Recent Advances in Fluorescent Theranostics for Alzheimer's Disease: A Comprehensive Survey on Design, Synthesis, and Properties

Alzheimer's disease (AD) is the most common form of neurodegenerative dementia that is rapidly becoming a major health problem, especially in developed countries because of their increasing life expectancy. Two main problems are often associated with the disease: (i) the absence of a widely accessible "gold-standard" for early diagnosis and (ii) lack of effective therapies with disease-modifying effects. The recent success of the monoclonal antibody lecanemab played an important role not only in clarifying a possible druggable pathway but also in spelling the revival of small molecule drug discovery. Unlike bulky biologics, small molecules are structurally less complex, generally cheaper, and compatible with at-home oral consumption, making it feasible for people to start their drug regimen early and stay on it longer. In this sense, small-molecule near-infrared fluorescent theranostics have been gaining more and more attention from the scientific community, as they have the potential to simultaneously provide diagnostic outputs and deliver therapeutic action, paving the way toward personalized medicine in AD patients. They also have the potential to shift the diagnostic "status-quo" from expensive and limited-access PET radiotracers toward inexpensive and handy imaging tools widely available for primary patient screening and preclinical animal studies. Herein, we review the most recent advances in the field of fluorescent theranostics for Alzheimer's disease, detailing their design strategies, synthetic approaches and imaging and therapeutic properties in vitro and in vivo. With this Review, we intend to provide a milestone in the acquired knowledge in the field of AD theranostics, encouraging the future development of properly designed theranostic compounds with improved chances to reach clinical applications.

Drug Discovery Based on Oxygen and Nitrogen (Non-)Heterocyclic Compounds Developed @LAQV-REQUIMTE/Aveiro

Artur Silva's research group has a long history in the field of medicinal chemistry. The development of new synthetic methods for oxygen (mostly polyphenols, e.g., 2- and 3-styrylchromones, xanthones, flavones) and nitrogen (e.g., pyrazoles, triazoles, acridones, 4-quinolones) heterocyclic compounds in order to be assessed as antioxidant, anti-inflammatory, antidiabetic, and anticancer agents has been the main core work of our research interests. Additionally, the synthesis of steroid-type compounds as anti-Alzheimer drugs as well as of several chromophores as important dyes for cellular imaging broadened our research scope. In this review article, we intend to provide an enlightened appraisal of all the bioactive compounds and their biological properties that were synthesized and studied by our research group in the last two decades.

Gossypetin Is a Novel Modulator of Inflammatory Cytokine Production and a Suppressor of Osteosarcoma Cell Growth

Osteosarcoma (OS) is a common childhood sarcoma, and its treatment is hindered by adverse effects, chemoresistance, and recurrence. Interleukin (IL)-6 production by tumors plays a significant role in inflammation, carcinogenesis, and metastasis. This study aimed to investigate the antiproliferative potential of luteolin derivatives in OS and to evaluate interleukin production. MG-63, Saos-2, HOS, and 143B human OS cell lines were incubated with luteolin and eight derivatives containing hydroxy, chlorine, or alkyl substitutions. The cell viability and growth were evaluated in the presence of these compounds. Apoptosis was also examined through the analysis of the Bax expression and caspase-3 activity. Finally, the gossypetin effects were measured regarding the production of proinflammatory cytokines interleukin (IL)-6, IL-1β, and IL-12p70. Our findings show that gossypetin was the most potent compound, with proliferation-suppressing activities that induced a series of critical events, including the inhibition of the cell viability and growth. Apoptosis was associated with enhanced caspase-3 activity and increased Bax expression, indicating the involvement of the intrinsic pathway of apoptosis. Moreover, pre-/co-treatment with gossypetin significantly reduced the autocrine production of proinflammatory cytokines. Further investigation is required; nevertheless, considering the link between inflammation, carcinogenesis, and metastasis in OS, our findings suggest that gossypetin exhibits anti-proliferative and anti-inflammatory properties that are potentially relevant in the clinical context.

Selective Induction of DNA Damage and Cell Cycle Arrest Mediated by Chromone-Triazole Dyads Derivatives: Effects on Breast and Prostate Cancer Cells

Chromones and triazoles are groups of heterocyclic compounds widely known to exhibit a broad spectrum of biological activities. The combination of these two pharmacophores could result in multiple mechanisms of action to increase the potency of anticancer drugs and reduce their side effects. The in vitro antitumor effect of eight chromone-based compounds was evaluated in breast (T-47D and MDA-MB-231) and prostate (PC3) cancer cell lines, and in non-cancerous human mammary epithelial cells (HuMEC) using a resazurin-based method. Flow cytometry was used to evaluate the cell cycle and cell death, and ɣ-H2AX detection to identify DNA damage. The compounds showed selective cytotoxicity against cancer cell lines, with (E)-2-(2-(5-(4-methoxyphenyl)-2H-1,2,3-triazol-4-yl)vinyl)-4H-chromen-4-one (compound 2 a) being more potent in non-metastatic T-47D cells (IC₅₀ 0.65 μM). Replacing the hydrogen by a methyl group on the triazole ring in compound 2 b enhanced the cytotoxic activity up to IC₅₀ 0.24 μM in PC3, 0.32 μM in MDA-MB-231 and 0.52 μM in T-47D. Compound 2 b was 3-fold more potent than doxorubicin in PC3 (IC₅₀ 0.73 μM) and 4-fold in MDA-MB-231 (IC₅₀ 1.51 μM). The addition of tetrahydroisoindole-1,3-dione moiety in compound 5 did not improve its effectiveness in any of the cell lines but it exerted the lowest cytotoxic effect in HuMEC (IC₅₀ 221.35 μM). The compounds revealed different cytotoxic mechanisms: 2 a and 2 b induced G2/M arrest, and compound 5 did not affect the cell cycle.

Steroid-Quinoline Hybrids for Disruption and Reversion of Protein Aggregation Processes

Reversing protein aggregation within cells may be an important tool to fight protein-misfolding disorders such as Alzheimer's, Parkinson's, and cardiovascular diseases. Here we report the design and synthesis of a family of steroid-quinoline hybrid compounds based on the framework combination approach. This set of hybrid compounds effectively inhibited Aβ1-42 self-aggregation in vitro by delaying the exponential growth phase and/or reducing the quantity of fibrils in the steady state. Their disaggregation efficacy was further demonstrated against preaggregated Aβ1-42 peptides in cellular assays upon their endocytosis by neuroblastoma cells, as they reverted both the number and the average area of fibrils back to basal levels. The antiaggregation effect of these hybrids was further tested and demonstrated in a cellular model of general protein aggregation expressing a protein aggregation fluorescent sensor. Together, our results show that the new cholesterol-quinoline hybrids possess wide and marked disaggregation capacities and are therefore promising templates for the development of new drugs to deal with conformational disorders.

An In Silico and an In Vitro Inhibition Analysis of Glycogen Phosphorylase by Flavonoids, Styrylchromones, and Pyrazoles

Glycogen phosphorylase (GP) is a key enzyme in the glycogenolysis pathway. GP inhibitors are currently under investigation as a new liver-targeted approach to managing type 2 diabetes mellitus (DM). The aim of the present study was to evaluate the inhibitory activity of a panel of 52 structurally related chromone derivatives; namely, flavonoids, 2-styrylchromones, 2-styrylchromone-related derivatives [2-(4-arylbuta-1,3-dien-1-yl)chromones], and 4- and 5-styrylpyrazoles against GP, using in silico and in vitro microanalysis screening systems. Several of the tested compounds showed a potent inhibitory effect. The structure–activity relationship study indicated that for 2-styrylchromones and 2-styrylchromone-related derivatives, the hydroxylations at the A and B rings, and in the flavonoid family, as well as the hydroxylation of the A ring, were determinants for the inhibitory activity. To support the in vitro experimental findings, molecular docking studies were performed, revealing clear hydrogen bonding patterns that favored the inhibitory effects of flavonoids, 2-styrylchromones, and 2-styrylchromone-related derivatives. Interestingly, the potency of the most active compounds increased almost four-fold when the concentration of glucose increased, presenting an IC₅₀ < 10 µM. This effect may reduce the risk of hypoglycemia, a commonly reported side effect of antidiabetic agents. This work contributes with important considerations and provides a better understanding of potential scaffolds for the study of novel GP inhibitors.

Microwave Irradiation: Alternative Heating Process for the Synthesis of Biologically Applicable Chromones, Quinolones, and Their Precursors

Microwave irradiation has become a popular heating technique in organic synthesis, mainly due to its short reaction times, solventless reactions, and, sometimes, higher yields. Additionally, microwave irradiation lowers energy consumption and, consequently, is ideal for optimization processes. Moreover, there is evidence that microwave irradiation can improve the regioselectivity and stereoselectivity aspects of vital importance in synthesizing bioactive compounds. These crucial features of microwave irradiation contribute to its inclusion in green chemistry procedures. Since 2003, the use of microwave-assisted organic synthesis has become common in our laboratory, making our group one of the first Portuguese research groups to implement this heating source in organic synthesis. Our achievements in the transformation of heterocyclic compounds, such as (E/Z)-3-styryl-4H-chromen-4-ones, (E)-3-(2-hydroxyphenyl)-4-styryl-1H-pyrazole, (E)-2-(4-arylbut-1-en-3-yn-1-yl)-4H-chromen-4-ones, or (E)-2-[2-(5-aryl-2-methyl-2H-1,2,3-triazol-4-yl)vinyl]-4H-chromen-4-ones, will be discussed in this review, highlighting the benefits of microwave irradiation use in organic synthesis.

Amyloid-β and tau aggregation dual-inhibitors: A synthetic and structure-activity relationship focused review

Alzheimer's disease (AD) is one of the most common types of dementia, especially in elderly, with an increasing number of people suffering from this disease worldwide. There are no available disease-modifying therapies and only four drugs are approved for the relief of symptoms. Currently, the therapeutic approach used for AD treatment is based on single target drugs, which are not capable to stop its progression. To address this issue, multi-target compounds, combining two or more pharmacophores in a single molecular entity, have gained increasing interest to deal with the multiple factors related to AD. The exact cause of AD is not yet completely disclosed, and several hallmarks have been associated to this neurodegenerative disease. Even though, the accumulation of both amyloid-β plaques (Aβ) and neurofibrillary tangles (NFTs) are fully accepted as the main AD hallmarks, being object of lots of research for early-stage diagnosis and pharmacological therapy. In this context, this review summarizes the state-of-the-art in the field of dual-target inhibitors of both Aβ and tau aggregation simultaneously, including the design and synthetic strategy of the dual-target compounds, as well as a brief structure-activity relationships (SAR) analysis.

Cholesterol-Based Compounds: Recent Advances in Synthesis and Applications

This review reports on the latest developments (since 2014) in the chemistry of cholesterol and its applications in different research fields. These applications range from drug delivery or bioimaging applications to cholesterol-based liquid crystals and gelators. A brief overview of the most recent synthetic procedures to obtain new cholesterol derivatives is also provided, as well as the latest anticancer, antimicrobial, and antioxidant new cholesterol-based derivatives. This review discusses not only the synthetic details of the preparation of new cholesterol derivatives or conjugates, but also gives a short summary concerning the specific application of such compounds.

First intramolecular Diels–Alder reactions using chromone derivatives: synthesis of chromeno[3,4-b]xanthones and 2-(benzo[c]chromenyl)chromones

Chromeno[3,4-b]xanthones and 2-(benzo[c]chromenyl) chromones were obtainedviaan MW-assisted intramolecular DA reaction, followed byin situdehydrogenation.