A Histone Deacetylase Inhibitor Induces Apoptosis, Differentiation and Cell Cycle Changes in STI571 Resistant CML Cell Line with No Change in BCR-ABL Expression

• Published in: Blood 2008-11, Vol.112 (11), p.4235-4235
• Main Authors: Shaklai, Matityahu, Zimra, Yael, Belyaeva, Inessa, Aviram, Adina, Rabizadeh, Esther
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V112.11.4235.4235

The hallmark of Chronic-myelogenous leukemia (CML) is high tyrosine kinase (TK) activity of the chimeric protein BCR-ABL, known to contribute to cell tumorogenity, resistance to apoptosis and differentiation. The gold-standard therapy for CML is treatment with the TK inhibitor Imatinib (STI571), but in some cases STI571 resistance appears due to BCR-ABL over expression, amplification or mutation in the ABL kinase domain. However, STI571 resistance due to other mechanisms which are BCR-ABL independent may not be excluded. BCR-ABL-positive cells can evade the inhibitory effect of STI571 by different mechanisms, such as reduced intake mediated by OCT-1 organic cation transporter-1), or enhanced efflux by Pgp, and, possibly, acquisition of compensatory mutations in genes other than BCR-ABL. One possible approach to overcome STI571 resistance involves the combination of Histone Deacetylase Inhibitors (HDACI). Previously we have shown: induced apoptosis, differentiation and reduced BCR-ABL protein levels in CML cell line (K562) by Pivaloyloxymethyl butyrate (Pivanex), a HDACI. In order to study STI571 resistance and the influence of HDACI on STI571 resistant CML cells we developed an STI571 K562 resistant cell line (K562-R). Our results show that s these K562-R cells had an IC50 33 times greater than that of K562 wild type (K562-S) cells. But K562-R cells had similar BCR-ABL protein and transcript levels as the K562-S and no mutations were found in the catalytic TK domain of K562-R cells. MDR protein expression and activity in K562-R were very low and similar to those of K562-S. However, the K562-R cell line had higher spontaneous apoptosis and G2M arrest and a slight but significant lower S phase. The K562-R cell line expressed more glycophorin A although spontaneous hemoglobin synthesis in K562-R cells was lower. Study of the signaling transduction pathway have shown no differences in p70S6, STAT3, Erk 1/2, CREB, Ikβ-a and JNK proteins levels (total and phosphorylated), however phosphorylated p38 was elevated in the K562-R cells. P21, a cell cycle regulatory protein, was higher in K562-R cells. HDACI induced viability loss, apoptosis and cell cycle changes in K562-R in a similar way to its effects on K562-S cells. However, it did not influence the levels of BCR-ABL. Taken together our results suggest that the STI571 resistance mechanism in these K562-R cells does not involve BCR-ABL but other regulatory mechanisms in the cell cycle, differentiation and signal