Abstract 2929: Comparative analysis of circulating human tumor DNA and bioluminescent imaging in monitoring tumor burden and therapeutic response of ionizing radiation in intratibial human prostate tumor xenografts
Authors: Mishra Alok , Zennami Kenji , Velarde Esteban , Coulter Jonathan B. , Yegnasubramanian Srinivasan , Lupold Shawn E. , DeWeese Theodore L. 
Published: July 2021

Purpose/Objective: Pre-clinical models of prostate cancer (PCa) metastases provide critical insight into tumor biology and therapeutic response. Current models require sophisticated reporter transgene models and/or expensive tools to noninvasively monitor tumors in metastatic sites, such as bone. Recent developments in the measurement of circulating tumor DNA (ctDNA) provide an alternative method to noninvasively assess tumor burden at a low cost. Here we present a comparative analysis of human PCa xenograft tumor growth and therapeutic response by simultaneous measurement of ctDNA and bioluminescence.

Materials and methods: Male athymic nude mice were used for intra-tibial (n=10) modeling. LNCaP-CMV-Luc cells were implanted in the tibial medullary canal. Tumor burden was evaluated at pre and post-IR (focal exposure 6 Gy on day 28 post-implantation) time-points by in vivo bioluminescent imaging and quantitative real-time polymerase chain reaction (qPCR) for human LINE1/Alu DNA. qPCR was performed on plasma-derived DNA consecutively on the same day as bioluminescence.

Results: Human genomic DNA quantification was sensitive to 0.1 pg and linear by hAlu (R2=0.98, for 0.1pg-150ng) and LINE DNA (R2=0.99, for 0.1pg-150ng) qPCR. hAlu DNA qPCR produces a much lower Ct value when compared to LINE1; possibly due to its higher copies in the human genome (Ct value 28 versus 22/0.1 pg). Following tumor inoculation, ctDNA level and tumor bioluminescence were strongly and significantly correlated over time (LINE1, r=0.65 and Alu, r=0.59, p&lt;0.002). Following radiation, we observed an immediate (day 32) but transient decrease in the levels of ctDNA and bioluminescence, followed by a gradual increase due to tumor relapse. The correlation between ctDNA level and bioluminescence was not maintained, but responses followed a similar trend.

Conclusions: In the present study, we report that the volume of human PCa xenografts can be accurately measured in the intra-tibial compartments of athymic nude mice by qPCR of circulating human Alu and LINE1 elements. Plasma-derived ctDNA levels highly correlated with tumor bioluminescence over time. Tumor directed radiation therapy exhibited slightly differential responses in ctDNA level and tumor bioluminescence, but overall both measurements followed a similar trend.

Citation Format: Alok Mishra, Kenji Zennami, Esteban Velarde, Jonathan B. Coulter, Srinivasan Yegnasubramanian, Shawn E. Lupold, Theodore L. DeWeese. Comparative analysis of circulating human tumor DNA and bioluminescent imaging in monitoring tumor burden and therapeutic response of ionizing radiation in intratibial human prostate tumor xenografts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2929.