Abstract A20: Use of cell-free plasma DNA for dynamic monitoring of response to cytotoxic chemotherapy

Abstract

Abstract Background: There is great interest in utilizing blood-based circulating biomarkers to gain molecular insight into cancer. Most of the published data examines circulating free DNA (cfDNA) obtained at a single time-point. Here, we developed and utilized an methodology for monitoring cfDNA at multiple time-points within 24 hours of cytotoxic chemotherapy infusions over sequential cycles. Methods: To monitor the short- and long-term responses to treatment, we analyzed cfDNA from plasma drawn immediately before (baseline), 5 hours and 24 hours after administration of docetaxel chemotherapy. We quantified the extracted cfDNA via qPCR of Long interspersed nuclear elements (LINE1). We then amplified and performed targeted deep sequencing (Illumina Miseq) of androgen receptor (AR) exon 8. To reduce PCR variability, we pooled 10 technical replicate amplifications. Results: Detailed data and time courses are presented for a patient with castrate resistant prostate cancer metastatic to bone treated with docetaxel/everolimus/bevacizumab according to a recently published trial (J Clin Oncol 33, 2015 suppl; abstr 5066). LINE1 was measured at 34.4 pg/mcl at baseline prior to treatment. Targeted deep sequencing of AR exon 8 revealed two independent mutations at 11% (H874A) and 13% (T877A), respectively. 5 hours after start of docetaxel infusion, total DNA content measured by LINE1 decreased to 0.4 pg/mcl. However, H874A and T877A mutations were observed at frequencies similar to the baseline values. A similar pattern was observed for samples obtained at Cycle 2 (21 days later). Specifically, baseline values for LINE1 (67.4 pg/mcl), H874A (3%), and T877A (7%) were noted to change to LINE1 (8.5 pg/mcl), H874A (6%), and T877A (17%) 5 hours later. Conclusion: We conclude that cytotoxic chemotherapy can produce effects immediately observable on cfDNA markers. The generalizability and clinical relevance of these findings will require follow up studies involving more patients. Citation Format: Daniel Ruderman, Katherin Patsch, Naim Matasci, Anjana Soundararajan, Patricia Diaz, Mitchell E. Gross. Use of cell-free plasma DNA for dynamic monitoring of response to cytotoxic chemotherapy. [abstract]. In: Proceedings of the AACR Special Conference on Engineering and Physical Sciences in Oncology; 2016 Jun 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2017;77(2 Suppl):Abstract nr A20.