Abstract 4286: Development of a safe and effective systemically administered multiple Toll-like receptor (TLR) agonist for anti-tumor immunotherapy

Abstract Summary We have developed methods for detoxification and killing of Gram-negative bacteria, which significantly reduce both lipopolysaccharide (LPS) and non-LPS-mediated endotoxin activity and pyrogenicity, without compromising stimulation of anti-tumor immune responses. Background The field of cancer immunotherapy was founded in the late 1800s, based on the observation of tumor regression in the setting of bacterial infection. This was reproduced with intentionally administered live bacteria, but the approach was not safe due to infection and septic shock. A mixture of heat killed bacteria (Coley's toxins) produced long-term responses in advanced cancer patients over 100 years, but was apparently too toxic for safe intravenous (iv) administration at effective doses. In addition, lack of understanding of efficacy and toxicity mechanisms prevented optimization. Discovery of the role of TLRs in immune function has provided a mechanistic rationale for reconsideration of this approach. Gram-negative bacteria were required for the anti-tumor activity of Coley's toxins, due to the presence of multiple TLR agonists, including LPS, which is not produced by Gram-positive bacteria. However, too much TLR activation can over-stimulate the immune system, leading to toxicity. Attempts to produce live, attenuated Gram-negative bacteria for systemic cancer therapy have not been successful. A Phase 1 trial of one product produced dose-limiting symptoms of bacterial infection and septic shock, without evidence of antitumor activity. These historical observations suggest that a killed and appropriately attenuated Gram-negative product might produce significant anti-tumor activity if it could be administered safely iv. Methods and Results Non-pathogenic Gram-negative bacteria were treated with polymyxin B and glutaraldehyde. Endotoxin activity and pyrogenicity were quantified using Limulus amebocyte lysate (LAL) and rabbit pyrogenicity assays. Bacterial integrity was assessed by EM. Antitumor activity was determined using syngeneic tumors in mice. Treatment was found to kill the bacteria and reduce LPS-mediated endotoxin activity by ≥12-fold and non-specific pyrogenicity by ≥30-fold, with retention of cell integrity. The first product, DB103, was approximately 2,500-fold less toxic in mice than a previously described live, attenuated preparation, and produced significant dose-dependent in vivo antitumor activity at non-toxic doses. DB103 was also additive or synergistic in vivo when combined with each of four different established antitumor immunotherapies, including IL-2, metronomic cyclophosphamide, and anti-CTLA-4 or anti-GITR antibodies. Conclusions We have developed a multiple TLR agonist that can be safely and effectively administered systemically alone or in combination with a wide variety of existing anti-tumor immunotherapies. Citation Format: Michael J. Newman. Development of a safe and effective systemically administered multiple Toll-like receptor (TLR) agonist for anti-tumor immunotherapy. [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 4286. doi:10.1158/1538-7445.AM2015-4286