Bioluminescent Pharmacokinetics Of Luciferin In Preclinical Brain Metastases Of Breast Cancer Models

Background: Approximately 20% of breast cancer patients with disseminated disease will develop brain metastases. Preclinical models of brain metastases of breast cancer rely on ex-vivo histology to evaluate drug efficacy. However, bioluminescence imaging allows more precise quantification of tumor burden and progression through counting photons per second without requiring animal sacrifice. This methodology has not readily been applied to hematogenously derived brain metastases models given the heterogeneity of tumor burden and growth. Herein we demonstrate repeatable methodology to quantify brain metastases of breast cancer progression which is verified with histology. Methods: Approximately 1.75 x 10 5 JIMT-1 (n=3) and 231-BrLuc (n=4) brain seeking subclones were injected intracardially to produce metastatic brain lesions. Mice were given 150 mg/kg of luciferin IP and luminescence was captured every 2-minutes for 60 minutes starting 24 hours after cell implantation. Radiance (photons per second per square centimeter per steridian) was plotted to observe peak luminescence. Imaging was repeated twice weekly to evaluate progression until euthanasia. Results: Following intracardiac injection, both brain seeking metastatic models produced a maximum luminescence signal between 14-20 minutes after luciferin injection. For all subsequent imaging, 5 minute imaging between 15-20 minutes after luciferin injection was used. Longitudinally, both tumor cell lines produce bioluminescence 24 hours after cell injection, which is used to ensure tumor implantation and randomization. The BLI signal decreases to undetectable limits in both models between 3-7 days after cell implantation. Re-emergence of signal occurs on day 14 for the JIMT-1 line and day 21 for 231-Br line. JIMT-1 bioluminescence on day 14 begins at ~10 5 photons/sec/cm 2 /sr and then over time signal increases with an ~slope of 5.6x10 5 until reaching a maximum of 10 7 units on day 28. 231-Br bioluminescence on day 21 begins at ~10 4 photons/sec/cm 2 /sr and then over time signal increases with an ~ slope of 1.1x10 6 until reaching a maximum of ~10 7 on day 53. Conclusion: To accurately measure bioluminescence as a surrogate for tumor burden in hematogenously implanted metastases, the optimal circulation time is approximately 15 minutes with a 5 minute imaging period. Bioluminescence of the 231Br line initially starts at a lower magnitude and later in time than the JIMT-1 line, but slopes of both intracardiac models are similar and result in similar bioluminescent curves. Citation Format: Neal Shah, Chris E. Adkins, Afroz S. Mohammad, Paul R. Lockman. Bioluminescent pharmacokinetics of luciferin in preclinical brain metastases of breast cancer models [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 1832. doi:10.1158/1538-7445.AM2017-1832