Abstract 965: Two in one: nanotechnology based strategies for the treatment of ER+ breast cancer

Abstract

Abstract Understanding endocrine resistance mechanisms is key to develop new therapeutic strategies. We focus on the role the tumor microenvironment plays as a modulator of endocrine therapy resistance in breast cancer, in particular associated to Tamoxifen. Studies show that the use of nanoparticles (NPs) as antitumor drug delivery systems is a good strategy to improve the efficacy and decrease secondary effects of conventional chemotherapies. In this context we hypothesize that a therapeutic strategy based on the use of Tamoxifen carried in NPs coated with the tumor penetrating peptide iRGD, would be more effective than conventional Tamoxifen. Neuropilin-1, that mediates iRGD induced endocytosis, has been shown to be associated to breast cancer stem cells. Thus, we postulate that our multifunctional NPs would be effective in reducing this cell population, contrary to what is observed with free Tamoxifen. Moreover, iRGD blocks the interaction between integrin β1 and fibronectin, a mechanism we have previously shown induces Tamoxifen resistance (Pontiggia et al. 2012). NPs were synthesized with polyethyleneglycol and polycaprolactone and coated with the iRGD peptide. This peptide was constructed with a FAM fluorophore in order to track the NPs. To evaluate the cell uptake, MCF-7 cells were incubated for 5 h with iRGD-NP or FAM-NP as a control. NP entry was higher when the NPs were coated with iRGD, both in 2D and in 3D cultures. Cell viability experiments revealed that Tamoxifen encapsulated in NPs was more effective than the free drug (p<0,05), and NPs coated with iRGD had an even stronger effect (p<0,01). Moreover, resistance to Tamoxifen induced by fibronectin was reversed with the iRGD-coated NPs, contrary to what is observed with the free drug. Previously, we demonstrated that treatment with Tamoxifen enhances the stem cell population in estrogen receptor-positive breast cancer cell lines (Raffo et al. 2013). In this context iRGD coated NPs lead to a decrease in breast cancer stem cells as evaluated by mammosphere assays (p<0,01). Finally, in vivo tumor homing was evaluated to test whether the iRGD peptide affected the biodistribution of the NPs. Nude mice carrying MCF-7 breast tumors were treated with iRGD-NP and control NPs. Tumors were collected at 4 and 24 hrs post inoculation. Frozen sections were analyzed by confocal microscopy revealing that only the mice treated with the iRGD-NPs had high levels of NPs in the tumor, compared to the control group. Moreover, frozen sections of kidneys, livers, lungs and spleen showed very low levels of iRGD-NPs, confirming that the targeting was effective. In vivo experiments of the impact of iRGD-NPs on tumor growth, metastasis and the stem cell population are ongoing. These results suggest that iRGD-NPs carrying Tamoxifen could be an effective strategy to avoid the development of endocrine resistance in breast cancer. Citation Format: Maria Ines Diaz Bessone, Lorena Simón-Gracia, Pablo Scodeller, Tambet Teesalu, Marina Simian. Two in one: nanotechnology based strategies for the treatment of ER+ breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 965. doi:10.1158/1538-7445.AM2017-965