Apoptosis inhibition through anti-apoptotic protein overexpression is a common characteristic of hematological cancers. One of the key regulators of apoptosis is cyclindependent kinase 9 (CDK9) due to its action on short-lived proteins of the BCL-2 family. Therefore, characterizing these molecules in the context of Richter's syndrome (RS) is crucial for identifying disease vulnerabilities. This study shows, for the first time, that direct inhibition of CDK9 suppresses MCL-1 expression, leading to the rapid reactivation of the intrinsic apoptotic pathway in RS cells. Furthermore, combining a CDK9 (CDK9i) and BCL-2 inhibitors (BCL-2i) offers a promising strategy to overcome resistance in refractory tumors. Utilizing four distinct patient-derived xenograft models of RS (RS-PDX) alongside U-RT1, the unique RS cell line available, we demonstrate that CDK9 inhibition reduces phosphorylation of the carboxyl-terminal domain (CTD) serine 2 and 5 of the RNA polymerase II (RNAP II) catalytic subunit B1 (Rpb1), resulting in a temporary transcriptional halt that depletes the cellular reservoir of MCL-1. As shown by flow cytometry and biochemical analyses, CDK9 inhibiting one of the latest and most specific small molecules, AZD4573 (CDK9i), in combination with Venetoclax induces robust apoptotic responses in all RS cells, without significantly modulating other anti-apoptotic molecules, including BCL-2, either in monotherapy or in combination. The CDK9/MCL-1 interplay is further elucidated by molecular silencing, which mirrors the results of pharmacological inhibition. Finally, treating RS-PDX mice with the combination of CDK9i and Venetoclax results in a marked inhibition of tumor growth, accompanied by in vivo evidence of activation of the apoptotic pathway. Ph.D. Thesis Lorenzo Brandimarte 3 Collectively, these findings highlight a novel potential use of CDK9i in combination with Venetoclax for some types of aggressive lymphomas.
Enhanced Apoptotic Responses in Richter's Syndrome Cells Through. Combined Inhibition of CDK9 and BCL-2(2024 Dec 06).
Enhanced Apoptotic Responses in Richter's Syndrome Cells Through. Combined Inhibition of CDK9 and BCL-2
BRANDIMARTE, LORENZO
2024-12-06
Abstract
Apoptosis inhibition through anti-apoptotic protein overexpression is a common characteristic of hematological cancers. One of the key regulators of apoptosis is cyclindependent kinase 9 (CDK9) due to its action on short-lived proteins of the BCL-2 family. Therefore, characterizing these molecules in the context of Richter's syndrome (RS) is crucial for identifying disease vulnerabilities. This study shows, for the first time, that direct inhibition of CDK9 suppresses MCL-1 expression, leading to the rapid reactivation of the intrinsic apoptotic pathway in RS cells. Furthermore, combining a CDK9 (CDK9i) and BCL-2 inhibitors (BCL-2i) offers a promising strategy to overcome resistance in refractory tumors. Utilizing four distinct patient-derived xenograft models of RS (RS-PDX) alongside U-RT1, the unique RS cell line available, we demonstrate that CDK9 inhibition reduces phosphorylation of the carboxyl-terminal domain (CTD) serine 2 and 5 of the RNA polymerase II (RNAP II) catalytic subunit B1 (Rpb1), resulting in a temporary transcriptional halt that depletes the cellular reservoir of MCL-1. As shown by flow cytometry and biochemical analyses, CDK9 inhibiting one of the latest and most specific small molecules, AZD4573 (CDK9i), in combination with Venetoclax induces robust apoptotic responses in all RS cells, without significantly modulating other anti-apoptotic molecules, including BCL-2, either in monotherapy or in combination. The CDK9/MCL-1 interplay is further elucidated by molecular silencing, which mirrors the results of pharmacological inhibition. Finally, treating RS-PDX mice with the combination of CDK9i and Venetoclax results in a marked inhibition of tumor growth, accompanied by in vivo evidence of activation of the apoptotic pathway. Ph.D. Thesis Lorenzo Brandimarte 3 Collectively, these findings highlight a novel potential use of CDK9i in combination with Venetoclax for some types of aggressive lymphomas.File | Dimensione | Formato | |
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