High cancerous inhibitor of PP2A (CIP2A) protein levels at diagnosis of chronic myeloid leukaemia (CML) are predictive of disease progression in imatinib-treated patients. It is not known whether this is true in patients treated with second generation tyrosine kinase inhibitors (2G TKI) from diagnosis, and whether 2G TKIs modulate the CIP2A pathway. Here, we show that patients with high diagnostic CIP2A levels who receive a 2G TKI do not progress, unlike those treated with imatinib (P=<0.0001). 2G TKIs induce more potent suppression of CIP2A and c-Myc than imatinib. The transcription factor E2F1 is elevated in high CIP2A patients and following 1 month of in vivo treatment 2G TKIs suppress E2F1 and reduce CIP2A; these effects are not seen with imatinib. Silencing of CIP2A, c-Myc or E2F1 in K562 cells or CML CD34+ cells reactivates PP2A leading to BCR-ABL suppression. CIP2A increases proliferation and this is only reduced by 2G TKIs. Patients with high CIP2A levels should be offered 2G TKI treatment in preference to imatinib. 2G TKIs disrupt the CIP2A/c-Myc/E2F1 positive feedback loop, leading to lower disease progression risk. The data supports the view that CIP2A inhibits PP2Ac, stabilising E2F1, creating a CIP2A/c-Myc/E2F1 positive feedback loop, which imatinib cannot overcome.

Key Points PP2A inhibition occurs in AML by 2 different pathways: CIP2A in normal karyotype patients and SETBP1 in adverse karyotype patients. AKTS473 phosphorylation is a predictor of survival, and diagnostic levels of AKTS473 could be a novel biomarker in AML.

The expression and activity of the uptake transporter human organic cation transporter 1 (hOCT1; SLC22A1) is an independent predictor of response to imatinib treatment in patients with chronic myeloid leukaemia (CML). We have recently shown that peroxisome proliferator-activated receptor (PPAR) activation can increase the killing effect of imatinib in CML cells, due to upregulated hOCT1 gene expression and increased imatinib uptake. To investigate the role of activation of nuclear receptors other than PPAR in the transcriptional regulation of hOCT1, CML cells were treated with agonists for 13 adopted orphan receptors and endocrine receptors. It was found that hOCT1 expression was upregulated by the agonists for pregnane X receptor (PXR), retinoid acid receptor (RAR) and retinoid X receptor (RXR) in CML cell line and primary CML cells (P = 0.04; Wilcoxon rank test). Hence, agonists for PXR, RAR and RXR may be potentially used to improve the efficacy of imatinib in patients with CML.

Background: It would be clinically useful to prospectively identify the risk of disease progression in chronic myeloid leukaemia (CML). Overexpression of cancerous inhibitor of protein phosphatase 2A (PP2A) (CIP2A) protein is an adverse prognostic indicator in many cancers. Methods: We examined CIP2A protein levels in diagnostic samples from the SPIRIT2 trial in 172 unselected patients, of whom 90 received imatinib and 82 dasatinib as first-line treatment. Results: High CIP2A levels correlated with inferior progression-free survival (p = 0.04) and with worse freedom from progression (p = 0.03), and these effects were confined to dasatinib recipients. High CIP2A levels were associated with a six-fold higher five-year treatment failure rate than low CIP2A levels (41% vs. 7.5%; p = 0.0002), in both imatinib (45% vs. 11%; p = 0.02) and dasatinib recipients (36% vs. 4%; p = 0.007). Imatinib recipients with low CIP2A levels had a greater risk of treatment failure (p = 0.0008). CIP2A levels were independent of Sokal, Hasford, EUTOS (EUropean Treatment and Outcome Study), or EUTOS long-term survival scores (ELTS) or the presence of major route cytogenetic abnormalities. No association was seen between CIP2A levels and time to molecular response or the levels of the CIP2A-related proteins PP2A, SET, SET binding protein 1 (SETBP1), or AKT. Conclusions: These data confirm that high diagnostic CIP2A levels correlate with subsequent disease progression and treatment failure. CIP2A is a simple diagnostic biomarker that may be useful in planning treatment strategies.

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