P1-15-02: Nanoparticles Overcome the Decreased Responsiveness of Breast Cancer Cells to a Chemotherapeutic Drug in the Presence of Adipocytes.

Abstract

Abstract Background: Excess adipose tissue plays a role in increasing breast cancer risk and tumor aggressiveness. However, the role of mature adipocytes in tumor progression and response to therapy remains unclear. Despite advances in breast cancer treatment, obese patients still show decreased response to chemotherapy. The incorporation of nanoparticles (NPs) in breast cancer therapeutics represents a novel approach for improving therapy efficacy. NPs increase the drug accumulation in the tumor site resulting in increased drug disposition, decreased cytotoxicity and decreased adverse side effects. However, few studies have evaluated the response to chemotherapy-loaded-NPs in the context of obesity. Gemcitabine is a widely used nucleoside analog that inhibits DNA synthesis. Previously, we prepared a novel gemcitabine formulation by incorporating 4-(N)-stearoyl gemcitabine in solid-lipid NPs (Gem-NPs). We hypothesized that the enhancement of tumor growth and decreased response to therapy in the presence of adipocytes can be offset by treatment with Gem-NPs. To test this we used an in vitro model of adipocyte-conditioned media (CM) and investigated the effects of mature adipocytes on breast cancer cells. Methods: Murine 3T3-L1 adipocytes were induced to differentiate; adipocyte-CM from these cells was collected, centrifuged and used for most assays. Murine (M-Wnt, E-Wnt) and human (MCF-7) cancer cells were grown in RPMI and DMEM, respectively, supplemented with 10% FBS and 1% penicillin/streptomycin at 37 C with 5% CO2. Once the cells were confluent, cells were split and then cultured in the presence of adipocyte-CM (1 or 10%). After gemcitabine and Gem-NPs (50 μM) treatment for 48 h, cell proliferation was measured using the commercial Calcein AM, Annexin V was used to assess apoptosis, and PI staining was used for cell cycle analysis. Invasiveness capacity was measured by culture in a Transwell system with a matrigel invasion assay. CM from undifferentiated 3T3-L1 adipocytes (fibroblasts-CM) were used as a negative control. Results: After 48 h of culture with CM, all cells (M-Wnt, E-Wnt, and MCF-7) showed increased proliferation (p <0.05) and the invasiveness capacity was increased in the presence of adipocyte-CM after 20 h in culture. Cells cultured with adipocyte-CM were less responsive to treatment with gemcitabine (p < 0.01) relative to cells cultured with fibroblasts-CM. The apoptotic response to gemcitabine was decreased, and s-phase arrest was not observed in the presence of adipocyte-CM. However, treatment with Gem-NP overcame the decrease in gemcitabine responsiveness caused by adipocyte-CM, restoring apoptotic response and S-phase arrest. Conclusion: Our results strongly support the role of mature adipocytes in promoting tumor growth and invasiveness while decreasing the response to a standard chemotherapy. Our findings also suggest that incorporating a chemotherapeutic drug into NPs can potentially decrease chemotherapy resistance, particularly in obese patients. Animal studies are underway to evaluate this response in an in vivo mouse model of obesity. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P1-15-02.