Lipophilicity Determines Routes of Uptake and Clearance, and Toxicity of an Alpha-Particle-Emitting Peptide Receptor Radiotherapy

eSOMA-DM1, a Maytansinoid-Based Theranostic Small-Molecule Drug Conjugate for Neuroendocrine Tumors

Background: The main challenges of conventional chemotherapy lie in its lack of selectivity and specificity, leading to significant side effects. Using a small-molecule drug conjugate (SMDC) ensures specific delivery of a cytotoxic drug to the tumor site by coupling it to a targeting vector. This promising strategy can be applied to neuroendocrine tumors (NETs) by choosing a targeting vector that binds specifically to somatostatin receptor subtype 2 (SSTR2). Additionally, incorporation of a bifunctional chelate into the molecule enables complexation of both diagnostic and therapeutic radionuclides. Thus, it facilitates monitoring of the distribution of the SMDC in the body and allows for the implementation of combination therapy. In our study, we designed eSOMA-DM1, a SMDC combining the SSTR2-targeted octreotate peptide and the cytotoxic agent DM1 via a chelate-bridged linker (N3-Py-DOTAGA). This approach warrants conjugation of the targeting vector and the drug at opposite sites to avoid undesired steric hindrance effects. Methods: Synthesis of the DM1 moiety (4) involved a three-step synthetic route, followed by the conjugation to the cyclic peptide, N3-Py-DOTAGA-d-Phe-cyclo[Cys-Tyr-d-Trp-Lys-Thr-Cys]-Thr-OH, through a copper-free click reaction, resulting in eSOMA-DM1. Subsequent labeling with [111In]InCl3 gave a high radiochemical yield and purity. In vitro assessments of eSOMA-DM1 binding, uptake, and internalization were conducted in SSTR2-transfected U2OS cells. Ex vivo biodistribution and fluorescence imaging were performed in H69-tumor bearing mice. Results: eSOMA-DM1 exhibited an IC50 value for SSTR2 similar to the gold standard DOTA-TATE. The uptake of [111In]In-eSOMA-DM1 in U2OS.SSTR2 cells was 1.2-fold lower than that of [111In]In-DOTA-TATE. Tumor uptake in H69-xenografted mice was higher for [111In]In-eSOMA-DM1 at all-time points compared to [111In]In-DOTA-TATE. Prolonged blood circulation led to increased accumulation of [111In]In-eSOMA-DM1 in highly vascularized tissues, such as the lungs, skin, and heart. Excretion through the kidneys, liver, and spleen was also observed. Conclusion: eSOMA-DM1 is a SMDC developed for NET showing promising characteristics in vitro. However, the in vivo results obtained with [111In]In-eSOMA-DM1 suggest the need for adjustments to optimize its distribution.

Second-generation piperazine derivatives as promising radiation countermeasures

The increasing threat of nuclear incidents and the widespread use of ionizing radiation (IR) in medical treatments underscore the urgent need for effective radiation countermeasures. Despite the availability of compounds such as amifostine, their clinical utility is significantly limited by adverse side effects and logistical challenges in administration. This study focuses on the synthesis and evaluation of novel piperazine derivatives as potential radioprotective agents, with the aim of overcoming the limitations associated with current countermeasures. We designed, synthesized, and evaluated a series of 1-(2-hydroxyethyl)piperazine derivatives. The compounds were assessed for cytotoxicity across a panel of human cell lines, and for their radioprotective effects in the MOLT-4 lymphoblastic leukemia cell line and in peripheral blood mononuclear cells (PBMCs) exposed to gamma radiation. The radioprotective efficacy was further quantified using the dicentric chromosome assay (DCA) to measure DNA damage mitigation. Among the synthesized derivatives, compound 6 demonstrated the most significant radioprotective effects in vitro, with minimal cytotoxicity across the tested cell lines. Compound 3 also showed notable efficacy, particularly in reducing dicentric chromosomes, thus indicating its potential to mitigate DNA damage from IR. Both compounds exhibited superior safety profiles and effectiveness compared to amifostine, suggesting their potential as more viable radioprotective agents. This study highlights the development of novel piperazine derivatives with promising radioprotective properties. Compound 6 emerged as the leading candidate, offering an optimal balance between efficacy and safety, with compound 3 also displaying significant potential. These findings support the further development and clinical evaluation of these compounds as safer, and more effective radiation countermeasures.

64Cu2+ Complexes of Tripodal Amine Ligands' In Vivo Tumor and Liver Uptakes and Intracellular Cu Distribution in the Extrahepatic Bile Duct Carcinoma Cell Line TFK-1: A Basic Comparative Study

Copper (Cu) is a critical element for cancer cell proliferation and considerably accumulates in the nucleus. 64Cu2+ is an anticancer radiopharmaceutical that targets the copper requirement of cancer cells. However, intravenously injected 64Cu2+ ions primarily accumulate in the liver. Ligand complexation of 64Cu2+ may be a promising method for increasing tumor delivery by reducing liver uptake. In this study, we used three tripodal amine ligands [tris(2-aminoethyl)amine (Tren), diethylenetriamine (Dien), and tris(2-pyridylmethyl)amine (TPMA)] to enclose 64Cu2+ ions and compared their in vivo tumor and liver uptakes using a tumor-bearing xenograft mouse model of the extrahepatic bile duct carcinoma cell line TFK-1. We examined intracellular Cu distribution using microparticle-induced X-ray emission (micro-PIXE) analysis of these compounds. 64Cu2+-Tren and 64Cu2+-Dien showed higher tumor uptake than 64Cu2+-TPMA and 64Cu2+ ions in TFK-1 tumors. Among the three 64Cu2+ complexes and 64Cu2+ ions, liver uptake was inversely correlated with tumor uptake. Micro-PIXE analysis showed that in vitro cellular uptake was similar to in vivo tumor uptake, and nuclear delivery was the highest for 64Cu2+-Tren. Conclusively, an inverse correlation between tumor and liver uptake was observed using three 64Cu2+ complexes of tripodal amine ligands and 64Cu2+ ions. These results provide useful information for the future development of anticancer 64Cu radiopharmaceuticals.

Construction of 5-Fluorouracil and Gallium Corrole Conjugates for Enhanced Photodynamic Therapy

Molecular hybridization is a well-established strategy for developing new drugs. In the pursuit of promising photosensitizers (PSs) with enhanced photodynamic therapy (PDT) efficiency, a series of novel 5-fluorouracil (5FU) gallium corrole conjugates (1-Ga-4-Ga) were designed and synthesized by hybridizing a chemotherapeutic drug and PSs. Their photodynamic antitumor activity was also evaluated. The most active complex (2-Ga) possesses a low IC50 value of 0.185 μM and a phototoxic index of 541 against HepG2 cells. Additionally, the 5FU-gallium corrole conjugate (2-Ga) exhibited a synergistic increase in cytotoxicity under irradiation. Excitedly, treatment of HepG2 tumor-bearing mice with 2-Ga under irradiation could completely ablate tumors without harming normal tissues. 2-Ga-mediated PDT could disrupt mitochondrial function, cause cell cycle arrest in the sub-G1 phase, and activate the cell apoptosis pathway by upregulating the cleaved PARP expression and the Bax/Bcl-2 ratios. This work provides a useful strategy for the design of new corrole-based chemo-photodynamic therapy drugs.

eTFC-01: a dual-labeled chelate-bridged tracer for SSTR2-positive tumors

BACKGROUND

Integrating radioactive and optical imaging techniques can facilitate the prognosis and surgical guidance for cancer patients. Using a single dual-labeled tracer ensures consistency in both imaging modalities. However, developing such molecule is challenging due to the need to preserve the biochemical properties of the tracer while introducing bulky labeling moieties. In our study, we designed a trifunctional chelate that facilitates the coupling of the targeting vector and fluorescent dye at opposite sites to avoid undesired steric hindrance effects. The synthesis of the trifunctional chelate N3-Py-DOTAGA-(tBu)3 (7) involved a five-step synthetic route, followed by conjugation to the linear peptidyl-resin 8 through solid-phase synthesis. After deprotection and cyclization, the near-infrared fluorescent dye sulfo-Cy.5 was introduced using copper free click chemistry, resulting in eTFC-01. Subsequently, eTFC-01 was labeled with [111In]InCl3. In vitro assessments of eTFC-01 binding, uptake, and internalization were conducted in SSTR2-transfected U2OS cells. Ex-vivo biodistribution and fluorescence imaging were performed in H69-tumor bearing mice.

RESULTS

eTFC-01 demonstrated a two-fold higher IC50 value for SSTR2 compared to the gold standard DOTA-TATE. Labeling of eTFC-01 with [111In]InCl3 gave a high radiochemical yield and purity. The uptake of [111In]In-eTFC-01 in U2OS.SSTR2 cells was two-fold lower than the uptake of [111In]In-DOTA-TATE, consistent with the binding affinity. Tumor uptake in H69-xenografted mice was lower for [111In]In-eTFC-01 at all-time points compared to [111In]In-DOTA-TATE. Prolonged blood circulation led to increased accumulation of [111In]In-eTFC-01 in highly vascularized tissues, such as lungs, skin, and heart. Fluorescence measurements in different organs correlated with the radioactive signal distribution.

CONCLUSION

The successful synthesis and coupling of the trifunctional chelate to the peptide and fluorescent dye support the potential of this synthetic approach to generate dual labeled tracers. While promising in vitro, the in vivo results obtained with [111In]In-eTFC-01 suggest the need for adjustments to enhance tracer distribution.

N-(2-Tetrafluoro(trifluoromethyl)-λ6-sulfanyl(CF3SF4)-ethyl) Amines: The Influence of the CF3SF4 Group on Lipophilicity and pKa

A practical synthetic path for the preparation of trans-CF3SF4-substituted amines has been described. Primary and secondary amines bearing a variety of different functional groups including amino acids, cyclic amines, and nucleosides were prepared. The desired amines were synthesized under mild conditions. The influence of the CF3SF4-group on the pKa and log D of a standard amine was established. The unusual conformation of the trans-CF3SF4-substituted tosylate has been verified via its crystal structure.

Microbial Metabolites of 3-n-butylphthalide as Monoamine Oxidase A Inhibitors

Novel compounds with antidepressant activity via monoamine oxidase inhibition are being sought. Among these, derivatives of 3-n-butylphthalide, a neuroprotective lactone from Apiaceae plants, may be prominent candidates. This study aimed to obtain the oxidation products of 3-n-butylphthalide and screen them regarding their activity against the monoamine oxidase A (MAO-A) isoform. Such activity of these compounds has not been previously tested. To obtain the metabolites, we used fungi as biocatalysts because of their high oxidative capacity. Overall, 37 strains were used, among which Penicillium and Botrytis spp. were the most efficient, leading to the obtaining of three main products: 3-n-butyl-10-hydroxyphthalide, 3-n-butylphthalide-11-oic acid, and 3-n-butyl-11-hydroxyphthalide, with a total yield of 0.38-0.82 g per g of the substrate, depending on the biocatalyst used. The precursor-3-n-butylphthalide and abovementioned metabolites inhibited the MAO-A enzyme; the most active was the carboxylic acid derivative of the lactone with inhibitory constant (K_i) < 0.001 µmol/L. The in silico prediction of the drug-likeness of the metabolites matches the assumptions of Lipinski, Ghose, Veber, Egan, and Muegge. All the compounds are within the optimal range for the lipophilicity value, which is connected to adequate permeability and solubility.

Preclinical evaluation of chemically reactive metabolites and mitigation of bioactivation in drug discovery

The formation of reactive metabolites (RMs) is thought to be one of the pathogeneses for some idiosyncratic adverse drug reactions (IADRs) which are considered one of the leading causes of some drug attritions and/or recalls. Minimizing or eliminating the formation of RMs via chemical modification is a useful tactic to reduce the risk of IADRs and time-dependent inhibition (TDI) of cytochrome P450 enzymes (CYPs). The RMs should be carefully handled before making a go-no-go decision. Herein, we highlight the role of RMs in the occurrence of IADRs and CYP TDI, the risk of structural alerts, the approaches of RM assessment at the discovery stage and strategies to minimize or eliminate RM liability. Finally, some considerations for developing a RM-positive drug candidate are suggested.

H3TPAN-Triazole-Bn-NH2: Tripicolinate Clicked-Bifunctional Chelate for [225Ac]/[111In] Theranostics

A new, high-denticity, bifunctional ligand─H₃TPAN-triazole-Bn-NH₂─has been synthesized and studied in complexation with [²²⁵Ac]Ac³⁺ and [¹¹¹In]In³⁺ for radiopharmaceutical applications. The bifunctional chelator is readily synthesized, using a high-yielding four-step prep, which is highly adaptable and allows for straightforward incorporation of different covalent linkers using Cu^I-catalyzed alkyne-azide cycloaddition (click) chemistry. Nuclear magnetic resonance (NMR) studies of H₃TPAN-triazole-Bn-NH₂ with La³⁺ and In³⁺ metal ions show the formation of a single, asymmetric complex with each ion in solution, corroborated by density functional theory (DFT) calculations. Radiolabeling studies with [²²⁵Ac]Ac³⁺ and [¹¹¹In]In³⁺ showed highly effective complexation, achieving quantitative radiochemical conversions at low ligand concentrations (<10^-6 M) under mild conditions (RT, 10 min), which is further accompanied by high stability in human serum. The bioconjugate─H₃TPAN-triazole-Bn-Aoc-Pip-Nle-CycMSH_hex─was prepared for targeting of MC1R-positive tumors, and the corresponding ¹¹¹In-radiolabeled tracer was studied in vivo. SPECT/CT and biodistribution studies in C57BL/6J mice bearing B16-F10 tumors were performed, with the radiotracer showing good in vivo stability; tumor uptake was achieved. This work highlights a new promising and versatile bifunctional chelator, easily prepared and encouraging for ²²⁵Ac/¹¹¹In theranostics.

Sawhorse-type ruthenium complexes with triazolopyrimidine ligands - what do they represent in terms of cytotoxic and CORM compounds?

Three sawhorse-type ruthenium(I) complexes containing purine analogs such as triazolopyrimidines of the general formula [Ru₂(CO)₄(μ-OOCCH₃)₂(L)₂], where L is 1,2,4-triazolo[1,5-a]pyrimidine (tp for 1), 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine (dbtp for 2) and 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine (dptp for 3), have been synthesized and characterized by elemental analysis, infrared analysis, multinuclear magnetic resonance spectroscopic techniques (¹H, ¹³C, ¹⁵N), and single-crystal X-ray diffraction (for 1 and 2). By assay with myoglobin, the photo-activated CO-releasing molecule (PhotoCORM) character of (1-3) has been confirmed, thus indicating the possibility of use in CO-based therapies. The importance of UV-induced modification has been investigated in the context of anticancer properties. Complexes (1) and (2) have been thoroughly screened for their in vitro cytotoxicity against various cancer cell lines: MCF-7 (breast cancer), HeLa (cervical cancer) and C32 (melanoma), as well as L929 normal fibroblasts in the dark and presence of UV-A light (365 nm). The results were compared with those for cisplatin and two reference ruthenium complexes, namely NAMI-A and KP1019. The most hydrophilic [Ru₂(CO)₄(μ-OOCCH₃)₂(tp)₂] (1) (log P = -1.12) was found to be more cytotoxic than (2), despite the lower cellular uptake measured by ICP-MS toward HeLa cells. Importantly, photo-induced stimulation of cells with (1) resulted in a lower decrease in the viability of L929 normal cells (IC₅₀ = 154.7 ± 6.5 μM) in comparison with HeLa cancer cells (IC₅₀ = 66.7 ± 3.4 μM). The photo-induced stimulation of (1) and (2) increases ROS generation, and their anticancer activity may be a partially ROS-dependent phenomenon.