Therapy of experimental hepatic cancers with cytotoxic peptide analogs targeted to receptors for luteinizing hormone-releasing hormone, somatostatin or bombesin

Sequence modification of heptapeptide selected by phage display as homing device for HT-29 colon cancer cells to improve the anti-tumour activity of drug delivery systems

Development of peptide-based conjugates for targeted tumour therapy is a current research topic providing new possibilities in cancer treatment. In this study, VHLGYAT heptapeptide selected by phage display technique for HT-29 human colon cancer was investigated as homing peptide for drug delivery. Daunomycin was conjugated to the N-terminus of the peptide directly or through Cathepsin B cleavable spacers. Conjugates showed moderate in vitro cytostatic effect. Therefore, sequence modifications were performed by Ala-scan and positional scanning resulting in conjugates with much higher bioactivity. Conjugates in which Gly was replaced by amino acids with bulky apolaric side chains provided the best efficacy. The influence of the cellular uptake, stability and drug release on the anti-tumour activity was investigated. It was found that mainly the difference in the cellular uptake of the conjugates generated the distinct effect on cell viability. One of the most efficient conjugate Dau = Aoa-LRRY-VHLFYAT-NH₂ showed tumour growth inhibition on orthotopically developed HT-29 colon cancer in mice with negligible toxic side effect compared to the free drug. We also indicate that this sequence is not specific to HT-29 cells, but it has a remarkable effect on many other cancer cells. Nevertheless, the Phe-containing conjugate was more active in all cases compared to the conjugate with the parent sequence. The literature data suggested that this sequence is highly overlapped with peptides that recognize Hsp70 membrane bound protein overexpressed in many types of tumours.

Target-specific delivery of siRNA into hepatoma cells' cytoplasm by bifunctional carrier peptide

RNA interference (RNAi) is among the most potential approach for the therapy of hepatocellular carcinoma and the major barrier hindering siRNA therapeutics is the low efficiency of delivery to the desired cells. The current study aimed at developing a novel peptide for more efficient hepatoma targeted siRNA delivery, by combining luteinizing hormone-releasing hormone with hepatoma targeting specificity and MPG^△NLS with cytoplasm-delivery tendency. The developed bifunctional peptide LHRH-MPG^△NLS and siRNA were mixed together and resulted in LHRH-MPG^△NLS/siRNA polyplexes through self-assembly. The polyplexes were characterized by agarose gel retardation and dynamic light scatting analysis. Hepatoma targeting specificity was analyzed with the GE IN Cell Analyzer 2000 High-Content Cellular Analysis System after cell transfection, and the effect of RNA interference was detected by RT-PCR. The results demonstrated that LHRH-MPG^△NLS was able to assemble with siRNA to form stable and nano-sized peptide/siRNA polyplexes, which could inhibit the expression of the target gene and was essentially non-cytotoxic, as compared with the commercial transfection reagent lipofectamine 2000.

Expression of hypothalamic neurohormones and their receptors in the human eye

Extrapituitary roles for hypothalamic neurohormones have recently become apparent and clinically relevant, based on the use of synthetic peptide analogs for the treatment of multiple conditions including cancers, pulmonary edema and myocardial infarction. In the eye, it has been suggested that some of these hormones and their receptors may be present in the ciliary body, iris, trabecular meshwork and retina, but their physiological role has yet to be elucidated. Our study intends to comprehensively demonstrate the expression of some hypothalamic neuroendocrine hormones and their receptors within different retinal and extraretinal structures of the human eye. Immunofluorescence, Western blot analysis, and RT-PCR were used to evaluate the qualitative and quantitative expression of Luteinizing Hormone Releasing Hormone (LHRH), Growth Hormone Releasing Hormone (GHRH), Thyrotropin Releasing Hormone (TRH), Gastrin Releasing Peptide (GRP) and Somatostatin as well as their respective receptors (LHRH-R, GHRH-R, TRH-R, GRP-R, SST-R1) in cadaveric human eye tissue and in paraffinized human eye tissue sections. The hypothalamic hormones LHRH, GHRH, TRH, GRP and Somatostatin and their respective receptors (LHRH-R, GHRH-R, TRH-R, GRPR/BB2 and SST-R1), were expressed in the conjunctiva, cornea, trabecular meshwork, ciliary body, lens, retina, and optic nerve.

Calf Spleen Extractive Injection (CSEI), a small peptides enriched extraction, induces human hepatocellular carcinoma cell apoptosis via ROS/MAPKs dependent mitochondrial pathway

Calf Spleen Extractive Injection (CSEI), a small peptides enriched extraction, performs immunomodulatory activity on cancer patients suffering from radiotherapy or chemotherapy. The present study aims to investigate the anti-hepatocellular carcinoma effects of CSEI in cells and tumor-xenografted mouse models. In HepG2 and SMMC-7721 cells, CSEI reduced cell viability, enhanced apoptosis rate, caused reactive oxygen species (ROS) accumulation, inhibited migration ability, and induced caspases cascade and mitochondrial membrane potential dissipation. CSEI significantly inhibited HepG2-xenografted tumor growth in nude mice. In cell and animal experiments, CSEI increased the activations of pro-apoptotic proteins including caspase 8, caspase 9 and caspase 3; meanwhile, it suppressed the expressions of anti-apoptotic protein B-cell lymphoma 2 (Bcl-2) and anti-oxidation proteins, such as nuclear factor-erythroid 2 related factor 2 (Nrf2) and catalase (CAT). The enhanced phosphorylation of P38 and c-JunN-terminalkinase (JNK), and decreased phosphorylation of extra cellular signal-regulated protein kinase (ERKs) were observed in CSEI-treated cells and tumor tissues. CSEI-induced cell viability reduction was significantly attenuated by N-Acetyl-l-cysteine (a ROS inhibitor) pretreatment. All data demonstrated that the upregulated oxidative stress status and the altered mitogen-activated protein kinases (MAPKs) phosphorylation contributed to CSEI-driven mitochondrial dysfunction. Taken together, CSEI exactly induced apoptosis in human hepatocellular carcinoma cells via ROS/MAPKs dependent mitochondrial pathway.

The use of peptide analogs for the treatment of gastrointestinal, pancreatic, liver and urinary bladder cancers

Peptide hormones can influence the development and growth of many cancers which are not considered classical hormone-dependent tumors. Analogs of somatostatin, bombesin/gastrin-releasing peptide (GRP), luteinizing hormone-releasing hormone (LH-RH) and growth hormone-releasing hormone (GH-RH) can interfere with receptors on tumor cells or intracellular pathways that are important in cell proliferation and in this way inhibit tumor growth. The first part of this review explains how these peptide hormones and their analogs affect tumors. The second part of this review describes how various hormone analogs can be used for the treatment of gastric, colorectal, pancreatic, liver and urinary bladder cancers. These tumors are major health problems worldwide and their treatment remains a great challenge. Receptors for somatostatin, bombesin/GRP, LH-RH and GH-RH are present in a large percentage of these cancers. We have developed a series of cytotoxic peptides based on doxorubicin or its derivative 2-pyrrolino-doxorubicin coupled to an analog of LH-RH, somatostatin or bombesin. This new class of targeted analogs might provide a more effective therapy for various cancers that express receptors for these carrier peptides, while producing significantly reduced peripheral toxicity. Under experimental conditions, these peptide hormone analogs strongly inhibited the growth of these tumors. Cytotoxic analogs were particularly effective on tumors that express the specific peptide receptors and acted more powerfully than the carrier peptide or the cytotoxic compound alone. Clinical trials on these peptide analogs are in progress.

TAT-LHRH conjugated low molecular weight chitosan as a gene carrier specific for hepatocellular carcinoma cells

To develop a chitosan-based nonviral gene carrier capable of delivering genes specifically into hepatoma cells, a bifunctional peptide composed of the TAT (transactivator of transcription) peptide and luteinizing hormone-releasing hormone (LHRH) was conjugated with low molecular weight chitosan, resulting in a TAT-LHRH-chitosan conjugate (TLC). TLC/DNA nanoparticles (TLCDNPs) were characterized by agarose gel retardation, atomic force microscopy, and dynamic light scattering analysis. In vitro targeting specificity and transfection efficiency were analyzed with a GE IN Cell Analyzer 2000 High-Content Cellular Analysis System. The results demonstrated that TLC had stronger DNA condensing power than unmodified chitosan, and that TLCDNPs were of roughly round shape with average diameter of 70-85 nm and zeta potential of +30 mV and were relatively stable in solution. The in vitro study demonstrated TLC was highly selective for hepatoma cells and essentially nontoxic.

Targeting triple-negative breast cancer through the somatostatin receptor with the new cytotoxic somatostatin analogue AN-162 [AEZS-124]

Previously, we have shown that the targeted cytotoxic somatostatin (sst) analogue AN-162 [AZSE-124] inhibits the growth of MDA-MB-231 human breast cancers xenografted into nude mice. In this study, we examined the trafficking of AN-162 into the cell, the expression of the somatostatin receptors (sstr) in specimens of human triple-negative breast cancers (TNBC), and the effect of AN-162 on HCC 1806 human TNBC xenografts. The expression of sstr in TNBC tumor samples was investigated by immunohistochemical staining. The expression of sstr in HCC 1806 was evaluated by reverse transcription PCR. Internalization studies with I-labeled AN-162 were carried out and the autofluorescence sign of doxorubicin moiety in the cell nucleus after incubation with AN-162 was measured using a fluorescence assay. The effects of AN-162 on the growth of HCC 1806 xenografted into nude mice were studied. A fluorescence microscopy cytotoxicity assay in vitro to detect cell death after treatment with AN-162 was also carried out. About 28% of TNBC tumor specimens showed a positive staining for sstr subtype 2a. HCC 1806 expresses all five subtypes of sstr. In the fluorescence cytotoxicity assay, dead HCC 1806 cells were found 24 h after incubation with AN-162. The growth of HCC 1806 tumors in nude mice was significantly inhibited by treatment with AN-162. AN-162 was internalized into the HCC 1806 cells and doxorubicin moiety was detected in the cell nuclei. This study is the first to show that the trafficking of the cytotoxic sst analogue AN-162 into the cell is mediated by sstr. Our work shows that the growth of xenografted HCC 1806 TNBCs can be effectively inhibited in vivo with AN-162. This investigation provides information on the mechanism of action and efficacy of this new targeted cytotoxic sst analogue and identifies in this relation the sstr as a favorable therapeutic target in TNBC.

Powerful inhibition of in-vivo growth of experimental hepatic cancers by bombesin/gastrin-releasing peptide antagonist RC-3940-II

Hepatic carcinoma is a major health problem worldwide. Its incidence is increasing in Western countries and there is currently no effective systemic therapy against it. Targeted treatment modalities developed in the past few years have provided very limited success. Development of new treatment strategies is therefore essential. We investigated the effects of bombesin/gastrin-releasing peptide (BN/GRP) antagonist RC-3940-II on experimental human liver cancers in nude mice. SK-Hep-1 and Hep-G2 cancers transplanted subcutaneously into nude mice were treated daily with 10 or 20 µg of RC-3940-II. Tumor growth was monitored for 50-184 days in five experiments. Tumor gene expression was analyzed with PCR array and protein expression by immunoblotting. Characteristics of BN/GRP receptors in the tumors were analyzed by binding assays. Effects of RC-3940-II on cell proliferation were investigated in vitro. RC-3940-II inhibited the growth of SK-Hep-1 cancers in nude mice by 65-98%, with total regression in 9 of 36 tumors in three experiments. The BN/GRP antagonist inhibited the growth of Hep-G2 cancers as well by 73-82% in two experiments, being effective even on originally large tumors. Gene expression analysis showed an increase in several angiogenesis inhibitors and decrease in proangiogenic genes after RC-3940-II treatment. Receptor assays demonstrated high-affinity binding sites for BN/GRP in both tumor lines. BN/GRP antagonist RC-3940-II powerfully inhibits growth of SK-Hep-1 and Hep-G2 cancers in nude mice. Its effect may be linked to changes in expression of those cancer genes important in angiogenesis, invasion, and metastasis. RC-3940-II may be considered for further investigations in treatment of liver cancers.

Growth inhibition of tumor cells in vitro by using monoclonal antibodies against gonadotropin-releasing hormone receptor

As the continuation of a previous study, synthetic peptides corresponding to the extracellular domains of human gonadotropin-releasing hormone (GnRH) receptor were used to generate additional monoclonal antibodies which were further characterized biochemically and immunologically. Among those identified to recognize GnRH receptor, monoclonal antibodies designated as GHR-103, GHR-106 and GHR-114 were found to exhibit high affinity (Kd < or = 1 x 10(-8) M) and specificity to GnRH receptor as judged by the whole cell binding immunoassay and Western blot assay. Both anti-GnRH receptor monoclonal antibodies and GnRH were shown to compete for the same binding site of GnRH receptor on the surface of cultured cancer cells. Growth inhibitions of cancer cells cultured in vitro were demonstrated by cellular apoptosis experiments (TUNEL and MTT assays) under different conditions of treatment with GHR-106 monoclonal antibody or GnRH analogs. It was generally observed that both GnRH I and GHR-106 effectively induce the apoptosis of cultured cancer cells as determined by TUNEL and MTT assays. Consistently, suppressions of gene expressions at mRNA levels were demonstrated with several ribosomal proteins (P0, P1, P2 and L37), when cancer cells were incubated with GnRH or GHR-106. The widespread expressions of GnRH receptor in almost all of the studied human cancer cell lines were also demonstrated by RT-PCR and Western blot assay, as well as indirect immunofluorescence assay with either of these monoclonal antibodies as the primary antibody. In view of the longer half life of antibodies as compared to that of GnRH or its analogs, anti-GnRH receptor monoclonal antibodies in humanized forms could function as GnRH analogs and serve as an ideal candidate of anti-cancer drugs for therapeutic treatments of various cancers in humans as well as for fertility regulations.

Receptor-mediated tumor targeting based on peptide hormones

IMPORTANCE OF THE FIELD

Tumor targeting with peptides is based on the discovery that receptors for many regulatory peptides are overexpressed in tumor cells, compared with their expression in normal tissues. Consequently, these peptides and their analogues can be used as carriers/targeting moieties for the preparation of diagnostic and therapeutic agents that have increased selectivity and decreased peripheral toxicity.

AREAS COVERED IN THIS REVIEW

Here an overview is given of the most relevant gonadotropin-releasing hormone (GnRH) and somatostatin derivatives, as well as of their applications in cancer diagnosis and therapy. For this purpose, recently published data in these areas (mostly articles published from 2000 to 2009) were reviewed.

WHAT THE READER WILL GAIN

In contrast to other regulatory peptides that stimulate the tumor growth, GnRH and somatostatin derivatives have inhibitory effect; therefore, they were used primarily for the preparation of various conjugates to be used in targeted chemotherapy, targeted radiotherapy, photodynamic therapy, boron neutron capture therapy and cancer diagnosis. Some of these conjugates have already found clinical applications, whereas others are now in preclinical and clinical trials.

TAKE HOME MESSAGE

Tumor targeting with hormone peptides provides a basis for the development of new diagnostic and therapeutic approaches for cancer.

Somatostatin and somatostatin receptors: implications for neoplastic growth and cancer biology

Somatostatin agonists (SM-As) are capable of achieving durable symptomatic relief and significant clinical responses in certain tumours. Herein, we review the diverse direct and indirect mechanisms of antineoplastic activity elicited by SM-As as well as the hurdles that complicate their use as monotherapies in a broader range of malignancies. Emphasis is placed on recent clinical attempts to neutralise the IGF-mediated survival factor effects in the bone metastasis microenvironment in advanced prostate cancer. The first clinical trials of this 'anti-survival factor manipulation' strategy utilised the ability of SM-As to suppress the growth hormone-dependent liver-derived IGF-I bioavailability in combination with other drugs, such as dexamethasone, zolendronate and oestrogens, acting systemically and at the bone metastasis microenvironment. These regimens restored androgen ablation responsiveness in stage D3 prostate cancer patients and successfully produced objective clinical responses while only mild toxicities were observed. Furthermore, we focus on the preclinical experimental data of a targeted SM-A coupled to the super-potent doxorubicin derivative AN-201. The resulting conjugate (AN-238) has shown increased antitumour potency with a favourable toxicity profile. The potential use of novel SM-As as anticancer drugs is discussed in relation to data suggesting other direct and indirect treatment approaches pertaining to the somatostatin system.

Preclinical evaluation of properties of a new targeted cytotoxic somatostatin analog, AN-162 (AEZS-124), and its effects on tumor growth inhibition

In view of findings that various tumors express receptors for somatostatin, a new targeted cytotoxic analog of somatostatin, AN-162 (AEZS-124), consisting of doxorubicin linked through glutaric acid to the somatostatin octapeptide RC-121 was developed in our laboratory. We studied the toxicity in vivo and the effect of AN-162 on growth of the MDA-MB-231 estrogen-independent human breast cancer cell line xenografted into nude mice. AN-162 induced significant tumor growth inhibition compared with the control and the group treated with doxorubicin in equimolar doses. We also evaluated the stability of AN-162 in various sera in vitro, as this conjugate is susceptible to hydrolysis by serum carboxylesterase enzymes in the circulation. This study shows for the first time that AN-162 is a safe and effective compound for the treatment of experimental breast cancer. Our findings support the concept of targeted chemotherapy based on cytotoxic peptide analog AN-162 for the treatment of breast cancers and other cancers expressing somatostatin receptors.