Tumor imaging with 57cobalt(III)-sandwich complexes and 57cobalt(III)-porphyrins

Radiosynthesis, molecular modeling and biodistribution of 99mTc-Protoporphyrin as a preclinical model for tumor diagnosis

Porphyrins are among the most important and widely used compounds involved in a variety of chemical and biochemical applications. These molecules exhibit very special properties that encourage researchers to label many derivatives with diagnostic or therapeutic radionuclides for medical applications. This study reports the radiolabeling and biodistribution of [Formula: see text]Tc-protoporphyrin IX ([Formula: see text]Tc-PPIX) as a novel potential solid-tumor imaging agent. The factors affecting the radiolabeling process were varied to achieve maximum radiochemical yield. [Formula: see text]Tc-PPIX was obtained in high yield of 97.34 ± 0.21% and high stability in serum up to 24 h. The radiochemical yield of [Formula: see text]Tc-PPIX was assessed by a combination of a paper chromatographic technique and HPLC. A computational analysis for all the potential structures that may be formed due to the interaction between protoporphyrin IX and technetium was performed via the DFT method of calculations in gas phase to predict the most likely structure. Molecular docking was further employed to shed light on the nature of the interaction between the most stable complexes with the target protein. Finally, the in-vivo biodistribution of [Formula: see text]Tc-PPIX complex was evaluated in solid-tumor-bearing mice and high tumor/tissue ratio of 5.17 ± 0.34 at 60 min post injection was obtained. Our finding clearly suggests [Formula: see text]Tc-PPIX as a potential SPECT agent for tumor imaging.

Production, quality control, biodistribution assessment and preliminary dose evaluation of [177Lu]-tetra phenyl porphyrin complex as a possible therapeutic agent

<p>Due to interesting therapeutic properties of ¹⁷⁷Lu and tumor avidity of tetraphenyl porphyrins (TPPs), ¹⁷⁷Lu-tetraphenyl porphyrin was developed as a possible therapeutic compound. ¹⁷⁷Lu of 2.6-3 GBq/mg specific activity was obtained by irradiation of natural Lu₂O₃sample with thermal neutron flux of 4 × 10¹³ n.cm^-2.s^-1. Tetraphenyl porphyrin was synthetized and labeled with ¹⁷⁷Lu. Radiochemical purity of the complex was studied using Instant thin layer chromatography (ITLC) method. Stability of the complex was checked in final formulation and human serum for 48 h. The biodistribution of the labeled compound in vital organs of wild-type rats was studied up to 7 d. The absorbed dose of each human organ was calculated by medical internal radiation dose (MIRD) method. A detailed comparative pharmacokinetic study was performed for ¹⁷⁷Lu cation and [¹⁷⁷Lu]-TPP. The complex was prepared with a radiochemical purity: >97±1% and specific activity: 970-1000 MBq/mmol. Biodistribution data and dosimetric results showed that all tissues receive approximately an insignificant absorbed dose due to rapid excretion of the complex through the urinary tract. [¹⁷⁷Lu]-TPP can be an interesting tumor targeting agent due to low liver uptake and very low absorbed dose of approximately 0.036 to the total body of human.</p>

PET/PDT theranostics: synthesis and biological evaluation of a peptide-targeted gallium porphyrin

In pursuit of the goal of a molecular theranostic suitable for use as a PET radiotracer and a photosensitiser for PDT, a novel ⁶⁸Ga radiolabelled peptide–porphyrin conjugate targeting the α₆β₁-integrin has been developed.

Radiolabelled porphyrins in nuclear medicine

Amongst tumour-specific substances, hematoporphyrin and synthetic porphyrin derivatives have been widely investigated to identify and delineate neoplastic and malignant tissue. Whilst the tumour localization exhibited by selected porphyrin species has been exploited through photodynamic therapy, several examples of porphyrin derivatives with varied peripheral functionality have been radiolabelled with the aim of developing porphyrin-based nuclear imaging and therapeutic agents. In this review, we look at the approaches and advances in the preparation and uses of such radiolabelled agents for imaging and therapy.

Effect of lipophilicity on biological properties of 109Pd-porphyrin complexes: a preliminary investigation

The present study is designed to investigate the effect of lipophilicity of 109Pd-porphyrin complexes on their biological properties which were evaluated in tumor-bearing animal model. The insight obtained could be utilized to develop other radiometalated porphyrin complexes with optimum tumor uptake and tumor to background ratio as potential agents for targeted tumor therapy. 109Pd was produced by thermal neutron bombardment on enriched (in 109Pd) metallic palladium target at a flux of 3 × 1013 n/cm2.s for 3 d. 109Pd complexes of three different porphyrin derivatives, namely, 5,10,15,20-tetrakis[3,4- bis(carboxymethyleneoxy)phenyl]porphyrin(I), 5,10,15,20-tetrakis[3,4-bis(carboethoxymethyleneoxy)phenyl]porphyrin(II) and 5,10,15,20-tetrakis[4-carboxymethyleneoxyphenyl]porphyrin(III), which differ in their peripheral substituents, were synthesized. The biological behavior of the complexes was studied in Swiss mice bearing fibrosarcoma tumors. 109Pd was produced with a specific activity of ~1.85 GBq/mg (50 mCi/mg) and radionuclidic purity of 100%. All the 109Pd complexes were obtained in high yield (>97%) and they exhibited satisfactory in vitro stability at room temperature. The lipophilicity of the complexes follows the order 109Pd-II ≫ 109Pd-III > 109Pd-I. Biodistribution studies revealed that the most lipophilic 109Pd-II complex exhibited highest initial tumor uptake but poor tumor/liver ratio, while 109Pd-III complex exhibited the best tumor/liver ratio with reasonably good tumor accumulation. The lipophilicity of 109Pd-porphyrin complexes was found to have considerable effect on their biological characteristics and radiometal-porphyrin complexes with optimum tumor uptake and adequately high tumor to background ratio could be synthesized by optimization of the lipophilicity through proper selection of peripheral substituents.

Preparation of 99mTc(CO)3-TPPS4 and its biological behavior evaluation

99mTc(CO)3-TPPS4 was prepared via the precursor [99mTc(CO)3(H2O)3]+ and a preliminary investigation on its stability and behavior in Hep2 tumor cells and hepatoma-bearing mice were conducted. Labeling yield and stability of 99mTc(CO)3-TPPS4 was radioactively analyzed by paper chromatography. Hep2 tumor cells were incubated with 99mTc(CO)3-TPPS4 complex system in the substrate and isolated from the substrate for radioactivity count. Then 99mTc(CO)3-TPPS4 complex system was intravenously injected in hepatoma-bearing mice and directly injected in tumor tissue of the mice. Mice were photographed using SPECT. Labeling yields of 99mTc(CO)3-TPPS4 were more than 90% at pH = 7–8, 30 min, in a boiling bath, and it was stable for at least 14 h at pH = 2–8, rt ~95 °C. The uptake of 99mTc(CO)3-TPPS4 in HepG2 tumor cells was only 3–4% with the maximum uptake-time of 20 min. The SPECT images of hepatoma-bearing nude mice showed no uptake or little retention of 99mTc(CO)3-TPPS4 in the tumor tissue. Then the differences between 99mTc(CO)3-TPPS4 and TPPS4 were analyzed by fluoroscopy and molecular structure. It was found that the paper chromatography, HepG2 tumor cell uptake and the optimized porphyrin ring conformation of 99mTc(CO)3-TPPS4 were quite different from those of TPPS4. It was indicated that 99mTc(CO)3-TPPS4 had no uptake or little retention in hepatic tumors, unlike those biological behaviors of TPPS4. This may be due to the modification of porphyrin ring conformation of TPPS4 by 99mTc(CO)3 core.

A novel [109Pd] palladium labeled porphyrin for possible use in targeted radiotherapy

The preferential accumulation of porphyrins in malignant tumor cells has been adequately documented. Hence, porphyrin derivatives radiolabeled with a suitable therapeutic radionuclide could be envisaged as potential agents for targeted tumor radiotherapy. Working in this direction, we have radiolabeled a porphyrin derivative, namely, 5,10,15,20-tetrakis[3,4-bis(carboethoxymethyleneoxy)phenyl]-porphyrin, synthesized in-house, with 109Pd [E β(max)=1.12 MeV, E γ=88 keV 3.6(%), T 1/2 = 13.7 h]. The envisaged rationale towards designing of this agent is based on the assumption that 109Pd would complex with the tetrapyrrole donor array constituting the porphyrin core, thereby providing a highly stable chelated complex, and the peripheral ester groups would impart optimum lipophilicity needed for sufficiently high tumor accumulation and retention therein. 109Pd was produced with a specific activity of ∼1.85 GBq/mg and radionuclidic purity of 100% by the thermal neutron bombardment of enriched (98% in 108Pd) metallic Pd target at a flux of 3×1013 n/cm2s1 for 3 d. The porphyrin derivative was synthesized by a multi-step reaction and characterized by normal spectroscopic techniques. 109Pd complex of the synthesized porphyrin derivative was prepared with excellent radiochemical purity (>98%) and the complex was observed to be stable upto 24 h at room temperature. Biodistribution studies carried out in Swiss mice bearing fibrosarcoma tumors revealed good tumor uptake [(5.28±1.46)% injected activity (IA)/g] within 30 min post-injection (p.i.). The complex exhibited favorable tumor/blood and tumor/muscle ratios [1.69±0.23 and 5.00±1.54, respectively at 3 h p.i.], albeit with high liver uptake throughout the time of study (>20% IA).

Synthesis and preliminary biological studies of the novel conjugate 188Re-labeled meso-tetrakis(4-sulfophenyl)porphyrin in mice

OBJECTIVE

The objective of this study was to evaluate the biological behaviors of a novel (188)Re-labeled meso-tetrakis(4-sulfophenyl)porphyrin (TPPS(4)) in normal mice and tumor-bearing mice.

METHODS

TPPS(4) was synthesized and labeled by (188)ReO(4)(-). Normal KM mice and BALB/c nude mice bearing melanoma or hepatoma were prepared for distribution studies.

RESULTS

The [(188)Re]TPPS(4) yield was >98% with a specific activity of 11.2 GBq/mol, and vitamin C could increase its stability in vitro. In normal KM mice, [(188)Re]TPPS(4) had a fast blood clearance ( approximately 90%, 24 h postinjection), low retention in vital organs and hepatotropic characteristics. In nude mice, uptakes of >4.1% and 6.5% ID/g tumor at 8 h postinjection were observed in melanoma and hepatoma, respectively; this remained at high levels of 4.7% and 5.7%, respectively, after 24 h. At 8 h, the tumor/blood and tumor/muscle ratios in melanoma-bearing and hepatoma-bearing mice were 6.2-15.2 and 6.1-24.2, respectively. Twenty-four hours later, these high ratios still continued at 8.6-22.1 and 12-26.1, respectively.

CONCLUSION

The results obtained in this study indicate that [(188)Re]TPPS(4) has a high tumor affinity and retainable accumulation characteristics in carcinoma, which can potentially be used for tumor-targeted therapy.

A novel [186/188Re]-labelled porphyrin for targeted radiotherapy

The concept of labelling a porphyrin, a tumour-avid agent, with a radionuclide to evaluate its potential as a therapeutic modality is reported. A novel water-soluble porphyrin, namely meso-tetrakis[3,4-bis(carboxymethyleneoxy)phenyl]porphyrin, with suitable dicarboxylic acid groups as aromatic substituents in the periphery, was synthesized and characterized. The labelling of this porphyrin with 186/188Re, a beta(-) emitter, was optimized by varying the reaction conditions. The complexation yield was >98% as estimated by paper chromatography in acetone and in saline. The radiochemical purity was found to remain at >98% when stored at 4 degrees C for 24 h. Biodistribution studies in Swiss mice bearing fibrosarcomas showed an uptake of approximately 3.5% per gram of tumour at 30 min post-injection. This uptake in the tumour was retained until 24 h post-injection with major activity showing renal clearance; no significant activity was present in other organs of interest. The tumour/blood and tumour/muscle ratios were observed to be 38 and 5, respectively, at 24 h post-injection, thereby indicating a possible therapeutic potential for tumours.

Mn[III] uroporphyrin I: a novel metalloporphyrin contrast agent for magnetic resonance imaging

We have used an intracranial 9L rat brain tumor model to determine whether a novel metalloporphyrin, Mn[III] uroporphyrin I (MnUROP-I), could function as an intravenous MRI contrast agent for brain tumors. In several experiments, 24 male Fischer 344 rats were inoculated intracranially with 9L brain tumor cells. On day 15 postinoculation, animals were anesthetized and the femoral vein exposed. Prior to the intravenous injection of the contrast agent, a precontrast scan (1 Tesla in a standard head coil) was performed. Thirty min after injection of the contrast agent, a postcontrast scan was performed. Although there was only a suggestion of abnormality on the precontrast scans, the presence of tumor was visibility enhanced in the postcontrast scans. In 3 animals scanned at 24 hr postinjection, persistent tumor enhancement was demonstrated. Measured tumor sizes on the MRI scans were consistent with sizes measured at autopsy and histologically. These results demonstrate that MnUROP-I is an effective MRI contrast agent for the detection of an intracranial brain tumor in the rat model.

In vivo assessment of 111In-labeled hematoporphyrin derivative in breast tumor-bearing animals

The biological behavior of 111In-labeled HPD has been investigated in tumor-bearing animals. Mice mammary adenocarcinomas and 7,12-dimethylbenz(a)anthracine induced breast tumors in Sprague-Dawley female rats were clearly visualized by 111In-HPD nuclear scintigraphy. Optimal scans were obtained after a 48 h delay. In normal and tumor-bearing animals, the highest uptake of 111In-HPD 72 h post-injection was found in the liver, the spleen and the kidneys. Depending on the size and the extent of necrosis, the uptake of 111In-HPD by malignant breast tumors varied from 2.5% injected dose (ID) (range 0.14-5.3% ID) in mice to 1% (range 0.22-8.1% ID) in rats. Benign breast tumor uptake of 111In-HPD was less than 1% ID. No significant amount of the radiopharmaceutical was found in pulmonary abscesses and abdominal cysts (less than 0.1% ID). Scintigrams of these infectious or inflammatory lesions were normal. Malignant tumor to blood, heart and lung ratios averaged 50:1, 10:1 and 3:1 respectively. Tumor to brain ratio ranged from 72 to 444:1.