Fluoride-mediated capture of a noncovalent bound state of a reversible covalent enzyme inhibitor: X-ray crystallographic analysis of an exceptionally potent α-ketoheterocycle inhibitor of fatty acid amide hydrolase.

Two cocrystal X-ray structures of the exceptionally potent α-ketoheterocycle inhibitor 1 (K(i) = 290 pM) bound to a humanized variant of rat fatty acid amide hydrolase (FAAH) are disclosed, representing noncovalently and covalently bound states of the same inhibitor with the enzyme. Key to securing the structure of the noncovalently bound state of the inhibitor was the inclusion of fluoride ion in the crystallization conditions that is proposed to bind the oxyanion hole precluding inhibitor covalent adduct formation with stabilization of the tetrahedral hemiketal. This permitted the opportunity to detect important noncovalent interactions stabilizing the binding of the inhibitor within the FAAH active site independent of the covalent reaction. Remarkably, noncovalently bound 1 in the presence of fluoride appears to capture the active site in the same "in action" state with the three catalytic residues Ser241-Ser217-Lys142 occupying essentially identical positions observed in the covalently bound structure of 1, suggesting that this technique of introducing fluoride may have important applications in structural studies beyond inhibiting substrate or inhibitor oxyanion hole binding. Key insights to emerge from the studies include the observations that noncovalently bound 1 binds in its ketone (not gem diol) form, that the terminal phenyl group in the acyl side chain of the inhibitor serves as the key anchoring interaction overriding the intricate polar interactions in the cytosolic port, and that the role of the central activating heterocycle is dominated by its intrinsic electron-withdrawing properties. These two structures are also briefly compared with five X-ray structures of α-ketoheterocycle-based inhibitors bound to FAAH recently disclosed.

The discovery and development of inhibitors of fatty acid amide hydrolase (FAAH).

A summary of the discovery and advancement of inhibitors of fatty acid amide hydrolase (FAAH) is presented.

Combination of Olaparib and Radiation Therapy for Triple Negative Breast Cancer: Preliminary Results of the RADIOPARP Phase 1 Trial.

PURPOSE: Preclinical studies have evidenced that triple-negative breast cancer (TNBC) cell lines are more sensitive to poly (ADP-ribose) polymerase inhibitors. This provides a strong rationale for developing a new therapeutic approach for TNBC management based on poly (ADP-ribose) polymerase inhibition. The primary goal of the RADIOPARP phase 1 trial was to evaluate the dose-limiting toxicities (DLT) and the maximum tolerated dose of olaparib combined with locoregional radiation therapy. METHODS AND MATERIALS: RADIOPARP was a single institutional phase 1 trial which evaluated olaparib-radiation therapy combination in patients with inflammatory, locoregionally advanced or metastatic TNBC who received neoadjuvant chemotherapy. Radiation therapy delivered 50 Gy to the breast or to the chest wall. Lymph nodes could be included in target volumes according to local guidelines. The dose-finding toxicity-based study was conducted in sequential and adaptive Bayesian scheme using the time-to-event continual reassessment method, with 4 olaparib dose levels (50 mg, 100 mg, 150 mg, and 200 mg twice per day). RESULTS: Twenty-four patients with Eastern Cooperative Oncology Group Performance Status of 0 or 1 were enrolled from September 2017 to November 2019. Twenty-one patients (87.5%) received the olaparib-radiation therapy combination after breast surgery owing to residual disease after neoadjuvant chemotherapy, and the 3 other patients (12.5%) had unresectable tumors which were refractory to neoadjuvant chemotherapy. All patients received full course combination treatment as follows: 4 patients (pts) at 50 mg twice a day, 8 pts at 100 mg twice a day, 7 pts at 150 mg twice a day, and 5 pts at 200 mg twice a day. No DLT was observed. CONCLUSIONS: Olaparib was escalated to the maximum target dose of 200 mg twice a day without DLT. Further follow-up is needed to evaluate the late toxicities. Pending the long-term results of the RADIOPARP trial, we suggest using 200 mg of olaparib twice per day for future trials.

Fatty acid amide signaling molecules.

Key studies leading to the discovery and definition of the role of endogenous fatty acid amide signaling molecules are summarized.

Optimization of alpha-ketooxazole inhibitors of fatty acid amide hydrolase.

A series of alpha-ketooxazoles containing conformational constraints in the flexible C2 acyl side chain of 2 (OL-135) and representative oxazole C5 substituents were prepared and examined as inhibitors of fatty acid amide hydrolase (FAAH). Exceptionally potent and selective FAAH inhibitors emerged from the series (e.g., 6, Ki = 200 and 260 pM for rat and rhFAAH). With simple and small C5 oxazole substituents, each series bearing a biphenylethyl, phenoxyphenethyl, or (phenoxymethyl)phenethyl C2 side chain was found to follow a well-defined linear relationship between -log Ki and Hammett sigmap of a magnitude (rho = 2.7-3.0) that indicates that the substituent electronic effect dominates, confirming its fundamental importance to the series and further establishing its predictive value. Just as significantly, the nature of the C5 oxazole substituent substantially impacts the selectivity of the inhibitors whereas the effect of the C2 acyl chain was more subtle but still significant even in the small series examined. Combination of these independent features, which display generalized trends across a range of inhibitor series, simultaneously improves FAAH potency and selectivity and can provide exquisitely selective and potent FAAH inhibitors.

Clinical study of the novel cyclin-dependent kinase inhibitor dinaciclib in combination with rituximab in relapsed/refractory chronic lymphocytic leukemia patients.

PURPOSE: Dinaciclib is a novel selective inhibitor of cyclin-dependent kinase (CDK)1, CDK2, CDK5, and CDK9. We conducted a phase I study to investigate the effects of dinaciclib when administered with rituximab. METHODS: In this phase I nonrandomized dose-escalation 3 + 3 trial, patients with relapsed/refractory chronic lymphocytic leukemia (CLL) were treated with dinaciclib and rituximab. Dinaciclib was administered intravenously (IV) over 2 h on days 1, 8 and 15 in cycles 2-13 (28-day cycles). Rituximab 375 mg/m(2) was administered IV on days 1, 8, 15 and 22 in cycle 1 (28-day cycle) and on day 1 during cycle 3-13. Rituximab was not administered in cycle 2. Rituximab and dinaciclib were given alone in cycles 1 and 2, respectively, and in combination in cycles 3-13. Primary objectives included determination of the recommended phase II dose of dinaciclib and evaluation of pharmacokinetics (PK) when administered with rituximab. RESULTS: Five patients completed the study due to early termination. All presented with drug-related adverse events (AEs), but no dose-limiting toxicities were observed. The most commonly observed toxicities included hematological, digestive and metabolic AEs. However, no tumor lysis syndrome has been reported in the study. Four patients achieved stable disease, and one patient achieved complete response according to 2008 iwCLL criteria at cycle 3. PK samples were collected from 5 patients, and no obvious interaction between dinaciclib and rituximab was observed. CONCLUSIONS: Limited data from this study shows dinaciclib in combination with rituximab was well tolerated and revealed encouraging clinical activity in relapsed/refractory CLL patients.

The fatty acid amide hydrolase (FAAH) inhibitor PF-3845 acts in the nervous system to reverse LPS-induced tactile allodynia in mice.

BACKGROUND AND PURPOSE: Inflammatory pain presents a problem of clinical relevance and often elicits allodynia, a condition in which non-noxious stimuli are perceived as painful. One potential target to treat inflammatory pain is the endogenous cannabinoid (endocannabinoid) system, which is comprised of CB1 and CB2 cannabinoid receptors and several endogenous ligands, including anandamide (AEA). Blockade of the catabolic enzyme fatty acid amide hydrolase (FAAH) elevates AEA levels and elicits antinociceptive effects, without the psychomimetic side effects associated with Δ(9) -tetrahydrocannabinol (THC). EXPERIMENTAL APPROACH: Allodynia was induced by intraplantar injection of LPS. Complementary genetic and pharmacological approaches were used to determine the strategy of blocking FAAH to reverse LPS-induced allodynia. Endocannabinoid levels were quantified using mass spectroscopy analyses. KEY RESULTS: FAAH (-/-) mice or wild-type mice treated with FAAH inhibitors (URB597, OL-135 and PF-3845) displayed an anti-allodynic phenotype. Furthermore, i.p. PF-3845 increased AEA levels in the brain and spinal cord. Additionally, intraplantar PF-3845 produced a partial reduction in allodynia. However, the anti-allodynic phenotype was absent in mice expressing FAAH exclusively in the nervous system under a neural specific enolase promoter, implicating the involvement of neuronal fatty acid amides (FAAs). The anti-allodynic effects of FAAH-compromised mice required activation of both CB1 and CB2 receptors, but other potential targets of FAA substrates (i.e. µ-opioid, TRPV1 and PPARα receptors) had no apparent role. CONCLUSIONS AND IMPLICATIONS: AEA is the primary FAAH substrate reducing LPS-induced tactile allodynia. Blockade of neuronal FAAH reverses allodynia through the activation of both cannabinoid receptors and represents a promising target to treat inflammatory pain. LINKED ARTICLES: This article is part of a themed section on Cannabinoids in Biology and Medicine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-8. To view Part I of Cannabinoids in Biology and Medicine visit http://dx.doi.org/10.1111/bph.2011.163.issue-7.

Reversible competitive α-ketoheterocycle inhibitors of fatty acid amide hydrolase containing additional conformational constraints in the acyl side chain: orally active, long-acting analgesics.

A series of α-ketooxazoles containing conformational constraints in the C2 acyl side chain of 2 (OL-135) were examined as inhibitors of fatty acid amide hydrolase (FAAH). Only one of the two possible enantiomers displayed potent FAAH inhibition (S vs R enantiomer), and their potency is comparable or improved relative to 2, indicating that the conformational restriction in the C2 acyl side chain is achievable. A cocrystal X-ray structure of the α-ketoheterocycle 12 bound to a humanized variant of rat FAAH revealed its binding details, confirmed that the (S)-enantiomer is the bound active inhibitor, shed light on the origin of the enantiomeric selectivity, and confirmed that the catalytic Ser241 is covalently bound to the electrophilic carbonyl as a deprotonated hemiketal. Preliminary in vivo characterization of the inhibitors 12 and 14 is reported demonstrating that they raise brain anandamide levels following either intraperitoneal (ip) or oral (po) administration indicative of effective in vivo FAAH inhibition. Significantly, the oral administration of 12 caused dramatic accumulation of anandamide in the brain, with peak levels achieved between 1.5 and 3 h, and these elevations were maintained over 9 h. Additional studies of these two representative members of the series (12 and 14) in models of thermal hyperalgesia and neuropathic pain are reported, including the demonstration that 12 administered orally significantly attenuated mechanical (>6 h) and cold (>9 h) allodynia for sustained periods consistent with its long-acting effects in raising the endogenous concentration of anandamide.

X-ray crystallographic analysis of alpha-ketoheterocycle inhibitors bound to a humanized variant of fatty acid amide hydrolase.

Three cocrystal X-ray structures of the alpha-ketoheterocycle inhibitors 3-5 bound to a humanized variant of fatty acid amide hydrolase (FAAH) are disclosed and comparatively discussed alongside those of 1 (OL-135) and its isomer 2. These five X-ray structures systematically probe each of the three active site regions key to substrate or inhibitor binding: (1) the conformationally mobile acyl chain-binding pocket and membrane access channel responsible for fatty acid amide substrate and inhibitor acyl chain binding, (2) the atypical active site catalytic residues and surrounding oxyanion hole that covalently binds the core of the alpha-ketoheterocycle inhibitors captured as deprotonated hemiketals mimicking the tetrahedral intermediate of the enzyme-catalyzed reaction, and (3) the cytosolic port and its uniquely important imbedded ordered water molecules and a newly identified anion binding site. The detailed analysis of their key active site interactions and their implications on the interpretation of the available structure-activity relationships are discussed providing important insights for future design.

Optimization of the central heterocycle of alpha-ketoheterocycle inhibitors of fatty acid amide hydrolase.

The synthesis and evaluation of a refined series of alpha-ketoheterocycles based on the oxazole 2 (OL-135) incorporating systematic changes in the central heterocycle bearing a key set of added substituents are described. The nature of the central heterocycle, even within the systematic and minor perturbations explored herein, significantly influenced the inhibitor activity: 1,3,4-oxadiazoles and 1,2,4-oxadiazoles 9 > tetrazoles, the isomeric 1,2,4-oxadiazoles 10, 1,3,4-thiadiazoles > oxazoles including 2 > 1,2-diazines > thiazoles > 1,3,4-triazoles. Most evident in these trends is the observation that introduction of an additional heteroatom at position 4 (oxazole numbering, N > O > CH) substantially increases activity that may be attributed to a reduced destabilizing steric interaction at the FAAH active site. Added heterocycle substituents displaying well-defined trends may be utilized to enhance the inhibitor potency and, more significantly, to enhance the inhibitor selectivity. These trends, exemplified herein, emerge from both enhancements in the FAAH activity and simultaneous disruption of binding affinity for competitive off-target enzymes.