Oligo- and polypeptide conjugates of cationic porphyrins: binding, cellular uptake, and cellular localization

Recently, we have characterized the DNA and nucleoprotein (NP) binding of bis(4-N-methylpyridyl)-15,20-di(4-carboxyphenyl)porphyrin (BMPCP) and meso-tri(4-N-methylpyridyl)-mono(4-carboxyphenyl)porphyrin (TMPCP) and their tetrapeptide conjugates (BMPCP-4P₂ and TMPCP-4P, respectively). In this work, we investigated the interaction of TMPCP conjugated to the tetrapeptide branches of branched chain polymeric polypeptide with poly-L-lysine backbone (AK) with DNA or NP using spectroscopic methods. Analysis of absorption spectra revealed the external binding but no intercalation of TMPCP-AK to DNA. There was no evidence for the interaction between TMPCP-AK and encapsidated DNA. Furthermore, we examined the cellular uptake of BMPCP and TMPCP and their tetra- or polypeptide conjugates by flow cytometry and analyzed how charge, size, and structure of the compounds affect their incorporation. In comparison, liposomal association constants of these derivatives were determined. BMPCP-4P₂ accumulated the most, and porphyrins with two positive charges (BMPCP and BMPCP-4P₂) showed better accumulation than the tri-cationic TMPCP or TMPCP-4P. Cellular uptake of polycationic TMPCP-AK was significantly lower than that of the free or tetrapeptide conjugated derivatives. The subcellular localization of all the five compounds was investigated in co-localization studies by confocal microscopy with special attention to their nuclear localization. Neither free nor conjugated BMPCP or TMPCP was co-localized with nuclear marker. Instead, these derivatives showed co-localization with lysosomal and mitochondrial fluorescent probes. TMPCP-AK conjugate had different localization patterns appearing mainly in mitochondria and cytoplasmic vesicles. Our results may contribute to the further design of DNA-targeting porphyrin-based constructs.