Cancer therapies commonly slow rather than cure disease and most patients ultimately relapse. Phenotypic variability and dynamics are a cause for relapsing disease and pose significant challenges to a successful cure. Here we show at the single-cell level that T lymphoma and leukemia cells are programmed to occupy a rare transient, drug-resistant state. Our work defines a panel of drug-resistance markers allowing early identification of the cells programmed to resist treatment and cause relapsing disease. Single-cell analyses in T cell lymphoma and leukemia lines reveal a small fraction of cells resisting cytotoxic drugs such as doxorubicin, methotrexate, and vorinostat. Repeat treatment cycles in recovered colonies indicate the transient and intrinsic nature of this drug resistant state. In cell fate analyses of bulk populations and xenograft tumors treated we observed that drug treatment leads to selective survival of label-retaining cells. Those cells then lead to population recovery and re-growth of tumors consistent with a relapse-inducing phenotype of the slow-cycling state. This was further supported by directly exposing isolated single cells to anticancer drugs with selective recovery and clonal expansion of cells in a pre-existing slow-cycling state at the time of drug exposure. Repeated exposure does not decrease the chemosensitivity of the surviving clones indicating that the drug-resistant state is transient and non-heritable. Label-retaining cells from different T cell lymphoma and leukemia lines display a transcriptional profile distinct from the parental population which is maintained in treatment-surviving cells. Cell line-independent similarities suggest T lineage-specific rather than disease-specific drug-resistance expression program. In particular, early growth response proteins 1-3 (Egr1-3) show increased expression levels in label-retaining cells serving as a biomarker for the drug-resistant subset of malignant T cells. Since Egr2 is critical for the induction of T cell anergy and activation, its overexpression in drug-resistant cells suggests a dual role of lineage-specific anergy mechanisms programming drug-response variability in malignant T cells. Tracing analyses demonstrated that single cells readily revert their phenotype to establish a clonal population with original heterogeneity indicating the dynamic nature of the slow-cycling state. This indicates that every single cell has a strong inherent drive to program daughter cells to occupy a rare transient slow-cycling state providing a high degree of stress- and, ultimately, treatment-resistance. The described resistance marker expression profile allows early identification of the drug-resistant state and helps to identify therapeutic targets in the rare-cell programming to prevent cells entering the relapse-inducing state in T cell leukemia and lymphoma.
Citation Format: Hamidullah Khan, Sushmita Roy, Ashish Anshu, Wasakorn Kittipongdaja, Stefan M. Schieke. Single cell dynamics maintain an intrinsic drug resistant state in T cell leukemia and lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2178.