Paul Adriaens

Magnetic resonance imaging-histomorphologic correlation studies on paramagnetic metalloporphyrins in rat models of necrosis

RATIONALE AND OBJECTIVES The authors intended to confirm previous findings that paramagnetic porphyrins are avid only for intratumoral nonviable tissues, but not for viable tumor cells, and to test the hypothesis that necrosis, regardless of location and origin, can be visualized by metalloporphyrin enhanced magnetic resonance imaging (MRI). METHODS Intravenous administrations of gadolinium mesoporphyrin (Gd-MP), manganese tetraphenylporphyrin (Mn-TPP), manganese methylpyrroporphyrin-gadopentetate dimeglumine complex (Mn-MPP-Gd) and manganese tetra(4-sulfonatophenyl)porphyrin (MnTPPS4) at 0.05 mmol/kg were compared with those of gadopentetate dimeglumine (Gd-DTPA) at 0.1 mmol/kg in 38 rats with cholestatic liver necrosis, alcohol- and laser-induced coagulation necrosis in liver, and skeletal muscle, reperfused hepatic infarction, and segmental renal infarction. T1-weighted spin echo MRI (TR/TE = 300/15 mseconds) was acquired before and as long as 48 hours after injection, matched with histologic findings, and correlated with Gd/ Mn tissue content measurements. RESULTS Both Gd-DTPA and the four metalloporphyrins initially caused a similar nonspecific negative contrast enhancement in the necrosis. However, a strong and persisting positive enhancement (necrosis-to-normal contrast ratio ranging from 1.5 to 2.0) developed only with metalloporphyrins in all types of necrosis. In liver and kidney, Gd and Mn concentrations at 24 hours were comparable in necrotic and normal tissues. In muscle, the concentrations were more than eight times higher in necrotic than in normal tissue. CONCLUSIONS The implied affinity of metalloporphyrins for necrosis with presumably increased relaxivity suggests a possible mode of targetability for MRI contrast media that may elicit novel applications.

Photophysical behaviour of new pyrrolocoumarin derivatives

Abstract— The photophysical behaviour of new pyrrolocoumarins with different substituents on the nitrogen are reported. The photophysical properties of these pyrrolocoumarins are generally in agreement with those of the psoralens: a strong absorption (240–400 nm), a weak fluorescence (400–680 nm) characterized by a short singlet lifetime, and a rather strong phosphorescence at 77 K (480–600 nm). The absorption and fluorescence properties were investigated in several solvents. The shift of the fluorescence maximum is interpreted on the basis of the solvatochromic parameters π*, α and β. The triplet‐triplet absorption spectra also depend on the nature of the solvent, while the triplet excited state has a lifetime of a few microseconds at room temperature (concentration 2.5 × 10−4M). Some absorption and fluorescence characteristics of the 4′,5′‐dihydropyrrolocoumarins, which are suitable models for the 4′,5′‐monoadducts to pyrrolocoumarins are reported.

Investigation of the labelling characteristics of 99mTc-mercaptoacetyltriglycine

S-Benzyl-, S-benzamidomethyl- and S-benzoylmercaptoacetyltriglycine were synthesized and compared in exchange labelling experiments for the preparation of 99mTc-MAG3. The rate of exchange from 99mTc-tartrate to 99mTc-MAG3 starting from the respective precursors was determined in different conditions. Labelling proceeded most rapidly starting from the S-benzoyl protected precursor but efficient labelling was also accomplished using the more stable S-benzamidomethyl- and S-benzylmercaptoacetyltriglycine. 99mTc-MAG3 was also prepared by direct labelling of unprotected mercaptoacetyltriglycine at alkaline pH. Radiochemical purity in these conditions is mainly dependent on the pH during labelling.

Presence of delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine in fermentations of Penicillium chrysogenum.

Cultures of Penicillium chrysogenum, growth with [35S]sulfate or labeled amino acids, were examined by ion-exchange chromatography for possible peptidic precursors of penicillin. A sulfur-containing compound, present in both the mycelial extracts and the culture filtrates, was eluted at the location of the synthetic lld-tripeptide δ-(l-α-aminoadipyl)-l-cysteinyl-d-valine. Since this compound was also labeled when the cultures were incubated with dl-[6-14C]α-aminoadipic acid, l-[3,3′-3H]cystine, or dl-[1-14C]valine, its identity with the synthetic lld-tripeptide can be accepted. No δ-(l-α-aminoadipyl)-l-cysteine or lll-tripeptide were detected. The implications of these findings for tripeptide and penicillin biosynthesis are discussed.

Effect of Clavulanic Acid on the Minimum Inhibitory Concentration of Benzylpenicillin, Ampicillin, Carbenicillin, or Cephalothin Against Clinical Isolates Resistant to Beta-Lactam Antibiotics

The effect of clavulanic acid on the minimum inhibitory concentration of benzylpenicillin, ampicillin, carbenicillin, or cephalothin against 353 clinical isolates of penicillin- and/or cephalothin-resistant strains was estimated.

Exploring Multifunctional Features of Necrosis Avid Contrast Agents

As demonstrated during previous CMR meetings, some porphyrin (e.g. Gadophrin-2) and non-porphyrin (e.g. CEIII-60) paramagnetic chelates are able to specifically accumulate in nonviable tissues and can be applied for contrast-enhanced MRI of acute myocardial infarction and therapeutic necrosis (1–3). These molecules have therefore been defined as necrosis-avid contrast agents or NACAs under the category of a unique pathological targetability (3,4). The potential role of NACAs in imaging diagnosis has been recognized after multi-institutional reproducibility studies (5–21). Since NACAs also bear other common properties including early systemic distribution, albumin binding, hepatocellular uptake and renal elimination, we hypothesized that besides necrosis specificity, these agents can also be exploited for multipurpose applications. The present experiments have been conducted to evaluate the potentials of NACAs as “all-in-one” T1-relaxivity enhancers in comparison with other existing nonspecific and specific agents such as extracellular agent Gd-DTPA, hepatobiliary agent Mn-DPDP and albumin-binding blood pool agent MP-2269. MATERIALS AND METHODS

Comparison of the labelling characteristics of mercaptoacetyltriglycine (MAG3) with different S-protective groups

A number of different thiol protective groups have been synthesized and attached to mercaptoacetyltriglycine (MAG3) ligand. The newly made MAG3 analogues were labelled with 99mTc by direct labelling under alkaline condition and by stannous tartrate exchange labelling method. In the latter method, the amount of the ligand, reaction temperature and pH varied and their effects on the labelling efficiencies were studied. Radiochemical purities of 51% to 70%, 58% to 75% and 46% to 81% respectively, were obtained by radio-HPLC analysis for the studied MAG3 precursors when, 0.1 mg, 0.4 mg and 1.6 mg of the ligand was used and labelling was performed at both low temperature (70°C) and pH (pH 3). All the studied ligands were efficiently labelled with 99mTc (up to 99%) when heated for 10 min at pH 9 and 100°C. The labelling efficiency obtained by the direct labelling method for MAG3 analogues varied from 32% to 94% and was in all cases lower than after the exchange labelling at pH 9 and 100°C. It was observed that the radiochemical purities can be improved significantly by heating the “direct labelling mixture” at elevated temperature.

Incorporation of double-labeled L-cystine and DL-valine in penicillin.

l-[3,3′-3H]cystine was incorporated into penicillin with retention of one tritium. This result can be explained by β-lactam formation through ring closure between C3 of cysteine and NH of valine. No radioactivity of dl-[2,3-3H]valine was incorporated into penicillin. The loss of isotope at C2 occurs during the inversion of configuration. The loss of label at C3 is discussed in terms of possible intermediates for the formation of the thiazolidine ring of penicillin.

Separationof degradation products of double-labeled benzylpenicillin on a cation-exchange column

By using a cation-exchange resin and eluting with a lithium citrate buffer gradient, good separations were obtained for several degradation products of double-labeled benzylpenicillin.

Standardizing 8-methoxypsoralen plasma profiles by using an emulsion form

Uniform 8-methoxypsoralen (8-MOP) absorption from the gastrointestinal tract is necessary to avoid day-to-day variations in 8-MOP plasma levels when treating patients with psoriasis by photochemotherapy. Because of its low water solubility, particle size and crystal form of the 8-MOP can significantly influence its bioavailability. The presentation form is also important, as is shown by the present study in which 8-MOP plasma levels were compared in thirty patients after oral administration in three different forms: formulation A consisted of gelatin capsules containing 8-MOP with a mean particle size of 200 mu; formulation B consisted of gelatin capsules containing 8-MOP in microcrystalline form with particle size between 20 mu and 30 mu; formulation C contained the same microcrystalline 8-MOP but in an emulsion base. Significantly higher plasma levels were found with formulations B and C than with formulation A. Furthermore, the individual differences in plasma profiles were markedly less with the emulsion base than with the capsule forms. Therefore, the clinical use of 8-MOP in emulsion form would constitute a major step in 8-MOP dose standardization and could lead to better control of subjective side effects and better therapeutic results.