CPSA Digest 2002

Proceedings -Thursday, October 10, 2002

ThOC2

Outsourcing Bioanalytical Support in Drug Discovery

Premise:
The perspectives of a sponsor, Purdue Pharma, are shared in this presentation which discussed factors influencing a decision to outsource drug discovery support to a CRO and described typical studies performed in discovery support at Purdue. In addition, perspectives from four+ years of discovery support at Purdue Pharma are shared, including data classification procedures and higher throughput sample analysis strategies. Analysis Discovery support at Purdue Pharma investigates the following:

• ADME variables in vitro
• Basic pharmacokinetics
• Potential for liver toxicity in vitro

• Rapidity/timing – method development, sample analysis, data reduction, results reporting; non-GLP
• Variety – multiple / novel methods, cell-based and otherwise
• Flexibility - in vivo & in vitro assays / protocols
• Reagents & materials – lab-to-lab variation
• Proprietary concerns – unpatented compounds

Various assays are in place for lead selection and optimization. These are termed "first-tier assays," "second-tier assays" and "third-tier assays." Their place and timing in the screening process are shown below. Some examples of second-tier assays include kinetic solubility, metabolite profiling, metabolic saturation, P-gp interaction and in vivo single dose studies, while third-tier assays include toxicology assays, thermodynamic solubility, bioavailability and escalating dose pharmacokinetics.

The first-tier pharmaceutical profiling assays for lead selection in early discovery are the focus of this presentation. The first-tier assays display certain general attributes. These features include the following: relatively high throughput, relatively simple experimental
protocols, sparing of new chemical entities, extremely well-validated and referenced, duplicate wells with a single determination per compound per assay, and categorical reporting for easy yes/no or go/no-go classification.

Examples of these first-tier assays at Purdue Pharma are listed below.

• Rat liver microsomal and human liver microsomal intrinsic clearance and metabolic stability (LC/MS)
• Membrane permeability via PAMPA & Caco-2 (LC/MS)
• Drug interaction potential via CYP450 enzyme inhibition (fluorimetry)
• P-glycoprotein interactions via inorganic phosphate release (spectrophotometry)
• Kinetic solubility (nephelometry)
• hERG interactions via 86Rb release (AA)

Some of the problems identified as analytical bottlenecks in discovery support are: size of libraries, closely related compounds in libraries, permeability, metabolic stability, intrinsic clearance and chemical stability. Some of the solutions implemented to solve these bottlenecks include the use of 8-probe autosamplers, 96-well microplates and fast
HPLC (eight columns with Micromass MUX™ technology for 8-channel inlets, short columns, high flow rates and steep gradients). Use of the MUX technology at Purdue has resulted in a throughput of 1,200 sample injections per day. Also, the automation of certain assays has been accomplished, such as the metabolic stability assay.

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