Presentation Abstract

Abstract Number: 906
Presentation Title: Gas1 and Kif27 genes are strongly up-regulated biomarkers of Hedgehog inhibition (PF-04449913) on leukemia stem cells in Phase I Acute Myeloid Leukemia and Chronic Myeloid Leukemia treated patients
Presentation Time: Sunday, Apr 01, 2012, 1:00 PM - 5:00 PM
Location: McCormick Place West (Hall F), Poster Section 34
Poster Section: 34
Poster Board Number: 17
Author Block: Viviana Guadagnuolo1, Cristina Papayannidis1, Ilaria Iacobucci1, Sandra Durante1, Carolina Terragna1, Emanuela Ottaviani1, Maria Chiara Abbenante1, Federica Cattina1, Simona Soverini1, Barbara Lama1, Lucia Toni1, Wendy Levin2, Rachel Courtney2, Carmen Baldazzi1, Antonio Curti1, Michele Baccarani1, Catriona Jamieson3, Jorge Cortes4, Vivian Oehler5, Karen McLachlan2, Todd VanArsdale2, Giovanni Martinelli1. 1University of Bologna, Bologna, Italy; 2Pfizer Oncology, San Diego, CA; 3University of California, San Diego, CA; 4M.D. Anderson Cancer Center, Houston, TX; 5Fred Hutchinson Cancer Research Center, Seattle, WA
Abstract Body: 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, we studied CD34+ leukemia stem cell population (LSC) 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 CML, chronic myelomonocytic leukemia (CMML) and AML patients (pts). We were able to collect and separate highly purified (98%) bone marrow CD34+ cells from 5 AML, 1 MF and 2 CML pts by immunomagnetic separation, and analysed them for gene expression profile using Affimetrix HG-U133 Plus 2.0 platform.
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+ LSC after 28 days exposure to PF-04449913 as compared to baseline, suggesting these two genes have potential as new biomarkers of activity.
GAS-1 is a Sonic Hedgehog (Shh)-binding protein; it acts to sequester Shh and inhibit the Shh signalling pathway. Kif27 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).
Conclusions: This data demonstrates that PF-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 pts selection strategies and subsequent eradication of the LSC.
Acknowledgments: Work supported by Pfizer, European LeukemiaNet, FIRB 2006, AIRC, AIL, COFIN, University of Bologna and BolognAIL.