July 7, 2004

NSLS 2004 Annual Users’ Meeting Workshop

Pharmaceutical Applications of Synchrotron Radiation

The workshop, Pharmaceutical Applications of Synchrotron Radiation, was held as part of the 2004 Annual Users’ Meeting of the National Synchrotron Light Source (NSLS) on May 17th. The main goal was to bring together people working in the pharmaceutical industry with those familiar with synchrotron radiation techniques. The workshop focused on issues related to later stages of the drug development cycle, i.e., polymorphism, selection of salts and hydrates, quantification of crystallinity, partial states of crystallinity, etc. Research in drug discovery, such as protein crystallography, was not covered, although that has grown to a very large user base at synchrotron facilities worldwide.

One of the co-organizers, Evgenyi Shalaev of Pfizer, opened the discussion with an overview of the drug development cycle. Of several million candidates screened, only one or two will be reduced to a profitable new drug, after a development period of approximately fifteen years. X-ray techniques are crucial to many of the steps along the way, as well as the protection of intellectual property during the marketing lifetime of the drug.

Peter Stephens of Stony Brook University and the NSLS (also a workshop co-organizer) discussed the differences between laboratory and synchrotron x-ray sources, first from the standpoints of source properties and later in terms of access issues. He showed several comparisons of laboratory vs. synchrotron powder diffraction patterns and concluded that the additional information available was often dramatic in its ability to solve technical problems. He also emphasized that synchrotron sources are strongly motivated to attract new users, and while there may be some barriers to a new user getting a synchrotron research program started, they are generally less than popularly assumed, and the rewards are substantial.

Bill David and Kenneth Shankland, both of Rutherford Appleton Laboratory (UK), discussed many aspects of structure determination of small molecules from powder x-ray data. David emphasized the value of detailed structural crystallography, illustrating with the structure determination of a transient phase which existed for only one minute during the hydration of paracetamol (acetaminophen). He also showed the remarkable detail of information available, primarily through changes in diffraction peak shapes, of the transformation process in a dehydration reaction of the hypnotic, zopiclone (see Figure 1). Shankland discussed the importance of various steps taken in experimental design and data collection to ensure the accurate solution of structures, emphasizing that these techniques, both experimental data collection and analysis through simulated annealing methods, are widely available to those who care to use them. His message is that you can solve, from powder diffraction, structures which are typical of the complexity of most pharmaceutical compounds.

Mike Pikal of the University of Connecticut discussed the degradation of pharmaceutical compounds such as freeze-dried proteins in the form of glassy solids. The stability of pharmaceutical solids can be extremely sensitive to formulation, and the relationship between thermodynamic measurements and structural relaxation is an important topic of research. The current state of understanding is largely empirical, and the development of other methods to characterize the state of glassy solids is an important challenge.

Shalaev discussed the nature of the disordered states, i.e., amorphous state and crystalline mesophases of pharmaceutically relevant solids. Amorphous solids can have advantages in solubility and bioavailability, but disadvantages of stability; they can also arise during certain standard processing techniques such as milling, drying, and compaction. He challenged the audience to help to clarify the possible existence of more than one amorphous phase of a given system, so-called polyamophism, and the extent to which nominally amorphous solids, e.g., protein/sugar mixtures, may be heterogeneous. Another important issue is the relationship between local structure of amorphous solids and the structure of crystalline phases of the same compounds.

The third co-organizer, Raj Suryanarayanan of the University of Minnesota, discussed x-ray measurements of the degree of crystallinity of pharmaceuticals, especially from the standpoint of monitoring physical instability of products that are prepared as non-crystalline phases. He discussed in situ measurements of the crystallization of amorphous sucrose, performed with synchrotron radiation and an area detector. These experiments avoid the difficulties associated with preparation of a large number of mixtures required for the traditional preparation of a calibration curve.

Satyendra Kumar, of Kent State University, discussed model systems related to the issue of delivering water-insoluble drugs. Such materials may be physically encapsulated in micelles, or at the level of individual molecules, which then have interesting mesophases. He reported on synchrotron x-ray scattering studies of aqueous solutions of cyclodextrin and small molecule dyes, which have a variety of self-organized structures with varying degrees of orientational and structural order. He demonstrated how the use of external electric, magnetic or mechanical (shear) fields can reveal important new structural details which otherwise cannot be obtained.

The final talk of the session was given by Heinz Amenitsch of the Austrian Institute of Biophysics and X-ray Structure Research outstation at the ELETTRA synchrotron source in Trieste. His topic was the use of simultaneous small- and wide-angle x-ray scattering to study nanostructural features of relevant solids. The size of domains of the different components of a pharmaceutical formulation, the nature of the internal surfaces and the degree of dispersion are all accessible to these techniques. He showed that these measurements can be made with sub-millisecond time scales, allowing real time study of the relevant structural changes during such processes as spray-drying.

At the end of the workshop, Bruno Hancock of Pfizer moderated a round table discussion of issues of collaboration between pharmaceutical scientists and facilities such as the NSLS. Some participants expressed concerns that the Federal Government might claim ownership of intellectual property derived from experiments at synchrotron sources, despite the user following procedures for proprietary access. Obviously, this is a matter to be addressed by lawyers, not scientists, but the large investment in protein crystallography by major drug companies at synchrotron sources indicates that this might not be a serious impediment to commercial use of these facilities. Participants who are not experienced with synchrotron radiation as a research tool probably came away thinking of synchrotron sources as a valuable commodity, not a heroic investment. And synchrotron experts should have seen that their expertise may be of real value to some important practical problems, with real scientific content.

ACKNOWLEDGEMENTS
This workshop was partially supported by Pfizer, Inc.

FOR MORE INFORMATION
Peter W. Stephens
National Synchrotron Light Source
Brookhaven National Laboratory
Upton, NY 11973
Tel.: (631) 632-8156
Fax: (631) 632-8774
Email: pstephens@sunysb.edu