Branched-chain amino acid aminotransferases (BCATs), existing as the two isoforms BCAT1 and BCAT2, are responsible for the catabolism of branched-chain amino acids (BCAAs) and are highly upregulated and implicated in a diverse range of cancers. BCAT1 inhibitors represent a potential class of therapeutic agents for cancers; however, none have yet progressed to clinical development. Our earlier research identified as a novel BCAT1 inhibitor featuring a unique bridged bicyclic skeleton and demonstrating both in vitro and in vivo antitumor activity against tyrosine kinase inhibitor (TKI)-resistant lung cancer with high BCAT1 expression. In the present study, we proceeded to modify the structure of by two-round structure-activity relationship (SAR) exploration, leading to the discovery of a bicyclo[3.2.1]octene-bearing GABA derivative . Compound exhibited a 6-fold enhancement in BCAT1 enzymatic inhibitory activity compared to the parent compound and could effectively suppress the growth of 67R cells that highly expressed BCAT1 and was resistant to third-generation TKIs. GABA derivatives are an important chemical class of BCAT1 inhibitors, and therefore, the findings in the present study represent great progress both in the discovery of potent BCAT1 inhibitors with new chemical structures and in the treatment of cancer resistance.