Combined AKT and MEK Pathway Blockade in Pre-Clinical Models of Enzalutamide-Resistant Prostate Cancer

PLoS One. 2016 Apr 5;11(4):e0152861. doi: 10.1371/journal.pone.0152861. eCollection 2016.

Abstract

Despite recent improvements in patient outcomes using newer androgen receptor (AR) pathway inhibitors, treatment resistance in castrate resistant prostate cancer (CRPC) continues to remain a clinical problem. Co-targeting alternate resistance pathways are of significant interest to treat CRPC and delay the onset of resistance. Both the AKT and MEK signaling pathways become activated as prostate cancer develops resistance to AR-targeted therapies. This pre-clinical study explores co-targeting these pathways in AR-positive prostate cancer models. Using various in vitro models of prostate cancer disease states including androgen dependent (LNCaP), CRPC (V16D and 22RV1) and ENZ-resistant prostate cancer (MR49C and MR49F), we evaluate the relevance of targeting both AKT and MEK pathways. Our data reveal that AKT inhibition induces apoptosis and inhibits cell growth in PTEN null cell lines independently of their sensitivity to hormone therapy; however, AKT inhibition had no effect on the PTEN positive 22RV1 cell line. Interestingly, we found that MEK inhibition had greater effect on 22RV1 cells compared to LNCaP, V16D or ENZ-resistant cells MR49C and MR49F cells. In vitro, combination AKT and MEK blockade had evidence of synergy observed in some cell lines and assays, but this was not consistent across all results. In vivo, the combination of AKT and MEK inhibition resulted in more consistent tumor growth inhibition of MR49F xenografts and longer disease specific survival compared to AKT inhibitor monotherapy. As in our in vitro study, 22RV1 xenografts were more resistant to AKT inhibition while they were more sensitive to MEK inhibition. Our results suggest that targeting AKT and MEK in combination may be a valuable strategy in prostate cancer when both pathways are activated and further support the importance of characterizing the dominant oncogenic pathway in each patient's tumor in order to select optimal therapy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antineoplastic Agents / pharmacology*
  • Apoptosis / drug effects
  • Benzamides
  • Cell Cycle / drug effects
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Cell Survival / drug effects
  • Disease Models, Animal
  • Drug Resistance, Neoplasm*
  • Extracellular Signal-Regulated MAP Kinases / metabolism*
  • Humans
  • Male
  • Nitriles
  • Phenylthiohydantoin / analogs & derivatives
  • Phenylthiohydantoin / pharmacology
  • Prostatic Neoplasms, Castration-Resistant / drug therapy
  • Prostatic Neoplasms, Castration-Resistant / metabolism*
  • Prostatic Neoplasms, Castration-Resistant / mortality
  • Prostatic Neoplasms, Castration-Resistant / pathology
  • Protein Kinase Inhibitors / pharmacology*
  • Proto-Oncogene Proteins c-akt / metabolism*
  • Receptors, Androgen / metabolism
  • Signal Transduction / drug effects*
  • Tumor Burden
  • Xenograft Model Antitumor Assays

Substances

  • Antineoplastic Agents
  • Benzamides
  • Nitriles
  • Protein Kinase Inhibitors
  • Receptors, Androgen
  • Phenylthiohydantoin
  • enzalutamide
  • Proto-Oncogene Proteins c-akt
  • Extracellular Signal-Regulated MAP Kinases

Grants and funding

Funding was provided by Discovery Grant, Prostate Cancer Canada and AstraZeneca to A. Zoubeidi. PT was supported by the Canadian Urological Association Scholarship Foundation. AstraZeneca was involved in discussions regarding the study design and review of the manuscript, but the data collection and analysis and decision to publish was made by the authors. The other funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.