Cyclooxygenase-2 (COX-2) is a key player in inflammation. Its overexpression is directly associated with various inflammatory diseases and, additionally, with several processes of carcinogenesis. The development of new selective COX-2 inhibitors (COXIBs) for use in cancer treatment is in the focus of the medicinal chemistry research field. For this purpose, a set of methods is available to determine COX-2 expression and activity in vitro and ex vivo but it is still a problem to functionally characterize COX-2 in vivo. This review focusses on imaging agents targeting COX-2 which have been developed for positron emission tomography (PET) and single photon emission computed tomography (SPECT) since 2005. The literature reveals that different radiochemical methods are available to synthesize COXIBs radiolabeled with fluorine-18, carbon-11, and isotopes of radioiodine. Unfortunately, most of the compounds tested did not show sufficient stability in vivo due to de[ ]methylation or they failed to bind specifically in the target region. So, suitable stability in vivo, matching lipophilicity for the target compartment and both high affinity and selectivity for COX-2 were identified as prominent criteria for radiotracer development. Up to now, it is not clear what approach and which model is the most suited to evaluate COX-2 targeting imaging agents in vivo. However, for proof of principle it has been shown that some radiolabeled compounds can bind specifically in COX-2 overexpressing tissue which gives hope for future work in this field.
The intentional binding
of radioligands to albumin gains increasing
attention in the context of radiopharmaceutical cancer therapy as
it can lead to an enhanced radioactivity uptake into the tumor lesions
and, thus, to a potentially improved therapeutic outcome. However,
the influence of the radioligand’s albumin-binding affinity
on the time profile of tumor uptake has been only partly addressed
so far. Based on the previously identified N
ε-4-(4-iodophenyl)butanoyl-lysine scaffold, we designed
“clickable” lysine-derived albumin binders (cLABs) and
determined their dissociation constants toward albumin by novel assay
methods. Structure–activity relationships were derived, and
selected cLABs were applied for the modification of the somatostatin
receptor subtype 2 ligand (Tyr3)octreotate. These novel
conjugates were radiolabeled with copper-64 and subjected to a detailed in vitro and in vivo radiopharmacological
characterization. Overall, the results of this study provide an incentive
for further investigations of albumin binders for applications in
endoradionuclide therapies.
Mefenamic acid represents
a widely used nonsteroidal anti-inflammatory
drug (NSAID) to treat the pain of postoperative surgery and heavy
menstrual bleeding. Like other NSAIDs, mefenamic acid inhibits the
synthesis of prostaglandins by nonselectively blocking cyclooxygenase
(COX) isoforms COX-1 and COX-2. For the improved selectivity of the
drug and, therefore, reduced related side effects, the carborane analogues
of mefenamic acid were evaluated. The
ortho
-,
meta
-, and
para
-carborane derivatives were
synthesized in three steps: halogenation of the respective cluster,
followed by a Pd-catalyzed B–N coupling and hydrolysis of the
nitrile derivatives under acidic conditions. The COX inhibitory activity
and cytotoxicity for different cancer cell lines revealed that the
carborane analogues have stronger antitumor potential compared to
their parent organic compound.
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