In vivo Longitudinal Imaging of RNAi Induced Endocrine Therapy Resistance in Breast Cancer

• Published in: Journal of biophotonics Vol. 13; no. 1; p. e201900180
• Main Authors: Biswal, Nrusingh C., Fu, Xiaoyong, Jagtap, Jaidip M., Shea, Martin J., Kumar, Vijetha, Lords, Tamika, Roy, Ronita, Schiff, Rachel, Joshi, Amit
• Format: Journal Article
• Language: English
• Published: 09.10.2019
• ISSN: 1864-063X; 1864-0648
• DOI: 10.1002/jbio.201900180

Endocrine therapy resistance in breast cancer is a major obstacle in the treatment of patients with estrogen receptor-positive (ER+) tumors. Herein, we demonstrate the feasibility of longitudinal, non-invasive, and semi-quantitative in vivo molecular imaging of resistance to three endocrine therapies by using an inducible fluorescence labelled shRNA system in orthotopic mice xenograft tumors. We employed a dual fluorescent doxycycline (Dox)-regulated lentiviral inducer system to transfect ER+ MCF-7L breast cancer cells, with GFP expression as a marker of transfection, and RFP expression as a surrogate marker of Dox-induced the tumor suppressor PTEN knockdown. Xenografted MCF-7L tumor-bearing nude mice were randomized to therapies comprising estrogen deprivation, tamoxifen, or an ER degrader (fulvestrant), and an estrogen-treated control group. Longitudinal imaging was performed by a home-built multispectral imaging system based on a cooled image intensified CCD camera. The GFP signal, which corresponds to number of viable tumor cells, exhibited excellent correlation to calliper-measured tumor size (p << 0.05). RFP expression was substantially higher in mice exhibiting therapy resistance, and strongly and significantly (p < 1e-7) correlated with the tumor size progression for the mice with shRNA-induced PTEN knockdown. PTEN loss was strongly correlated with resistance to estrogen deprivation, tamoxifen, and fulvestrant therapies. In vivo images of GFP and RFP channels for treatment with (a) −Dox and (b) +Dox in mice. (c) The tumor exhibiting resistance to endocrine therapy has been demonstrated with typical images from ED+Dox and Ful+Dox.