Receptor tyrosine kinases (RTKs) inhibitors' activity in advanced
osteosarcoma is significant but short-lived. To prevent or at least delay drug resistance, we explored a vertical inhibition by combining drugs acting at different levels of the RTK pathways (
pazopanib +
trametinib). We studied
pazopanib +
trametinib antitumor activity both in vitro and in vivo (
MNNG-HOS and KHOS xenografts in NOD/SCID mice) investigating the molecular mechanisms and potential escapes. The involvement of MAPK-PI3K pathways was validated by Nanostring technology, western blot and by silencing/overexpression experiments.
Pazopanib targets were expressed on seven
osteosarcoma cell lines and their pathways were activated.
Pazopanib +
trametinib exhibited synergistic antitumor activity by inducing apoptosis and inhibiting ERK1/2 and Akt. In vivo antitumor activity was shown in
osteosarcoma-bearing mice. The
drug combination significantly down-modulated RTK
Ephrin Type-A Receptor 2 (EphA2) and
Interleukin-7 Receptor (IL-7R), whereas induced
mitogen-activated protein-kinase kinase (
MAPKK) MEK6. EphA2 silencing significantly reduced
osteosarcoma cell proliferation and migration, while impeding MEK6 up-regulation in the treated cells significantly increased the antitumor effect of the studied drugs. Moreover, the up-regulation of MEK6 reduced combination activity.
Pazopanib +
trametinib demonstrated synergistic antitumor effects in
osteosarcoma models through ERK and Akt inhibition and EphA2 and IL-7R down-modulation. MEK6 up-regulation might evoke escaping mechanism.