Siderol Inhibits Proliferation of Glioblastoma Cells and Acts Synergistically with Temozolomide.

Glioblastoma (GBM) is the most aggressive primary central nervous system (CNS) tumor in adults with dismal prognosis. Currently, the therapeutic interventions include gross total resection, when possible, followed by radiotherapy and chemotherapy. However, despite treatment, tumor usually recurs within 7-9 months. The presence of glioma cells with stem-like properties and tumor's heterogeneity have been identified as the most important factors driving recurrence. Recently, research efforts have been focused on the use of natural substances as treatment for GBM. Siderol is an ent-kaurane diterpenoid, isolated from the genus Sideritis. Sideritis extracts have already been investigated for their anti-inflammatory, antioxidant, and anticancer effects. In this study, we investigated the antitumoral effects of siderol in GBM T98 and U87 cell lines, as well as the effects of combined treatment with temozolomide (TMZ). Cell viability was evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and trypan blue exclusion assay. Different concentrations of siderol were used in order to calculate the IC50 values at 72 h after treatment. Flow cytometry used for the DNA cell cycle analysis after treatment with siderol in concentrations of IC50 and twice the IC50 values for 72 h. Furthermore, the effect of siderol in cell's migratory ability was tested using wound healing assay. Cell viability and proliferation, after combined treatment with siderol and TMZ, also were evaluated with the trypan blue exclusion assay and the effects of the combination treatment were analyzed with CompuSyn software. Treatment with siderol significantly reduced cell viability in T98 and U87 cell lines in a dose-dependent manner and IC50 values were calculated, 18 µM and 13 µM, respectively. Moreover, siderol induced G0/G1 cell cycle arrest in a dose-dependent manner and inhibited the migration in both cell lines. In addition, siderol and TMZ seem to have synergistic action in the majority of tested concentrations in both T98 and U87 cells. In conclusion, siderol may represent an innovative strategy for the treatment of GBM, and further studies are needed on siderol's efficacy and mode of action.

Preparation and Evaluation of Siderol Amorphous Solid Dispersions: Selection of Suitable Matrix/Carrier.

The present study investigates the preparation of amorphous solid dispersions (ASD) for the ent-kaurane diterpenoid siderol (SDR). Initially, evaluation of the pure drug (isolated from Sideritis scardica) revealed that the API is a non-stable glass former, and hence the selection of a suitable ASD's matrix/carrier needs special attention. For this reason, four commonly used polymers and copolymers, namely poly(vinylpyrrolidone), copovidone, hydroxypropyl cellulose, and Soluplus® (SOL), were screened via film casting and crystal growth rate measurements. Amongst them, SOL showed the highest SDR's crystal growth rate reduction, and, since it was also miscible with the drug, it was selected for further testing. In this direction, SDR-SOL ASDs were successfully prepared via melt-quench cooling. These formulations showed full API amorphization, while good physical stability (i.e., a stable SDR amorphous dispersions) were obtained after storage for several months. Finally, evaluation of molecular interactions (with the aid of ATR-FTIR spectroscopy) showed strong H-bonds between SOL and SDR, while the use of molecular dynamics (MD) simulations unraveled the nature of these interactions. Therefore, based on the findings of the present work, SOL seems to be an appropriate matrix/carrier for the preparation of SDR ASDs, although further studies are needed in order to explore its full potentials.

Preparation and Evaluation of Amorphous Solid Dispersions for Enhancing Luteolin's Solubility in Simulated Saliva.

Luteolin (LUT), a bioactive flavonoid, possesses various pharmacological properties, including antioxidant, antimicrobial, anti-allergic, cardio-protective, and anti-cancer activity. Among them, LUT's administration for the treatment of periodontal disease is very promising. However, its low water solubility magnifies the challenge of formulating LUT into an effective dosage form. In this vein, the aim of the present study examines the preparation of amorphous solid dispersions (ASD) for the solubility improvement of LUT in saliva. At first, the physicochemical properties of the active pharmaceutical ingredient (API) were studied before the selection of the most suitable ASD matrix/carrier. For this reason, six commonly used polymeric ASD matrix/carriers (namely, povidone, PVP; copovidone, coPVP; hydroxypropyl cellulose, HPC-SL; hydroxypropyl methyl cellulose acetate succinate, HPMC-AS; Eudragit® RS, Eud-RS; and Soluplus®, SOL) were screened via the film casting method, as to whether they could suspend the drug's recrystallization. The most promising matrix/carriers were then evaluated, based on their ability to inhibit LUT's precipitation after its solubilization, via the solvent shift method. Based on both screening methods, it was determined that PVP was the most promising matrix/carrier for the preparation of LUT's ASDs. Hence, in a further step, after the successful testing of components' miscibility, LUT-PVP ASDs were prepared via the solvent evaporation method. These systems (examined via powder X-ray diffractometry, pXRD) showed full API amorphization immediately after preparation and excellent physical stability (since they were stable after 3 months of storage). The study of LUT-PVP ASD's ATR-FTIR (Attenuated Total Reflectance-Fourier Transform Infrared) spectra demonstrated strong H-bonds between the molecules of the drug and the matrix/carrier, while molecular dynamics (MD) simulations were able to shed light on these drug-matrix/carrier interactions, at a molecular level. Finally, in vitro dissolution studies in simulated saliva proved that the prepared ASDs were able to significantly enhance LUT's dissolution profile. Hence, according to findings of the present work, the preparation of LUT-ASDs utilizing PVP as the polymeric matrix/carrier is regarded as a highly promising technique for the improvement of API's solubility in the oral cavity.