Gastrin releasing protein receptor specific gold nanorods: breast and prostate tumor avid nanovectors for molecular imaging

Abstract

Gastrin releasing protein receptor specific bombesin (BBN) peptide-gold nanoconjugates were successfully synthesized using gold nanorods and dithiolated peptide. The gold nanorod-bombesin (GNR-BBN) conjugates showed extraordinary in vitro stabilities against various biomolecules including NaCl, cysteine, histidine, bovine serum albumin, human serum albumin, and dithiothreitol. Quantitative measurements on the binding affinity (IC(50)) of GNR-BBN conjugates toward prostate and breast tumor cells were evaluated. The IC(50) values establish that GNR-BBN conjugates have strong affinity toward the gastrin releasing peptide receptors on both the tumors. Detailed cellular interaction studies of GNR-BBN conjugates revealed that nanorods internalize via a receptor-mediated endocytosis pathway. The receptor specific interactions of GNR-BBN conjugates provide realistic opportunities in the design and development of in vivo molecular imaging and therapy agents for cancer.

Figure 1

General structure of GNR-BBN conjugates.

Figure 2

GNR-CTAB and GNR-BBN conjugates (a) UV-Visible spectra; (b) TEM images.

Figure 3

In vitro stability studies of GNR-BBN conjugate 2c in various biological media (a) UV-Visible spectra of 2c after 12 hours of treatment with 0.9 % NaCl, cysteine, histidine, HSA or BSA; (b) UV- Visible spectra of 2c in various time points after treatment with DTT at 40 °C.

Figure 4

IC₅₀ values of 2c against ¹²⁵I-BBN in GRP receptors expressing (a) prostate tumor PC-3 cells; (b) breast tumor T-47D cells.

Figure 5

(a) Dark-field image of breast tumor cells (T47D) after treatment with GNR-BBN conjugate 2c; (b) Fluorescence image of nucleus of breast tumor cells; (c) Dark-field and fluorescence overlap images indicating that GNRs are not localized in nuclei.

Figure 6

TEM images of cells after treatment with GNR-BBN conjugate 2c (a) PC-3 cells (b) T-47D. GNR-BBN conjugates are present in cytosol and showing no formation of endosomes.

Figure 7

TEM image of NIH-3T3 cells after treatment with GNR-BBN conjugate 2c.

Scheme 1

Synthesis of GNR-BBN conjugates (2a–2c) followed by treatment with 10% NaCl. Plasmon resonance band of 2a and 2b show broadening after mixing with 10% NaCl; whereas, the plasmon band of 2c remains unaltered.