The comparative anti-cancer effects of krill oil and oxaliplatin in an orthotopic mouse model of colorectal cancer

Abstract

Background: Our in vitro studies demonstrated that krill oil (KO) has anti-cancer potential. This study aimed to compare the anti-cancer effects of KO with a commonly used chemotherapeutic drug, oxaliplatin and to identify the molecular mechanisms associated with KO supplementation in a mouse model of colorectal cancer (CRC).

Methods: Thirty-six male Balb/c mice were randomly divided into six groups. Five groups received standard chow diet supplemented with KO (150 g/kg)), corn oil (150 g/kg), KO combined with ½ dose of oxaliplatin (1.5 mg/kg body weight/3 times per week), corn oil combined with ½ dose of oxaliplatin (1.5 mg/kg body weight/3 times per week), or a full dose of oxaliplatin (3 mg/kg body weight/3 times per week). The control (sham) group received a standard chow diet. Treatments started three weeks before and continued for three weeks after orthotopic CRC induction. The number of metastases, tumour weight and volume were quantified ex-vivo. The expression of cytochrome c, cleaved caspase-9 and -3, DNA damage, PD-L1, PD-L2 and HSP-70 were determined.

Results: A significant reductions in the weight and volume of tumours were observed in mice treated with KO and KO plus a ½ dose of oxaliplatin compared to the sham group, similar to oxaliplatin-treated mice. KO, and KO plus ½ dose of oxaliplatin significantly increased the expression of cytochrome c, cleaved caspase-9 and -3, and DNA damage and decreased expression of PD-L1, PD-L2 and HSP-70 in tumour tissues compared to the sham group.

Conclusions: The in vivo anti-cancer effects of KO are comparable with oxaliplatin. Thus, dietary KO supplementation has a great potential as a therapeutic/adjunctive agent for CRC treatment.

Keywords: Caspase 3/9; HSP-70; Krill oil; Orthotopic model of colorectal cancer; Oxaliplatin; PD-L1/PD-L2.

Fig. 1

The schematic overview of study design

Fig. 2

Effects of treatments on the body weight, survival rate, and tumour growth in Balb/c mice with orthotopic CRC. A The effects of treatments on the animal body weight. B Kaplan–Meier survival plot representing the percentage of survival of mice after treatment. C Representative images of orthotopic tumours excised from different treatment groups. D Representative histology images of tumour tissues (H&E stained, Magnification = 20X). E The mean tumour weight and F volume following various treatments. N = 6 mice per group. The results are expressed as mean ± SEM; ***P < 0.001 compared to the sham group

Fig. 3

Expression of cytochrome c and cleaved caspase-9 following treatments. The expression of cytochrome c (A) and cleaved caspase-9 (B) in tumours following different treatments determined immunohistochemically using monoclonal antibodies. Quantitative analysis of the fluorescence intensity of cytochrome c (C) and cleaved caspase-9 (D) expression in tumour tissues following various treatments determined by immunohistochemistry. Scale bar = 50 µM. Magnification = 40X. N = 6 mice per group. The level of fluorescence was measured using 8 randomly taken images that provide a total area of 1 mm². The results are expressed as mean ± SEM; *P < 0.05, ***P < 0.001 compared to the sham group; ^^^P  < 0.001 compared to the oxaliplatin-treated group. E The expression of cytochrome c and cleaved caspase-9 measured by western blotting in tumours from different treatment groups

Fig. 4

Expression of cleaved caspase-3 and DNA damage following treatments. The expression of cleaved caspase-3 (A) and DNA damage (B) in tumours following different treatments determined immunohistochemically using monoclonal antibodies. Quantitative analysis of the fluorescence intensity of cleaved caspase-3 (C) and DNA damage (D) expression in tumour tissues following various treatments determined by immunohistochemistry. Scale bar = 50 µM. Magnification = 40X. N = 6 mice per group. The level of fluorescence was measured using 8 randomly taken images that provide a total area of 1 mm². The results are expressed as mean ± SEM; *P < 0.05, **P < 0.01, ***P < 0.001 compared to the sham group; ^^^P < 0.001 compared to the oxaliplatin-treated group. E The expression of cleaved caspase-3 and DNA damage measured by western blotting in tumours following various treatments

Fig. 5

Expression of PD-L1 and PD-L2 following treatments. The expression of PD-L1 (A) and PD-L2 (B) in tumours following the treatments determined immunohistochemically using monoclonal antibodies. Quantitative analysis of the fluorescence intensity of PD-L1 (C) and PD-L2 (D) expression in tumour tissues following various treatments determined by immunohistochemistry. Scale bar = 50 µM. Magnification = 40X. N = 6 mice per group. The level of fluorescence was measured using 8 randomly taken images that provide a total area of 1 mm². The results are expressed as mean ± SEM; *P < 0.05, **P < 0.01, ***P < 0.001 compared to the sham group. E The expression of PD-L1 and PD-L2 measured by western blotting in tumours following various treatments

Fig. 6

Expression of PD-1 and HSP-70 following treatments. The expression of PD-1 (A) and HSP-70 (B) in tumours following various treatments determined immunohistochemically using monoclonal antibodies. Quantitative analysis of the fluorescence intensity of PD-1 (C) and HSP-70 (D) expression in tumour tissues following various treatments determined by immunohistochemistry. Scale bar = 50 µM. Magnification = 40X. N = 6 mice per group. The level of fluorescence was measured using 8 randomly taken images per specimen at 40 × magnification that provide a total area of 1 mm². The results are expressed as mean ± SEM; *P < 0.05, **P < 0.01 compared to the sham group