Effects of nanoparticle size on antitumor activity of 10-hydroxycamptothecin-conjugated gold nanoparticles: in vitro and in vivo studies

Abstract

Gold nanoparticles (AuNPs) have emerged as a promising anticancer drug delivery scaffold. However, some controversial points still require further investigation before clinical use. A complete understanding of how animal cells interact with drug-conjugated AuNPs of well-defined sizes remains poorly understood. In this study, we prepared a series of 10-hydroxycamptothecin (HCPT)-AuNP conjugates of different sizes and compared their cytotoxic effect in vitro and antitumor effect in vivo. Transmission electron micrographs showed that the NPs had a round, regular shape with a mean diameter of ~10, 25, and 50 nm. An in vitro drug release study showed that HCPT was continuously released for 120 hours. HCPT-AuNPs showed greater cytotoxic effects on the MDA-MB-231 cell line compared with an equal dose of free HCPT. Notably, HCPT-AuNPs of an average diameter of 50 nm (HCPT-AuNPs-50) had the greatest effect. Furthermore, administration of HCPT-AuNPs-50 showed the most tumor-suppressing activity against MDA-MB-231 tumor in mice among all treatment groups. The results indicate that AuNPs not only act as a carrier but also play an active role in mediating biological effects. This work gives important insights into the design of nanoscale delivery and therapeutic systems.

Keywords: cancer treatment; drug delivery; drug-containing nanocomposites; particle size.

Figure 1

Characterization of nanoparticles. Notes: (A–C) Transmission electron micrographs and (D) UV–vis absorption spectra of different-sized HCPT-AuNP formulations (scale bar 50 nm). HCPT-AuNPs-10, 25 and 50: HCPT-AuNPs of an average diameter of 10, 25 and 50 nm. The magnification of the picture is (×100,000). Abbreviations: UV–vis, ultraviolet–visible; HCPT, 10-hydroxycamptothecin; AuNPs, gold nanoparticles.

Figure 2

Stability analyses of HCPT-AuNPs-50 conjugates as a function of time in different environments. Notes: (A) Dispersion stability of nano-conjugate. (B) Size variation of nano-conjugate. HCPT-AuNPs-10, 25 and 50: HCPT-AuNPs of an average diameter of 10, 25 and 50 nm. Abbreviations: HCPT, 10-hydroxycamptothecin; AuNPs, gold nanoparticles; PBS, phosphate-buffered saline; DMEM, Dulbecco’s Modified Eagle’s Medium; FBS, fetal bovine serum.

Figure 3

HCPT adsorption onto and release from AuNPs. Notes: (A) Adsorption curve of HCPT onto HCPT-AuNPs conjugate. (B) The in vitro release of HCPT from HCPT-AuNPs conjugate in PBS. (C) The in vitro release of HCPT from HCPT-AuNPs conjugate in cell culture medium at 37°C±0.5°C. HCPT-AuNPs-10, 25 and 50: HCPT-AuNPs of an average diameter of 10, 25 and 50 nm. Abbreviations: HCPT, 10-hydroxycamptothecin; AuNPs, gold nanoparticles; PBS, phosphate-buffered saline.

Figure 4

Uptake of HCPT-AuNPs and HCPT into MDA-MB-231 cells. Notes: Results are expressed as mean ± SD. ^#P<0.05 and ^##P<0.01 compared with free HCPT. HCPT-AuNPs-10, 25 and 50: HCPT-AuNPs of an average diameter of 10, 25 and 50 nm. Abbreviations: HCPT, 10-hydroxycamptothecin; AuNPs, gold nanoparticles; SD, standard deviation; PBS, phosphate-buffered saline.

Figure 5

Cytotoxicity studies assayed by the MTT method. Notes: (A) The influence of HCPT, different-sized PSH-AuNPs, and HCPT-AuNPs on the survival of MDA-MB-231 cells (HCPT concentration 50 μg/mL). (B) Cytotoxicity studies of different concentrations of HCPT-AuNPs and HCPT on MDA-MB-231 cells. The results are expressed as mean ± SD. HCPT-AuNPs-10, 25 and 50: HCPT-AuNPs of an average diameter of 10, 25 and 50 nm. Abbreviations: MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; HCPT, 10-hydroxycamptothecin; PSH, α-methoxy-poly (ethylene glycol)-ω-mercapto; AuNPs, gold nanoparticles; SD, standard deviation.

Figure 6

Antitumor effect of different sizes of PSH-AuNPs, HCPT-AuNPs, free HCPT, and a control in a xenograft model of MDA-MB-231 subcutaneous breast cancer implanted into nude mice. Notes: (A) Bioluminescent imaging by luciferase. (B) Quantification analysis of bioluminescent imaging. ^#P<0.05 and ^##P<0.01 vs 0 day as control. (C) Tumor volume changes. (D) Tumor tissue weight 21 days post-therapy. (E) Body weight changes. Data were represented as mean ± SD (n=5). HCPT-AuNPs-10, 25 and 50: HCPT-AuNPs of an average diameter of 10, 25 and 50 nm. Abbreviations: PSH, α-methoxy-poly (ethylene glycol)-ω-mercapto; AuNPs, gold nanoparticles; HCPT, 10-hydroxycamptothecin; SD, standard deviation.

Figure 7

Histological assessment. Notes: Representative H&E staining photomicrographs of the (A) heart, (B) liver, (C) spleen, (D) lung, and (E) kidney in HCPT-AuNPs-50 group (×100). HCPT-AuNPs-50: HCPT-AuNPs of an average diameter of 50 nm. Abbreviations: H&E, hematoxylin and eosin, HCPT, 10-hydroxycamptothecin; AuNPs, gold nanoparticles.