avidinandbiotinas

Paganellidescribes avidinandbiotinas a “fantastic
natural system” (it’s been described as nature’s gift to
molecular biology).Avidin – found in the eggwhites
of birds and in bird and reptile tissues – is a protein
that binds to themuch smaller biotinmolecule (also
knownas vitaminH)withtremendous affinity. Inhis
earlyworkwith brain tumour patientswith grade III
and IV astrocytoma, he employed a three-stage
process–first injecting amonoclonal antibody tagged
with biotin that binds to the tumour, then avidin,
which binds to the antibody, and finally the radionuclide
– in this case yttrium-90-labelled biotin.
Although the number of patientswas small, and the
work took several years, a quarter (12 patients)
showed a reduction in tumour size and three people
had complete remission.
Now PAGRIT – pretargeted antibody guided
radioimmunotherapy (anda trademark)–has entered
the oncologist’s lexicon, and is suitable for several
other applications, notably in lymphoma,which is a
cancer with good radiosensitivity and which also
expresses tenascin. It also has potential in other cancers,
according toPaganelli.Aformof pretargeting is
also nowplaying a role in hismost importantwork to
date, on breast cancer.
The complex nature of thiswork is obvious – and
a furtherpotentialbarrier is the availability of reagents.