Synthesis of new porphyrinoid conjugates and porphyrinoid nanoparticles for photodynamic therapy applications

Photodynamic therapy (PDT) has become a feasible modality for the treatment of numerous cancers using a combination of a photosensitizer, light (600-800nm range) and molecular oxygen. To date, PhotofrinRTM is the only porphyrin-based photosensitizer approved by the FDA for cancer therapy. However due to its poor selectivity, the development of novel porphyrin conjugates is a primary goal in research. Therefore cell recognition and/or selectivity by chromophores are key issues in PDT research. It has been shown that the chemical attachment of polyethylene glycol (PEG) and polyamines to peptides, proteins and other drugs have numerous advantages. Pegylation improves drug solubility, greatly increases its retention time in the circulation system (thereby reducing dosing frequency), improves stability and decreases immunogenicity. Whereas polyamine have been shown to target some cancer cells.; Therefore, in the search for new PDT candidates, the attachment of PEGs and/or polyamine derivatives to the porphyrin should increase the relative uptake and phototoxicity toward a given cancer cell line. Therefore, a series of protected PEG and amino acid porphyrin conjugates have been synthesized. Synthesis begins with 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin, due to the high reactivity of the fluoro group at the para position in nucleophilic substitution reactions. The synthesis and characterization of various porphyrin derivatives, and small solution phase combinatorial libraries of these macrocycles, are reported herein. Binding studies based both on fluorescence microscopy and photodynamic activities quantify the extent that these porphyrin conjugates are selectively taken up into cancer cells. A new method to select winning compounds from the solution phase porphyrin libraries based on mass spectrometric analysis of extracts of cells treated with the library is also reported. One major finding is that porphyrins bearing amphipathic motifs spontaneously form 5-50 nm nanoparticles in the cell culture media and that these are taken up into MDA-231 (a human breast cancer cell line). Strategies to induce disaggregation once inside the cell and the photodynamic activity of these systems indicate that upon disaggregation these porphyrins are highly active PDT agents. Reduction of a pyrrole double bond to yield the chlorin analogues, which have a strong absorption in the red region of the spectra where biofluids are more transparent, results in highly fluorescent molecules, but reduced triplet quantum yields.