MEK inhibition with FeADC enables dose intensity in combination therapies. (A) Mouse body weight changes normalized to the baseline after the treatment with the vehicle, 30 mg/kg RMC-4550 monotherapy, or combinations comprising 30 mg/kg RMC-4550 combined with COBI at either 7.5 mg/kg or 10 mg/kg or RMC-4550 with comparable (equimolar) 12.5 mg/kg or 16 mg/kg doses of TRX-COBI. Error bars represent mean ± SEM, n = 6 mice/group and analyzed by a two-sample t-test. **, P < 0.01. (B) Tumor volume changes of PDX TM00186 tumors after the treatments in D. Error bars represent mean ± SEM, n = 6 mice/group and analyzed by one-way ANOVA; **, P < 0.01. (C) Western blot for phosphorylated ERK of tumor xenografts and spleen from NSG mice after treatment with vehicle, RMC 30 mg per kg (mpk) + COBI 10 mpk or RMC 30 mpk + TRX-COBI 16 mpk in the cohort of A and B. (D) Quantification of phosphorylated ERK expression in C, error bars represent mean ± SEM, and analyzed by a two-sample t-test. *, P < 0.1; **, P < 0.01.