Novel macropinocytosis inducers selectively modulate intracellular delivery of small and macromolecules in cancer cells

Macromolecule translocation across the plasma membrane remains a major challenge for therapeutic development. In this study, we evaluated whether macropinocytosis inducers (MPIs) increase therapeutic internalization in colorectal cancer cell (CRC) lines. We synthesized 15 novel MPI compounds (3-(((3-mercapto-5-(pyridin-4-yl)-4H-1,2,4-triazol-4-yl)imino)methyl)quinolin-2-ol (BAPT))), of which, two lead compounds, BAPT 78 (50 μM) and BAPT 54 (50 μM), significantly increased high-molecular-weight dextran and albumin uptake, in SW620 and HCT116 CRC cells by macropinocytosis, which was confirmed by the CF-488A green fluorescent probe. BAPT 78 vacuoles contained early endosomal markers and interacted with lysosomes, indicating acidic endosomes. In addition, BAPT 54 and BAPT 78 increased the uptake of anti-tubulin antibodies in SW620 and HCT116 cells. However, the plant toxin, saporin (10.9–350 nM), and small-interfering RNA (siRNA; 50 nM) delivery to SW620 cells was limited, perhaps due to low endolytic capacity of the MPI compounds. Combining BAPT 78 with the low-molecular-weight anticancer drugs, doxorubicin and paclitaxel, significantly enhanced their cytotoxicity in CRC (SW620, HCT116) and in the triple-negative breast cancer (TNBC) cell lines, SUM159 and SUM159-PAC200 (paclitaxel-resistant TNBC). Overall, this study provides proof-of-concept to deliver macromolecules and small molecule therapeutics intracellularly by activating macropinocytosis.