Abstract
Abstract 1535
Recent studies show that uncontrolled Hedgehog (Hh) pathway activation contributes to leukemia development and growth, and that targeted pathway inhibition is likely to offer an efficient therapeutic opportunity. PF-04449913, a Hh pathway inhibitor, is a new selective and potent inhibitor of leukemia self-renewal and is currently being evaluated in phase I clinical trials.
In order to identify new potential clinical biomarkers for the PF-04449913 (Hh inhibitor), we studied leukemia stem cell population (CD34+ subpopulation) collected before and after 28 days treatment in a phase I dose escalation protocol (Clinical Trial Gov. NTC00953758) enrolling selected hematological malignancies. This experimental clinical trial enrolled Myelofibrosis (MF), MDS, blastic phases Chronic Myeloid Leukemia (CML), chronic myelomonocytic leukemia (CMML) and Acute Myeloid Leukemia (AML) patients. We were able to collect and separate highly purified (98%) bone marrow hematopoietic progenitor cells (CD34+ populations) from 5 AML, 1 MF and 2 CML patients by immunomagnetic separation, and analysed them for gene expression profile (GEP) using Affimetrix HG-U133 Plus 2.0 platform.
We have observed that 1197 genes were differentially expressed between CD34+ cells collected before and after 28 days of PF-04449913 dose finding oral therapy. Clustering of their expression profiles showed that mostly genes differentially expressed are mainly related to Hh signaling,this providing further evidences that PF-04449913 really therapeutically targets the Hh pathway.
Regarding genes involved in Hh signaling pathway, Gas1 and Kif27 were strongly upregulated (fold change 1.0947 and 1.12757 respectively; p-value 0.01 and 0.02 respectively) in CD34+ leukemia stem cells after 28 days exposure to PF-04449913 as compared to baseline, suggesting these two genes have potential as new biomarkers of activity.
GAS-1 (growth arrest specific 1 gene) is a Sonic Hedgehog (Shh)-binding protein; it acts to sequester Shh and inhibit the Shh signalling pathway. Kif27 (kinesin family member 27) mainly acts as a negative regulator in the Hh signaling pathway, and inhibits the transcriptional activator activity of Gli1 by inhibiting its nuclear translocation.
Other genes were differentially expressed after ‘ex- vivo’ treatment with PF-04449913 as compared to baseline: we observed a down regulation of Bcl2 (fold change −1.03004), ABCA2 (fold change −1.08966), LEF1 (fold change −1.28457), Gli1 (fold change −1.0775), Smo (fold change −1.07702), and an upregulation of Gli2 (fold change 1.08191).
This data demonstrates thatPF-04449913 specifically targets the Hh Pathway in CD34+ cells, suggesting that Hh inhibition may impair leukemia stem cell maintenance. In addition, we identify several new potential biomarkers (e.g. Gas1 and KIF27). Taken together, these data may be useful for patient selection strategies and subsequent eradication of the leukaemia stem cell.
Work supported by Pfizer, European LeukemiaNet, FIRB 2008, PRIN 2009, AIRC, AIL, COFIN, University of Bologna and BolognAIL.
Soverini:Novartis: Consultancy; ARIAD: Consultancy; Bristol-Myers Squibb: Consultancy. Levin:Pfizer Oncology: Employment; Pfizer Oncology: Equity Ownership. Courtney:Pfizer Oncology: Employment; Pfizer Oncology: Equity Ownership. Baccarani:Pfizer Oncology: Consultancy; Novartis: Consultancy; BMS: Consultancy; Ariad: Consultancy; Novartis: Research Funding; Pfizer Oncology: Honoraria; Novartis: Honoraria; BMS: Honoraria; Ariad: Honoraria; Novartis: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; Ariad: Membership on an entity's Board of Directors or advisory committees. Cortes:Novartis: Consultancy; Novartis: Research Funding; BMS: Consultancy, Research Funding; Ariad: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding. Oehler:Pfizer Oncology: Research Funding. McLachlan:Pfizer: Employment. Van Arsdale:Pfizer: Employment. Martinelli:Novartis: Consultancy, Honoraria; BMS: Consultancy, Honoraria.
Author notes
Asterisk with author names denotes non-ASH members.
