Abstract 1099: Resistance to anti-EGFR therapy can spread horizontally among cancer cells
Authors: Junqueira-Neto Susana , Oliveira Ana Rita , Marques Joana , Melo Sónia , Costa José Luís , Machado José Carlos 
Published: July 2021

Abstract
Targeted therapies almost universally fail due to the development of resistance. EGFR-mutant non-small cell lung cancer (NSCLC) is a well characterized model of such mechanism. In this model, treatment with anti-EGFR therapy leads to resistance driven by the presence of the EGFR T790M mutation in about 50% of the cases. However, clinical data shows the EGFR resistance mutation is present only in a subpopulation of the relapsing cells. How cancer cells devoid of the EGFR T790M mutation become resistant is not known. The aim of this study is to explore if T790M-mediated resistance to anti-EGFR therapy can spread horizontally, through a mitosis-independent mechanism, among NSCLC cells. Immunodeficient mice (Rag2-/-Il2rg-/-) were engrafted with NSCLC HCC827 cells, harboring the Erlotinib-sensitive mutation EGFR E746-A750del, and H1975 cells, carrying the EGFR T790M Erlotinib-resistant mutation. These animals received a single inoculation of HCC827 cells in a single flank (n=10), or dual inoculation of HCC827 and H1975 cells in opposite flanks (n=20). Erlotinib was orally administered three times a week (25 mg/Kg) and tumors were collected at humane endpoint for genetic and transcriptomic analysis by next generation sequencing and digital PCR. T790M-driven resistance to Erlotinib was transferred in vivo from resistant to sensitive cells in dual inoculated animals, resulting in a significant decrease of relapse-free survival. Short tandem repeat profiling of the tumors showed absence of H1975 cells in sensitive tumors in dual inoculated animals, ruling out cell migration as the mechanism of resistance. This result can also not be explained by transfer of mutated DNA from resistant to sensitive cells because high-end sequencing detected the presence of the T790M mutation only in few sensitive tumors from dual inoculated mice and with an extremely low allele frequency (&lt;0,1%). These results support our contention that anti-EGFR therapy resistance does not imply the presence of the T790M mutation in every resistant cell. RNA sequencing revealed differences in transcriptomic profiles from sensitive tumors between single and dual inoculated mice. Gene ontology analysis identified several pathways, such as endocytosis, lysosome biogenesis and RNA transport, as segregators of sensitive tumors that relapsed in the presence or absence of resistant tumors. Our findings suggest that mutation-driven resistance to anti-EGFR can spread horizontally among lung cancer cells and results in alteration of the transcriptional landscape of sensitive cells. Our results question the established concept that acquisition of resistance to targeted therapies relies solely on the selection of tumor cells carrying a specific resistance mutation, which is then passed on to its progeny. PhD Scholarship: SFRH/BD/115099/2016; FEDER funds: COMPETE 2020—(POCI), Portugal 2020; FCT: PTDC/DTP-PIC/2500/2014, NORTE 2020: NORTE- 01-0145-FEDER-000029.
Citation Format: Susana Junqueira-Neto, Ana Rita Oliveira, Joana Marques, Sónia Melo, José Luís Costa, José Carlos Machado. Resistance to anti-EGFR therapy can spread horizontally among cancer cells [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 1099.