Abstract 3354: Relationship between tumor-associated macrophages (TAMs), tumor delivery, and efficacy of PEGylated liposomal doxorubicin (PLD) and non-liposomal doxorubicin (NL-doxo) in genetically engineered mouse models (GEMMs) of breast cancer (BC).

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Introduction: Solid tumors consist of both malignant cells and non-malignant stromal cells. Stromal cells typically include vascular, mesenchymal, and pro-inflammatory cells. Macrophages are the most abundant pro-inflammatory cell type in solid tumors and are termed TAMs. TAMs are derived from monocytes (mononuclear phagocyte system, MPS) and are associated with tumor progression, angiogenesis, and metastasis. The MPS are responsible for the clearance and distribution of nanoparticle (NP) anticaner agents such as PLD. However, the role of MPS in the tumor delivery of NP have not been evaluated. In this study, we evaluated the relationship between TAM-related tumor microenvironment factors, tumor delivery, and efficacy of PLD and NL-doxo in GEMMs of BC. Methods: Basal-like (C3(1)T-antigen) and claudin-low (T11/TP53-/-) GEMMs of human BC subtypes were evaluated. PLD or NL-doxo was administered at 6 mg/kg IV x 1 via a tail vein. For each GEMM, mice (n=3) were sacrificed prior to dose, and from 5 min to 96 h post dose. Plasma encapsulated and released doxo and sum total doxo conc in tumor was measured by HPLC. Area under the plasma and tumor conc versus time curves (AUC) were calculated. TAM infiltration was visualized and measured via immunohistochemistry (IHC) for F4/80. Endothelial cells in tumors were detected by CD31 IHC. Density of TAMs and endothelial cells in tumors were measured by the Aperio analysis algorithms. In efficacy study, PLD or NL-doxo at 6 mg/kg was administered every week for 6 weeks (n=20 per model). Tumor growth and overall survival were monitored. Results: Mean ± SD of plasma AUC of PLD encapsulated doxo in T11 and C3tag were1,449 ± 57 and 1,610 ± 111 (μg·h/ml), respectively. Mean ± SD of tumor sum total AUC of PLD in T11 and C3tag were 210 ± 26 and 480 ± 71 (μg·h/ml), respectively. Mean ± SD of tumor AUC of NL-doxo in T11 and C3tag were 61 ± 12 and 57 ± 10 (μg·h/ml), respectively. Mean ± SD baseline % positive cells of TAM in T11 and C3tag were 113 ± 45 and 110 ± 50, respectively. Mean ± SD baseline microvessel density in T11 and C3tag were 8.8 ± 2.5 and 6.1 ± 1.8 (number of vessels x10ˆ5 per unit area), respectively. C3tag demonstrated greater antitumor response to PLD compared to T11. Conclusions: There was a substantial difference in tumor exposure of PLD, but not NL-doxo, in the two GEMMs. These findings suggest that TM factors in BC may affect the delivery of NP agents, but not small molecules (SM). However, the similar TAM and microvessel baseline density in GEMMs suggest alternative tumor factors specifically affecting the delivery of NP agents. Further studies are warranted to elucidate the mechanisms underlying the delivery of NP agents in these and other tumors which may explain different tumor phenotypes and therapeutic outcomes related to treatment with NP and SM agents. Citation Format: Gina Song, David B. Darr, Charlene M. Santos, Taylor F. White, Jamie L. Jordan, Mimi Kim, Bentley R. Midkiff, Nana N. Feinberg, Ryan Miller, Arlin B. Rogers, Andrew C. Dudley, Charles M. Perou, William C. Zamboni. Relationship between tumor-associated macrophages (TAMs), tumor delivery, and efficacy of PEGylated liposomal doxorubicin (PLD) and non-liposomal doxorubicin (NL-doxo) in genetically engineered mouse models (GEMMs) of breast cancer (BC). [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 3354. doi:10.1158/1538-7445.AM2013-3354