the tetrapyrrole core lacked significant tumor localization, whereas hematoporphyrin labeled with
109
Pd was shown to accumulate in the tumor [16]. Sulfonated
metallophthalocyanines were studied as potential radiopharmaceuticals for tumor
imaging and later as candidate drugs for tumor PDT [17]. Table 3.1 shows applications of derivatives of porphyrin and Pc radiolabeled by different metallic
radioisotopes.
3.2 Coordination Chemistry of Metalloporphyrins
and Metallophthalocyanines
Many naturally occurring porphyrins are metal-bound and do not show toxicity
towards living organisms in the presence of light. Also, it was observed that the
introduction of a metal into the porphyrin molecule does not destroy the tendency
of the porphyrin to concentrate in tumors [18]. Understanding coordination
chemistry of metalloporphyrins and metallopthalocyanines is important for their use
in radiolabeling for biological applications. Porphyrin and many derivatives readily
form complexes with a variety of metals by deprotonation of one or two, of the
pyrrole NH protons and the resulting metal complexes are thermodynamically and
kinetically stable [19]. Usually, it tends to form a planar four-coordinated complexes with square-planar geometry. In addition to this, it has a tendency to form
some 5–8 higher coordination geometries during the course of addition of extra
ligands. Amongst all, the most studied complexes are four coordinated
square-planar, five coordinated square-pyramidal and six coordinated octahedral
metalloporphyrins [20]. Scheldt studied the influence of occupied or unoccupied
3d x
2 −y
2 and 3d z
2 orbitals on the bond lengths of metal-porphyrin nitrogen (M-N) and
metal-axial ligand (M-L) [20]. Detailed discussion on stable oxidation states of
metal ions in metalloporphyrins and optical absorption spectra of metalloporphyrins
were reported by Dolphin et al. [21]. Like porphyrins, the coordination chemistry of
metallophthalocyanines also received attention and have similar structures as
metalloporphyrins [22].
3.3 Porphyrin Radiolabeling
3.3.1 Cobalt-57
Transition metals often play a major role in designing metalloporphyrin PET
imaging agents.
57 Co, with a half-life of 271.8 days, was chelated in porphyrins and
employed to detect tumors in vivo over thirty years ago [23]. Two
57 Co porphyrins,
Co(III)-Corproporphyrin (CoCorp) and Co(III)-Uroporphyrin (CoUro) were used as
tumor specific agents. Tumor distribution of CoCorp and CoUro showed that the
3 Porphyrin and Phthalocyanine Radiolabeling
53
109
Pd was shown to accumulate in the tumor [16]. Sulfonated
metallophthalocyanines were studied as potential radiopharmaceuticals for tumor
imaging and later as candidate drugs for tumor PDT [17]. Table 3.1 shows applications of derivatives of porphyrin and Pc radiolabeled by different metallic
radioisotopes.
3.2 Coordination Chemistry of Metalloporphyrins
and Metallophthalocyanines
Many naturally occurring porphyrins are metal-bound and do not show toxicity
towards living organisms in the presence of light. Also, it was observed that the
introduction of a metal into the porphyrin molecule does not destroy the tendency
of the porphyrin to concentrate in tumors [18]. Understanding coordination
chemistry of metalloporphyrins and metallopthalocyanines is important for their use
in radiolabeling for biological applications. Porphyrin and many derivatives readily
form complexes with a variety of metals by deprotonation of one or two, of the
pyrrole NH protons and the resulting metal complexes are thermodynamically and
kinetically stable [19]. Usually, it tends to form a planar four-coordinated complexes with square-planar geometry. In addition to this, it has a tendency to form
some 5–8 higher coordination geometries during the course of addition of extra
ligands. Amongst all, the most studied complexes are four coordinated
square-planar, five coordinated square-pyramidal and six coordinated octahedral
metalloporphyrins [20]. Scheldt studied the influence of occupied or unoccupied
3d x
2 −y
2 and 3d z
2 orbitals on the bond lengths of metal-porphyrin nitrogen (M-N) and
metal-axial ligand (M-L) [20]. Detailed discussion on stable oxidation states of
metal ions in metalloporphyrins and optical absorption spectra of metalloporphyrins
were reported by Dolphin et al. [21]. Like porphyrins, the coordination chemistry of
metallophthalocyanines also received attention and have similar structures as
metalloporphyrins [22].
3.3 Porphyrin Radiolabeling
3.3.1 Cobalt-57
Transition metals often play a major role in designing metalloporphyrin PET
imaging agents.
57 Co, with a half-life of 271.8 days, was chelated in porphyrins and
employed to detect tumors in vivo over thirty years ago [23]. Two
57 Co porphyrins,
Co(III)-Corproporphyrin (CoCorp) and Co(III)-Uroporphyrin (CoUro) were used as
tumor specific agents. Tumor distribution of CoCorp and CoUro showed that the
3 Porphyrin and Phthalocyanine Radiolabeling
53