Targeting Somatostatin Receptors By Functionalized Mesoporous Silica Nanoparticles - Are We Striking Home?

Abstract

The concept of delivering nanoformulations to desired tissues by means of targeting membrane receptors of high local abundance by ligands anchored to the nanocarrier has gained a lot of attention over the last decade. Currently, there is no unanimous opinion on whether surface functionalization of nanocarriers by targeting ligands translates into any real benefit in terms of pharmacokinetics or treatment outcomes. Having examined the published nanocarriers designed to engage with somatostatin receptors, we realized that in the majority of cases targetability claims were not supported by solid evidence of targeting ligand-targeted receptor coupling, which is the very crux of a targetability concept. Here, we present an approach to characterize targetability of mesoporous silica-based nanocarriers functionalized with ligands of somatostatin receptors. The targetability proof in our case comes from a functional assay based on a genetically-encoded cAMP probe, which allows for real-time capture of receptor activation in living cells, triggered by targeting ligands on nanoparticles. We elaborate on the development and validation of the assay, highlighting the power of proper functional tests in the characterization pipeline of targeted nanoformulations.

Superparamagnetic Iron Oxide Nanoparticles Carrying Chemotherapeutics Improve Drug Efficacy in Monolayer and Spheroid Cell Culture by Enabling Active Accumulation

“…Additionally, certain peptides can be used as coatings to bind directly to cancer cells [69,70]. Provided that tumors develop respective receptors, active targeting can also be achieved by using certain ligands [71,72]. As many strategies are capable of sparing non-malignant tissue, combining them with magnetic accumulation may be a step towards selective killing of cancer cells.…”

iGIST - a kinetic bioassay for pertussis toxin based on its effect on inhibitory GPCR signaling

“…Cell lines -Human embryonic kidney cell line (HEK293) was obtained from American Type Culture Collection (ATCC, #CRL-1573). HEK293 with stable overexpression of Gs22/cAMP probe, as well as the derived sensor cells with stable overexpression of SSTR2 (aka HEK-Gs/SSTR2_HA), were developed and characterized by us earlier [31][32][33] . Chinese hamster ovary cells (CHO) were either recovered from the local cell line repository of the Institute of Biomedicine, University of Turku, Finland (liquid N2 storage -a cryovial of the stock culture of 1998; aka CHO#1) or provided as a kind gift by Dr Aylin C. Hanyaloglu (Institute of Reproductive and Developmental Biology, Imperial College London, UK; aka CHO#2).…”

“…GloSensor-22F, originally introduced by Wood et al 35,36 , represents a cAMP-binding domain of protein kinase A fused to a circularly permuted Photinus pyralis luciferase, jointly functioning as a sensitive and reversible cAMP probe in living cells. The sensor cells were earlier established in-house in HEK293 background, which has low endogenous expression of SSTR2 32,33 , and used to measure SSTR2mediated signaling upon exposure to various ligands. In iGIST, activities of SSRT2 and ACs are controlled with a high-affinity synthetic peptide agonist octreotide (Oct) 37 and forskolin (FSK), respectively.…”

“…In iGIST, activities of SSRT2 and ACs are controlled with a high-affinity synthetic peptide agonist octreotide (Oct) 37 and forskolin (FSK), respectively. Oct induces potent and dose-dependent activation of SSTR2 with an IC50 of 0.3 nM (in iGIST typically used at 10 nM) 32 . FSK activates ACs by intercalating the C1 and C2 subunits into the catalytically active form 30 , which readily boosts intracellular cAMP levels and facilitates registration of counter-acting stimuli, i.e.…”

In vitro Targetability Validation of Peptide-Functionalized Mesoporous Silica Nanoparticles in the Presence of Serum Proteins

“…Besides, experiments to validate the engagement of targeted receptors with targeting ligands on nanoparticles tend to be substituted with indirect methods, inferring targetability from subsequent events, such as the differential uptake of nanoparticles by cells or alterations in cellular phenotypes upon study treatments. Thus, the direct proof of active targeting is often missing (Paramonov et al, 2018).…”