Contributions
Abstract: EP617
Type: E-Poster Presentation
Session title: Chronic lymphocytic leukemia and related disorders - Biology & Translational Research
Background
Chronic Lymphocytic Leukemia (CLL) accounts for about 30% of all adult leukemia and is common in Western countries. In the clinical treatment, although innumerable advances have been made, the disease is still incurable. To identify new treatment strategies it is necessary to take into account that leukemic cellsentertaina complex crosstalk with the surrounding tumor microenvironment (TME) and for this reason is important to consider a “double hit” therapeutic approaches.
The indoleamine 2,3-dioxygenase (IDO)-kynurenine (Kyn)-aryl hydrocarbon receptor (AhR) pathway is active in several types of human cancer, including hematologic malignancies, that pathologically exploit tryptophan (Trp) metabolism along the kynurenine pathway (KP) to promote growth and escape immune surveillance. IDO-derived kyn produced during cancer progression and inflammation have both autocrine and paracrine action and seem to be one of the pathways that link the leukemic cell and the TME.
Aims
We wondered to investigate the functional role of the KP and the effects of its inhibition in CLL.
Methods
Gene transcription and protein expression were evaluated by real time PCR and western blot. Enzymatic activity was assessed through ELISA. Survival was measured with annexinV/PIassay. Overexpression and silencing of target genes was obtained by nucleofection.
Results
Previously we have demonstrated that CLL cells expressed IDO at variable levels and we found that several TME stimuli were able to up-regulate IDO mRNA and protein. We have showed that IFNγ induced an active IDO protein through STAT1 signaling as assessed measuring Kyn production and Trp consumption by ELISA. Interestingly, when we up-regulated IDO in CLL cells they showed an increased survival. Same results were obtained treating cells with Kyn. We also observed that Kyn mediated AhR translocation from the cytoplasm to the nuclei, inducing its activation as assessed by up-regulation of CYP1A1, a known AhR target gene. Analyzing the anti-apoptotic proteins of the Bcl2 family after Kyn treatment, we found the induction of Mcl1, that was affected by adding CH-223191, an antagonist of AhR. Then we decided to silence AhR in CLL cells and we found that the survival of leukemic cells was compromised as they had reduced levels of Mcl1.We then analyzed to what extent KP-induced survival could affect ABT-199 sensitivity in CLL samples. Our results indicated that pre-treatment with Kynmitigated the effect of ABT-199, which produced less apoptosis, while the use of CH-223191 has been shown to have a synergistic effect in inducing apoptosis of leukemic cells.
Conclusion
Our data demonstrated that IDO-Kyn-AhR axis is active in CLL cells and promotes Mcl1 expression,sustaining the survival of leukemic cells. Our results indicated the KP as a new potential therapeutic target in the CLL microenvironment.
Keyword(s): Chronic lymphocytic leukemia, Mcl-1, Microenvironment, Survival
Abstract: EP617
Type: E-Poster Presentation
Session title: Chronic lymphocytic leukemia and related disorders - Biology & Translational Research
Background
Chronic Lymphocytic Leukemia (CLL) accounts for about 30% of all adult leukemia and is common in Western countries. In the clinical treatment, although innumerable advances have been made, the disease is still incurable. To identify new treatment strategies it is necessary to take into account that leukemic cellsentertaina complex crosstalk with the surrounding tumor microenvironment (TME) and for this reason is important to consider a “double hit” therapeutic approaches.
The indoleamine 2,3-dioxygenase (IDO)-kynurenine (Kyn)-aryl hydrocarbon receptor (AhR) pathway is active in several types of human cancer, including hematologic malignancies, that pathologically exploit tryptophan (Trp) metabolism along the kynurenine pathway (KP) to promote growth and escape immune surveillance. IDO-derived kyn produced during cancer progression and inflammation have both autocrine and paracrine action and seem to be one of the pathways that link the leukemic cell and the TME.
Aims
We wondered to investigate the functional role of the KP and the effects of its inhibition in CLL.
Methods
Gene transcription and protein expression were evaluated by real time PCR and western blot. Enzymatic activity was assessed through ELISA. Survival was measured with annexinV/PIassay. Overexpression and silencing of target genes was obtained by nucleofection.
Results
Previously we have demonstrated that CLL cells expressed IDO at variable levels and we found that several TME stimuli were able to up-regulate IDO mRNA and protein. We have showed that IFNγ induced an active IDO protein through STAT1 signaling as assessed measuring Kyn production and Trp consumption by ELISA. Interestingly, when we up-regulated IDO in CLL cells they showed an increased survival. Same results were obtained treating cells with Kyn. We also observed that Kyn mediated AhR translocation from the cytoplasm to the nuclei, inducing its activation as assessed by up-regulation of CYP1A1, a known AhR target gene. Analyzing the anti-apoptotic proteins of the Bcl2 family after Kyn treatment, we found the induction of Mcl1, that was affected by adding CH-223191, an antagonist of AhR. Then we decided to silence AhR in CLL cells and we found that the survival of leukemic cells was compromised as they had reduced levels of Mcl1.We then analyzed to what extent KP-induced survival could affect ABT-199 sensitivity in CLL samples. Our results indicated that pre-treatment with Kynmitigated the effect of ABT-199, which produced less apoptosis, while the use of CH-223191 has been shown to have a synergistic effect in inducing apoptosis of leukemic cells.
Conclusion
Our data demonstrated that IDO-Kyn-AhR axis is active in CLL cells and promotes Mcl1 expression,sustaining the survival of leukemic cells. Our results indicated the KP as a new potential therapeutic target in the CLL microenvironment.
Keyword(s): Chronic lymphocytic leukemia, Mcl-1, Microenvironment, Survival