Cancer cells have reduced capacity for gap junctional inter-cellular communication (GJIC). One feasible approach to reduce growth of cancer cells is to enhance GJIC. This report shows that a second-generation substituted quinoline, PQ7, has anti-tumor effect. Scrape load/dye transfer and colony growth assays were performed to measure GJIC and tumor formation of T47D breast cancer cells. PQ7 at 500 nM induced a 16-fold increase in the GJIC in T47D cells. In addition to an increase in GJIC, a 50% decrease of colony growth was observed with 100 nM of PQ7. PQ7-treated nu/nu mice showed a 100% regression of xenograft tumor growth of T47D cells. The results show that PQ7 has a promising role in exerting anti-tumor activity in human breast cancer cells.