Similar to RA, both 4-HPR and its active metabolite N-(4-methoxyphenyl)retinamide (4-MPR) effectively impeded the growth of MCF7 and T-47D human breast cancer cell lines, except that 4-HPR also inhibited the proliferation of RA-resistant BT-20 cells.
Among nine EPBCCs consistently grown in vitro, three were resistant to the above retinoids, five were susceptible to atRA, four to 4-HPR and two to 9cRA, suggesting that patients with breast carcinomas may differentially respond to various retinoids.
A dose of 4-HPR that alone is ineffective in killing TRAIL-resistant MCF-7 cells, synergized with recombinant TRAIL to induce breast cancer cell death.