Enzyme Responsive Rigid-Rod Aromatics Target “Undruggable” Phosphatases to Kill Cancer Cells in Mimetic Bone Microenvironment

Bone metastasis remains a challenge in cancer treatment. Here we show that enzymatic responsive rigid-rod aromatics, acting as the substrates of “undruggable” phosphatases, to kill cancer cells in mimetic bone microenvironment. By phosphorylating the hydroxyl and conjugating nitrobenzoxadiazole (NBD) to the carboxylate of hydroxybiphenylcarboxylate (BP), we obtained pBP-NBD (<b>1P</b>) as a substrate of both acid and alkaline phosphatases. <b>1P</b> effectively kill both metastatic castration-resistant prostate cancer cells (mCRPCs) (e.g., VCaP or PC3) and osteoblast mimic cells (Saos2) in their co-culture. Fluorescent imaging reveals that <b>1P</b> enter Saos2 almost instantly to target the endoplasmic reticulum (ER) of the cells and that co-culturing with Saos2 cells boosts the cellular uptake of <b>1P</b> by mCRPCs. Using cryo-EM, we determined the nanotube structures of both enzyme substrate <b>1P</b> (2.4 Å resolution, pH 5.6) and enzymatic processed compound <b>1</b> (2.2 Å resolution, pH 7.4). The helical packing of both nanotubes is identical, held together by strong pi-stackings interactions. Besides reporting the atomistic structure of nanotubes formed by the assembly of rigid-rod aromatics, this work expands the pool of molecules for designing EISA substrates that selectively target TME.