The Use of Tritium in Pharmaceutical Research and Development

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The Use of Tritium in Pharmaceutical Research and
Development

•   Larry E. Weaner
• Johnson Johnson Pharmaceutical Research and
  Development, L.L.C.
• PO Box 776
• Welsh and McKean Roads
• Spring House, PA 19477-0776 USA

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Radioisotopes as Tracers in Pharmaceutical
Research

• A wide variety of radionuclides are used in all
  phases of pharmaceutical research and development
• Incorporated into new drug candidates as tracers
• how and where a drug interacts
• how long it takes to come out
• Common radionuclides 3H, 14C, 35S, 33P/32P,
  125I, 11C/18F

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Radiolabeled Tracers

• 3H and 14C are the radionuclides of choice
• Incorporated into the chemical backbone of the
  molecules of interest without altering the
  molecular structure
• Physical and chemical properties are identical to
  those of the unlabeled compounds

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Advantages of Tritium Over 14C

• Tritium labeling is generally faster
• easily introduced into complex molecules in one
  or two reaction steps
• Provides radiotracers with very high specific
  activity
• hundreds of times those obtained with 14C
• greatly enhanced detection and sensitivity

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Labeling with Tritium

• Type of study determines the amount of
  radioactivity that must be incorporated
• 2 - 4 tritium atoms incorporated in specific
  positions in a molecule
• Specific activities of 40-110 Ci/mmol (1.85 -
  4.07 TBq/mmol) are regularly prepared

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Synthesis

• Scale 1 - 3 mg
• Reaction Volumes 1 - 5 mL
• The most common tritium labeling reactions
  involve
• metal catalyzed reactions of dehalogenation,
  hydrogenation of double and triple bonds
• isotopic exchange with tritium gas using a
  catalyst

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Starting Materials

• Tritium gas
• Tritiated water (T2 PtO2 -gt T2O)
• Synthetic intermediates
• tritiated metal hydrides (e.g., NaBH3T)
• tritiated methyl iodide

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Labeling with Tritium

• Reactions are completed in a closed manifold
• Activity 100s mCi to 10s of curies (10 - 370
  GBq)
• 100s mCi of tritium exchanged into water and
  solvents during reaction
• Radioactive releases 3 - 10 mCi (2 - 3 curie T2)

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Uranium Beds
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Reaction Flask
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Storage of Tritium-Labeled Compounds

• Chemical and radiochemical purities 98-99
• Radiolytic-self decomposition
• In solution ethanol (water) in glass bottles
• Radioactive concentration 1 mCi/mL
• Cold 20 to 76 0C

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HPLC Radiochromatogram of 3H
3-Ethoxyrapamycin 6.5 Ci/mmol (98 radiochemical
purity)
HPLC Radiochromatogram after storage at 76 0C
for 10 months (30 radiochemical purity)
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Uses of 3H Tracers in RD

• Studying drug interactions with receptors in the
  body
• early drug discovery
• Following the fate of a drug candidate after
  administration
• How the drug is distributed in the body
• How the body metabolizes and eliminates the drug

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Drug Candidate
3H
Receptors
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Uses of 3H Tracers in RD

• Studying drug interactions with receptors in the
  body
• early drug discovery
• Following the fate of a drug candidate after
  administration.
• How the drug is distributed in the body
• How the body eliminates the drug
• Distribution studies are usually done in rats

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Whole-body autoradiograph of a rat after
injection with rat 1 protein (SMR1)-derived
3Hpentapeptide. Black areas correspond to
highest areas of uptake. From C. Rougeot, R.
Vienet, A. Cardona, L. Le Doledec, J.M. Grognet,
F. Rougeon, Am. J. Physiol. Regulatory
Integrative Comp. Physiol. 273, 1309-1320, 1997.
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Tritium Handling in a Radiosynthesis Laboratory

• Fume hoods principal protection device
• Primary exposure concerns are
• Inhalation and skin absorption from tritium gas,
  tritiated solvents and volatile tritiated
  intermediates
• Particulates
• Aerosols generated during reaction workup
  (pressurized)
• Worker exposures are typically very low

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Tritium Handling

• High-velocity fume hoods 125-150 FPM
• 110 Air changes per hour
• HEPA  filtration for particulates
• Local trapping to control releases of volatiles
  and gases

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Energy Efficiency

• Night set-back system that reduces both the
  exhaust and supply air handling systems to 45
  airflow
• 125-150 FPM only 8 hours/day
• nights (16 hours), weekends and holidays 45
  airflow
• designed for 150 FPM with hood sash at 6 inches
  open

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TYPES OF RADIOACTIVE WASTE GENERATED

• Solid Dry Waste paper towels and absorbent
  materials, rubber gloves, and other debris
• Wastes Containing Biohazardous Materials Aqueous
  mixtures that may contain bacteria, viruses,
  fungi, parasites, prions, protozoa, infected
  cells
• Cultures, tissues, and specimens of body fluids,
  that may not be fully solubilized

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TYPES OF RADIOACTIVE WASTE GENERATED

• Mixed Waste Organic and Aqueous Mixtures
• 100-150 Liters per year
• 10s of Ci of 3H per year
• Wide variety of solvents and chemicals
• Separated based on chemical composition
  hydrocarbon, halogenated, aromatic, aqueous, etc.
• Separated based on isotope
• Liquid Scintillation Fluid
• Vacuum Pump Oil

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Destruction of Organic Materials in Mixed Waste
O2, Catalyst
3H Organic Waste
CO2 H2O Byproducts
1) High Temperature (750-850 0C, O2) 2)
Catalytic Oxidation (O2) 3) Steam Reforming
(H2O)

• Organic and aqueous samples processed directly
• Totally enclosed system
• High DREs
• Waste effluent trapped in a simple trapping
  system

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High-Temperature Catalytic Oxidation Apparatus
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Operating Parameters

• Temperature 750 to 850 degrees C
• Sample Feed Rate 1 to 5 mL/min
• Throughput 0.5 to 2 L/8 h
• Catalyst 0.5 Pt on Alumina (100 g)
• Catalyst lasts 450 hours
• Releases 1 - 3 mCi processing 6 Ci samples

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Destruction and Removal Efficiency for Various
Organics and Mixtures

• Methanol 99.999990
• Tetrahydrofuran 99.999997
• Cyclohexane 99.999991
• Acetone 99.999991
• 50 Acetonitrile-Water 99.999996
• 10 Formaldehyde-Water 99.99993
• 40 Chloroform in methanol/water 99.999997
• 20 Toluene in methanol/water 99.99999
• 20 Pyridine in water 99.99996