DNA intercalation, topoisomerase II inhibition and cytotoxic activity of the plant alkaloid neocryptolepine

Cryptolepine and neocryptolepine are two indoloquinoline alkaloids isolated from the roots of the African plant Cryptolepis sanguinolenta. Both drugs have revealed antibacterial and antiparasitic activities and are strongly cytotoxic to tumour cells. We have recently shown that cryptolepine can intercalate into DNA and stimulates DNA cleavage by human topoisomerase II. In this study, we have investigated the mechanism of action and cytotoxicity of neocryptolepine, which differs from the parent isomer only by the orientation of the indole unit with respect to the quinoline moiety. The biochemical and physicochemical results presented here indicate that neocryptolepine also intercalates into DNA, preferentially at GC-rich sequences, but exhibits a reduced affinity for DNA compared with cryptolepine. The two alkaloids interfere with the catalytic activity of human topoisomerase II but the poisoning activity is slightly more pronounced with cryptolepine than with its isomer. The data provide a molecular basis to account for the reduced cytotoxicity of neocryptolepine compared with the parent drug.     

Cytotoxic activity of cyclosporin A and [3-keto-Bmt1]-[Val2]-cyclosporin (SDZ PSC 833) on tumour cells from patients with haematological malignancies

Objective and method: The fluorometric microculture cytotoxic assay was employed for characterisation of the cytotoxic effect of cyclosporin A (CsA) and its non-immunosuppressive analogue SDZ PSC 833, [3-keto-Bmt¹]-[Val²]-cyclosporin (PSC) in tumour cells from patients with haematological or solid tumours. Results: Tumour cells from patients with chronic lymphocytic leukaemia (CLL) or non-Hodgkin's lymphoma (NHL) were found to be more sensitive to both drugs than those of tumour cells from patients with acute lymphocytic leukaemia (ALL), acute myoblastic leukaemia (AML) and various solid tumours. There was a close correlation between the effects of the two drugs (correlation coefficient 0.71), but CsA was slightly more active than PSC in most diagnoses. No tumour cell sample showed sensitivity to PSC without also being sensitive to CsA. There was a moderate level of correlation between the activity pattern of CsA and doxorubicin (correlation coefficient 0.66), whereas the correlations with other cytostatics, such as vincristine, cytarabine and melphalan, were low (correlation coefficient −0.11 to 0.33). Conclusion: The results indicate that PSC shares the direct cytotoxic properties of CsA, but is slightly less potent. Clinical testing of the cytotoxic effect of these agents in haematological malignancies seems warranted and the apparent non-cross-resistance with standard agents makes cyclosporins a potentially useful adjunct to chemotherapy in those diagnoses. Received: 12 August 1996 / Accepted in revised form: 10 December 1996     

Cytotoxicity and cell cycle effects of the plant alkaloids cryptolepine and neocryptolepine: relation to drug-induced apoptosis

Cryptolepine and neocryptolepine are two indoloquinoline derivatives isolated from the roots of the african plant Cryptolepis sanguinolenta. These two alkaloids, which only differ by the respective orientation of their indole and quinoline rings, display potent cytotoxic activities against tumour cells and present antibacterial and antiparasitic properties. Our previous molecular studies indicated that these two natural products intercalate into DNA and interfere with the catalytic activity of human topoisomerase II. Here we have extended the study of their mechanism of action at the cellular level. Murine and human leukemia cells were used to evaluate the cytotoxicity of the drugs and their effects on the cell cycle were measured by flow cytometry. Cryptolepine, and to a lesser extent neocryptolepine, provoke a massive accumulation of P388 murine leukemia cells in the G2/M phase. With HL-60 human leukemia cells, the treatment with cryptolepine leads to the appearance of a hypo-diploid DNA content peak (sub-G1) characteristic of the apoptotic cell population. With both P388 and HL-60 cells, cryptolepine proved about four times more toxic than its isomer. But the use of the HL-60/MX2 cell line resistant to the anticancer drug mitoxantrone suggests that topoisomerase II may not represent the essential cellular target for the alkaloids, which are both only two times less toxic to the resistant HL-60/MX2 cells compared to the parental cells. The capacity of the drugs to induce apoptosis of HL-60 human leukemia cells was examined by complementary biochemical techniques. Western blotting analysis revealed that cryptolepine, but not neocryptolepine, induces cleavage of poly(ADP-ribose) polymerase but both alkaloids induce the release of cytochrome c from the mitochondria. The cleavage of poly(ADP-ribose) polymerase observed with cryptolepine correlates with the appearance of a marked sub-G1 peak in the cell cycle experiments. The proteolytic activity of Asp-Glu-Val-Asp- or Ile-Glu-Thr-Asp-caspases was found to be enhanced much more strongly with cryptolepine than with its isomer, as expected from their different cytotoxic potential. Despite the activation of the caspase cascade, we did not detect internucleosomal cleavage of DNA in the HL-60 cells treated with the alkaloids. Altogether, the results shed light on the mechanism of action of these two plant alkaloids.     

Cryptolepis sanguinolenta: antimuscarinic properties of cryptolepine and the alkaloid fraction at M1, M2 and M3 receptors.

From an ethanol extract of the roots of Cryptolepis sanguinolenia the alkaloid fraction and its main constituent cryptolepine were isolated by partitioning at pH 11 and column chromatography using silica gel and chloroform/methanol as eluent. Cryptolepine was identified mainly by EI-MS and 1H/13C-NMR spectroscopy. Cryptolepine (3-30 microM) and the alkaloid fraction of Cryptolepis sanguinolenta (3-10 micrograms/ml) antagonized muscarinic effects at M1 receptors in rabbit vas deferens, M2 receptors in guinea-pig atria, and M3 receptors in guinea-pig ileum. The experiments, using N-methylatropine as reference drug, showed a significant antimuscarinic activity for both cryptolepine and the alkaloid fraction, but no appreciable receptor subtype selectivity (pA2 = 5.00-5.73). Cryptolepine was determined as the antimuscarinic principle of Cryptolepis sanguinolenta. At higher concentrations both materials displayed negative inotropic effects.     

In vitro study of P-glycoprotein induction as an antidotal pathway to prevent cytotoxicity in Caco-2 cells

The Caco-2 cell line is a reliable in vitro model for predicting drug intestinal absorption and P-glycoprotein (P-gp)-mediated excretion in humans. Recent in vivo studies suggested the induction of P-gp as a cellular protection tool against paraquat poisoning, through the increase in its pulmonary and intestinal excretion. Thus, the aim of the present work was to evaluate P-gp expression and activity in Caco-2 cells exposed to doxorubicin (a known P-gp inducer) and to correlate these changes with paraquat toxic effects. Cytotoxicity of doxorubicin (0–100 μM) and paraquat (0–1,000 μM) was evaluated for a maximum period of 96 h. In doxorubicin-exposed cells, P-gp expression and transport activity were evaluated by flow cytometry, using a fluorescein isothiocyanate–conjugated antibody and the P-gp fluorescent subtract rhodamine 123, respectively. A significant increase in P-gp expression was observed as soon as 6 h after exposure to 5 μM doxorubicin. P-gp activity also increased after 6 h, but only at higher doxorubicin concentrations (over 50 μM). Paraquat (0–5,000 μM) cytotoxicity was then evaluated with or without previous exposure of the cells to doxorubicin (5–100 μM, a concentration range causing both an increase in P-gp expression and activity). Under P-gp induction, a significant reduction in paraquat cytotoxicity was observed. Furthermore, when these cells were incubated with a specific P-gp inhibitor (UIC2 antibody) the doxorubicin protective effects were blocked, confirming the involvement of P-gp in the reduction in paraquat cytotoxicity. In conclusion, the human Caco-2 cell line model can be used for the study of P-gp induction as an antidotal pathway against substrates of this transporter system.     

Toxic-dose warfarin-induced apoptosis and its enhancement by gamma ionizing radiation in leukemia K562 and HL-60 cells is not mediated by induction of oxidative stress

The purpose of this study was to test the hypothesis that warfarin may enhance free radical production and oxidative damage on cancer cells. We examined the possible concentration-dependent effect of warfarin on cytotoxicity with respect to oxidative stress on leukemia cell lines (K562 and HL-60) and normal human peripheral blood mononuclear cells (PBMC). Gamma radiation was used as a positive control agent for oxidative stress. At all concentrations of warfarin (5–200 μM), 5-amino-2,3-dihydro-1,4-phthalazinedione (luminol)- and bis-N-methylacridinium nitrate (lucigenin)-amplified chemiluminescence responses and lipid peroxidation and protein oxidation were stable after 72 h incubation at 37°C. However, The 2′,7′-dichlorofluorescein diacetate (DCFH-DA) oxidation was increased when cells were incubated with high concentrations (50–200 μM) of warfarin. In these concentration ranges, warfarin reduced cell growth in a dose-dependent manner, producing apoptosis. Our results also revealed that at concentrations above 5 μM, warfarin had a potentiating effect on radiation-mediated growth inhibition and apoptosis. Furthermore, marked effects were observed on leukemic cells compared with PBMC. We report here that the increase of DCFH oxidation might be due to the increase in the release of cytochrome C caused by warfarin, as cytosolic cytochrome C content was significantly elevated in the warfarin-treated cells compared with control cells, and because cotreatment with antioxidants N- acetylcysteine or 4,5-dihydroxy-1,3-benzene-disulfonic acid (Tiron) was unable to prevent cytochrome C release and DCFH oxidation induced by the drug. Taken together, these results suggest that high warfarin concentrations may be toxic to leukemic cells in vitro through apoptosis, although at the pharmacological concentrations (<50 μM), warfarin has no prooxidant or cytotoxic effect on PBMC, K562, and HL-60 cells. In addition, when the treatment of leukemic cells with warfarin at concentrations above 5 μM is combined with radiation, we observed an increase in radiation-induced cytotoxicity. The mechanism by which warfarin potentiates this cytotoxicity is unclear, but it may not be directly due to toxic damage induced by warfarin-generated free radicals.     

Pharmacological profiling of novel non-COX-inhibiting indole-pyran analogues of etodolac reveals high solid tumour activity of SDX-308 in vitro

SDX-308 and SDX-309 are potent indole-pyran analogues of SDX-101 (R-etodolac) which has anti-tumour activity unrelated to cyclooxygenase-2 inhibition. Their cytotoxic activity was further studied herein using a well-characterized human tumour cell-line panel containing ten cell lines, as well as in 58 primary tumour cell samples from a variety of diagnoses. The indole-pyran analogues of SDX-101 were in general considerably more active in both cancer cell lines and primary tumour samples. Low cross-reactivity with standard agents was observed, indicating a unique mechanism of action. No apparent influence on efficacy was observed via classical mechanisms of multidrug-resistance. SDX-101 and SDX-309 showed higher relative activity in haematological compared to solid tumour samples, while SDX-308 had pronounced solid-tumour activity. High SDX-308 cytotoxic efficacy was observed in non-small cell lung cancer, renal cancer and ovarian cancer samples, and also in chronic lymphocytic leukaemia. In conclusion, the indole-pyran analogues showed a favourable pharmacological profile and represent a potentially important new class of drugs for cancer treatment.     

Cytostatic activity of the duplex drug linking 2′-deoxy-5-fluorouridine (5FdU) with 3′-C-ethynylcytidine (ECyd) against gastric adenocarcinoma cell lines

The cytostatic potential of the new duplex drug 2′-deoxy-5-fluorouridylyl-(5′➔5′)-3′-C-ethynylcytidine (5FdU(5′-5′)ECyd) was evaluated in comparison to those of 5-fluorouracil (5FU), 2′-deoxy-5-fluorourindine (5FdU), 3′-C-ethynylycytidine (ECyd), cisplatin, an equimolar mixture of 5FdU + ECyd and a three component-mixture of 0.75 μM epirubicin/0.90 μM cisplatin/3.0 μM 5FU (ECF) by incubation of the two human gastric adenocarcinoma cell lines 23132/87 and MKN-45. The molar composition of ECF was taken from data of a triple combination chemotherapy for human gastric cancer. Time and dose depending inhibition of cell growth was determinated using the CASY technology. A growth decrease of both cell lines from 100% to about 20% was observed by treatment with ECF over a course of 14 days. This result provided basis to estimate the cytostatic potential of all tested drugs and combinations thereof. Corresponding high activities in respect to ECF were achieved by incubation of 23132/87 cells with single drugs 49 μM 5FU, 10 μM cisplatin, 3.4 μM 5FdU, 0.65 μM ECyd, the mixture 0.32 μM 5FdU + 0.32 μM ECyd and 0.32 μM 5FdU(5′-5′)ECyd. The less sensitive MKN-45 cells require a 1.5–4 fold higher dose of the standard chemotherapeutics in order to achieve an equivalent cytostatic effect, in respect to the 23132/87 cell line,. However, the effect of the duplex drugs on MKN-45 cells was gained with a 5-fold lower dose than ECF. Due to its high cytostatic potential the duplex drug, which covalently links two active anticancer compounds, could be a new therapeutic alternative for chemotherapy in gastric cancer, currently treated with different combinations.     

Metabolism of cryptolepine and 2-fluorocryptolepine by aldehyde oxidase

Objectives To investigate the metabolism of cryptolepine and some cryptolepine analogues by aldehyde oxidase, and to assess the implications of the results on the potential of cryptolepine analogues as antimalarial agents. Methods The products resulting from the oxidation of cryptolepine and 2‐fluorocryptolepine by a rabbit liver preparation of aldehyde oxidase were isolated and identified using chromatographic and spectroscopic techniques. The antiplasmodial activity of cryptolepine‐11‐one was assessed against Plasmodium falciparum using the parasite lactate dehydrogenase assay. Key findings Cryptolepine was oxidized by aldehyde oxidase give cryptolepine‐11‐one. Although 2‐fluorocryptolepine was found to have less affinity for the enzyme than cryptolepine, it was a better substrate for aldehyde oxidase than the parent compound. In contrast, quindoline, the 11‐chloro‐ , 2,7‐dibromo‐ and 2‐methoxy analogues of cryptolepine were not readily oxidized. Cryptolepine‐11‐one was found to be inactive against P. falciparum in vitro raising the possibility that the effectiveness of cryptolepine as an antimalarial, may be compromised by metabolism to an inactive metabolite by liver aldehyde oxidase. Conclusions Cryptolepine and 2‐fluorocryptolepine are substrates for aldehyde oxidase. This may have implications for the design and development of cryptolepine analogues as antimalarial agents.     

New thiazolidinedione-5-acetic acid amide derivatives: synthesis, characterization and investigation of antimicrobial and cytotoxic properties

The present work describes the synthesis, antimicrobial and cytotoxic activity of 2,4-thiazolidinedione-5-acetic acid amides 3a–n. The structures of the compounds were confirmed by IR, ¹H, ¹³C NMR and elemental analysis. All compounds were tested for antimicrobial activity by twofold serial dilution technique. The preliminary results revealed that the compound 3d exhibits promising antibacterial and antifungal activity. The cytotoxic (MTT) activity of 2,4-thiazolidinedione-5-acetic acid amides were tested in four tumour cell lines. We found that compound 3j inhibited proliferation of HeLa, HT29, A549 and MCF-7 cell lines with IC₅₀ values of 33, 35, 30 and 36 μM, respectively.     

Asparaginase induces selective dose- and time-dependent cytotoxicity,apoptosis, and reduction of NFκB expression in oral cancer cells

Asparaginase is fundamental to the treatment of haematological malignancies. However, little has been studied on the effects that asparaginase could exert on solid tumours. Thus, this study aimed to evaluate the effects of asparaginase on an oral carcinoma cell line. The cytotoxicity of asparaginase in SCC-9 (tongue squamous cell carcinoma) and HaCaT (human keratinocyte) cell lines was evaluated with MTT cell viability assay. The cells were treated with asparaginase at 0.04, 0.16, 0.63, 1.0, 1.5, 2.5, and 5.0 IU/mL. Dose-response curves and IC₅₀ values were obtained and the Tumour Selectivity Index (TSI) was calculated. The effect of asparaginase on procaspase-3 and nuclear factor κB (NFκB) expression was evaluated with western blot because it was reported that the overexpression of NFκB has been shown to contribute to tumour cell survival, proliferation, and migration. Caspase 3/7 staining was performed to identify cell death using flow cytometry. Effective asparaginase concentrations were lower for SCC-9 cells when compared to HaCaT cells. The cytotoxicity results at 48 and 72 hours were significantly different for SCC-9 cells. The TSI indicated that asparaginase was selective for the tumour cells. A decrease in procaspase-3 and NFκB protein levels was observed in SCC-9 cells. Furthermore, asparaginase resulted in significant apoptosis after 48 and 72 hours. Based on these results, asparaginase was cytotoxic in a dose- and time-dependent manner, induces apoptosis, and reduces NFκB expression in oral cancer cells. These results encourage further studies on the effectiveness of this enzyme as a treatment for solid tumours, especially head and neck cancer.     

Synthesis and identification of a new class of <Emphasis Type="Italic">(S)</Emphasis>-2,6-diamino-4,5,6,7-tetrahydrobenzo[d]thiazole derivatives as potent antileukemic agents

Benzothiazoles are multitarget agents with broad spectrum of biological activity. Among the antitumor agents discovered in recent years, the identification of various 2-(4-aminophenyl) benzothiazoles as potent and selective antitumor drugs against different cancer cell lines has stimulated remarkable interest. Some of the benzothiazoles are known to induce cell cycle arrest, activation of caspases and interaction with DNA molecule. Based on these interesting properties of benzothiazoles and to obtain new biologically active agents, a series of novel 4,5,6,7-tetrahydrobenzo[d]thiazole derivatives 5(a–i) were synthesized and evaluated for their efficacy as antileukemic agents in human leukemia cells (K562 and Reh). The chemical structures of the synthesized compounds were confirmed by ¹H NMR, LCMS and IR analysis. The cytotoxicity of these compounds were determined using trypan blue exclusion, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assays. Results showed that, these compounds mediate a significant cytotoxic response to cancer cell lines tested. We found that the compounds having electron withdrawing groups at different positions of the phenyl ring of the thiourea moiety displayed significant cytotoxic effect with IC₅₀ value less than 60 μM. To rationalize the role of electron withdrawing group in the induction of cytotoxicity, we have chosen molecule 5g (IC₅₀ ~15 μM) which is having chloro substitution at ortho and para positions. Flow cytometric analysis of annexin V-FITC/ propidium iodide (PI) double staining and DNA fragmentation suggest that 5g can induce apoptosis.     

Effects of verapamil enantiomers and major metabolites on the cytotoxicity of vincristine and daunomycin in human lymphoma cell lines

Summary Verapamil, a calcium channel blocker, is used as the racemate. Recently, racemic verapamil has been shown to increase the cytotoxicity of vinca alkaloid and anthracycline derivatives in several resistant tumour cell lines. With respect to its cardiovascular activity S-verapamil is an order of magnitude more potent than R-verapamil. Since it was not known whether the effect on multidrug resistance was also enantioselective a comparison has been made of the potency of the R and S enantiomers and racemic verapamil in their ability to increase the cytotoxicity of vincristine and daunomycin in sensitive (MOLT 4B) and drug resistant human T-lymphoma cell lines (MOLT/VCR-5×9, MOLT/DAU-8 and VCR 1000, a highly resistant subline of CCRF-CEM). Two major metabolites, norverapamil and D617 were tested in the same system.(+)-R, (–)-S-, racemic verapamil, norverapamil and D617 alone had no effect on cell growth in sensitive or resistant cell lines in concentrations up to 20 M. In combination with vincristine, verapamil and norverapamil but not D617 produced a concentration dependent increase in the sensitivity of the resistant lines. Racemic verapamil, its individual enantiomers and norverapamil were equipotent. The concentration of the modifiers required to elicit 50% of the maximum effect (EC₅₀) was of the order of 0.5 M. No significant difference in the slopes of the concentration-effect curves were observed. The effect of verapamil and norverapamil was additive. In the sensitive MOLT 4B cell line both enantiomers and norverapamil increased sensitivity towards vincristine. However, the EC₅₀ values were at least an order of magnitude higher (2.5–8 M) than in the resistant cell lines. In contrast to the vincristine resistant cell lines, no effect on the potentiation of daunomycin cytotoxicity was observed in sensitive and daunomycin-resistant cells in the presence of a modifier. Since the activity of verapamil as a modifier of drug resistance is not enantioselective, the weaker calcium antagonist R-enantiomer appears to be better suited for clinical trials. Because of its lesser cardiovascular activity much higher doses could be given, and a higher plasma concentration would be achieved. As norverapamil, the major plasma metabolite formed during first pass elimination, is as potent as the parent drug as a modifier of drug resistance, the oral route of administration is preferable to i. v. administration in clinical trials employing R-verapamil as a modifier.Presented in part at the 30^th Spring Meeting of the Deutsche Gesellschaft für Pharmakologie und Toxikologie, Mainz, 1989, and at the IV. World Conference on Clinical Pharmacology and Therapeutics, Mannheim-Heidelberg, 1989     

Synthesis of piperine–amino acid ester conjugates and study of their cytotoxic activities against human cancer cell lines

Abstract  

A series of piperine–amino acid ester conjugates (4a–4r) were synthesized under mild conditions and screened for their cytotoxic activities against a panel of human cancer cell lines (IMR-32, MCF-7, PC-3, DU-145, Colo-205, and Hep-2). The parent compound piperine lacked significant activity but the analogues were effective to in all tested human cancer cell lines. The introduction of d- and l-amino acid side chain to piperine through peptide linkage significantly increased cytotoxic activity. Among the tested conjugates, 4p showed significant cytotoxic activity against DU-145 cell lines with IC₅₀ of 21 μM. The synthetic protocol is suitable for generating piperine derivatives with various structural motifs for exploring the desired activity.     

Erratum to: Use of two validated in vitro tests to assess the embryotoxic potential of mycophenolic acid

Mycophenolate mofetil is a widely used immunosuppressive drug that recently has been categorized as a human teratogen. Animal experiments indicate a teratogenic potential of the drug, but so far, it has not been studied in embryotoxicity in vitro assays. The aim of this study was to evaluate the in vitro embryotoxic potential of mycophenolic acid and investigate the ability of such tests to detect its embryotoxic potential. We used two validated assays: the rat whole embryo culture and the murine embryonic stem cell test. Rat embryos cultured from gestational day 9.5 for 48 h with the drug showed dysmorphogenic development already at a concentration of 250 μg mycophenolic acid/l medium. At concentrations of 750 μg/l and more, all rat embryos exhibited malformations. The main effects were defective yolk sac blood circulation, neural tube defects (open cranial neural pore), malformations of the head with missing eye anlagen and heart anomalies. Moreover, the exposed embryos showed a concentration-dependent decrease in protein content, crown-rump length, number of somites and morphological score. The murine embryonic stem cell test was slightly more sensitive. Proliferation and differentiation of the ES-D3-cells were significantly impaired at concentrations of 31 and 125 μg mycophenolic acid/l medium, respectively. In the differentiation assay, at a concentration of 125 μg mycophenolic acid/l medium and more, the number of wells with differentiated cardiomyocytes significantly decreased. Additionally, a cytotoxicity assay with balb/c 3T3 mouse fibroblasts was used to compare the proliferation and vitality of embryonic cells with adult cells. In the balb/c 3T3 cytotoxicity assay, the number of vital mouse fibroblasts significantly decreased at a mycophenolic acid concentration of 62 μg/l and more. In conclusion, by using the two validated in vitro tests, we showed that mycophenolic acid exhibits a pronounced embryotoxic potential at cytotoxic concentrations. This result from validated in vitro tests is of special interest, because it supports the use of the tests to detect human teratogens.     

Comparison of the cytotoxic effect of lapachol, α-lapachone and pentacyclic 1,4-naphthoquinones on human leukemic cells

The pentacyclic 1,4-naphthoquinones 1a–d were cytotoxic (IC₅₀ ∼ 2–7 μM) to human leukemic cell lines K562 (oxidative stress-resistant), Lucena-1 (MDR phenotype) and Daudi. Fresh leukemic cells obtained from patients, some with the MDR phenotype, were also sensitive to these compounds. The pentacyclic 1,4-naphthoquinones 1a and 1c induced apoptotic cell death in cells from leukemic patients as determined by flow cytometry. Conversely, the cell lines were highly insensitive to lapachol (2) and α-lapachone (3). Mitomycin-C inhibited cell proliferation at concentrations as low as 0.5 μM. The low toxicity against lymphocytes activated by phytohemagglutinin shows that these compounds are selective for the cancer cells studied. Previous data suggest that these compounds (1a–d) can be bioactivated in situ by reduction followed by rearrangement leading to enones, which are powerful alkylating agents. In contrast, lapachol (2) and β-lapachone (3), which cannot be bioactivated by reduction, showed little activity against the same cell lines.     

Relative sensitivity of fish and mammalian cells to the antibiotic, trimethoprim: cytotoxic and genotoxic responses as determined by neutral red retention, Comet and micronucleus assays

Relative cytotoxicity and genotoxicity of a widely used antibiotic, trimethoprim (TRIMP) was evaluated under in vitro conditions using rainbow trout gonad-2 (RTG-2) and Chinese hamster ovary-K1 (CHO-K1) cells. Whilst cytotoxicity was determined using neutral red retention (NRR) assay, the genotoxicity was determined using single cell gel electrophoresis or the Comet assay and cytokinesis-block micronucleus (CBMN) assay. For NRR assay, concentration-dependent cytotoxic effect was observed for both the cell lines (estimated EC₅₀ values: 671.82 ± 21.78 and 611.6 ± 20.4 μg ml⁻¹ for RTG-2 and CHO-K1 cells, respectively). There was no statistically significant difference between the two cell lines for this assay. For the Comet assay, standard 6 h exposure to TRIMP did not show any positive response for any of the cell types used. However, 48 h exposure to RTG-2 cells showed a concentration-dependent induction of DNA damage (r = 0.86). The highest concentration of TRIMP used (i.e. 100 μg ml⁻¹) showed relatively higher DNA damage, compared to ethyl methane sulfonate (EMS; 1 μg ml⁻¹ or 8 mM), a reference genotoxic agent, used concurrently. In contrast, 24 h exposure time for CHO-K1 cells did not show any concentration-dependent increase for this assay. For MN assay, a significant correlation was found between the MN induction and TRIMP concentration for both the cell lines (RTG-2: r = 0.68; CHO-K1: r = 0.79), although only the highest concentration used showed a significant increase for binucleated (BN) cell with micronuclei (BNMN). The study suggests that whilst the cells of different origin could exhibit similar cytotoxicity, they could display differential genotoxic effects. Furthermore, genotoxic effects of TRIMP are primarily exposure period dependent phenomena and, in addition to inhibiting the action of dihydrofolate reductase, oxidative stress could also contribute for the observed toxic effects, fish cells in general being more sensitive for genotoxic effects.     

The influence of tumour microenvironmental factors on the efficacy of cisplatin and novel platinum(IV) complexes

The chemotherapeutic drug cisplatin is an important treatment for many types of solid tumours, in particular non-small cell lung cancer (NSCLC). Platinum(IV) complexes offer several advantages to cisplatin due to their requirement for reduction to the active platinum(II) form to elicit cytotoxicity. This should minimise non-specific effects and facilitate higher amounts of the active complexes reaching the target DNA. Hypoxia and a quiescent cell population are features of the tumour microenvironment known to lead to resistance to many chemotherapeutic agents. It is unclear how these microenvironmental factors will impact on the efficacy of novel platinum(IV) complexes. Consequently, the cytotoxicities of several platinum drugs were determined in monolayer and tumour spheroid cultures derived from NSCLC lines. Platinum(IV) reduction potential correlated well with cytotoxicity. The complex containing a chloro axial ligand demonstrated the greatest potency and the drug with the hydroxy ligand was the least effective. Although drug cytotoxicity was not enhanced under hypoxic conditions, both cisplatin and the platinum(IV) complexes retained full potency. In addition, all of the platinum drugs retained the ability to evoke apoptosis in quiescent cells. In summary, unlike many anticancer drugs, the platinum(IV) complexes retain cytotoxic potency under resistance-inducing tumour microenvironmental conditions and warrant further investigation as more selective alternatives to current platinum-based therapy for the treatment of solid tumours.     

Cytotoxic,Antitumour and Antimetastatic Activity of Two New Polyacetylenes Isolated from Vernonia scorpioides (Lam.) Pers

Vernonia scorpioides (Lam.) Pers., popularly known as Enxuga, Erva‐de‐São Simão and Piracá, has been used in folk medicine for its anti‐inflammatory, wound healing and antimicrobial properties. Two polyacetylenes, 5‐octa‐2,4,6‐triynyl‐furan‐2(5H)‐one ( 1 ) and 8′‐hydroxy 3‐4 dihydrovernoniyne ( 2 ), were isolated from the dichloromethane extract fraction of V. scorpioides. In this study, polyacetylene 1 demonstrated a more potent cytotoxic activity than 2 in the tumour cell lines examined, and cytotoxicity was found to be comparable to a commercial drug (p > 0.05) in melanoma cells. No significant cytotoxic effect was observed in normal cell lines. Furthermore, polyacetylene 1 induced an in vitro increase in caspase‐3 activity in B16F10 cells. When polyacetylene 1 was administered intraperitoneally (i.p.) in mice, a reduction in solid tumour volume and metastasis was observed in mice injected with B16F10 cells. An increase in locomotor activity was also observed in mice with solid tumours, and an inhibition of mechanical hypersensitivity was observed in a mouse model of metastasis. Notably, no significant morphological change was observed in several organs harvested from the treated mice. In conclusion, in vitro and in vivo anticancer activity of polyacetylene 1 was consistently observed and involved the induction of apoptosis by the activation of caspase‐3. The anticancer activity demonstrated by polyacetylene 1 , together with the absence of preliminary toxicological effects, represents a new and interesting option for the management of neoplastic disease.     

Cytotoxicity of sphingoid marine compound analogs in mono- and multilayered solid tumor cell cultures

Summary A subset of four synthetic sphingoid marine compound analogs was chosen from a preliminary in vitro cytotoxicity study for further analysis. The selected analogs were initially screened in monolayer cultures for their anticancer potential against a panel of eight human tumor cell lines, ovarian, colon and lung cancer, squamous cell carcinoma and leukemia producing IC₅₀ values ranging from 1.5 to 6.9 μM. In a secondary screening, the sphingoid analogs were evaluated against multilayered postconfluent cultures of A2780 ovarian cancer and WiDr colon cancer cells. In this model, compounds 5 and 8 were the most active derivatives showing EC₅₀ values in the range 25–32 μM. The performance of 5 and 8 against both cell lines was not dependent on the cell culture model as shown with resistance factor values in the range 8–12. Cell cycle studies in HL60 leukemia cells showed an arrest in G ₀/G ₁ at a low drug concentration (3 μM) but accumulation in S phase at a high drug concentration (9 μM). It can be concluded that the analogs showed a cell line independent activity, with an apparent selectivity against cells grown in more physiological three-dimensional condition compared to standard anticancer drugs.