Recent evidence suggests that genetically “normal” tumor microenvironment may react to pathway inhibitors by upregulating signaling pathways and modulating the sensitivity of cancer cells to targeted agents. The aim of this study was to uncover the mechanisms by which stromal cells modulate the sensitivity of tumor cells in response to signaling inhibitors.
We monitored the functional effects of MEK and PI3K/mTOR inhibitors (trametinib/gedatolisib) on isogenic CRC cell lines (HCT116 and HCT116 PTEN-/-) in the presence or absence of stromal fibroblasts or fibroblast/endothelial cell conditioned medium (CM); moreover, we evaluated pathway activation under different culture conditions and analysed the cytokine/chemokine profile.
Trametinib/gedatolisib combinations were additive in HCT116 (combination index, CI = 1) and strongly synergistic in HCT116 PTEN-/- (CI = 0.25). Under conditions of direct cell-cell contact, co-culture with HCT116 PTEN-/- rendered fibroblasts hypersensitive to combined trametinib/gedatolisib combinations, while co-culture with HCT116 actually protected the stromal component. CM from different types of stromal cells (fibroblasts: HFF, HF, BJ; endothelial cells: EA.hy926) differentially affected the response of HCT116 (but not HCT116 PTEN-/-) to signalling inhibitors: in particular, HFF- and EA.hy926-CM rendered HCT116 hypersensitive to PI3K/mTOR blockade by single-agent gedatolisib moreover, EA.hy926 rendered HCT116 PTEN-/- more sensitive to trametinib. Pathway activation analysis showed more prominent downregulation of AKT phosphorylation in response to PI3K/mTOR inhibition in the presence of fibroblast-conditioned medium. Angiogenesis microarrays demonstrated a diversified profile of cytokine/chemokine production in stromal cells from different sources, particularly in terms of IL-6, IL-8 and MCP-1 production.
Stromal cells differentially affected response of CRC to agents targeting the MAPK and PI3K pathways; such effects varied depending on the genetic background of the tumor cell (PTEN-competent or PTEN-loss) and on the modality of tumor stroma interaction (direct cell contact or soluble factors).
Clinical trial identification
Legal entity responsible for the study
IFO- Regina Elena National Cancer Institute
AIRC 18622, 14362, 9979
All authors have declared no conflicts of interest.