Ferenc Hollósy

Plant-derived protein tyrosine kinase inhibitors as anticancer agents.

Protein tyrosine kinases play a fundamental role in signal transduction pathways regulating a number of cellular functions such as cell growth, differentiation and cell death. Tyrosine kinases are, therefore attractive targets for the design of new therapeutic agents, not only against cancer, but also against many other diseases. Numerous tyrosine kinase inhibitors have been discovered by screening of plant extracts based on ethnopharmacological and chemotaxonomical knowledge. Specific screening approaches have led to the isolation of structurally distinct classes of inhibitors, including phenylpropanes, chalcones, flavonoids, coumarins, styrenes, quinones and terpenes. These natural inhibitors have served as valuable leads for further design and synthesis of more active analogues. Many of these inhibitors have also been used in probing the molecular and cellular mechanisms involved in the protein tyrosine kinase mediated signal transduction. In this review, plant-derived protein tyrosine kinase inhibitors and their synthetic analogues were systematically evaluated based on their plant origin, structure-activity relationship and anticancer efficacy.

New antitumor leads from a peptidomimetic library

A parallel combinatorial library of over 1600 compounds has been designed and synthesized for the development of new potential peptidomimetic protein tyrosine kinase (PTK) inhibitor leads. These peptidomimetic molecules are aimed at intervening with the substrate binding site of the pp60c−src enzyme. The new structures were based on kown PTK inhibtors with at least two variously substituted aromatic moieties attached by spacer groups of different length and flexibility. Eleven bis-aryl-type inhibitory compounds were found in the range of 18–100 μM IC50 concentrations from combinations of 12 different substituents. Molecular modeling of the active compounds showed a characteristic distance of 12–14 Å between the farthest sp2 carbon atoms of the two aromatic rings. Conformational analysis of several peptide substrates recently found for pp60c−src PTK showed that the energyminimized conformers had the same distance between the two aromatic moieties. Several compounds in the library not only showed remarkable PTK inhibitory activity but also a significant apoptosis-inducing effect on HT-29 human colon tumor cells.

EVALUATION OF HYDROPHOBICITY AND ANTITUMOR ACTIVITY OF A MOLECULE LIBRARY OF MANNICH KETONES OF CYCLOALKANONES

A series of Mannich ketones of cycloalkanones were synthesized to study the relative importance of structure and specific substitutions in relation to their hydrophobicity and antitumor activity. Substitutions were carried out with morpholinyl, pirrolidinyl, piperidyl, and tetrahydro-isoquinolyl groups in various position on four different base structures. Hydrophobicity of Mannich ketones was characterized by chromatography data (log k′) and by software calculated parameters (c log P). Cell proliferation inhibitory activity of cycloalkanones was evaluated by MTT and apoptosis assays on A431 human adenocarcinoma cells. Our results suggest that the higher the hydrophobicity values (log k′ and c log P) the higher the antitumor- and apoptotic activity of Mannich ketones. Determination of hydrophobicity by measuring the log k′ or by calculating the c log P values of the compounds may help to predict their biological activities.

A NOVEL NORMALIZED RETENTION FACTOR IN MICELLAR ELECTROKINETIC CHROMATOGRAPHY

Characteristic properties of the expression k″ = (tm—to)/(tmc—to) and its applicability in micellar electrokinetic capillary chromatography (MEKC) were compared to the previous expression, k′ = (tm—to)/to(1‐tm/tmc), introduced by Terabe. It was proved with theoretical calculations (curve shape analysis) that the properties of function k″ are in full accordance with the properties of the MEKC system and k″ could be applied advantageously to characterize hydrophobicity of the analytes. This conclusion is now supported by experimental data obtained with homolog series of alkylbenzenes and alkylphenones as well as with hydrophobic protected peptides. Migration times, k′, k″ values, and software‐calculated hydrophobicity data are summarized and analyzed in the present study. Since k″ is a normalized parameter, good relationships between the migration time, the software‐calculated hydrophobicity, and the k″ values were obtained. Differences in hydrophobicity of the analytes could be estimated in a more realistic way with the aid of function k″ than by using function k′. Hydrophobicity data estimated on the basis of the k″ values proved to be in good accordance with the expectations based on the migration times and on the chemical structures of the compounds investigated.

CALCULATION OF PHASE RESIDENCE TIMES IN MICELLAR ELECTROKINETIC CHROMATOGRAPHY

Method to calculate micellar phase residence time [tmic = tmc k‴, time spent by the analyte in the micellar phase] and aqueous phase residence time [taq, = t0 (1 − k‴), time spent by the analyte in the aqueous phase] was developed, where tm, to and tmc are the migration time of the analyte, the flow marker and the micelles, respectively. It was proved that migration time of the analyte is the sum of the phase residence times [tm = tmic + taq = t0 (1 − k‴) + k‴ tmc]. Two physico-chemical parameters characterizing hydrophobicity of the analyte, namely the ratio of the moles of the analyte in the micellar (nmc) and aqueous (naq) phase (nmc/naq = tmic/taq) as well as distribution coefficient (K) have also been determined from the phase residence times. Good correlation was found between the micellar phase residence times and computer calculated hydrophobicity values (S) in the case of hydroxy- and aldehyde benzene derivatives, benzene- and alkyl phenone homolog series and in the case of seven hydrophobic protected peptides. Comparison of hydrophobicity values and phase residence times showed that the higher the hydrophobicity of the analyte the longer the time spent in the micellar (hydrophobic) phase. The micellar phase residence time determinable experimentally in MEKC reflects the hydrophobicity of the molecule investigated.

HPLC Analysis, Modeling, and Biological Studies of Antiproliferative Heterocyclic Carboxamides

Reversed phase HPLC and MEKC [1] provide excellent possibilities to measure the hydrophobic properties of compounds, characterizing them directly from the chromatographic retention time. The aim in this respect is to estimate the hydrophobic character of the molecules on the basis of their retention factors (k′) determined in various separation processes [1]. The expected biological activity of the compounds can be reliably predicted on the basis of the measured hydrophobicity data [2]. Another possibility is the use of highly sophisticated computer programs to calculate hydrophobicity on the basis of the structural moieties building up the molecule being investigated.

Screening of peptidomimetic tyrosine kinase inhibitors for inducing programmed cell death

G. KÉRI, L. ÔRFI1, F. HOLLÓSY, T. VÁNTUS, J. ÉRCHEGYI, M. IDEI, A. HORVÁTH, I. TEPLÁN, A. GAZIT3, I. PETÁK2, Z. SZEGEDI2 and B. SZENDE2 Peptide Biochem Res Unit., Dept of Medical Chemistry, 1Institute of Pharmaceutical Chemistry, and 2 1st Institute of Pathology Semmelweis University of Medicine, Budapest, P.O.Box 260, Hungary-1444, 3 Dept. of Biol. Chemistry, The Hebrew University of Jerusalem, Israel-91904