Nucleoside conjugates of quantum dots for characterization of G protein-coupled receptors: strategies for immobilizing A2A adenosine receptor agonists

Table 1 In vitro pharmacological data for various QDs, dendrons (D5), and their complexes with nucleosides and solubilizing moieties.

Compd.	K_iapp at hA_2AAR, μM or *% inhibition*^a	Solubility
1a	0.015	+++
1b	0.010	+++
2a	NT	-
2b	NE^e	+++
3	NE^e	++
4	< 20% ^e	+
5	< 20% ^e	-
6	< 20% ^e	+
7	< 20% ^e	+
8 ^b	< 20% ^e	++(72.3 nM in DMSO)^d
9	< 20% ^e	++
10	9.8 ± 7.4% (at 1.0 μM)	+++
11	1.02 ± 0.15	+++
12	2.2 ± 1.1% (at 1.0 μM)	+++
13 ^c	0.118 ± 0.054	+++ (66.1 μM in DMSO)^d

^a All experiments were done on HEK-293 cells stably expressing the human A_2AAR. The binding affinity (n = 3-5) and was determined by using agonist radioligands [³H]CGS21680. The concentrations of the ligand complexes were measured by the concentration of the macromolecule, not the attached nucleoside. Therefore, binding K_i values calculated from the IC₅₀ using the Cheng-Prusoff equation[37] of large conjugates are expressed as K_iapp values.
^b 8, MRS5252.
^c 13, MRS5303.
^d In order to determine more exactly the solubility of the compounds in two cases we plotted a standard curve graph. We measured the fluorescence intensity of the underivatized QDs (2a and 2b) in DMSO at different concentrations; then, we measured the fluorescence intensity of each conjugate, 8 and 13, in DMSO to determine its maximal solubility, based on comparison to the standard curve of the chemical precursor 2a or 2b.
^e NE, no effect, or less than 20% inhibition at the maximal concentration tested. This concentration was intended to be 1 μM, however in most cases this was not reached due to precipitation.
NT, not tested.

ISSN: 1477-3155