Synergistic effects of p53 activation via MDM2 inhibition in combination with inhibition of Bcl-2 or Bcr-Abl in CD34+ proliferating and quiescent chronic myeloid leukemia blast crisis cells.

Bing Z Carter,Teresa Mcqueen,Jorge Cortes,Richard E Champlin,Duncan H Mak,Po Yee Mak,Hagop M Kantarjian,Marina Konopleva,Vivian R Ruvolo,Michael Andreeff,Wendy Schober

doi:10.18632/oncotarget.5890

Bing Z Carter, Teresa Mcqueen + Show 9 more

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https://doi.org/10.18632/oncotarget.5890

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Abstract

The Bcr-Abl tyrosine kinase regulates several Bcl-2 family proteins that confer resistance to apoptosis in chronic myeloid leukemia (CML) cells. Given p53's ability to modulate the expression and activity of Bcl-2 family members, we hypothesized that targeting Bcr-Abl, Bcl-2, and p53 concomitantly could have therapeutic benefits in blast crisis (BC) CML and in quiescent CML CD34+ cells that are insensitive to tyrosine kinase inhibitors (TKI). We examined the effects of the MDM2 inhibitor nutlin3a and its combination with the dual Bcl-2 and Bcl-xL inhibitor ABT-737, and the Bcr-Abl inhibitor nilotinib on BC CML patient samples. We found that in quiescent CD34+ progenitors, p53 expression is significantly lower, and MDM2 is higher, compared to their proliferating counterparts. Treatment with nutlin3a induced apoptosis in bulk and CD34+CD38- cells, and in both proliferating and quiescent CD34+ progenitor CML cells. Nutlin3a synergized with ABT-737 and nilotinib, in part by inducing pro-apoptotic, and suppressing anti-apoptotic, Bcl-2 proteins. Nilotinib inhibited the expression of Bcl-xL and Mcl-1 in BC CML cells. These results demonstrate that p53 activation by MDM2 blockade can sensitize BC CML cells, including quiescent CD34+ cells, to Bcl-2 inhibitor- and TKI-induced apoptosis. This novel strategy could be useful in the therapy of BC CML.

Highlights

The development of Bcr-Abl tyrosine kinase inhibitors (TKIs) for the treatment of chronic myeloid leukemia (CML) is the most successful molecular targeted therapy to date
We previously demonstrated that inhibition of Bcl-2/Bcl-xL by ABT-737 alone can induce apoptosis in CD34+ CML blast crisis (BC) progenitor cells, and this effect is further enhanced by combining ABT-737 with imatinib [14]
We examined the expression of p53 and MDM2 in BC CML cells, including proliferating and quiescent CD34+ CML progenitor cells, and assessed the effects of nutlin3a and its combination with the Bcl-2 inhibitor ABT-737 and the TKI nilotinib on the viability of these cells

Summary

Introduction

The development of Bcr-Abl tyrosine kinase inhibitors (TKIs) for the treatment of chronic myeloid leukemia (CML) is the most successful molecular targeted therapy to date. We previously demonstrated that inhibition of Bcl-2/Bcl-xL by ABT-737 alone can induce apoptosis in CD34+ CML BC progenitor cells, and this effect is further enhanced by combining ABT-737 with imatinib [14] This finding suggested an important role for anti-apoptotic Bcl-2 family members in the survival of CML progenitor cells. P53 stabilization with the MDM2 inhibitor MI-219 was shown to induce apoptosis in BC CML cells [38] These studies suggest the potential for p53 activation by inhibition of MDM2 as a novel CML therapy, and a potential therapeutic benefit of p53 activation alone or as a sensitizer to other therapeutic agents. We examined the expression of p53 and MDM2 in BC CML cells, including proliferating and quiescent CD34+ CML progenitor cells, and assessed the effects of nutlin3a and its combination with the Bcl-2 inhibitor ABT-737 and the TKI nilotinib on the viability of these cells. Our findings suggest that MDM2 inhibition acts synergistically with ABT-737 and nilotinib, even in the presence of MSCs, at least in part by regulating the expression of Bcl-2 family proteins

Results

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Materials and Methods