Contributions
Abstract: PB2338
Type: Publication Only
Background
High-grade B-cell lymphoma with recurrent chromosomal translocations of 8q24/MYC and 18q21/BCL2 (HGBL-MBR) is a subtype of aggressive lymphoma with poor prognosis in spite of showing germinal center B-cell (GCB) phenotype. New therapeutic strategies against HGBL-MBR are needed due to the resistance to conventional chemoimmunotherapy.
Aims
We examined in vitro sensitivity of HGBL-MBR cells to topo-II inhibitor doxorubicin, bromodomain inhibitor JQ-1, BH3 mimetics venetoclax, and Mcl-1 inhibitor S63845.
Methods
Three GCB-type cell lines (Karpas231, OCI-Ly8, and BJAB) were used. The translocations were confirmed by FISH analysis, and the expressions of Myc and Bcl-2 family proteins were assessed by Western blot analysis. At 24 and 48 hours after treatment with each drug, the cell count and viability were evaluated by dye exclusion test. Annexin V binding assay was also performed to detect apoptotic changes.
Results
FISH analyses confirmed that Karpas231 and OCI-Ly8 have both IGH-BCL2 fusion and a split of MYC and that BJAB has only IGH-MYC fusion. Although the expression levels of Myc and Bcl-xL were varied, those of Bcl-2 were similarly high in the three lines. Compared with BJAB, Karpas231 and OCI-Ly8 showed the minimal expression of Mcl-1. Doxorubicin and JQ-1 suppressed the proliferation in a dose-dependent manner in the three lines. Although venetoclax showed growth suppression in both HGBL-MBR cell lines but not in BJAB, S63845 had the minimal effect only in BJAB. After treatment with 200 nM of venetoclax, annexin V-positive cells increased above 70% of total cells in Karpas231 and OCI-ly8, while apoptotic changes were hardly detected in BJAB (1.3%). After treatment with venetoclax, dephosphorylation of Bcl-2 rapidly occurred in both HGBL-MBR cell lines. Furthermore, the sensitivity of BJAB to venetoclax was restored in combination with 100 nM of S63845, suggesting that the resistance to venetoclax in BJAB seemed to be attributed to Mcl-1.
Conclusion
Our data indicate that the anti-apoptotic activity of both HGBL-MBR cell lines more strongly depends on Bcl-2 than Mcl-1, and that venetoclax may be a promising agent to overcome the resistance to conventional chemoimmunotherapy in HGBL-MBR.
Session topic: 19. Non-Hodgkin lymphoma Biology & Translational Research
Keyword(s): Apoptosis, B cell lymphoma, BCL2, Mcl-1
Abstract: PB2338
Type: Publication Only
Background
High-grade B-cell lymphoma with recurrent chromosomal translocations of 8q24/MYC and 18q21/BCL2 (HGBL-MBR) is a subtype of aggressive lymphoma with poor prognosis in spite of showing germinal center B-cell (GCB) phenotype. New therapeutic strategies against HGBL-MBR are needed due to the resistance to conventional chemoimmunotherapy.
Aims
We examined in vitro sensitivity of HGBL-MBR cells to topo-II inhibitor doxorubicin, bromodomain inhibitor JQ-1, BH3 mimetics venetoclax, and Mcl-1 inhibitor S63845.
Methods
Three GCB-type cell lines (Karpas231, OCI-Ly8, and BJAB) were used. The translocations were confirmed by FISH analysis, and the expressions of Myc and Bcl-2 family proteins were assessed by Western blot analysis. At 24 and 48 hours after treatment with each drug, the cell count and viability were evaluated by dye exclusion test. Annexin V binding assay was also performed to detect apoptotic changes.
Results
FISH analyses confirmed that Karpas231 and OCI-Ly8 have both IGH-BCL2 fusion and a split of MYC and that BJAB has only IGH-MYC fusion. Although the expression levels of Myc and Bcl-xL were varied, those of Bcl-2 were similarly high in the three lines. Compared with BJAB, Karpas231 and OCI-Ly8 showed the minimal expression of Mcl-1. Doxorubicin and JQ-1 suppressed the proliferation in a dose-dependent manner in the three lines. Although venetoclax showed growth suppression in both HGBL-MBR cell lines but not in BJAB, S63845 had the minimal effect only in BJAB. After treatment with 200 nM of venetoclax, annexin V-positive cells increased above 70% of total cells in Karpas231 and OCI-ly8, while apoptotic changes were hardly detected in BJAB (1.3%). After treatment with venetoclax, dephosphorylation of Bcl-2 rapidly occurred in both HGBL-MBR cell lines. Furthermore, the sensitivity of BJAB to venetoclax was restored in combination with 100 nM of S63845, suggesting that the resistance to venetoclax in BJAB seemed to be attributed to Mcl-1.
Conclusion
Our data indicate that the anti-apoptotic activity of both HGBL-MBR cell lines more strongly depends on Bcl-2 than Mcl-1, and that venetoclax may be a promising agent to overcome the resistance to conventional chemoimmunotherapy in HGBL-MBR.
Session topic: 19. Non-Hodgkin lymphoma Biology & Translational Research
Keyword(s): Apoptosis, B cell lymphoma, BCL2, Mcl-1