Novel Link between PI 3′ Kinase/p38 Map Kinase Pathway in Dasatinib (BMS354825) Mediated Effect in BCR-ABL Expressing Cells.

Background: Dasatinib (BMS354825), a dual Src/Abl tyrosine kinase inhibitor, exhibits potent antileukemic effects in vitro and in vivo. Despite the well-established role of BMS354825 in the treatment of imatinib-resistant chronic myelogenous leukemia (CML), the molecular mechanisms that result in generation of antileukemic responses remain unknown.

Methods: BCR/ABL (wild type and those carrying mutations: E255K, H396P, Y253F, M351T and T315I) expressing murine BAF3 cell lines were exposed to varying concentrations of BMS354825 for variable times to evaluate for effect on phosphorylation/activation of p38 MAP Kinase and PI3′ Kinase pathway in presence or absence of pharmacologic inhibitors of p38 MAP Kinase and mTOR respectively.

Results: In the present study we provide evidence that BMS354825 induces phosphorylation of the p38 MAP Kinase, and activation of its kinase domain, in BCR-ABL expressing cell lines except for those carrying T315I mutation. We also identify the kinases MapKapK-2 which is upregulated in response to BMS354825 as shown by increased phosphorylation of hsp27. Importantly, pharmacological inhibition of p38 MAP Kinase by SB203580 reverses the growth inhibitory effects of BMS354825 on primary leukemic CFU-GM progenitors from patients with CML (see figure). Moreover, SB203580 leads to impairment of the BMS354825 mediated antiproliferative effects in both wild type and mutated CML lines except for those carrying T315I. On the other hand, BMS354825 leads to dephosphorylation of p70S6 Kinase and its downstream effector pathway including down regulation of ribosomal S6. We also report that the pharmacological inhibition of mTOR by Rapamycin augments the growth inhibitory effects of BMS354825 on primary leukemic CFU-GM progenitors from CML patients (see figure). Furthermore, pharmacologic inhibition of p38 MAP Kinase by SB203580 led to reversal of the BMS354825 mediated dephosphorylation of p70 S6 Kinase demonstrating that it maybe downstream of p38 MAP Kinase activation. Altogether, our data establish that activation of the p38 MAP Kinase signaling cascade plays an important role in the generation of the effects of BMS354825 on BCR-ABL expressing cells.

Conclusion:

1. We have identified a novel crosstalk mechanism between the p38 MAPK and the PI3′ Kinase pathway which is unique to the effect of BMS354825 in CML.

2. p38 MAP Kinase pathway may play an important role in developing of resistance to BMS354825 in CML.

3. mTOR inhibition may augment effect of BMS354825 in CML and its role in combination with BMS354825 should be explored in resistant disease.

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