Development of Tat-fused drug binding protein to improve anti-cancer effect of mammalian target of rapamycin inhibitors

The mammalian target of rapamycin (mTOR) is known to regulate cell growth, protein stability and cell-cycle progression, and many human tumors result from the dysregulation of mTOR signaling. Although various mTOR inhibitors have been developed, effective delivery systems are still needed to enhance the anti-cancer effects of mTOR inhibitors. In this study, we developed the Tat-fused mTOR inhibitor binding domain (Tat-MBD/TMBD) for the enhancement of the anti-cancer effect of mTOR inhibitors, due to the improvement of intracellular uptake. A TMBD/mTOR inhibitors complex spontaneously formed by biological affinity between MBD and mTOR inhibitors without chemical conjugation and modification. We constructed that a recombinant fusion protein expression vector composed of Tat (protein transduction domain) and mTOR inhibitor-binding domain (Tat-MBD) to deliver the mTOR inhibitors. The MBD spontaneously bound with mTOR inhibitors including sirolimus, everolimus, and temsirolimus, resulting in the formation of a TMBD/mTOR inhibitors complex. The enhancement of the delivery efficacy of mTOR inhibitors into various breast cancer cells was confirmed and improved anti-cancer efficacy was observed. We demonstrated the effective delivery systems of mTOR inhibitors without chemical conjugation of mTOR inhibitors.