Abstract 259: Ibrutinib enhances the anti-tumor efficacy of CTLA-4 blockade in lymphoma and colon cancer models

Abstract

Abstract The anti-CTLA-4 antibody ipilimumab was the first immune checkpoint blockade antibody to show significant clinical efficacy. However, only a subset of the treated melanoma patients had long-term survival benefits (Schadendorf, D., et al. ECCO 2013). Combining ipilimumab with an agent that modulates immunity by a different mechanism may improve efficacy. Ibrutinib is a first-in-class, oral, covalent inhibitor of Bruton's tyrosine kinase (Btk), an essential enzyme in the B-cell receptor signaling pathway. Ibrutinib also inhibits the interleukin-2-inducible Tec kinase (Itk) that is required for the activation/survival of Th2 T cells. This activity is consistent with preclinical studies that demonstrated ibrutinib could potentiate Th1 immunity (Dubovsky, JA., et al. Blood 2013). We investigated whether ibrutinib could enhance the anti-tumor effect of CTLA-4 blockade using the A20 B-cell lymphoma and the CT26 colon carcinoma mouse models. BALB/c mice (9-11/group) were implanted with tumor cells subcutaneously on the hind flanks. Animals bearing 80-100 mm3 (D x d2 x 0.4) tumors were dosed daily with oral ibrutinib (24 mg/kg) with or without the anti-mouse CTLA-4 antibody 9D9 (100 μg/mouse) given every 2 days by intraperitoneal injections. Animals in the lymphoma and colon cancer models were treated for 13 and 37 days, respectively. Tumor volume was measured and survival recorded for up to 2 months after tumor inoculation. Neither the A20 tumors, which express Btk, nor the CT26 tumors were inhibited by ibrutinib. In the A20 model, although 9D9 alone resulted in complete tumor regression in 7 of 9 treated animals, tumors in 2 of the 7 mice relapsed after treatment had ended. In contrast, 9D9 in combination with ibrutinib led to rapid, complete, and durable responses in 7 of 9 treated animals that lasted until the end of the study. In the CT26 model, treatment with 9D9 alone had minimal effects on tumor growth, but the addition of ibrutinib led to complete tumor regression in 6 of 10 treated animals. Thus, ibrutinib enhanced the anti-tumor efficacy of an anti-CTLA-4 antibody in B-cell lymphoma and colon carcinoma mouse models. The mechanism of tumor eradication by the combination therapy is under investigation and will be discussed at presentation. Citation Format: Patrick Ng, Daniel Lu, Betty Chang. Ibrutinib enhances the anti-tumor efficacy of CTLA-4 blockade in lymphoma and colon cancer models. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 259. doi:10.1158/1538-7445.AM2015-259