Abstract 1859: Hsp90 targeted near infrared molecular imaging to detect mammografically occult invasive lobular breast cancer

Background: Early diagnosis of Invasive lobular carcinomas (ILCs) is clinically challenging due to its histopathologic features making it difficult to detect using mammography. Because of the diffuse infiltration of ILC cells into the surrounding stroma, ILC is also associated with a higher incidence of positive resection margins after breast-conserving surgery. Therefore, there is a significant unmet need for improved imaging for early detection, clinical staging, and possibly intraoperative imaging to assess surgical margins. We propose to detect mammografically occult ILC by the in vivo detecting of malignant signaling pathways activated in ILC. Heat shock protein 90 (Hsp90) comprises 1-3% of the total cellular protein in most cells and acts as a molecular chaperone for more than 200 reported client proteins. Recently, we developed a series of tethered Hsp90 inhibitors that specifically target a tumor specific form of Hsp90 associated with poor outcomes. Using near infrared (nIR) probe-tethered Hsp90 inhibitors, we demonstrated that Hsp90 is actively re-internalized and can be used to image murine and human breast cancer in vitro and in vivo. Methods and Results: We tested the imaging efficacy of the nIR-tethered Hsp90 inhibitor, HS196, in ILC models in vitro and in vivo. An inactive structural analog HS199 was used as a control to monitor for non-specific (non-Hsp90 dependent) uptake. Two ILC cell lines, MDA-MB-134 VI and SUM44-PE, and one patient-derived ILC xenograft, HCI-013 EI, were tested. nIR signals of HS196 in vitro and in vivo were detected by Odyssey (LI-COR) and Pearl Trilogy (LI-COR)/SPY ELITE imager (Novadaq), respectively. High uptake of HS196 was observed in vitro by both cell lines (> 1 µM), while the control HS199 resulted in weaker nIR signals in these cells. In vivo imaging efficacy of HS196 was tested using HCI-013 EI xenograft in SCID-beige mice. After injection of 10 nmol compounds via tail vein, quick and stronger accumulation and longer retention of the HS196 in the ILC xenograft was observed, while HS199 showed significantly weaker accumulation and faster clearance (by 24 h after injection). Significant uptake of HS196 by HCI-013 EI tumors was confirmed by ex vivo imaging of tumors 24 h after compound injection. Histological and flow cytometry analysis of HCI-013 EI tumors showed strong nIR signals in tumor cells. Conclusions: The non-radioactive, nIR imaging strategy, using a novel nIR-Hsp90 inhibitor compound, HS196, was effective in the non-invasive imaging of ILC tumors. This finding suggests that new molecular imaging techniques, not dependent on micro calcifications or architectural distortion, may be a novel strategy to met the need of ILC patients to detect, clinically stage and assess margins during surgical resection. Ongoing pre-clinical models will be employed and first in human testing of this approach in planned. Citation Format: Takuya Osada, Kensuke Kaneko, Zachary Hartman, Amy Hobeika, Philip Hughes, Timothy Haystead, Michael Morse, H. Kim Lyerly. Hsp90 targeted near infrared molecular imaging to detect mammografically occult invasive lobular 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 1859. doi:10.1158/1538-7445.AM2017-1859