Joerg G. Moser

Dimeric Cyclodextrin Carriers with High Binding Affinity to Porphyrinoid Photosensitizers

The aim of our investigation was to develop carrier systems for an application of inert drugs in photodynamic cancer therapy. β-Cyclodextrin dimers linked at their primary and secondary faces by spacers of varying lengths were synthesized as carrier systems. The binding constants of the inclusion complexes of these cyclodextrin dimers and porphyrinoid photosensitizers were determined by competitive spectrofluorometry. Particularly the secondary face linked dimers exhibited extremely high binding constants with values of 106-107 L/mol. Theoretical studies were carried out on these inclusion complexes to confirm the influence of spacer length and connecting side on complex stability.

Photodynamic cancer therapy: fluorescence localization and light absorption spectra of chlorophyll-derived photosensitizers inside cancer cells

The first prerequisite for an optimum effect of photodynamic therapy with chlorophyll-derived photosensitizers is irradiation at the S1 absorption maximum in the red spectral region. This absorption maximum changes its position due to molecular association by 20 to 100 nm depending on the subcellular environment, and must be determined by direct absorption spectrometry in the region of subcellular sensitizer localization. Fluorescence-intensifying video microscopy allows for localization of the sensitizer storage site at or near the Golgi apparatus of OAT 75 small-cell lung carcinoma cells. The absorption maximum at 760 nm taken from spectra of single cells and cell layers determines the postulated optimum condition for dye laser irradiation with bacteriopheophorbide a methyl ester as the sensitizer.

Porphyrins and phthalocyanines as model compounds for detoxification of tumor chemotherapeutic drugs

The fluorescence behavior of porphyrins and phthalocyanines allows one to discriminate between monomeric and associated states of the dyes. These criteria are necessary prerequisites to decide about the inclusion behaviour of the dyes in oligomeric cyclodextrins. Masking the hydrophobic portion of the dyes by cyclodextrins allows one to transport these substances as inert through the body of an animal. The story is depicted here of how to proceed from functionalized porphyrinoids to tumor therapeutic drugs.

Synthesis of β-cyclodextrin dimers as carrier systems for photodynamic therapy of cancer

The aim of our investigation was the development of carrier systems for an application of inert drugs in polyphasic photodynamic tumor therapy. As carrier systems, β-cyclodextrin dimers linked at their primary and secondary faces by spacers of varying lengths were synthesized. Cyclodextrins are known to form stable inclusion complexes with porphyrinoid photosensitizers. The influence of spacer length on the β-cyclodextrin dimer inclusion complexes with porphyrinoid photosensitizers was studied.

Taxol Inclusion Complexes with a Cyclodextrin Dimer: Possibilities to Detoxify Chemotherapeutics and to Target Drugs Specifically to Tumors?

The natural drug, paclitaxel (taxol), is highly effectiveas a tumor chemotherapeuticwith a low probability of inducing chemoresistance,but shows severe toxic side effectsat the therapeutic dose. How can this toxicitybe overcome? Here we report the synthesisof cyclodextrin dimers connected at thesecondary face by amide-bonded aliphatic spacers.The spacer length of one of the dimers referred to asdiβCD(2N-A4C5A4) or dimer 7cmatches the distance between the twobenzoic acid residues of paclitaxel. We investigated the physical inclusion of taxol into this dimer using the TNS-label competition method. Affinity constants with the dimer in comparison to free β-cyclodextrin are found to be of the order of 107 l/mole.When included into the cyclodextrin dimer, the drug shows a considerable time delay of incorporation into human tumor cell cultures (OAT SCLC cells) or a total exclusion from the cells. This is the prerequisite to avoid intoxication of other organs of a patient. Possibilities are discussed to detoxify chemotherapeutics and to target their inclusioncomplexes specifically to tumors using specific biological signals.

Carrier systems in PDT II: accumulation strategies of biotin-avidin coupled photosensitizers developed on cultured tumor cells

Two possibilities to accumulate photosensitizing drugs at the surface of cultured tumor cells were exploited: biotinylation of the cell surface followed by avidin and dibiotin, and reaction with a biotinylated antibody followed by avidin and biotinylated sulfophthalocyanin. Both reactions were performed successfully. The latter leads to enhanced phototoxicity of the accumulated drug.

How many molecules of a photosensitizer are necessary to photosensitize a tumor cell

Diglycosylated porphyrinoids were shown to stack at the outer cell membrane of tumor cells in vitro. Similar phototoxicities are acquired as with the non-glycosylated drugs at amounts of only 1% of that normally taken up of the non-glycosylated drugs. This means that a strict positioning of sensitizers at sensitive compartments may reduce the amount of sensitizer necessary to sensitize a tumor cell to about 106 molecules per cell. Similar numbers were seen only in erythrocytes and with immunoconjugates in ovarian cancer. This low amount facilitates photosensitizer transport against intratumoral pressure gradients.

Peripheral substitution of pheophorbides and bacteriopheophorbides to promote inclusion into inert carrier systems for PDT

Pheophorbide a ethyl ester, pyropheophorbide a ethyl ester, and bacteriopheophorbide ethyl ester were substituted in 31-position with tert.butyl phenoxy or tert.butyl benzoic acid ester groups resp. in order to enhance affinity to (beta) -cyclodextrin dimers which form inclusion complexes with these photosensitizing drugs. This is a first step to construct inert transport complexes in order to photosensitize specifically cancer cells.

Carrier systems in PDT: on the way to novel antitumor drugs

A novel mode to apply photosensitizing drugs specifically to tumor tissue using the principles of polyphasic tumor therapies is outlined. Key compounds are tumor specific functionalized antibodies with reduced immunogenicity. These bind to drug inclusion complexes in a multiplicative manner. Drug inclusion complexes are designed on the basis of tethered functionalized (beta) -cyclodextrin dimers with maximum affinity to porphyrinoid photosensitizers forming monomeric chlathrates. To enhance porphyrin-cyclodextrin interaction peripheral groups of the porphyrin have to be chemically modified. The development of the method is not yet completed. First results are demonstrated.

Pharmakokinetics of 132-hydroxy-bacteriopheophorbide: a methyl ester studied by fluorescence spectroscopy on Lewis lung carcinoma bearing mice

The pharmacokinetics of 132-hydroxy-bacteriopheophorbide a methyl ester (OH-BPME) was studied on Lewis lung carcinoma bearing mice by fluorescence spectroscopy. The sensitizer distribution in different organs and in the tumor was investigated in dependence on the incubation time. A very fast cleaning of the blood and the skin was observed. The results of our investigations suggest that PDT using OH-BPME could be effective at sensitizer incubation times of about 12 h.