• Andrea Li Ann Wong, Joline Si Jing Lim, Arvind Sinha, Anil Gopinathan, Robert Lim, Chee-Seng Tan, Thomas Soh, Sudhakar Venkatesh, Christina Titin, Nur Sabrina Sapari, Soo-Chin Lee, Wei-Peng Yong, David Shao Ping Tan, Brendan Pang, Ting-Ting Wang, Ying-Kiat Zee, Richie Soong, Zuzana Trnkova, Chetan Lathia, Jean-Paul Thiery, Scott Wilhelm, Michael Jeffers, and Boon-Cher Goh.
• Department of Haematology-Oncology, National University Health System, 1E Kent Ridge Road, Singapore, 119228, Singapore. Andrea_la_wong@nuhs.edu.sg.
• J Transl Med. 2015 Feb 12; 13: 57.

BackgroundRegorafenib, a multi-kinase inhibitor, is used in the treatment of patients with metastatic colorectal cancer refractory to standard therapy. However, this benefit was limited to 1.4 months improvement in overall survival, with more than half of patients experiencing grade 3 to 4 adverse events. We aim to elucidate the pharmacodynamic effects of regorafenib in metastatic colorectal cancer and discover potential biomarkers that may predict clinical benefit.MethodsPatients with metastatic colorectal adenocarcinoma refractory to standard therapy with tumours amenable to biopsy were eligible for the study. Regorafenib was administered orally at 160 mg daily for 3 out of 4 weeks with tumour assessment every 2 cycles. Metabolic response was assessed by FDG PET-CT scans (pre-treatment and day 15); paired tumour biopsies (pre-treatment and day 21 post-treatment) were sampled for immunohistochemistry and proteomic profiling analyses. Plasma circulating cell free DNA was quantified serially before and after treatment.ResultsThere were 2(6%) partial responses out of 35 patients, and 8(23%) patients had stable disease for more than 7 months. Adverse event profile was similar to reported data. Recurrent somatic mutations in K-RAS, PIK3CA and BRAF were detected in plasma circulating cell free DNA in 14 patients; some mutations were not found in archival tumour. Total plasma circulating cell free DNA inversely correlated with progression free survival (PFS), and presence of KRAS mutations associated with shorter PFS. Immunohistochemistry of pre- and post- treatment biopsies showed majority of patients had downregulation of phosphorylated-VEGFR2, podoplanin, phosphorylated-AKT, Ki-67 and upregulation of the MEK-ERK axis, phosphorylated-C-MET, phosphorylated-SRC, phosphorylated-STAT3 and phosphorylated-JUN. Proteomic analysis of fine needle tumour aspirates showed down-regulation of PI3K was associated with longer PFS.ConclusionPlasma circulating cell free DNA may yield potential predictive biomarkers of regorafenib treatment. Downregulation of the PI3K-AKT axis may be an important predictor of clinical benefit.

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