In vivo fluorescent imaging of tumor bombesin and transferrin receptor expression as early indicators of sorafenib efficacy in small animal models Jen-Chieh Tseng and Jeffrey D. Peterson. Life Sciences and Technology, PerkinElmer Inc., Hopkinton, MA Metabolic tumor imaging of the sorafenib dose response 2 using fluorescent imaging agents 1 HCT116/luc tumor is responsive to sorafenib treatment by BLI and tumor volume assessment A. Bioluminescence imaging of tumor viability A. Fluorescence molecular tomographic (FMT) imaging of tumor metabolic changes in response to sorafenib treatment Day 2 BombesinRSense 680 n=5 n=5 # # # To more accurately assess the impact of treatment between day 1 and day 3, taking into account modest increases in tumor size, the quantitative BLI and FLI results were normalized to tumor volume. A. Tumor volume during the first three days of treatments. B. BLI signals normalized against tumor volume data. C. BR680 epi-FLI signals normalized against tumor volume data (t-test, n = 5, bar: s.e.m.). D. TfV750 epi-FLI signal normalized against tumor volume (t-test, n = 5, bar: s.e.m.). *p < 0.01. B. Longitudinal Imaging # * ** ** ** BombesinRSense 680 (BR680) and Transferrin-Vivo 750 (TfV750) detect early tumor metabolic changes in response to sorafenib treatment. A. PerkinElmer’s FMT® 4000 fluorescence molecular tomography imaging system was used to detect BR680 or TfV750 uptake in the HCT116-luc tumors treated with different doses of sorafenib (t-test, bar: s.e.m.). B. FMT imaging of BR680 and TfV750 tumor signals in subcutaneous HCT116-luc tumors treated with vehicle or 120 mg/kg sorafenib daily (t-test, bar: s.e.m.). Graphs represent longitudinal metabolic changes in HCT116luc tumors in response to the treatment. #p < 0.05; *p < 0.01; **p < 0.001. FLI, but not BLI, detects early tumor metabolic 3 changes from moderate dose sorafenib treatment Day 2 Day 9 Day 1 Vehicle Day 2 Sorafenib 40 mg/kg Radiance (109) 0.5 6.0 0.5 3.0 2.0 1.0 7.0 C. Early detection of dosedependent responses 5.0 3.0 # ** 1.0 Radiant Efficiency (108) C. Transferrin-Vivo 750 imaging *** *** *** *** ns # * D. Histology validation Sorafenib * H&E TfV750 Epi-FLI 50 mm There are several tumor biological changes during disease progression and in response to targeted anti-cancer drug. Without treatment, the cancer cells actively divide and increase its metabolic activity and tumor volume. Active cancer cell proliferation also triggers new vasculature formation in tumor (angiogenesis) that is critical for tumor growth. On the other hand, treatment with sorafenib suppresses metabolic activities, inhibits angiogenesis, and triggers inflammatory responses and recruitment of granulocytes and macrophages. These changes can occur prior to overt death or regression of the tumor. Summary D. Quantification A. Longitudinal bioluminescence imaging (BLI) of HCT116-luc tumors in response to daily treatments of 120, 80 or 40 mg/kg sorafenib using the IVIS® Spectrum CT preclinical optical imaging system. Oral gavage treatments were given daily on day 0-4 and day 7-11. B. Relative tumor BLI signals and tumor volumes of each treatment group were calculated using the day 0 signals as 100% (p-value calculated by two-way ANOVA, bar: s.e.m.). C. Relative BLI signals of each dose group on day 2 (t-test, bar: s.e.m.); relative tumor volumes on day 2 (one-way ANOVA, bar: s.e.m.). D. H&E staining of tumor tissue sections harvested from the vehicle and sorafenib-treated (120 mg/kg) tumors on day 10. The drug effectively induced necrosis and regression in tumors. Bar: 50 mm. #p < 0.05; **p < 0.001; ***p < 0.0001. Late B. BombesinRSense 680 imaging 4.0 Vehicle Early 2.0 5.0 B. Sorafenib suppresses tumor growth No Treatment Day 9 1.0 1.0 Sorafenib Treatment A. Luciferase BLI imaging 1.5 1.5 Model for concepts in molecular imaging of 5 metabolism in cancer Tumor Biology Changes in Progression and Treatment Day 1 3.0 Day 2 Transferrin-Vivo 750 Radiance (109) Targeted cancer therapy aims to block key signaling pathways that are critical for tumor cell growth and survival. The blockage eventually results in cell death via apoptosis and eventual tumor growth suppression. This strategy has proven to be quite effective, and the FDA has approved several targeted therapeutics in the past decade. Encouraged by the success in clinical development, many academic and pharmaceutical researchers are in active pursuit of improved next generation targeted anti-cancer drugs. As a result, many new chemical and biological entities are emerging from initial screening of in vitro, in vitro and/or in silico selection processes. From the perspective of drug development, it poses a great challenge for the next stage of in vivo validation and demands a robust, accurate, and efficient method for assessment of these candidates in living animal models. Cancer cells are known to have abnormally increased cellular metabolism, and in the early stages of effective drug treatment, cancer cells show decreased metabolism and proliferation. These events occur prior to overt signs of cell destruction, and often multiple days or weeks of treatment are required to see overt changes in tumor size. In some instances, bioluminescence imaging can be used to detect early changes in tumor viability in response to targeted therapy when using luciferase-expressing tumor cell lines, however, with many therapeutic treatments these early changes in tumor viability cannot be seen by bioluminescence imaging. To assess whether molecular imaging of biomarkers related to tumor metabolic state would be useful in early detection of treatment efficacy, the utility of non-invasive near infrared (NIR) fluorescence imaging, using NIR fluorescent imaging agents, was assessed. Highly metabolic cancer cells have accompanying elevations in receptors for bombesin and transferrin on their surface that can be readily imaged using targeted fluorescent agents (BombesinRSenseTM 680 [BR680] and Transferrin-VivoTM 750 [TfV750]; PerkinElmer Inc.). In this report, we demonstrate the synergistic use of fluorescence (FLI) and bioluminescence imaging (BLI) to profile tumor metabolism and viability, respectively, in response to a targeted anti-cancer drug, sorafenib. Sorafenib is a clinically approved tyrosine kinase inhibitor that effectively blocks VEGFR, PDGFR and Raf signaling in cancer. At Sorafenib doses ranging from 40-120 mg/kg, there was a dosedependent decrease in viability of HCT116-luc human colon xenograft tumors evident as early as 2 days at the higher doses but only after several days for low doses. Interestingly, even at a lower dose of 40 mg/kg, both BR680 and TfV750 signal reduction can still be observed as early as 48 hours, a time/dose in which no significant reduction of tumor viability or size was observed. These results suggest the potential use of metabolic fluorescent imaging agents as sensitive and efficient and early biomarkers for preclinical assessment of targeted cancer drugs. Radiant Efficiency (108) Abstract 4 Quantification of the early therapeutic response to 40 mg/kg sorafenib with tumor size normalization ** Vehicle 40 mg/kg ** BLI and FLI monitoring of tumor changes in response to a moderate dose of sorafenib. A. BLI imaging of tumors in animals treated with vehicle or 40 mg/kg sorafenib (bar: s.e.m.) using PerkinElmer’s IVIS Spectrum CT imaging system. B. Epi-fluorescence imaging (epi-FLI) of BR680 uptake in tumors showing images and quantification (t-test, bar: s.e.m.). C. Epi-FLI of TfV750 uptake in tumors showing images and quantification (t-test, bar: s.e.m.). #p < 0.05; **p < 0.001; ***p < 0.0001; ns = not significant. In these studies, we demonstrated that bioluminescence and fluorescence imaging can work synergistically in order to obtain a comprehensive picture of tumor viability and metabolic status. PerkinElmer’s IVIS imaging systems have been widely adopted for pre-clinical imaging of bioluminescent tumor xenografts that stably express firefly luciferase. Since firefly luciferase is only expressed in tumor cells but not present in any normal tissues, bioluminescence imaging (BLI) shows high sensitivity, broad dynamic range and excellent specificity. More importantly, the need of ATP for luciferase-mediated light production can make BLI a useful indicator for assessing tumor viability in response to different anti-cancer treatments, especially when conventional tumor volume measurement fails to indicate any difference. In this report, we used BLI imaging to perform a dosetitration study and identified the minimal effective dosage of sorafenib that suppresses but does not reduce tumor burden or viability (assessed by BLI). Statistically significant changes were seen on day 2 post-treatment with 80-120 mg/kg sorafenib treatment, with 40 mg/kg showing little or no effect on tumor burden at this time point. For visualizing early metabolic changes in tumors, we used non-invasive near infrared (NIR) fluorescence imaging agents to monitor tumor’s metabolic responses to a targeted therapeutics. Due to the spectral wavelength in the NIR, and the accompanying low tissue absorbance, NIR fluorescent imaging generall shows enhanced deep tissue penetration. Bombesin- and transferrin-targeted (BRS680 and TfV750, respectively) imaging agents, showed the ability to detect day 2 sorafenib efficacy at a dose of 40 mg/kg, lower than needed for BLI detection. BR680 signal reduction can still be observed early within 48 hours, but no significant reduction of tumor size or BLI signal was observed until a week later. In addition to metabolic imaging, PerkinElmer provides a variety of NIR fluorescent imaging agents for multiplex imaging of biophysiological changes in tumor. We believe the collaborative use of both imaging methods is of significant benefit for pre-clinical anti-cancer drug development. PerkinElmer, Inc., 68 Elm Street, Hopkinton, MA USA (800) 762-4000 or (+1) 203 925-4602 www.perkinelmer.com