Treatment with TKIs Overcomes Imatinib Resistance through the PLCgamma-1 Signaling Pathway In Imatinib Resistant Human CML Cell Lines

Abstract 4468

Suppression of BCR-ABL1 catalytic activity by the tyrosine kinase inhibitor (TKI) Imatinib Mesylate (IM) has dramatically improved the natural history of Chronic Myeloid Leukemia (CML) and - to date - represents the first and most successful example of effective anti-cancer targeted therapy {Druker, 2009}. Despite the success, patients can become resistant. Since IM-resistance in CML patients occurs despite adequate suppression of BCR-ABL activity, it is likely due to the activation of other pathways, and for this reason we need to discover novel Bcr-Abl independent pathways than can become the targets of resistant cells.

Therefore we used immortalized CML human cell lines K562 and LAM84, both sensitive and resistant to Imatinib, to study the signaling in sensitive/resistant cell lines following treatment with 4 different compounds. Reverse-Phase protein microarrays were used to quantitatively map 35 cell signaling pathway endpoints, including survival, proliferation, drug resistance, apoptosis, and autophagy. Cells were incubated with IM 1uM, Dasatinib 1uM, Nilotinib 1uM or LY-29400210 uM and after 2 or 12 hours were placed in a preservative that suppresses fluctuations in kinase pathway proteins (Espina, 2008).

5/35 protein endpoints were linked together and suppressed by Dasatinib, even in the resistant cell line: PLC-y-1-Tyr783, and its upstream (ShCTyr317 SrcTyr416) and downstream targets (mTORSer2448, STAT5Tyr694, ERKThr202/Tyr204) without interfering with AKT activation status on Ser473 compared to Imatinib (p=0.0031 for K562, p= 0.042 for LAM84), Nilotinib (p=0.0034 for K562, p= 0.043 for LAM84), LY-294002 (p=0.0009 for K562, p= 0.015 for LAM84).

In Imatinib-sensitive cell line LAM84 there were no differences between Dasatinib and Imatinib in the modulation of the pathway, compared to IM-sensitive K562 cell line (p=0.005), thus confirming the different profile among these two CML models.

Dasatinib showed a greater suppression of the PLC-y-1 pathway compared to LY-294002 in both resistant cell lines (K562, p=0.0009 and LAM84, p=0.015).

These data confirm and extend the conclusions of Markova et al. (Oncogene 2010) showing PLC-y-1 as a mechanism of death in sensitive cells. Our data showed the mechanism by which second generation TKIs (dasatinib) can overcome Imatinib resistance by suppressing the PLC-y-1 pathway.