Synthesis and Evaluation of ePSMA-DM1:A New Theranostic Small-Molecule Drug Conjugate (T-SMDC) for Prostate Cancer

Small-molecule drug conjugates (SMDCs) are compounds in which a therapeutic payload is conjugated to a targeting vector, for specific delivery to the tumor site. This promising approach can be translated to the treatment of prostate cancer by selecting a targeting vector which binds to the prostate-specific membrane antigen (PSMA). Moreover, the addition of a bifunctional chelator to the molecule allows for the use of both diagnostic and therapeutic radionuclides. In this way, the distribution of the SMDC in the body can be monitored, and combination therapy regimes can be implemented. We combined a glutamate-urea-lysine vector to the cytotoxic agent DM1 and a DOTA chelator via an optimized linker to obtain the theranostic SMDC (T-SMDC) ePSMA-DM1. ePSMA-DM1 retained a high binding affinity to PSMA and demonstrated PSMA-specific uptake in cells. Glutathione stability assays showed that the half-life of the T-SMDC in a reducing environment was 2 h, and full drug release was obtained after 6 h. Moreover, 100 nM of ePSMA-DM1 reduced the cell viability of the human PSMA-positive LS174T cells by &gt;85% after 72 h of incubation, which was comparable to a 10-fold higher dose of free DM1. [111In]In-ePSMA-DM1 and [177Lu]Lu-ePSMA-DM1 were both obtained in high radiochemical yields and purities (&gt;95%), with &gt;90% stability in PBS and &gt;80% stability in mouse serum for up to 24 h post incubation at 37 °C. SPECT/CT imaging studies allowed for a faint tumor visualization of [111In]In-ePSMA-DM1 at 1 h p.i., and the ex vivo biodistribution showed tumor uptake (2.39 ± 0.29% ID/g) at 1 h p.i., with the compound retained in the tumor for up to 24 h. Therefore, ePSMA-DM1 is a promising T-SMDC candidate for prostate cancer, and the data obtained so far warrant further investigations, such as therapeutic experiments, after further optimization.</p

Synthesis and radiolabelling of PSMA-targeted derivatives containing GYK/MVK cleavable linkers

Targeted radionuclide therapy (TRT) is a promising strategy to treat different types of cancer. TRT relies on a targeting vector used to deliver a therapeutic radionuclide specifically to the tumour site. Several low molecular weight ligands targeting the prostate-specific membrane antigen (PSMA) have been synthesized, but their pharmacokinetic properties still need to be optimized. Hereby, we describe the synthesis of new conjugates, featuring the cleavable linkers Gly-Tyr-Lys (GYK) and Met-Val-Lys (MVK), to reduce the dose delivered to the kidneys. Compounds were synthesized by solid-phase peptide synthesis (SPPS) and obtained in greater than 95% chemical purity. Radiolabelling was performed with both In-111 and Lu-177 to validate potential use of the compounds as both imaging and therapeutic agents. Radiochemical purity greater than 80% was obtained for both nuclides, but significant radiolysis was observed for the methionine-containing analogue. The results obtained thus far with the GYK-PSMA conjugate could warrant further biological investigations

Preclinical Evaluation of a PSMA-Targeting Homodimer with an Optimized Linker for Imaging of Prostate Cancer

Prostate-specific membrane antigen (PSMA) targeting radiopharmaceuticals have been successfully used for diagnosis and therapy of prostate cancer. Optimization of the available agents is desirable to improve tumor uptake and reduce side effects to non-target organs. This can be achieved, for instance, via linker modifications or multimerization approaches. In this study, we evaluated a small library of PSMA-targeting derivatives with modified linker residues, and selected the best candidate based on its binding affinity to PSMA. The lead compound was coupled to a chelator for radiolabeling, and subject to dimerization. The resulting molecules, 22 and 30, were highly PSMA specific (IC50 = 1.0-1.6 nM) and stable when radiolabeled with indium-111 (>90% stable in PBS and mouse serum up to 24 h). Moreover, [111In]In-30 presented a high uptake in PSMA expressing LS174T cells, with 92.6% internalization compared to 34.1% for PSMA-617. Biodistribution studies in LS174T mice xenograft models showed that [111In]In-30 had a higher tumor and kidney uptake compared to [111In]In-PSMA-617, but increasing T/K and T/M ratios at 24 h p.i. Tumors could be clearly visualized at 1 h p.i. by SPECT/CT after administration of [111In]In-22 and [111In]In-PSMA-617, while [111In]In-30 showed a clear signal at later time-points (e.g., 24 h p.i.)

Radiochemical and Biological Evaluation of 3p-<i>C</i>-NETA-ePSMA-16, a Promising PSMA-Targeting Agent for Radiotheranostics

Bifunctional chelators (BFCs) are a key element in the design of radiopharmaceuticals. By selecting a BFC that efficiently complexes diagnostic and therapeutic radionuclides, a theranostic pair possessing almost similar biodistribution and pharmacokinetic properties can be developed. We have previously reported 3p-C-NETA as a promising theranostic BFC, and the encouraging preclinical outcomes obtained with [18F]AlF-3p-C-NETA-TATE led us to conjugate this chelator to a PSMA-targeting vector for imaging and treatment of prostate cancer. In this study, we synthesized 3p-C-NETA-ePSMA-16 and radiolabeled it with different diagnostic (111In, 18F) and therapeutic (177Lu, 213Bi) radionuclides. 3p-C-NETA-ePSMA-16 showed high affinity to PSMA (IC50 = 4.61 ± 1.33 nM), and [111In]In-3p-C-NETA-ePSMA-16 showed specific cell uptake (1.41 ± 0.20% ID/106 cells) in PSMA expressing LS174T cells. Specific tumor uptake of [111In]In-3p-C-NETA-ePSMA-16 was observed up to 4 h p.i. (1.62 ± 0.55% ID/g at 1 h p.i.; 0.89 ± 0.58% ID/g at 4 h p.i.) in LS174T tumor-bearing mice. Only a faint signal could be seen at 1 h p.i. in the SPECT/CT scans, whereas dynamic PET/CT scans performed after administration of [18F]AlF-3p-C-NETA-ePSMA-16 in PC3-Pip tumor xenografted mice resulted in a better tumor visualization and imaging contrast. Therapy studies with short-lived radionuclides such as 213Bi could further elucidate the therapeutic potential of 3p-C-NETA-ePSMA-16 as a radiotheranostic

Direct comparison of [ 18F]AlF-NOTA-JR11 and [ 18F]AlF-NOTA-octreotide for PET imaging of neuroendocrine tumors: Antagonist versus agonist.

BACKGROUND: [ 18F]AlF-NOTA-octreotide is an 18F-labeled somatostatin analogue which is a good clinical alternative for 68Ga-labeled somatostatin analogues. However, radiolabeled somatostatin receptor (SSTR) antagonists might outperform agonists regarding imaging sensitivity of neuroendocrine tumors (NETs). No direct comparison between the antagonist [ 18F]AlF-NOTA-JR11 and the agonist [ 18F]AlF-NOTA-octreotide as SSTR PET probes is available. Herein, we present the radiosynthesis of [ 18F]AlF-NOTA-JR11 and compare its NETs imaging properties directly with the established agonist radioligand [ 18F]AlF-NOTA-octreotide preclinically. METHODS: [ 18F]AlF-NOTA-JR11 was synthesized in an automated synthesis module. The in vitro binding characteristics (IC 50) of [ natF]AlF-NOTA-JR11 and [ natF]AlF-NOTA-octreotide were evaluated and the in vitro stability of [ 18F]AlF-NOTA-JR11 was determined in human serum. In vitro cell binding and internalization was performed with [ 18F]AlF-NOTA-JR11 and [ 18F]AlF-NOTA-octreotide using SSTR2 expressing cells and the pharmacokinetics were evaluated using μPET/CT in mice bearing BON1.SSTR2 tumor xenografts. RESULTS: Excellent binding affinity for SSTR2 was found for [ natF]AlF-NOTA-octreotide (IC 50 of 25.7 ± 7.9 nM). However, the IC 50 value for [ natF]AlF-NOTA-JR11 (290.6 ± 71 nM) was 11-fold higher compared to [ natF]AlF-NOTA-octreotide, indicating lower affinity for SSTR2. [ 18F]AlF-NOTA-JR11 was obtained in a good RCY (50 ± 6 %) but with moderate RCP of 94 ± 1 %. [ 18F]AlF-NOTA-JR11 demonstrated excellent stability in human serum (>95 % after 240 min). 2.7-fold higher cell binding was observed for [ 18F]AlF-NOTA-JR11 as compared to [ 18F]AlF-NOTA-octreotide after 60 min. μPET/CT images demonstrated comparable pharmacokinetics and tumor uptake between [ 18F]AlF-NOTA-JR11 (SUV max: 3.7 ± 0.8) and [ 18F]AlF-NOTA-octreotide (SUV max: 3.6 ± 0.4). CONCLUSIONS: [ 18F]AlF-NOTA-JR11 was obtained in good RCY, albeit with a moderate RCP. The cell binding study showed significant higher binding of [ 18F]AlF-NOTA-JR11 compared to [ 18F]AlF-NOTA-octreotide, despite the higher IC 50 value of AlF-NOTA-JR11. However, pharmacokinetics and in vivo tumor uptake was comparable for both radiotracers. Novel Al 18F-labeled derivatives of JR11 with higher SSTR2 affinity should be developed for increased tumor uptake and NET imaging sensitivity

Chloroquine analogs as antimalarial candidates with potent in vitro and in vivo activity

In spite of recent efforts to eradicate malaria in the world, this parasitic disease is still considered a major public health problem, with a total of 216 million cases of malaria and 445,000 deaths in 2016. Artemisinin-based combination therapies remain effective in most parts of the world, but recent cases of resistance in Southeast Asia have urged for novel approaches to treat malaria caused by Plasmodium falciparum. In this work, we present chloroquine analogs that exhibited high activity against sensitive and chloroquine-resistant P. falciparum blood parasites and were also active against P. berghei infected mice. Among the compounds tested, DAQ, a chloroquine analog with a more linear side chain, was shown to be the most active in vitro and in vivo, with low cytotoxicity, and therefore may serve as the basis for the development of more effective chloroquine analogs to aid malaria eradication. Keywords: Malaria, Chloroquine, Resistance, Drug desig