Mechanistic Characterization of CDK9 Inhibition in T-Cell Lymphoma
by Nora Anna Maria Ksionsko
Date of Examination:2024-05-23
Date of issue:2024-08-20
Advisor:PD Dr. Raphael Koch
Referee:PD Dr. Raphael Koch
Referee:Prof. Dr. Matthias Dobbelstein
Persistent Address:
http://dx.doi.org/10.53846/goediss-10686
Files in this item
Name:Mechanistic Characterization of CDK9 Inhibit...pdf
Size:4.07Mb
Format:PDF
The following license files are associated with this item:
Abstract
English
Mature T-cell lymphomas (mTCL) comprise a rare group of lymphoid malignancies with very diverse genetical, clinical, and pathological characteristics that are in many cases associated with poor prognosis. Current therapy options for mTCL are limited and result in unsatisfying outcomes with high relapse rates, leaving a need for innovative treatment regimens. In recent years, transient CDK9 inhibition (CDK9i) has emerged as a promising approach to target transcriptionally addicted cancers, including aggressive lymphoma. To evaluate the potential of CDK9i in mTCL, clinical grade inhibitors were tested on a panel of genetically and transcriptionally characterized cell lines. Treatment resulted in a subtype specific, heterogeneous pattern of sensitivity and resistance. While CDK9i sensitivity is associated with the ALCL subtype and high MCL1 dependence/gene expression, resistance is correlated with the CTCL subtype, high GATA3 expression and functional BCL-xL dependence. Addressing cellular escape mechanisms to pharmacological CDK9i, transcriptomic profiling and immunoblotting after short-term CDK9i revealed increased activation of AKT signaling as a potential resistance mechanism. This finding was further supported by a decreased sensitivity towards CDK9i upon introduction of a mysristoylated and thus constitutively activated AKT in cell line models. Vice versa, inhibition of the PI3K/AKT pathway with clinical grade PI3K inhibitors sufficiently suppressed AKT phosphorylation upon CDK9i. In an in-vitro combinational screening, dual inhibition of CDK9 and PI3K induced synergistic effects in multiple mTCL cell lines. Furthermore, this combinational approach displayed enhanced cytotoxic effects in an ex-vivo treatment of patient derived xenograft cells, providing a rationale for further in-vivo experiments and clinical testing. Lastly, the phenomenon of acquired resistance was investigated through the establishment of AZD4573 resistant (AZD4573res) clones from an initially sensitive cell line. On a genetic level, AZD4573res clones acquired a frame-shift mutation in the tumor suppressor gene LATS2. Further characterization of the acquired resistance on a functional level through transcriptional profiling identified downregulation of p53 signaling and cell death pathways in AZD4573res cells. Consistently, functional apoptosis profiling through dynamic BH3 profiling after short-term CDK9i revealed diminished apoptotic priming, in association with decreased expression of the pro-apoptotic effector protein BAK, indicating decreased susceptibility to pro-apoptotic stimuli in AZD4573res cell lines.
Keywords: CDK9; T-Cell Lymphoma
