Yttrium-90 and Rhenium-188 Radiopharmaceuticals for Radionuclide Therapy

FIG. 13.10. RP HPLC chromatograms of non-radioactive Re(CO) 3 DPA ale: (a) UV detection
(254 nm), t R = 13.14 min and 5; (b) β detection, t R = 13.12 min). The difference in peak width
is because of the larger cell volume of the γ/β detector.
To achieve the maximum therapeutic efficiency, 188 Re compounds must
remain stable and bound to the target during at least one to three half-lives
of 188 Re (16.9 h). One of the most important drawbacks of 188 Re HEDP is its
lack of stability both in vivo and in vitro. To assess the in vitro stability of 5
in comparison with 188 Re HEDP, both compounds were incubated in PBS for
48 h at 37°C. RP HPLC and TLC analyses demonstrated that 5 did not degrade
over this time, whereas most of the 188 Re HEDP oxidized to 188 ReO 4 – (up to 75%)
(see Fig. 13.11).
Incubation of both compounds in human serum showed that most of the
radioactivity from the 188 Re HEDP sample remains bound to serum proteins
during the first 24 h. After this time, ~70% of the radioactivity was free in
solution. ITLC analyses demonstrated, however, that the non-protein bound
radioactivity was 188 ReO 4 – , the decomposition product of 188 Re HEDP. Complex 5,
on the other hand, remained non-protein bound and unmodified throughout the
48 h incubation period (see Fig. 13.11).
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