Figure 5.

The influence of DPP-4 knockdown on promoting primary tumor growth, metastasis and chemoresistance in vivo. Eight-week-old female BALB/c mice were orthotopically implanted with DPP-4 shRNA knockdown (DPP-4-kd) and shRNA-control (control) 4T1 cells into mammary fat pads of each mouse. Concomitantly, the mice were randomly allocated to one of the following four groups: (1) control; (2) DPP-4-kd; (3) control + DOX and (4) DPP-4-kd+DOX groups. When the tumor volumes reached 80–100 mm³, mice were intraperitoneally injected with DOX (5 mg/kg, once a week). Twenty-one days after treatment, the mice were sacrificed, and the primary tumors and lungs were analyzed. (A) The tumor volume in each group was measured ever day during treatment (* p < 0.05). (B) Immunofluorescence analysis of DPP-4 expression in control and DPP-4-kd primary tumors. Western blot analysis of P-gp and ABCG2 expressions in the primary tumor tissue. Densitometric analysis of protein expression relative to β-actin levels (n = 6 per group) was performed by using ImageJ. (C) The lung surface metastases (left panel) were imaged, and the quantification of lung metastases (right panel) was performed by Bouin staining. Black arrows indicated lung surface metastases. The data in the graphs was shown as mean ± SEM; n = 9.