Abstract 2198: Integrin αvβ3-targeted lipase-labile docetaxel-prodrug micelles preferentially treat breast cancer bone metastases
Authors: Ross Michael H. , Esser Alison K. , Schmieder Anne H. , Cui Grace , Yang Xiaoxia , Su Xinming , Pan Dipanjan , Lanza Gregory M. , Weilbaecher Katherine N. 
Published: July 2016

Background: Bone metastases occur in 70% of metastatic breast cancer patients and are a leading cause of morbidity. Current therapies are often palliative, in part due to a lack of specificity for tumor targets within the bone. Integrin αvβ3 is overexpressed on neo-angiogenic blood vessels, tumor-promoting macrophages, osteoclasts, and more aggressive breast cancer cells, making it an attractive therapeutic target.

Objective: The goal of this study was to use Sn2 lipase-labile docetaxel-prodrug nanoparticle, targeted against activated integrin αvβ3, to attenuate breast cancer metastases.

Methods: A novel phospholipid-based micelle (∼12.5 nm) was functionalized with a peptidomimetic for activated integrin αvβ3, and designed to carry either rhodamine for fluorescent labeling or Sn2 lipase-labile prodrug of docetaxel (DTX-PD) for drug delivery. For microscopic localization studies, fluorescently labeled micelles were prepared with or without integrin αvβ3-targeting. C57BL/6 female mice received MMTV-PyMT breast cancer cell line (luciferase-labeled) via intracardiac (IC) injection to achieve tumor metastasis in all major organs. On day 8 post-IC injection, micelle preparations were administered i.v. and circulated within C57BL/6 mice for 3 hours prior to sacrifice and tissue collection. For drug efficacy studies, Sn2 lipase-labile docetaxel-prodrug was incorporated into αvβ3-micelles (αvβ3-DTX-PD). C57BL/6 female mice IC injected with MMTV-PyMT cells (luciferase-labeled) were treated with αvβ3-DTX-PD, or molar equivalent dose of free-DTX, or saline. Beginning on day 4 post-IC injection, mice were treated 3 times, once every 3 days (1.85mg/kg DTX per treatment). On day 12 post-IC injection, metastatic burden in the major organs was analyzed via ex vivo bioluminescent imaging.

Results: Fluorescent histological analysis of the tibiofemoral bone region showed significant colocalization of αvβ3-micelles with breast cancer bone metastases, as compared with non-targeted micelles (6.5-fold increase, p&lt;0.001). αvβ3-micelles did not localize within tumor-free bones. In drug efficacy analysis, αvβ3-DTX-PD micelles significantly attenuated bone metastases (3-fold, p = 0.007) and significantly reduced osteolytic bone destruction as assessed by x-ray analysis (3.5-fold, p = 0.021). Serum chemistry analysis of enzymes indicative of liver damage were elevated in the DTX treated group, but not in αvβ3-DTX-PD or saline treated groups. Interestingly, αvβ3-DTX-PD micelles did not attenuate breast cancer metastases within the liver, lungs, or kidneys. Histological examination of metastatic tumor tissue demonstrated elevated integrin β3 expression in bone metastases, as compared to the other sites.

Conclusion: These findings suggest that the unique elevated expression of integrin αvβ3 within breast cancer bone metastases could be exploited with αvβ3-DTX-PD micelles for effective therapy.

Citation Format: Michael H. Ross, Alison K. Esser, Anne H. Schmieder, Grace Cui, Xiaoxia Yang, Xinming Su, Dipanjan Pan, Gregory M. Lanza, Katherine N. Weilbaecher. Integrin αvβ3-targeted lipase-labile docetaxel-prodrug micelles preferentially treat breast cancer bone metastases. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2198.