Alterations of gallium-67 uptake in tumors by cis-platinum

Excitation function measurements and integral yields estimation for natZnp,x reactions at low energies

Excitation functions have been measured for a number of proton-induced nuclear reactions on natural zinc in the energy range from 27.5 MeV down to their threshold energy, using the activation method on stacked foils. Excitation functions and thick target yield for the reactions leading to the formation of (67)Ga,(66)Ga,(68)Ga,(62)Zn and (65)Zn are presented and compared with earlier reported experimental data. The experimental cross-sections and the production yields are tabulated; the excitation functions and the thick target yield curves are plotted in graphs.

Gallium in cancer treatment

Gallium (Ga) is the second metal ion, after platinum, to be used in cancer treatment. Its activities are numerous and various. It modifies three-dimensional structure of DNA and inhibits its synthesis, modulates protein synthesis, inhibits the activity of a number of enzymes, such as ATPases, DNA polymerases, ribonucleotide reductase and tyrosine-specific protein phosphatase. Ga alters plasma membrane permeability and mitochondrial functions. Ga salts are taken up more efficiently and more specifically by tumour cells when orally administered. New compounds have been prepared: Ga maltolate, doxorubicin-Ga-transferrin conjugate and Tris(8-quinolinolato)Ga(III), which show interesting activities. Ga toxicity is well documented in vitro and in vivo in animals. In humans, the oral administration Ga is less toxic, and allows a chronic treatment, allowing an improvement of its bioavailability in tumours, by comparison with the parenteral use. The anticancer activity of Ga salts has been demonstrated but other effects have also been noted such as many bone effects that could be useful in bone metastatic patients. Its has also been shown that a long period of administration could induce tumour fibrosis. Ga is synergistic with other anticancer drugs. Although not as potent as platinum in vitro, the anticancer activity of Ga should not be ignored, but the schedule of administration still needs to be optimised and new compounds are now under clinical investigations.

Immediate and delayed effects of cis-platinum treatment on the short term biodistribution of 67Ga-citrate in mice

The co-administration of a single medium toxic dose (5 mg/kg) of the chemotherapeutic drug cis-platinum (cis-Pt) with 67Ga-citrate was found to have minimal effects on the 3 h tissue distribution of the radiopharmaceutical in mice. When the same drug dose was given at two day intervals preceding the co-administered dose, virtually all tissues accumulated 67Ga to a greater extent. The tissue distribution of radiolabeled cis-Pt supported the development of drug-induced renal dysfunction as the primary cause.

Effect of cis-platinum on the protein binding and pharmacokinetics of 67Ga-citrate

Cis-platinum, a widely used chemotherapeutic drug, and K2PtCl4, a related complex, were found to inhibit the in vitro protein binding of 67Ga to human transferrin in isolated solution but not to whole serum. Cis-platinum treatment of rabbits resulted in enhanced protein binding and delayed blood clearance of subsequently injected 67Ga-citrate. These effects are related to the toxicity of the drug in vivo.