Comprehensive Mechanistic View of the Hydrolysis of Oxadiazole-Based Inhibitors by Histone Deacetylase 6 (HDAC6)

Histone deacetylase (HDAC) inhibitors used in the clinic typically contain a hydroxamate zinc-binding group (ZBG). However, more recent work has shown that the use of alternative ZBGs, and, in particular, the heterocyclic oxadiazoles, can confer higher isoenzyme selectivity and more favorable ADMET profiles. Herein, we report on the synthesis and biochemical, crystallographic, and computational characterization of a series of oxadiazole-based inhibitors selectively targeting the HDAC6 isoform. Surprisingly, but in line with a very recent finding reported in the literature, a crystal structure of the HDAC6/inhibitor complex revealed that hydrolysis of the oxadiazole ring transforms the parent oxadiazole into an acylhydrazide through a sequence of two hydrolytic steps. An identical cleavage pattern was also observed both in vitro using the purified HDAC6 enzyme as well as in cellular systems. By employing advanced quantum and molecular mechanics (QM/MM) and QM calculations, we elucidated the mechanistic details of the two hydrolytic steps to obtain a comprehensive mechanistic view of the double hydrolysis of the oxadiazole ring. This was achieved by fully characterizing the reaction coordinate, including identification of the structures of all intermediates and transition states, together with calculations of their respective activation (free) energies. In addition, we ruled out several (intuitively) competing pathways. The computed data (ΔG^‡ ≈ 21 kcal·mol^-1 for the rate-determining step of the overall dual hydrolysis) are in very good agreement with the experimentally determined rate constants, which a posteriori supports the proposed reaction mechanism. We also clearly (and quantitatively) explain the role of the -CF₃ or -CHF₂ substituent on the oxadiazole ring, which is a prerequisite for hydrolysis to occur. Overall, our data provide compelling evidence that the oxadiazole warheads can be efficiently transformed within the active sites of target metallohydrolases to afford reaction products possessing distinct selectivity and inhibition profiles.

Development of PSMA-1007-Related Series of 18F-Labeled Glu-Ureido-Type PSMA Inhibitors

In recent years, a number of drugs targeting the prostate-specific membrane antigen (PSMA) have become important tools in the diagnosis and treatment of prostate cancer. In the present work, we report on the synthesis and preclinical evaluation of a series of ¹⁸F-labeled PSMA ligands for diagnostic application based on the theragnostic ligand PSMA-617. By applying modifications to the linker structure, insight into the structure-activity relationship could be gained, highlighting the importance of hydrophilicity and stereoselectivity on interaction with PSMA and hence the biodistribution. Selected compounds were co-crystallized with the PSMA protein and analyzed by X-rays with mixed results. Among these, PSMA-1007 (compound 5) showed the best interaction with the PSMA protein. The respective radiotracer [¹⁸F]PSMA-1007 was translated into the clinic and is, in the meantime, subject of advanced clinical trials.

2-Aminoadipic Acid-C(O)-Glutamate Based Prostate-Specific Membrane Antigen Ligands for Potential Use as Theranostics

The design and synthesis of prostate specific membrane antigen (PSMA) ligands derived from 2-aminoadipic acid, a building block that has not previously been used to construct PSMA ligands, are reported. The effects of both the linker length and of an N-substituent of our PSMA ligands were probed, and X-ray structures of five of these ligands bound to PSMA were obtained. Among the ligands disclosed herein, 13b showed the highest inhibitory activity for PSMA. As ligand 13b can readily be radiolabeled since its fluorine atom is adjacent to the nitrogen atom of its pyridine ring, the use of this and related compounds as theranostics can be pursued.

The Information Technology Aided Relapse Prevention Programme in Schizophrenia: an extension of a mirror-design follow-up

AIMS

Decreasing a number of hospital admissions is important for improving outcomes for people with schizophrenia. The Information Technology Aided Relapse Prevention Programme in Schizophrenia (ITAREPS) programme enables early pharmacological intervention in psychosis by identification of prodromal symptoms of relapse using home telemonitoring via a phone-to-PC SMS platform.

METHODS

This study was a 1-year extension of a previously published mirror-design follow-up evaluation of programme clinical effectiveness. In total, 73 patients with psychotic illness (45 patients from original sample and 28 newly added subjects) collaborating with 56 family members participated in the clinical evaluation.

RESULTS

There was a statistically significant 77% decrease in the number of hospitalisations during the mean 396.8 +/- 249.4 days of participation in ITAREPS, compared with the same time period before participation in ITAREPS (Wilcoxon-signed ranks test, p < 0.00001), as well as significantly reduced number of hospitalisation days when in the ITAREPS (2365 hospitalisation days before and 991 days after ITAREPS enrolment respectively, Wilcoxon-signed ranks test, p < 0.003).

CONCLUSION

The ITAREPS programme represents an effective tool in the long-term treatment of patients with psychotic disorders.

Psychoeducation as an indispensable complement to pharmacotherapy in schizophrenia

Antipsychotic drugs are the most effective medication for the treatment of schizophrenia. Their side effects, however, affect most patients; some of them suffer from them for the rest of their lives, with little chance of improvement. In general, the side effects are perceived differently by patients, their relatives, psychiatrists, and the public. Being informed about the side effects of antipsychotics does not negatively affect compliance and is essential for establishing patients' confidence in doctors and in the medication.

Effects of haloperidol treatment on prolactin response to D-fenfluramine challenge in acute schizophrenia

We have previously described an association between higher serotonin (5-HT) responsivity, indexed by prolactin response to D-fenfluramine challenge, and poorer treatment response to haloperidol in non-medicated schizophrenics. The aim of the present study was to investigate the effects of antidopaminergic treatment on the prolactin response in the repeated challenge test. D-Fenfluramine was administered to 22 young, acutely ill schizophrenics (11 females and 11 males) after 4 weeks of haloperidol treatment. Whereas neuroleptic administration significantly raised basal prolactin levels (P < 0.0001), subsequent D-fenfluramine challenge produced an additional significant increase (P < 0.001). Moreover, the magnitude of this increase was not different from the pretreatment response. Our results demonstrate that prolactin response to the challenge is mediated through the 5-HT system. An observed negative association between posttreatment prolactin response and therapeutic response to haloperidol did not reach statistical significance.

Prolactin response to D-fenfluramine challenge test as a predictor of treatment response to haloperidol in acute schizophrenia

D-fenfluramine has been identified as a highly selective serotonin (5-HT) releaser and re-uptake inhibitor. The objective of our study was to investigate prolactin response to D-fenfluramine challenge in non-medicated, first episode schizophrenics. We hypothesized that 5-HT reactivity can predict a response to the neuroleptic treatment. Twenty-three inpatients, 11 males and 12 females, at the Prague Psychiatric Center participated in the study. Inclusion criteria were: ICD-10 diagnosis of schizophrenia, first episode or duration of illness shorter than 36 months. D-fenfluramine challenge test was performed before 4 weeks of the haloperidol treatment. During the test, prolactin plasma levels were measured. The Brief Psychiatric Rating Scale (BPRS) was administered before and after the treatment. A statistically significant negative correlation was found between prolactin response to the D-fenfluramine challenge and improvement of psychopathology measured by the change in total BPRS score (p = 0.0004), in positive (p = 0.0403), negative (p = 0.0267), and anxiety-depression symptoms of BPRS (p = 0.0014). Our data support the original hypothesis that there is a relationship between 5-HT system activity and treatment response. The higher responsiveness of the 5-HT system in first episode, non-medicated schizophrenics, was associated with a poorer treatment response to haloperidol, an antidopaminergic neuroleptic.