Abstract P5-04-11: Targeting hormone receptor positive breast cancer for immune destruction by natural killer cells
Authors: Chiu Emily , Johnson Ivy R , Miller Jeffrey S , Felices Martin , Sachdev Deepali 
Published: March 2020

Abstract
Hormone receptor positive (HR+) breast cancers that express estrogen receptor (ER) can recur 5-20 years after initial diagnosis and treatment, often as bone metastases. More than 30% of patients with early-stage HR+ breast cancer treated with endocrine or hormonal therapy will relapse and all patients with metastatic breast cancer expressing ER eventually acquire resistance to endocrine therapy. The metastases are caused by slowly dividing well-differentiated cancer cells. These cells are not susceptible to chemotherapy, which only acts on dividing cells, and they are also resistant to endocrine therapy. Recent analyses indeed show that chemotherapy added to endocrine therapy for patients with lower risk early stage breast cancer did not increase overall survival. Thus, patients with metastatic HR+ breast cancer need new therapeutic options. Unfortunately HR+ breast cancers have not responded to current T-cell based immunotherapies. Therefore the objective of this study is to target HR+ breast cancers using a natural killer (NK) cell based approach. The type I IGF receptor (IGF1R) is expressed on hormone receptor positive (HR+) breast cancers and its expression is tightly related to ER function. We hypothesized that a drug that would target NK cells to IGF1R expressing HR+ cells will be effective in eliminating them.
We generated a novel NK cell based immunotherapy called Tri specific Killer Engagers (TriKE) and these are much smaller molecules than conventional trispecific antibodies. The IGF1R TriKE consists of humanized single domain antibody (VHH) sequence of a camelid nanobody against CD16 to engage and activate NK cells, humanized VHH sequence of a nanobody against IGF1R to target HR+ breast cancer cells, and an IL-15 molecule between the two single domain antibodies to drive NK cell priming, expansion and survival. The IGF1R TriKE specifically bound to breast cancer cells expressing IGF1R and did not bind mouse embryonal fibroblasts from IGF1R knock out mice (R- cells). It bound R-/IGF1R cells (R- cells engineered to express human IGF1R) indicating specific binding to IGF1R on cells. The IGF1R TriKE did not cause downregulation of cell surface IGF1R levels in multiple HR+ breast cancer cells. The IGF1R TriKE specifically induced NK cell degranulation, measured by surface CD107a expression, against IGF1R expressing HR+ target breast cancer cells (MCF-7, T-47D and ZR-75-1) in a functional assay compared to treatment with anti-IGF1R nanobody or IL-15 alone. It did not induce degranulation of NK cells against R- cells but enhanced degranulation against R-/IGF1R cells suggesting that the functionality was specific for IGF1R expressing targets. Furthermore, the IGF1R TriKE also enhanced cell killing of ZR-75-1 breast cancer cells compared to IGF1R nanobody as measured by number of live breast cancer cells at the end of a 48 hour cytotoxicity assay. We are currently testing the IGF1R TriKE’s functionality in causing degranulation of NK cells from blood of breast cancer patients.
These data indicate that this NK cell based immunotherapeutic strategy could be an effective treatment for HR+ metastatic breast cancer and make them responsive to immunotherapy. Our approach generates targeted off-the-shelf immunotherapy that does not require a personalized approach for each patient that is required with CAR T-cell based approaches that is expensive and time consuming.
Citation Format: Emily Chiu, Ivy R Johnson, Jeffrey S Miller, Martin Felices, Deepali Sachdev. Targeting hormone receptor positive breast cancer for immune destruction by natural killer cells [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-04-11.