Amphiphilic-Polymer-Guided Plasmonic Assemblies and Their Biomedical Applications

Plasmonic nanostructures with unique physical and biological properties have attracted increased attention for potential biomedical applications. Polymers grafted on metal nanoparticle surface can be used as assembly regulating molecules to guide nanoparticles organize into ordered or hierarchical structures in solution, within condensed phases, or at interfaces. In this Topical Review, we will highlight recent efforts on self-assembly of gold nanoparticles coated with polymer brushes. How and what kind of polymer graft can be used to adjust nanoparticle interactions, to dictate interparticle orientation, and to determine assembled nanostructures will be discussed. Furthermore, the Topical Review will shed light on the physicochemical properties, including self-assembly behavior and kinetics, tunable localized surface plasmon resonance effect, enhanced surface enhanced Raman scattering, and other optical and thermal properties. The potential of self-assembled nanostructures for applications in different fields, especially in biomedicine, will also be elaborated

Site-Specifically Biotinylated VEGF₁₂₁ for Near-Infrared Fluorescence Imaging of Tumor Angiogenesis

The vascular endothelial growth factor (VEGF)/VEGF receptor (VEGFR) pathway is considered to be one of the most important regulators of angiogenesis and a key target in anticancer treatment. Imaging VEGFR expression can serve as a new paradigm for assessing the efficacy of antiangiogenic cancer therapy, improving cancer management, and elucidating the role and modulation of VEGF/VEGFR signaling during cancer development and intervention. In this study we developed an Avi-tagged VEGF121 protein, which is site-specifically biotinylated in the presence of bacterial BirA biotin ligase. BirA biotinylated VEGF121-Avi (VEGF121-Avib) forms a stable complex with streptavidin-IRDye800 (SA800) that retains high affinity for VEGFR in vitro and allows receptor specific targeting in vivo in a 67NR murine xenograft model. In contrast, chemical coupling of IRDye800 abrogated the VEGFR binding ability of the modified protein both in vitro and in vivo. The VEGF121-Avib/SA800 complex (VEGF-Avib/SA800) may be used for quantitative and repetitive near-infrared fluorescence imaging of VEGFR expression and translated into clinic for evaluating cancer and other angiogenesis related diseases

Delayed postconditioning (DPC) mitigated edema after stroke.

<p>Rat brains were harvested at 48 h after stroke for edema measurement. The rat brains were sectioned coronally at 2 mm intervals, generating a total of 6 blocks from rostral to caudal. A. Rostral to caudal slice water content. Water contents in all 6 slices are presented. * vs. sham, P<0.001; # vs. control, P<0.001. B. Mean water content from all slices of the ischemic and non-ischemic hemisphere from rats with sham surgery, control ischemia, and delayed postconditioning. The mean value from the 6 blocks of each hemisphere was calculated, and a mean value from all rats (n = 6/group) is presented. DPC attenuated overall edema after stroke. Ischemic, ischemic hemisphere; non-ischemic, non-ischemic hemisphere; con, control ischemia. * vs. Sham-L, P<0.05; # vs. con, P<0.05; † vs. ischemic hemisphere, P<0.05.</p

Delayed postconditioning attenuated behavioral deficits up to 2 months post-ischemia.

<p>Delayed postconditioning (DPC) was conducted with 6 cycles of 15 min occlusion/15 min release in the ipsilateral CCA occlusion 6 h after stroke. Four tests were performed: A. Vibrissae-elicited forelimb placement test. All sham rats showed normal forelimb placing. There was unsuccessful placing of the contralateral forelimb after stroke in control rats; postconditioning attenuated the overall deficit from 1 to 51 d after stroke. The analysis of Two-way repeated measures ANOVA show that there are significant differences between groups: sham vs DPC, P = 0.037; sham vs control ischemia, P<0.001; DPC vs control ischemia, P = 0.003. * vs. before ischemia, P<0.5; #, ##, ###vs. sham, P<0.05, 0.01, 0.001; ††, †††, vs. postconditioning, P<0.01, 0.001. N = 6/each group. B. Postural reflex test. Scores significantly increased in control rats at 1, 2, 7, 10, and 21 d after stroke; postconditioning reduced scores at 1, 2, 7, 10 d after stroke. Two-way repeated measures ANOVA shows that there are significant differences between groups: sham vs DPC, P = 0.058; sham vs control ischemia, P<0.001; DPC vs control ischemia, P<0.001.. *, *** vs. before ischemia, P<0.01, 0.001. ### vs. sham, P<0.001; ††,††† vs. postcon, P<0.01, 0.001; . C.Tail hang test. The number of large right turns induced by tail hanging increased in control rats; postconditioning blocked right turns at 7, 10, and 14 d. Two-way repeated measures ANOVA: Control vs sham, P = 0.022; control vs DPC, P = 0.014; DPC vs sham, P = 0.805. *, vs. before ischemia, P<0.05; ##, ###, vs. sham, P<0.01, 0.001; †, ††, vs. postconditioning, P<0.05, 0.01. D. Home cage forelimb use test. Left-limb-use increased at 1, 2, 7, 10, 14, 21 and 44 d, which was blocked by postconditioning. Two-way repeated measures ANOVA: control ischemia vs sham, P = 0.004; control ischemia vs DPC, P = 0.010; DPC vs sham, P = 0.375. # , ## vs. sham, P<0.05, 0.001; †, ††, vs. postcon, P<0.05, 0.001; ** vs. before ischemia.</p

The definition of the ischemic penumbra and core.

<p>The gray region (p) plus the black region (C) represent ischemic injury in a control rat with ischemia alone; C represents infarction in a rat that received ischemia plus postconditioning. The region P spared by postconditioning is defined as the penumbra and the region C is defined as the ischemic core.</p

Delayed postconditioning (DPC) inhibited BBB leakage.

<p>The ischemic core and penumbra and the non-ischemic hemisphere were dissected for Evan's blue detection. A. Time course of BBB leakage after stroke. The amount of Evan's blue in the ischemic and non-ischemic hemisphere was detected at 6, 24, and 48 h after stroke. Evan's blue penetrated into the ischemic brain tissue as early as 6 h, and persisted up to 48 h. More leakage occurred in the core than in the penumbra. Pen, penumbra; contra, contralateral hemisphere. ** vs. corresponding contralateral hemisphere, P<0.01; ### vs. corresponding penumbra and contralateral hemisphere, P<0.001; & vs. 6 h and 24 h in the penumbra, P<0.05 (Rank sum test). B. The effect of DPC on BBB was detected at 24 h and 48 h after stroke. DPC reduced BBB leakage at 48 h but not at 24 h after stroke in the penumbra; it had no effect on BBB leakage in the ischemic core. N = 5–6/group. C, control ischemia; P, delayed postconditioning. * vs. corresponding contralateral hemisphere, P<0.05; *** vs. corresponding contralateral hemisphere or penumbra, P<0.001. # vs. 48 h-control penumbra, P<0.05.</p

Delayed postconditioning with a series of <i>ipsilateral</i> CCA occlusion and reperfusion reduced infarction.

<p>A. Comparative timelines for delayed postconditioning, in which postconditioning was conducted by occluding or releasing the ipsilateral CCA alone. Delayed postconditioning was performed by 6 cycles of occluding or releasing the left CCA alone; each occlusion or release lasted for 15 min. Delayed postconditioning was initiated at 3 h (group 2), 6 h (group 3), or 12 h (group 4) after reperfusion. Rats in group 1 received 1–2% isoflurane for 3h starting from 6h after reperfusion; this group serves as a control for postconditioning. L. left CCA; R, right CCA. B. Representative infarcts stained with TTC from each group. C. Average infarct size in rats treated with delayed postconditioning. Conditions for each group are indicated below the bar. *, vs. ischemic control (Group 1), P<0.05; # vs group 2, P<0.05.</p

Delayed postconditioning (DPC) attenuated t-PA's worsening effect on infarction.

<p>T-PA (2 mg/kg) was injected intravenously for 1h started at 5 h after ischemia of 30 min bCCA occlusion plus permanent dMCA occlusion; postconditioning with 6 cycles of 15 min occlusion/15 release of the left CCA was performed from 6 h after stroke. Rats were killed 48h later for TTC staining and infarct size measurement. T-PA injection significantly worsened ischemic injury compared with control ischemia; delayed postconditioning attenuated its exacerbating effect. N = 6/group. * P<0.05 vs con or t-PA; # P<0.05,vs t-PA (ANOVA on ranks).</p

Pilot tests for delayed postconditioning.

*<p>, for these tests, the occlusion was conducted one time only, so reperfusion was maintained for 2 days till the animals were euthanized. LCCAO, left CCA occlusion; RCCAO, right CCA occlusion; BCCAO, bilateral CCA occlusion.</p

Effects of delayed postconditioning on FDG uptake.

<p>A. Representative PET imaging for FDG uptake and corresponding TTC staining. PET imaging was conducted 11 h after stroke; delayed postconditioning (DPC) was 6 cycles of 15 min occlusion/15 min release in the ipsilateral CCA. In the ischemic core, no apparent FDG uptake was detected (* indicated by the dark region defined as the ischemic core); in the penumbra, the signal was weaker than that in the contralateral hemisphere. There is a non-specific signal caused by the skin incision outside the brain (arrow). Rats were euthanized 2 d after stroke for TTC staining. The infarct region corroborates with the region with reduced FDG uptake. B. Delayed postconditioning (DPC) did not affect ischemic core sizes measured from PET imaging. PET images from a total of 10 levels, with a 1 mm distance between adjacent levels, were selected. The core area was measured and normalized to the whole contralateral hemisphere and expressed as a percentage; an average value from all measured levels is presented. There was no difference in the core size between rats receiving control ischemia and delayed postconditioning, suggesting that delayed postconditioning did not change FDG uptake in the ischemic core. C. DPC improved FDG uptake. The optical densities of Region of interest (ROI) in the selected 10 coronal slices from rostral (level 1) to caudal (level 10) were measured; ROIs are indicated on the inserted diagram (right corner). Optical densities in three ROIs (1 mm diameter circle) in the cortex from the ipsilateral and contraleral cortex were measured. The average density in the ipsilateral hemisphere was divided by that in the contralateral hemisphere and expressed as a percentage. FDG uptake is significantly higher in the caudal slices (slices 5–10) vs. rostral slices (slices 1–4) in rats receiving DPC; it is also significantly higher in slice 10 than in other slices in rats receiving control ischemia. DPC improved FDG uptake in slices 5 to 10 compared with corresponding slices in control rats. *, *** vs. corresponding time points in control rats, P<0.05, 0.001, respectively. † vs slice 2,3,4,5, P<0.05;. # vs. slice 1,2,3,4, P<0.01; ##, vs. slice 1, 2, 3, 4, 5, P<0.05 (Anova on Ranks followed with Dunn's test). *, *** P<0.05, 0.001, vs corresponding slices in the DPC groups. D. Square means of overall values from all 10 slices. DPC significantly improved overall FDG uptake. *** vs. control ischemia, P<0.001.</p