Suppression of tumor growth by intra-muscular transfer of naked DNA encoding adrenomedullin antagonist

Targeting the adrenomedullin-2 receptor for the discovery and development of novel anti-cancer agents

INTRODUCTION

Adrenomedullin (AM) is a peptide responsible for many physiological processes including vascular health and hormone regulation. Dysregulation of AM signaling can stimulate cancers by promoting proliferation, angiogenesis and metastasis. Two AM receptors contribute to tumor progression in different ways. Adrenomedullin-1 receptor (AM₁R) regulates blood pressure and blocking AM signaling via AM₁R would be clinically unacceptable. Therefore, antagonizing adrenomedullin-2 receptor (AM₂R) presents as an avenue for anti-cancer drug development.

AREAS COVERED

We review the literature to highlight AM's role in cancer as well as delineating the specific roles AM₁R and AM₂R mediate in the development of a pro-tumoral microenvironment. We highlight the importance of exploring the residue differences between the receptors that led to the development of first-in-class selective AM₂R small molecule antagonists. We also summarize the current approaches targeting AM and its receptors, their anti-tumor effects and their limitations.

EXPERT OPINION

As tool compounds, AM₂R antagonists will allow the dissection of the functions of CGRPR (calcitonin gene-related peptide receptor), AM₁R and AM₂R, and has considerable potential as a first-in-class oncology therapy. Furthermore, the lack of detectable side effects and good drug-like pharmacokinetic properties of these AM₂R antagonists support the promise of this class of compounds as potential anti-cancer therapeutics.

Adrenomedullin blockade suppresses sunitinib-resistant renal cell carcinoma growth by targeting the ERK/MAPK pathway

PURPOSE

To evaluate the mechanisms underlying sunitinib resistance in RCC and to identify targets that may be used to overcome this resistance.

RESULTS

Reanalysis of transcriptome microarray datasets (GSE64052 and GSE76068) showed that adrenomedullin expression was increased in sunitinib-resistant tumors. And adrenomedullin expression was increased in sunitinib-resistant tumor xenografts, accompanied by upregulation of phospho-ERK levels. However, blocking adrenomedullin inhibited sunitinib-resistant tumor growth. Treatment of RCC cells with sunitinib and ADM22-52 was superior to monotherapy with either agent. Additionally, adrenomedullin upregulated cAMP and activated the ERK/MAPK pathway, promoting cell proliferation, while knockdown of adrenomedullin inhibited RCC cell growth and invasion in vitro.

MATERIALS AND METHODS

We searched the Gene Expression Omnibus (GEO) database to find data regarding sunitinib-resistant RCC. These data were subsequently reanalyzed to identify targets that contribute to sunitinib resistance, and adrenomedullin upregulation was found to mediate sunitinib resistance in RCC. Then, we created an RCC mouse xenograft model. Mice were treated with sunitinib, an adrenomedullin receptor antagonist (ADM22-52), a MEK inhibitor (PD98059) and different combinations of these three drugs to investigate their effects on tumor growth. RCC cells (786-0) were cultured in vitro and treated with an ADM22-52 or PD98059 to determine whether adrenomedullin activates the ERK/MAPK pathway. Adrenomedullin was knocked down in 786-0 cells via siRNA, and the effects of this knockdown on cell were subsequently investigated.

CONCLUSIONS

Adrenomedullin plays an important role in RCC resistance to sunitinib treatment. The combination of sunitinib and an adrenomedullin receptor antagonist may result in better outcomes in advanced RCC patients.

Bench-to-bedside pharmacology of adrenomedullin

The bioactive peptide adrenomedullin (AM) exerts pleiotropic actions in various organs and tissues. In the heart, AM has an inhibitory effect on ventricular remodeling, suppressing cardiomyocyte hypertrophy and the proliferation of cardiac fibroblasts. This pharmacological property was shown not only in rat models of acute myocardial infarction, but also clinically in patients with this cardiac disease. An originally characterized feature of AM was a potent vasodilatory effect, but this peptide was found to be important for vascular integrity and angiogenesis. AM-induced angiogenesis is involved in tumor growth, while AM inhibits apoptosis of some types of tumor cell. A unique pharmacological property is anti-inflammatory activity, which has been characterized in sepsis and inflammatory bowel diseases; thus, there is an ongoing clinical trial to test the efficacy of AM for patients with intractable ulcerative colitis. These activities are assumed to be mediated via the specific receptor formed by calcitonin receptor-like receptor and receptor activity-modifying protein 2 or 3, while some questions remain to be answered about the molecular mechanisms of this signal transduction system. Taking these findings together, AM is a bioactive peptide with pleiotropic effects, with potential as a therapeutic tool for a wide range of human diseases from myocardial infarction to malignant tumors or inflammatory bowel diseases.

Adrenomedullin and tumour microenvironment

Adrenomedullin (AM) is a regulatory peptide whose involvement in tumour progression is becoming more relevant with recent studies. AM is produced and secreted by the tumour cells but also by numerous stromal cells including macrophages, mast cells, endothelial cells, and vascular smooth muscle cells. Most cancer patients present high levels of circulating AM and in some cases these higher levels correlate with a worst prognosis. In some cases it has been shown that the high AM levels return to normal following surgical removal of the tumour, thus indicating the tumour as the source of this excessive production of AM. Expression of this peptide is a good investment for the tumour cell since AM acts as an autocrine/paracrine growth factor, prevents apoptosis-mediated cell death, increases tumour cell motility and metastasis, induces angiogenesis, and blocks immunosurveillance by inhibiting the immune system. In addition, AM expression gets rapidly activated by hypoxia through a HIF-1α mediated mechanism, thus characterizing AM as a major survival factor for tumour cells. Accordingly, a number of studies have shown that inhibition of this peptide or its receptors results in a significant reduction in tumour progression. In conclusion, AM is a great target for drug development and new drugs interfering with this system are being developed.

Tumor-expressed adrenomedullin accelerates breast cancer bone metastasis

Introduction

Adrenomedullin (AM) is secreted by breast cancer cells and increased by hypoxia. It is a multifunctional peptide that stimulates angiogenesis and proliferation. The peptide is also a potent paracrine stimulator of osteoblasts and bone formation, suggesting a role in skeletal metastases—a major site of treatment-refractory tumor growth in patients with advanced disease.

Methods

The role of adrenomedullin in bone metastases was tested by stable overexpression in MDA-MB-231 breast cancer cells, which cause osteolytic bone metastases in a standard animal model. Cells with fivefold increased expression of AM were characterized in vitro, inoculated into immunodeficient mice and compared for their ability to form bone metastases versus control subclones. Bone destruction was monitored by X-ray, and tumor burden and osteoclast numbers were determined by quantitative histomorphometry. The effects of AM overexpression on tumor growth and angiogenesis in the mammary fat pad were determined. The effects of AM peptide on osteoclast-like multinucleated cell formation were tested in vitro. A small-molecule AM antagonist was tested for its effects on AM-stimulated ex vivo bone cell cultures and co-cultures with tumor cells, where responses of tumor and bone were distinguished by species-specific real-time PCR.

Results

Overexpression of AM mRNA did not alter cell proliferation in vitro, expression of tumor-secreted factors or cell cycle progression. AM-overexpressing cells caused osteolytic bone metastases to develop more rapidly, which was accompanied by decreased survival. In the mammary fat pad, tumors grew more rapidly with unchanged blood vessel formation. Tumor growth in the bone was also more rapid, and osteoclasts were increased. AM peptide potently stimulated bone cultures ex vivo; responses that were blocked by small-molecule adrenomedullin antagonists in the absence of cellular toxicity. Antagonist treatment dramatically suppressed tumor growth in bone and decreased markers of osteoclast activity.

Conclusions

The results identify AM as a target for therapeutic intervention against bone metastases. Adrenomedullin potentiates osteolytic responses in bone to metastatic breast cancer cells. Small-molecule antagonists can effectively block bone-mediated responses to tumor-secreted adrenomedullin, and such agents warrant development for testing in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-014-0458-y) contains supplementary material, which is available to authorized users.

Pancreatic cancer: gene therapy approaches and gene delivery systems

IMPORTANCE OF THE FIELD

Due to the absence of early diagnosis, the highly invasive and metastatic features and the lack of effective therapeutic modalities, the prognosis of patients with pancreatic cancer is poor. Gene therapy is currently regarded as a potential and promising therapeutic modality for pancreatic cancer.

AREAS COVERED IN THIS REVIEW

This article summarizes an update of gene therapy approaches and reviews the latest progress in gene delivery systems that have been tested on pancreatic cancer.

WHAT THE READER WILL GAIN

The treatment effectiveness of gene combination therapy is better than that of the regulation of single-gene or single gene therapy approaches. Naked DNA is limited because of degradation by intracellular and extracellular nucleases. Virus vectors show high transfection efficiency but are limited due to immunogenicity, inflammatory response and potential carcinogenicity. Non-viral vectors, such as cationic polymers or inorganic nanoparticles, show an important feature that they can be easily modified, and the progress of materials science will provide more and better non-viral vectors, accordingly improving the efficiency and safety of gene therapy, which will make them the most promising vectors for pancreatic cancer.

Adrenomedullin is expressed in pancreatic cancer and stimulates cell proliferation and invasion in an autocrine manner via the adrenomedullin receptor, ADMR

The current study investigated adrenomedullin as a potential autocrine regulator of pancreatic cancer cell function. Adrenomedullin was localized in the neoplastic epithelium of 90% (43 of 48) of human pancreatic adenocarcinomas analyzed by immunohistochemistry and was expressed by 100% (8 of 8) of pancreatic cancer cell lines analyzed by reverse transcription-PCR. Pancreatic cancer cell lines also secreted adrenomedullin into the culture medium as determined by ELISA (5 of 5). Exogenous adrenomedullin treatment of Panc-1, BxPC3, and MPanc96 cells in vitro stimulated cell proliferation, invasion, and nuclear factor kappaB activity, indicating the ability of the cells to respond to adrenomedullin. Treatment of the cell cultures with an adrenomedullin antagonist inhibited basal levels of proliferation and nuclear factor kappaB activity, supporting the autocrine function of this molecule. Furthermore, increasing adrenomedullin levels by gene transfer to Panc-1 cells increased, whereas adrenomedullin small hairpin RNA silencing in MPanc96 cells inhibited tumor growth and metastasis in vivo. Adrenomedullin is able to act through at least two different receptors, adrenomedullin receptor (ADMR) and calcitonin receptor-like receptor (CRLR). Reverse transcription-PCR and Western blotting indicated that pancreatic cancer cells expressed only ADMR but not CRLR. In contrast, cells found in the tumor microenvironment, primary human pancreatic stellate and endothelial (HUVEC) cells, expressed both ADMR and CRLR. Small hairpin RNA silencing of ADMR in pancreatic cancer cells blocked adrenomedullin-induced growth and invasion, indicating that this receptor is involved in the autocrine actions of adrenomedullin. These data indicate that adrenomedullin acting via ADMR increases the aggressiveness of pancreatic cancer cells and suggests that these molecules may be useful therapeutic targets.