Abstract 3386: Detection of TGFbR2 frameshift mutation

Abstract TGFβR2 a10→a9 frameshift mutation is an early occurring cancer driver mutation and mutant TGFβR2 cell free DNA (cfDNA) is therefore a potential biomarker for early detection of cancer (E.G. Lynch Syndrome) as well as for monitoring response to cancer treatment. The frameshift mutation is associated with micro satellite instability (MSI) and is found in 80% of MSI-colorectal cancers (MSI-CRC) and in over 90% of hereditary nonpolyposis colorectal cancer. Here we show that cell free mutant (a9) TGFβR2 DNA is present in liquid biopsies from MSI-CRC patients and that the a9 micro satellite of mutant TGFβR2 can be selectively detected by using specially designed PCR primers modelled after the a9 microsatellite. PCR and primers defining a fragment of TGFβR2 comprising the a10/a9 microsatellite was used to amplify cfDNA extracted from MSI-CRC and microsatellite stable-CRC (MSS-CRC) patients. The resulting PCR products were analysed and confirmed by DNA sequencing after gel electrophoresis. In addition, primers modelled after the shorter a9 microsatellite was designed and tested using synthetic DNA of both TGFβR2 variants. Despite the naturally established mismatch between the a10 sequence and primers modelled after the a9 sequence, conventionally designed primers could not differentiate enough for specific annealing to the a9 sequence. A further mismatch with the a10 sequence was introduced at the 3’ end of the primer, which, in combination with the already established mismatch, denied the primer tail-end annellation with the a10 sequence that is necessary for polymerase amplification of this sequence. Experiments to optimise PCR conditions and buffer solution were conducted prior to analysing the cfDNA extracted from the patient samples. It was found that TGFβR2 DNA was present in cfDNA from all (10/10) CRC patients tested and that TGFβR2 a10→a9 frameshift was present in all (5/5) MSI-CRC patients and none (0/5) of MSS-CRC patients tested, shown by sequencing. PCR using the selected a9 modelled primer yielded a PCR product that was clearly detectable on the electrophoresis gel only for cfDNA from the MSI-CRC patients (5/5). The results show that TGFβR2 a10→a9 frameshift DNA is present in cfDNA of liquid biopsies from MSI-CRC patients which establishes cell free TFGβR2 frameshift DNA as a potential biomarker for early detection of hereditary CRC (Lynch Syndrome) as well as for monitoring cancer progression and remission of sporadic MSI-CRC. Citation Format: Henrik K. Eriksen, Jon A. Eriksen. Detection of TGFbR2 frameshift mutation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3386.