CB039 is a selective degrader targeting RBM39 (RNA binding motif protein 39). It facilitates the formation of a ternary complex between RBM39 and the E3 ubiquitin ligase CUL4-DCAF15, resulting in the proteasomal degradation of RBM39. CB039 holds promise for research into cancers dependent on RBM39, such as acute myeloid leukemia (AML) and ovarian cancer.