Abstract 3981: Reprogramming tumor associated macrophages toward an anti-tumor phenotype by targeting the NF-κB pathway using novel targeted nanotherapeutics.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Tumor associated macrophages (TAMs) can modify the tumor microenvironment to create an inflammatory, pro-tumor niche. Activation of the NF-κB pathway has been implicated in creating a pro-tumor phenotype in TAMs. Manipulation of TAM phenotype is a new approach to engage anticancer immunity, but has been limited by a lack of methods capable of therapeutic delivery to TAMs in vivo. We have successfully utilized mannosylated polymer nanoparticles capable of disrupting the endosomal compartment to deliver siRNA for RNAi of NF-κB proteins into bone marrow derived macrophages (BMDMs) derived from transgenic mice with a GFP/Luciferase reporter of NF-κB activity (NGL). In in vitro studies, the nanoparticles are comparable to commercial transfection agents using both gene and protein level readouts for knockdown. The transfection protocol utilizing these novel vehicles has been optimized with respect to transfection time, siRNA dose, and siRNA:polymer ratio with the intent to inform in vivo experiments. The presence of serum does not significantly affect transfection efficiency in vitro, presumably due to an almost neutral particle surface charge. Preliminary in vivo studies have revealed no significant particle toxicity. Delivering siRNA specific to the p52/p100 protein in the alternative pathway achieves knockdown of total NF-κB activity by approximately 80% in NGL BMDMs stimulated by TNF-α. By targeting proteins in the classical pathway, we have decreased total NF-κB activity by approximately 50% in the same model. While inhibition of NF-κB activity may be desirable in some contexts, we recently reported that induced activation of NF-κB in macrophages can result in anti-tumor activity. We have delivered a liposomal formulation of muramyl tripeptide (Mifamurtide), a synthetic derivative of a bacterial cell wall peptide and an activator of macrophages, to NGL BMDMs. Mifamurtide delivery increases both NF-κB activity, and the production of reactive oxygen species, indicating a preliminary mechanistic explanation for the therapeutic potential of NF-κB activation. Mifamurtide is used clinically in the European Union to treat osteosarcoma, potentially providing an avenue for rapid clinical translation of NF-κB modulating therapy for other tumor types. However, Mifamurtide has the potential to activate multiple pathways simultaneously. A more elegant approach would be to target knockdown of an NF-κB inhibitor to macrophages to mediate pathway specific activation. In preliminary studies we have demonstrated the ability to increase total NF-κB activity by treating NGL macrophages with nanoparticles carrying siRNA against the IκBα inhibitor of NF-κB. Our data provides evidence that delivering siRNA specifically to macrophages to modulate their functions using nanoparticles has potential as a therapeutic approach to cancer treatment. Citation Format: Ryan A. Ortega, Whitney Barham, Bharat Kumar, Shann S. Yu, Fiona Yull, Todd D. Giorgio. Reprogramming tumor associated macrophages toward an anti-tumor phenotype by targeting the NF-κB pathway using novel targeted nanotherapeutics. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3981. doi:10.1158/1538-7445.AM2013-3981