Selective Antitumour Agent Research Articles

Antitumour, acute toxicity and molecular modeling studies of 4-(pyridin-4-yl)-6-(thiophen-2-yl) pyrimidin-2(1H)-one against Ehrlich ascites carcinoma and sarcoma-180

In an effort to discover an effective and selective antitumour agent, synthesis and anti-cancer potential of 4-(pyridin-4-yl)-6-(thiophen-2-yl) pyrimidin-2(1H)-one (SK-25), which has been reported earlier by us with significant cytotoxicity towards MiaPaCa-2 malignant cells, with an IC50 value of 1.95 μM and was found to instigate apoptosis. In the present study, the antitumour efficacy of SK-25 was investigated on Ehrlich ascites tumour (EAT, solid), Sarcoma 180 (solid) tumour and Ehrlich ascites carcinoma. The compound was found to inhibit tumour development by 94.71% in Ehrlich ascites carcinoma (EAC), 59.06% in Ehrlich tumour (ET, solid) and 45.68% in Sarcoma-180 (solid) at 30 mg/kg dose. Additionally, SK-25 was established to be non-toxic at a maximum tolerated dose of 1000 mg/kg in acute oral toxicity in Swiss-albino mice. Computer-based predictions also show that the compounds could have an interesting DMPK profile since all 51 computed physicochemical parameters fall within the recommended range for 95% of known drugs. The current study provides insight for further investigation of the antitumour potential of the molecule.

Synthesis, structure elucidation and identification of antiproliferative activities of a novel class of thiophene bioisosteres bearing the privileged 7,8-dihydroimidazo[2,1-c][1,2,4]triazin-4(6H)-one scaffold

The straightforward and practical synthesis route and remarkable antitumour activities in vitro of a novel class of thiophene bioisosteres (10–18) are disclosed. These molecules were obtained with good overall yields via the reaction of 1-aryl-2-hydrazonoimidazolidine hydroiodides with ethyl 2-oxo-2-(2-thienyl)acetate in the presence of triethylamine in refluxing DMF/methanol mixture. All the synthesized compounds proved to be markedly effective against human tumour cells: A549, HeLa, T47D and TOV112D and more cytotoxic than pemetrexed against A549, HeLa and T47D cells. Among these strongly antiproliferative active molecules, the disclosed three thiophene bioisosteres (11, 17 and 18) are proposed as the most promising anticancer lead structures for the rational design of more selective antitumour agents because they proved to be markedly lower cytotoxic towards normal than tumour cells. Results from the bioassay based on a double fluorochrome staining were worthy to be described because they provide a clue to the mode of action of one (18) of the most promising anticancer lead structures of the series.

Synthesis, structure elucidation and in vitro anticancer activities of novel derivatives of diethyl (2E)-2-[(2E)-(1-arylimidazolidin-2-ylidene)hydrazono]succinate and ethyl (4-oxo-8-aryl-4,6,7,8-tetrahydroimidazo[2,1-c][1,2,4]triazin-3-yl)acetate

The worked out and optimized synthesis routes and remarkable antitumour activities in vitro of novel polynitrogenated derivatives of diethyl (2E)-2-[(2E)-(1-arylimidazolidin-2-ylidene)hydrazono]succinate (7–10) and ethyl (4-oxo-8-aryl-4,6,7,8-tetrahydroimidazo[2,1-c][1,2,4]triazin-3-yl)acetate (11–16) are presented. Small molecules based on the privileged 7,8-dihydroimidazo[2,1-c][1,2,4]triazin-4(6H)-one scaffold (11–16) were obtained with fairly modest to good overall yields by very facile addition reactions of the nucleophilic centred 1-aryl-2-hydrazonoimidazolidine hydroiodides to diethyl acetylenedicarboxylate (DEAD) in the presence of triethylamine (TEA) and a subsequent cyclocondensation of the putative intermediate chain hydrazones. Heterobicyclic products 12 and 14–16 could also be prepared in high overall yields by an effective intramolecular cyclocondensation of the isolated stable and antiproliferative active heterocyclic hydrazones, namely, diethyl (2E)-2-[(2E)-(1-arylimidazolidin-2-ylidene)hydrazono]succinates (7–10), performed in refluxing DMF. These intermediates are the first products to be formed in the result of an addition of the nucleophilic reactants, namely, 1-aryl-2-hydrazonoimidazolidines of the 1–6 type, bearing the basic nitrogen atom of the hydrazono moiety (N–NH2), to the carbon–carbon triple bond of the highly electrophilic alkyne, that is, DEAD. Molecular structures of the synthesized compounds (7–16) in the DMSO-d6 solutions were verified by 1H NMR and 13C NMR spectral data. These were finally confirmed based on the advanced 2D HMBC and HMQC NMR experiments, which were performed for the two representatives (8 and 11) of the two synthesized sets of the bioactive substances. Among the majority of antiproliferative active molecules, the disclosed herein ethyl [4-oxo-8-(3-chlorophenyl)-4,6,7,8-tetrahydroimidazo[2,1-c][1,2,4]triazin-3-yl]acetate (14) is proposed as a promising lead structure for the design of novel highly selective antitumour agents because of the distinctly marked lower cytotoxicity towards the primary cell line of normal HSF cells and several-fold higher against cancer cells used. A double fluorochrome mix-staining was performed in order to find out about the possible mode of action by which this novel small heterobicycle reveals remarkable antiproliferative effects in vitro. Taking into account the obtained double staining results, this small molecule was identified as capable of inducing significantly higher levels of necrotic cells in human cancer cell lines (T47D and HeLa) than in normal HSF cells. Furthermore, its cytotoxicity against cells was found to be connected to the predominant induction of necrosis over apoptosis.

VDAC Phosphorylation in Control of Mitochondrial Respiration

Tubulin has been recently identified as a powerful regulator of voltage dependent anion channel (VDAC). Dimeric tubulin induces reversible blockage of VDAC reconstituted into planar lipid membranes and blocks the flux of ATP/ADP across the mitochondrial outer membrane. Here we show that phosphorylation of VDAC by cytosolic kinases protein kinase A (PKA) and glycogen synthase kinase-3β (GSK3β) increases the on-rate of tubulin binding by orders of magnitude, but only for tubulin at the cis (or cytosolic) side of the membrane. This and the fact that the basic properties of VDAC, such as single-channel conductance and selectivity, remained unaltered by phosphorylation allowed us to suggest the phosphorylation regions positioned on the cytosolic loops of VDAC and establish channel orientation in our reconstitution experiments. Experiments on human hepatoma cells HepG2 are in agreement with our findings that phosphorylation state of VDAC determines its blockage by tubulin. When HepG2 cells were treated with the microtubule-destabilizing agent colchicine that is known to increase free tubulin, mitochondrial potential, as measured by tetramethylrhodamine methyester (TMRM) uptake, decreased. Inhibition of PKA activity with H89 increased mitochondrial potential and, furthermore, reversed mitochondrial depolarization induced by colchicine. To further explore a role VDAC-tubulin interaction in cell proliferation and survival, we studied the effect of erastin, the selective anti-tumour agent involved in the RAS-RAF-MEK signalling pathway, on VDAC blockage by tubulin. We found that erastin reverses tubulin blockage of VDAC isolated from HepG2 cells, promoting the unblocked state of the channel. Our findings suggest a novel functional link between serine/threonine kinase signalling pathways, mitochondrial respiration, and highly dynamic microtubule network which is characteristic of carcinogenesis and cell proliferation.

Synthesis and antitumour evaluation of novel 2-phenylbenzimidazoles

A new series of fluorinated and non-fluorinated 2-phenylbenzimidazoles bearing oxygenated substituents on the phenyl ring has been synthesized. Synthesis of the new series was based on our previous discovery of 2-(3,4-dimethoxyphenyl)-5-fluorobenzothiazole (PMX 610) as a potent and selective antitumour agent in vitro (sub-nanomolar GI50 in sensitive human cancer cell lines), but with poor aqueous solubility and lack of a definitive cellular target limiting further development. In this study we test the hypothesis that 2-phenylbenzimidazoles with similar substitution patterns to PMX 610 would retain potent antitumour activity but with potentially superior pharmaceutical properties. In general the new compounds were less active than the former benzothiazole series in vitro when tested against the breast cancer cell lines MCF-7 and MDA 468; however the two most active compounds in the present series (3j and 3k) exhibit low micromolar GI50 values in both cell lines and provide the opportunity for further chemical derivatization with a view to target identification.

RAS–RAF–MEK-dependent oxidative cell death involving voltage-dependent anion channels

Therapeutics that discriminate between the genetic makeup of normal cells and tumour cells are valuable for treating and understanding cancer. Small molecules with oncogene-selective lethality may reveal novel functions of oncoproteins and enable the creation of more selective drugs. Here we describe the mechanism of action of the selective anti-tumour agent erastin, involving the RAS-RAF-MEK signalling pathway functioning in cell proliferation, differentiation and survival. Erastin exhibits greater lethality in human tumour cells harbouring mutations in the oncogenes HRAS, KRAS or BRAF. Using affinity purification and mass spectrometry, we discovered that erastin acts through mitochondrial voltage-dependent anion channels (VDACs)--a novel target for anti-cancer drugs. We show that erastin treatment of cells harbouring oncogenic RAS causes the appearance of oxidative species and subsequent death through an oxidative, non-apoptotic mechanism. RNA-interference-mediated knockdown of VDAC2 or VDAC3 caused resistance to erastin, implicating these two VDAC isoforms in the mechanism of action of erastin. Moreover, using purified mitochondria expressing a single VDAC isoform, we found that erastin alters the permeability of the outer mitochondrial membrane. Finally, using a radiolabelled analogue and a filter-binding assay, we show that erastin binds directly to VDAC2. These results demonstrate that ligands to VDAC proteins can induce non-apoptotic cell death selectively in some tumour cells harbouring activating mutations in the RAS-RAF-MEK pathway.

The discovery of the potent and selective antitumour agent 2-(4-amino-3-methylphenyl)benzothiazole (DF 203) and related compounds.

The development of a series of potent and selective antitumour agents, the 2-(4-aminophenyl)benzothiazoles, is described. The original lead compound in this series, CJM 126, exhibits nanomolar in vitro activity against certain human breast cancer cell lines. Structure-activity relationship studies within this simple antitumour benzothiazole pharmacophore revealed that 2-(4-aminophenyl) benzothiazoles bearing a 3'- methyl, 3'-bromo, 3'-iodo or 3'-chloro substituent are especially potent, extending the spectrum of in vitro antitumour activity to ovarian, lung, renal and colon carcinoma cell lines with a remarkable selectivity profile (NCI analysis). Other interesting features of this series include the highly unusual transient biphasic dose response relationship and possible unique mechanism of action (NCI COMPARE analysis). 2-(4-Amino-3-methylphenyl)benzothiazole (DF 203) has been selected as the lead compound in this series on the basis of superior in vivo results

Synthesis and antineoplastic activity of cyclolignan aldehydes

Several aldehydes related to methyl 9-deoxy-9-oxo-α-apopicropodophyllate, a selective antitumour agent against the HT-29 colon carcinoma, have been prepared and evaluated for their cytotoxic activities on four neoplastic cell lines (P-388, A-549, HT-29 and MEL-28). All of them lacked the lactone ring but maintained their cytotoxicity at, or under, the μM level.

Anti-tumour activity in vitro and in vivo of selective differentiating agents containing hydroxamate.

A series of hydroxamates, which are not metalloprotease inhibitors, have been found to be selectively toxic to a range of transformed and human tumour cells without killing normal cells (fibroblasts, melanocytes) at the same concentrations. Within 24 h of treatment, drug action is characterized by morphological reversion of tumour cells to a more normal phenotype (dendritic morphology), and rapid and reversible acetylation of histone H4 in both tumour and normal cells. Two hydroxamates inhibited growth of xenografts of human melanoma cells in nude mice; resistance did not develop in vivo or in vitro. A third hydroxamate, trichostatin A, was active in vitro but became inactivated and had no anti-tumour activity in vivo. Development of dendritic morphology was found to be dependent upon phosphatase activity, RNA and protein synthesis. Proliferating hybrid clones of sensitive and resistant cells remained sensitive to ABHA, indicating a dominant-negative mechanism of sensitivity. Histone H4 hyperacetylation suggests that these agents act at the chromatin level. This work may lead to new drugs that are potent, and selective anti-tumour agents with low toxicity to normal cells. © 1999 Cancer Research Campaign

Structural and solution chemistry of gold(I) and silver(I) complexes of bidentate pyridyl phosphines: selective antitumour agents

The 1:2 adducts of Ag(I) and Au(I) with 1,2-bis(di- n-pyridylphosphino)ethane (d npype) for n=2, 3 and 4 have been synthesised and solution properties characterised by multinuclear NMR spectroscopy. The complexes are hydrophilic analogs of the lipophilic Au(I) antitumour complex [Au(dppe) 2] + and the degree of hydrophilicity depends critically on the position of the N atom in the pyridyl ring. The complexes of d3pype and d4pype are simple monomeric [M(d3pype) 2] + and [M(d4pype) 2] + species which have a much higher water solubility than the 2-pyridyl complexes which crystallise in the solid state as dimeric [{M(d2pype) 2} 2] 2+. In solution these 1:2 M:d2pype species exist as equilibrium mixtures of monomeric, dimeric and trimeric (Ag) or tetrameric (Au) clusters. The Au(I) and Ag(I)pyridyl phosphine complexes have been evaluated for antitumour activity against a panel of cultured human ovarian carcinoma cell lines. The results show both potent and selective activity for the compounds with IC 50 values ranging from 0.18 to 1500 μM. There is a correlation between the degree of antitumour selectivity and the octanol/water partition coefficients with the greatest selectivity (500-fold range) found for the most hydrophilic complex [Au(d4pype) 2]Cl. Clinical development of the parent compound [Au(dppe) 2] + was halted by liver toxicity and the hydrophilic pyridylphosphine analogs are significantly less toxic than [Au(dppe) 2] + when exposed to isolated rat hepatocytes. Convenient synthetic routes to the bidentate pyridyl phosphines d2pype, d3pype and d4pype are also described.

1-Naphthol: A potential selective antitumour agent

1-Naphthol: A potential selective antitumour agent

Cytotoxic sulphonamides designed for selective deposition in malignant tissue

The tumour and liver concentrations of a range of sulphonamides of different pKa values have been measured. Although a number of them concentrated to a much greater extent in the mouse plasma cell tumour than in liver, no correlation was observed between this property and pKa value. A series of dimethyltriazenes were prepared from the sulphonamides and tested for their anti-tumour activity. Two dimethyltriazenes derived from sulphamerazine and sulphapyridine are highly selective anti-tumour agents but no evidence was obtained that this effect was due to their selective concentration in tumours. In tests against the TLX 5 lymphoma, a phenyltriazene was shown to be dose-schedule dependent, daily administration of the compound being more effective than single doses. The biological half-life of the phenyltriazenes was shown to be of importance in determining their anti-tumour effects, agents with longer half-lives being more active than agents of shorter half-lives.

Enzyme activated anti-tumor agents conjugates of p-hydroxyaniline mustard as substrates for hydrolytic enzymes

The O-phosphate, O-sulphate and O-glucuronide of p-hydroxyaniline mustard were synthesised with the objective that they might be selective anti-tumour agents for tumours with high levels of phosphatase, sulphatase and glucuronidase respectively. This paper shows that the O-phosphate and O-glucuronide can be deconjugated by the appropriate enzymes in vitro to release the rapidly reacting p-hydroxyaniline mustard. The O-sulphate however proved refractory to hydrolysis by all aryl sulphatases tested.