Ethan Sternberg

Biodistribution of tritiated benzoporphyrin derivative (3H-BPD-MA), a new potent photosensitizer in normal and tumor-bearing mice

The biodistribution of a new and very potent photosensitizer, benzoporphyrin derivative-monoacid, ring A (BPD-MA), was determined in normal and P815 (mastocytoma) or M1 (rhabdomyosarcoma) tumor-bearing DBA/2J mice. A dose of 80 micrograms of 3H-BPD-MA was determined at 3, 24, 48, 72, 96 and 168 h post injection. The following tissues were tested: blood, brain, heart, intestine, kidney, lung, liver, muscle, skin, stomach, spleen, thymus and tumor. The biodistribution of 3H-BPD-MA in normal and tumor-bearing mice was comparable overall. 3H-BPD-MA localized in tumors better than in other tissues except kidney, liver and spleen. The tumor to tissue ratios were in the range 1.5-3 at 24 h post injection and increased further during the next 72 h. The highest levels of 3H-BPD-MA were observed in all tissues at 3 h post injection and decreased rapidly during the first 24 h. After 24 h the clearance from tissues was rather slow. The preliminary clearance data obtained in a group of five normal mice indicated that the majority of the injected dose (60%) cleared from the body via the bile and feces, while only about 4% cleared via kidneys and urine. Studies in which 3H-BPD-MA was extracted from tumor, kidney and liver 3 and 24 h after injection showed that, at 3 h, all the photosensitizing activity in tumor was retained. At 24 h only 39% of the activity was retained and considerably less active material was present in liver and kidney.

In vitro EVALUATION OF PHOTOTOXIC PROPERTIES OF FOUR STRUCTURALLY RELATED BENZOPORPHYRIN DERIVATIVES

Abstract— Four structural analogs of benzoporphyrin derivative (BPD) have been studied and compared for photosensitizing activity in vitro. All analogs have an identical reduced tetrapyrrol porphyrin ring, and differ by the position of a cyclohexadiene ring (fused at either ring A or ring B of the porphyrin) and the presence of either two acid groups or one acid and one ester group at rings C and D of the porphyrin. Photosensitizer activity was tested with the Ml tumor cell line using an assay (the MTT assay) which detects mitochondrial hydrogenases as a measure of cell viability. This assay was shown to be equivalent to the standard clonogenicity or [3H]thymidine uptake assay. Comparative studies with the BPD analogs showed that the monoacid derivatives had equivalent cytotoxicity and were about five‐fold more active than the diacid forms. This was the case whether the assays were performed in the presence or absence of fetal calf serum.

Inhibition of Autophagosome Formation by the Benzoporphyrin Derivative Verteporfin

Autophagy enables cells to degrade and recycle cytoplasmic materials both as a housekeeping mechanism and in response to extracellular stress such as nutrient deprivation. Recent studies indicate that autophagy also functions as a protective mechanism in response to several cancer therapy agents, making it a prospective therapeutic target. Few pharmacological inhibitors suitable for testing the therapeutic potential of autophagy inhibition in vivo are known. An automated microscopy assay was used to screen >3,500 drugs and pharmacological agents and identified one drug, verteporfin, as an inhibitor of autophagosome accumulation. Verteporfin is a benzoporphyrin derivative used in photodynamic therapy, but it inhibits autophagy without light activation. Verteporfin did not inhibit LC3/Atg8 processing or membrane recruitment in response to autophagic stimuli, but it inhibited drug- and starvation-induced autophagic degradation and the sequestration of cytoplasmic materials into autophagosomes. Transient exposure to verteporfin in starvation conditions reduced cell viability whereas cells in nutrient-rich medium were unaffected by drug treatment. Analysis of structural analogs indicated that the activity of verteporfin requires the presence of a substituted cyclohexadiene at ring A of the porphyrin core but that it can tolerate a number of large substituents at rings C and D. The existence of an autophagy inhibitor among FDA-approved drugs should facilitate the investigation of the therapeutic potential of autophagy inhibition in vivo.

Characterization Of Benzoporphyrin Derivative, A New Photosensitizer

Benzoporphyrin derivative (BPD), synthesized from protoporphyrin and involving the formation of Diels-Alder adducts, contains four components, mono and di-acid derivatives of either ring A or ring B fused porphyrins. These compounds have been isolated and tested individually as photosensitizers both in vitro and in vivo. All forms of BPD are potent photosensiters in vitro and have a strong absorption peak at about 690 nm. 3H-BPDs were tested for biodistribution in tumor bearing mice. Distribution appeared to be similar to distribution data published by others for dihematoporphyrin ethers, with the exception that levels in skin were lower for BPD. Extraction of 3H-BPD from tissue, followed by in vitro testing of extracts for photosensitizing activity, indicated that BPD is aTly degraded in vivo. When BPDs were compared to Photofrin II for causing skin photosensitivity following intravenous administration, it was found that monoacid derivatives caused photosensitivity at 3 hours but not after 24 hours. The diacid forms did not cause appreciable skin photosensitivity even at 3 hours. Photodynamic therapy of tumors in mice with BPD showed that these compounds had comparable efficacy to Photofrin II under the experimental conditions used here.

Photosensitizing efficiency of two regioisomers of the benzoporphyrin derivative monoacid ring A (BPD-MA)

Benzoporphyrin derivative, monoacid ring A (BPD-MA), currently in clinical trials as a photosensitizer for photodynamic therapy for cancer, consists of two regioisomers (A1 and A2) present in equal proportions. The contribution of the regioisomers to the overall photosensitizing potency of BPD-MA was tested in vitro and in vivo. The in vitro photosensitizing potencies of BPD-MA-A1 and -A2 were tested in a standard cytotoxicity assay using M1 (rhabdomyosarcoma of DBA/2 mice) tumor cells and were found to be equivalent. The in vivo photosensitizing efficacies of the regioisomers were tested in the M1 tumor model in DBA/2 mice and were also found to be equivalent. Biodistribution of the regioisomers in mouse plasma, tumor and liver was studied in M1 tumor-bearing DBA/2 mice at 15 min and 3 hr post intravenous injection of [14C]BPD-MA-A1/A2 at 4 mg/kg body weight. Plasma and extracts from tumor and liver were analysed by HPLC and tested for radioactivity. The two regioisomers were eliminated from plasma and liver at different rates, which resulted in A1:A2 ratios of 1:0.28 in plasma and 1:0.75 in liver at 3 hr post injection. The differential elimination was not observed to any significant degree in the tumor, where even at 3 hr post injection the A1:A2 ratio was 1:1.15. Therefore, we concluded that in tumor tissue, at 3 hr post injection, the time at which laser photodynamic therapy is carried out, both regioisomers were present in about equal proportions. Further, both regioisomers were fully active as determined by an in vitro cytotoxicity assay following extraction.

5,10-Diphenyltripyrrane, a useful building block for the synthesis of meso-phenyl substituted expanded macrocycles

Pyrrole and benzaldehyde were condensed under acidic conditions to produce a mixture of 5-phenyldipyrromethane and 5,10-diphenyltripyrrane; the tripyrrane was utilized in syntheses of meso-phenylsapphyrins, meso-diphenylpentaphyrin and meso-hexaphenylhexaphyrin.

Chiral separation of benzoporphyrin derivative mono-and di-acids by laser-induced fluorescence capillary electrophoresis

A method for the separation of benzoporphyrin derivative mono‐ and diacid (BPDMA, BPDDA) enantiomers by laser induced fluorescence‐capillary electrophoresis (LIF‐CE) has been developed. By using 300 mM borate buffer, pH 9.2, 25 mM sodium cholate and 10% acetronitrile as electrolyte, +10 kV electrokinetic sampling injection of 2 s and an applied +20 kV voltage across the ends of a 37 cm capillary (30 cm to the detector, 50 νm ID), all six BPD stereoisomers were baseline‐separated within 20 min. Formation constants, free electrophoretic and complexation mobilities with borate and cholate were determined based on dynamic complexation capillary electrophoresis theory. The BPD enantiomers can be quantitatively determined in the range of 10–2–10–5 mg mL–1. The correlation coefficients (r2) of the least‐squares linear regression analysis of the BPD enantiomers are in the range of 0.9914–0.9997. Their limits of detection are 2.18–3.5×10–3 mg mL–1. The relative standard deviations for the separation were 2.90–4.64% (n = 10). In comparison with high‐performance liquid chromatography (HPLC), CE has better resolution and efficiency. This separation method was successfully applied to the BPD enantiomers obtained from a matrix of bovine serum and from liposomally formulated material as well as from studies with rat, dog and human microsomes.

Cross-metathesis of the vinyl group on tetrapyrrolic macrocycles: reactivity, selectivity, and mechanism.

To find a general strategy for modifying the peripheral structure of vinylchlorin and porphyrin substrates, cross-metathesis on the vinyl group of these tetrapyrrolic macrocycles was investigated. The N-heterocyclic carbene-containing ruthenium complex 3 efficiently catalyzed the cross-metathesis (CM) of vinylchlorins and vinylporphyrins with a variety of olefins in high E-stereoselectivity. Different substituents on the olefin dramatically influenced the reaction. While the chlorins were more reactive than the porphyrins (as free bases), the corresponding zinc complexes showed higher activity. The reaction mechanism was investigated, and an empirical model for selective CM was applied to our studies to direct further reactions.

Cellular and Antitumor Activity of a New Diethylene Glycol Benzoporphyrin Derivative (Lemuteporfin)

Abstract A newly synthesized diethylene glycol functionalized chlorin-type photosensitizer, lemuteporfin, was characterized for use in photodynamic therapy (PDT) in a panel of in vitro and in vivo test systems. The photosensitizer was highly potent, killing cells at low nanomolar concentrations upon exposure to activating light. The cellular uptake of lemuteporfin was rapid, with maximum levels reached within 20 min. Mitogen-activated lymphoid cells accumulated more of the lemuteporfin than their quiescent equivalents, supporting selectivity. Photosensitizer fluorescence in the skin increased rapidly within the first few minutes following intravenous administration to mice, then decreased over the next 24 h. Skin photosensitivity reactions indicated rapid clearance of the photosensitizer. Intravenous doses as low as 1.4 μmol/kg combined with exposure to 50 J/cm2 red light suppressed tumor growth in a mouse model. In conclusion, this new benzoporphyrin was found to be an effective photosensitizer, showing rapid uptake and clearance both in vitro and in vivo. This rapid photosensitization of tumors could be useful in therapies requiring a potent, rapidly accumulating photosensitizer, while minimizing the potential for skin photosensitivity reactions to sunlight following treatment.

Nitrogen extrusion from pyrazoline-substituted porphyrins and chlorins using long wavelength visible light

Protoporphyrin reacts with diazomethane to give pyrazolines which at long wavelength (approximately 630 nm) extrude nitrogen to give the corresponding cyclopropyl derivatives.