Therapeutic sensitivity to Rac GTPase inhibition requires consequential suppression of mTORC1, AKT, and MEK signaling in breast cancer.

Abstract

Rac GTPases have oncogenic roles in cell growth, survival, and migration. We tested response to the Rac inhibitor EHT1864 in a panel of breast cancer cell lines. EHT1864-induced growth inhibition was associated with dual inhibition of the PI3K/AKT/mTORC1 and MEK/ERK pathways. Breast cancer cells harboring PIK3CA mutations or HER2 overexpression were most sensitive to Rac inhibition, suggesting that such oncogenic alterations link Rac activation with PI3K/AKT/mTORC1 and MEK/ERK signaling. Interestingly, EHT1864 decreased activation of the mTORC1 substrate p70S6K earlier than AKT inhibition, suggesting that Rac may activate mTORC1/p70S6K independently of AKT. Comparison of the growth-inhibitory profile of EHT1864 to 137 other anti-cancer drugs across 656 cancer cell lines revealed significant correlation with the p70S6K inhibitor PF-4708671. We confirmed that Rac complexes contain MEK1/2 and ERK1/2, but also contain p70S6K; these interactions were disrupted by EHT1864. Pharmacokinetic profiles revealed that EHT1864 was present in mouse plasma at concentrations effective in vitro for approximately 1 h after intraperitoneal administration. EHT1864 suppressed growth of HER2+ tumors, and enhanced response to anti-estrogen treatment in ER+ tumors. Further therapeutic development of Rac inhibitors for HER2+ and PIK3CA-mutant cancers is warranted.

• Authors: Riley A Hampsch, Kevin Shee, Darcy Bates, Lionel D Lewis, Laurent Désiré, Bertrand Leblond, Eugene Demidenko, Kurtis Stefan, Yina H Huang, Todd W Miller
• Journal: Oncotarget (Oncotarget) Vol. 8 Issue 13 Pg. 21806-21817 (Mar 28 2017) ISSN: 1949-2553 [Electronic] United States
• PMID: 28423521 (Publication Type: Journal Article)

Chemical References

• Antineoplastic Agents
• Multiprotein Complexes
• Protein Kinase Inhibitors
• Mechanistic Target of Rapamycin Complex 1
• Proto-Oncogene Proteins c-akt
• TOR Serine-Threonine Kinases
• MAP Kinase Kinase Kinases

Topics

• Animals
• Antineoplastic Agents (pharmacology)
• Breast Neoplasms (metabolism)
• Drug Resistance, Neoplasm (physiology)
• Female
• Humans
• MAP Kinase Kinase Kinases (metabolism)
• Mechanistic Target of Rapamycin Complex 1
• Mice
• Mice, Inbred NOD
• Mice, SCID
• Multiprotein Complexes (metabolism)
• Protein Kinase Inhibitors (pharmacology)
• Proto-Oncogene Proteins c-akt (antagonists & inhibitors, metabolism)
• Signal Transduction (drug effects)
• TOR Serine-Threonine Kinases (metabolism)
• Xenograft Model Antitumor Assays