Mridula Misra

Assessment of the effect of Bacopa monnieri (L.) Wettst. extract on the labeling of blood elements with technetium-99m and on the morphology of red blood cells

Bacopa monnieri (L.) Wettst. (BM), a traditional Ayurvedic medicine, used for centuries as a memory enhancing, anti-inflammatory, antipyretic, sedative and antiepileptic agent. BM extract have been extensively investigated by several authors for their neuropharmacological effects. In nuclear medicine, red blood cells (RBC) labeled with technetium-99m (99mTc) have several clinical applications. However, data have demonstrated that synthetic or natural drugs could modify the labeling of RBC with 99mTc. As Bacopa monnieri is extensively used in medicine, we evaluated its influence on the labeling of RBC and plasma proteins using technetium-99m (99mTc). This labeling procedure depends on a reducing agent and usually stannous chloride is used. Blood was incubated with BM extracts. Stannous chloride solution and 99mTc were added. Blood was centrifuged and plasma (P) and blood cells (BC) were isolated. Samples of P or BC were also precipitated, centrifuged and insoluble fraction (IF) and soluble fraction (SF) were separated. The percentage of radioactivity (%ATI) in BC, IF-BC and IF-P were calculated. The %ATI significantly decreased on BC from 95.53±0.45 to 35.41±0.44, on IF-P from 80.20±1.16 to 7.40±0.69 and on IF-BC from 73.31±1.76 to 21.26±1.40. The morphology study of RBC revealed important morphological alterations due to treatment with BM extracts. We suggest that the BM extract effect could be explained by an inhibition of the stannous and pertechnetate ions or oxidation of the stannous ion or by damages induced in the plasma membrane.

Pre-clinical risk assessment and therapeutic potential of antitumor lipopeptide ‘Iturin A’ in an in vivo and in vitro model

Lipopeptides are versatile bio-active weapons having antifungal, antibacterial, antimycoplasma and anticancer properties. In this study, the therapeutic potential and safety assessment of a lipopeptide molecule ‘Iturin A’ were evaluated. Iturin A was found to inhibit in vivo tumor growth in a sarcoma 180 mouse xenograft model. The antitumor efficacy of Iturin A was correlated with increased DNA fragmentation and modulation of CD-31, Ki-67, P-Akt, P-MAPK, apoptotic and anti-apoptotic proteins. Further, safety assessment was carried out in Sprague Dawley rats by 28 days repeated dose (28 days) toxicity and a bio-distribution study. In the toxicity study, Iturin A (10, 20 and 50 mg per kg per day) was administered to the animals for 28 days. Another group was kept for another 14 days without drug exposure after 28 days of treatment to access the reversibility of the toxicity. At the end of the treatment, body weight, food and water intake, organ weight, motility, hematology, serum biochemistry and histopathology of the major organs were evaluated. The bio-distribution of Iturin A was also performed in plasma as well as in different major organs by a well-developed and validated administration of Iturin A radiolabeled with 99mTc. The in vitro cytotoxic effect of Iturin A was also evaluated in BRL-3A rat liver cells. In the treated groups, various toxicities were found in the liver and spleen. However, these adverse effects were transient and reversible after discontinuation of Iturin A treatment. In conclusion, this pre-clinical study offered a preliminary investigation regarding the efficacy and safety assessment of Iturin A.

Synthesis, radiolabeling and biological evaluation of a neutral tripeptide and its derivatives for potential nuclear medicine applications

Peptides are important regulators of growth and cellular functions not only in normal tissue but also in tumors. So they are becoming radioligands of increasing interest in nuclear oncology for targeted tumor diagnosis and therapy. So development of new peptide radiopharmaceuticals is becoming one of the most important areas in nuclear medicine research. A small tripeptide derivative NH(2)PhePheCys was synthesized by Fmoc solid phase peptide synthesis using an automated synthesizer. The oxidized form, i.e. NH(2)PhePheCysCysPhePheNH(2,) was also prepared by iodine oxidation method from NH(2)PhePheCys(ACM). The ligands were analyzed by HPLC and mass spectroscopy. They were radiolabeled with (99m)Tc using SnCl(2). In vitro analytical studies and biological characterizations were performed using the peptide radiopharmaceuticals. Images taken under gamma camera showed very high uptake in the liver, lung and spleen. Significant uptake was also observed in bone marrow and brain for (99m)Tc-NH(2)PhePheCys. Metabolites were produced in vivo when the radiopharmaceuticals were injected intravenously and were identified from rat brain and liver homogenate studies. Clearance through kidney did not show any evidence of breaking of the labeled compounds and formation of free (99m)Tc. Radiopharmaceuticals prepared using tripeptide and hexapeptide ligands were transported into the brain through blood brain barrier depending on the size and sequence characteristics. Using this property of peptide new derivatives can be prepared to develop (99m)Tc radiopharmaceuticals for imaging normal brain tissues as well as for diagnosing various brain disorders.

Comparative evaluation of Tc-99m cystine and Tc-99m MAG3 in normals and patients with renal functional impairment.

Tc-99m cystine has been proved to be a good renal agent in animals for morphologic as well as the functional status of the kidney. In this study, we compared Tc-99m cystine with Tc-99m mercaptoacetyltriglycine, which is used for evaluation of renal function in normal patients, and those with various degrees of renal functional impairment. The clearance values and static images are compared with Tc-99m mercaptoacetyltriglycine. The results show that Tc-99m cystine has good radiopharmaceutical characteristics suitable for evaluation of both renal function as well as morphology.

Preparation and evaluation of technetium-99m labeled cardiac glycoside derivatives as potential myocardial imaging agent

Three cardiac glycosides, two natural, cymarin and convallotoxin and one synthetic, strophanthidin-beta-D-glucoside were converted to their thiosemicarbazone and subsequently radiolabeled with 99mTc by chelation. The resulting radioactive chelate complexes were evaluated in animals to determine the suitability of this class of compounds for myocardial imaging. It was observed from the animal biodistribution data of the three radioactive compounds, there was a considerable variation in the heart to non-target organ uptake ratio. A possible explanation of this variation was offered in the light of their lipophilic character, protein binding ability and affinity towards non-target receptors. It is anticipated that this study may help to develop a 99mTc-cardiac glycoside complex with better distribution characteristics, and such a compound may offer a suitable alternative to 201Tl, which is at present used for myocardial imaging.

Metabolic stability and biological evaluation of 99mTc-HYNIC-Tyr3-Octreotide as somatostatin receptor positive tumor imaging agent

In this study, metabolic stability and biological evaluation of 99mTc labelled 6-hydrazinopyridine-3-carboxylic-acid (HYNIC)-Tyr3-Octreotide was reported as a candidate for imaging somatostatin-receptor (SSTR)-positive tumors. The metabolic stability analysis did not show any evidence of breaking of the labeled compound and formation of free 99mTc. In biodistribution and scintigraphy imaging study, radiopeptide have showed high and receptor-specific uptake in the SSTR2 positive organs, tumor with rapid renal excretion from non-target tissues, illustrating the excellent properties of this agent for SSTR tumor imaging.

Biodistribution of two 99mTc-cardiac glycosides with end glucose unit: Effect of lipophilicity on their relative myocardial accumulation

In biodistribution experiments with tritium labelled cardiac glycoside it was observed that compounds of low lipophilicity showed a considerably higher affinity towards myocardium with respect to other tissues and organs. A similar trend was also observed with 99mTc-cardiac glycosides except for one compound with glucose residue, which in spite of its lower lipophilicity exhibited an unexpectedly low heart to non-target concentration ratio, thereby indicating a possible influence of carbohydrate residue on biodistribution. To confirm this, in this article we radiolabelled two glucose containing cardiac glycosides (K-strophanthin-beta and K-strophanthoside) with 99mTc and, in biodistribution experiments, less lipophilic 99mTc-K-strophanthoside showed a much better heart to non-target ratio over 99mTc-K-strophanthin-beta. It is thus concluded that, in addition to lipophilicity, the affinity of the carbohydrate residue for non-target organs is also an important consideration in determining the structure-distribution relationship of 99mTc-cardiac glycosides.

Preparation and biodistribution of 99mTc chelate of strophanthidin—a cardiac aglycone

Cardiac glycosides are well known to exert a specific and powerful effect on myocardial tissue, and there is a possibility that this class of compound with a 99mTc radiolabel may behave as a superior myocardial imaging agent in comparison to 201Tl which is at present used clinically. Because of the extreme chemical complexity of cardiac glycosides a simpler aglycone, strophanthidin was selected as the pilot compound for preliminary labelling and in vivo distribution studies. Strophanthidin was converted to 19-thiosemicarbazone which nicely accommodated 99mTc to produce a pure radiopharmaceutical of high specific activity. The distribution pattern in animal models was studied which is in accordance with the metabolic studies performed earlier with the ligand itself.