Neuropilin-2 expression in cancer

AIMS

Neuropilin-2 is a coreceptor for vascular endothelial growth factor family members. Blockade of neuropilin-2 is able to suppress lymphogenous metastasis in preclinical models. The aim of this study was to validate a protocol for the evaluation of neuropilin-2 protein expression in situ, by comparison with in-situ hybridization, western blotting, and mRNA expression levels.

METHODS AND RESULTS

Immunohistochemistry was performed on normal human tissues, and whole sections for 79 primary non-small-cell lung carcinomas, 65 primary breast carcinomas, 79 primary colorectal cancers, and 52 metastases. Neuropilin-2 expression was observed in lymphatic and blood vessels from all normal and malignant tissues examined. In addition, 32% of primary non-small-cell lung carcinomas, 15% of primary breast carcinomas and 22% of primary colorectal cancers showed tumour cell expression. Fifty-five primary and nine secondary malignant melanomas were also examined for neuropilin-2 expression by in-situ hybridization. All showed vascular expression, and 85% of primary malignant melanomas showed tumour cell expression.

CONCLUSIONS

In the majority of lung, breast and colorectal cancers, the effects of anti-neuropilin-2 are likely to be restricted to the vasculature. These results will assist in pharmacokinetic evaluations, tolerability assessments and the choice of setting to evaluate the activity of anti-neuropilin-2 therapies.

Neuropilin-1 expression in cancer and development

Neuropilin (NRP)-1 is a co-receptor for vascular endothelial growth factor (VEGF). Preclinical data suggest that blockade of NRP1 suppresses tumour growth by inhibiting angiogenesis, in addition to directly inhibiting tumour cell proliferation in certain models. A humanized monoclonal antibody to NRP1 is currently being evaluated as a potential anti-cancer therapy in clinical trials. However, the expression of NRP1 in cancer and physiological angiogenesis has yet to be systematically described. Here we characterize the in situ expression of NRP1 in human cancer and during mammalian development. A monoclonal antibody to human NRP1 was generated and validated for immunohistochemistry by western blotting, use of formalin-fixed cell pellets transfected with NRP1, immunofluorescence, and comparison with in situ hybridization. NRP1 expression was assessed in whole sections of 65 primary breast carcinomas, 95 primary colorectal adenocarcinomas, and 90 primary lung carcinomas. An additional 59 human metastases, 16 xenografts, and three genetically engineered mouse tumour models were also evaluated. Immunoreactivity for NRP1 was seen in vessels from normal tissues adjacent to cancer and in 98-100% of carcinomas. Tumour cell expression of NRP1 was also observed in 36% of primary lung carcinomas and 6% of primary breast carcinomas, but no colorectal adenocarcinomas. NRP1 was evaluated in mouse embryos, where expression was limited to the nervous system, endocardium, vascular smooth muscle, and, focally, endothelium on subsets of vessels. Moreover, in a model of VEGF-dependent angiogenesis in the postnatal mouse trachea, blockade of NRP1 signalling resulted in defective angiogenesis and recapitulated the effects of anti-VEGF treatment. These observations confirm NRP1 as a valid anti-angiogenic target in malignancy, and as a potential direct anti-tumour target in a subset of cancers. The data also confirm a role for NRP1 in physiological, VEGF-mediated angiogenesis.

Abstract 5130: Neuropilin-1 expression in breast, colorectal and lung cancer

Neuropilin-1 is a coreceptor for vascular endothelial growth factor, which is expressed by endothelial cells and tumor cells. Preclinical data suggest that targeting neuropilin-1 would directly inhibit tumor cell growth and invasion, in addition to suppressing angiogenesis with indirect suppression of tumor growth. A humanized monoclonal antibody to neuropilin-1 is currently being evaluated in a phase one clinical trial of patients with solid malignancies. The aim of this study was to characterize the in situ expression of neuropilin-1 in normal and neoplastic human tissues.

A monoclonal antibody to human neuropilin-1 was generated and validated for immunohistochemistry by comparison with isotopic in situ hybridization data, use of formalin-fixed human embryonic kidney (HEK)-293 cell pellets transfected with neuropilin-1, western blotting and quantitative reverse transcriptase (RT)-PCR on microdissected pure cell populations. Neuropilin-1 expression was assessed in whole sections of 65 primary breast carcinomas, 95 primary colorectal adenocarcinomas and 80 primary non-small cell lung carcinomas. An additional 50 breast, colorectal and lung metastases were also evaluated.

The neuropilin-1 monoclonal antibody showed appropriate reactivity by western blotting and in formalin-fixed cell pellet controls, with co-localization of protein (immunohistochemistry) and mRNA (in situ hybridization and laser-capture microdissection followed by quantitative RT-PCR). Immunoreactivity for neuropilin-1 was seen in endothelium from normal tissues adjacent cancer and 98 to 100% of primary and secondary carcinomas. Tumor cell expression of neuropilin-1 was also observed in 34% of primary non-small cell lung carcinomas and 6% of primary breast carcinomas, but no colorectal adenocarcinomas.

This is the first comprehensive analysis of neuropilin-1 protein expression in neoplastic human tissue with validated reagents. The assay will inform the likely activity and toxicity of agents that target neuropilin-1 and warrants evaluation as a biomarker of anti-neuropilin-1 activity.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5130. doi:10.1158/1538-7445.AM2011-5130

Preclinical evaluation of carcinoembryonic cell adhesion molecule (CEACAM) 6 as potential therapy target for pancreatic adenocarcinoma

Despite the availability of new targeted therapies, ductal pancreatic adenocarcinoma continues to carry a poor prognosis. Carcinoembryonic antigen-related cell adhesion molecule (CEACAM)6 has been reported as a potential biomarker and therapy target for this malignancy. We have evaluated CEACAM6 as a potential therapy target, using an antibody-drug conjugate (ADC). Expression of CEACAM6 in pancreatic adenocarcinomas was determined using immunohistochemistry on tissue microarrays. The expression pattern in granulocytes and granulocytic precursors was measured by flow cytometry. Murine xenograft and non-human primate models served to evaluate efficacy and safety, respectively. Robust expression of CEACAM6 was found in > 90% of invasive pancreatic adenocarcinomas as well as in intraepithelial neoplastic lesions. In the granulocytic lineage, CEACAM6 was expressed at all stages of granulocytic maturation except for the early lineage-committed precursor cell. The anti-CEACAM6 ADC showed efficacy against established CEACAM6-expressing tumours. In non-human primates, antigen-dependent toxicity of the ADC consisted of dose-dependent and reversible depletion of granulocytes and their precursors. This was associated with preferential and rapid localization of the antibody in bone marrow, as determined by sequential in vivo PET imaging of the radiolabelled anti-CEACAM6. Localization of the radiolabelled tracer could be attenuated by predosing with unlabelled antibody confirming specific accumulation in this compartment. Based on the expression pattern in normal and malignant pancreatic tissues, efficacy against established tumours and limited and reversible bone marrow toxicity, we propose that CEACAM6 should be considered for an ADC-based therapy approach against pancreatic adenocarcinomas and possibly other CEACAM6-positive neoplasms.

Plasmalemmal vesicle-associated protein (PLVAP) is expressed by tumour endothelium and is upregulated by vascular endothelial growth factor-A (VEGF)

Vascular endothelial growth factor-A (VEGF) is an important regulator of vascular permeability. In preclinical studies, VEGF induces endothelial fenestrations in pre-existing and neo-vasculature, while inhibition of VEGF leads to a reduction in endothelial fenestrations. Recently, vascular regression in response to VEGF inhibition has been shown to correlate with the presence of endothelial fenestrations. Plasmalemmal vesicle-associated protein (PLVAP) is believed to be a component of diaphragmed endothelial fenestrations, but a direct relationship with VEGF signalling has not been established. The aim of this study was to characterize the expression pattern of PLVAP and investigate whether PLVAP is a transcriptional target of VEGF signal transduction. The expression pattern of PLVAP was characterized in normal and neoplastic human tissues by in situ hybridization and/or immunohistochemistry. The role of VEGF signal transduction in the regulation of PLVAP expression was investigated in vitro using receptor-selective engineered forms of VEGF, a neutralizing monoclonal antibody against VEGF, and inhibitors of downstream signalling pathways. PLVAP mRNA and protein were widely expressed in the endothelium of normal and neoplastic tissues. In cultured endothelial cells, VEGF signalling through receptor 2 stimulated expression of PLVAP total RNA and protein. This induction could be blocked with an anti-VEGF monoclonal antibody and by inhibitors of phosphatidylinositol 3-kinase (LY294002) or p38 mitogen-activated protein kinase (SB203580), but not by PD98059, a mitogen-activated protein/extracellular signal-regulated kinase 1 inhibitor. These data show that PLVAP is more widely expressed in the vasculature of normal tissues than previously thought and that it is expressed in the vasculature of most human tumours. We suggest that PLVAP is a downstream target of VEGF signalling. This work solidifies the association between VEGF and the appearance and maintenance of fenestrations by providing a potential mechanistic link.

Structure of human parathyroid hormone(1-34) in the presence of solvents and micelles

The structure of the N-terminal 34-residue fragment of human parathyroid hormone was determined in 40% trifluoroethanol employing two-dimensional 1H nuclear magnetic resonance spectroscopy. The proton chemical shifts were assigned from magnitude and phase-sensitive COSY, relayed COSY, and NOESY spectra. Distance constraints, estimated from NOESY spectra, were used to create a set of structures by distance geometry (DGEOM) which were subsequently refined by restrained energy minimization and restrained molecular dynamics (CHARMm). The resulting structures contained two helices spanning residues 3-12 and residues 17-26. The NOE constraints for residues 13-16 did not provide a single structural solution; however, their conformations were not disordered. The structures prepared by DGEOM and refined with CHARMm contained either an irregular turn or a helical structure at residues 13-16. The secondary structure of human parathyroid hormone(1-34) was also assessed by circular dichroism in the presence of methanol, trifluoroethanol, and dodecylphosphocholine micelles. Under all three conditions, the peptide formed structures containing various amounts of helical content. The formation of helical secondary structure in the presence of micelles supports the proposal that the trifluoroethanol-induced structure of human parathyroid(1-34) was not an artifact of its environment but perhaps was an indication of the conformation that the molecule adopts when in close proximity to a membrane surface and possibly when bound to the parathyroid receptor.

Amino and iodotamoxifens: synthesis, estrogen receptor affinity and biodistribution

Both geometrical isomers (E and Z) of an aminotamoxifen (2) have been prepared as precursors of the corresponding E and Z iodotamoxifens (1). The ability of E and Z-1 and 2 to compete with [3H]estradiol for estrogen receptors in rat uterine cytosol was measured relative to Z-tamoxifen and estradiol. The four tamoxifen derivatives showed affinities ranging from 50% to 1600% of that of tamoxifen. Under the same conditions, tamoxifen's relative binding affinity was 0.2% of that of estradiol. Preparative routes to the radioiodo-tamoxifens, [131I]-E and Z-1, were also developed and provided approximately 100 MBq of 'no carrier added' material in 40-60% radiochemical yield. Study of the biodistribution of these radioligands in tumor-bearing mice demonstrated significant radioactivity in the tumors and in the uterus. For [131I]-E-1, target to background ratios reached 28 for uterus/blood and 10 for tumor/blood; corresponding optimum ratios for [131I]-Z-1 were 10 and 5. A washout study using estradiol indicated selective uptake in the uterus of Swiss white mice. However, tumor uptake and image contrast in humans following intravenous administration of either [131I]-E or Z-1 were insufficient to allow diagnostic use of the radioiodotamoxifens.