Supportive Methods for Testing CML Progression in Addition to BCR-ABL Transcript Monitoring – What to Do If BCR-ABL Monitoring doesn't Work?

Abstract 4902

BCR-ABL expression level is the exclusive and irreplaceable marker for monitoring the response to treatment in patients with chronic myeloid leukemia (CML). CML therapy by tyrosine kinase inhibitors (TKIs) is very succesfull, nevertheless resistance to imatinib treatment develops in about 25 –30% of patients. This resistance can have different reasons, both BCR-ABL-dependent and independent. According to our experience, CML patients exhibiting suboptimal response or therapy failure represent a highly heterogenous group in terms of relaps emergence and the molecular monitoring of BCR-ABL transcript not always provides sufficient evaluation of the risk of relaps. Additional markers are thus required to detect the arising resistance early before disease deterioration.

In our previous studies we found supportive markers that can describe the disease status and the progression probability in addition to commonly used methods for CML characterization (hematological, cytogenetical and BCR-ABL transcript monitoring). We analysed Hsp90 protein level in CML pacients with various therapy responses –HSP90/HSP70 protein levels tested by western blots indicate the probability of disease deterioration if the ratio is higher than 0,26 (EHA2011 – Zackova et.al.). Second possible marker, WT1 transcription level (real-time PCR according to Cilloni et al. 2006, B2M was applied as control gene), also correlated with relaps emergence during further course of the disease - expression levels above 0,1 (2ΔΔct) suggested higher (90%) probability of relapse. (Lopotova et.al. EHA 2011). Another method we used is in vitro cultivation of patient leukocytes with TKIs and the subsequent analysis of Crkl phosphorylation status as an indicator of BCR-ABL inhibition. Testing of the in vitro sensitivity to TKIs can give clues to current sensitivity to treatment and partially answer the further course of disease development (Zackova et. al. ASH2010).

In the current study we tested these three methods in CML patients. Up to now we have included a) at diagnosis (DG) (8), b) nonresponders - with stable BCR-ABL transcript level (10) and c) patients in major molecular response (MMR) (3).

Ad a) All patients tested at diagnosis with 100% sensitivity to TKIs and with low levels of HSP90 protein and WT1 transcript achieved MMR (5/8). Patients without 100% inhibition of BCR-ABL kinase by TKIs and with high levels of HSP90 protein or WT1 transcript didn't respond or relapsed (3/8).

Ad b) Patients with BCR-ABL transcript fluctuating about a constant level could relapsed or stay without relapse. The testing of HSP90 protein or WT1 transcript levels could predict probability of relaps. High levels of both markers preceeded all relapses (4/10).

Ad c) All patients in MMR had low levels of HSP90 protein and WT1 transcript, sensitivity to TKIs was 100%.

Our results suggest that WT1 transcript level, HSP90 protein level and in vitro tests of sensitivity patients leukocytes to TKI can help to characterise the real state of disease and to predict the disease evolution.