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Purpose: To study the anatomy of the latero-lateral joint (LLJ) between the upper lateral (ULC) and lower lateral (LLC) crus of the nasal cartilages, usually described as a scroll articulation., Methodology: Six nasal pyramids were taken in monobloc from fresh cadavers and imaged on micro-MRI with 0.4 mm slice thickness. Images were jointly interpreted by two head and neck radiologists and one surgeon. The junction between the ULC and LLC, the presence of ligaments and of sesamoid or accessory cartilages were assessed., Results: Eight LLJs could be analyzed, with four types of junctions: hook-shaped cephalic border of the LLC turned towards the nasal fossa and linear caudal border of the ULC (n = 3), hook-shaped caudal border of the ULC and linear cephalic border of the LLC lateral crus (n = 1), hook-shaped border of both cartilaginous edges with clinging (n = 1) (scroll articulation) or without clinging (n = 3). No ligament or sesamoid cartilage was found, but posterior accessory cartilages were seen in 75% of the cases., Conclusion: The classical scroll articulation of the LLJ has been observed in only 1/8 cases on micro-MRI images. The anatomy of the LLJ could explain the surgical difficulty in raising the tip of the nose in some patients and not in others., (© 2022. The Author(s), under exclusive licence to Springer-Verlag France SAS, part of Springer Nature.)

Purpose: To determine which combination of imaging modalities/contrast, radiomics models, and how many features provides the best diagnostic performance for the differentiation between low- and high-grade soft tissue sarcomas (STS) using a radiomics approach., Methods: MRI and CT from 39 patients with a histologically confirmed STS were prospectively analyzed. Images were evaluated both quantitatively by radiomics models and qualitatively by visual evaluation (used as reference) for grading (low-grade vs high-grade). In radiomics analysis, 120 radiomic features were extracted and contributed into three models: least absolute shrinkage and selection operator with logistic regression(LASSO-LR), recursive feature elimination and cross-validation (RFECV-SVC) and analysis of variance with SVC (ANOVA-SVC). Those were applied to different combinations of imaging modalities acquisition, with and without contrast medium administration, as well as selected number of features., Results: Fat-saturated T2w (FS-T2w) MR images using RFECV-SVC radiomic models involving five features yielded the best results with mean sensitivity, specificity, and accuracy of 92% ± 10%, 78% ± 30%, and 89% ± 12%, respectively. The performance of radiomics was better than that of conventional analysis (67% accuracy) for STS grading. Combination of multiple contrast or imaging modalities did not increase the diagnostic performance., Conclusion: FS-T2w MR images alone with a five-feature radiomics analysis usingh REFCV-SVC model may be able to provide sufficient diagnositic performance compared to conventional visual evaluation with multiple MRI contrast and CT imaging., Competing Interests: Two authors of this manuscript (P.T. and A.B.) participated in a non-remunerated research agreement with Canon Medical Systems, manufacturer of the CT scanner used in this work. The other authors of this manuscript declare no relationships with any companies whose products or services may be related to the subject matter of the article., (© 2022 The Authors.)

Loss of elbow motion can lead to disability in everyday gestures, recreational activities, and work. Unfortunately, the elbow joint is particularly prone to stiffness because of its complex anatomy and biomechanics. The etiology of elbow stiffness is varied and must be diagnosed accurately in order to allow optimal treatment, which may be challenging for surgeons and physiotherapists. Its treatment can be either conservative, arthroscopic or surgical, with a trend for arthroscopic procedures when conservative treatment fails. There is no consensus on the optimal imaging workup for elbow joint stiffness, which may have an impact on patient management. This article reviews the current classification systems of elbow stiffness and the various imaging techniques used for diagnosis. Report checklists and clarifications on the role of each imaging method, as well as the imaging findings of normal and stiff elbows, are presented, leading to a proposed diagnostic algorithm. The main concern in imaging is to determine the cause of elbow stiffness, as many concomitant abnormalities might be present depending on the clinical scenario.

Objectives: To evaluate the added value of DWI, qualitative proton MR spectroscopy (H-MRS) and dynamic contrast-enhanced perfusion (DCE-P) to conventional MRI in differentiating benign and malignant non-fatty soft tissue tumors (NFSTT)., Methods: From November 2009 to August 2017, 288 patients with NFSTT that underwent conventional and advanced MRI were prospectively evaluated. The study was approved by the local ethics committee. All patients signed an informed consent. A musculoskeletal (R1) and a general (R2) radiologist classified all tumors as benign, malignant, or indeterminate according to morphologic MRI features. Then, DWI, H-MRS, and DCE-P data of indeterminate tumors were analyzed by two additional radiologists (R3 and R4). Advanced techniques were considered individually and in combination for tumor benign-malignant differentiation using histology as the gold standard., Results: There were 104 (36.1%) malignant and 184 (63.9%) benign tumors. Conventional MRI analysis classified 99 tumors for R1 and 135 for R2 as benign or malignant, an accuracy for the identification of malignancy of 87.9% for R1 and 83.7% for R2, respectively. There were 189 indeterminate tumors for R1. For these tumors, the combination of DWI and H-MRS yielded the best accuracy for malignancy identification (77.4%). DWI alone provided the best sensitivity (91.8%) while the combination of DCE-P, DWI, and H-MRS yielded the best specificity (100%). The reproducibility of the advanced imaging parameters was considered good to excellent (Kappa and ICC > 0.86). An advanced MRI evidence-based evaluation algorithm was proposed allowing to characterize 28.1 to 30.1% of indeterminate non-myxoid tumors., Conclusion: The prioritized use of advanced MRI techniques allowed to decrease by about 30% the number of non-myxoid NFSTT deemed indeterminate after conventional MRI analysis alone., Key Points: • When morphological characterization of non-fatty soft tissue tumors is possible, the diagnostic performance is high and there is no need for advanced imaging techniques. • Following morphologic analysis, advanced MRI techniques reduced by about 30% the number of non-myxoid indeterminate tumors. • DWI is the keystone of advanced imaging techniques yielding the best sensitivity (91.8%). Optimal specificity (> 90%) is obtained by a combination of advanced techniques.

A wide variety of pathologies can affect the hallux sesamoid complex of the foot, including traumatic, micro traumatic, degenerative, inflammatory, vascular, infectious, and neoplastic conditions. Symptoms are quite nonspecific, mainly related to pain in the plantar surface of the first metatarsal head. In this context, imaging is important for the etiologic diagnosis of hallux sesamoid complex pathology with implications in patient management. The hallux sesamoid complex has a complex anatomy, and pathologic processes of this region are poorly known of radiologists. Besides, some entities such as "sesamoiditis" remain poorly defined in the literature. Schematically, conditions affecting sesamoids will be divided into two major groups: intrinsic anomalies (sesamoid bone being the center of the pathologic process) and extrinsic anomalies (diseases secondarily involving sesamoid bones). Thus, in this article, after a review of anatomical key points and pathologies affecting the hallux sesamoid complex, a practical multimodality approach for the diagnosis of hallux sesamoid pathologies will be proposed.

Three-dimensional (3D) imaging and post processing are common tasks used daily in many disciplines. The purpose of this article is to review the new postprocessing tools available. Although 3D imaging can be applied to all anatomical regions and used with all imaging techniques, its most varied and relevant applications are found with computed tomography (CT) data in musculoskeletal imaging. These new applications include global illumination rendering (GIR), unfolded rib reformations, subtracted CT angiography for bone analysis, dynamic studies, temporal subtraction and image fusion. In all of these tasks, registration and segmentation are two basic processes that affect the quality of the results. GIR simulates the complete interaction of photons with the scanned object, providing photorealistic volume rendering. Reformations to unfold the rib cage allow more accurate and faster diagnosis of rib lesions. Dynamic CT can be applied to cinematic joint evaluations a well as to perfusion and angiographic studies. Finally, more traditional techniques, such as minimum intensity projection, might find new applications for bone evaluation with the advent of ultra-high-resolution CT scanners. These tools can be used synergistically to provide morphologic, topographic and functional information and increase the versatility of CT., (Copyright © 2020 Société française de radiologie. Published by Elsevier Masson SAS. All rights reserved.)

Rationale and Objectives: This study aimed to determine the value of dual-energy thoracic radiography in the diagnosis of pneumothorax considering the reader's experience., Materials and Methods: Forty patients with a suspected pneumothorax, imaged with dual-energy chest radiographs, were divided into two groups: those with pneumothorax as the final diagnosis (n = 19) and those without (n = 21). The images were analyzed by 36 readers (5 interns, 16 residents, 15 senior physicians) for the presence or absence of pneumothorax during three readout sessions at 2-week intervals: standard images alone (session 1), dual-energy images with bone subtraction alone (session 2), and a combination of the two (session 3)., Results: The number of correct responses increased 13.3% between sessions 1 and 2 (P < .001) and 9.4% between sessions 1 and 3 (P < .001). The mean sensitivity for pneumothorax detection was higher in sessions 2 (82%) and 3 (79%) compared to session 1 (70%). There was no statistically significant difference in specificity between the sessions. The number of correct responses for small volume pneumothoraces was higher in sessions 2 (10.6 ± 1.8) and 3 (10.1 ± 2.0) than in session 1 (8.9 ± 2.3), with a statistically significant difference between sessions 1 and 2 (P = .002) and between sessions 1 and 3 (P = .048)., Conclusion: Bone subtracted dual-energy thoracic radiographs improve the detection sensitivity of pneumothorax, including in cases of small pneumothoraces, regardless of the reader's level or expertise., (Copyright © 2018 The Association of University Radiologists. Published by Elsevier Inc. All rights reserved.)

A simple mathematical model of the dynamics of malaria invasion is proposed. The model is based on the hypothesis that replication slippage (slipped strand mispairing occurring in replicating DNAs), likely to take place within regular, low-complexity, regions of the plasmodium genome, is a significant mechanism of the ability for the parasite to escape the host immune defence. The model reconciles the conclusions of other formal approaches like periodic bursts of parasitaemia and, in particular, it predicts that antibody cross-reactivity affects the level and the time profile of malaria recrudescence. It also suggests that an efficient strategy for the parasite to escape host humoral immune defences is to express a single antigen. Linking local complexity to antigenic variability tentatively allows prediction of new potentially immunogenic sequences in the plasmodium genome.

The protection effect of verbascoside (Ver) against Fenton reaction on plasmid pBR322 DNA was studied using agarose gel electrophoresis and UV-visible spectroscopy. The pBR322 plasmid DNA is damaged by hydroxyl radical (OH*) generated from the Fenton reaction with H2O2 and Fe(II) or Fe(III). This DNA damage is characterized by the diminution of supercoiled DNA forms or by the increase of relaxed or linear DNA forms after oxidative attack. The UV spectrum study showed that verbascoside can form complexes with Fe(II) or Fe(III), and the complexation can be reversed by the addition of EDTA. The formation constants of verbascoside-Fe complexes were estimated as 10(21.03) and 10(31.94) M(-2) for Fe(II) and Fe(III) respectively. The inhibition of Fenton reaction by verbascoside could be partially explained by the sequestration of Fe ions.

A correlation function that compares each base in a DNA sequence to its various neighbours and which is subsequently processed by Fourier and wavelet transforms has been developed. The procedure has been applied to sequences from the human chromosome 22, to nef genes from various HIV clones and to myosin heavy chain DNA. It permits to readily visualize regular features in DNA which are related to the stability of heteroduplexes formed upon strand slippage., (Copyright 2000 Academic Press.)

The solution structures of d(GAAAACGTTTTC)2 and of its methylated derivative d(GAAAAMe5CGTTTTC)2 have been determined by NMR and molecular modelling in order to examine the impact of cytosine methylation on the central CpG conformation. Detailed 1H NMR and 31P NMR investigation of the two oligomers includes quantitative NOESY, 2D homonuclear Hartmann-Hahn spectroscopy, double-quantum-filtered COSY and heteronuclear 1H-31P correlation. Back-calculations of NOESY spectra and simulations of double-quantum-filtered COSY patterns were performed to gain accurate information on interproton distances and sugar phase angles. Molecular models under experimental constraints were generated by energy minimization by means of the molecular mechanics program JUMNA. The MORASS software was used to iteratively refine the structures obtained. After methylation, the oligomer still has a B-DNA conformation. However, there are differences in the structural parameters and the thermal stability as compared to the unmethylated molecule. Careful structural analysis shows that after methylation CpG departs from the usual conformation observed in other ACGT tetramers with different surroundings. Subtle displacements of bases, sugars and backbone imposed by the steric interaction of the two methyl groups inside the major groove are accompanied by severe pinching of the minor groove at the C-G residues.

The determination of the solution structure of two self-complementary oligomers d(ATGACGTCAT)2 (CG10) and d(GAAAACGTTTTC)2 (CG12), both containing the 5'-pur-ACGT-pyr-3' sequence, is reported. The impact of the base context on the conformation of the central CpG site has been examined by a combined approach of: (a) 2D 1H-NMR and 31P-NMR; (b) molecular mechanics under experimental constraints; (c) back-calculations of NOESY spectra and iterative refinements of distances; and (d) 3D-homology search of the central tetrad ACGT within the complete oligonucleotides. A full NMR study of each fragment is achieved by means of standard 2D experiments: NOESY, 2D homonuclear Hartmann-Hahn spectroscopy, double-quantum-filtered COSY and heteronuclear 1H-31P correlation. Sugar phase angle, epsilon-zeta difference angle and NOE-derived distances are input as experimental constraints to generate molecular models by energy minimization with the help of jumna. The morass program is used to iteratively refine the structures obtained. The similarity of the two ACGTs within the whole oligonucleotides is investigated. Both the decamer and the dodecamer adopt a B-like DNA conformation. However, the helical parameters within this conformational type are significantly different in CG12 and CG10. The central CpG step conformation is not locked by its nearest environment (5'A and 3'T) as seen from the structural analysis of ACGT in the two molecules. In CG12, despite the presence of runs of A-T pairs, CpG presents a high twist of 43 degrees and a sugar phase at the guanine of about 180 degrees, previously observed in other ACGT-containing-oligomers. Conversely, ACGT in CG10 exhibits strong inclinations, positive rolls, a flat profile of sugar phase, twist and glycosidic angles, as a result of the nucleotide sequence extending beyond the tetrad. The structural specificity of CG10 and its flexibility (as reflected by its energy) are tentatively related to the process of recognition of the cyclic AMP response element by its cognate protein.

When tested on HeLa cells, bis-pyridinium oximes (BPO), a family of newly synthesized molecules whose charged pyridinium moieties are linked by a linear polymethylene chain of variable length (N = 3 to 12) have been shown to possess an inhibitory effect on cell growth and finally to provoke cell death. BPO-affected cells displayed reduced mitochondrial oxygen consumption and ATP stores and were blocked in the G1 phase of the cell cycle. Mitochondrial membrane potential, as assayed with the dye 3,3'-diexyloxacarbocyanine iodide [DiOC6(3)], increased in BPO-treated cells with time of exposure. Cell growth inhibition as well mitochondrial dysfunction were observed only with derivatives having a long polymethylene linking chain (N > or = 6). Furthermore, the concentration of the compound eliciting such effects was inversely related to the number of methylene groups in the linking chain. None of the BPO with N = 6 to 12 modified the mitochondrial DNA content, relative to the nuclear DNA content. In BPO (N = 8 and N = 12)-treated cells, chromatin fragmentation and internucleosomal DNA cleavage occurred massively, indicating that the death mode induced by these compounds is apoptosis. The possible pathway of action and the potential pharmacological interest of these compounds are discussed.

Bridged aldehyde substituted pyridinium dimers bind to DNA. Binding induces retardation of the electrophoretic migration of circular plasmid due to relaxation of supercoiling. Binding to DNA is slow and reversible and depends on the length of linking chain, pH, ionic strength and temperature. It is postulated that release of topological stress results from the disruption of hydrogen bonding between complementary bases, a hypothesis consistent with facilitated attack of DNA by formaldehyde promoted by the bridged compounds.

Bis-pyridium oximes and methoximes from a newly synthesized series are weak DNA binders (K = 3.10(4) M-1 under physiological conditions). From the number of binding sites per phosphate, 0.25, the ionic strength dependence of the binding constant and the negative electric dichroism, it is concluded that monointercalation is the mode of association. In contrast to methoxy compounds, the oxime derivatives are able both to induce the mutated "petite" phenotype in yeast S. cerevisiae and to cause "in vitro" extensive condensation of single stranded DNA. This reaction is postulated to be relevant to the mutational process that leads to "peptide" cells. The absence of nuclear mutation is interpreted in terms of sequestration of the drug in mitochondria under the effect of the organelle inner membrane electrochemical potential.

The 3,3'-[omega,omega'-alkanediylbis(oxy)]bis[2- (hydroxyimino)methyl]-1-methylpyridinium derivatives bearing a linking chain of 4, 5 and 6 methylene groups are accumulated in mitochondria with increasing efficiency under the effect of the electrical potential. Accumulation does not take place with derivatives carrying a 2 and 3 methylene-long linking chain. The uptake process is saturable. The efficiency of the various derivatives to induce the "petite" phenotype in yeast reflects the uptake rate observed with purified mitochondria.

Viscosimetric and kinetic results allow one to characterize three modes of DNA binding in the ellipticine series: (1) Ellipticine and its 9 methoxy derivative, which present maximal DNA lengthening properties and bind DNA through a single step mechanism, can be considered as pure intercalators. (2) Ellipticinium derivatives and short-chain substituted oxazolopyridocarbazoles, which present intermediate DNA lengthening properties, bind DNA through a two-step mechanism, one being intercalation. (3) Long-chain substituted oxazolopyridocarbazole derivatives, which display the smallest DNA lengthening properties, bind DNA through a single-step mechanism, probably resulting from an outside binding mode. The viscosimetric and kinetic results are compared with the thermodynamic results obtained from the temperature dependence of the binding constants. It appears that drugs binding on the outside of the DNA double helix tend to have large enthalpy and small entropy contributions, whereas pure intercalating drugs have contributions from both enthalpy and entropy, with entropy dominating by about 2:1. Drugs showing two binding modes exhibit a continuum between the aforementioned extremes, with no breaks in behavior. From this comparison, a correlation between thermodynamic data and DNA binding modes is proposed. Possible molecular implications of both enthalpy and entropy to DNA binding free energy are discussed.

Ditercalinium (a 7H-pyridocarbazole dimer) has been designed to bisintercalate into double-stranded DNA with high affinity. In this paper we provide evidence for inhibitory interactions of ditercalinium with electron transport in isolated rat liver mitochondria. It is shown that ditercalinium probably inhibits the electron transfer between membrane cytochrome c and oxygen (cytochrome c oxidase activity) and the electron transfer between the matrix side of inner membrane (Complexes II and III) and membrane cytochrome c. The level of inhibition of the last oxidation step of the respiratory chain appears to be highly dependent on the drug/membrane diphosphatidylglycerol ratio. It is suggested that the mechanism of cytochrome c oxidase inhibition by ditercalinium could be due to the complexation with the diphosphatidylglycerol environment essential for its activity rather than to a drug-enzyme direct interaction. This hypothesis is strengthened by experiments with pure cytochrome oxidase. Therefore, the interaction of ditercalinium with diphosphatidylglycerol may be envisaged as one factor, among others, responsible for its hepatotoxicity.

The unprotonated form of the anti-tumor alkaloid ellipticine binds to beta-lactoglobulins A and B from bovine milk with an affinity constant of 7 +/- 3 x 10(5) M-1. There is one binding site/dimeric protein molecule (the stable form at medium pH). The attachment site is not the beta-barrel nor the hydrophobic site identified as the retinol site in beta-lactoglobulin but a domain located at the interface of the two monomeric units where the ligand lies close to Trp61 of both polypeptide chains. The positive binding enthalpy observed in temperature-jump relaxation experiments is overcome by a strong entropy increase, tentatively thought to result from water release at the binding domain. Accordingly, desolvation is assumed to be the rate-determining step in the process of ellipticine binding.

The temperature-jump (T-jump) method has been used to investigate the binding mechanism to calf-thymus DNA of ellipticine and some of its derivatives. The results show that the plant alkaloid, ellipticine, interacts with DNA at a unique intercalation site whereas most of its synthetic derivatives, such as ellipticinium, 9-hydroxy-ellipticinium and related alkyl-oxazolopyridocarbazoles recognize two distinct DNA sites. Parallel analysis of kinetic data and DNA lengthening abilities of these derivatives suggests that only one of these two DNA sites is an intercalation site. Owing to the determination of the genuine number of drug-DNA complexes (inferred from T-jump experiments) and with the results of thermodynamic investigations (Van't Hoff plots), further characterization of the molecular interactions involved in the binding process was proposed. Thus, the formation of the unique intercalation complex of ellipticine was found to be entropy driven whereas binding of drugs which recognize the second class of binding sites was essentially enthalpy driven. These different thermodynamic behaviors suggest that intercalation essentially results from hydrophobic solvent structure effects in contrast to the second binding mode which principally arises from hydrogen bonding interactions through DNA grooves.

We have determined the acid-base properties of the alkaloid ellipticine, bound to DNA and to micelles and liposomes, taken as models for membranes, in the prospect of characterizing the actual structure of the bound ligand, this being relevant to the mode of action of the drug. The acid-base properties of ellipticine bound to sonicated calf thymus DNA and SDS micelles are similar as regards their pK values and their dependence on NaCl concentrations. This observation is satisfactorily understood in terms of sodium ion condensation around the negative phosphate and sulphate groups. The slope of pK vs log(Na+) is -1, a value predicted by Friedman theory. The pK of ellipticine bound to cationic (CTAB, DDTAB) or to neutral (Triton X100) micelles and to neutral liposomes (PC) is significantly lower than water (7.4), and, in contrast to the situation in DNA and SDS micelles, does not vary with addition of NaCl. Interestingly, this result is good evidence for ellipticine having a specific pK when bound to a hydrophobic structure. This view is likely to hold for ellipticine bound to DNA.

The acid-basic properties of ellipticine have been re-estimated. The apparent pK of protonation at 3 microM drug concentration is 7.4 +/- 0.1. The ellipticine free base (at pH 9, I = 25 mM) intercalates into calf-thymus DNA with an affinity constant of 3.3 +/- 0.2 X 10(5) M-1, and a number of binding sites per phosphate of 0.23. The ellipticinium cation (pH 5, I = 25 mM) binds also to DNA with a constant of 8.3 +/- 0.2 x 10(5) M-1 and at a number of binding sites (n = 0.19). It is postulated that the binding of the drug to DNA at pH 9 is driven by hydrophobic and/or dipolar effects. Even at pH 5, where ellipticine exists as a cation, it is thought that the hydrophobic interaction is the main contribution to binding. The neutral and cationic forms share common binding within DNA sites but yield to structurally different complexes. The free base has 0.04 additional specific binding sites per phosphate. As determined from temperature-jump experiments, the second-order rate constant of the binding of the free base (pH 9) is 3.4 x 10(7) M-1 s-1 and the residence time of the base within the DNA is 8 ms. The rate constant for the binding of the ellipticinium cation is 9.8 x 10(7) M-1 s-1 when it is assumed that drug attachment occurs via a pathway in which the formation of an intermediate ionic complex is not involved (competitive pathway).

The magnesium chelate of the N(3)H tautomer of orotate, L3Mg, is the true substrate in the biosynthesis of orotidine 5'-monophosphate (OMP) catalyzed by yeast orotate phosphoribosyltransferase (OPRTase, E.C. 2.4.210) with a Michaelis constant KmL3Mg equal to 12(2) muM. It is postulated that Mg++ cations activate the transport of orotate to the active site by neutralizing the orotate charges; the ligand N(3)H is then exchanged between the incoming cation and the cation bound to the enzyme, thus ensuring the stabilization of the appropriate isomeric structure of orotate. This scheme, together with kinetic and thermodynamic data on orotate complexation by Mg++ and Ca++, accounts for the role of Ca++ cations that neither activate nor inhibit OMP synthesis. Cu++ and Ni++ inhibiting properties arise from the formation of inert complexes of orotate. Ni++ complexes have a poor affinity for the protein, whereas Cu++ complexes have a Michaelis constant similar to that of the L3Mg active species. The inertness of these complexes is tentatively understood in terms of low phosphoribosyl transfer rates as postulated from the kinetic study of the protonation of the complexes in water.

Ditercalinium, a 7H-pyridocarbazole dimer designed to bisintercalate into DNA, forms tight ion pairs in water with inorganic and organic anions. The thermodynamics and kinetics of the acetate-ditercalinium pairing has been investigated by means of T-jump spectroscopy. The formation of the pair has a constant estimated to 1000 M-1 and proceeds via a fast two-step mechanism with a relaxation time of 12 microseconds (acetate pH 5) to 50 microseconds (cacodylate, pH 7.5) involving an intermediate solvent-separated ion pair. A strong association of ditercalinium to cardiolipid has been observed and is expected to be involved in the respiratory chain inhibition induced by ditercalinium (unpublished results). Direct estimates of the binding constants of the drug to calf thymus DNA were obtained by means of UV titrations at high drug/base ratio (greater than 0.17). The maximum number of binding sites per base both at pH 5 and pH 7.5 was found to be 0.22, a value consistent with monointercalation as expected from the prediction of Shafer's model for the interaction of bifunctional ligands to DNA. This work also supports the hypothesis that significant ionic binding may account for the ditercalinium/DNA interaction at high base/drug ratios (0.2).

Among the DNA-intercalating drugs in the ellipticinium series, 9-hydroxy derivatives elicit the highest antitumoral properties. In water these drugs display a very low fluorescence quantum yield. Replacement of H2O by D2O partially restores the fluorescence of the ellipticinium chromophore. The possibility that such a proton-exchange mechanism could be involved in a base-recognizing process at the DNA level (and therefore be responsible for some base preference) was examined by direct fluorescence titration in deuterated buffer and DNA/drug fluorescence energy transfer. These experimental approaches provide mutually consistent results showing that the 9-hydroxylated drug recognizes specific DNA sites that are not recognized by the non-hydroxylated drug. When compared to 2-N-methyl ellipticinium, the 2-N-methyl 9-hydroxyellipticinium presents: (1) higher binding constants for each DNA studied; (2) a base dependence of the fluorescence properties of the bound form (fluorescence increment upon DNA binding varying over 5-11); (3) a base dependence of its DNA affinity constants (1.1-3.3 x 10(6) M-1) and of its site size (exclusion parameters varying over 3.0-4.4); (4) a base dependence of its energy transfer from DNA bases. Analysis of the binding data suggests that the 9-hydroxyl group of 2-N-methyl ellipticinium is responsible for a G.C base-pair preference, the preferred binding site being a doublet sequence of two adjacent G.C which could be flanked either by a additional G.C base pair or by an A.T base pair.

Codon repeats encountered in DNA sequences may formally lead to several double-stranded structures of similar stabilities. This is observed in the highly repetitive sequences of some Plasmodium antigens (S-antigen, CS proteins). It is postulated that gene recombination may occur via various heteroduplex molecules thus leading to antigenic polymorphism of Plasmodium parasites.

The temperature-jump method has been used to compare the binding of 2-N methyl ellipticinium (NME) and 2-N methyl 9 hydroxy ellipticinium (NMHE) to three natural DNA's of different AT/GC composition. The relaxation signals, analyzed by the Padé-Laplace method, are characterized by two distinct relaxation times, tau 1 and tau 2, respectively in the 1-4 ms and 20-80 ms range. In the case of the NMHE/DNA interaction, the slower relaxation time tau 2 depends on the DNA composition, as follows: tau 2 (Micrococcus lysodeikticus) greater than tau 2 (Calf thymus) greater than tau 2 (Clostridium perfringens). Contrary to NMHE, NME which does not possess an OH group at the C-9 position, shows no relaxation time dependence upon DNA base composition. The observation of two relaxation times indicates that the binding equilibria are associated with at least two distinct drug/DNA complexes (probably arising from two distinct DNA binding sites). Three kinetic models, involving the formation of a weak intermediate ionic complex, are given to explain the binding reaction between these cationic drugs and the DNA. They allow the determination of the four rate constants associated with the two binding steps and lead to equilibrium association constants in agreement with those obtained from spectroscopic studies. The validity of the models is discussed and it is shown that the best kinetic scheme, for either NMHE or NME, could be that in which the ionic step is not a prerequiste to intercalation. The kinetic results show that the residence time of 9 hydroxy ellipticinium is markedly increased in GC rich DNA's and this could be related to the higher in vitro and in vivo cytotoxic properties of 9 hydroxy substituted ellipticines.