Biophysical Methods for Characterization of Antibody-Drug Conjugates

Antibody-drug conjugates (ADC) are made up of three components: (1) a mAb specific to cells of choice, (2) a small molecule with desired end goal, and (3) a linker to covalently link drug molecule to the antibody. Bringing together the mAb, drug molecule, and the linker results in the formation of an immunoconjugate designed to selectively deliver the drug molecule to a cell of interest. Synergic effects of the mAb and drug molecule lead to destroying the target tumor cells while leaving the normal cells unharmed. However, the development of ADCs is associated with challenges due to the heterogeneity of the ADC molecules created from the conjugation process. Addition of the linker and drug moieties during processing as well as the hydrophobicity of the drug itself can lead to structural changes that may affect the stability and functional profile of the conjugated molecule. Furthermore, linkers site of attachment plays a major role in determining the conformational and colloidal properties of the ADCs. In this chapter, several characterization methods are introduced to determine the biophysical characteristics of the ADC. Protocols, data analysis as well as notes for circular dichroism, intrinsic fluorescence, ANS fluorescence, differential scanning calorimetry, and dynamic scanning fluorimetry are outlined in detail.

Dissolution enhancement of glimepiride using modified gum karaya as a carrier

OBJECTIVE

The aim of present investigation is to enhance in vitro dissolution of poorly soluble drug glimepiride by preparing solid dispersions using modified gum karaya.

MATERIALS AND METHODS

Solid dispersions of drug were prepared by solvent evaporation method using modified gum karaya as carrier. Four batches of solid dispersion (SD1, SD4, SD9, and SD14) and physical mixture (PM1, PM4, PM9, and PM14) were prepared and characterized by differential scanning colorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, powder X-Ray diffraction (X-RD), and scanning electron microscopy (SEM) studies. Equilibrium solubility studies were carried out in shaker incubator for 24 h and in vitro drug release was determined using USP Dissolution Apparatus-II.

RESULTS

Maximum solubility and in vitro dissolution were observed with Batch SD4. No significant enhancement of dissolution characteristics were observed in the corresponding physical mixture PM4. Low viscosity with comparable swelling characteristics as compared to GK of modified form of gum karaya may lead to improvement in dissolution behavior of solid dispersion batches. Also, the conversion of crystalline form of drug to amorphous form may be a responsible factor, which was further confirmed by DSC, FTIR studies, and X-RD studies. SEM photographs of batch SD4 revealed porous nature of particle surface.

CONCLUSION

Modified forms of natural carriers prove beneficial in dissolution enhancement of poorly soluble drugs and exhibited a great potential in novel drug delivery systems.