Discovery of dual targeting PEGylated BG-P1600-TAT to norepinephrine transporter (NET) and thyrointegrin αvβ3 in the treatment of neuroblastoma

Polymer-drug conjugates are growing in interest as novel anticancer agents for targeted cancer therapy. The aim of this study was to synthesize a poly(ethylene glycol) (PEG) conjugated anticancer drug for neuroblastoma, which is the most common extracranial solid tumor of childhood and the deadliest tumor of infancy. In our previous studies, we designed and synthesized a dual targeting agent using benzylguanidine (BG) conjugated with the high affinity thyrointegrin αvβ3 antagonist TriAzole Tetraiodothyroacetic acid (TAT) via non-cleavable bonding to PEG400 to make BG-P₄₀₀-TAT and its derivatives as agents against neuroblastoma. Here, we improved the pharmacodynamic properties and increased the solubility by changing the polymer length to 1600 molecular weight. The TAT group, which acts as an integrin αvβ3 antagonist, and the BG group, which can be taken up by neuroblastoma cells through the norepinephrine transporter (NET) system, are conjugated to PEG₁₆₀₀ to make BG-PEG₁₆₀₀-TAT. The binding affinity of BG-PEG₁₆₀₀-TAT was 40-fold higher to integrin αvβ3 versus BG-P₄₀₀-TAT and was associated with greater anticancer activities against neuroblastoma cells (SK-N-F1 and SKNAS) implanted in SCID mice along with broad spectrum anti-angiogenesis activities versus the FDA approved anti-Vascular Endothelial Growth Factor (VEGF) monoclonal antibody Avastin (bevacizumab). In conclusion, our novel dual targeting of NET and αvβ3 receptor antagonist, BG-P1600-TAT demonstrated broad spectrum anti-angiogenesis and anti-cancer activities in suppressing neuroblastoma tumor progression and metastasis. Thus, BG-PEG₁₆₀₀-TAT represents a potential clinical candidate for targeted therapy in neuroblastoma management.

Norepinephrine Transporter in Major Depressive Disorder: A PET Study

OBJECTIVE

The norepinephrine transporter has been suggested to play a crucial role in major depressive disorder. However, norepinephrine transporter availability in major depressive disorder and its role with clinical symptoms are not known. The authors tested norepinephrine transporter availability in patients with major depressive disorder with the aim to identify any associations between test results and clinical symptoms.

METHOD

The present research was a cross-sectional study in which 19 patients with major depressive disorder and 19 age- and sex-matched healthy comparison subjects underwent positron emission tomography scanning to evaluate the norepinephrine transporter availability measured by the radioligand (S,S)-[¹⁸F]FMeNER-D₂. Norepinephrine transporter availability in the thalamus and its subregions was quantified in terms of nondisplaceable binding potential (BP_ND). The authors also analyzed the association between norepinephrine transporter availability and clinical symptoms.

RESULTS

Compared with healthy subjects, patients with major depressive disorder showed 29.0% higher BP_ND values in the thalamus and, in particular, 28.2% higher values in the thalamic subregion anatomically connected to the prefrontal cortex. Elevated norepinephrine transporter availability in the thalamus in patients was positively correlated with attention, as measured by the Trail Making Test, part A.

CONCLUSIONS

These findings revealed altered norepinephrine transmission in patients with major depressive disorder, suggesting that this alteration could be related to attention in this patient population.

Improved selectivity of mIBG uptake into neuroblastoma cells in vitro and in vivo by inhibition of organic cation transporter 3 uptake using clinically approved corticosteroids

INTRODUCTION

Radiolabeled meta-iodobenzylguanidine (mIBG) is used for imaging and therapy of neuroblastoma as well as pheochromocytoma. However, non-tumorous tissues also incorporate mIBG mainly by organic cation transporters (OCTs). In this study, we tested different clinically approved corticosteroids as potential inhibitors of the OCT3-mediated uptake in vitro and in vivo, to achieve a more selective mIBG tumor uptake.

METHODS

The in vitro incorporation of [(3)H]norepinephrine ([(3)H]NE), [(3)H]dopamine ([(3)H]DA) and [(123)I]mIBG in neuroblastoma cells (SK-N-SH, Kelly, IMR-32) and in HEK-293 cells transfected with human OCT3 was measured with and without supplemental corticosteroids (hydrocortisone, prednisolone, dexamethasone, corticosterone). The in vivo biodistribution of [(123)I]mIBG in absence and presence of corticosteroids was studied in non-tumor bearing NOD scid gamma mice. Retrospectively, we selected patients with and without corticosteroid treatment prior to [(123)I]mIBG scintigraphy.

RESULTS

A concentration-dependent inhibitory effect of different corticosteroids on the [(3)H]NE and [(3)H]DA uptake via OCT3 was illustrated in vitro. The highest OCT3 inhibition was observed for corticosterone, but clinically used corticosteroids, showed also promising inhibitory effects. In contrast, the uptake in neuroblastoma cells was reduced only moderately. Hydrocortisone or prednisolone had only minor effects on [(123)I]mIBG uptake of both neuroblastoma cells, but reduced uptake in OCT3 expressing cells significantly. In mice tissues, [(123)I]mIBG uptake was inhibited by corticosteroids especially in the small intestine and kidney. Finally, in one patient with hydrocortisone treatment performed prior to [(123)I]mIBG scan, heart and liver uptake was reduced compared to untreated patients.

CONCLUSIONS

The OCT3 is widely spread in many organs and responsible for non-targeted uptake of radiolabeled mIBG. In our study, clinically approved corticosteroids inhibited mIBG uptake in OCT3 expressing cells effectively, whereas tracer accumulation in NT (norepinephrine transporter) expressing neuroblastoma cells showed consistency. We conclude, that a single dose of hydrocortisone or prednisolone prior to [(123)I]mIBG scintigraphy may improve specificity and reduce radiation dose to non-target organs.

Extracellular norepinephrine clearance by the norepinephrine transporter is required for skeletal homeostasis

Changes in bone remodeling induced by pharmacological and genetic manipulation of β-adrenergic receptor (βAR) signaling in osteoblasts support a role of sympathetic nerves in the regulation of bone remodeling. However, the contribution of endogenous sympathetic outflow and nerve-derived norepinephrine (NE) to bone remodeling under pathophysiological conditions remains unclear. We show here that differentiated osteoblasts, like neurons, express the norepinephrine transporter (NET), exhibit specific NE uptake activity via NET and can catabolize, but not generate, NE. Pharmacological blockade of NE transport by reboxetine induced bone loss in WT mice. Similarly, lack of NE reuptake in norepinephrine transporter (Net)-deficient mice led to reduced bone formation and increased bone resorption, resulting in suboptimal peak bone mass and mechanical properties associated with low sympathetic outflow and high plasma NE levels. Last, daily sympathetic activation induced by mild chronic stress was unable to induce bone loss, unless NET activity was blocked. These findings indicate that the control of endogenous NE release and reuptake by presynaptic neurons and osteoblasts is an important component of the complex homeostatic machinery by which the sympathetic nervous system controls bone remodeling. These findings also suggest that drugs antagonizing NET activity, used for the treatment of hyperactivity disorders, may have deleterious effects on bone accrual.