CA in the initiation or progression of tumorigenesis, we generated mice in which a PIK3CA mutation commonly detected in human cancers (the H1047R mutation) could be conditionally knocked into the endogenous Pik3ca locus. Activation of this mutation in the mouse ovary revealed that alone, Pik3caH1047R induced premalignant hyperplasia of the ovarian surface epithelium but no tumors. Concomitantly, we analyzed several human ovarian cancers and found PIK3CA mutations coexistent with KRAS and/or PTEN mutations, raising the possibility that a secondary defect in a co-regulator of PI3K activity may be required for mutant PIK3CA to promote transformation. Consistent with this notion, we found that Pik3caH1047R mutation plus Pten deletion in the mouse ovary led to the development of ovarian serous adenocarcinomas and granulosa cell tumors. Both mutational events were required for early, robust Akt activation. Pharmacological inhibition of PI3K/mTOR in these mice delayed tumor growth and prolonged survival. These results demonstrate that the Pik3caH1047R mutation with loss of Pten is enough to promote ovarian cell transformation and that we have developed a model system for studying possible therapies.

Reconstitution of stratified murine and human oesophageal epithelia in an in vivo transplant culture system

OBJECTIVE

The molecular and cellular events responsible for regulating development of the oesophageal epithelium are not well understood. At least in part, this is due to the lack of a suitable model system with which to study the process. Here, we report development of a manipulable in vivo transplant model for mouse or human oesophageal epithelium.

MATERIAL AND METHODS

Epithelial cells were isolated from mouse or human oesophagus and inoculated into de-epithelialized and devitalized rat tracheas. The rat trachea, containing cells, was placed subcutaneously under the dorsal skin of immunodeficient mice.

RESULTS

We show that a multilayered stratified squamous epithelium can be generated in 4-6 weeks from as few as 5 x 10(4) isolated oesophageal epithelial cells. The reconstituted epithelium recapitulates many of the structural and histological features of the normal oesophageal epithelium, including a basal layer of cuboidal-like cells, suprabasal layers of differentiating squamous cells and, in the case of murine cells, a superficial layer of cornified material.

CONCLUSION

Our model can be used to generate a multilayered normal murine or human epithelium from a single cell suspension of oesophageal epithelial cells. The ability to genetically manipulate the cells prior to growth in the model is a powerful tool with which to study the molecular mechanisms involved in the development of normal oesophagus or in pathogenic processes such as Barrett's metaplasia or tumorigenesis.

Effects of Advanced Glycation End Products on Ezrin-Dependent Functions in LLC-PK1 Proximal Tubule Cells

We have recently shown that advanced glycation products (AGEs) bind to the ERM (ezrin, radixin, moesin) family of proteins. ERM proteins act as cross-linkers between cell membrane proteins and the actin cytoskeleton. They are also involved in signal transduction pathways. They therefore have a critical role in normal cell processes, including modulation of cell shape, adhesion, and motility. We postulate that AGEs may contribute to diabetic complications by disrupting ERM function. In support of this hypothesis, AGEs inhibit ezrin-dependent tubulogenesis of proximal tubule cells. Phosphorylation is an important activating mechanism for ERM proteins, and AGEs inhibit ezrin phosphorylation mediated by the epidermal growth factor receptor.

Localization of the Ezrin Binding Epitope for Glycated Proteins

ERM proteins (ezrin, radixin, and moesin) have recently been identified as a new class of AGE-binding proteins. ERM proteins link the plasma membrane with the actin cytoskeleton and regulate cell shape, motility, adhesion, and signal transduction. ERM proteins have three structural domains: the N-terminal domain, a coiled midregion, and the C-terminal domain. The N-terminal domain binds to a number of plasma membrane ligands and is involved in signal transduction, while the C-domain binds to actin filaments. Binding studies with isolated structural domains showed that glycated proteins bind to an epitope within the N-terminal domain of ezrin (aa 1-324). It is postulated that some of the cellular effects of AGEs leading to diabetic complications may be mediated by binding to this region of ezrin, thereby interrupting the cross-linking between the plasma membrane and actin cytoskeleton and downstream signaling pathways. Indeed, changes in actin arrangement, cell shape, and adhesion have been described in diabetes, and AGE-BSA inhibits ezrin-dependent tubulogenesis of LLC-PK1 proximal tubular cells. For future development of antagonists, further identification of the ezrin-binding epitope for glycated proteins is required.

Advanced Glycation End Products Inhibit Tubulogenesis and Migration of Kidney Epithelial Cells in an Ezrin-Dependent Manner

Nonenzymatic glycation of proteins to form advanced glycation end products (AGE) is implicated in diabetic complications, including nephropathy. It was shown recently that AGE bind to the ERM (ezrin, radixin, and moesin) family of membrane-cytoskeletal linker proteins in renal homogenates. Herein is reported the effects of AGE-BSA on ezrin-dependent LLC-PK1 kidney epithelial cellular functions: migration and hepatocyte growth factor (HGF)-induced tubulogenesis. LLC-PK1 cells were stably transfected with cDNA for ezrin sense, ezrin antisense, and N-ezrin. Transfection of LLC-PK1 cells with ezrin antisense and dominant negative N-ezrin decreased basal tubulogenesis and migration relative to vector-only transfection, establishing the ezrin dependency of these processes. AGE-BSA (20 or 40 microM) significantly decreased HGF-induced tubulogenesis and basal migration in two vector control lines relative to BSA-treated cells. However, AGE-BSA inhibition of both HGF-induced tubulogenesis and migration was overcome by overexpressing ezrin. These results demonstrate that the AGE-ezrin interaction significantly alters cellular function. These changes may be relevant to detrimental renal consequences as a result of diabetes.

A clue to the therapy of neurofibromatosis type 2: NF2/merlin is a PAK1 inhibitor

BACKGROUND

Neurofibromatosis type 2 is a group of tumors caused by loss-of-function mutations of a tumor suppressor gene encoding NF2/merlin. Development of chemotherapeutics for this disease, which often threatens the life of young children, has been hampered by a limited information on the signaling function of NF2. NF2 can inhibit Ras-induced malignant transformation. However, the primary (signaling) target of NF2 in the oncogenic pathway has not been previously identified.

RESULTS

Here, using a series of NF2 constructs, we show that NF2 inhibits directly the Rac/CDC42-dependent Ser/Thr kinase PAK1, which is essential for both Ras transformation and neurofibromatosis type 1 (NF1), through two separate domains. A mutant of NF2, that lacks the PAK1-inhibiting domain of 78 amino acids (NF78C, residues 447-524), fails to suppress Ras transformation. Furthermore, PAK1-specific inhibitors CEP-1347 and WR-PAK18 selectively inhibit the growth of NF2-deficient cancer cells, but not NF2-positive cells.

CONCLUSIONS

These results suggest that PAK1 is essential for the malignant growth of NF2-deficient cells, and that PAK1-blocking drugs could be potentially useful forthe treatment of neurofibromatosis types 2, in addition to Ras-induced cancers and neurofibromatosis type 1.

Tissue distribution of Diablo/Smac revealed by monoclonal antibodies

Diablo/Smac is a mammalian pro-apoptotic protein that can antagonize the inhibitor of apoptosis proteins (IAPs). We have produced monoclonal antibodies specific for Diablo and have used these to examine its tissue distribution and subcellular localization in healthy and apoptotic cells. Diablo could be detected in a wide range of mouse tissues including liver, kidney, lung, intestine, pancreas and testes by Western blot analysis. Immunohistochemical analysis found Diablo to be most abundant in the germinal cells of the testes, the parenchymal cells of the liver and the tubule cells of the kidney. In support of previous subcellular localization analysis, Diablo was present within the mitochondria of healthy cells, but released into the cytosol following the induction of apoptosis by UV.

HtrA2 promotes cell death through its serine protease activity and its ability to antagonize inhibitor of apoptosis proteins

Inhibitor of apoptosis (IAP) proteins inhibit caspases, a function counteracted by IAP antagonists, insect Grim, HID, and Reaper and mammalian DIABLO/Smac. We now demonstrate that HtrA2, a mammalian homologue of the Escherichia coli heat shock-inducible protein HtrA, can bind to MIHA/XIAP, MIHB, and baculoviral OpIAP but not survivin. Although produced as a 50-kDa protein, HtrA2 is processed to yield an active serine protease with an N terminus similar to that of Grim, Reaper, HID, and DIABLO/Smac that mediates its interaction with XIAP. HtrA2 is largely membrane-associated in healthy cells, with a significant proportion observed within the mitochondria, but in response to UV irradiation, HtrA2 shifts into the cytosol, where it can interact with IAPs. HtrA2 can, like DIABLO/Smac, prevent XIAP inhibition of active caspase 3 in vitro and is able to counteract XIAP protection of mammalian NT2 cells against UV-induced cell death. The proapoptotic activity of HtrA2 in vivo involves both IAP binding and serine protease activity. Mutations of either the N-terminal alanine of mature HtrA2 essential for IAP interaction or the catalytic serine residue reduces the ability of HtrA2 to promote cell death, whereas a complete loss in proapoptotic activity is observed when both sites are mutated.

p190-A, a human tumor suppressor gene, maps to the chromosomal region 19q13.3 that is reportedly deleted in some gliomas

To date, two distinct genes coding for Ras GAP-binding phosphoproteins of 190kDa, p190-A and p190-B, have been cloned from mammalian cells. Rat p190-A of 1513 amino acids shares 50% sequence identity with human p190-B of 1499 amino acids. We have previously demonstrated, using rat p190-A cDNA, that full-length p190-A is a tumor suppressor, reversing v-Ha-Ras-induced malignancy of NIH 3T3 cells through both the N-terminal GTPase (residues 1-251) and the C-terminal Rho GAP (residues 1168-1441) domains. Here we report the cloning of the full-length human p190-A cDNA and its first exon covering more than 80% of this protein, as well as its chromosomal mapping. Human p190-A encodes a protein of 1514 amino acids, and shares overall 97% sequence identity with rat p190-A. Like the p190-B exon, the first exon of p190-A is extremely large (3.7 kb in length), encoding both the GTPase and middle domains (residues 1-1228), but not the remaining GAP domain, suggesting a high conservation of genomic structure between two p190 genes. Using a well characterized monochromosome somatic cell hybrid panel, fluorescent in situ hybridization (FISH) and other complementary approaches, we have mapped the p190-A gene between the markers D19S241E and STD (500 kb region) of human chromosome 19q13.3. Interestingly, this chromosomal region is known to be rearranged in a variety of human solid tumors including pancreatic carcinomas and gliomas. Moreover, at least 40% glioblastoma/astrocytoma cases with breakpoints in this region were previously reported to show loss of the chromosomal region encompassing p190-A, suggesting the possibility that loss or mutations of this gene might be in part responsible for the development of these tumors.

Treatment of ras-induced cancers by the F-actin-bundling drug MKT-077

A rhodacyanine dye called MKT-077 has shown a highly selective toxicity toward several distinct human malignant cell lines, including bladder carcinoma EJ, and has been subjected to clinical trials for cancer therapy. In the pancreatic carcinoma cell line CRL-1420, but not in normal African green monkey kidney cell line CV-1, it is selectively accumulated in mitochondria. However, both the specific oncogenes responsible for its selective toxicity toward cancer cells, and its target proteins in these cancer cells, still remain to be determined. This study was conducted using normal and ras-transformed NIH 3T3 fibroblasts to determine whether oncogenic ras mutants such as v-Ha-ras are responsible for the selective toxicity of MKT-077 and also to identify its targets, using its derivative called "compound 1" as a specific ligand. We have found that v-Ha-ras is responsible for the selective toxicity of MKT-077 in both in vitro and in vivo. Furthermore, we have identified and affinity purified at least two distinct proteins of 45 kD (p45) and 75 kD (p75), which bind MKT-077 in v-Ha-ras-transformed cells but not in parental normal cells. Microsequencing analysis has revealed that the p45 is a mixture of beta- and gamma-actin, whereas the p75 is HSC70, a constitutive member of the Hsp70 heat shock adenosine triphosphatase family, which inactivates the tumor suppressor p53. MKT-077 binds actin directly, bundles actin filaments by cross-linking, and blocks membrane ruffling. Like a few F-actin-bundling proteins such as HS1, alpha-actinin, and vinculin as well as F-actin cappers such as tensin and chaetoglobosin K (CK), the F-actin-bundling drug MKT-077 suppresses ras transformation by blocking membrane ruffling. These findings suggest that other selective F-actin-bundling/capping compounds are also potentially useful for the chemotherapy of ras-associated cancers.

Cytoskeletal tumor suppressors that block oncogenic RAS signaling

Several distinct peptides or drugs that block the Rho family GTPases-mediated pathways were found to suppress RAS-induced malignant phenotype. They include (1) C3 enzyme that selectively inactivates Rho, (2) ACK42, a peptide that blocks the interaction of CDC42 with its effectors such as ACKs, (3) PAK18, a peptide that blocks the activation of PAK and membrane ruffling, and (4) actin-binding drugs, chaetoglobosin K (CK) and MKT-077, that block membrane ruffling by capping and bundling actin filaments, respectively.

G proteins, phosphoinositides, and actin-cytoskeleton in the control of cancer growth

Almost three decades have passed since actin-cytoskeleton (acto-myosin complex) was first discovered in non-muscle cells. A combination of cell biology, biochemistry, and molecular biology has revealed the structure and function of many actin-binding proteins and their physiological role in the regulation of cell motility, shape, growth, and malignant transformation. As molecular oncologists, we would like to review how the function of actin-cytoskeleton is regulated through Ras/Rho family GTPases- or phosphoinosites-mediated signaling pathways, and how malignant transformation is controlled by actin/phosphoinositides-binding proteins or drugs that block Rho/Rac/CDC42 GTPases-mediated signaling pathways.

Treatment of Ras-induced cancers by the F-actin cappers tensin and chaetoglobosin K, in combination with the caspase-1 inhibitor N1445

For transforming normal fibroblasts to malignant cells, oncogenic Ras mutants such as v-Ha-ras require Rho family GTPases (Rho, Rac, and CDC42) that are responsible for controlling actin-cytoskeleton organization. Ras activates Rac through a PI-3 kinase-mediated pathway. Rac causes uncapping of actin filaments (F-actin) at the plus-ends, through phosphatidylinositol 4,5 bisphosphate (PIP2), and eventually induces membrane ruffling. Several distinct F-actin/PIP2-binding proteins, such as gelsolin, which severs and caps the plus-ends of actin filaments, or HS1, which cross-links actin filaments, have been shown to suppress v-Ha-Ras-induced malignant transformation when they are overexpressed. Interestingly, an F-actin cross-linking drug (photosensitizer) called MKT-077 suppresses Ras transformation. Thus, an F-actin capping/severing drug might also have an anticancer potential.

PURPOSE

This study was conducted to determine first whether Ras-induced malignant phenotype (anchorage-independent growth) is suppressed by overexpression of the gene encoding a large plus-end F-actin capping protein called tensin and second to test the anti-Ras potential of a unique fungal antibiotic (small compound) called chaetoglobosin K (CK) that also caps the plus-ends of actin filaments.

METHODS AND RESULTS

DNA transfection with a retroviral vector carrying the tensin cDNA was used to overexpress tensin in v-Ha-Ras-transformed NIH 3T3 cells. All stable tensin transfectants rarely formed colonies in soft agar, indicating that tensin suppresses the anchorage-independent growth. The anti-Ras action of CK was determined by incubating the Ras-transformants in the presence of CK in soft agar. Two microM CK almost completely inhibited their colony formation, indicating that CK also suppresses the malignant phenotype. However, unlike tensin, CK causes an apoptosis of Ras-transformed NIH 3T3 cells and, less effectively, of normal NIH 3T3 cells, indicating that CK has an F-actin capping-independent side effect(s). CK-induced apoptosis is at least in part caused by CK-induced inhibition of the kinase PKB/AKT. However, a specific ICE/caspase-1 inhibitor called N1445 completely abolished the CK-induced apoptosis by reactivating PKB, but without affecting the CK-induced suppression of Ras transformation.

CONCLUSIONS

Like the F-actin cross-linking drug MKT-077, the F-actin capping drug CK may be useful for the treatment of Ras-associated cancers if it is combined with the ICE inhibitor N1445, which abolishes the side effect of CK. Our observations that two distinct F-actin capping molecules (i.e., tensin and CK) suppress Ras-induced malignant phenotype strongly suggest, if not prove, that capping of actin filaments at the plus-ends alone is sufficient to block one of the Ras signaling pathways essential for its oncogenicity. This notion is compatible with the fact that Ras induces the uncapping of actin filaments at the plus-ends through the Rac/PIP2 pathway.

Enteropathogenicity and antimicrobial susceptibility of new Escherichia spp

To determine the mechanism of enteropathogenicity of the newly described Escherichia species, a total of 50 clinical isolates of Escherichia spp. from diarrhoeal stools were studied. Twelve isolates (24%) were found to be E. vulneris, 6 (12%) E. fergusonii, 2 (4%) E. hermannii, and the rest 30 (60%) were E. coli. Most isolates of the new species were resistant to ampicillin, tetracycline, and co-trimoxazole, but were susceptible to cephalosporins and aminoglycosides. The representative strains of all the new species produced significant fluid accumulation in the rat ileal loops both by live cells and their culture filtrates. E. vulneris, isolated from stools, showed maximum fluid accumulation. Thus, it can be inferred that these species are diarrhoeagenic, but their roles on extra-intestinal infections remain to be determined.

The GTPase and Rho GAP domains of p190, a tumor suppressor protein that binds the M(r) 120,000 Ras GAP, independently function as anti-Ras tumor suppressors

p190 is a Tyr-phosphorylatable G protein of M(r) 190,000 that binds NH2-terminal SH2 domains of GAP1, a Ras GAP of M(r) 120,000. p190 contains at least two functional domains: a GTPase domain at the NH2 terminus and a GAP domain at the COOH terminus that can attenuate signal-transducing activity of three distinct G proteins (Rac, Rho, and CDC42). Here, we demonstrate that overexpression of either an antisense p190 RNA or a dominant negative mutant (Asn36) of p190 GTPase domain (residues 1-251) but not the wild-type p190 GTPase domain is able to transform normal NIH/3T3 fibroblasts. Furthermore, overexpression of either the wild-type p190 GTPase domain or the COOH-terminal GAP domain can suppress v-Ha-Ras-induced malignant transformation. These results indicate that p190 contains at least two distinct anti-Ras tumor suppressor domains, the GTPase and GAP domains, and suggest that one of the mechanisms underlying the suppression of Ras-transformation by p190 is the attenuation by p190 GAP domain of Rac/Rho/CDC42 signalings, which are essential for Ras-transformation. In fact, the p190 GAP domain alone suppresses the expression of the c-Fos gene, which is mediated by Rac/Rho/CDC42 and is required for oncogenicity of Ras.

Production of the new cholera toxin by environmental isolates of Vibrio cholerae non-O1

One of five strains of Vibrio cholerae non-O1 isolated from environmental sources caused fluid accumulation in an initial rabbit ileal loop (RIL) test. The four strains that caused little or no accumulation of fluid gave a positive response after one-to-three consecutive passages through RILs. The amount of fluid produced increased after each passage. Filtrates of cultures of all five environmental isolates caused fluid accumulation similar to that produced by live cells. The enterotoxin showed a precipitin band with new cholera antitoxin and was neutralised completely by new cholera antitoxin diluted 1 in 32, indicating its close immunobiological relationship to the new cholera toxin. The present study indicates that V. cholerae non-O1 strains produce an enterotoxin that is similar to the new cholera toxin.

Development of an improved synthetic medium for a better production of the new cholera toxin and its immunological relationship with the toxin produced by Vibrio cholerae O139 strains

An improved synthetic medium (M4) comprising syncase medium supplemented with sodium chloride (1%) and sucrose (0.5%) pH adjusted to 7.4 was developed for a better production of the new cholera toxin (NCT). The culture filtrates prepared in the M4 medium caused significantly (P > 0.05) more fluid accumulation than that in syncase medium. Crude toxin, prepared in the M4 medium with V. cholerae O1 strains (X-392 and 2740-80) caused a reaction similar to that of the same amount of NCT (32 micrograms) prepared in the syncase medium. The neutralization of the optimal loop reacting dose of the NCT prepared in the M4 medium by anti-NCT raised against syncase prepared toxin indicates the release of the same kind of toxin in both media. These observations indicate that the modified M4 medium may be used for NCT preparation and further characterization. All the strains of Vibro cholerae O139 used in this study produced a toxin antigenically similar to NCT.

The minimal fragments of c-Raf-1 and NF1 that can suppress v-Ha-Ras-induced malignant phenotype

v-Ha-Ras, an oncogenic Ras mutant, causes malignant transformation of mammalian cells by recruiting c-Raf-1, a cytosolic Ser/Thr kinase, to the plasma membranes/cytoskeleton. The kinase activity of c-Raf-1 resides in the C-terminal half, which activates mitogen-activated protein (MAP) kinase kinase, while it is the N-terminal half of c-Raf-1 (Raf257, residues 1-257) that binds the Ras-GTP complex and can compete Ras GTPase-activating proteins such as NF1 for binding to Ras. However, it still remains to be clarified whether overexpression of Raf257 or its minimal Ras-binding fragment alone is sufficient to suppress Ras-induced malignancy. In this paper we demonstrate for the first time that the 81-amino acid fragment (Raf81, residues 51-131), the minimal Ras-binding fragment of Raf, indeed can suppress v-Ha-Ras-induced malignant phenotype. A further deletion of the first 6 amino acids causes 65% reduction in the Ras binding of Raf81. The resultant 75 amino acid fragment (Raf75, residues 57-131) consists of a single alpha-helix, five anti-paralleled beta-sheets and five loops. We have found that a further deletion of either the first beta-sheet/loop or the last two beta-sheets/loops completely abolishes Ras binding. In addition we have found that the removal of the C-terminal 35 amino acids from a Ras-binding 91-amino acid fragment of NF1 (NF91, residues 1441-1531) does not abolish its ability to suppress the Ras-induced malignancy.

An anti-Ras function of neurofibromatosis type 2 gene product (NF2/Merlin)

Previously, we have cloned a candidate for the 595-amino acid neurofibromatosis type 2 tumor suppressor called NF2 or Merlin, with striking sequence similarity in its N-terminal half to an F-actin-binding protein family called TERM, which includes talin, ezrin, radixin, and moesin (Trofatter, J. A., MacCollin, M. M., Rutter, J. L., Murrell, J. R., Duyao, M. P., Parry, D. M., Eldridge, R., Kley, N., Menon, A. G., Pulaski, K., Haase, V. H., Ambrose, C. M., Munro, D., Bove, C., Haines, J. L., Martuza, R. L., MacDonald, M. E., Seizinger, B. R., Short, M. P., Buckler, A. J., and Gusella, J. F. (1993) Cell 72, 791-800). In an attempt to determine whether NF2 serves as a tumor suppressor and if so whether its N-terminal half is involved in its anti-oncogenicity, both full-length NF2 and its N-terminal half (NF2-N, residues 9-359) have been expressed in v-Ha-Ras-transformed NIH/3T3 cells. Like neurofibromatosis type 1 (NF1) fragments (Nur-E-Kamal, M. S. A., Varga, M., and Maruta, H. (1993) J. Biol. Chem. 268, 22331-22337), full-length NF2 can reverse the Ras-induced malignant phenotype, i.e. anchorage-independent growth in a soft agar, and restore contact inhibition of cell growth, indicating that NF2 is indeed a tumor suppressor. Furthermore, NF2-N also suppresses the Ras-induced malignant phenotype, although it appears to be less effective than the full-length NF2. These observations indicate that the anti-Ras function of NF2 resides in part in its N-terminal half. Thus, NF2 appears to be a new member of the tumor suppressor family of actin-cytoskeleton-associated proteins, which includes vinculin, alpha-actinin, tropomyosin-1, gelsolin, and tensin.

Influence of animal passage on haemolysin and enterotoxin production in Vibrio cholerae O1 biotype El Tor strains

Of 43 strains of Vibrio cholerae O1 biotype El Tor isolated over a span of almost three decades (1964-1990) from stools of children and adults with diarrhoea (25 isolates) and from sewage (three) and water from the river Ganges (15) examined for production of haemolysin and its correlation with enterotoxin production, 17 isolates showed haemolysis. The majority of isolates (26), including 68% of diarrhoeal and 50% of environmental origin, were non-haemolytic. The titre of haemolysin produced was 4-16 HU/ml, irrespective of the source of isolation. Haemolytic strains caused significantly more fluid accumulation than the non-haemolytic strains in the rabbit ileal loop (RIL) test. Twenty nine (67.4) V. cholerae biotype El Tor isolates--all the haemolytic and most (61.5%) of the non-haemolytic isolates tested--caused fluid accumulation. The remaining non-haemolytic strains that caused little or no accumulation of fluid did so after one to four consecutive passage(s) through RIL without change in haemolytic character; these strains required more consecutive passage through rabbit gut to show haemolysis. All these strains reverted to their original non-haemolytic character on repeated subculture or on storage in the laboratory but continued to show enterotoxic activity. The present study indicated that El Tor haemolysin is not responsible for fluid accumulation in rabbit gut.

Hematological lesions in rat following heavy alcohol ingestion

Hematological fluctuations following large alcohol oral administration (2 mL per animal per day) in rats were monitored at intervals ranging from 10 to 22 weeks and the findings were compared to those in control animals that were fed sucrose isocalorically. Following alcohol ingestion, there was a significant decrease in the total blood cellularity at all treatment intervals. A fall in the erythrocyte count per millimeter3 was accompanied by decreased hematocrit values and hemoglobin levels in the alcohol-treated animals. On the other hand, the MCV and MCH values were significantly elevated after alcohol ingestion. Despite overall leukopenia observed after alcohol ingestion, there was a significant increase in the absolute neutrophil count. The absolute lymphocyte count, however, fell significantly in the alcohol-treated animals. Eosinophils and basophils were not significantly altered by alcohol toxicity.