Radionuclides for therapy

Radionuclides which have potential for targeted therapy are the a, p, and Auger particle emitters. Though particle-emitting radionuclides

Table 40.1 Targeting agents for targeted radiotherapy

Biological differential

Targeting agent

Target tumour

Epitope

Antibodies

Various

Noradrenaline transporter

MIBG

Neuroblastoma

Melanin synthetic pathway

Methylene blue

Melanoma

EGF receptor overexpression

EGF

Squamous carcinoma, glioma

Proliferative differential

IUDR

Brain tumours

Oestrogen nuclear receptor

Oestrogen

Breast cancer

Genomic aberration

Oligonucleotide

?

usually produce some 7-ray photons as well, the photons make little contribution to the therapeutic effect.

The physical half-life of a targeting radionuclide must be long enough to allow radiochemical conjugation and the homing of the conjugate to its target tumour cells. However, it is not optimal to use radionuclides with half-lives longer than the time scale over which the conjugate will maintain its biochemical integrity and therefore targeting specificity.

In practice, clinical experience with targeted radiotherapy is largely confined to p-emitters, particularly 131I and, to a lesser extent, 90Y. The advantages of 131I are its availability, ease of conjugation, and clinical familiarity. 90Y has some physical advantages but is unfamiliar and the conjugates are less stable.

a-emitters have high radiobiological effectiveness and short-range emissions but are difficult to obtain and have inconveniently short half-lives. Experience with a-emitters is so far confined to the laboratory, but encouraging clinical potential has been demonstrated.

Auger electron emitters have been little used for targeted therapy because the short range of the Auger electron requires a DNAtargeting agent.

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