Structure based antibody-like peptidomimetics

Biologics such as monoclonal antibodies (mAb) and soluble receptors represent new classes of therapeutic agents for treatment of several diseases. High affinity and high specificity biologics can be utilized for variety of clinical purposes. Monoclonal antibodies have been used as diagnostic agents when coupled with radionuclide, immune modulatory agents or in the treatment of cancers. Among other limitations of using large molecules for therapy the actual cost of biologics has become an issue. There is an effort among chemists and biologists to reduce the size of biologics which includes monoclonal antibodies and receptors without a reduction of biological efficacy. Single chain antibody, camel antibodies, Fv fragments are examples of this type of deconstructive process. Small high-affinity peptides have been identified using phage screening. Our laboratory used a structure-based approach to develop small-size peptidomimetics from the three-dimensional structure of proteins with immunoglobulin folds as exemplified by CD4 and antibodies. Peptides derived either from the receptor or their cognate ligand mimics the functions of the parental macromolecule. These constrained peptides not only provide a platform for developing small molecule drugs, but also provide insight into the atomic features of protein-protein interactions. A general overview of the reduction of monoclonal antibodies to small exocyclic peptide and its prospects as a useful diagnostic and as a drug in the treatment of cancer are discussed.

Efficiency of G2/M-related tumor-associated antigen-targeting cancer immunotherapy depends on antigen expression in the cancer stem-like population

The aim of this study was to establish a novel efficient cancer DNA vaccine approach. Many tumor-associated antigens (TAAs) have been reported; however, there is little information of the efficiency of each TAA. Normal cells barely undergo mitosis, whereas cancer cells divide frequently and grow well. Thus, G2/M-related antigens are cancer cell-specific and are regarded to be suitable candidates as targets of cancer immunotherapy. In this study, we compared the efficiencies of G2/M-related antigens including Birc5, Aurka, Nke2 and Plk1 by using a DNA vaccination model. Mice that had been immunized with G2/M-related antigens coding plasmid were challenged with CT26 colon cancer cells. Interestingly, Birc5- and Aurka-immunized mice showed an anti-tumor effect, whereas Nek2- and Plk1-immunized mice did not show any anti-tumor effect. We investigated the expression of G2/M-related antigens in cancer stem-like cell (CSC)/cancer-initiating cell (CIC) population to verify the difference in the anti-tumor effect. CSCs/CICs were isolated as side population (SP) cells using Hoechst 33342 dye from CT 26 cells. It was found that Birc5 and Aurka are expressed in both CSCs/CICs and non-CSCs/CICs (shared antigens), whereas Nek2 and Plk1 are expressed preferentially in non-CSCs/CICs (non-CSC antigens). Therefore, antigen expression in the CSC/CIC population might be related to the anti-tumor efficiency of cancer immunotherapy. Furthermore, we established a heat shock protein (Hsp90)-fused Birc5 plasmid to improve anti-cancer immunity. Birc5 fused to the N-terminal region of Hsp90 showed a stronger anti-tumor effect, whereas Birc5 fused to the C-terminal region of Hsp90 did not show enhancement compared with Birc5. These observations indicate that expression in the CSC/CIC population is essential to achieve tumor regression and that fusing antigens to the N-terminal region of Hsp90 enhances the anti-tumor effect.

Structure of Sad1-UNC84 homology (SUN) domain defines features of molecular bridge in nuclear envelope

The SUN (Sad1-UNC-84 homology) domain is conserved in a number of nuclear envelope proteins involved in nuclear migration, meiotic telomere tethering, and antiviral responses. The LINC (linker of nucleoskeleton and cytoskeleton) complex, formed by the SUN and the nesprin proteins at the nuclear envelope, serves as a mechanical linkage across the nuclear envelope. Here we report the crystal structure of the SUN2 protein SUN domain, which reveals a homotrimer. The SUN domain is sufficient to mediate binding to the KASH (Klarsicht, ANC-1, and Syne homology) domain of nesprin 2, and the regions involved in the interaction have been identified. Binding of the SUN domain to the KASH domain is abolished by deletion of a region important for trimerization or by point mutations associated with nuclear migration failure. We propose a model of the LINC complex, where the SUN and the KASH domains form a higher ordered oligomeric network in the nuclear envelope. These findings provide the structural basis for understanding the function and the regulation of the LINC complex.

Expression and function of ErbB receptors and ligands in the pituitary

The role of ErbB family in discreet pituitary functions is reviewed. Several ErbB receptor ligands, EGF, TGFα, and heregulin are differentially expressed in normal gonadotroph and lacto-somatotroph lineages, and other elements of the anterior pituitary. ErbB receptors, i.e. EGFR and ErbB2, are also localized to the anterior pituitary with preferential EGFR lactosomatotroph expression. EGF regulates CRH and ACTH secretion and corticotroph proliferation as well as exhibiting autocrine and paracrine effects on gonadotrophs and on lactosomatotroph proliferation, gene and protein expression, and hormonal secretion. EGF and EGFR are expressed in both functioning and non-functioning pituitary adenomas, with higher expression in more aggressive tumor subtypes. ErbB2 receptor is detected in all tumor subtypes, particularly in invasive tumors. ErbB tyrosine kinase inhibitors regulate hormonal secretion, cell morphology, and proliferation in lacto-somatotroph tumors, reflecting the emerging application of targeted pituitary therapeutics.

Structural insights into the down-regulation of overexpressed p185(her2/neu) protein of transformed cells by the antibody chA21

p185(her2/neu) belongs to the ErbB receptor tyrosine kinase family, which has been associated with human breast, ovarian, and lung cancers. Targeted therapies employing ectodomain-specific p185(her2/neu) monoclonal antibodies (mAbs) have demonstrated clinical efficacy for breast cancer. Our previous studies have shown that p185(her2/neu) mAbs are able to disable the kinase activity of homomeric and heteromeric kinase complexes and induce the conversion of the malignant to normal phenotype. We previously developed a chimeric antibody chA21 that specifically inhibits the growth of p185(her2/neu)-overexpressing cancer cells in vitro and in vivo. Herein, we report the crystal structure of the single-chain Fv of chA21 in complex with an N-terminal fragment of p185(her2/neu), which reveals that chA21 binds a region opposite to the dimerization interface, indicating that chA21 does not directly disrupt the dimerization. In contrast, the bivalent chA21 leads to internalization and down-regulation of p185(her2/neu). We propose a structure-based model in which chA21 cross-links two p185(her2/neu) molecules on separate homo- or heterodimers to form a large oligomer in the cell membrane. This model reveals a mechanism for mAbs to drive the receptors into the internalization/degradation path from the inactive hypophosphorylated tetramers formed dynamically by active dimers during a "physiologic process."

Development of anti-EGF receptor peptidomimetics (AERP) as tumor imaging agent

EGFR is over-expressed in several solid tumors including breast, prostate, pancreas, and lung cancers and is correlated to the metastatic potential of the tumor. Anti-EGFR receptor-binding peptidomimetics (AERP) were examined to assess the small molecule's potential use as tumor-specific imaging agents. The aim of this work was to design and characterize the binding specificity of the radiolabeled peptidomimetics to EGFR over-expressing cell lysate and to A431 xenograft tumors. Our newly designed peptidomimetic, AERP, was conjugated to DTPA and labeled with (99m)Tc. The in vivo tumor accumulation of [(99m)Tc] DTPA-AERP-2 was 1.6±0.1%ID/g and tumor to muscle ratio was 5.5. Our studies suggest that this novel peptidomimetic, AERP-2, warrants further development as an EGFR specific tumor-imaging agent.

Targeting erbB receptors

Our work is concerned with the origins and therapy of human cancers. Members of the epidermal growth factor receptor (EGFR) family of tyrosine kinases, also known as erbB or HER receptors, are over expressed and/or activated in many types of human tumors and represent important therapeutic targets in cancer therapy. Studies from our laboratory identified targeted therapy as a way to treat cancer. Rational therapeutics targeting and disabling erbB receptors have been developed to reverse the malignant properties of tumors. Reversal of the malignant phenotype, best seen with disabling the HER2 receptors using monoclonal antibodies is a distinct process from that seen with blocking of ligand binding to cognate receptors as has been done for EGFr receptors. Here we review the mechanisms of action deduced from a number of approaches developed in our laboratory and elsewhere, including monoclonal antibodies, peptide mimetics, recombinant proteins and small molecules. The biochemical and biological principles which have been uncovered during these studies of disabling HER2 homomeric or HER2-EGFr heteromeric receptors will help the development of novel and more efficient therapeutics targeting erbB family receptors.

Common genetic variants and modification of penetrance of BRCA2-associated breast cancer

The considerable uncertainty regarding cancer risks associated with inherited mutations of BRCA2 is due to unknown factors. To investigate whether common genetic variants modify penetrance for BRCA2 mutation carriers, we undertook a two-staged genome-wide association study in BRCA2 mutation carriers. In stage 1 using the Affymetrix 6.0 platform, 592,163 filtered SNPs genotyped were available on 899 young (<40 years) affected and 804 unaffected carriers of European ancestry. Associations were evaluated using a survival-based score test adjusted for familial correlations and stratified by country of the study and BRCA2*6174delT mutation status. The genomic inflation factor (λ) was 1.011. The stage 1 association analysis revealed multiple variants associated with breast cancer risk: 3 SNPs had p-values<10(-5) and 39 SNPs had p-values<10(-4). These variants included several previously associated with sporadic breast cancer risk and two novel loci on chromosome 20 (rs311499) and chromosome 10 (rs16917302). The chromosome 10 locus was in ZNF365, which contains another variant that has recently been associated with breast cancer in an independent study of unselected cases. In stage 2, the top 85 loci from stage 1 were genotyped in 1,264 cases and 1,222 controls. Hazard ratios (HR) and 95% confidence intervals (CI) for stage 1 and 2 were combined and estimated using a retrospective likelihood approach, stratified by country of residence and the most common mutation, BRCA2*6174delT. The combined per allele HR of the minor allele for the novel loci rs16917302 was 0.75 (95% CI 0.66-0.86, ) and for rs311499 was 0.72 (95% CI 0.61-0.85, ). FGFR2 rs2981575 had the strongest association with breast cancer risk (per allele HR = 1.28, 95% CI 1.18-1.39, ). These results indicate that SNPs that modify BRCA2 penetrance identified by an agnostic approach thus far are limited to variants that also modify risk of sporadic BRCA2 wild-type breast cancer.

The feasibility of Cep55/c10orf3 derived peptide vaccine therapy for colorectal carcinoma

In our previous study, we demonstrated that a peptide derived from the novel centrosome residing protein Cep55/c10orf3 can be targeted by the cytotoxic T lymphocytes (CTLs) in peripheral blood mononuclear cells (PBMCs) of breast carcinoma patients. In this report, we evaluated the feasibility of cancer immunotherapy using Cep55/c10orf3 peptide for colorectal carcinoma (CRC). To evaluate the expression of Cep55/c10orf3 in CRC tissues, we performed immunohistochemical staining of using anti-Cep55/c10orf3 monoclonal antibody. Sixty-three percent cases showed weak positive for Cep55/c10orf3 in total 70 CRC cases. The Cep55/c10orf3 expression intention was collated with high histological grade of CRC. Thus, we hypothesized that Cep55/c10orf3 can also be the target of CTLs in CRC cases. We generated CTLs from PBMCs of human leukocyte antigen (HLA)-A24-positive colorectal carcinoma patients using HLA-A24-restricted Cep55/c10orf3 peptides. Two of 6 colorectal cancer patients were reactive for the Cep55/c10orf3_193(10) peptide, which was the only immunogenic peptide in breast carcinoma patients. CTL clone specific for Cep55/c10orf3_193(10) recognized and lysed HLA-A24 (+) and Cep55/c10orf3 (+) colorectal carcinoma cell lines. In addition, 1 of 6 colorectal carcinoma patients was reactive for the Cep55/c10orf3_402(11) and Cep55/c10orf3_283(12) peptides, but not for Cep55/c10orf3_193(10) with the ELISPOT assay. These observations suggest that the antigenic peptide repertoire presented by HLA-A24 in colorectal carcinoma might be different from that in breast carcinoma. Thus, these peptide vaccination peptide mixture of Cep55/c10orf3_193(10), Cep55/c10orf3_402(11) and Cep55/c10orf3_283(12) might be more effective than a single peptide in the treatment of colorectal carcinoma patients.

Histone acetyltransferase mediated regulation of FOXP3 acetylation and Treg function

Regulatory T cells (Tregs) are required for the maintenance of immune homeostasis as first clearly described by Herman Waldmann's laboratory. Dysfunction of Treg cells also leads to fatal autoimmunity in humans and mice. Conversely, the activation of different classes of Tregs operative systemically and within the cancer microenvironment can suppress host anti-tumor immune responses and promote tumor progression. Therefore, the development of new therapeutic approaches to regulate the activity of Treg cells may have considerable clinical potential. FOXP3 is the key transcriptional regulator of Treg development and function. The activity of FOXP3 is regulated by acetylation, a process catalyzed by distinct types of histone/protein acetyltransferases (HATs) that regulate the functions of many transcription factors, independently of FOXP3, as well as non-histone proteins, in addition to their effects on chromatin accessibility. Interactions between FOXP3 and these enzymes determine the suppressive function of FOXP3. Clearly, small molecules targeting these enzymes are candidates for the regulation of Treg function in vaccines and tumor therapies.

Nek2 targets the mitotic checkpoint proteins Mad2 and Cdc20: a mechanism for aneuploidy in cancer

In mitosis, the duplicated chromosomes are separated and equally distributed to progeny cells under the guidance of the spindle, a dynamic microtubule network. Previous studies revealed a mitotic checkpoint that prevents segregation of the chromosomes until all of the chromosomes are properly attached to microtubules through the kinetochores. A variety of kinetochore-localized proteins, including Mad2 and Cdc20, have been implicated in controlling the mitotic checkpoint. Here we report that both Mad2 and Cdc20 can physically associate with Nek2, a serine/threonine kinase implicated in centrosome functions. We show that, similar to Nek2, the endogenous Cdc20 protein can be detected in the centrosome and the spindle poles. Both Cdc20 and Mad2 can be phosphorylated by Nek2. Moreover, our studies demonstrate that overexpression of Nek2 enhances the ability of Mad2 to induce a delay in mitosis. These observations indicate that Nek2 may act upon the Mad2-Cdc20 protein complex and play a critical role in regulating the mitotic checkpoint protein complex. We propose that overexpression of Nek2 may promote aneuploidy by disrupting the control of the mitotic checkpoint.

Immunomodulatory effects of deacetylase inhibitors: therapeutic targeting of FOXP3+ regulatory T cells

Classical zinc-dependent histone deacetylases (HDACs) catalyse the removal of acetyl groups from histone tails and also from many non-histone proteins, including the transcription factor FOXP3, a key regulator of the development and function of regulatory T cells. Many HDAC inhibitors are in cancer clinical trials, but a subset of HDAC inhibitors has important anti-inflammatory or immunosuppressive effects that might be of therapeutic benefit in immuno-inflammatory disorders or post-transplantation. At least some of these effects result from the ability of HDAC inhibitors to enhance the production and suppressive functions of FOXP3(+) regulatory T cells. Understanding which HDACs contribute to the regulation of the functions of regulatory T cells may further stimulate the development of new class- or subclass-specific HDAC inhibitors with applications beyond oncology.

Deacetylase inhibition increases regulatory T cell function and decreases incidence and severity of collagen-induced arthritis

Collagen-induced arthritis (CIA) is an established mouse model of disease with hallmarks of clinical rheumatoid arthritis. Histone/protein deacetylase inhibitors (HDACi) are known to inhibit the pathogenesis of CIA and other models of autoimmune disease, although the mechanisms responsible are unclear. Regulatory T cell (Treg) function is defective in rheumatoid arthritis. FOXP3 proteins in Tregs are present in a dynamic protein complex containing histone acetyltransferase and HDAC enzymes, and FOXP3 itself is acetylated on lysine residues. We therefore investigated the effects of HDACi therapy on regulatory T cell function in the CIA model. Administration of an HDACi, valproic acid (VPA), significantly decreased disease incidence (p<0.005) and severity (p<0.03) in CIA. In addition, VPA treatment increased both the suppressive function of CD4(+)CD25(+) Tregs (p<0.04) and the numbers of CD25(+)FOXP3(+) Tregs in vivo. Hence, clinically approved HDACi such as VPA may limit autoimmune disease in vivo through effects on the production and function of FOXP3(+) Treg cells.

The role of HER2 in early breast cancer metastasis and the origins of resistance to HER2-targeted therapies

The HER2 gene encodes the receptor tyrosine kinase HER2 and is often over-expressed or amplified in breast cancer. Up-regulation of HER2 contributes to tumor progression. Many aspects of tumor growth are favorably affected through activation of HER2 signaling. Indeed, HER2 plays a role in increasing proliferation and survival of the primary tumor and distant lesions which upon completion of full transformation cause metastases. P185(HER2/neu) receptors and signaling from them and associated molecules increase motility of both intravasating and extravasating cells, decrease apoptosis, enhance signaling interactions with the microenvironment, regulate adhesion, as well as a multitude of other functions. Recent experimental and clinical evidence supports the view that the spread of incompletely transformed cells occurs at a very early stage in tumor progression. This review concerns the identification and characterization of HER2, the evolution of the metastasis model, and the more recent cancer stem cell model. In particular, we review the evidence for an emerging mechanism of HER2(+) breast cancer progression, whereby the untransformed HER2-expressing cell shows characteristics of stem/progenitor cell, metastasizes, and then completes its final transformation at the secondary site.

FOXP3 activation in Treg cells, - atomic level aspects of FOXP3 structure and biochemistry that govern function (89.4)

The path by which signaling transduction from the cell surface to the nucleus leads to FOXP3 activation and function is undefined. The additional complexity of creation of an ordered FOXP3 ensemble of transcriptional cofactors on chromatin is not understood. FOXP3 activation in Treg cells may be regulated by extra-cellular stimuli that occur through innate, toll-like and cytokine receptors. Our studies found that TCR receptor and pro-inflammatory cytokine signals including TGF-beta and IL-6 regulate FOXP3 binding to DNA in human CD4+CD25+ Treg cells. Here we report our recent progress in understanding the role of cell surface receptor signals and pro-inflammatory cytokines in regulating biochemical modifications of the FOXP3 molecule altering its activity in Treg cells. We have now determined the biochemical features of how pro-inflammatory cytokines and pharmaceutical agents affect FOXP3 activity, and consequently how they may affect immune responses in human inflammatory disease. Moreover, we also have deduced the atomic structure of large parts of the FOXP3 molecule including the zinc finger and leucine zipper domains. These regions are important for dimerization and oligomerization of FOXP3 as well as interactions with other molecules. Our structural and biochemical studies establish the atomic and molecular basis for understanding human XLAAD/IPEX autoimmune diseases.

Research grants include NIH AI073489-01A1 (M.I.G.) and Nidus Laboratories (B.L., and Z.Z.).

Structural aspects of the FOXP3 regulatory complex as an immunopharmacological target

The forkhead family transcription factor FOXP3 plays a fundamental role in immune homeostasis. FOXP3 dysfunction in regulatory T cells (Tregs) contributes to multiple disease processes such as autoimmunity, tumor development, and viral infection. FOXP3 cooperates and associates with a group of other transcriptional factors, co-repressors and co-activators in Tregs to form one or more dynamic regulatory complexes. These ensembles communicate with multiple key signaling pathways to either upregulate or downregulate the expression of downstream target genes such as cytokines and cell surface receptors, which are critical for the control of normal immune responses. Although the details of the underlying mechanism by which FOXP3 operates as a transcriptional repressor or an activator is largely undefined, FOXP3(+) Tregs based cellular therapies have been studied in animal models. Our recent studies concerning the FOXP3 complex ensemble provide structural and biochemical insights into FOXP3 function of Tregs, which are essential to the development of novel immunopharmacological agents for treating human immunological disease.

Mechanisms of resistance to ErbB-targeted cancer therapeutics

The ErbB receptors, such as EGFR, have been intensely pursued as targets for cancer therapeutics. However, a large percentage of patients who are initially responsive to ErbB-targeted therapies experience tumor recurrence and become refractory to therapy. In this issue of the JCI, Guix et al. demonstrate that downregulation of IGF-binding protein 3 (IGFBP-3) and -4, the negative regulators of IGF-I receptor signaling, contributes to the resistance of human squamous cell carcinomas to the EGFR inhibitor gefitinib (see the related article beginning on page 2609). Understanding the mechanisms involved in the resistance of some tumors to ErbB-targeted molecules may provide guidelines for developing more efficient therapeutic approaches.

TGF-beta and IL-6 signals modulate chromatin binding and promoter occupancy by acetylated FOXP3

Expression of FOXP3, a potent gene-specific transcriptional repressor, in regulatory T cells is required to suppress autoreactive and alloreactive effector T cell function. Recent studies have shown that FOXP3 is an acetylated protein in a large nuclear complex and FOXP3 actively represses transcription by recruiting enzymatic corepressors, including histone modification enzymes. The mechanism by which extracellular stimuli regulate the FOXP3 complex ensemble is currently unknown. Although TGF-beta is known to induce murine FOXP3(+) Treg cells, TGF-beta in combination with IL-6 attenuates the induction of FOXP3 functional activities. Here we show that TCR stimuli and TGF-beta signals modulate the disposition of FOXP3 into different subnuclear compartments, leading to enhanced chromatin binding in human CD4(+)CD25(+) regulatory T cells. TGF-beta treatment increases the level of acetylated FOXP3 on chromatin and site-specific recruitment of FOXP3 on the human IL-2 promoter. However, the proinflammatory cytokine IL-6 down-regulates FOXP3 binding to chromatin in the presence of TGF-beta. Moreover, histone deacetylation inhibitor (HDACi) treatment abrogates the down-regulating effects of IL-6 and TGF-beta. These studies indicate that HDACi can enhance regulatory T cell function via promoting FOXP3 binding to chromatin even in a proinflammatory cellular microenvironment. Collectively, our data provide a framework of how different signals affect intranuclear redistribution, posttranslational modifications, and chromatin binding patterns of FOXP3.

Non-invasive, ultra-sensitive, high-throughput assays to quantify rare biomarkers in the blood

Many diseases are easier to treat and control when detected at an early stage of disease progression. Often, disease-related antigens or biomarkers are shed from the primary site and present in the blood. Unfortunately, there are very few tests capable of detecting these rare biomarkers in the blood. A blood test would be very useful to diagnose the disease earlier, monitor effectiveness of treatments, predict recurrence, and monitor recurrence. There is certainly a need to develop assays that are ultra-sensitive, non-invasive, and high-throughput. Here we describe several highly sensitive immunological assays we have developed to detect rare serum antigens. Initially we created an assay named immuno-detection amplified by T7 RNA polymerase (IDAT). To enhance the effectiveness and streamline the procedure, this assay was amended to the facile amplification system termed fluorescent amplification catalyzed by T7 polymerase technique (FACTT). These assays have been used to analyze the tumor antigen HER2 and the prion protein PrPSc. They can also be applied to other tumor markers or antigens from a variety of diseases such as cardiovascular disease, rheumatoid arthritis, Alzheimer's disease, Parkinson's disease, and hepatitis. These tests are not limited to testing only serum, but may also be applicable to detecting biomarkers in tissue, saliva, urine, cerebrospinal fluid, etc. Clearly, the FACTT-based technology represents an important step in the detection of rare molecules in fluids or tissues for a variety of diseases.