Abstract 3740: The pursue of genetic mechanisms underlying supreme response to pazopanib treatment
Authors: Saloustros Emmanouil , Latsoudis Helen , Vassou Despoina , Kallergi Galateia , Stratidaki Irene , Gounalaki Niki-Antonia , Fadouloglou Vasiliki , Drositis Ioannis , Kontopodis Emmanouil , Pavlakis Kitty , Mavroudis Dimitrios , Androulakis Nikolaos , Kafetzopoulos Dimitrios 
Published: July 2017

Aim: Studying exceptional responders to standard treatments may provide broader insights into the genetic mechanisms underlying such responses and suggest therapeutic options that weren’t previously apparent. In this study we unravelled the genetic signature of undifferentiated sarcoma in order to disclose the molecular mechanisms that may underlie the patient’s exquisite sensitivity to Pazopanib.

Methods: A female patient with massive undifferentiated gynecological sarcoma experienced a dramatic response to Pazopanib that made debulking surgery possible. We performed whole exome sequencing on DNA isolated from both blood and formalin fixed paraffin-embedded (FFPE) tumour employing Ion Torrent technology. Variant annotation was performed using the Ion ReporterTM v5.0 (MA, USA) tool after application of specific filters. Subsequent curation of annotated data was completed using a combined semi-automated data analyses workflow developed by Minotech Genomics Facility with the implementation of two in house-developed lists regarding 24 pazopanib-related genes, and 96 angiogenesis-associated genes. We also performed targeted sequencing of Ion Ampliseq Comprehensive Cancer panel (CCP) that is strategically designed to interrogate coding DNA sequences and splice variants across 409 tumour suppressor genes and oncogenes.

Results: Whole exome sequencing was conducted at 20x coverage for 91.9% and 60.5% of &gt;19,000 genes for germline and FFPE DNA samples, respectively. Targeted sequencing was conducted at 20x for &gt;97% of 409 genes of the comprehensive cancer panel. Comparative analyses revealed two variants common in germline and FFPE samples, localized in LTK(p.Val541Ile) and FGFR4 (p.Gly388Arg). Interestingly, examination of the annotated data for biologically plausible mechanisms revealed 2 yet uncharacterized heterozygous variants in two other members of the FGFR family, FGFR2 (c.2183A&gt;G, p.Asn728Ser) and FGFR3 (c.2050G&gt;A, p.Val684Ile) that were present only in the FFPE samples. Even though both variants reside within the catalytic tyrosine kinase domains, they are predicted to exert tolerated effects on the encoded FGFR2 and FGFR3 proteins. Since, Asn728Ser is highly conserved among different kinases of the FGFR family we chose this variant to predict a possible effect on Pazopanib binding. Specifically, protein structure simulation of FGFR2 revealed that asparagine residue at position 728 is located in the external side of the drug binding cavity and is thus predicted to not affect Pazopanib binding.

Conclusion: We pursue the possible genetic or somatic modifiers underling the excessive response to Pazopanib. The detection of two, yet uncharacterised, variants in known Pazopanib targets highlights the potential of next generation sequencing in disclosing the genetic signature of undifferentiated sarcomas in relation to the activity and effectiveness of certain therapeutic agents.

Note: This abstract was not presented at the meeting.

Citation Format: Emmanouil Saloustros, Helen Latsoudis, Despoina Vassou, Galateia Kallergi, Irene Stratidaki, Niki-Antonia Gounalaki, Vasiliki Fadouloglou, Ioannis Drositis, Emmanouil Kontopodis, Kitty Pavlakis, Dimitrios Mavroudis, Nikolaos Androulakis, Dimitrios Kafetzopoulos. The pursue of genetic mechanisms underlying supreme response to pazopanib treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3740. doi:10.1158/1538-7445.AM2017-3740