Radioactive Imagine Agents: 99mTc-Toxicological Study

DOI: https://doi.org/10.53523/ijoirVol9I1ID150 Abstract Radioactive pharmaceutical materials (radiopharmaceuticals) that contain radioactive atom or/ and ion (emits nuclear (α, β, or / and γ) ray according to its energy and half-life duration) companied with organic or inorganic molecule are important materials in nuclear imaging or therapeutically medicine. Many biomolecules labeled with Technetium99 in relationship to toxicity issues can be transported, distributed, and detected with the computerized algorithm detector depending upon chemical, biological, metabolic, and functional properties of tissue or organ (bone, liver, heart, kidney, and others). According to literatures' review about this subject, this is the first try in Iraq and other countries to study Technetium – radiomolecules with in Silico depending on two approachs. LD50, Class, Polar Surface Area PSA, logP, Hepatotoxicity, Carcinogenity, Immunotoxicity, Mutagenicity, Cytotoxicity, AMES test, Max. tolerated dose (human), hERG I and II inhibitor, Oral Rat Acute (LD50) and Chronic (LOAEL) Toxicity, Hepatotoxicity besides Skin Sensitisation showed that Tc-biomolecules under study are structurally unsafe having toxic response to liver, immune system, cellular components, DNA, and/or cardiac repolarization through hERG inhibition of action. These mainly conclusion notes depended upon Technetium oxidation state, heteroatoms presence, surface properties besides bio-target specifications, concentration, exposure time, genetic factors of human, and health problems.


Introduction
Radioactive pharmaceutical materials (radiopharmaceuticals) are important materials in nuclear imaging or therapeutically medicine. These materials contain radioactive atom or/ and ion companied with organic or inorganic molecule. The important component in these molecules is the radioactive element (radionuclide) that emits nuclear (α, β, or / and γ) ray according to its energy and half-life duration like Rhenium Re-186 or Re-188, iodine-131 or Iodine -129, Gallium-67, and Technetium-99 that used in nuclear medicinal therapy as shown in Figure (1) where radioactive Rhenium emits beta and gamma rays while others emit gamma as shown in Table (1) and Figure (2). Clinical situation of human, radionuclide energy and halflife time, target organ or tissue penetration, kinetic-dynamic behavior of these pharmaceutics specify the choosing of the nuclear tracker or monitor such as gamma camera [1].

Iraqi Journal of Industrial Research (IJOIR)
Journal homepage: http://ijoir.gov.iq Figure (1). Image of radiopharmaceutical molecule emits (α, β, or / and γ) ray towards bio-target.  To get best results of molecular nuclear imaging, radioactive material must be transported, distributed, and detected with the computerized algorithm detector. So, intravenously administration of any radiopharmaceuticals mainly depends upon chemical, biological, metabolic, and functional properties of tissue or organ (bone, hepatic, cardiac, renal, and others) [2].
Man-made Tc-99 isotope can be found in nuclear waste having very long half-life (2.1x10 5 years) that extends its presence in environment and concentrates in some plants or animals. Human exposure to this radioactive represents a high chance of cancer where it can be concentrated in thyroid and gastrointestinal tract [3].
In contrast to Carbon -11, iodine-123, or Fluorine -18, Technetium -99m does not substituted any carbon or hydrogen atom in any pharmaceutical molecule to form Technetium -99m imaging agent or any labeling molecule [8].

Results and Discussion
Tc-pharmaceuticals as a chelating complex composed of Tc-radionuclide (essential core) in a certain oxidation state and tagged molecule. 99mTc -biomolecules target particular organ such as liver, heart, lung, brain, thyroid, bone, and kidney to detect cancer occurrence basing on cellular blood flowing, or ionic transportation, molecular charge, lipophilic-hydrophilic balance, blood-brain barrier transportation [12].
According to [13], toxicity definition is the ''mount or degree of a substance needed to be poisonous depending on its concentration, frequency of use, personal interaction(s) that determine reversibility and acute-chronic states. When it is at cell level causing organ failure with possible death, this terms systemic toxicity, while local type is reflection of reversibility effects.'' In lab, single pure material assessment is concerned as actual toxicity testing that may be supported by computerized models [14] known as in Silico, QSAR, ADMET models including online website prediction. This prediction or testing may include natural or synthesized materials.
With above abbreviated statements, two free online websites were selected to predict toxicity of thirty Technetium radioactive materials that may use in imaging of suspected human cancer or other diseases. As a new prediction try of these radiopharmaceuticals, both online (https://tox-new.charite.de/protox_II/ and http://biosig.unimelb.edu.au/pkcsm/) websites were easily to use with the help of isomeric SMILES (Table (2

2R)-2-[(2S)-2-[(2S)-3-[[(4R)-4-[[4-[(2amino-4-oxo-3H-pteridin-6yl)methylamino]benzoyl]amino]-4carboxybutanoyl]amino]-2azanidylpropanoyl]azanidyl-3carboxypropanoyl]azanidyl-3-hydroxy-3-
oxopropane-1thiolate;oxo(99Tc)technetium-99(2+)    Polar surface area (PSA) is topological molecular descriptor depends upon polar atoms like oxygen, phosphor, or nitrogen attached to hydrogen (functional groups) as a basic in biological conformations in cooperation with QSAR prediction descriptors like octanol/ water partitioning coefficient (logP) in drug transport study. This virtual screener presents a primary image of molecular polar interaction affected barrier crossing in medicinal chemistry subject [15,16]. Lipophilic-hydrophilic ratio (logP) measures partitioning target molecule in n-octanol/water phases in equilibrium state expressed in logarithm form ranged from -3 (low hydrophobic or high hydrophilic) to +10 (high hydrophobic or low hydrophilic). Usually, this character is measured by shake-flask method [17]. It is important in drug research and development, toxicity, chromatographic methods especially High Performance Liquid Chromatography (HPLC) [18]. From Table (3) and Figures (6 and 7), both PSA and logP were influenced by Technetium oxidation state, heteroatoms presence, molecular weight, stereo-structure, ring (aromatic, hetero, aliphatic), branching, length of chain, and other effective factors.  Among toxicity characters, medium lethal dose (LD50) and toxicity class are important factors in characterization of chemicals which are classified according EPA (U.S Environmental Protection Agency) and GHS (Globally Harmonized System of Classification and Labelling of Chemicals). LD50 can be defined as the required dose of chemical that kills 50% (half) of the rats under test and ranges from toxic to nontoxic (safe) (in numbers, it ranges from less than 50 mg/Kg to more than 2000 mg/Kg). Table (3) and Figure (8) show medium lethal dose to rodent (LD50) ranged from (100-10000)mg/Kg calculated by https://tox-new.charite.de/protox_II/ while http://biosig.unimelb.edu.au/pkcsm/ showed Oral Rat Acute Toxicity (LD50) range (0.92 to 3.117) mol/Kg. LD50 values were influenced by PSA and logP and their determinants as mentioned above. Pentetate was predicted as the most toxic material (Class 2).   To detect acute liver failure resulted by chemical substance especially with radionuclide, hepatotoxicity character is the correct scientific classification. Age, gender, smoking, incorrect consumption of drug especially nonhydrophilic or alcohol, genetic, changing in β-oxidation of fatty acids, mitochondrial abnormality in its function, or other factors may increase liver toxicity in either self-compatibility or predictable form towards cell or organ death [19]. According to [20], more than 1000 drugs have been linked to this failure where hepatitis histological characterizations are acute, chronic fulminant, cholestatic, biliary plugs, macro-or micro-lipid droplet in the cytoplasm with non-particular symptoms. Also, High level of special liver enzymes may highly influence liver damage that may be cooperated with candidate toxic materials [19]. Highest Drug Induced liver injury (Hepatotoxicity) probability of these Tc-complexes in percentage term was with MDP(97%) then Pentetate (96%), and GHate (96%) as predicted by https://tox-new.charite.de/protox_II/. Other online website http://biosig.unimelb.edu.au/pkcsm/ prediction showed 50% of Tc-molecules were with (Yes) response including Pentetate but not MDP or GHate.

C1=CC(=CC=C1C(=O)N[C@H](CCC( =O)NC[C@@H](C(=O)[N-][C@@H](CC(=O)O)C(=O)[N-][C@@H](C[S-])C(=O)O)[NH-])C(=O)O)NCC2=CN=C3C(=N2)C(=O )NC(=N3)N.O=[99Tc+2]
Encyclopedia of Toxicology [21] states that'' potential occupational carcinogen means any substance or combination or mixture of substance, which causes an increased incidence of benign and / or malignant neoplasms or a substantial decrease in the latency period between exposure and onset of neoplasms in human or in one or more experimental mammalian species as the result of any oral, respiratory, or dermal exposure, or any other exposure which results in the induction of tumors at a site other than the site of administration''. Even with its expensive and time consuming, carcinogenicity is essential requirement in drug and/or its metabolite(s) industry research and development for short -or long-term testing after mutagenicity evaluation to prevent tumor initiation as a result of using candidate medication [22]. Time and cost require primer, ultimate and post-final carcinogenicity testing. This post-validation testing is necessary to overcome any accidental health problems including new lab and in Silico trials. From this objective point, Table (3) and Figure (9) show the prediction probability of carcinogenicity where its percentage range was (50% -85%) and DMSA (85%), GHate (83%), and TMPDA (82%) were with highest point in this study.
Every living body has a defense system against foreign material(s) and immune system in human is the protector against tumor, fungi, bacteria, virus, parasites, chemicals, etc. with makeable distinguishing roles (self-from nonself-component(s)). Immunotoxics may generate reactive oxygen species, and/ or induce severe damage in DNA or P53 gene expression [23]. In Silico study is among other evaluating methods depending on tissue, blood, and urine examinations that assess mechanism, response, then outcome of Tc-radiomaterials (and other toxins). It is noticeable results that most of Tc-materials under study were with high probability of immunotoxicity (Table (3  Percentage range (69-99)%.  More than 55% (seventeen Tc-molecules from thirty tested molecules) had 99% prediction probability of immunotoxicity.  More than 12% (four Tc-molecules from thirty tested molecules) had 99% prediction probability of immunotoxicity. So, 70% of tested molecules had more than 98% prediction probability of immunotoxicity (twenty-one Tc-molecules from thirty tested molecules).
By another online website http://biosig.unimelb.edu.au/pkcsm/, mutagenicity (Ames test) was with (No) response for all Tc-molecules expect MIBI (Yes) response. Reasons behind these data variations by the same website or in comparison of both online websites may be related to oxidation state of Technetium radionuclide, heteroatoms presence, concentration, surface properties, bio-target specifications, and mathematical base of each website.
The other toxicity term that deals with in vitro compatibility of chemical under experimental cellular conditions is cytotoxicity. In this term, primary cell structures and functions may be changed when it exposures to toxic substance and this changing may observed by computational prediction and lab methods [26,27]. In lab, its mechanism assay mainly involves substance chemistry and response with using cell lines of corneal, lung, ovary, renal, three-dimensional tissue culture and various microorganisms [28]. In human body, inducing cell-lysis and apoptosis mechanisms are the main role in cellular cytotoxicity that can be measured in vitro with radioactive and non-radioactive reagent(s) release as measurable label target in short time with non-inflammatory response [29]. But these cost-time measuring methods can be in advanced replaced with computational models as approximated approach.
In this study, cytotoxicity probability (Table (3), Figure (9)) ranged from 52% to 83% where 99m Tc-HYNIC-EGF had the highest prediction probability (83%). As initial conclusion about this predictor, high cytotoxicity range is an elementary indication of deficiency in cellular biological mechanisms.  Table (3) and Figure (10). These results were ranged ((0.0549-0.079) mg/Kg/day), (0.92-3.117) mol./Kg, and (1.588-768423829.33) mg/Kg.BW/day respectively. Maximum tolerated dose data display an obvious form about Tc-molecules action dose threshold in human as a starting point in clinical trial, Phase I. LD50 of rat in its definition submit the amount leads to 50% death of test animals. While, Oral Rat Chronic Toxicity (LOAEL) outcomes offer lowest dose over long time of exposure in an observed adverse effect. All three toxicological predictors ensure that Tc-molecules under this evaluation were toxic even at low numerical data [30].
In cardiac repolarization, hERG blockage by chemical causes a lethal action in life-threatening. Here, all Tcmolecules showed (No) response to hERG I inhibition while 23% of them showed (Yes) to hERG II inhibition as tabulated in Table (3) that match with some antibiotic, antipsychotics, and others [31] as they exhibit in www.crediblemeds.org website. Finally, it is remarkable notice that only H191 had skin sensation (Table (3)). So, more than 96% of tested Tcmolecules were with no allergic contact dermatitis induction in all cutaneous sensation points related to the median nerve [32]. To get an apparent vision about this study, Pentetate molecule is an example. This substance is a radionuclide imaging complex for renal, lung, and gastrointestinal tract, and it is stable to oxidation by ascorbic acid or other free radical scavengers. Also, it is bounded to protein and excreted by kidney where it used in blood flow in brain and heart, cerebrospinal fluid, and inhalation studies. It is produced by several trademarks including DRAXMAGE ® with health notice about eye and skin irritations at high quantity. According to this prediction study, this substance belongs to class 2 (fatal if swelled, inhaled, in contact to eye) with very highly toxic probability to liver and immune system. It may have considered as mutagen-cytotoxic agent but not as an inhibitor of hERG Types I and II or skin sensation. It is structurally unsafe compound where it may be interacted with molecular target giving toxic response. Here, toxicity notes are mainly depending upon concentration, exposure time, genetic factors of human, health problems, and others.