Properties and Stability of a Liquid Crystal Form of Cyclosporine—The First Reported Naturally Occurring Peptide That Exists as a Thermotropic Liquid Crystal

doi:10.1002/jps.10444

Journal of Pharmaceutical Sciences

Volume 92, Issue 9, September 2003, Pages 1821-1831

https://doi.org/10.1002/jps.10444 Get rights and content

Abstract

A new solid-state form of cyclosporine produced by spray-drying exhibited characteristics consistent with a liquid crystal. No sharp diffraction peaks were observed by powder X-ray diffraction; however, analysis by both small-angle X-ray diffraction (SAXR) and microscopic under polarized light (PLM) confirmed the existence of two-dimensional ordered liquid crystal. Hot stage microscopy revealed a solid-to-liquid transition, in the range of 118 to 125°C. Moreover, the solid-to-liquid transition showed frequency dependence by dielectric analysis (DEA), and was coincidental with a stepwise heat capacity change measured by differential scanning Calorimetry (DSC). The two-dimensional order was maintained above the solid-to-liquid transition temperature indicated by low-angle diffraction by SAXR and birefringence by PLM. However, birefringence was lost at temperatures above 170°C, indicating the conversion of the liquid crystal into an isotropic liquid. In situ annealing experiments, by DSC, revealed the presence of an endotherm, unexplained by either a phase transition or solvent loss, and it is believed to be the result of a structural rearrangement that has no impact on the macroscopic properties of the material. Spray-dried cyclosporine at room temperature is therefore a frozen thermotropic liquid crystal due to the presence of two-dimensional order and the lack of substantial residual solvent. This is, to our knowledge, the first report of the existence of a thermotropic liquid crystal of a naturally occurring peptide. © 2003 Wiley-Liss, Inc. and the American Pharmacists Association.

Section snippets

INTRODUCTION

Cyclosporine (Cyclosporin A) is a selective immunosuppressive drug, with antifungal and antiinflammatory properties, isolated from a fungal culture. The cyclic peptide has been used as an immunosuppressive agent in organ and bone marrow transplantation. Aerosolized cyclosporine has been delivered to the lung for the treatment of lung transplant rejection. A portable dry powder inhaler may have advantages over nebulized delivery.¹^,²

The challenge of preparing a cyclosporine dry powder suitable

Spray-Dried Cyclosporine

Cyclosporine is a cyclic peptide composed of eleven amino acids (seven of which are methylated), whose molecular formula is C₆₂H₁₁₁O₁₂, with a molecular weight of 1201 daltons. Cyclosporine was reconstituted in 95% ethanol and spray-dried on a modified Buchi 190 minispray dryer (Brinkman, Westbury, NY). Nitrogen was employed as the drying gas and oxygen content in the system was maintained at less than 5%.

Cyclosporine Recrystallization

Cyclosporine dihydrate was obtained from Polichimica S.A. (Milano, Italy). Orthorhombic

RESULTS

Spray-dried cyclosporine exhibited no characteristic sharp peaks on the PXRD pattern, where it was compared to two of the known crystal forms, tetragonal and orthorhombic (Figure 1). The spray-dried cyclosporine pattern suggested no long range three-dimensional order; however, two broad peaks with maxima at 7 and 17° in 2θ were observed. The diffraction patterns of the orthorhombic and tetragonal crystal forms corresponded with those found in the literature.¹⁷ The orthorhombic monohydrate

Interpretation of Solid-State Characterizations

Spray-dried cyclosporine is a solid phase with characteristics of an amorphous phase, such as: (1) the lack of three-dimensional order characterized by the absence of sharp peaks in PXRD, (2) a heat capacity change in the solid-to-liquid transition, determined by DSC (a second order T_g-like transition), and (3) a frequency dependent transition observed in dielectric analysis. However, additional data supported the formation of a supercooled liquid crystalline phase: (1) birefringence under

CONCLUSIONS

Cyclosporine was spray-dried from an ethanolic solution to form a new solid state form exhibiting characteristics of a liquid crystal. No sharp diffraction peaks were observed by PXRD indicating the lack of three-dimensional order. However, SAXR and PLM both confirmed the existence of two-dimensional ordered thermotrope. Hot stage microscopy revealed a solid-to-liquid transition, that showed a frequency dependence by DEA, and a step-wise ΔC_p change by DSC. The sharp peak by SAXR and the

Acknowledgements

The contribution of our colleagues at Nektar Therapeutics (formerly Inhale Therapeutic Systems, Inc.) has made this work possible. The advice of John Patton and analytical contributions of Kathy Cogan Farinas, Trixie Tan, Lisa Williams, Kirsten Cabot, Darren Nelson, and May Wang are appreciated. SAXR analysis was performed at the University of Minnesota through a Prof. David J. W. Grant.

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Research ArticlesProperties and Stability of a Liquid Crystal Form of Cyclosporine—The First Reported Naturally Occurring Peptide That Exists as a Thermotropic Liquid Crystal

Abstract

Section snippets

INTRODUCTION

Spray-Dried Cyclosporine

Cyclosporine Recrystallization

RESULTS

Interpretation of Solid-State Characterizations

CONCLUSIONS

Acknowledgements

J Thorac Cardiovasc Surg

J Pharm Sci

Treatment of transplant rejection by aerosolized cyclosporine

Ciclosporin form for pulmonary administration

Eur Pat EP 0504760

Aerosol drug development of a spray dried liquid crystalline formulation of cyclosporine

Liquid crystal forms of cyclosporin

Liquid crystals a colorful state of matter

Chem Eng News

Liquid crystals

Melting behavior and thermotropic mesomorphism of fenoprofen salts

Eur J Biopharm

The conformation of cyclosporin A in the crystal and in solution

Helvet Chim Acta

Research Articles
Properties and Stability of a Liquid Crystal Form of Cyclosporine—The First Reported Naturally Occurring Peptide That Exists as a Thermotropic Liquid Crystal