Radiofrequency ablation combined with KS-IL2 immunocytokine (EMD 273066) results in an enhanced antitumor effect against murine colon adenocarcinoma

Abstract

Purpose: Radiofrequency ablation (RFA) is a common treatment modality for surgically unresectable tumors. However, there is a high rate of both local and systemic recurrence.

Experimental design: In this preclinical study, we sought to enhance the antitumor effect of RFA by combining it with huKS-IL2 immunocytokine [tumor-specific monoclonal antibody fused to interleukin-2 (IL2)] in mice bearing CT26-KS colon adenocarcinoma. Mice were treated with RFA, huKS-IL2 via intratumoral injection, or combination therapy.

Results: Treatment of mice bearing s.c. tumors with RFA and huKS-IL2 resulted in significantly greater tumor growth suppression and enhanced survival compared with mice treated with RFA or huKS-IL2 alone. When subtherapeutic regimens of RFA or huKS-IL2 were used, tumors progressed in all treated mice. In contrast, the combination of RFA and immunocytokine resulted in complete tumor resolution in 50% of mice. Treatment of a tumor with RFA and intratumoral huKS-IL2 also showed antitumor effects against a distant untreated tumor. Tumor-free mice after treatment with RFA and huKS-IL2 showed immunologic memory based on their ability to reject subsequent challenges of CT26-KS and the more aggressive parental CT26 tumors. Flow cytometry analysis of tumor-reactive T cells from mice with complete tumor resolution showed that treatment with RFA and huKS-IL2 resulted in a greater proportion of cytokine-producing CD4 T cells and CD8 T cells compared with mice treated with RFA or huKS-IL2 alone.

Conclusions: These results show that the addition of huKS-IL2 to RFA significantly enhances the antitumor response in this murine model, resulting in complete tumor resolution and induction of immunologic memory.

Figures

Figure 1

RFA and huKS-IL2 IC synergize in induction of antitumor effects. A, Groups of Balb/c mice (7–8 mice per group) were implanted with 5 × 105 CT26-KS tumor cells s.c. on the abdomen on day 0. Mice were treated with partial RFA (25 seconds, day 11), huKS-IL2 (15 μg, days 11–15), or both RFA and huKS-IL2 IC. Untreated tumor-bearing mice served as controls. Data shown are mean tumor volume ± SEM. B, RFA and huKS-IL2 IC therapy prolongs survival of mice. Balb/c mice bearing CT26-KS tumors were treated as described above and followed until euthanasia due to large tumor size was required. Results in A and B are representative of 3 similar experiments. C, Groups of Balb/c mice (n = 8 mice per group) were implanted with CT26-KS tumors as above and treated with partial RFA alone, RFA and 15 μg huKS-IL2 IC on days 10–14, or RFA and 37.5 μg huKS-IL2 IC on days 10 and 14. Data shown are mean tumor volume ± SEM.

Figure 2

RFA and huKS-IL2 synergize in inducing T cell activation. Splenocytes from animals rendered tumor-free after “complete” RFA, huKS-IL2 IC, complete surgical excision, or combination therapy were followed for 30 days for tumor recurrence.. Mice were sacrificed and splenocytes were isolated, along with age-matched naive animals. Cytokine production was measured via flow cytometry after 5 days of in vitro stimulation with CT26-KS tumor cells. Numbers represent percent CD4 or CD8 positive cells expressing IFN-γ or GM-CSF. A, single representative experiment; B, mean of 3–5 experiments.