Design, synthesis and evaluation of 177Lu-labeled inverso and retro-inverso A9 peptide variants targeting HER2-overexpression.

Several HER2-specific peptides are being continuously explored to find a candidate with suitable pharmacokinetic properties for development of effective radiopharmaceutical that can find applications for clinical screening of breast cancer patients. In the present work with an aim of preparing a radiopeptide with improved metabolic stability and in vivo pharmacokinetic performance we modified our previously reported [177Lu]DOTA-L-A9 peptide. Here we designed an 'inverso' peptide with all d-amino acids and a 'retro-inverso' peptide where sequence of d-amino acids was reversed. Higher secondary structure stabilization of retro- inverso A9 variant compared to inverso A9 peptide was evident by circular dichroism studies. The two radiopeptides [177Lu]DOTA-D-A9 and [177Lu]DOTA-rD-A9 exhibited significantly improved in vivo metabolic stability over the original l-peptide. The retro-inverso variant, [177Lu]DOTA-rD-A9 demonstrated better pharmacokinetic behavior with significantly higher tumor uptake than the inverso peptide, [177Lu]DOTA-D-A9 and the original peptide, [177Lu]DOTA-L-A9. In the present case of A9 peptide, reversal of the peptide sequence of d-amino acids boosted the uptake and retention of radioactivity in HER2-positive tumor. The present study can thus guide the design and development of newer and improved versions of peptides.

Targeting HER2-receptors with 177Lu-labeled triazole stapled cyclic peptidomimetic.

In this study on-resin Cu(I)-catalyzed click reaction was performed to synthesize triazole-stapled cyclic peptidomimetic, DOTA-c[TZ]A9 targeting HER2 receptor expression in breast cancers. Spectroscopic (circular dichroism) and docking analysis provided evidence of enhanced helicity and secondary structure stabilization along with improved HER2 affinity in comparison to the corresponding linear peptide, DOTA-[Pra1, Aza7]A9. 177Lu-labeled cyclic peptide, 177Lu-DOTA-c[TZ]A9 displayed higher in vitro serum stability and in vivo metabolic stability and better HER2 binding affinity {Kd of 16.93 ± 3.02 nM} than the linear counterpart, [177Lu]DOTA-[Pra1, Aza7]A9 {Kd of 26.28 ± 2.87 nM}. Biodistribution profile in SKBR3 tumor bearing SCID mice demonstrated elevated radioactivity levels and prolonged retention of cyclic peptide in the tumor compared to the linear peptide. Thus, solid phase click cyclization technique can be extended towards preparation of triazole-stapled peptides targeting different receptors with improved stability and efficacy.

Mechanochemical synthesis of mesoporous tin oxide: a new generation nanosorbent for (68)Ge/(68)Ga generator technology.

The present article reports the synthesis and characterization of mesoporous tin oxide (MTO) nanoparticles by a solid-state mechanochemical route. The synthesized material was used as an advanced sorbent material for (68)Ge/(68)Ga radionuclide generator technology. Gallium-68 (t½ = 68 min) obtained from the (68)Ge/(68)Ga generator is an important diagnostic radioisotope which holds tremendous potential in the non-invasive monitoring of various diseases, including cancer, using positron emission tomography (PET). The crystallite size of the MTO nanoparticles was in the range of 6-12 nm with a large surface area of 265 ± 16 m(2) g(-1), while the mean pore radius was found to be 2.1 ± 0.6 nm. Determination of the zeta-potential of the MTO nanoparticles dispersed in solutions at different pH values aided in understanding the sorption and separation mechanisms, which were based on the surface charge developed on the nanosorbent. The sorption capacity observed under column-flow conditions was 85 ± 5 mg Ge per g of nanosorbent. A clinical-scale (68)Ge/(68)Ga generator (740 MBq) was developed using this nanosorbent. Gallium-68 could be regularly eluted from this generator over a prolonged period of 1 year with >70% elution yield and met all the requirements for clinical use. The suitability of (68)Ga obtained from it was evaluated in preclinical settings by the preparation of a (68)Ga-labeled peptide containing the arginine-glycine-aspartic acid (RGD) motif. To the best of our knowledge, this is the first report on the synthesis of MTO nanoparticles by a mechanochemical route which could be effectively utilized for the routine preparation of clinical-scale (68)Ge/(68)Ga generators. The promising results obtained in this study would facilitate greater implementation of mechanochemistry for the synthesis of nanosorbents for radionuclide generator technology since this method is simple, economical and convenient.

(131)I-Nimotuzumab - A potential radioimmunotherapeutic agent in treatment of tumors expressing EGFR.

The anti-EGFR antibody Nimotuzumab was radioiodinated with I-131 by Chloramine T and Iodogen methods. The (131)I-Nimotuzumab was purified and characterized by HPLC. Purified (131)I-Nimotuzumab exhibited radiochemical purity of >95% and retained good in vitro stability upto 24h at room temperature by both the methods. Cell binding studies carried out in A431 cells expressing EGF receptors showed good immunoreactivity of the product upto 5 days post radioiodination. Biodistribution studies in normal Swiss mice showed fast clearance by both renal and gastrointestinal routes with minimal thyroid uptake.

Radiosynthesis and bioevaluation of [68Ga]-labeled 5,10,15,20-tetra(4-methylpyridyl)-porphyrin for possible application as a PET radiotracer for tumor imaging.

PURPOSE: Porphyrins have inherent ability to localize preferentially in tumor lesions. Cationic porphyrins are readily water soluble and reported to exhibit strong DNA-binding capabilities. Therefore, attempt has been made to prepare a water soluble [(68)Ga]-labeled cationic porphyrin, viz., 5,10,15,20-tetra(4-methylpyridyl)porphyrin (TMP), and evaluate its potential as a positron emission tomography (PET) radiotracer for tumor imaging. PROCEDURES: The cationic porphyrin TMP was synthesized following a two-step procedure and subsequently radiolabeled with Ga-68, eluted from a commercial (68)Ge/(68)Ga generator. Purification of the [(68)Ga]-labeled porphyrin derivative was carried out using Sep-Pak(®) cartridges. The tumor-targeting potential of the [(68)Ga]-labeled-5,10,15,20-tetra(4-methylpyridyl)porphyrin was evaluated by biodistribution studies in Swiss mice bearing fibrosarcoma tumor. RESULTS: Under optimized reaction conditions, [(68)Ga]-labeled TMP was obtained with ~90 % radiochemical purity which was subsequently improved to >99 % after purification through Sep-Pak(®) cartridges. Biodistribution studies revealed high tumor uptake of the radiotracer within 30-min post-injection (6.47 ± 0.87 % of injected activity) and retention until the final 2 h post-administration (4.48 ± 1.11 % of injected activity) time point. The initial uptake observed in non-target organs cleared away with time resulting in gradually improving tumor/blood and tumor/muscle ratios. CONCLUSION: Preliminary bioevaluation studies indicated the potential of the radiolabeled porphyrin derivative for tumor imaging, and further detailed studies are warranted to evaluate the true potential of the developed radiotracer.

Single vial freeze-dried TRODAT-1 kit: preparation and demonstration of clinical efficacy of [(99m)Tc]TRODAT-1 in Indian scenario.

A single vial freeze-dried kit formulation for preparation of three patients' dose of [(99m)Tc]TRODAT-1 has been developed for early diagnosis of Parkinson's disease (PD). Kits were evaluated to ascertain the purity, stability and batch to batch variations. Preclinical evaluation was carried out in laboratory animals and clinical imaging was performed in human patients with PD. The labeling yield and purity of [(99m)Tc]TRODAT-1 was >90%. Swiss mice showed retention of [(99m)Tc]TRODAT-1 in the mid brain region. Clinical studies showed decreased striatal uptake with increasing severity of PD.

99mTc carbonyl DTPA-rituximab: preparation and preliminary bioevaluation.

The anti CD20 antibody Rituximab was conjugated with para isothiocyanato benzyl diethylene triamine penta acetic acid (p-NCS-Bz-DTPA) and subsequent radiolabeling with (99m)Tc was carried out via the (99m)Tc carbonyl synthon. The (99m)Tc labeled antibody conjugate exhibited >95% radiochemical purity after purification and retained good in vitro stability when studied up to 24h at room temperature. In vitro cell binding studies carried out in Raji cells expressing CD20 antigen validated the biological efficacy of the preparation.

Biocompatibility, biodistribution and efficacy of magnetic nanohydrogels in inhibiting growth of tumors in experimental mice models.

We report in vivo evaluation of a thermo-responsive poly(N-isopropylacrylamide)-chitosan based magnetic nanohydrogel (MNHG) incorporated with Fe3O4 nanoparticles (NPs) in mice models with expandible scope for use in localized delivery of chemotherapeutics. Biocompatibility and biodistribution of the MNHG are studied in normal Swiss mice while efficacy in tumor growth inhibition is studied in a subcutaneous fibrosarcoma tumor. The ex vivo time-dependent pattern of accumulated MNHG into vital organs; lung, liver, spleen, kidney and brain collected at 1 h, 48 h, 7 d and 14 d post intravenous administration are investigated using both a vibrating sample magnetometer (VSM) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) method. The doses of MNHG (dose I ∼ 650 and dose II ∼ 325 µg g-1 body wt) used in the study are determined based on induced thermal activation of MNHG under an AC magnetic field (AMF). Fibrosarcoma tumor bearing mice are subjected to hyperthermia with a field of 325 Oe and 265 kHz for 30 min following intratumoral administration of dose I. Tumor size measured at an interval of 72 h for a period of 2 weeks reveals that the NPs mediated therapy decelerated the growth of the transplanted tumor by about three-fold (size, 1545 ± 720 mm3) as compared to the exponential growth of the tumor (size, 4510 ± 735 mm3) in control mice. These results suggest the feasibility of using poly(NIPAAm)-chitosan hydrogels loaded with NPs for combined thermo-chemotherapy where the efficacy may further be improved by temperature dependent release of the drugs from the magneto hydrogels.

Preparation and biological studies of 125I-DOTA-TATE.

DOTA-TATE, a somatostatin analog was radiolabeled with (125)I in good yields and high radiochemical purity. The product exhibited good stability in vitro. Pharmacokinetic studies in normal Swiss mice showed rapid blood clearance with low thyroid uptake. Biodistribution studies in murine melanoma showed 3.0+/-1.3% ID/g uptake in tumor at 3h post injection (p.i.), with negligible reduction at 24h p.i. Inhibition studies carried out in vivo using cold DOTA-TATE confirmed the tumor specificity of the product.