Synthesis and first evaluation of [18F]fluorocyano- and [18F]fluoronitro-quinoxalinedione as putative AMPA receptor antagonists

Abstract:Derivatives of quinoxalinedione (QX) were chosen as chemical lead for the development of new radioligands of the AMPA receptor, since there are several examples of QX-derivatives with high affinity. The radiosyntheses of the new compounds 6-[18F]fluoro-7-nitro-QX ([18F]FNQX) and 7-[18F]fluoro-6-cyano-QX ([18F]FCQX) with radiochemical yields of 8 ± 2 and 3 ± 2 %, respectively, as well as the evaluation of their binding properties to the AMPA-receptor were performed. A comparison of the Ki-values of the new QX-derivatives FCQX and FNQX with mono-substituted cyanoand nitro-QX shows negligibly small differences of affinity (within the range of 1.4 to 5 µM), but exhibits a tenfold lower affinity than derivatives with two electron withdrawing groups like the 7-cyano-6-nitro-compound CNQX and the 6,7- dinitro compound DNQX. Thus, with respect to the low affinity and a high non-specific binding with in vitro and ex vivo autoradiographic studies, the new compounds do not lend themselves for in vivo imaging.- See more at: http://www.eurekaselect.com/121871/article#sthash.JGpS3IVS.dpu

Synthesis and preliminary pharmacological evaluation of a new putative radioiodinated AMPA receptor ligand for molecular imaging

Summary A new (radio)iodinated AMPA receptor ligand has been developed and pharmacologically evaluated in vitro and ex vivo using rodents. The new radioligand was directly labeled by electrophilic radioiodo-destannylation with iodine- 131 in high radiochemical yields of 97% within 2 min. The new radioligand showed an excellent initial brain uptake of 2.1%ID/g at 10 min post injection, but a fast wash-out reduced the uptake by about 10-fold at 60 min post injection. Due to high nonspecific binding accompanied with a uniform distribution in brain tissue, however, the new radiotracer appears not suitable for AMPA receptor imaging in vivo.</jats:p

Radiolabeled Cetuximab Conjugates for EGFR Targeted Cancer Diagnostics and Therapy

The epidermal growth factor receptor (EGFR) has evolved over years into a main molecular target for the treatment of different cancer entities. In this regard, the anti-EGFR antibody cetuximab has been approved alone or in combination with: (a) chemotherapy for treatment of colorectal and head and neck squamous cell carcinoma and (b) with external radiotherapy for treatment of head and neck squamous cell carcinoma. The conjugation of radionuclides to cetuximab in combination with the specific targeting properties of this antibody might increase its therapeutic efficiency. This review article gives an overview of the preclinical studies that have been performed with radiolabeled cetuximab for imaging and/or treatment of different tumor models. A particularly promising approach seems to be the treatment with therapeutic radionuclide-labeled cetuximab in combination with external radiotherapy. Present data support an important impact of the tumor micromilieu on treatment response that needs to be further validated in patients. Another important challenge is the reduction of nonspecific uptake of the radioactive substance in metabolic organs like liver and radiosensitive organs like bone marrow and kidneys. Overall, the integration of diagnosis, treatment and monitoring as a theranostic approach appears to be a promising strategy for improvement of individualized cancer treatment

Preparation of 5-[I-131]iodotubercidin for the detection of adenosine kinase

5-Iodotubercidin is a prototype adenosine kinase (AK) inhibitor with potent anti-seizure activity in rodent epilepsy models. Using the chloramine-T method for radioiodination of tubercidin with I-131, we prepared no-carrier-added 5-[I-131]iodotubercidin (5-[I-131]IT) in a radiochemical yield of 61 +/- 13% and with a radiochemical purity of > 99% (molar activity = 10-40 GBq/mu mol). In vitro competition and saturation experiments demonstrated specific binding of 5-[I-131]IT in rodent brain slices (K-D similar to 31 nM), but ex vivo autoradiography revealed its accumulation in cerebral vessels. We conclude that 5-[I-131]IT could be a useful tool for the detection and quantification of AK in in vitro studies

Bispecific PSMA-617 / RM2 Heterodimer for Theranostics Applications in Prostate Cancer

PSMA and GRPR protein receptors are upregulated during prostate cancer (PCa) progression, and thus they have both been used for diagnostic molecular imaging and therapy of the disease. To address tumor heterogeneity, we synthesized and evaluated the bispecific PSMA/GRPR ligand (3) with a 10 atom spacer between PSMA-617 (1) and the GRPR antagonist RM2 (2) generated with click chemistry and coupled with chelator DOTA, to enable radiolabelling. Ligand 3 was radiolabelled with 68Ga, [68Ga]Ga-3 and 177Lu, [177Lu]Lu-3. [68Ga]Ga-3 was tested with PCa cell lines PC-3 and LNCaP for its affinity for GRPR and PSMA receptors, lipophilicity, for its cell-binding specificity, time kinetic binding affinities and cell-internalization. Heterodimer 3 showed specific cell binding, similar affinities for PSMA receptor and GRPR and higher lipophilicity compared to monomers PSMA-617 (1) and RM2 (2), while total internalization rates and cell-binding were superior over monomers. Docking calculations showed that the PSMA-617 (1) /RM2 (2) heterodimer 3 can have binding interactions of PSMA-617 (1) inside the PSMA receptor funnel and of RM2 (2) inside the GRPR. In vivo biodistribution studies for [68Ga]Ga-3 showed dual targeting of PSMA-positive tumors and GRPR-positive tumors and fast pharmacokinetic properties, higher cancer cell-uptake and lower kidney uptake in comparison to the monomers

Melanoma targeting with [99mTc(N)(PNP3)]-labeled α-melanocyte stimulating hormone peptide analogs: Effects of cyclization on the radiopharmaceutical properties

none12The purpose of this study was to evaluate the effect of cyclization on the biological profile of a [99mTc(N)(PNP3)]-labeled α-melanocyte stimulating hormone peptide analog. A lactam bridge-cyclized H-Cys-Ahx-βAla3-c[Lys4-Glu-His-D-Phe-Arg-Trp-Glu10]-Arg11-Pro-Val-NH2 (NAP-NS2) and the corresponding linear H-Cys-Ahx-βAla-Nle-Asp-His-D-Phe-Arg-Trp-Gly-NH2 (NAP-NS1) peptide were synthetized, characterized by ESI-MS spectroscopy and their melanocortin-1 receptor (MC1R) binding affinity was determined in B16/F10 melanoma cells. The consistent [99mTc(N)(PNP3)]-labeled compounds were readily obtained in high specific activity and their stability and biological properties were assessed. As an example, the chemical identity of [99mTc(N)(NAP-NS1)(PNP3)]+ was confirmed by carrier added experiments supported by radio/UV HPLC analysis combined with ESI(+)-MS. Compared with the linear peptide, cyclization negatively affected the biological properties of NAP-NS2 peptide by reducing its binding affinity for MC1R and by decreasing the overall excretion rate of the corresponding [99mTc(N)(PNP3)]-labeled peptide from the body as well as its in vivo stability. [99mTc(N)(NAP-NS1)(PNP3)]+ was evaluated for its potential as melanoma imaging probe in murine melanoma model. Data from in vitro and in vivo studies on B16/F10 melanoma model of [99mTc(N)(NAP-NS1)(PNP3)]+ clearly evidenced that the radiolabeled linear peptide keeps its biological properties up on the conjugation to the [99mTc(N)(PNP3)]-building block. The progressive increase of the tumor-to-nontarget ratios over the time indicates a quite stable interaction between the radio-complex and the MC1R.noneCarta, Davide; Salvarese, Nicola; Morellato, Nicolò; Gao, Feng; Sihver, Wiebke; Pietzsch, Hans Jurgen; Biondi, Barbara; Ruzza, Paolo; Refosco, Fiorenzo; Carpanese, Debora; Rosato, Antonio; Bolzati, CristinaCarta, Davide; Salvarese, Nicola; Morellato, Nicolo'; Gao, Feng; Sihver, Wiebke; Pietzsch, Hans Jurgen; Biondi, Barbara; Ruzza, Paolo; Refosco, Fiorenzo; Carpanese, Debora; Rosato, Antonio; Bolzati, Cristin

Molecular Response to Combined Molecular- and External Radiotherapy in Head and Neck Squamous Cell Carcinoma (HNSCC)

Combination treatment of molecular targeted and external radiotherapy is a promising strategy and was shown to improve local tumor control in a HNSCC xenograft model. To enhance the therapeutic value of this approach, this study investigated the underlying molecular response. Subcutaneous HNSCC FaDuDD xenografts were treated with single or combination therapy (X-ray: 0, 2, 4 Gy; anti-EGFR antibody (Cetuximab) (un-)labeled with Yttrium-90 (90Y)). Tumors were excised 24 h post respective treatment. Residual DNA double strand breaks (DSB), mRNA expression of DNA damage response related genes, immunoblotting, tumor histology, and immunohistological staining were analyzed. An increase in number and complexity of residual DNA DSB was observed in FaDuDD tumors exposed to the combination treatment of external irradiation and 90Y-Cetuximab relative to controls. The increase was observed in a low oxygenated area, suggesting the expansion of DNA DSB damages. Upregulation of genes encoding p21cip1/waf1 (CDKN1A) and GADD45α (GADD45A) was determined in the combination treatment group, and immunoblotting as well as immunohistochemistry confirmed the upregulation of p21cip1/waf1. The increase in residual γH2AX foci leads to the blockage of cell cycle transition and subsequently to cell death, which could be observed in the upregulation of p21cip1/waf1 expression and an elevated number of cleaved caspase-3 positive cells. Overall, a complex interplay between DNA damage repair and programmed cell death accounts for the potential benefit of the combination therapy using 90Y-Cetuximab and external radiotherapy