Delivery of porphin to cancer cells by organometallic Rh(III) and Ir(III) metalla-cages

• Preparation and characterization of organometallic rhodium and iridium metalla-prisms.
• Delivery vectors to transport porphin to cancer cells.
• Quenching of the fluorescence of porphin upon encapsulation.
• After internalization and release of porphin, cancer cells were killed by photo-activation.

Two pentamethylcyclopentadienyl (Cp*) rhodium(III) and iridium(III) metalla-prisms of the general formula [(Cp*M)6(tpt)2(dhnq)3]6+ (tpt = 2,4,6-tri-(pyridin-4-yl)-1,3,5-triazine, dhnq = 5,8-dihydroxy-1,4-naphthoquinonato; M = Rh, [1]6+; M = Ir, [2]6+) have been synthesized by mixing in methanol the neutral dinuclear complexes (Cp*M)2(dhnq)Cl2 (M = Rh, Ir), AgCF3SO3 and tpt. In a similar fashion, the addition of porphin during the formation of [1]6+ and [2]6+ leads to the carceplex systems [porphin⊂1]6+ and [porphin⊂2]6+. All complexes were isolated as their triflate salts and characterized by different analytical techniques including for the carceplex [porphin⊂1][CF3SO3]6 by a single-crystal X-ray structure analysis. The hosts were evaluated as drug delivery vectors on the HT-29 cancer cell line, and after internalization, porphin was photo-activated to generate phototoxicity. Interestingly, the IC50 values of the empty and filled metalla-cages are around 1 μM, while upon irradiation (20 J/cm2) only lower nanomolar concentrations of the [porphin⊂cage][CF3SO3]6 systems are necessary to inhibit cell growth by 50%, showing an excellent ratio between cytotoxicity and phototoxicity.

Organometallic rhodium(III) and iridium(III) metalla-prisms have been used to transport porphin to cancer cells. After internalization, porphin was activated by light to produce reactive oxygen species and to kill cells, thus showing an excellent photo-activity.Figure optionsDownload as PowerPoint slide