Imaging zinc trafficking in vivo by positron emission tomography with zinc-62

Non-invasive imaging techniques to dynamically map whole-body trafficking of essential metals in vivo in health and diseases are needed. Despite 62Zn having appropriate physical properties for positron emission tomography (PET) imaging (half-life, 9.3 h; positron emission, 8.2%), its complex decay via 62Cu (half-life, 10 min; positron emission, 97%) has limited its use. We aimed to develop a method to extract 62Zn from a 62Zn/62Cu generator, and to investigate its use for in vivo imaging of zinc trafficking despite its complex decay. 62Zn prepared by proton irradiation of natural copper foil was used to construct a conventional 62Zn/62Cu generator. 62Zn was eluted using trisodium citrate and used for biological experiments, compared with 64Cu in similar buffer. PET/CT imaging and ex vivo tissue radioactivity measurements were performed following intravenous injection in healthy mice. [62Zn]Zn-citrate was readily eluted from the generator with citrate buffer. PET imaging with the eluate demonstrated biodistribution similar to previous observations with the shorter-lived 63Zn (half-life 38.5 min), with significant differences compared to [64Cu]Cu-citrate, notably in pancreas (>10-fold higher at 1 h post-injection). Between 4 and 24 h, 62Zn retention in liver, pancreas, and kidney declined over time, while brain uptake increased. Like 64Cu, 62Zn showed hepatobiliary excretion from liver to intestines, unaffected by fasting. Although it offers limited reliability of scanning before 1 h post-injection, 62Zn-PET allows investigation of zinc trafficking in vivo for >24 h and hence provides a useful new tool to investigate diseases where zinc homeostasis is disrupted in preclinical models and humans.

MDR1 causes resistance to the antitumour drug miltefosine

Miltefosine (hexadecylphosphocholine) is used for topical treatment of breast cancers. It has been shown previously that a high percentage of breast carcinomas express MDR1 or MRP. We investigated the sensitivity of MDR1 -expressing cells to treatment with miltefosine. We show that cells overexpressing MDR1 (NCI/ADR-RES, KB-8-5, KB-C1, CCRF/VCR1000, CCRF/ADR5000) were less sensitive to miltefosine treatment when compared to the sensitive parental cell lines. HeLa cells transfected with MDR1 exhibited resistance to the compound, indicating that expression of this gene is sufficient to reduce the sensitivity to miltefosine. The resistance of MDR1-expressing cells to miltefosine was less pronounced than that to adriamycin or vinblastine. Expression of MDR2 did not correlate with the resistance to miltefosine. As shown by a fluorescence quenching assay using MIANS-labelled P-glycoprotein (PGP), miltefosine bound to PGP with a K(d)of approximately 7 microM and inhibited PGP-ATPase activity with an IC(50)of approximately 35 microM. Verapamil was not able to reverse the resistance to miltefosine. Concentrations of miltefosine up to approximately 60 microM stimulated, whereas higher concentrations inhibited the transport of [3H]-colchicine with an IC(50)of approximately 297 microM. Binding studies indicated that miltefosine seems to interact with the transmembrane domain and not the cytosolic nucleotide-binding domain of PGP. These data indicate that expression of MDR1 may reduce the response to miltefosine in patients and that this compound interacts with PGP in a manner different from a number of other substrates.