Atoms in Medicine

1. Atoms in Medicine (or Science can be Good…)

2. Radioisotopes in Medicine • The nucleus of every atom is made up of protons and neutrons. The specific combination of protons and neutrons determines the isotope • Some nuclei are unstable and emit one or more of the following • an alpha particle (group of 2 protons + 2 neutrons) = • a beta particle (electrons) = • positron (short-lived, positively-charged particle with the same mass as an electron) = • electromagnetic radiation (gamma rays) = g • Approximately 200 radioisotopes are used on a regular basis • Making radioisotopes • most common: neutron capturein a nuclear reactor (shown) - cobalt-60 used for radiation therapy • proton capture in a cyclotron

3. Specific Examples (Radiotracers) • Technetium-99 • half-life of six hours • one of the most widely used radioisotopes (80% of all procedures) • combination of short half-life, extensive chemistry and favorable decay processes that produce relatively low-energy particles makes it ideal • used to image the heart, bones, liver and lungs • Iodine-131 • half-life of 8.04 days • used to determine thyroid activity • Carbon-11 (20.4 min), nitrogen-13 (10 min), oxygen-15 (2 min), and fluorine-18 (110 min) • isotopes are incorporated into molecules such as sugars and rapidly injected • positron emitters used in PET for studying brain physiology and pathology • fluorine-18 has become very important in detection of cancers and the monitoring of progress in their treatment (incorporated into 2-fluoro-2-deoxy-D-glucose)

4. Boron Neutron Capture Therapy (BNCT) • BNCT is a form of Targeted Alpha Therapy (TAT), a means to selectively deliver high doses of radiation to cancer cells • BNCT uses boron-10 compounds that selectively concentrate in malignant brain tumors • The patient is irradiated with thermal neutrons which are strongly absorbed (“captured”) by the boron-10 • The resulting boron decays, producinghigh-energy alpha particles which kill the cancer • Advantages: potentially highly targeted, localized radiation • Disadvantages: the procedure requires the patient to be brought to a nuclear reactor, rather than the radioisotopes being taken to the patient.

5. anti-parallel parallel field Magnetic Resonance Imaging (MRI) • The nuclei of atoms have quantum properties just like atoms and electrons • One quantum-mechanical property called “spin” causes the nuclei to act like little magnets • In the presence of a magnetic field the spin of the nuclei can either line up parallel or anti-parallel to the magnetic field • MRI uses radio waves to probe the difference in energy between these two arrangements Magnetic field no field in all water molecules

6. Anti-Cancer Drugs – cisplatin • One of the most-prescribed anticancer drugs, cisplatin (cis-diamminedichloroplatinum(II)), was discovered by accident while scientists were studying the effects of electric fields on the growth of cells • Several platinum compounds were formed from the combination of the platinum electrodes and the electrolyte • The most active anti-tumor compound was found to be cis-diamminedichloroplatinum(II) • “Testicular cancer went from a disease that normally killed about 80% of the patients, to one which is close to 95% curable. This is probably the most exciting development in the treatment of cancers that we have had in the past 20 years. It is now the treatment of first choice in ovarian, bladder, and osteogenic sarcoma [bone] cancers as well.” - Dr. Barnett Rosenberg

7. Anti-Cancer Drugs – Taxol • 1962 – large-scale screening of plant compounds shows that an extract of the yew tree is active against tumors • 1967 – compound is identified • 1971 – structure of Taxol determined by x-ray crystallography • 1983 – Phase I clinical trials begin, but the extract is in short supply due to limited number of Pacific Yew trees • 1990 – synthesis route discovered that allows production of Taxol from the European Yew tree • 1992-1994 – Taxol is approved for treatment of ovarian and breast cancers