Prodrug Candidates Research Articles

Machine Learning-Based Prediction of Reduction Potentials for PtIV Complexes.

Some of the well-known drawbacks of clinically approved PtII complexes can be overcome using six-coordinate PtIV complexes as inert prodrugs, which release the corresponding four-coordinate active PtII species upon reduction by cellular reducing agents. Therefore, the key factor of PtIV prodrug mechanism of action is their tendency to be reduced which, when the involved mechanism is of outer-sphere type, is measured by the value of the reduction potential. Machine learning (ML) models can be used to effectively capture intricate relationships within PtIV complex data, leading to highly accurate predictions of reduction potentials and other properties, and offering significant insights into their electrochemical behavior and potential applications. In this study, a machine learning-based approach for predicting the reduction potentials of PtIV complexes based on relevant molecular descriptors is presented. Leveraging a data set of experimentally determined reduction potentials and a diverse range of molecular descriptors, the proposed model demonstrates remarkable predictive accuracy (MSE = 0.016 V2, RMSE = 0.13 V, R2 = 0.92). Ab initio calculations and a set of different machine learning algorithms and feature engineering techniques have been employed to systematically explore the relationship between molecular structure and similarity and reduction potential. Specifically, it has been investigated whether the reduction potential of these compounds can be described by combining ML models across different combinations of constitutional, topological, and electronic molecular descriptors. Our results not only provide insights into the crucial factors influencing reduction potentials but also offer a rapid and effective tool for the rational design of PtIV complexes with tailored electrochemical properties for pharmaceutical applications. This approach has the potential to significantly expedite the development and screening of novel PtIV prodrug candidates. The analysis of principal components and key features extracted from the model highlights the significance of structural descriptors of the 2D Atom Pairs type and the lowest unoccupied molecular orbital energy. Specifically, with just 20 appropriately selected descriptors, a notable separation of complexes based on their reduction potential value is achieved.

Influence of diimine bidentate ligand in the nitrosyl and nitro terpyridine ruthenium complex on the HSA/DNA interaction and antiviral activity

Nitric oxide (NO) acts in different physiological processes, such as blood pressure control, antiparasitic activities, neurotransmission, and antitumor action. Among the exogenous NO donors, ruthenium nitrosyl/nitro complexes are potential candidates for prodrugs, due to their physicochemical properties, such as thermal and physiological pH stability. In this work, we proposed the synthesis and physical characterization of the new nitro terpyridine ruthenium (II) complexes of the type [RuII(L)(NO2)(tpy)]PF6 where tpy = 2,2':6′,2″-terpyridine; L = 3,4-diaminobenzoic acid (bdq) or o-phenylenediamine (bd) and evaluation of influence of diimine bidentate ligand NH.NHq-R (R = H or COOH) in the HSA/DNA interaction as well as antiviral activity. The interactions between HSA and new nitro complexes [RuII(L)(NO2)(tpy)]+ were evaluated. The Ka values for the HSA–[RuII(bdq)(NO2)(tpy)]+ is 10 times bigger than HSA–[RuII(bd)(NO2)(tpy)]+. The sites of interaction between HSA and the complexes via synchronous fluorescence suppression indicate that the [RuII(bdq)(NO2)(tpy)]+ is found close to the Trp-241 residue, while the [RuII(bd)(NO2)(tpy)]+ complex is close to Tyr residues. The interaction with fish sperm fs-DNA using direct spectrophotometric titration (Kb) and ethidium bromide replacement (KSV and Kapp) showed weak interaction in the system fs-DNA-[RuII(bdq)(NO)(tpy)]+. Furthermore, fs-DNA–[RuII(bd)(NO2)(tpy)]+ and fs-DNA–[RuII(bd)(NO)(tpy)]3+ system showed higher intercalation constant. Circular dichroism spectra for fs-DNA–[RuII(bd)(NO2)(tpy)]+ and fs-DNA–[RuII(bd)(NO)(tpy)]3+, suggest semi-intercalative accompanied by major groove binding interaction modes. The [RuII(bd)(NO2)(tpy)]+ and [RuII(bd)(NO)(tpy)]3+ inhibit replication of Zika and Chikungunya viruses based in the nitric oxide release under S-nitrosylation reaction with cysteine viral.

Antiproliferative activity of platinum(II) and copper(II) complexes containing novel biquinoxaline ligands.

Nowadays, cancer represents one of the major causes of death in humans worldwide, which renders the quest for new and improved antineoplastic agents to become an urgent issue in the field of biomedicine and human health. The present research focuses on the synthesis of 2,3,2',3'-tetra(pyridin-2-yl)-6,6'-biquinoxaline) and (2,3,2',3'-tetra(thiophen-2-yl)-6,6'-biquinoxaline) containing copper(II) and platinum(II) compounds as prodrug candidates. The binding interaction of these compounds with calf thymus DNA (CT-DNA) and human serum albumin were assessed with UV titration, thermal decomposition, viscometric, and fluorometric methods. The thermodynamical parameters and the temperature-dependent binding constant (K'b) values point out to spontaneous interactions between the complexes and CT-DNA via the van der Waals interactions and/or hydrogen bonding, except Cu(ttbq)Cl2 for which electrostatic interaction was proposed. The antitumor activity of the complexes against several human glioblastomata, lung, breast, cervix, and prostate cell lines were investigated by examining cell viability, oxidative stress, apoptosis-terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, in vitro migration and invasion, in vitro-comet DNA damage, and plasmid DNA interaction assays. The U87 and HeLa cells were investigated as the cancer cells most sensitive to our complexes. The exerted cytotoxic effect of complexes was attributed to the formation of the reactive oxygen species in vitro. It is clearly demonstrated that Cu(ttbq)Cl2, Pt(ttbq)Cl2, and Pt(tpbq)Cl2 have the highest DNA degradation potential and anticancer effect among the tested complexes by leading apoptosis. The wound healing and invasion analysis results also supported the higher anticancer activity of these two compounds.

RAPTA-coordinated polydiacetylene self-assembly: A chameleon-like prodrug with a dual-lock strategy for real-time release monitoring of metallodrug.

Herein, we report the first-ever design strategy of modifying RAPTA-C into a self-reporting prodrug candidate based on Ru-coordinated polydiacetylene self-assembly. This nanosystem exhibits a dual lock strategy that responds to visible light and pH-stimuli sequentially one by one with a concomitant color change for controlled RAPTA-C release and real-time release monitoring in human gastric cancer cells.

Novel Psilocin Prodrugs with Altered Pharmacological Properties as Candidate Therapies for Treatment-Resistant Anxiety Disorders.

The psychedelic prodrug psilocybin has shown therapeutic benefits for the treatment of numerous psychiatric conditions. Despite positive clinical end points targeting depression and anxiety, concerns regarding the duration of the psychedelic experience produced by psilocybin, associated with enduring systemic exposure to the active metabolite psilocin, pose a barrier to its therapeutic application. Our objective was to create a novel prodrug of psilocin with similar therapeutic benefits but a reduced duration of psychedelic effects compared with psilocybin. Here, we report the synthesis and functional screening of 28 new chemical entities. Our strategy was to introduce a diversity of cleavable groups at the 4-hydroxy position of the core indole moiety to modulate metabolic processing. We identified several novel prodrugs of psilocin with altered pharmacokinetic profiles and reduced pharmacological exposure compared with psilocybin. These candidate prodrugs have the potential to maintain the long-term benefits of psilocybin therapy while attenuating the duration of psychedelic effects.

T-705-Derived Prodrugs Show High Antiviral Efficacies against a Broad Range of Influenza A Viruses with Synergistic Effects When Combined with Oseltamivir.

Emerging influenza A viruses (IAV) bear the potential to cause pandemics with unpredictable consequences for global human health. In particular, the WHO has declared avian H5 and H7 subtypes as high-risk candidates, and continuous surveillance of these viruses as well as the development of novel, broadly acting antivirals, are key for pandemic preparedness. In this study, we sought to design T-705 (Favipiravir) related inhibitors that target the RNA-dependent RNA polymerase and evaluate their antiviral efficacies against a broad range of IAVs. Therefore, we synthesized a library of derivatives of T-705 ribonucleoside analogues (called T-1106 pronucleotides) and tested their ability to inhibit both seasonal and highly pathogenic avian influenza viruses in vitro. We further showed that diphosphate (DP) prodrugs of T-1106 are potent inhibitors of H1N1, H3N2, H5N1, and H7N9 IAV replication. Importantly, in comparison to T-705, these DP derivatives achieved 5- to 10-fold higher antiviral activity and were non-cytotoxic at the therapeutically active concentrations. Moreover, our lead DP prodrug candidate showed drug synergy with the neuraminidase inhibitor oseltamivir, thus opening up another avenue for combinational antiviral therapy against IAV infections. Our findings may serve as a basis for further pre-clinical development of T-1106 prodrugs as an effective countermeasure against emerging IAVs with pandemic potential.

Safety and Pharmacokinetics of Intravenous and Oral Fosmanogepix, a First-in-Class Antifungal Agent, in Healthy Volunteers

Fosmanogepix (FMGX, APX001), a first-in-class, intravenous (i.v.) and oral (p.o.) antifungal prodrug candidate is currently in clinical development for the treatment of invasive fungal infections. Manogepix (MGX, APX001A), the active moiety of FMGX, interferes with cell wall synthesis by targeting fungal glycosylphosphatidylinositol-anchored cell wall transfer protein 1, thereby causing loss of cell viability. Data from two phase 1, placebo-controlled, single-ascending dose (SAD) and multiple-ascending dose (MAD) studies evaluating safety, tolerability, and pharmacokinetics of FMGX (doses up to 1,000 mg, i.v. and p.o.) are presented. Eligible participants were healthy adults (aged 18 to 55 years) randomized to receive either FMGX or placebo. Across both phase 1 studies, 151 of 154 participants (aged 23 to 35 years; FMGX: 116, placebo: 38) completed the study. Administration of FMGX i.v. demonstrated linear- and dose-proportional pharmacokinetics of MGX in terms of geometric mean maximum concentration of drug in serum (Cmax) (SAD: 0.16 to 12.0 μg/mL, dose: 10 to 1,000 mg; MAD: 0.67 to 15.4 μg/mL, dose: 50 to 600 mg) and area under the concentration-time curve (AUC) (SAD: 4.05 to 400, MAD: 6.39 to 245 μg · h/mL). With single and repeat p.o., dose-proportional increases in Cmax (SAD: 1.30 to 6.41 μg/mL, dose: 100 to 500 mg; MAD: 6.18 to 21.3 μg/mL, dose: 500 to 1,000 mg) and AUC (SAD: 87.5 to 205, MAD: 50.8 to 326 μg · h/mL) were also observed, with high oral bioavailability (90.6% to 101.2%). Administration of FMGX p.o. under post cibum conditions improved tolerability versus ante cibum conditions. No severe treatment-emergent adverse events (TEAEs), serious AEs, or withdrawals due to a drug-related TEAEs were reported with single or multiple i.v. and p.o. doses. Preclinical target exposures were achieved and were not accompanied by any serious/unexpected concerns with generally safe and well-tolerated dose regimens.

A DUSP6 inhibitor suppresses inflammatory cardiac remodeling and improves heart function after myocardial infarction.

Acute myocardial infarction (MI) results in loss of cardiomyocytes and abnormal cardiac remodeling with severe inflammation and fibrosis. However, how cardiac repair can be achieved by timely resolution of inflammation and cardiac fibrosis remains incompletely understood. Our previous findings have shown that dual-specificity phosphatase 6 (DUSP6) is a regeneration repressor from zebrafish to rats. In this study, we found that intravenous administration of the DUSP6 inhibitor (E)-2-benzylidene-3-(cyclohexylamino)-2,3-dihydro-1H-inden-1-one (BCI) improved heart function and reduced cardiac fibrosis in MI rats. Mechanistic analysis revealed that BCI attenuated macrophage inflammation through NF-κB and p38 signaling, independent of DUSP6 inhibition, leading to the downregulation of various cytokines and chemokines. In addition, BCI suppressed differentiation-related signaling pathways and decreased bone-marrow cell differentiation into macrophages through inhibiting DUSP6. Furthermore, intramyocardial injection of poly (D, L-lactic-co-glycolic acid)-loaded BCI after MI had a notable effect on cardiac repair. In summary, BCI improves heart function and reduces abnormal cardiac remodeling by inhibiting macrophage formation and inflammation post-MI, thus providing a promising pro-drug candidate for the treatment of MI and related heart diseases. This article has an associated First Person interview with the first author of the paper.

Succinate prodrugs as treatment for acute metabolic crisis during fluoroacetate intoxication in the rat.

Sodium fluoroacetate (FA) is a metabolic poison that systemically inhibits the tricarboxylic acid (TCA) cycle, causing energy deficiency and ultimately multi-organ failure. It poses a significant threat to society because of its high toxicity, potential use as a chemical weapon and lack of effective antidotal therapy. In this study, we investigated cell-permeable succinate prodrugs as potential treatment for acute FA intoxication. We hypothesized that succinate prodrugs would bypass FA-induced mitochondrial dysfunction, provide metabolic support, and prevent metabolic crisis during acute FA intoxication. To test this hypothesis, rats were exposed to FA (0.75mg/kg) and treated with the succinate prodrug candidate NV354. Treatment efficacy was evaluated based on cardiac and cerebral mitochondrial respiration, mitochondrial content, metabolic profiles and tissue pathology. In the heart, FA increased concentrations of the TCA metabolite citrate (+ 4.2-fold, p < 0.01) and lowered ATP levels (-1.9-fold, p < 0.001), confirming the inhibition of the TCA cycle by FA. High-resolution respirometry of cardiac mitochondria further revealed an impairment of mitochondrial complex V (CV)-linked metabolism, as evident by a reduced phosphorylation system control ratio (-41%, p < 0.05). The inhibition of CV-linked metabolism is a novel mechanism of FA cardiac toxicity, which has implications for drug development and which NV354 was unable to counteract at the given dose. In the brain, FAinduced the accumulation of β-hydroxybutyrate (+ 1.4-fold, p < 0.05) and the reduction of mitochondrial complex I (CI)-linked oxidative phosphorylation (OXPHOSCI) (-20%, p < 0.01), the latter of which was successfully alleviated by NV354. This promising effect of NV354 warrants further investigations to determine its potential neuroprotective effects.

Design and synthesis of NAD(P)H: Quinone oxidoreductase (NQO1)-activated prodrugs of 23-hydroxybetulinic acid with enhanced antitumor properties

A series of NQO1 selectively activated prodrugs were designed and synthesized by introducing indolequinone moiety to the C-3, C-23 or C-28 position of 23-hydroxybetulinic acid (23-HBA) and its analogues. Among them, the representative compound 32j exhibited significant antiproliferative activities against NQO1-overexpressing HT-29 cells and A549 cells, with IC50 values of 1.87 and 2.36 μM, respectively, which were 20–30-fold more potent than those of parent compound 23-HBA. More importantly, it was demonstrated in the in vivo antitumor experiment that 32j effectively suppressed the tumor volume and largely reduced tumor weight by 72.69% with no apparent toxicity, which was more potent than the positive control 5-fluorouracil. This is the first breakthrough in the improvement of in vivo antitumor activities of 23-HBA derivatives. The further molecular mechanism study revealed that 32j blocked cell cycle arrest at G2/M phase, induced cell apoptosis, depolarized mitochondria and elevated the intracellular ROS levels in a dose-dependent manner. Western blot analysis indicated that 32j induced cell apoptosis by interfering with the expression of apoptosis-related proteins. These findings suggest that compound 32j could be considered as a potent antitumor prodrug candidate which deserves to be further investigated for personalized cancer therapy.

Design, synthesis and evaluation of alpha lipoic acid derivatives to treat multiple sclerosis-associated central neuropathic pain

Multiple sclerosis-associated central neuropathic pain (MS-CNP) is difficult to alleviate with clinically used pain-killers and so there is a large unmet medical need for novel treatments for alleviating MS-CNP. Although (R)-alpha lipoic acid (ALA) evoked significant pain relief efficacy in a mouse model of multiple sclerosis-associated central neuropathic pain (MS-CNP), this dietary supplement has poor oral bioavailability due to low gastric stability. Eight ester prodrugs of the R enantiomer of ALA [(R)-ALA] were designed encompassing a range of biocompatible hydrophobic and hydrophilic features and synthesized in an effort to identify a prodrug candidate that was stable at gastric and upper gastrointestinal tract (GIT) pH, and that could be released (hydrolyzed by esterases) in the blood to (R)-ALA immediately after absorption into the portal vein (i.e., highly desirable features for pain relief development). These biocompatible hydrophobic and hydrophilic (R)-ALA pro-dugs underwent comprehensive preliminary screening to reveal PD-ALA4 HCl salt (10) as a promising candidate and PD-ALA 7 (8) could be a viable substitute, utilizing enzyme-free gastric and intestinal stability assessments, LogP evaluations, in vitro plasma stability and caco-2 cell monolayer permeability.

Abstract 4050: Effect of benzofuran pharmacophores on CYP-activated duocarmycin bioprecursors

Abstract Duocarmycins are natural DNA alkylators which have potent toxicity with no established mechanism of resistance. Prodrug versions need to be developed to ensure a sufficient therapeutic window for cancer treatment (1). A series of duocarmycin bioprecursors have been developed in-house which lack a key hydroxyl trigger group, required for spirocyclisation and subsequent activation. This hydroxyl group can be regioselectivity restored by specific Cytochrome P450 enzymes (CYPs), with a primary focus on cancer associated isoforms CYP1A1 and CYP2W1 (2). An exploratory library of analogues of our lead compound, ICT2700 (CYP1A1 and CYP2W1 activated), has been synthesized and elucidated aspects of the structure-activity relationship (SAR) between the compound and subsequent toxicity in CYP transfected and mock cell lines, using MTT assays. The data shows the importance of having an indole in the DNA recognition subunit (the non-alkylating subunit) for CYP1A1 and CYP2W1 activation. Further, a compound with thus far unexplained activity was identified. ICT11038 has a benzofuran instead of an indole in the recognition subunit and subsequently demonstrates inherent nanomolar toxicity consistently in all cell lines tested, including a range of cancerous and non-cancerous cells, which is not dependent on cytochrome expression. CYP1A1 has been shown to enhance the toxicity of ICT11038 further but is not required for nanomolar toxicity. Further SAR exploration and western blots confirm that the inherent toxicity is achieved through DNA damage despite lacking the key trigger group, suggesting a novel activation pathway. Additionally, our SAR studies show that replacing the indole of the DNA alkylation subunit with a benzofuran ablates CYP dependent activity, with one exception, ICT2724. ICT2724 is non-toxic in mock transfected cells but is toxic in CYP1A1 transfected cells, albeit it at higher concentration than ICT2700. ICT2724 is analogous to ICT2700, except for the direct indole to benzofuran substitution. Other compounds with benzofurans in the alkylating subunit compounds are not metabolized to a toxic compound by CYP1A1 or CYP2W1 despite their indole equivalents being good prodrug candidates. To conclude, the introduction of the benzofuran functional group into the CYP-activated duocarmycin bioprecursor pharmacophores produces an unexplained pattern of CYP activation and, in one example, an intrinsically toxic DNA damaging agent (ZYP-11038). References (1) Z. Jukes et al, Drug Discov Today, 2020, 26(2), 577-584, https://doi.org/10.1016/j.drudis.2020.11.020 (2) H. Sheldrake et al, J. Med. Chem, 2013, 56(16); 6273-6277, dx.doi.org/10.1021/jm4000209 Citation Format: Zoe H. Jukes. Effect of benzofuran pharmacophores on CYP-activated duocarmycin bioprecursors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4050.

Protecting-group- and microwave-free synthesis of β-glycosyl esters and aryl β-glycosides of N-acetyl-d-glucosamine

A protecting-group-free method for synthesis of β-glycosyl esters and aryl β-glycosides was developed by using latent chemical reactivity of N-acetyl-d-glucosamine (GlcNAc) oxazoline. The GlcNAc oxazoline was spontaneously reacted with carboxylic acids and phenol derivatives via the oxazoline ring opening without the use of a catalyst or heating conditions (i.e., microwave irradiation), affording the desired products in moderate to excellent yields with β-selectivity. This simple protecting-group-free method exhibits a wide substrate scope and good functional group tolerance, and it allows the efficient production of a novel class of GlcNAc-conjugated biomaterials and prodrug candidates.

Trimethoxy Trityl Groups as a Potent Substituent for Anti-cancer Cytidine Analog Prodrugs

Methoxy trityl groups are acid-responsive protecting groups that are routinely used in the process of nucleoside analog synthesis. This study investigated the potential of methoxy trityl groups, monomethoxy trityl (MMT), dimethoxy trityl (DMT), and trimethoxy trityl (TMT), as acid-responsive substituents for designing anti-cancer cytidine analog prodrugs. For this purpose, we synthesized six gemcitabine (GEM) derivatives, which were modified either 4-(N)- or 5′-(O)-sites with MMT, DMT, and TMT, as candidates for anti-cancer cytidine analog prodrugs. In vitro dissociation test of methoxy trityl groups clearly showed that the acid responsivity of the methoxy trityl moieties was in the order TMT>DMT>MMT. Furthermore, the rate of 5′-(O)-methoxy tritylation was higher than that of 4-(N)-methoxy tritylation. Along with high acid-responsivity, trimethoxy trityl-O-GEM (TMT-O-GEM) showed superior cytotoxicity against 2D cultured human breast cancer cells (MCF-7 and MDA-MB-231) and human pancreatic cancer cells (AsPC-1) compared to other methoxy-tritylated GEM derivatives. Moreover, TMT-O-GEM suppressed the growth of MCF-7 spheroids compared with trimethoxy trityl-N-GEM (TMT-N-GEM). Both TMT-O-GEM and TMT-N-GEM were negligibly deprotected and metabolized in mouse or human serum after 72 h, indicating that trimethoxy tritylation inhibits deamination by cytidine deaminase. These results indicate that 5′-(O)-trimethoxy tritylation is a potent approach for the development of anti-cancer cytidine analog prodrugs.

Cationic N,N-Dimethylglycine Ester Prodrug of 2R-α-Tocotrienol Promotes Intestinal Absorption via Efficient Self-Micellization with Intrinsic Bile Acid Anion.

The intestinal absorption of hydrophobic compounds is severely influenced by their transportation rate through the unstirred water layer in the intestinal lumen. A member of the vitamin E family, α-Tocotrienol (α-T3) has remarkable pharmacological effects, but its intestinal absorption is hampered due to its hydrophobicity. Here, we prepared three ester derivatives of 2R-α-T3, and we selected a suitable prodrug compound using rat plasma and liver microsomes. The micellization profile of the selected compound in the presence of taurocholic acid (TCA) was evaluated. After gastrostomy administration of the prodrug candidate or α-T3 solution containing TCA, AUC values were determined for α-T3 in plasma obtained from bile duct-ligated rats. Among the three types in the efficiency of the reconversion to the parent drug, α-T3 N,N-dimethylglycinate (α-T3DMG) was the best prodrug; α-T3DMG formed mixed micelles via ion pairs with anionic TCA. The solubility of α-T3DMG in n-octanol/water depended on its ratio to TCA. The AUC after α-T3DMG administration to ligated rats was 2-fold higher than that after α-T3 administration, suggesting a smooth interaction with intrinsic bile acids. In conclusion, utilization of the prodrug synthesized using N,N-dimethylglycine ester may be a beneficial approach to promote intestinal absorption of α-T3 via self-micellization with intrinsic bile acid.

Targeting the tumor microenvironment by an enzyme-responsive prodrug of tubulin destabilizer for triple-negative breast cancer therapy with high safety

In response to the long-term potential toxicity concerns of tubulin destabilizer, an enzyme-responsive prodrug therapy for triple-negative breast cancer was developed based on the different β-glucuronidase levels between tumor and normal tissues in this study. All the prodrugs synthesized herein showed remarkable stability in phosphate buffer and bovine serum solution, among which 17a was found to be more susceptible to enzymatic cleavage. 17a exhibited excellent selectivity between the in vitro antiproliferative activities against β-glucuronidase-pretreated and -untreated cancer cells (IC50 (+Enz) = 8.9–15.7 nM, IC50 (-Enz) > 50 μM), along with favorable liver microsomal metabolic stability and improved aqueous solubility. Furthermore, as a candidate prodrug 17a showed potent antitumor efficacy in MDA-MB-231 xenograft mouse model without causing perceptible injury to organs. Importantly, 17a exhibited superior safety profiles with higher LD50 value and no perceivable cardiotoxicity, which was a major dose-limiting adverse effect for the parent compound 1. These salient toxicity-reduced effects of 17a would merit further in-depth assessment of this compound for preclinical therapeutic usages.

Memantine-Derived Schiff Bases as Transdermal Prodrug Candidates.

Condensation reactions of salicylaldehyde, 2-pyridinecarboxaldehyde, and pyridoxaldehyde with memantine (Me) produced novel memantine-derived Schiff bases (1–3). Speciation predictions and calculations of Log P, Log D, and of the percentage (%) of neutral species for (1–3) were carried out. In comparison with Me, the Schiff bases presented increased log P and log D in all cases and pH values, suggesting higher hydrophobicity. The determined solubilities in n-octanol were 34.7 mg/mL for memantine hydrochloride and 67.3 mg/mL for (3). According to the molecular weights and calculated logP, compounds (1–3) are suitable for transdermal administration, especially compound (3). In addition, hydrolysis of 3 with the release of pyridoxal, a daily cofactor in human metabolism, was observed. The results suggested that 3 is the most promising compound and that formation of the pyridoxal Schiff base with Me might be an effective strategy to obtain a prodrug candidate with increased lipophilicity, which would be able to passively cross biological barriers during transdermal delivery and might have applications in the treatment of Alzheimer’s disease and other neurological disorders.

Boc-Protected Proline-Containing Monoamines as Promising Prodrugs

In recent years, drug designers have increasingly focused on creating complex compounds containing biologically active molecules of various chemical classes in their structure. Such modifications increase the stability of resulting molecules in the organism and increase their ability to achieve the desired targeting effect. Regulatory peptides-based drugs are of particular interest. In this work, we combined the monoamines (serotonin or dopamine) and N-terminal-protected biologically active peptides or amino acids in a single compound and characterized the resulting molecules' enzymatic stability and possible molecular activity. Boc-Pro-5HT and Вос-Pro-DA were stable for at least 180 min of incubation in the presence of PEP, amino-and carboxy-peptidases, as well as blood plasma. This time is enough to reach their corresponding biological targets in the organism and become additional monoamines and regulatory peptides. It was also shown that these complex compounds possess specific targets on cell plasmatic membranes and can affect some neuroreceptor systems (GABA and Ach, in particular) as highly selective allosteric modulators. The above features make these molecules promising candidates for prodrugs and require further research on the mechanisms of their action.

Restoring Tumour Selectivity of the Bioreductive Prodrug PR-104 by Developing an Analogue Resistant to Aerobic Metabolism by Human Aldo-Keto Reductase 1C3.

PR-104 is a phosphate ester pre-prodrug that is converted in vivo to its cognate alcohol, PR-104A, a latent alkylator which forms potent cytotoxins upon bioreduction. Hypoxia selectivity results from one-electron nitro reduction of PR-104A, in which cytochrome P450 oxidoreductase (POR) plays an important role. However, PR-104A also undergoes ‘off-target’ two-electron reduction by human aldo-keto reductase 1C3 (AKR1C3), resulting in activation in oxygenated tissues. AKR1C3 expression in human myeloid progenitor cells probably accounts for the dose-limiting myelotoxicity of PR-104 documented in clinical trials, resulting in human PR-104A plasma exposure levels 3.4- to 9.6-fold lower than can be achieved in murine models. Structure-based design to eliminate AKR1C3 activation thus represents a strategy for restoring the therapeutic window of this class of agent in humans. Here, we identified SN29176, a PR-104A analogue resistant to human AKR1C3 activation. SN29176 retains hypoxia selectivity in vitro with aerobic/hypoxic IC50 ratios of 9 to 145, remains a substrate for POR and triggers γH2AX induction and cell cycle arrest in a comparable manner to PR-104A. SN35141, the soluble phosphate pre-prodrug of SN29176, exhibited superior hypoxic tumour log cell kill (>4.0) to PR-104 (2.5–3.7) in vivo at doses predicted to be achievable in humans. Orthologues of human AKR1C3 from mouse, rat and dog were incapable of reducing PR-104A, thus identifying an underlying cause for the discrepancy in PR-104 tolerance in pre-clinical models versus humans. In contrast, the macaque AKR1C3 gene orthologue was able to metabolise PR-104A, indicating that this species may be suitable for evaluating the toxicokinetics of PR-104 analogues for clinical development. We confirmed that SN29176 was not a substrate for AKR1C3 orthologues across all four pre-clinical species, demonstrating that this prodrug analogue class is suitable for further development. Based on these findings, a prodrug candidate was subsequently identified for clinical trials.

Synthesis and evaluation of hydrogen peroxide sensitive tofacitinib prodrugs

Tofacitinib (CP-690,550), an approved Janus kinase (JAK) inhibitor, has been proven highly efficacious in treating rheumatoid arthritis (RA). Unfortunately, tofacitinib's clinical application has been limited by adverse side effects that arise from its pan-JAKs inhibition and ubiquitous biodistribution. In this study, we have examined whether a reactive oxygen species (ROS)-activated prodrug design could be applied to tofacitinib to potentially avoid its systemic JAK inhibition and thereby reduce its adverse effects. The prodrug strategy selected is based on ROS-labile 4-methylphenylboronic acid pro-moieties linked to the drugs via a carbamate linkage (prodrug 1) or a direct C–N bond (prodrug 2). Activation under pathophysiological concentrations of H2O2 was investigated and conversion to desired tofacitinib assessed. The most promising prodrug candidate, prodrug 2, was selected in agreement with relevant in vitro physicochemical assay and in silico predicted ADME properties. Selected candidate prodrug 2 showed a remarkable potency window compared to tofacitinib in an in vitro kinase assay against JAK1 and JAK3 kinases. Importantly, prodrug 2 displayed a similar pharmacokinetic profile to tofacitinib after single dose i.p. administration to DBA/1 mice. This study supports the promising applications of ROS-sensitive tofacitinib prodrugs. Their further development and applicability would enhance tofacitinib's therapeutic efficacy, and may provide an opportunity for future development of safer tofacitinib dosing regimens.