Highly selective mitochondria-targeting amphiphilic silicon(IV) phthalocyanines with axially ligated rhodamine B for photodynamic therapy.

Two axially ligated rhodamine-Si(IV)-phthalocyanine (Rh-SiPc) conjugates, bearing one and two rhodamine B, were synthesized and their linear and two-photon photophysical, subcellular localization and photocytotoxic properties were studied. These Rh-SiPc conjugates exhibited an almost exclusive mitochondrial localizing property in human nasopharyngeal carcinoma (HK-1) cells and human cervical carcinoma (HeLa) cells. Strong photocytotoxic but low dark cytotoxic properties were also observed for the two Rh-SiPc conjugates toward the HK-1 cells. Using nuclei staining method and flow cytometric DNA content analysis, apoptotic cell death was induced by these conjugates upon photoactivation. This observation is consistent with their mitochondrial localization property. The observed properties of these conjugates qualify them as promising PDT agents.