Abstract 1496: Paired, single-cell profiling of circulating tumor cell-derived xenograft models of small cell lung cancer reveals intratumoral heterogeneity and emergence of new cell clusters following treatment relapse
Authors: Stewart C. Allison , Gay Carl M. , Xi Yuanxin , Sivajothi Santhosh , Fujimoto Junya , Hartsfield Patrice M. , Tran Hai , Swisher Stephen G. , Roth Jack A. , Zhang Jianjun , Glisson Bonnie , Heymach John V. , Wistuba Ignacio , Robson Paul , Wang Jing , Byers Lauren A. 
Published: September 2020

Abstract
Small cell lung cancer (SCLC), the most aggressive form of lung cancer, is notable for early dissemination and impressive, yet transient, responses to frontline chemotherapy that are rapidly undone by refractory relapses. To gain a better understanding of resistance mechanisms, we generated circulating tumor cell-derived xenograft (CDX) models from liquid biopsies of SCLC patients and treated them with chemotherapy or targeted agents. As expected, CDXs demonstrate similar chemotherapy response to the patient from whom they were derived. We have previously established that baseline chemosensitive CDXs are molecularly homogeneous at the single cell level, while chemoresistant CDXs exhibit increased intratumoral heterogeneity (ITH) with distinct variations in gene expression between cancer cell populations. We hypothesize that paired analyses of chemosensitive CDXs will demonstrate increased ITH after developing acquired resistance and are likely to offer more specific insights into resistance mechanisms than prior work with unrelated CDX models. Platinum-sensitive CDXs were treated with cisplatin or DNA damage response targeted therapies (PARP inhibitor or CHK inhibitor) continuously until tumor progression was observed. To identify transcriptional changes associated with onset of resistance, single-cell RNAseq analysis was performed on vehicle-treated and relapsed CDX tumors. We found globally increased ITH including heterogeneous expression of therapeutic targets and potential resistance pathways, such as EMT, between cellular subpopulations following treatment-resistance. Relapse was consistently associated with increased ITH score (P&lt;0.001) and cell cluster number. To determine whether transcriptional diversity in either therapeutic targets (ex., MYC, DLL3, TOP2A, PARP1, CHEK1, EZH2, etc.) or EMT genes (ex., ZEB1, ZEB2, TWIST1, VIM, AXL) was detectable between the paired tumors after onset of resistance, we compared transcriptional differences between clusters present in vehicle-treated versus cisplatin or targeted therapy-treated tumors. We discovered the emergence of new cell clusters in relapsed tumors in all CDX models (4 CDXs, 3 distinct treatments), including clusters expressing EMT or NOTCH signaling genes. These data suggest that, in response to treatment, SCLC develops increasing transcriptional ITH marked by concurrent, diverse resistant cell clusters. Clinically, these data underscore the importance of maximizing and maintaining the initial response in platinum-sensitive SCLC tumors and highlight the intrinsic transcriptional fluidity underlying SCLC's profound treatment resistance following initial therapy.
Citation Format: C. Allison Stewart, Carl M. Gay, Yuanxin Xi, Santhosh Sivajothi, Junya Fujimoto, Patrice M. Hartsfield, Hai Tran, Stephen G. Swisher, Jack A. Roth, Jianjun Zhang, Bonnie Glisson, John V. Heymach, Ignacio Wistuba, Paul Robson, Jing Wang, Lauren A. Byers. Paired, single-cell profiling of circulating tumor cell-derived xenograft models of small cell lung cancer reveals intratumoral heterogeneity and emergence of new cell clusters following treatment relapse [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1496.