(A) Cell Titer Glo assay of MLN4924 10-point DRC for parental A673-M1 cells and MLN4924-resistant clones A, C, D, E, F, and H. Data are represented as mean ± SD. (B) Table showing EC50 for MLN4924 from parental A673-M1 and each resistant clone. (C) UBA3 is the only gene mutated in all six clones. (D) UBA3 mutations identified in MLN4924-resistant clones. DRC, dose response curve.