Abstract PS8-13: Silicone implant based sustained localized drug delivery of fulvestrant to prevent breast cancer

Abstract

Background: Hereditary breast cancer is common. With enhanced awareness and the recent introduction in affordable multi-gene germ line testing, an estimated 0.5-1 million women will learn that they carry a considerable risk to develop breast cancer. Thus, a rapidly increasing number of women, many of them very young, will be in need of effective strategies for breast cancer prevention. Current options to prevent breast cancer in women at high risk include bilateral mastectomies or systemic anti-estrogen therapy. Both options, while effective, may have a detrimental impact on the physical and emotional well-being of the patient. Localized delivery of an established anti-estrogen to breast tissue only may thus offer an attractive alternative for cancer prevention and may replace systemic therapy for ductal carcinoma in situ and early stage breast cancer with minimal risk for metastases. Methods: As such, we have sought to develop a silastic-silicone device, which when placed under breast tissue, will deliver the anti-estrogen fulvestrant directly to the target tissue. Sustained slow release of fulvestrant from a silastic-silicone device directly into the mammary tissue will provide the risk reducing benefits of systemic hormonal therapy while minimizing systemic exposure and the resulting poor compliance due to adverse effects. Results: Using a combination of in vitro and in vivo studies, we show that fulvestrant can be delivered through a silastic-silicone device. Implanted adjacent to mammary tissue, this drug delivery device provides sustained high levels of fulvestrant to inhibit estrogen receptor signaling and breast cancer cell proliferation. In a MCF-7 breast cancer xenograft model we have shown that silastic-silicone delivers fulvestrant selectively to mouse mammary tissue for more than 1 year with anti-tumor effects similar to those achieved with systemic fulvestrant exposure. Using the Sprague-Dawley rat DMBA spontaneous breast cancer induction model, we further demonstrate that fulvestrant delivered by silastic-silicone devices implanted adjacent to mammary tissue significantly delays time to first tumor compared to control animals (n=90, HR = 0.42, 95% CI 0.21-0.83) with minimal systemic exposure (plasma average 1.1 ng/mL, SD ±1.5 ng/mL). Initial large animal safety and toxicity studies in female sheep (ewes, n=2) support the surgical strategy to place the device between breast tissue (i.e. udder) and the chest wall (abdominal wall in ewes). Following 1 month of fulvestrant release, gross and histopathological analysis found no adverse effects or implant related toxicity. Bioanalytical analysis of mammary tissues suggested that drug was found highest near the implant (max 341 ng/g, udder average 58.4 ng/g, SD ±17.1 ng/g), with diminishing levels distal from the implant. Systemic exposure was low, with plasma levels 1.2 ng/mL, SD ±0.22 ng/mL, comparing favorably to clinical plasma levels achieved by intramuscular fulvestrant of 500 mg: 28.0 ng/mL, SD ±27.9 ng/mL (FDA package insert). Subsequent large animal studies will focus on the safety and pharmacokinetics of device delivered fulvestrant in longer studies (e.g. 3 to 6 months). Conclusions: The greater awareness and genetic identification of individuals at risk for breast cancer brings about an increased need for novel approaches to breast cancer prevention. The development of a silastic-silicone based device for sustained and localized drug delivery with an approved and effective anti-estrogen should allow rapid transition into clinical testing. This strategy will provide an alternative option to mastectomies and allow breast conservation for women identified to have a more than 40% lifetime chance of developing breast cancer, as well as provide an alternative to systemic hormonal therapy in women with ductal carcinoma in situ or stage I breast cancer. Citation Format: Pamela N Munster, Pujan K Desai, Nela Pawlowska, Elysia Roche, Romain Pacaud, Maxim A Daud, Emily Hsu, David Gingrich, Amelia Deitchman, Fran Aweeka, Scott Thomas. Silicone implant based sustained localized drug delivery of fulvestrant to prevent breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS8-13.