Targeted nanoagents for the detection of cancers

Abstract

Nanotechnology has enabled a renaissance in the diagnosis of cancers. This is due, in part to the ability to develop agents bearing multiple functionalities, including those utilized for targeting, imaging, and therapy, allowing for the tailoring of the properties of the nanomaterials. Whereas many nanomaterials exhibit localization to diseased tissues via intrinsic targeting, the addition of targeting ligands, such as antibodies, peptides, aptamers, and small molecules, facilitates far more sensitive cancer detection. As such, this review focuses upon some of the most poignant examples of the utility of affinity ligand targeted nanoagents in the detection of cancer.

Figure 1

Commonly utilized modalities for in vivo fluorescence imaging. A) Simplified schematic representation of a fluorescence reflectance imaging (FRI) system. B) FRI yields a planar image lacking information regarding the depth of the fluorophore. C) Simplified schematic representation of a fluorescence molecular tomography (FMT) system. D) FMT yields images that can be reconstructed in three dimensions, such as the hybrid FMT‐CT image shown. Reproduced, in part, with permissions from Nahrendorf et al. (2009) and Ntziachristos, 2006.

Figure 2

MRI nodal abnormalities in two patients with prostate cancer. As compared with conventional MRI (A), MRI obtained 24 h after the administration of superparamagnetic nanoparticles (B) shows a homogeneous decrease in signal intensity due to the accumulation of the nanoparticles in a normal lymph node (arrow). Conventional MRI shows a high signal intensity in an unenlarged iliac lymph node completely replaced by tumor (arrow in C). Nodal signal intensity remains high (arrow in D). Reproduced, in part, with permission from Harisinghani et al. (2003).

Figure 3

In vivo near‐infrared imaging of EGFR‐positive tumors. MDA‐MB‐231 or MCF‐7 cells were injected into the left chest mammary gland fat pad of female athymic nude mice. Representative whole‐body NIR images of MDA‐MB‐231 and MCF‐7 xenograft mice at 24 h post‐injection of cetuximab‐Cy5.5 conjugate are shown. A and C) Fluorescence signal is clearly visualized in the left thoracic tumor region of MDA‐MB‐231 and MCF‐7 xenografts. B and D) Blocking experiment indicates an apparent decrease of fluorescent signals by pre‐injection of excess cetuximab (tumors indicated by arrows). Reproduced with permission from Wang et al. (2009).

Figure 4

Generalized screening repertoire for the discovery of targeting peptides and aptamers. A) Libraries of aptamers or bacteriophage are plated with the target of interest. This may be purified protein immobilized on a plate or cell‐based. B) Non‐bound sequences are removed from the target by repetitive washing. C) Bound sequences are isolated from the target of interest. D) The isolated aptamers and phage are amplified by polymerase chain reaction (PCR) or via infection of E. coli, respectively. E) The expanded aptamers or phage are either subjected to additional rounds of screening, or are sequenced in order to identify the targeting ligand.

Figure 5

Surface plasmon resonance (SPR) characterization of the binding of small molecule‐modified nanoagents to their target protein. A) Schematic representation of SPR for free small molecules (top) and those bound multivalently to nanoparticles (bottom). B‐I) Conjugation of a series of synthetic derivatives of FK506. B‐II) Conjugation of a small molecule that binds aurora A kinase. C) Rate maps summarizing binding affinity and kinetics. Different combinations of ka and kd that result in the same KD are indicated by dashed lines. Data for free ligands are depicted by open symbols; for each ligand, the corresponding nanoparticles are depicted by a solid symbol of the same shape, with conjugation valency listed in parentheses next to the solid symbol. Reproduced with permission from Tassa et al. (2010).

Figure 6

Dual modality imaging of mouse mammary tumor using magnetofluorescent uPA receptor‐targeted nanoagent. A) NIR optical imaging of tumor targeting and tissue distribution of targeted nanoparticles over time. Pink arrows, tumor; green arrows, kidneys. B) Back and side images are at 72 h. C) Simultaneous magnetic resonance and optical imaging of mammary tumor. Optical imaging reveals the NIR signal in the tumor area corresponding well with the MR imaging results (bottom, pink dashed lined). T2 contrast change is not detected in the s.c. tumor of the mouse that received non‐targeted iron oxide nanoparticles (top). Reproduced with permission from Yang et al. (2009b).

Figure 7

Imaging of prostate cancer. A and B) Mice bearing tumors derived from PC‐3 (left flank) or LNCaP (right flank) were coinjected with IPL‐modified nanoagent and then imaged, illustrating preferential localization by HPN‐expressing cancers. The HPN‐targeted nanoparticles were also able to identify human prostate cancer. The IPL‐modified nanoparticle was incubated with tissue microarrays consisting of six normal and five cancer human radical prostatectomy specimens. Results shown are representative images. C and E) binding of nanoagent to cancer glands. D and F) binding to benign glands. Reproduced with permission from Kelly et al. (2008).