MALDI‐TOF mass spectrometric analysis for the characterization of the 5,10,15,20‐tetrakis‐ (m‐hydroxyphenyl)bacteriochlorin (m‐THPBC) photoproducts in biological environment

Abstract

Photoproducts formation upon irradiation (739 nm) of 5,10,15,20-tetrakis(m-hydroxyphenyl)bacteriochlorin (m-THPBC) in phosphate buffer saline (PBS) supplemented with human serum albumin (HSA) were studied by means of absorption spectroscopy and MALDI-TOF mass spectrometry. The experiments were performed with a freshly prepared PBS-HSA solution of m-THPBC and with a PBS-HSA m-THPBC solution incubated for 6 h at 37 degrees C. The incubation of m-THPBC solution leads to the dye monomerisation, whereas in the freshly prepared solution, m-THPBC is under an aggregated form. Regardless of the incubation condition, photobleaching experiments carried out by absorption spectroscopy demonstrate the degradation of the photosensitizer and its phototransformation in m-THPC. Moreover, m-THPC was the sole photoproduct detected using absorption spectroscopy. Together with a degradation of m-THPBC and formation of m-THPC, MALDI-TOF mass spectrometry evidenced several other photoinduced modifications. Photoproducts such as dihydroxy m-THPBC and dihydroxy m-THPC were detected in both conditions; however, the formation of hydroxylated photoproducts was significantly greater in incubated solution. In addition, small molecules arising from the degradation of the photosensitizer and identified as dipyrin derivatives and dipyrrolic synthon were observed.

Unusual Photoinduced Response of mTHPC Liposomal Formulation (Foslip)

“…3). This discrepancy between fluorescence and absorbance decays has been reported earlier for porphyrins and chlorins (14,31,32) and was attributed to the preferential photodegradation of photolabile monomer forms of photosensitizers. In our case, this explanation should be discarded as mTHPC embedded in liposomes exists only in monomeric form (Fig.…”

Temoporfin (Foscan®, 5,10,15,20‐Tetra(m‐hydroxyphenyl)chlorin)—A Second‐generation Photosensitizer†,‡

“…Recent results indicate the rate of photobleaching of m THPBC to be strongly dependent on the degree of aggregation of the PS (72). A combined use of HPLC and electrospray ionization tandem MS (ESI‐MS) identified m THPP and several hydroxylated derivatives of both m THPC and m THPP as initial photobleaching products (73).…”

“…This bacteriochlorin undergoes photobleaching at ca 20 times the rate of m THPC (490). It also suffers partial phototransformation to m THPC in buffer solution (491) and can form other photoproducts as well (72). Initial tests with a mouse colon cancer cell line indicated that m THPBC is prone to aggregation and oxidation in aqueous media (492).…”

Characterization of cationic glycoporphyrins by electrospray tandem mass spectrometry

“…Tandem mass spectrometry (MS/MS) has been used for the structural characterization of porphyrinic derivatives,11–15 and has already proved to be useful for the characterization of neutral glycoporphyrin derivatives 16. MS/MS can also be an excellent and valuable tool to assess structural modification or degradation of photosensitizers that can occur during the in vivo cellular metabolism 17. Nevertheless, the study of cationic porphyrins by MS was only carried out in the identification of the molecular ions, and, as far as we know, only one study reports the fragmentation under MS/MS of cationic porphyrinic complexes 18…”