Effects of YM218, a nonpeptide vasopressin V1A receptor-selective antagonist, on vasopressin-induced growth responses in human mesangial cells

Development of a triazolobenzodiazepine-based PET probe for subtype-selective vasopressin 1A receptor imaging

OBJECTIVES

To enable non-invasive real-time quantification of vasopressin 1A (V1A) receptors in peripheral organs, we sought to develop a suitable PET probe that would allow specific and selective V1A receptor imaging in vitro and in vivo.

METHODS

We synthesized a high-affinity and -selectivity ligand, designated compound 17. The target structure was labeled with carbon-11 and tested for its utility as a V1A-targeted PET tracer by cell uptake studies, autoradiography, in vivo PET imaging and ex vivo biodistribution experiments.

RESULTS

Compound 17 (PF-184563) and the respective precursor for radiolabeling were synthesized in an overall yield of 49% (over 7 steps) and 40% (over 8 steps), respectively. An inhibitory constant of 0.9 nM towards the V1A receptors was measured, while excellent selectivity over the related V1B, V2 and OT receptor (IC50 >10,000 nM) were obtained. Cell uptake studies revealed considerable V1A binding, which was significantly reduced in the presence of V1A antagonists. Conversely, there was no significant blockade in the presence of V1B and V2 antagonists. In vitro autoradiography and PET imaging studies in rodents indicated specific tracer binding mainly in the liver. Further, the pancreas, spleen and the heart exhibited specific binding of [11C]17 ([11C]PF-184563) by ex vivo biodistribution experiments.

CONCLUSION

We have developed the first V1A-targeted PET ligand that is suitable for subtype-selective receptor imaging in peripheral organs including the liver, heart, pancreas and spleen. Our findings suggest that [11C]PF-184563 can be a valuable tool to study the role of V1A receptors in liver diseases, as well as in cardiovascular pathologies.

Novel and facile synthesis of 1-benzazepines via copper-catalyzed oxidative C(sp3)–H/C(sp2)–H cross-coupling

A novel synthetic strategy for the facile construction of 1-benzazepines has been developedviacopper-catalyzed oxidative C(sp³)–H/C(sp²)–H cross-coupling.

Early, but not late therapy with a vasopressin V1a-antagonist ameliorates the development of renal damage after 5/6 nephrectomy

Introduction. Vasopressin, mainly through the V1a-receptor, is thought to be a major player in the maintenance of hyperfiltration. Its inhibition could therefore lead to a decrease in progression of chronic renal failure.To this end, the effect of the vasopressin V1a-receptor-selective antagonist, YM218, was studied on proteinuria and focal glomerulosclerosis in early and late intervention after 5/6 nephrectomy in rats, and compared with an angiotensin-converting enzyme inhibitor (ACE-I).

Materials and methods. After 5/6 nephrectomy, early intervention was performed between week 2 and 10 thereafter with the V1a-receptor-selective antagonist (VRA, 10 mg/kg/day, n=10), enalapril (ACE-I, 10 mg/kg/day, n=9), or vehicle (n=8). Late intervention was performed in another group between week 6 and 12 with VRA (10 mg/kg/day, n=7), lisinopril (ACE-I, 5 mg/kg/day, n=7), or vehicle (n=7).

Results. In early intervention, proteinuria and focal glomerulosclerosis were significantly decreased by VRA compared to vehicle (44 7% and 59+8% respectively). ACE-I significantly decreased proteinuria (67 7%) and a trend towards a decrease in focal glomerulosclerosis was observed (30 18%). In late intervention, VRA did not decrease proteinuria and focal glomerulosclerosis compared to vehicle (21 20% and 0%, respectively),ACE-I significantly lowered proteinuria (92 2%) and a focal glomerulosclerosis (69+1%) lowering trend was observed.

Conclusion. These results indicate that VRA may protect against early progression of renal injury after 5/6 nephrectomy, whereas its effectiveness seems limited in established renal damage.

Receptor for activated protein kinase C1 regulates cell proliferation by modulating calcium signaling

Receptor for activated protein kinase C1 (RACK1) is an intracellular scaffolding protein known to interact with the inositol-1,4,5-trisphosphate receptor and thereby enhance calcium release from the sarcoplasmic reticulum. Because calcium signaling may affect vascular smooth muscle cell proliferation, we investigated whether RACK1 regulates proliferation of rat preglomerular microvascular smooth muscle cells. Western blot analysis indicated that preglomerular microvascular smooth muscle cells robustly express RACK1 protein, and coimmunoprecipitation experiments demonstrated that RACK1 binds the inositol-1,4,5-trisphosphate receptor. RACK1 small interfering RNA (siRNA) decreased RACK1 mRNA and protein expression, significantly (P=0.0225) reduced steady-state basal levels of intracellular calcium (6712±156 versus 7408±248, arbitrary fluorescence units in RACK1 siRNA-treated versus control cells, respectively) and significantly (P<0.0001) decreased cell proliferation by ≈50%. Xestospongin C and 2-aminoethoxydiphenyl borate (antagonists of inositol-1,4,5-trisphosphate receptors), cyclopiazonic acid (sarcoplasmic reticulum Ca(2+)-ATPase inhibitor), and calmidazolium (calmodulin inhibitor) mimicked the effects of RACK1 siRNA on proliferation, and RACK1 siRNA had no additional effects on proliferation in the presence of these agents. RACK1 siRNA did not affect the expression of cyclin D1/2 or phosphorylation of retinoblastoma protein (progrowth cell cycle regulators), yet it caused compensatory decreases in the expression of p21(Cip1/Waf1) and p27(Kip1) (antigrowth cell cycle regulators). Like preglomerular microvascular smooth muscle cells, glomerular mesangial cells also expressed high levels of RACK1, and RACK1 siRNA inhibited their proliferation. In conclusion, RACK1 modulates proliferation of preglomerular microvascular smooth muscle cells and glomerular mesangial cells, likely via the inositol-1,4,5-trisphosphate receptor/calcium/calmodulin pathway. RACK1 may represent a novel druggable target for treating renal diseases, such as glomerulosclerosis.

Vasopressin induces human mesangial cell growth via induction of vascular endothelial growth factor secretion

Vasoactive hormones, growth factors, and cytokines are important in promoting mesangial cell growth, a characteristic feature of many glomerular diseases. Vascular endothelial growth factor (VEGF) is an endothelial mitogen and promoter of vascular permeability that is constitutively expressed in human glomeruli, but its role in the kidney is still unclear. In the present study, we investigated the ability of vasopressin (AVP) to stimulate VEGF secretion by and correlation with AVP-induced cell growth in human mesangial cells. AVP caused time- and concentration-dependent increases in VEGF secretion from human mesangial cells, which was in turn potently inhibited by a V(1A) receptor-selective antagonist, confirming that this secretion is a V(1A) receptor-mediated event. VEGF also induced mesangial cell growth which was completely inhibited on administration of an anti-VEGF neutralizing antibody. Further, AVP-induced mesangial cell growth was completely abolished by the V(1A) receptor-selective antagonist and partially inhibited by an anti-VEGF neutralizing antibody. These results suggest that AVP stimulates VEGF secretion by human mesangial cells via V(1A) receptors. This secreted VEGF may function as an autocrine hormone to regulate mesangial cell growth, a mechanism by which AVP might contribute to progressive glomerular diseases such as diabetic nephropathy.

Increased prolyl endopeptidase activity in human neoplasia

Prolyl endopeptidase (EC 3.4.21.26) (PEP) is a serine peptidase that converts several biologically active peptides. This enzyme has been linked to several neurological, digestive, cardiovascular and infectous disorders. However, little is known about its involvement in neoplastic processes. This study analyzes fluorimetrically cytosolic and membrane-bound PEP activity in a large series (n=122) of normal and neoplastic tissues from the kidney, colon, oral cavity, larynx, thyroid gland and testis. Cytosolic PEP activity significantly increased in clear cell renal cell carcinoma, urothelial carcinoma of the renal pelvis and head and neck squamous cell carcinoma. Both cytosolic and membrane-bound PEP activity were also increased in colorectal adenomatous polyps. These data suggest the involvement of PEP in some mechanisms that underlie neoplastic processes.

Cystinyl aminopeptidase activity is decreased in renal cell carcinomas

The involvement of peptidases in carcinogenetic processes of several tumor types has been researched in recent years. Although kidney is one of the major tissues known to express cystinyl-aminopeptidase (CAP), little is known about its role in renal neoplasia. This study analyzes fluorimetrically membrane-bound and soluble CAP activity in the three main renal cancers: clear cell (CCRCC), papillary (PRCC), and chromophobe (ChRCC) renal cell carcinomas. Overall, a marked decrease of membrane-bound CAP activity in all the three renal cell carcinomas was detected when compared with their respective surrounding non-tumor tissues. So, the tumor vs. non-tumor CAP ratios (units of peptidase per mg of protein) was as follows: 926+/-111 vs. 3778+/-276 for CCRCCs, 737+/-181 vs. 4351+/-950 for PRCCs, and 592+/-118 vs. 4905+/-935 for ChRCCs. In contrast, the soluble fraction of this enzyme displayed minor and non-significant changes when comparing tumor and non-tumor CAP activities in the whole series. After stratification by stage and grade, CCRCCs displayed significant differences: pT3 category had significantly higher levels of membrane-bound activity than pT1, and high grade cases (G3-4) had higher soluble CAP activity than low grade ones (G1-2). These data may open additional possibilities in the study of renal cell carcinoma with regard to the prognosis of patients.