Synthetic peptide derived from alpha-fetoprotein inhibits growth of human breast cancer: investigation of the pharmacophore and synthesis optimization

AFP peptide (AFPep) as a potential growth factor for prostate cancer

Prostate cancer is the most common cancer among men in the USA. A peptide derived from the active site of alpha-fetoprotein (AFP), known as AFPep, has been shown to be efficacious in inhibiting breast cancer growth. The role of this derived peptide AFPep in the development of prostate cancer has yet to be studied. To investigate the role of AFPep on prostate cancer, we used the PC-3 and DU-145 cell lines. We found that through key anti-apoptosis and pro-proliferation molecules, AFPep enhances the proliferation of DU-145 prostate cancer cells. The anti-proliferative molecules p18, p21, and p27, along with the pro-apoptotic molecules Fas and Bax, were all down-regulated in DU-145 cell lines treated with AFPep. Conversely, AFPep was not found to have a proliferative effect on the PC-3 prostate cancer cell line. This finding suggests the effects of AFPep to be cell line-specific in prostate cancer. Further investigation into the effects of AFPep could lead to new areas of treating prostate cancer.

Elucidating Solution Structures of Cyclic Peptides Using Molecular Dynamics Simulations

Protein-protein interactions are vital to biological processes, but the shape and size of their interfaces make them hard to target using small molecules. Cyclic peptides have shown promise as protein-protein interaction modulators, as they can bind protein surfaces with high affinity and specificity. Dozens of cyclic peptides are already FDA approved, and many more are in various stages of development as immunosuppressants, antibiotics, antivirals, or anticancer drugs. However, most cyclic peptide drugs so far have been natural products or derivatives thereof, with de novo design having proven challenging. A key obstacle is structural characterization: cyclic peptides frequently adopt multiple conformations in solution, which are difficult to resolve using techniques like NMR spectroscopy. The lack of solution structural information prevents a thorough understanding of cyclic peptides' sequence-structure-function relationship. Here we review recent development and application of molecular dynamics simulations with enhanced sampling to studying the solution structures of cyclic peptides. We describe novel computational methods capable of sampling cyclic peptides' conformational space and provide examples of computational studies that relate peptides' sequence and structure to biological activity. We demonstrate that molecular dynamics simulations have grown from an explanatory technique to a full-fledged tool for systematic studies at the forefront of cyclic peptide therapeutic design.

Efficacy and tolerability of AFPep, a cyclic peptide with anti-breast cancer properties

PURPOSE

The purpose of this study is to assess the efficacy and safety profile of AFPep, a 9-amino acid cyclic peptide prior to its entry into pre-clinical toxicology analyses en route to clinical trials.

METHODS

AFPep was assessed for anti-estrogenic activity in a mouse uterine growth assay and for breast cancer therapeutic efficacy in a human tumor xenograft model in mice. AFPep was assessed for tolerability in a variety of in vivo models, notably including assessment for effects on rat liver and human hepatocellular carcinoma cell lines and xenografts.

RESULTS

AFPep arrests the growth of human MCF-7 breast cancer xenografts, inhibits the estrogen-induced growth of mouse uteri, and does not affect liver growth nor stimulate growth of human hepatocellular carcinoma cell lines when growing in vitro or as xenografts in vivo. AFPep is well tolerated in mice, rats, dogs, and primates.

CONCLUSIONS

AFPep is effective for the treatment of ER-positive breast cancer and exhibits a therapeutic index that is substantially wider than that for drugs currently in clinical use. The data emphasize the importance of pursuing pre-clinical toxicology studies with the intent to enter clinical trials.

Orally Absorbed Cyclic Peptides

Peptides and proteins are not orally bioavailable in mammals, although a few peptides are intestinally absorbed in small amounts. Polypeptides are generally too large and polar to passively diffuse through lipid membranes, while most known active transport mechanisms facilitate cell uptake of only very small peptides. Systematic evaluations of peptides with molecular weights above 500 Da are needed to identify parameters that influence oral bioavailability. Here we describe 125 cyclic peptides containing four to thirty-seven amino acids that are orally absorbed by mammals. Cyclization minimizes degradation in the gut, blood, and tissues by removing cleavable N- and C-termini and by shielding components from metabolic enzymes. Cyclization also folds peptides into bioactive conformations that determine exposure of polar atoms to solvation by water and lipids and therefore can influence oral bioavailability. Key chemical properties thought to influence oral absorption and bioavailability are analyzed, including molecular weight, octanol-water partitioning, hydrogen bond donors/acceptors, rotatable bonds, and polar surface area. The cyclic peptides violated to different degrees all of the limits traditionally considered to be important for oral bioavailability of drug-like small molecules, although fewer hydrogen bond donors and reduced flexibility generally favored oral absorption.

High efficiency intranasal drug delivery using Intravail® alkylsaccharide absorption enhancers

A new class of alkylsaccharide transmucosal delivery enhancement agents are described that overcome the principal limitations preventing broad acceptance of intranasal administration for many potential applications in systemic drug delivery, namely, poor transmucosal absorption and damage to the nasal mucosa. This review will describe recent developments in use of these excipients in human clinical trials and preclinical studies along with their chemical and pharmacological properties and explore commercial implications of the use of these excipients in introduction of new intranasal formulations of peptidic and nonpeptidic drugs.

Synthesis and evaluation of technetium-99m-labeled bioreductive pharmacophores conjugated with amino acids and peptides for tumor imaging

Development of molecular imaging agents to target tumor has become a major trend in nuclear medicine. With the aim to develop new potential 99mTc-radiopharmaceuticals for targeting tumor, we have synthesized 5-nitroimidazolyl amino acids and RGD-coupled 2-nitroimidazoles. Technetium-99m radiolabeling with high radiochemical purity (>90%) was achieved for all the compounds. The radiolabeled complexes exhibited substantial in vitro stability in saline, serum, and histidine solution (10(-2) m). Cell binding studies in EAC and B16F10 cell lines also revealed rapid and comparatively high cellular internalization. Among all the compounds studied, the binding of 99mTc(CO)3-5 to B16F10 cells was moderately inhibited by the competitive peptide c[RGDfV], suggesting specificity of the radioligand toward αvβ3 receptor. However, no significant displacement of bound radioligand was observed when the binding of the 99mTc-labeled complexes to above cells was challenged with excess competitive peptide. Fluorescent microscopy study provided direct evidence of intracellular localization of 5(6)-carboxyfluorescein-labeled 2-nitroimidazolyl-RGD-peptide in αvβ3-positive B16F10 mouse melanoma cell line. The ligands caused only 8-13% of hemolysis toward rat erythrocytes at concentrations as high as 100 μm. Imaging and biodistribution studies were performed in Swiss albino mice bearing induced tumor. 99mTc-1 and 99mTc(CO)3-5 demonstrated a very favorable in vivo profile. Selective uptake and retention in tumor with encouraging tumor/muscle and tumor/blood ratio and significant cellular uptake of fluorescence-labeled-2-nitroimidazolyl RGD indicate the great potentiality of the pharmacophore for further evaluation as potential molecular imaging agent in cancer diagnosis.

Design and synthesis of biologically active peptides: a 'tail' of amino acids can modulate activity of synthetic cyclic peptides

In earlier work, we synthesized a cyclic 9-amino acid peptide (AFPep, cyclo[EKTOVNOGN]) and showed it to be useful for prevention and therapy of breast cancer. In an effort to explore the structure-function relationships of AFPep, we have designed analogs that bear a short 'tail' (one or two amino acids) attached to the cyclic peptide distal to its pharmacophore. Analogs that bore a tail of either one or two amino acids, either of which had a hydrophilic moiety in the side chain (e.g., cyclo[EKTOVNOGN]FS) exhibited greatly diminished biological activity (inhibition of estrogen-stimulated uterine growth) relative to AFPep. Analogs that bore a tail of either one or two amino acids which had hydrophobic (aliphatic or aromatic) side chains (e.g., cyclo[EKTOVNOGN]FI) retained (or had enhanced) growth inhibition activity. Combining in the same biological assay a hydrophilic-tailed analog with either AFPep or a hydrophobic-tailed analog resulted in decreased activity relative to that for AFPep or for the hydrophobic-tailed analog alone, suggesting that hydrophilic-tailed analogs are binding to a biologically active receptor. An analog with a disrupted pharmacophore (cyclo[EKTOVGOGN]) exhibited little or no growth inhibition activity. An analog with a hydrophilic tail and a disrupted pharmacophore (cyclo[EKTOVGOGN]FS) exhibited no growth inhibition activity of its own and did not affect the activity of a hydrophobic-tailed analog, but enhanced the growth inhibition activity of AFPep. These results are discussed in the context of a two-receptor model for binding of AFPep and ring-and-tail analogs. We suggest that tails on cyclic peptides may comprise a useful method to enhance diversity of peptide design and specificity of ligand-receptor interactions.

Mechanism of Cancer Growth Suppression of Alpha-Fetoprotein Derived Growth Inhibitory Peptides (GIP): Comparison of GIP-34 versus GIP-8 (AFPep). Updates and Prospects

The Alpha-fetoprotein (AFP) derived Growth Inhibitory Peptide (GIP) is a 34-amino acid segment of the full-length human AFP molecule that inhibits tumor growth and metastasis. The GIP-34 and its carboxy-terminal 8-mer segment, termed GIP-8, were found to be effective as anti-cancer therapeutic peptides against nine different human cancer types. Following the uptake of GIP-34 and GIP-8 into the cell cytoplasm, each follows slightly different signal transduction cascades en route to inhibitory pathways of tumor cell growth and proliferation. The parallel mechanisms of action of GIP-34 versus GIP-8 are demonstrated to involve interference of signaling transduction cascades that ultimately result in: (1) cell cycle S-phase/G2-phase arrest; (2) prevention of cyclin inhibitor degradation; (3) protection of p53 from inactivation by phosphorylation; and (4) blockage of K+ ion channels opened by estradiol and epidermal growth factor (EGF). The overall mechanisms of action of both peptides are discussed in light of their differing modes of cell attachment and uptake fortified by RNA microarray analysis and electrophysiologic measurements of cell membrane conductance and resistance. As a chemotherapeutic adjunct, the GIPs could potentially aid in alleviating the negative side effects of: (1) tamoxifen resistance, uterine hyperplasia/cancer, and blood clotting; (2) Herceptin antibody resistance and cardiac (arrest) arrhythmias; and (3) doxorubicin's bystander cell toxicity.

Characterization of surface modification on self-assembled monolayer-based piezoelectric crystal immunosensor for the quantification of serum α-fetoprotein

Self-assembled monolayers (SAMs) on coinage metallic material can provide versatile modeling systems for studies of interfacial electron transfer, biological interactions, molecular recognition and other interfacial phenomena. Recently, a bio-sensing system has been produced by analysis of the attachment of antibody using alkanethiols, to form SAMs on the face of Au-quartz crystal microbalance (QCM) surfaces. In this study, the attachment of anti-α-fetoprotein monoclonal antibody to a SAMs surface of 11-mercaptoundecanoic acid was achieved using water-soluble N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide as coupling agents. Surface analyses were utilized by X-ray photoelectron spectroscopy and atomic force microscopy. The quantization of immobilized antibody was characterized by the frequency shift of QCM and the radioactivity change of ¹²⁵I labeled antibody. The limit of detection and linear range of the calibration curve of the QCM method were 15 ng/ml and 15-850 ng/ml. The correlation coefficients of α-fetoprotein concentration between QCM and radioimmunoassay were 0.9903 and 0.9750 for the standards and serum samples, respectively. This report illustrates an investigation of SAMs for the preparation of covalently immobilized antibody biosensors.

Estrogen action: a historic perspective on the implications of considering alternative approaches

In the 50 years since the initial reports of a cognate estrogen receptor (ER), much has been learned about the diverse effects and mechanisms of estrogens, such as 17beta-estradiol (E(2)). This expert narrative review briefly summarizes perspectives and/or recent work of the authors, who have been addressing different aspects of estrogen action, but take a common approach of using alternative considerations to gain insight into mechanisms with clinical relevance, and inform future studies, regarding estrogen action. Their "Top Ten" favorite alternatives that are discussed herein are as follows. 1 - E(2) has actions by binding to a receptor that do not require its enzymatic conversion. 2 - Using a different strategy for antibody binding could make the estrogen receptor (ER) more discernible. 3 - Blocking ERs, rather than E(2) production, may be a useful strategy for breast cancer therapy. 4 - Secretion of alpha-fetoprotein (AFP), rather than only levels of E(2) and/or progesterone, may influence breast cancer risk. 5 - A peptide derived from the active site of AFP can produce the same benefits of the entire endogenous protein in endocrine cancers. 6 - Differential distribution of ER subtypes in the body and brain may underlie specific effects of estrogens. 7 - ERbeta may be sufficient for the trophic effects of estrogen in the brain, and ERalpha may be the primary target of trophic effects in the body. 8 - ERbeta may play a role in the trophic effects of androgens, and may also be relevant in the periphery. 9 - Downstream of E(2)'s effects at ERbeta, there may be consequences for biosynthesis of progestogens and/or androgens. 10 - Changes in histones and/or other factors, which may be downstream of ERbeta, potentially underlie the divergent effects of E(2) in the brain and peripheral tissues.

Computational approaches for the design of peptides with anti-breast cancer properties

Background: Breast cancer is the most common cancer among women. Tamoxifen is the preferred drug for estrogen receptor-positive breast cancer treatment, yet many of these cancers are intrinsically resistant to tamoxifen or acquire resistance during treatment. Therefore, scientists are searching for breast cancer drugs that have different molecular targets. Methodology: Recently, a computational approach was used to successfully design peptides that are new lead compounds against breast cancer. We used replica exchange molecular dynamics to predict the structure and dynamics of active peptides, leading to the discovery of smaller bioactive peptides. Conclusions: These analogs inhibit estrogen-dependent cell growth in a mouse uterine growth assay, a test showing reliable correlation with human breast cancer inhibition. We outline the computational methods that were tried and used along with the experimental information that led to the successful completion of this research.

A peptide derived from alpha-fetoprotein inhibits the proliferation induced by estradiol in mammary tumor cells in culture

This study was aimed to obtain additional information on the activity of a cyclized 9-amino acid peptide (cP) containing the active site of alpha fetoprotein, which inhibits the estrogen-stimulated proliferation of tumor cells in culture and of xenografts in immunodeficient mice. Breast cancer cells cultured in the presence of 2 nM estradiol were exposed to cP for different periods and their proliferation, estradiol binding parameters, clustering tendency and expression of E-cadherin and p21Cip1 were analyzed by biochemical and cell biology methods. The proliferation of MCF7 cells was significantly decreased by the addition of 2 microg/ml cP to the medium. cP did not increase cell death rate nor alter the number of binding sites for estradiol nor the endogenous aromatase activity of MCF7 cells. cP also decreased the proliferation of estrogen-dependent ZR75-1 cells but had no effect on estrogen-independent MDA-MB-231 cells. An increased nuclear p21Cip1 expression detected after cP treatment suggests that cP slows MCF7 cell proliferation via this regulator. We propose that cP could represent a novel breast cancer therapeutic agent whose mechanism of action is different from that of tamoxifen or of inhibitors of aromatase.

The alpha-fetoprotein-derived growth inhibitory peptide 8-mer fragment: review of a novel anticancer agent

This review describes the antigrowth and anticancer activities of the alpha-fetoprotein (AFP)-derived growth inhibitory peptide (GIP) 8-mer fragment. The 8-amino acid peptide (GIP-8) comprises the carboxy-terminal portion of a 34-amino acid peptide (GIP-34) previously identified as an occult epitopic segment of the full-length human AFP molecule. The GIP-8 segment has been chemically synthesized, purified, characterized, and bioassayed. The purified 8-mer segment was characterized as a random coil (disordered) structure extending from a C-terminal beta-hairpin that forms a horseshoe-shaped partially cyclic octapeptide; this structure can be formulated into a fully cyclic form by the addition of asparagine or glutamine residues. The pharmacophore of the octo- and nanopeptide forms is largely composed of a PXXP motif known to interact with Src-3 (SH3) domains of serine/theronine kinases. The GIP-8 has been shown to be growth-suppressive largely in estradiol (E2)-dependent neonatal and tumor-cell proliferation models and to inhibit tumor-cell adhesion to extracellular matrices. The 8-mer GIP displays antigrowth properties in immature mouse uterine cells and anticancer cell proliferation traits in estrogen receptor positive (ER(+)), but not (ER()) negative breast tumor cells. Even though its mechanism of action has not been fully elucidated, GIP-8 has been shown by computer modeling to dock with the extracellular loops of G-coupled seven transmembrane helical-like receptors, which could possibly interfere with signal transduction through MAP kinase pathways. It was apparent that the GIP-8 derived from the 34-mer GIP fragment of HAFP represented an E2-sensitive growth inhibitory motif, which allows the participation in cellular events, such as receptor binding, contact inhibition, extracellular matrix adhesion, angiogenesis, and T-cell activation. Thus, it was proposed that the 8-mer fragment derived from GIP could potentially serve as a lead compound for targeted cancer therapeutic agents of the biologic-response modifier type.

An alpha-fetoprotein-derived peptide reduces the uterine hyperplasia and increases the antitumour effect of tamoxifen

Tamoxifen (Tam) is effective for the treatment and prevention of breast cancer. However, it has toxic drawbacks and has limited-duration utility because, over time, human tumours become refractory to Tam. Recently, a new nontoxic peptide, alpha-fetoprotein-derived peptide (AFPep) has been proposed for the treatment and prevention of breast cancer. The purpose of this paper is to determine whether combining AFPep with Tam would increase efficacy and reduce toxicity in experimental models of breast cancer. Low doses of AFPep and Tam were more effective in combination than either agent alone against breast cancer growth in cell culture, in tumour-xenografted mice, and in carcinogen-exposed rats. alpha-Fetoprotein-derived peptide interfered with Tam-induced uterine hyperplasia in immature mice, and showed no toxic effects. Unlike Tam, AFPep did not inhibit binding of oestradiol (E(2)) to oestrogen receptor (ER). Thus, these two agents utilise different mechanisms to interfere with ER functionality, yet work cooperatively to reduce breast cancer growth and alleviate Tam's troubling toxicity of uterine hyperplasia and appear to be a rational combination for the treatment of ER-positive breast cancer.

Computational design and experimental discovery of an antiestrogenic peptide derived from alpha-fetoprotein

Breast cancer is the most common cancer among women, and tamoxifen is the preferred drug for estrogen receptor-positive breast cancer treatment. Many of these cancers are intrinsically resistant to tamoxifen or acquire resistance during treatment. Consequently, there is an ongoing need for breast cancer drugs that have different molecular targets. Previous work has shown that 8-mer and cyclic 9-mer peptides inhibit breast cancer in mouse and rat models, interacting with an unsolved receptor, while peptides smaller than eight amino acids did not. We show that the use of replica exchange molecular dynamics predicts the structure and dynamics of active peptides, leading to the discovery of smaller peptides with full biological activity. Simulations identified smaller peptide analogues with the same conserved reverse turn demonstrated in the larger peptides. These analogues were synthesized and shown to inhibit estrogen-dependent cell growth in a mouse uterine growth assay, a test showing reliable correlation with human breast cancer inhibition.

AFPep: an anti-breast cancer peptide that is orally active

BACKGROUND

We have synthesized a cyclic nonapeptide (AFPep) that is effective, after being administered by parenteral routes, for the treatment or the prevention of breast cancer. To test the hypothesis that AFPep remains safe and efficacious after oral administration, three different whole-animal bioassays were utilized, and the mechanism by which AFPep functions was investigated.

METHODS

Using a human breast cancer xenograft model in mice for therapeutic activity, a carcinogen-induced breast cancer model in rats for prevention efficacy, and a mouse uterus growth inhibition model of anti-estrogenic activity, AFPep was administered by oral gavage (p.o.) and its effects compared to those following intraperitoneal (i.p.) and subcutaneous (s.c.) administration. Toxicity studies evaluated body weights and organ weights in mice and rats receiving AFPep. Preliminary mechanistic studies were carried out in T47D human breast cancer cells growing in culture and evaluated the effect of AFPep on estrogen-stimulated cell growth, phosphorylation of the estrogen receptor (ER), and on level of ER-related kinases.

RESULTS

Orally administered AFPep stopped the growth of human tumor xenografts in mice, decreased the incidence and multiplicity of breast cancers in carcinogen-exposed rats, and inhibited the estrogen-stimulated growth of mouse uteri. In each of these systems, orally administered AFPep produced an effect similar to that obtained for AFPep administered by either i.p or s.c. routes. In rodents, no evidence of toxicity was seen for the peptide, even at very high doses. In culture, AFPep inhibited the estrogen-stimulated growth, but not the basal growth, of T47D cells, and it inhibited the estrogen-stimulated phosphorylation of Serine 118 in the ER of these cells, which was not explainable by early changes in ER-related kinases.

CONCLUSIONS

Chronic oral administration of AFPep appears to be safe and effective for the treatment or prevention of breast cancer in animal models.

Prevention of N-methyl-N-nitrosourea-induced breast cancer by alpha-fetoprotein (AFP)-derived peptide, a peptide derived from the active site of AFP

PURPOSE

alpha-Fetoprotein (AFP) is a protein of pregnancy associated with a decrease in lifetime risk of breast cancer in parous women. A synthetic, cyclic nonapeptide has been developed that mimics the antioncogenic active site of AFP. To test the hypothesis that the AFP-derived peptide (AFPep) can prevent breast cancer, the N-methyl-N-nitrosourea-induced breast cancer model was used in rats.

EXPERIMENTAL DESIGN

AFPep was given daily by injection beginning 10 days after N-methyl-N-nitrosourea treatment and continued for 23 days (a time designed to mimic pregnancy) or for other times to assess efficacy as a function of drug duration. Tumor incidence, multiplicity, and latency were noted as end points. At necropsy, pathology analysis of tumors and major organs were obtained.

RESULTS

AFPep prevented cancer in a dose-dependent fashion. Significantly longer mean tumor-free days (P < 0.02), lower tumor incidence (P = 0.004), and lower tumor multiplicity were observed for AFPep-treated groups. No evidence of host toxicity as measured by body weight, cage activity, fur texture, and organ weights (liver, uterus, heart, kidney, and spleen) were found in animals treated with AFPep. Mechanistic studies using transplantable human breast cancer xenografts showed that the peptide interfered with estrogen-dependent breast cancer growth inhibited the phosphorylation of the estrogen receptor and activated phosphorylation of p53.

CONCLUSIONS

AFPep is a well-tolerated, mechanistically novel, chemopreventive agent in models of breast cancer and warrants further development for the prevention and treatment of this disease in humans.