Neoadjuvant Gold Nanoshell-Based Photothermal Therapy Combined with Liposomal Doxorubicin in a Mouse Model of Colorectal Cancer

Abstract

Introduction: Traditional cancer treatments, such as chemotherapy, are often incapable of achieving complete responses as standalone therapies. Hence, current treatment strategies typically rely on a combination of several approaches. Nanoparticle-based photothermal therapy (PTT) is a technique used to kill cancer cells through localized, severe hyperthermia that has shown promise as an add-on treatment to multiple cancer therapies. Here, we evaluated whether the combination of gold nanoshell (NS)-based PTT and liposomal doxorubicin could improve outcome in a mouse model of colorectal cancer.

Methods: First, NS-based PTT was performed on tumor-bearing mice. Radiolabeled liposomes were then injected at different timepoints to follow their accumulation in the tumor and determine the ideal injection time after PTT. In addition, fluorescent liposomes were used to observe the liposomal distribution in the tumor after PTT. Finally, we combined PTT and doxorubicin-loaded liposomes and studied the effect of the treatment strategy on the mice by following tumor growth and survival.

Results: PTT significantly improved liposomal accumulation in the tumor, but only when the liposomes were injected immediately after the therapy. The liposomes accumulated mostly in regions adjacent to the ablated areas. When PTT was combined with liposomal doxorubicin, the mice experienced a slowdown in tumor growth and an improvement in survival.

Conclusion: According to our preclinical study, NS-based PTT seems promising as an add-on treatment for liposomal chemotherapy and potentially other systemic therapies, and could be relevant for future application in a clinical setting.

Keywords: PET imaging; chemotherapy; gold nanoparticles; hyperthermia; liposomes.

Graphical abstract

Figure 1

Distribution of ⁶⁴Cu-loaded liposomes after PTT in mice bearing CT26 tumors. (A). Representative images of a tumor at different time points during irradiation, captured with a thermal camera. (B). Temperature increase for all three groups of mice undergoing PTT, detected with the thermal camera (0 h, 6 h and 24 h). Data were shown as mean ± standard error of the mean (SEM). (C). Representative PET/CT images of mice 10 minutes and 24 hours after administration of ⁶⁴Cu-loaded liposomes. (D). Liposome accumulation in the tumor shown as mean percentage of injected dose per gram of tissue (%ID/g) for the different groups of mice (Control, 0 h, 6 h, and 24 h; n = 5 per group), 10 minutes and 24 hours after liposome administration. * represents p < 0.05, ** represents p < 0.01, and *** represents p < 0.001. n.s. means non-significant. (E). Correlation between the mean %ID/g (from the PET scans) and the maximum temperature reached during PTT (recorded with the thermal camera) for each mouse.

Figure 2

DiI liposomal distribution ex vivo in CT26 tumors and histological analysis. (A). Fluorescent DiI signal on 20 μm tumor slices for the different groups detected on the Amersham Typhoon Biomolecular Analyzer (n = 3). (B). Fluorescent signal on 4 μm tumor slices detected by microscopy. (C). HE staining. (D). Ki-67 staining. Arrows point to positive staining, denoted by brown color. T refers to treated tissue and H refers to healthy tissue. (E). CD31 staining.

Figure 3

PTT as neoadjuvant treatment to DOX-loaded liposomes in mice bearing CT26 tumors. (A). Simplified timeline of the treatment schedule for mice undergoing combination treatment. Mice were injected with NS 24 hours before PTT. The following day, they were treated with the laser and immediately after they were injected with DOX-loaded liposomes. Tumor growth was followed by mechanical caliper measurements until endpoints were reached. Created with BioRender.com. (B). Temperature increase for all groups of mice undergoing PTT (PTT, PTT + DOX, and PTT + LIP), detected with a thermal camera. Data shown as mean ± SEM. (C). Survival curves for all groups included in the study; PTT (n = 16), LIP (n = 15), DOX (n = 15), PTT + LIP (n = 16), PTT + DOX (n = 15), and Control (n = 15). Study was terminated on day 60. (D–I). Growth curves for the individual mice in each of the groups.