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Inclusion complexes of 2-methoxyestradiol with dimethylated and permethylated ?-cyclodextrins: models for cyclodextrin-steroid interaction.

ABSTRACT: The interaction between the potent anticancer agent 2-methoxyestradiol (2ME) and a series of cyclodextrins (CDs) was investigated in the solid state using thermal analysis and X-ray diffraction, while the possibility of enhancing its poor aqueous solubility with CDs was probed by means of equilibrium solubility and dissolution rate measurements. Single crystal X-ray diffraction studies of the inclusion complexes between 2ME and the derivatised cyclodextrins heptakis(2,6-di-O-methyl)-?-CD (DIMEB) and heptakis(2,3,6-tri-O-methyl)-?-CD (TRIMEB) revealed for the first time the nature of the encapsulation of a bioactive steroid by representative CD host molecules. Inclusion complexation invariably involves insertion of the D-ring of 2ME from the secondary side of each CD molecule, with the 17-OH group generally hydrogen bonding to a host glycosidic oxygen atom within the CD cavity, while the A-ring and part of the B-ring of 2ME protrude from the secondary side. In the case of the TRIMEB·2ME complex, there is evidence that complexation proceeds with mutual conformational adaptation of host and guest molecules. The aqueous solubility of 2ME was significantly enhanced by CDs, with DIMEB, TRIMEB, randomly methylated ?-CD and hydroxypropyl-?-CD being the most effective hosts. The 2:1 host-guest ?-CD inclusion complex, prepared by two methods, yielded very rapid dissolution in water at 37 °C relative to untreated 2ME, attaining complete dissolution within 15 minutes (co-precipitated complex) and 45 minutes (complex from kneading).

SUBMITTER: Caira MR

PROVIDER: S-EPMC4685897 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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Project description:A detailed comprehensive study on how the formation of soluble and insoluble carbamazepine/cyclodextrins (CBZ/CD) complexes (with consequent changes in the solid-phase composition) depends on the CD structure is not yet available. Moreover, the study of possible influence of this drug on the tendency of CDs and their complexes to self-aggregate is still lacking. Phase-solubility studies demonstrated that CDs and CBZ form a range of soluble (AL-type: αCD, βCD, and hydroxypropylated CDs) and insoluble (BS-type: γCD) complexes depending on CD used. HPβCD proved to be the best CD solubilizer for CBZ forming the most stable complex with highest apparent solubility, whereas γCD was shown to be the best native CD. For the native CDs, CBZ solubilization increases with increasing CD cavity diameter (αCD ≪ βCD < γCD). Solid phases collected from phase-solubility studies were characterized by Fourier-transformed infrared spectroscopy, differential scanning calorimetry, and X-ray powder diffraction to elucidate their composition and crystalline structure. They provided similar conclusions being overall supportive of phase-solubility, osmolality, and permeation studies results. Solid CBZ was the only detected component for AL-type profiles over the CD concentration range studied, whereas precipitation of poorly soluble CBZ/γCD complexes (BS-type) was observed (i.e., at and beyond plateau region). Osmometry and permeation studies were applied to evaluate the effect of CBZ on the aggregate formation and also to elucidate their influence on CD complex solubility and permeation profile. Permeation method was shown to be the most effective method to detect and evaluate aggregate formation in aqueous γCD and HPβCD solutions containing CBZ. CBZ did not affect the HPβCD tendency to self-aggregate but CBZ did modify the aggregation behavior of γCD decreasing the apparent critical aggregation concentration value from 4.2% (w/v) (in pure aqueous γCD solution) to 2.5% (w/v) (when CBZ was present).

Dataset Information

Inclusion complexes of 2-methoxyestradiol with dimethylated and permethylated ?-cyclodextrins: models for cyclodextrin-steroid interaction.

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