title: Small molecule inhibition of group I p21-activated kinases in breast cancer induces apoptosis and potentiates the activity of microtubule stabilizing agents.
abstract: BACKGROUND
  Breast cancer, the most common cause of cancer-related deaths worldwide among women, is a molecularly and clinically heterogeneous disease. Extensive genetic and epigenetic profiling of breast tumors has recently revealed novel putative driver genes, including p21-activated kinase (PAK)1. PAK1 is a serine/threonine kinase downstream of small GTP-binding proteins, Rac1 and Cdc42, and is an integral component of growth factor signaling networks and cellular functions fundamental to tumorigenesis.
  
  
  METHODS
  PAK1 dysregulation (copy number gain, mRNA and protein expression) was evaluated in two cohorts of breast cancer tissues (n=980 and 1,108). A novel small molecule inhibitor, FRAX1036, and RNA interference were used to examine PAK1 loss of function and combination with docetaxel in vitro. Mechanism of action for the therapeutic combination, both cellular and molecular, was assessed via time-lapse microscopy and immunoblotting.
  
  
  RESULTS
  We demonstrate that focal genomic amplification and overexpression of PAK1 are associated with poor clinical outcome in the luminal subtype of breast cancer (P=1.29×10(-4) and P=0.015, respectively). Given the role for PAK1 in regulating cytoskeletal organization, we hypothesized that combination of PAK1 inhibition with taxane treatment could be combined to further interfere with microtubule dynamics and cell survival. Consistent with this, administration of docetaxel with either a novel small molecule inhibitor of group I PAKs, FRAX1036, or PAK1 small interfering RNA oligonucleotides dramatically altered signaling to cytoskeletal-associated proteins, such as stathmin, and induced microtubule disorganization and cellular apoptosis. Live-cell imaging revealed that the duration of mitotic arrest mediated by docetaxel was significantly reduced in the presence of FRAX1036, and this was associated with increased kinetics of apoptosis.
  
  
  CONCLUSIONS
  Taken together, these findings further support PAK1 as a potential target in breast cancer and suggest combination with taxanes as a viable strategy to increase anti-tumor efficacy.
authors.affiliation: Department of Translational Oncology, Genentech, Inc., South San Francisco, CA, USA. ong.christy@gene.com.
authors.forename: Christy C
authors.initials: CC
authors.lastname: Ong
authors.affiliation: Department of Pathology, Genentech, Inc., South San Francisco, CA, USA. gierke.sarah@gene.com.
authors.forename: Sarah
authors.initials: S
authors.lastname: Gierke
authors.affiliation: Department of Translational Oncology, Genentech, Inc., South San Francisco, CA, USA. cameron.pitt@ucsf.edu.|New address: University of California, San Francisco, CA, USA. cameron.pitt@ucsf.edu.
authors.forename: Cameron
authors.initials: C
authors.lastname: Pitt
authors.affiliation: Department of Pathology, Genentech, Inc., South San Francisco, CA, USA. sagolla.meredith@gene.com.
authors.forename: Meredith
authors.initials: M
authors.lastname: Sagolla
authors.affiliation: Department of Translational Oncology, Genentech, Inc., South San Francisco, CA, USA. ccheng@cal.berkeley.edu.
authors.forename: Christine K
authors.initials: CK
authors.lastname: Cheng
authors.affiliation: Department of Translational Oncology, Genentech, Inc., South San Francisco, CA, USA. zhou.wei@gene.com.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhou
authors.affiliation: Department of Pathology, Genentech, Inc., South San Francisco, CA, USA. jubb.adrian@gene.com.
authors.forename: Adrian M
authors.initials: AM
authors.lastname: Jubb
authors.affiliation: Department of Diagnostics, Genentech, Inc., South San Francisco, CA, USA. sanders.laura@gene.com.
authors.forename: Laura
authors.initials: L
authors.lastname: Strickland
authors.affiliation: Department of Diagnostics, Genentech, Inc., South San Francisco, CA, USA. schmidt.maike@gene.com.
authors.forename: Maike
authors.initials: M
authors.lastname: Schmidt
authors.affiliation: Afraxis, La Jolla, CA, USA. sduron@coipharma.com.|New address: COI Pharmaceuticals, La Jolla, CA, USA. sduron@coipharma.com.
authors.forename: Sergio G
authors.initials: SG
authors.lastname: Duron
authors.affiliation: Afraxis, La Jolla, CA, USA. dcampbell@coipharma.com.|New address: COI Pharmaceuticals, La Jolla, CA, USA. dcampbell@coipharma.com.
authors.forename: David A
authors.initials: DA
authors.lastname: Campbell
authors.affiliation: National Center for Advancing Translational Sciences, Bethesda, MD, USA. wzheng@mail.nih.gov.
authors.forename: Wei
authors.initials: W
authors.lastname: Zheng
authors.affiliation: National Center for Advancing Translational Sciences, Bethesda, MD, USA. seameen.dehdashti@fda.hhs.gov.|New address: Food and Drug Administration, Silver Spring, MD, USA. seameen.dehdashti@fda.hhs.gov.
authors.forename: Seameen
authors.initials: S
authors.lastname: Dehdashti
authors.affiliation: National Center for Advancing Translational Sciences, Bethesda, MD, USA. shenmin@mail.nih.gov.
authors.forename: Min
authors.initials: M
authors.lastname: Shen
authors.affiliation: National Center for Advancing Translational Sciences, Bethesda, MD, USA. na.yang@nih.gov.
authors.forename: Nora
authors.initials: N
authors.lastname: Yang
authors.affiliation: National Center for Advancing Translational Sciences, Bethesda, MD, USA. mark.behnke@nih.gov.
authors.forename: Mark L
authors.initials: ML
authors.lastname: Behnke
authors.affiliation: National Center for Advancing Translational Sciences, Bethesda, MD, USA. huangwe@mail.nih.gov.
authors.forename: Wenwei
authors.initials: W
authors.lastname: Huang
authors.affiliation: National Center for Advancing Translational Sciences, Bethesda, MD, USA. john.mckew@gmail.com.|New address: aTyr Pharma, San Diego, CA, USA. john.mckew@gmail.com.
authors.forename: John C
authors.initials: JC
authors.lastname: McKew
authors.affiliation: Fox Chase Cancer Center, Philadelphia, PA, USA. Jonathan.Chernoff@fccc.edu.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Chernoff
authors.affiliation: Department of Biostatistics, Genentech, Inc., South San Francisco, CA, USA. forrest.bill@gene.com.
authors.forename: William F
authors.initials: WF
authors.lastname: Forrest
authors.affiliation: Department of Bioinformatics, Genentech, Inc., South San Francisco, CA, USA. haverty.peter@gene.com.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Haverty
authors.affiliation: Cancer Research UK, University of Cambridge, Cambridge, UK. Suet-Feung.Chin@cruk.cam.ac.uk.
authors.forename: Suet-Feung
authors.initials: SF
authors.lastname: Chin
authors.affiliation: Histopathology, Division of Cancer and Stem Cells, School of Medicine, University of Nottingham and Nottingham University Hospitals, Nottingham, UK. emadrakha@yahoo.com.
authors.forename: Emad A
authors.initials: EA
authors.lastname: Rakha
authors.affiliation: Histopathology, Division of Cancer and Stem Cells, School of Medicine, University of Nottingham and Nottingham University Hospitals, Nottingham, UK. Andrew.Green@nottingham.ac.uk.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Green
authors.affiliation: Histopathology, Division of Cancer and Stem Cells, School of Medicine, University of Nottingham and Nottingham University Hospitals, Nottingham, UK. Ian.Ellis@nottingham.ac.uk.
authors.forename: Ian O
authors.initials: IO
authors.lastname: Ellis
authors.affiliation: Cancer Research UK, University of Cambridge, Cambridge, UK. Carlos.Caldas@cruk.cam.ac.uk.
authors.forename: Carlos
authors.initials: C
authors.lastname: Caldas
authors.affiliation: Department of Translational Oncology, Genentech, Inc., South San Francisco, CA, USA. obrien.tom@gene.com.
authors.forename: Thomas
authors.initials: T
authors.lastname: O'Brien
authors.affiliation: Department of Translational Oncology, Genentech, Inc., South San Francisco, CA, USA. friedman.lori@gene.com.
authors.forename: Lori S
authors.initials: LS
authors.lastname: Friedman
authors.affiliation: Department of Pathology, Genentech, Inc., South San Francisco, CA, USA. koeppen.hartmut@gene.com.
authors.forename: Hartmut
authors.initials: H
authors.lastname: Koeppen
authors.affiliation: Discovery Chemistry, Genentech, Inc., South San Francisco, CA, USA. rudolph.joachim@gene.com.
authors.forename: Joachim
authors.initials: J
authors.lastname: Rudolph
authors.affiliation: Department of Translational Oncology, Genentech, Inc., South San Francisco, CA, USA. klaushoeflich@hotmail.com.|New address: Blueprint Medicines, Cambridge, MA, UK. klaushoeflich@hotmail.com.
authors.forename: Klaus P
authors.initials: KP
authors.lastname: Hoeflich
mesh_terms: D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000401:mortality / Q000473:pathology; D059447:Cell Cycle Checkpoints / Q000187:drug effects; D045744:Cell Line, Tumor; D056915:DNA Copy Number Variations; D000077143:Docetaxel; D004357:Drug Synergism; D005260:Female; D005784:Gene Amplification; D015870:Gene Expression; D006801:Humans; D008870:Microtubules / Q000378:metabolism*; D011379:Prognosis; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D043823:Taxoids / Q000494:pharmacology; D050257:Tubulin Modulators / Q000494:pharmacology*; D054462:p21-Activated Kinases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism
chemical_list: D047428:Protein Kinase Inhibitors; D043823:Taxoids; D050257:Tubulin Modulators; D000077143:Docetaxel; D054462:p21-Activated Kinases