Advantages of a unique DNA-based vaccine in comparison to paclitaxel in treatment of an established intracerebral breast cancer in mice

Abstract

In this study we compared the benefits of treating C3H/He mice with an established intracerebral breast carcinoma by immunization with a unique DNA-based vaccine to chemotherapy with paclitaxel. Prior studies revealed the immunotherapeutic properties of a vaccine prepared by transfer of genomic DNA from breast cancer cells into a highly immunogenic cell line. Here, C3H/He mice with an established intracerebral breast cancer were treated either by injection into the tumor bed through a unique cannula system with the cell based vaccine or with paclitaxel administered intraperitoneally. Both treatment strategies were effective in prolonging survival and stimulating a systemic anti-tumor immune response (p< 0.025). However, unlike mice treated with the vaccine, the animals that received paclitaxel alone displayed significant toxic side effects. No additional therapeutic advantage was detected when these two treatment strategies were combined. The vaccine tended to provide a somewhat better therapeutic and clearly better systemic immunologic effect based on two independent spleen cell assays in comparison to paclitaxel.

Figure 1

Treatment of C3H/He mice with intracerebral SB5b breast carcinoma with paclitaxel. C3H/He mice (6 animals per group) were injected intracerebrally with 1.0 × 10⁴ SB5b cells into the right frontal lobe. The mice received a single intraperitoneal injection of paclitaxel on the following day. Mean survival time (MST) in days: Untreated Control, 23.1 ± 2.3; Paclitaxel 1.75 mg/kg, 21.8 ± 2.3; Paclitaxel 2.25 mg/kg, 25.2 ± 4.4; Paclitaxel 2.75 mg/kg, 25.8 ± 8.0.

Figure 2

Peripheral white cell count following intraperitoneal injection of paclitaxel. C3H/He mice age received a single intraperitoneal injection of paclitaxel (2.25 mg/kg). Blood samples were then taken from 2 mice each day for one week in order to determine the peripheral white blood cell count. The blood samples were obtained infraorbitally and counted using a hemocytometer. The white blood cell count is the number of cells × 10⁶. Error bars represent one standard deviation.

Figure 3

Treatment of an established intracerebral breast cancer with paclitaxel and/or cytokine-secreting allogeneic fibroblasts transfected with a spontaneous breast neoplasm (SB5b). A cannula was inserted into the right frontal lobe of C3H/He mice (ten animals/group). On the following day each animal received through the cannula a single injection of 1.0 × 10⁴ SB5b cells. On the following day those animals treated with paclitaxel received a single intraperitoneal (i.p.) injection of 2.25 mg/kg paclitaxel. On the following day (day two following tumor injection) and one week later (day 9 following tumor injection) those animals treated with the vaccine received 1.0 × 10⁶ syngeneic/allogeneic fibroblasts transfected with DNA from the breast cancer cells and modified to secrete IL-2 introduced through the cannula into the tumor region. Mean survival time (MST) in days: Untreated, 16.6 ± 1.4; Paclitaxel, 18.4 ± 1.5; Vaccine, 19.2 ± 3.0; Paclitaxel + Vaccine; 18.4 ± 2.6. Probability values were as follows: Paclitaxel vs untreated, p < 0.005; Vaccine vs untreated, p < 0.025; Paclitaxel + vaccine vs untreated, p < 0.05.

Figure 4

MTS assay for determination of cytotoxicity from spleen cells taken from the animals 2 weeks following the intracerebral injection of tumor cells. The target cells used in this study were SB5b breast cancer cells, and the effector (spleen cell) to target cell ratios (E:T) were 50:1 and 100:1. Mononuclear cells from the spleens of the immunized mice obtained through Ficoll-Hypaque centrifugation were used for this assay. The error bars represent one standard deviation. Probability values were as follows: Paclitaxel vs untreated, p = 0.005, 0.011 and 0.025 at E: T ratio 25:1, 50:1 and 100:1 respectively; Vaccine vs untreated, p = 0.011, 0.005 and 0.028 at E: T ratio 25:1, 50:1 and 100:1 respectively; Paclitaxel + vaccine vs untreated, p = 0.020, 0.001 and 0.029 at E: T ratio 25:1, 50:1 and 100:1 respectively; Paclitaxel + vaccine vs Paclitaxel, p= 0.102, 0.7, 0.22 at E: T ratio 25:1, 50:1 and 100:1 respectively.

Figure 5

ELISPOT assay detecting INF-γ secretion by spleen cells (number of spots/10⁶ cells) in the animals two weeks following injection of tumor cells. Mononuclear cells from the spleens of the immunized mice obtained through Ficoll-Hypaque centrifugation were used in this assay. The assay was performed in the presence (SB5b stimulated) and absence (unstimulated) of SB5b tumor cells. The frequency of tumor-specific effector cells in the spleen before vaccination was 0.002%. Probability values were as follows: Paclitaxel vs untreated, p = 0.030; Vaccine vs untreated, p = 0.048; Paclitaxel + vaccine vs untreated, p = 0.029; Paclitaxel + vaccine vs Paclitaxel, p = 0.064.

Terry Lichtor