99m Technetium-HMPAO-labeled platelet scan in practice: Preparation, quality control, and biodistribution studies

Abstract There is no biodistribution or imaging data on 99mtechnetium (Tc)-hexamethyl propylamine oxime (HMPAO)-labeled platelets in the literature. The current study aimed to present updated information about the clinical procedures for preparation and use of labeled platelets. Following two-step centrifugation at 1500 and 2500 rpm, the platelets were extracted from whole blood into platelet-rich plasma (PRP) above the buffy coat and then from PRP into a platelet pellet at the bottom of the tube. The 99mTc-HMPAO-labeled platelets were inspected for purity, viability, release of 99mTc from platelets, and sterility. Also, microscopic examination and thin layer chromatography (TLC) were performed. Biodistribution was assessed following necropsy in BALB/c mice and through imaging of New Zealand rabbits. The separation ratio was estimated at 98%, and radiochemical purity was measured to be 80%. The labeling efficiency was above 30% in more than half of the assays (range: 17-43%). The release of 99mTc from platelets was 9% per hour at 37ºC. After 24 hours, stability was estimated at 54% in the human serum. The target organs of mice included the spleen and liver. In rabbits, the imaging results indicated liver as the target organ. Thyroid uptake was negligible up to 90 minutes. Based on the findings, extraction of platelets and labeling them with 99mTc-HMPAO is a feasible and safe approach in routine practice.

Synthesis and preliminary evaluation of a new[99m]Tc labeled substance P analogue as a potential tumor imaging agent

Neurokinin 1 receptors [NK[1]R] are overexpressed on several types of important human cancer cells. Substance P [SP] is the most specific endogenous ligand known for NK1Rs. Accordingly,a new SP analogue was synthesized and evaluated for detection of NK[1]R positive tumors.[6-hydrazinopyridine-3-carboxylic acid [HYNIC]-Tyr[8]-Met[O][11]-SP] was synthesized and radiolabeled with 99mTc using ethylenediamine-N,N-diacetic acid [EDDA]and Tricine as coligands. Common physicochemical properties of radioconjugate were studied and in-vitro cell line biological tests were accomplished to determine the receptor mediated characteristics. In-vivo biodistribution in normal and tumor bearingnude mice was also assessed. The cold peptide was prepared in high purity [>99%] and radiolabeled with [99m]Tc at high specific activities [84-112GBq/ micro mol] with an acceptable labeling yield [>95%]. The radioconjugate was stable in-vitro in the presence of human serum and showed 44% protein binding to human serumalbumin. In-vitro cell line studies on U373MG cells showed an acceptable uptake up to 4.91 +/- 0.22% with the ratio of 60.21 +/- 1.19% for its specific fraction and increasing specific internalization during 4 h. Receptor binding assays on U373MG cells indicated a mean Kd of 2.46 +/- 0.43 nM and Bmax of 128925 +/- 8145 sites/cell. In-vivo investigations determined the specific tumor uptake in 3.36 percent of injected dose per gram [%ID/g] for U373MG cells and noticeable accumulations of activity in the intestines and lung. Predominant renal excretion pathway was demonstrated. Therefore, this new radiolabeled peptide could be a promising radiotracer for detection of NK[1]R positive primary or secondary tumors

Radiolabeling of herceptin with [99m]Tc as a her2 tracer

Trastuzumab is a monoclonal antibody that is used in treatment of breast cancer. We labeled this monoclonal antibody with Technetium-99m and performed in vitro and in vivo quality control tests as a first step in the production of a new radiopharmaceutical. Trastuzumab was labeled with Technetium-99m using Succinimidyl Hydrazinonicotinamide [HYNIC] as a chelator. Radiochemical Purity and stability in buffer and serum were determined. Immunoreactivity and toxicity of the complex were tested on SKBR3, MCF7 and A431 breast cancer cell lines. Bioedistribution study was performed in normal mice at 4 and 24 h post injection. The radiochemical purity of the complex was 95+/-1.4%. The stabilities in phosphate buffer and in human blood serum at 24 h post preparation were 85 +/- 3.5% and 74 +/- 1.2%, respectively. The immunoreactivity of the complex was 86 +/- 1.4%. The binding of labeled antibody to the surface of SKBR3, MCF7 and A431 cells were increased by increasing the human epithelial growth factor receptor 2 [Her2] concentration on the cells surface. These findings showed that the new radiopharmaceutical can be a promising candidate as Her2 antigen scanning for human breast cancer

Preparation and biodistribution study of [99m]Tc-EC-Annexin-SPIO as a tracer of radiation induced apoptosis in mice model

Apoptosis is a major consequence of ionizing radiation in proliferative tissues and quantification of the apoptotic cells could be helpful for noninvasive assessment and estimation of the radiation absorbed dose. Annexin V conjugated with super paramagnetic iron oxide nanoparticles [ANX-SPIO] is a biological probe for detection of apoptotic cells using magnetic resonance imaging. This study aimed at assessing the biodistribution alterations of the labeled ANXSPIO within the mice body shortly after exposure to different doses of ionizing radiation. [99m]Tc-EC-ANX-SPIO was prepared and its in vitro stability was tested. The binding affinity of radiocomplex to apoptotic cells was validated in vitro. Mice irradiated whole body with 2, 4 and 6 Gy [[60]Co gamma rays] and six hours later, radiocomplex was administrated intravenously and the biodistribution study was conducted 0.5, 1 and 2 hours later. The radiochemical purity of radiocomplex was 94% +/- 3.4% and it showed a good stability in PBS and serum. The radiocomplex maintained its efficacy for in vitro binding to apoptotic cells. radiocomplex accumulated in the bone marrow of all irradiated mice [p <0.05]. However, statistical analysis did not show significant correlation between the %ID/g of the femoral bones and the received radiation doses. Quantification of ANX-SPIO in bone marrow can be used as an indicator for radiation exposure but development and optimization of the assay are necessary for discrimination between different radiation doses

Synthesis, radiolabeling and biological evaluation of [99m]Tc-labeled deoxyglucose derivatives for molecular imaging

Two deoxyglucose [DG] derivatives, [alpha, beta]-2-deoxy-2-amino[ethylcarbamate]-D-glucose [ECB-DG] and [alpha, beta]-2-deoxy-2-amino[1,2-dihydroxypropyl]-D-glucose [DHP-DG], were synthesized and radiolabeled successfully with [[99m]Tc[H[2]O][3][CO][3]][+] complex. [[99m]Tc]-ECB-DG and [[99m]Tc]-DHP-DG complexes were prepared [96% and 93% radiochemical purities respectively] by using 46 mCi of Na[99m]TcO[4] in 1 mL saline. Radio-HPLC analysis of [[99m]Tc]-ECB-DG at pH = 7.4, revealed that labeling with [99m]Tc leads to formation of one radiochemical species with t[R] = 381 second. Three radiochemical species, Na[99m]TcO[4], [[99m]Tc]-DHP-DG and [[99m]Tc[H[2]O][3][CO][3]][+] complexes with t[R] = 342 sec, t[R]= 567 sec and t[R] = 1586 sec respectively, were obtained when [[99m]Tc]-DHP-DG complex evaluated by HPLC. Biodistribution of two complexes were studied on normal mice at 10, 30 and 60 min post-injections. Compared to the [18]F-FDG, [[99m]Tc]-ECB-DG displayed a 2.8-fold reduction in brain uptake [1.7 +/- 0.2 versus 0.61% +/- 0.09], whereas [[99m]Tc]-DHP-DG just showed 1.9-fold reduction in heart uptake [2.2 +/- 0.05towards 1.16 +/- 0.10] at 1 h post-injection.On the basis of our results, it seems that ECB-DG and DHP-DG analogues could be used as brain and heart imaging agent respectively

improved synthesis and preliminary biodistribution study of a technetium-99m-labeled 2-amino-2-deoxy[thioacetyl]-D-glucose complex [[99mTc]-TA-DG] as a tumor imaging agent

This report describes the synthesis of 2-Amino-2-deoxy[S-benzoylthioacetyl]-D-glucose [S-Bz-TA-DG], radiolabeled with [99mTc[CO]3[OH2]3]+complex with a procedure including deprotection of the benzoyl group, characterization by HPLC using a C18 reverse phase column and preliminary biodistribution study in normal mice. [99mTc[CO]3[H2O]3]+complex was used to label TA-DG with 99mTc. This complex was prepared using up to 46 mCi of Na99mTcO4 in 1mL saline. The radiochemical purity [>95%] was determined by TLC in normal saline solution as the mobile phase. Radio-HPLC analysis of [99mTc]-[TA-DG] at pH=9.5-10, revealed that labeling with 99mTc resulted in the formation of three radiochemical species [Na99mTcO4 with tR=5.7 min, [99mTc[CO]3[H2O]3]+complex with tR=27.5 min and [99mTc]-[TA-DG] [yield>85%] with tR=8.2 min] with different HPLC-profiles. The biodistribution of the [99mTc]-[TA-DG] complex was studied in normal mice [body mass 25-35 g] at 30 min and 1 h post-injection, according to a published procedure. This complex showed negligible brain uptake [0.13% +/- 0.03 ID] at 30 min post-injection, an efficient clearance from the blood, a rapid excretion to the urine and a low retention in the liver and kidneys. Nonfunctionalized carbohydrate compounds such as glucose are generally weak ligands for chelating with 99mTc. Therefore, functionalization with an external chelating group or the insertion of some functional groups is essential to obtain strong metal-binding compounds. On the basis of our results, it seems that [99mTc]-[TA-DG] has not most of the favorable properties as an imaging agent for brain tumors