Structure-activity relationships in a series of newly synthesized 1-amino-substituted ellipticine derivatives

Selective Antitumor Activity of Datelliptium toward Medullary Thyroid Carcinoma by Downregulating RET Transcriptional Activity

Simple Summary

Medullary thyroid carcinoma (MTC) is a rare aggressive type of thyroid cancer with a propensity for metastasizing to the lymph nodes, liver, bones, and lungs. Previous studies have demonstrated that activated REarranged during Transfection (RET) mutants are key regulators of invasive and metastatic behaviors in MTC. The present study aimed to evaluate the antiinvasive and antimetastatic potential of a novel RET transcription inhibitor, datelliptium, which stabilizes the RET G-quadruplex structures and suppresses RET oncogene transcription by examining its effects on epithelial-to-mesenchymal transition (EMT), cancer stem cells (CSCs), and MTC cell migration. Interestingly, the ablation of RET with datelliptium resulted in decreased EMT, spheroid formation, and MTC cell migration. In this study, we also demonstrated the in vivo antitumor activity in TT tumor-bearing mice with about 75% tumor growth inhibition.

Abstract

Medullary thyroid carcinoma (MTC) is a rare aggressive form of thyroid cancer with high rates of metastasis. Sporadic and hereditary MTC are strongly driven by somatic and germline mutations, respectively, in the transmembrane REarranged during Transfection (RET) proto-oncogene, which encodes a receptor tyrosine kinase. Our previous study identified datelliptium as a novel RET transcription inhibitor, which stabilizes the RET G-quadruplex structures and suppresses RET oncogene transcription. The present study aimed to elucidate the effect of datelliptium on the suppression of epithelial-to-mesenchymal transition (EMT) and metastasis-related behaviors of MTC cells, including cell migration and formation of cancer stem cells (CSCs). Our results demonstrated that datelliptium downregulated the expression of the mesenchymal markers, including N-cadherin, vimentin, slug, snail, and claudin-1. Compared to untreated cells, datelliptium significantly decreased the migration of TT cells in a dose-dependent manner in a wound healing assay. Additionally, datelliptium significantly reduced the size of preformed spheroids from TT cells over the time course. Finally, datelliptium inhibited approximately 75% of MTC xenograft growth with minimal systemic toxicity. In conclusion, datelliptium exerts its antitumor activity against MTC cells by reducing the EMT program, migratory ability, and self-renewal capacity of TT cells, thus preventing invasive and metastatic behavior of MTC.

Bioactive Olivacine Derivatives-Potential Application in Cancer Therapy

Olivacine and its derivatives are characterized by multidirectional biological activity. Noteworthy is their antiproliferative effect related to various mechanisms, such as inhibition of growth factors, enzymes, kinases and others. The activity of these compounds was tested on cell lines of various tumors. In most publications, the most active olivacine derivatives exceeded the effects of doxorubicin (a commonly used anticancer drug), so in the future, they may become the main new anticancer drugs. In this publication, we present the groups of the most active olivacine derivatives obtained. In this work, the in vitro and in vivo activity of olivacine and its most active derivatives are presented. We describe olivacine derivatives that have been in clinical trials. We conducted a structure-activity relationship (SAR) analysis that may be used to obtain new olivacine derivatives with better properties than the available anticancer drugs.

Isoquinolines: Important Cores in Many Marketed and Clinical Drugs

BACKGROUND

Isoquinoline analogs are an important, structurally diverse class of compounds that are extensively used as pharmaceuticals. Derivatives containing the isoquinoline scaffold have become a focus of therapeutic research because of their wide range of biological characteristics. Examples of these drugs, many of which are in clinical application or at the pre-clinical stage, are used to treat a broad swathe of ailments, such as tumors, respiratory diseases, infections, nervous system diseases, cardiovascular and cerebrovascular diseases, endocrine and metabolic diseases.

METHODS

Data were collected from PubMed, Web of Science, and SciFinder, through searches of drug names.

RESULTS

At least 38 isoquinoline-based therapeutic drugs are in clinical application or clinical trials, and their chemical structure and pharmacokinetics are described in detail.

CONCLUSION

The isoquinoline ring is a privileged scaffold which is often preferred as a structural basis for drug design, and plays an important role in drug discovery. This review provides a guide for pharmacologists to find effective preclinical/clinical drugs and examines recent progress in the application of the isoquinoline scaffold.

Novel polyazaheterocyclic systems: Synthesis, antitumor, and antimicrobial activities

A series of new polyazaheterocyclic ring systems was synthesized via the reaction of enaminone 5 with active methylene compounds, hydrazine hydrate, hydroxylamine, and heterocyclic amines. The structures of the newly synthesized compounds were substantiated on the basis of spectral data and elemental analyses. The antitumor activity of the enaminone 5 against the human breast cell line MCF-7, the liver carcinoma cell line HEPG2-1, and HELA cells was determined. In addition, the antimicrobial activity of some selected products was evaluated.

Syntheses of Pyrazolo-, Isoxazolo-, Pyrido- and Pyrimido-Carbazoles from 2-(3′,4′-Dimethoxybenzylidene)-2,3,4,9-Tetrahydrocarbazol-1-Ones

Mixed aldol condensation of 2,3,4,9-tetrahydrocarbazol-1-ones with 3,4-dimethoxybenzaldehyde (veratraldehyde) yielded 2-(3′,4′-dimethoxybenzylidene)-2,3,4,9-tetrahydrocarbazol-1-ones. These enones on reaction with hydrazine hydrate, hydroxylamine hydrochloride, malononitrile and guanidinium nitrate under different conditions yielded the corresponding pyrazolo[3,4-a]-, isoxazolo[3,4-a]-, pyrido[2,3-a]-, and pyrimido[4,5-a]-carbazoles respectively. The molecular and crystal structure of 2-(3′,4′-dimethoxybenzylidene)-2,3,4,9-tetrahydro-1H-carbazol-1-one resolved by single crystal X-ray diffraction is discussed.

Synthesis and biological activity of 5-aza-ellipticine derivatives

Novel 5-aza-ellipticine derivatives were synthesized and tested as antitumor agents. The new compounds were prepared more readily than the analogous ellipticine derivatives, which are known to be potent anti-tumor agents Although the novel 5-aza-ellipticine derivatives are not as biologically active as their corresponding ellipticine analogues, the new compounds represent a new, readily accessible class of heteroaromatic catalytic inhibitors of topoisomerase II and possible anti-tumor agents.

SR Proteins as Potential Targets for Therapy

Serine- and arginine-rich (SR) proteins constitute a highly conserved family of pre-mRNA splicing factors that play key roles in the regulation of splice site selection, and thereby in the control of alternative splicing processes. In addition to conserved sequences at the splice junctions, splice site selection also depends upon different sets of auxiliary cis regulatory elements known as exonic and intronic splicing enhancers (ESEs and ISEs) or exonic and intronic silencers (ESSs and ISSs). Specific binding of SR proteins to their cognate splicing enhancers as well as binding of splicing repressor to silencer sequences serve to enhance or inhibit recognition of weak splice sites by the splicing machinery. Given that the vast majority of human genes contain introns and that most pre-mRNAs containing multiple exons undergo alternative splicing, mutations disrupting or creating such auxiliary elements can result in aberrant splicing events at the origin of various human diseases. In the past few years, numerous studies have reported several approaches allowing correction of such aberrant splicing events by targeting either the mutated sequences or the splicing regulators whose binding is affected by the mutation. The aim of the present review is to highlight the different means by which it is possible to modulate the activity of SR splicing factors and to bring out those holding the greatest promises for the development of therapeutic treatments.

4-Anilinopyrimido[4',5':4,5]selenolo(2,3-b)quinoline and 4-piperazino pyrimido[4',5':4,5]selenolo(2,3-b)quinoline: new DNA intercalating chromophores with antiproliferative activity

We have used circular dichroism, hydrodynamic methods, absorbance, and fluorescence titration to study the interaction of 4-anilinopyrimido[4',5':4,5] selenolo (2,3-b)quinoline (APSQ) and 4-piperazinopyrimido[4',5':4,5] selenolo(2,3-b)quinoline (PPSQ) with DNA. The association constants of APSQ and PPSQ were of the order of 10(4)M(-1). The fluorescence properties at ionic strength 0.01M are best fit by the neighbor exclusion model, with K=0.58-9.2 x 10(4)M(-1) and an exclusion parameter of 0.9-6.4 bp. Binding to the GC-rich DNA of Micrococcus lysodeikticus was stronger than the binding to calf thymus DNA, suggest that drug binds preferentially to G+C pairs at low r. CD spectra indicate that stacking of these compounds with DNA induces a strong helicity in the usually disordered structure of this double strand. Viscosity experiments show with sonicated calf thymus DNA with PPSQ an twice increase in slope (m) as that with APSQ. PPSQ increases the T(m) for calf thymus DNA melting by approximately 10 degrees C as binding approaches saturation, with biphasic melting. The cytotoxicities of these compounds on leukemia HL-60, K-562, B16F10 melanoma and Colo-205 are quite similar and inhibition (IC(50)) was in the range of 0.39-9.80 microM. The anticancer efficacy against B16F10 melanoma has provided evidence of major anticancer activity for PPSQ. Single or multiple intraperitonial (i.p.) doses of drug proved high level activity against the subcutaneous (s.c.) grafted B16 melanoma, significantly increase in life span (ILS 139% and 170%). The aim of this study was to analyze the physiochemical properties of these compounds in an attempt to understand its superior biological activity.

Selective modification of alternative splicing by indole derivatives that target serine-arginine-rich protein splicing factors

The prevalence of alternative splicing as a target for alterations leading to human genetic disorders makes it highly relevant for therapy. Here we have used in vitro splicing reactions with different splicing reporter constructs to screen 4,000 chemical compounds for their ability to selectively inhibit spliceosome assembly and splicing. We discovered indole derivatives as potent inhibitors of the splicing reaction. Importantly, compounds of this family specifically inhibit exonic splicing enhancer (ESE)-dependent splicing, because they interact directly and selectively with members of the serine-arginine-rich protein family. Treatment of cells expressing reporter constructs with ESE sequences demonstrated that selected indole derivatives mediate inhibition of ESE usage in vivo and prevent early splicing events required for HIV replication. This discovery opens the exciting possibility of a causal pharmacological treatment of aberrant splicing in human genetic disorders and development of new antiviral therapeutic approaches.

CoMFA and CoMSIA Analyses of Pneumocystis carinii Dihydrofolate Reductase, Toxoplasma gondii Dihydrofolate Reductase, and Rat Liver Dihydrofolate Reductase

In a continuing effort to develop potent and selective dihydrofolate reductase (DHFR) inhibitors against opportunistic pathogens, we developed three-dimensional quantitative structure-activity relationship (3D QSAR) models for the inhibitory activity against Pneumocystis carinii (pc) DHFR, Toxoplasma gondii (tg) DHFR, and rat liver DHFR, using a data set of 179 structurally diverse compounds. To ensure a balanced distribution of more potent and less potent drugs in the training set, three different 90-compound training sets taken from the main data set were used, one for each enzyme, while the remaining 89 compounds in the main data set in each case were used as the test set. Three methods, namely, conventional CoMFA, all orientation search (AOS) CoMFA, and CoMSIA were applied to the training sets. While the AOS CoMFA models gave the best internal predictions (cross-validated r(2) values from the training sets), which are satisfactory, CoMSIA models gave the best external predictions (predictive r(2) values from the test sets). Both AOS CoMFA and CoMSIA analyses were used to construct stdev*coefficient contour maps which can be used to design new compounds in an interactive fashion.

Synthetic Utility of 2-Benzylidene-1,2,3,4-tetrahydrocarbazol-1-ones. A Facile Syntheses of Pyrano[2,3-a]carbazoles, Pyrido[2,3-a]carbazoles and Pyridazino[3,4-a]carbazoles

2-Benzylidene-1,2,3,4-tetrahydrocarbazol-1-ones 1, synthons easily accessible from the corresponding 1,2,3,4-tetrahydrocarbazol-1-ones, were utilized in the synthesis of fused carbazoles. In accordance, the reaction of 1 with malononitrile yielded pyrano[2,3-a]carbazoles 2a and 2d or pyrido[2,3-a]carbazoles 2b, 2c and 2e. The reaction of 1 with thiocarbohydrazide or thiosemicarbazide under basic conditions afforded pyridazino[3,4-a]carbazoles 3 or thiol substituted pyridazino[3,4-a]carbazoles 4, respectively, in good yields. The formation of the hitherto unknown compounds was well supported by plausible mechanisms. The products formed were characterized by IR, 1H NMR, 13C NMR, mass spectral methods and by elemental analysis.

Development of neural network QSPR models for Hansch substituent constants. 2. Applications in QSAR studies of HIV-1 reverse transcriptase and dihydrofolate reductase inhibitors

In this paper, the applications of a Hansch substituent constant predictor(1) to Quantitative Structure-Activity Relationships (QSAR) studies of E. coli dihydrofolate reductase (DHFR) inhibitors 2,4-diamino-5-(substituted-benzyl)pyrimidines as well as HIV-1 reverse transcriptase (RT) inhibitors 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymine (HEPT) derivatives are demonstrated. Both data sets contain functional groups for which the substituent constants (pi, MR, F and R) could not be found in standard substituent constant tables. The substituent constant predictor allowed us to derive predicted pi, MR, F and R values for all substituents in both data sets, thus enabling the generation of easily interpretable QSAR models of comparable or better predictivity than previous models.

Antitumor activity of 4-amino and 8-methyl-4-(3diethylamino propylamino)pyrimido[4′,5′:4,5]thieno (2,3-b) quinolines

The interaction of 4-aminopyrimido [4',5':4,5] thieno (2,3-b) quinoline and 8-methyl-4-(3-diethylaminopropylamino) pyrimido [4',5':4,5] thieno (2,3-b) quinoline with DNA was studied by UV-Vis and fluorescence spectrophotometry as well as by hydrodynamic methods. On binding to DNA, the absorption spectra underwent bathochromic and hypochromic shifts and the fluorescence was quenched. These compounds are able to bind to DNA with an affinity of about 10(6) M(-1) for calf thymus DNA at ionic strength 0.01 M and their intercalating characteristic (lengthening of the DNA) depends upon the length of the chain. Binding to the GC-rich DNA of Micrococcus lysodeikticus was stronger than the binding to calf thymus DNA at ionic strength 0.01 M. The cytotoxicities of these compounds on leukemia HL-60, melanoma B16F10 and neuro 2a cells are quite similar and inhibition (IC50) is in the range of 0.992-3.968 microM. The anticancer efficacy against B16 melanoma, has provided evidence of major antitumor activity for 8-methyl-4-(3diethylaminopropylamino) pyrimido [4',5':4,5] thieno(2,3-b)quinoline. Single or multiple intraperitonial (i.p) doses of drug proved high level activity against the subcutaneous (s.c) grafted B16 melanoma, significantly increasing survival (p<0.001) and inhibiting tumor growth (T/C of 4%). This study offers a new intercalation functional group to DNA-targeted drug design.

Quantitative structure-activity relationships of 2, 4-diamino-5-(2-X-benzyl)pyrimidines versus bacterial and avian dihydrofolate reductase

Quantitative structure-activity relationships (QSAR) have been formulated for a set of 15 2,4-diamino-5-(2-X-benzyl)pyrimidines versus dihydrofolate reductase from Lactobacillus casei and chicken liver. QSARs were also developed for comprehensive data sets containing mono-, di-, and trisubstituted benzyl derivatives. Particular emphasis was placed on the role played by ortho substituents in the overall binding process and subsequent inhibition of the catalytic process in both the prokaryotic and eucaryotic DHFRs. Comparisons between the two QSARs reveal subtle differences at specific positions which can be optimized to design more selective antibacterial agents.

1H-NMR studies of the interaction between a self-complementary deoxyoligonucleotide duplex and indolo[2,3-b]quinoxaline derivatives active against herpes virus

1H NMR has been used to study the interactions of ellipticine and the ellipticine analogues 2-3-dimethyl-6-(2-dimethylaminoethyl)6H-indolo-[2,3-b]quinoxaline and 6-(2-dimethylaminoethyl)6H-indolo-[2,3-b]quinoxaline with the self-complementary decadeoxyribonucleotide d(CGCGATCGCG)2. The Watson-Crick H-bonded imino proton resonances were studied. The drugs were shown to bind to the duplex by intercalation involving slow exchange kinetics for the imino proton resonances on the NMR time scale (500 MHz). Ellipticine and the 2,3-dimethyl analogue were found not to show strong base preferences, while the other analogue was found to have a preferred primary binding site between the A.T base pairs with a probable minor secondary binding site between the A.T and adjacent G.C base pairs. The new drug-shifted imino proton resonances were assigned through saturation transfer experiments. The base-specific interactions were accompanied by drug-induced non-uniform broadening of the resonances (due to intermediate chemical exchange kinetics), in the spectral region of the non-exchangeable aromatic and sugar H1' proton resonances of the oligonucleotide at 25 degrees C.

Recognition and photo-induced cleavage and cross-linking of nucleic acids by oligonucleotides covalently linked to ellipticine

Oligopyrimidines covalently linked to ellipticine derivatives form duplex and triplex structures with target single-stranded oligopurine sequences. They also bind to duplex DNA at homopurine-homopyrimidine sequences where they form local triple helices. Irradiation at wavelengths longer than 300 nm of the complex formed by an oligonucleotide-ellipticine conjugate with its target sequence induced (i) cleavage of the target at bases located in close proximity to the dye and (ii) cross-linking of the target sequence to the derivatized oligonucleotide. Both cross-linking and cleavage reactions decreased when temperature increased with a half-transition corresponding to the dissociation of the oligonucleotide-ellipticine conjugate from its target nucleic acid, demonstrating that the observed photochemical effects are dependent on hybrid formation. When the target was a double-stranded DNA, photochemical reactions were observed on both strands of the duplex. Photo-induced cross-linking was more efficient than cleavage when the target was single-stranded; the reverse was observed when the target was duplex DNA.

Sequence-selective binding of an ellipticine derivative to DNA

The DNA sequence specificity of an ellipticine derivative bearing an aminoalkyl side chain has been determined by a variety of footprinting methods. The drug exhibits sequence selective binding and discriminates against runs of adenines or thymines. Binding is shown to occur at various sequences with a preference for GC rich regions of DNA. A large enhancement of DNAase I and of hydroxyl radical cleavage in regions rich in A's or T's is observed together with hyperreactivity of adenines towards diethylpyrocarbonate in the presence of drug. This indicates the occurrence of drug-induced changes in critical conformational features of DNA. The total absence of hyperreactivity of guanine residues towards diethylpyrocarbonate appears to be related to the sequence selectivity of drug binding. No alteration of the dimethyl sulphate and methylene blue-induced cleavage of DNA is observed. Irradiation of ellipticine derivative-DNA complexes with UV light followed by alkali treatment leads to selective photocleavage at guanine residues, consistent with the deduced degree of selectivity of the binding reaction.

Sequence-specific artificial photo-induced endonucleases based on triple helix-forming oligonucleotides

Homopyrimidine oligonucleotides bind to homopurine-homopyrimidine sequences of duplex DNA forming a local triple helix. This binding can be demonstrated either directly by a footprinting technique, gel assays, or indirectly by inducing irreversible reactions in the target sequence, such as photocrosslinking or cleavage. Binding occurs in the major groove with the homopyrimidine oligonucleotide orientated parallel to the homopurine strand. Thymine and protonated cytosine in the oligonucleotide form Hoogsteen-type hydrogen bonds with A.T and G.C Watson-Crick base pairs, respectively. Here we report that an 11-residue homopyrimidine oligonucleotide covalently attached to an ellipticine derivative by its 3' phosphate photo-induces cleavage of the two strands of a target homopurine--homopyrimidine sequence. To our knowledge, this is the first reported case of a sequence-specific artificial photoendonuclease. In addition we show that a strong binding site for a free ellipticine derivative is induced at the junction between the triplex and duplex structures on the 5' side of the bound oligonucleotide. On irradiation, cleavage is observed on both strands of DNA. This opens new possibilities for inducing irreversible reactions on DNA at specific sites by the synergistic action of a triple helix-forming oligonucleotide and an intercalating agent.

Role of the superoxide anion in the oxidative activation of the new antitumor drug BD40: a radiolysis study

BD40, a new antitumor drug derived from 9-azaellipticine, is thought to have an oxygen-dependent metabolism in vivo. We have investigated the one-electron oxidation of this drug by gamma radiolysis using OH. free radicals as oxidants and the reaction of O2-. with the BD40 oxidized transient(s). The absorption spectrum of the one-electron oxidized free radical was determined by pulse radiolysis using OH. or N.3 as reactant. In the absence of O2 and O2-., the initial yield of disappearance of the drug is equal to 2.5 x 10(-7) mol J-1 independently of the initial concentration of the drug and of the dose rate. When BD40 is oxidized by OH. radicals in the presence of O2 and O2-., the yield is the same. This yield is halved if superoxide dismutase is present during irradiation. Superoxide anions do not react directly with the drug. Thus it is suggested that these radicals oxidize the BD40 free radical produced by oxidation with OH. Biological implications are discussed.

Interrelationship between affinity for DNA, cytotoxicity and induction of DNA-breaks in cultured L1210 cells for two series of tricyclic intercalators. Simplified analogues of ellipticine derivatives

The interrelationship between affinity for DNA, cytotoxicity and induction of single-strand DNA breaks in cultured L1210 cells was studied for 21 compounds belonging to two series of tricyclic intercalators: 1-amino-substituted 4-methyl-5H-pyrido[4,3-b]indoles (gamma CARB) and 1-amino-substituted 4-methyl-5H-pyrido[3',4':4,5]pyrrolo[2,3-c]pyridines (PPP), which are simplified analogues of Ellipticine derivatives obtained by deletion of one cycle. Adriamycin, m-AMSA (4'-(9-acridinylamino) methanesulfon-m-anisidide), PZE (10-[diethylaminopropyl amino]-6-methyl-5H-pyrido[3',4':4,5]-pyrrolo[2,3-g] isoquinoline and RTE [( 1-(3-diethylaminopropylamino)-9-methoxy ellipticine, bimaleate) are used as reference compounds. The intercalation of these compounds into DNA was strongly suggested by three experimental observations: (i) the competitive inhibition of ethidium bromide intercalation, (ii) bathochromic and hypochromic effects on absorption spectra induced by DNA, and (iii) drug-induced increase of the DNA length, measured by viscosimetry. PPP derivatives are generally less cytotoxic and induce DNA breaks less efficiently than the gamma CARB ones, both in terms of maximum breakage frequencies and required drug concentrations. The most active compounds induced SSB in the DNA of L1210 cells, in a bell-shaped manner: the SSB frequency increased, rose to a maximum and then decreased as the drug concentrations increased. The maximum SSB frequencies induced by the most active compounds are of the same order as those of reference compounds Adriamycin and PZE. The structurally important requirements are essentially the same for both DNA breakage activity and cytotoxicity: (i) a N-CH3 in the 5-position, (ii) a CH3 in the 4-position, (iii) a hydroxy in the 8-position and (iv) the presence of an (aminoalkyl)amino side chain with preferentially a 3 carbon unit. There is no direct relationship between DNA affinity in vitro and induction of DNA breaks in cells, although a relatively high affinity seemed to be a necessary condition, since the most active compounds have the highest affinities and compounds having a very low affinity are totally inactive. The close correlation between cytotoxicity and extent of induction of DNA breaks suggests that these breaks may be in fact the lethal lesions responsible for cell death and thereby for the antitumor properties of these tricyclic intercalators.

Interaction of ellipticine and an indolo[2,3b]-quinoxaline derivative with DNA and synthetic polynucleotides

The non-covalent DNA interaction of the anticancer drug ellipticine (Scheme I, 1a) as well as an indolo[2,3-b]-quinoxaline derivative (Scheme I, 3b) with a dimethylaminoethyl side chain has been studied by light absorption, linear dichroism (LD) and fluorescence. Compound 3b (Scheme I) has antitumorigenic as well as antiviral activity. Both compounds bind to DNA or synthetic polynucleotides such as poly(dA-dT).(dA-dT) and poly(dG-dC).(dG-dC) by intercalation. In contrast to ellipticine, compound 3b (Scheme I) exhibits a significant binding specificity for alternating AT sequences. Its fluorescence is strongly enhanced in AT sequences and quenched in GC sequences. Fluorescence titrations evaluated as Scatchard plots show that both ellipticine and compound 3b (Scheme I) bind to the nucleic acids according to a non-cooperative neighbor exclusion model.

Cytostatic, cytotoxic and mutagenic effects of voacristine, an indole alkaloid in wild-type and repair-deficient yeasts

Voacristine, an indole alkaloid isolated from the leaves of Ervatamia coronaria (Stapf.) (Apocynaceae) has dose-dependent cytostatic and cytotoxic effects on cultures of Saccharomyces cerevisiae. These inhibitory effects take place only in growing cells. Among the different repair-deficient mutants examined, a mutant defective in excision-resynthesis repair pathway (rad3-e5) was found to be the most sensitive to such a toxic effect. The mutant rad52-1 blocked in the DNA strand break repair pathway showed an intermediary sensitivity to the lethal effect induced by this indole alkaloid, whereas the mutant defective in the mutagenic repair pathway (rad6-1) demonstrated practically the same sensitivity as the wild-type strain. The nuclear reversion mutation for the locus lysl-1 was induced by voacristine, whereas the mitochondrial "petite" mutation was not induced by this alkaloid. These results indicate that the lesions induced by voacristine in vivo are likely to be of the adducts type; such damage is repairable in the wild-type; the DNA strand break repair pathway plays a minor role in the repair of voacristine-induced lesions.