ATRA can enhance apoptosis that is induced by Flt3 tyrosine kinase inhibition in Flt3-ITD positive cells

• Published in: Leukemia research Vol. 30; no. 5; pp. 633 - 642
• Main Authors: Scholl, S., Müller, R., Clement, J.H., Loncarevic, I.F., Böhmer, F.D., Höffken, K.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-05-2006
• Subjects: Apoptosis; Apoptosis - drug effects; ATRA; Cell Differentiation - drug effects; Cell Line, Tumor; Enzyme Activation - drug effects; Flt3-ITD; fms-Like Tyrosine Kinase 3 - antagonists & inhibitors; fms-Like Tyrosine Kinase 3 - biosynthesis; fms-Like Tyrosine Kinase 3 - genetics; Granulocyte Colony-Stimulating Factor - pharmacology; Humans; Indoles - pharmacology; Mutation; Protein Kinase Inhibitors - pharmacology; Proto-Oncogene Proteins c-bcl-2 - biosynthesis; Proto-Oncogene Proteins c-bcl-2 - drug effects; Survivin; Tretinoin - pharmacology; Flt3-ITD; Survivin; ATRA; Apoptosis
• ISSN: 0145-2126; 1873-5835
• DOI: 10.1016/j.leukres.2005.10.005

Among activating Flt3 mutations that have been shown in 25–30% of acute myeloid leukaemia (AML) Flt3-internal tandem duplication (ITD) mutations are predominant.
We investigated the influence of all-
trans-retinoic acid (ATRA) and granulocyte colony stimulating factor (G-CSF) for their effects on differentiation and apoptosis in human cell lines with different Flt3 variants (THP-1 versus MV4-11 and MOLM13) dependent on the inhibition of Flt3 tyrosine kinase by the bis(lH-2-indolyl)methanone D-65476.
While myeloid differentiation was not observed in both Flt3-ITD cell lines (MV4-11 and MOLM13), we demonstrate an enhanced proapoptotic effect of D-65476 in the presence of ATRA that was restricted to the Flt3-ITD expressing cells. The combined treatment with ATRA and D-65476 also led to a pronounced down-regulation of surviv in on mRNA and protein level in Flt3-ITD but not in Flt3 wildtype expressing cells (THP-1). Surprisingly, there was no differential expression of important proteins like Bcl-X
L, Bcl-2 or Bax that might explain enhanced apoptosis. Furthermore, Akt phosphorylation after stimulation with Flt3 ligand dependent on D-65476 was not affected by pretreatment with ATRA.
We suggest that regulation of inhibitors of apoptosis might play a crucial role how ATRA can increase the proapoptotic effect of Flt3 inhibitors in myeloid leukemia cells expressing Flt3-ITD. This effect can potentially be exploited for the treatment of Flt3-ITD positive acute myeloid leukemia.