Oxadiazole compound shows potent selectivity against oligodendroglioma cells

Researchers have synthesized a series of 1,3,4-oxadiazole derivatives and evaluated their anticancer potential against HS683 human oligodendroglioma cells, identifying one compound, designated B2, as a lead candidate with an IC50 of 37.71 µg/mL and a selectivity index of 14.55. The findings, published in Pharmacia, position this thienyl-substituted oxadiazole as a promising starting point for the development of new anti-glioma agents, particularly given the unmet therapeutic need in oligodendroglioma, a molecularly distinct subtype of adult-type diffuse glioma characterized by an IDH mutation and 1p/19q codeletion.

The 1,3,4-oxadiazole ring is a five-membered heterocycle comprising one oxygen and two nitrogen atoms, widely investigated in medicinal chemistry for its aromatic stability and bioisosterism with the carbonyl group in amides and esters. Heterocyclic scaffolds make up more than 85 percent of FDA-approved drug molecules, owing to their ability to form various intermolecular interactions including hydrogen bonding, metal coordination, π–π stacking, hydrophobic interactions, and van der Waals contacts. Several biological activities have been reported for 1,3,4-oxadiazoles, including antimicrobial, anti-inflammatory, antioxidant, and anticancer effects, with reported anticancer mechanisms including inhibition of growth factor receptors such as EGFR and VEGFR and induction of apoptosis in several tumor types. However, oxadiazole-based compounds had not previously been explored specifically for oligodendroglioma.

The synthesis proceeded through acid-catalyzed condensation of the appropriate hydrazides with aromatic aldehydes in absolute ethanol under reflux to afford hydrazone intermediates, which were then oxidatively cyclized using iodine and potassium carbonate in dimethyl sulfoxide at 100 °C for three to six hours to yield the final oxadiazole derivatives. Seven compounds were produced, designated A1 through A3 and B1 through B4, with the A series bearing a 5-chloro-2-nitrophenyl substituent and the B series bearing a 4-cyanophenyl substituent at the C-5 position of the oxadiazole ring. Characterization was carried out by FT-IR, proton NMR, carbon-13 NMR, and electron ionization mass spectrometry, with the infrared spectra supporting complete ring closure by the disappearance of the N–H stretching band and the amide carbonyl C=O stretching band of the hydrazones, alongside the appearance of characteristic C=N stretching of the oxadiazole ring and C–O–C asymmetric stretching.

Biological evaluation used the MTT colorimetric assay, which is based on the reduction of a yellow tetrazolium salt by mitochondrial dehydrogenase enzymes in metabolically active cells, producing an insoluble purple formazan product whose absorbance correlates directly with cell viability. Cells were plated at 10,000 cells per well in 96-well microplates, incubated for 24 hours, and exposed to serial concentrations of the test compounds ranging from 10 to 1,000 µg/mL, with cisplatin run in parallel as a reference drug. The IC50 values of all seven compounds were lower than that of cisplatin, which recorded an IC50 of 212.27 µg/mL against HS683 cells. Compounds bearing the 4-cyanophenyl group at C-5 were consistently more active than their A analogs, with IC50 values approximately half those of the matched pairs.

The selectivity index, calculated as the ratio of the IC50 against normal human astrocytes to the IC50 against HS683 cells, showed a clear advantage of the synthesized compounds over cisplatin, whose SI of 1.25 indicates near-equal toxicity toward tumor and normal cells. All seven compounds gave SI values greater than 1, with B2 achieving the highest SI of 14.55, followed by A2 with an SI exceeding 12.15, whose IC50 against normal human astrocytes exceeded 1,000 µg/mL, indicating minimal toxicity toward healthy brain cells. This favorable selectivity profile is particularly significant given that treatment-related adverse effects remain difficult to manage with current oligodendroglioma therapies, which typically involve radiotherapy and chemotherapy with temozolomide or the PCV regimen in conjunction with surgical resection.

Structure–activity relationship analysis revealed that the thiophen-2-yl group at the C-2 position produced the lowest IC50 values in both series, lower than those of their phenyl-substituted counterparts. Within compounds B, the activity order was B2 with the thienyl substituent, followed by B1 with pyridin-4-yl, B4 with 4-methylphenyl, and B3 with 4-fluorophenyl. Notably, pyridin-4-yl was the least active substituent among compounds A but the second-most active among compounds B, indicating that its contribution to activity depends on the electronic and steric character of the C-5 substituent. The thienyl compounds also possessed the highest selectivity indices in both series, suggesting that the thiophen-2-yl group was beneficial not only for cytotoxic potency but also for selectivity toward HS683 cells over normal astrocytes.

Molecular docking studies were performed against three kinase targets selected for their relevance to glioma pathogenesis: phosphatidylinositol 3-kinase alpha, cyclin-dependent kinase 2, and focal adhesion kinase. PI3Kα was included because of its role in the PI3K/AKT/mTOR pathway, CDK2 was included because of its overexpression in low-grade glioma subtypes, and FAK was selected based on its overexpression in glioma. The docking protocol was validated by re-docking the co-crystallized ligands, with root-mean-square deviation values all below 2.0 Å, confirming that the computational approach reliably reproduced experimental binding modes. Against PI3Kα, compounds B1 and B2 formed the strongest predicted interactions in the study, both forming hydrogen-acceptor contacts with LYS890 at distances of approximately 2.95 Å, with per-contact interaction energies of −9.0 and −8.8 kcal/mol respectively, involving the nitrile nitrogen of the 4-cyanophenyl group.

Against CDK2, compounds A produced scores of −6.654 to −7.087 kcal/mol, while compounds B ranged from −5.914 to −6.101 kcal/mol. B1 formed the richest interaction network among compounds B, with six contacts including two hydrogen-donor/acceptor interactions with LEU83 and PHE82, two hydrogen-acceptor contacts with LYS129 and ASN132, and a π–H contact with ILE10. B2 achieved a hydrogen-donor interaction between its sulfur atom and ASP145, suggesting that the sulfur atom of the thiophen-2-yl group is directly involved in the interaction. Against FAK, A2 achieved the strongest score among the synthesized compounds, and in both A2 and B2 the oxadiazole ring nitrogens served as the primary interaction atoms, forming two hydrogen-acceptor contacts with CYS502. This sulfur-specific contact with ASP145 was not observed for the phenyl- or heteroaryl-substituted analogs, providing a computational rationale for the superior activity of the thienyl compounds.

All seven compounds satisfied Lipinski’s rule of five, with molecular weights ranging from 248.24 to 319.68 g/mol and cLogP values ranging from 2.13 to 3.25, indicating moderate lipophilicity suitable for membrane permeation. The synthesized compounds had no hydrogen-bond donors and four to six hydrogen-bond acceptors, all below the maximum recommended limit. Topological polar surface area values ranged from 62.71 to 112.98 Ų, with compounds A showing higher values than compounds B. All final compounds were predicted to have high gastrointestinal absorption, and none were predicted to act as P-glycoprotein substrates, which may indicate a lower likelihood of efflux-mediated resistance. Notably, B1, B3, and B4 were predicted to permeate the blood–brain barrier, a relevant physicochemical feature for compounds intended to target glioma, although these predictions reflect theoretical permeability rather than confirmed central nervous system distribution and would require experimental validation.

The authors acknowledge that the proposed kinase targets are based on molecular docking and require experimental confirmation, and that further evaluation across additional glioma cell lines and in vivo models would help establish the broader therapeutic relevance of B2. Within the context of prior research, thioacetamide-based 1,3,4-oxadiazole derivatives have shown activity against C6 rat glioma cells, while ferulic acid- and caffeic acid-based oxadiazole hybrid derivatives have demonstrated activity against human glioblastoma cell lines U87, T98G, and LN229. Oxadiazole-based Akt/FAK inhibitors have also shown cytotoxic effects against C6 cells, supporting the relevance of FAK as a target within this chemical class. B2 extends this body of evidence to a previously unexamined glioma cell line and substituent pattern, reinforcing its potential as a lead candidate for future anti-glioma development.

Subject of Research: 1,3,4-Oxadiazole derivatives as potential anti-glioma agents: synthesis, characterization, in vitro cytotoxic activity against HS683 cells, and molecular docking

Article Title: 1,3,4-Oxadiazole derivatives as potential anti-glioma agents: synthesis, characterization, in vitro cytotoxic activity against HS683 cells, and molecular docking

Article References: Hashim, R. J., Alsaad, H. N., & Salman, H. H. (2026). 1,3,4-Oxadiazole derivatives as potential anti-glioma agents: synthesis, characterization, in vitro cytotoxic activity against HS683 cells, and molecular docking. Pharmacia, 73, Article e198079. https://doi.org/10.3897/pharmacia.73.e198079

Image Credits: AI Generated

DOI: 10.3897/pharmacia.73.e198079

Keywords: 1,3,4-oxadiazole, anti-glioma agents, HS683, oligodendroglioma, molecular docking, MTT assay, selectivity index, drug-likeness, medicinal chemistry, kinase inhibitors, Oxadiazole, derivatives