APS-2-79 is an inhibitor of MAPK signaling dependent on kinase suppressor of Ras (KSR). It inhibits ATPbiotin binding to KSR2 in KSR2-MEK1 complexes (IC50 = 120 nM), stabilizes KSR2 in an inactive state, and reduces interactions between B-RAF and KSR2-MEK1 complexes. APS-2-79 (5 μM) inhibits KSR-stimulated phosphorylation of MEK and ERK in HEK293H cells. It enhances the efficacy of the MEK inhibitor trametinib , further reducing cell viability in HCT116 and A549 cell lines containing K-Ras mutations, but not B-RAF mutant SK-MEL-239 and A375 cell lines, when used at a concentration of 1 μM.
APS-2-79 is a modulator of KSR-dependent MAPK signaling, antagonizing RAF heterodimerization as well as the conformational changes required for phosphorylation as well as the activation of KSR-bound MEK (mitogen-activated protein kinase).
aps-2-79 was found to be able to suppress ksr-stimulated mek and erk phosphorylation. this mapk signalling suppression caused by aps-2-79 was dependent on direct targeting of ksr as an active site mutant, which had been demonstrated to stimulate ksr-based mapk outputs independent of atp-binding, which could significantly diminish the activity of aps-2-79. moreover, the ksr-stimulated mek phosphorylation caused by raf was reduced by the addition of aps-2-79 markedly. in addition, aps-2-79 was no effetive when ksr was absent or when the ksr2(a690f) mutant was used for in vitro assays, indicating that the activity of aps-2-79 was from direct targeting of ksr. however, aps-2-79 was found to lack direct activity against the highly homologous active raf family kinases, such as recombinant braf and craf, or cellular braf(v600e) [1].
[1] dhawan ns, scopton ap, dar ac. small molecule stabilization of the ksr inactive state antagonizes oncogenic ras signalling. nature. 2016 sep 1;537(7618):112-116.
