Contributions
Abstract: EP389
Type: E-Poster Presentation
Session title: Acute myeloid leukemia - Biology & Translational Research
Background:
The BCL2 inhibitor Venetoclax is a promising targeted anti-cancer agent for the treatment of AML. Despite its overall success, the understanding of molecular mechanisms that modulate Venetoclax efficacy is of utmost importance for successful personalized therapy. It is well established that ATP-binding cassette (ABC-) transporters are important mediators of cancer chemotherapy resistance, but it was unknown if ABC-transporters can modulate the efficiency of BCL2-inhibitors in AML.
Aims:
We aim to understand the complex interplay of ABC-transporters and BCL2-inhibitors by systematically evaluating their essentiality in untreated versus BCL2-inhibitor treated AML cell lines.
Methods:
We used CRISPR/Cas9-enabled functional genomics, pharmacological and cell biological approaches in human AML cell lines to systematically evaluate the genetic requirements for ABC-transporters in drug-naïve AML. Furthermore, we analyzed how particular ABC-transporters affect the sensitivity of AML cells towards BCL2-inhibitors.
Results:
Using CRISPR/Cas9-mediated knockout of all 48 genes encoding ABC-transporters in human AML cells, we show that only ABCE1, TAP2, ABCA3 and ABCF1 were essential for cell growth of drug-naïve cells. However, we found that knockout of ABCC1 (MRP1) strongly increased the sensitivity of AML cells to the BCL-2 inhibitor Venetoclax. Genetic and pharmacological inhibition of ABCC1 also sensitized AML cells to the BCL2-inhibitors ABT-737, navitoclax and AZD-4320, but not to other drugs that are used to treat AML, such as cytarabine, midostaurine or IDH inhibitors. ABCC1 overexpression induced Venetoclax resistance in leukemia cells. Importantly, MCL1-overexpressing Venetoclax-resistant AML cells could be re-sensitized to BCL2 inhibition by knockout or inhibition of ABCC1.
It has been shown that ABCC1-mediated export of molecules requires their conjugation to oxidized glutathione (GSSG). To test whether the ABCC1-mediated effect on BCL2-inhibition requires this pathway, we used buthionine sulfoximine (BSO). As an inhibitor of the glutamate cysteine ligase (GCL), BSO reduces intracellular glutathione (GSH) levels. While BSO treatment alone did not affect the viability of AML cells, it strongly synergized with BCL2 inhibition, improving the efficacy of Venetoclax and AZD-4320.
Conclusion:
Currently, we are investigating the molecular mechanisms underlying the synergy between glutathione homeostasis, ABCC1 and BCL2-inhibition in vitro and in vivo. In addition to novel molecular insights, our findings could help to establish ABCC1 as a biomarker that helps to predict the efficiency of Venetoclax in the treatment of AML.
Abstract: EP389
Type: E-Poster Presentation
Session title: Acute myeloid leukemia - Biology & Translational Research
Background:
The BCL2 inhibitor Venetoclax is a promising targeted anti-cancer agent for the treatment of AML. Despite its overall success, the understanding of molecular mechanisms that modulate Venetoclax efficacy is of utmost importance for successful personalized therapy. It is well established that ATP-binding cassette (ABC-) transporters are important mediators of cancer chemotherapy resistance, but it was unknown if ABC-transporters can modulate the efficiency of BCL2-inhibitors in AML.
Aims:
We aim to understand the complex interplay of ABC-transporters and BCL2-inhibitors by systematically evaluating their essentiality in untreated versus BCL2-inhibitor treated AML cell lines.
Methods:
We used CRISPR/Cas9-enabled functional genomics, pharmacological and cell biological approaches in human AML cell lines to systematically evaluate the genetic requirements for ABC-transporters in drug-naïve AML. Furthermore, we analyzed how particular ABC-transporters affect the sensitivity of AML cells towards BCL2-inhibitors.
Results:
Using CRISPR/Cas9-mediated knockout of all 48 genes encoding ABC-transporters in human AML cells, we show that only ABCE1, TAP2, ABCA3 and ABCF1 were essential for cell growth of drug-naïve cells. However, we found that knockout of ABCC1 (MRP1) strongly increased the sensitivity of AML cells to the BCL-2 inhibitor Venetoclax. Genetic and pharmacological inhibition of ABCC1 also sensitized AML cells to the BCL2-inhibitors ABT-737, navitoclax and AZD-4320, but not to other drugs that are used to treat AML, such as cytarabine, midostaurine or IDH inhibitors. ABCC1 overexpression induced Venetoclax resistance in leukemia cells. Importantly, MCL1-overexpressing Venetoclax-resistant AML cells could be re-sensitized to BCL2 inhibition by knockout or inhibition of ABCC1.
It has been shown that ABCC1-mediated export of molecules requires their conjugation to oxidized glutathione (GSSG). To test whether the ABCC1-mediated effect on BCL2-inhibition requires this pathway, we used buthionine sulfoximine (BSO). As an inhibitor of the glutamate cysteine ligase (GCL), BSO reduces intracellular glutathione (GSH) levels. While BSO treatment alone did not affect the viability of AML cells, it strongly synergized with BCL2 inhibition, improving the efficacy of Venetoclax and AZD-4320.
Conclusion:
Currently, we are investigating the molecular mechanisms underlying the synergy between glutathione homeostasis, ABCC1 and BCL2-inhibition in vitro and in vivo. In addition to novel molecular insights, our findings could help to establish ABCC1 as a biomarker that helps to predict the efficiency of Venetoclax in the treatment of AML.