CXCR4 is a G-protein-coupled receptor that interacts with its cognate ligand, CXCL12, to synchronize many physiological responses and pathological processes. Disruption of the CXCL12-CXCR4 circuitry by small-molecule antagonists has emerged as a promising strategy for cancer intervention. We previously disclosed a hit-to-lead effort that led to the discovery of a series of tetrahydroisoquinoline-based CXCR4 antagonists exemplified by the lead compound TIQ15. Herein, we describe our medicinal-chemistry efforts toward the redesign of TIQ15 as a result of high mouse-microsomal clearance, potent CYP2D6 inhibition, and poor membrane permeability. Guided by the in vitro ADME data of TIQ15, structural modifications were executed to provide compound 12a, which demonstrated a reduced potential for first-pass metabolism while maintaining CXCR4 potency. Subsequent SAR studies and multiparameter optimization of 12a resulted in the identification of compound 25o, a highly potent, selective, and metabolically stable CXCR4 antagonist possessing good intestinal permeability and low risk of CYP-mediated drug-drug interactions.