Water-soluble 99mTc-labeled dendritic novel porphyrins tumor imaging and diagnosis

Dendrimer: An update on recent developments and future opportunities for the brain tumors diagnosis and treatment

A brain tumor is an uncontrolled cell proliferation, a mass of tissue composed of cells that grow and divide abnormally and appear to be uncontrollable by the processes that normally control normal cells. Approximately 25,690 primary malignant brain tumors are discovered each year, 70% of which originate in glial cells. It has been observed that the blood-brain barrier (BBB) limits the distribution of drugs into the tumour environment, which complicates the oncological therapy of malignant brain tumours. Numerous studies have found that nanocarriers have demonstrated significant therapeutic efficacy in brain diseases. This review, based on a non-systematic search of the existing literature, provides an update on the existing knowledge of the types of dendrimers, synthesis methods, and mechanisms of action in relation to brain tumours. It also discusses the use of dendrimers in the diagnosis and treatment of brain tumours and the future possibilities of dendrimers. Dendrimers are of particular interest in the diagnosis and treatment of brain tumours because they can transport biochemical agents across the BBB to the tumour and into the brain after systemic administration. Dendrimers are being used to develop novel therapeutics such as prolonged release of drugs, immunotherapy, and antineoplastic effects. The use of PAMAM, PPI, PLL and surface engineered dendrimers has proven revolutionary in the effective diagnosis and treatment of brain tumours.

Dendrimers based cancer nanotheranostics: An overview

Cancer is a known deadliest disease that requires a judicious diagnostic, targeting, and treatment strategy for an early prognosis and selective therapy. The major pitfalls of the conventional approach are non-specificity in targeting, failure to precisely monitor therapy outcome, and cancer progression leading to malignancies. The unique physicochemical properties offered by nanotechnology derived nanocarriers have the potential to radically change the landscape of cancer diagnosis and therapeutic management. An integrative approach of utilizing both diagnostic and therapeutic functionality using a nanocarrier is termed as nanotheranostic. The nanotheranostics platform is designed in such a way that overcomes various biological barriers, efficiently targets the payload to the desired locus, and simultaneously supports planning, monitoring, and verification of treatment delivery to demonstrate an enhanced therapeutic efficacy. Thus, a nanotheranostic platform could potentially assist in drug targeting, image-guided focal therapy, drug release and distribution monitoring, predictionof treatment response, and patient stratification. A class of highly branched nanocarriers known as dendrimers is recognized as an advanced nanotheranostic platform that has the potential to revolutionize the oncology arena by its unique and exciting features. A dendrimer is a well-defined three-dimensional globular chemical architecture with a high level of monodispersity, amenability of precise size control, and surface functionalization. All the dendrimer properties exhibit a reproducible pharmacokinetic behavior that could ensure the desired biodistribution and efficacy. Dendrimers are thus being exploited as a nanotheranostic platform embodying a diverse class of therapeutic, imaging, and targeting moieties for cancer diagnosis and treatment.

Current outlook on radionuclide delivery systems: from design consideration to translation into clinics

Radiopharmaceuticals have proven to be effective agents, since they can be successfully applied for both diagnostics and therapy. Effective application of relevant radionuclides in pre-clinical and clinical studies depends on the choice of a sufficient delivery platform. Herein, we provide a comprehensive review on the most relevant aspects in radionuclide delivery using the most employed carrier systems, including, (i) monoclonal antibodies and their fragments, (ii) organic and (iii) inorganic nanoparticles, and (iv) microspheres. This review offers an extensive analysis of radionuclide delivery systems, the approaches of their modification and radiolabeling strategies with the further prospects of their implementation in multimodal imaging and disease curing. Finally, the comparative outlook on the carriers and radionuclide choice, as well as on the targeting efficiency of the developed systems is discussed.

Preparation and evaluation of 99mTc-labeled porphyrin complexes prepared using PNP and HYNIC cores: studying the effects of core selection on pharmacokinetics and tumor uptake in a mouse model

Porphyrins are tetrapyrrolic macrocyclic ligands known for their affinity towards neoplastic tissues and once radiolabeled with a suitable diagnostic radioisotope could potentially be used for the imaging of tumorous lesions. In the present study, an unsymmetrically substituted porphyrin derivative namely 5-(p-amino-propyloxyphenyl)-10,15,20-tris(carboxymethyleneoxyphenyl)-porphyrin was synthesized and modified further to enable radiolabeling with ^99mTc using two different ^99mTc-cores viz. ^99mTc-HYNIC (hydrazino nicotinic acid) and ^99mTc(N)PNP2 (PNP2 = bis-[(2-dimethylphosphino)ethyl]-methoxy-ethylamine) in order to study the effect of employing different ^99mTc-cores on tumor affinity and pharmacokinetic behavior of the resultant ^99mTc-labeled porphyrin complexes. ^99mTc-Porphyrin complexes were characterized by reversed phase HPLC studies and could be prepared with >95% radiochemical purity under optimized radiolabeling conditions. Both ^99mTc-complexes were found to be adequately stable in human blood serum till 3 h post-preparation. Bio-distribution studies, carried out in Swiss mice bearing fibrosarcoma tumors, revealed relatively higher tumor uptake for the ^99mTc-HYNIC-porphyrin complex (3.95 ± 1.42 and 3.28 ± 0.27% IA per g) compared to that exhibited by the ^99mTc(N)PNP-DTC-porphyrin complex (1.52 ± 0.53 and 1.56 ± 0.10% IA per g) at 1.5 and 3 h post-administration, although the former complex exhibited comparatively lower lipophilicity in the octanol-water system. Higher uptake and longer retention in the blood were observed for the ^99mTc-HYNIC-porphyrin complex (6.63 ± 0.75 and 4.36 ± 0.25% IA per g) compared to that exhibited by the ^99mTc(N)PNP-DTC-porphyrin complex (2.41 ± 0.54 and 2.30 ± 0.16% IA per g) at both 1.5 and 3 h post-administration. However, relatively lower liver uptake was observed for the former complex (19.26 ± 3.48 and 18.45 ± 1.05% IA per g) than that exhibited by the latter one (39.37 ± 3.88 and 34.15 ± 8.25% IA per g) at both 1.5 and 3 h post-administration. This study indicates that the in vivo behavior exhibited by the ^99mTc-labeled porphyrins not only depends on their lipophilicity/hydrophilicity but is also governed by the Tc-cores employed for radiolabeling.

Modifications of Porphyrins and Hydroporphyrins for Their Solubilization in Aqueous Media

The increasing popularity of porphyrins and hydroporphyrins for use in a variety of biomedical (photodynamic therapy, fluorescence tagging and imaging, photoacoustic imaging) and technical (chemosensing, catalysis, light harvesting) applications is also associated with the growing number of methodologies that enable their solubilization in aqueous media. Natively, the vast majority of synthetic porphyrinic compounds are not water-soluble. Moreover, any water-solubility imposes several restrictions on the synthetic chemist on when to install solubilizing groups in the synthetic sequence, and how to isolate and purify these compounds. This review summarizes the chemical modifications to render synthetic porphyrins water-soluble, with a focus on the work disclosed since 2000. Where available, practical data such as solubility, indicators for the degree of aggregation, and special notes for the practitioner are listed. We hope that this review will guide synthetic chemists through the many strategies known to make porphyrins and hydroporphyrins water soluble.

Radiolabelled Polymeric Materials for Imaging and Treatment of Cancer: Quo Vadis?

Owing to their tunable blood circulation time and suitable plasma stability, polymer-based nanomaterials hold a great potential for designing and utilising multifunctional nanocarriers for efficient imaging and effective treatment of cancer. When tagged with appropriate radionuclides, they may allow for specific detection (diagnosis) as well as the destruction of tumours (therapy) or even customization of materials, aiming to both diagnosis and therapy (theranostic approach). This review provides an overview of recent developments of radiolabelled polymeric nanomaterials (natural and synthetic polymers) for molecular imaging of cancer, specifically, applying nuclear techniques such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT). Different approaches to radiolabel polymers are evaluated from the methodical radiochemical point of view. This includes new bifunctional chelating agents (BFCAs) for radiometals as well as novel labelling methods. Special emphasis is given to eligible strategies employed to evade the mononuclear phagocytic system (MPS) in view of efficient targeting. The discussion encompasses promising strategies currently employed as well as emerging possibilities in radionuclide-based cancer therapy. Key issues involved in the clinical translation of radiolabelled polymers and future scopes of this intriguing research field are also discussed.

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>

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).

Compared to purpurinimides, the pyropheophorbide containing an iodobenzyl group showed enhanced PDT efficacy and tumor imaging (124I-PET) ability

Two positional isomers of purpurinimide, 3-[1'-(3-iodobenzyloxyethyl)] purpurin-18-N-hexylimide methyl ester 4, in which the iodobenzyl group is present at the top half of the molecule (position-3), and a 3-(1'-hexyloxyethy)purpurin-18-N-(3-iodo-benzylimide)] methyl ester 5, where the iodobenzyl group is introduced at the bottom half (N-substitued cyclicimide) of the molecule, were derived from chlorophyll-a. The tumor uptake and phototherapeutic abilities of these isomers were compared with the pyropheophorbide analogue 1 (lead compound). These compounds were then converted into the corresponding 124I-labeled PET imaging agents with specific activity >1 Ci/micromol. Among the positional isomers 4 and 5, purpurinimide 5 showed enhanced imaging and therapeutic potential. However, the lead compound 1 derived from pyropheophorbide-a exhibited the best PET imaging and PDT efficacy. For investigating the overall lipophilicity of the molecule, the 3-O-hexyl ether group present at position-3 of purpurinimide 5 was replaced with a methyl ether substituent, and the resulting product 10 showed improved tumor uptake, but due to its significantly higher uptake in the liver, spleen, and other organs, a poor tumor contrast in whole-body tumor imaging was observed.

Design and synthesis of water-soluble bioconjugatable trans-AB-porphyrins

Three free base porphyrins have been prepared that bear a polar and facially encumbering 2,4,6-tris(carboxymethoxy)phenyl motif at one meso (5-) position. The only other substituent (15-position) comprises phenyl, formyl, or p-aminophenyl. The porphyrins exhibit solubility in water (or aqueous buffer solutions) at pH >/=7 and concentrations >1 mM at room temperature. The concise syntheses, water-solubility, and bioconjugatable handle make these porphyrin constructs suitable for biological applications.

Bioconjugatable porphyrins bearing a compact swallowtail motif for water solubility

A broad range of applications requires access to water-soluble, bioconjugatable porphyrins. Branched alkyl groups attached at the branching site to the porphyrin meso position are known to impart high organic solubility. Such "swallowtail" motifs bearing a polar group (hydroxy, dihydroxyphosphoryl, dihydroxyphosphoryloxy) at the terminus of each branch have now been incorporated at a meso site in trans-AB-porphyrins. The incorporation of the swallowtail motif relies on rational synthetic methods whereby a 1,9-bis(N-propylimino)dipyrromethane (bearing a bioconjugatable tether at the 5-position) is condensed with a dipyrromethane (bearing a protected 1,5-dihydroxypent-3-yl unit at the 5-position). The two hydroxy groups in the swallowtail motif of each of the resulting zinc porphyrins can be transformed to the corresponding diphosphate or diphosphonate product. A 4-(carboxymethyloxy)phenyl group provides the bioconjugatable tether. The six such porphyrins reported here are highly water-soluble (> or =20 mM at room temperature in water at pH 7) as determined by visual inspection, UV-vis absorption spectroscopy, or 1H NMR spectroscopy. Covalent attachment was carried out in aqueous solution with the unprotected porphyrin diphosphonate and a monoclonal antibody against the T-cell receptor CD3epsilon. The resulting conjugate performed comparably to a commercially available fluorescein isothiocyanate-labeled antibody with Jurkat cells in flow cytometry and fluorescence microscopy assays. Taken together, this work enables preparation of useful quantities of water-soluble, bioconjugatable porphyrins in a compact architecture for applications in the life sciences.

Small animal imaging. current technology and perspectives for oncological imaging

Advances in the biomedical sciences have been accelerated by the introduction of many new imaging technologies in recent years. With animal models widely used in the basic and pre-clinical sciences, finding ways to conduct animal experiments more accurately and efficiently becomes a key factor in the success and timeliness of research. Non-invasive imaging technologies prove to be extremely valuable tools in performing such studies and have created the recent surge in small animal imaging. This review is focused on three modalities, PET, MR and optical imaging which are available to the scientist for oncological investigations in animals.