Building homogeneous time-resolved fluorescence resonance energy transfer assays for characterization of bivalent inhibitors of an inhibitor of apoptosis protein target.

XIAP (X-chromosome-linked inhibitor of apoptosis protein) is a central apoptosis regulator that blocks cell death by inhibiting caspase-3, caspase-7, and caspase-9 via binding interactions with the XIAP BIR2 and BIR3 domains (where BIR is baculovirus IAP repeat). Smac protein, in its dimeric form, effectively antagonizes XIAP by concurrently targeting both its BIR2 and BIR3 domains. Here we describe the development of highly sensitive homogeneous time-resolved fluorescence resonance energy transfer (HTRF) assays to measure binding affinities of potent bivalent peptidomimetic inhibitors of XIAP. Our results indicate that these assays can differentiate Smac-mimetic inhibitors with a wide range of binding affinities down to the picomolar range. Furthermore, we demonstrate the utility of these fluorescent tools for characterization of inhibitor off-rates, which as a crucial determinant of target engagement and cellular potency is another important parameter to guide optimization in a structure-based drug discovery effort. Our study also explores how increased inhibitor valency can lead to enhanced potency at multimeric proteins such as IAP.

Pharmacology of smac mimetics; chemotype differentiation based on physical association with caspase regulators and cellular transport.

Cellular levels of inhibitor of apoptosis (IAP) proteins are elevated in multiple human cancers and their activities often play a part in promoting cancer cell survival by blocking apoptotic pathways, controlling signal transduction pathways and contributing to resistance. These proteins function through interactions of their BIR (baculoviral IAP repeat) protein domains with pathway components and these interactions are endogenously antagonized by Smac/Diablo (second mitochondrial activator of caspases/direct IAP binding protein with low isoelectric point). This report describes development of synthetic smac mimetics (SM) and compares their binding, antiproliferative and anti-tumor activities. All dimeric antagonists inhibit in vitro smac tetrapeptide binding to recombinant IAP proteins, rescue IAP-bound caspase-3 activity and show anti-proliferative activity against human A875 melanoma cells. One heterodimeric SM, SM3, binds tightly to IAP proteins in vitro and slowly dissociates (greater than two hours) from these protein complexes compared to the other antagonists. In addition, in vitro SM anti-proliferation potency is influenced by ABCB1 transporter (ATP-binding cassette, sub-family B; MDR1, P-gp) activities and one antagonist, SM5, does not appear to be an ABCB1 efflux pump substrate. All dimeric smac mimetics inhibit the growth of human melanoma A875 tumors implanted in athymic mice at well-tolerated doses. One antagonist, SM4, shows broad spectrum in vivo anti-tumor activity and modulates known pharmacodynamic markers of IAP antagonism. These data taken together demonstrate the range of diverse dimeric IAP antagonist activities and supports their potential as anticancer agents.

KRAS G12D Mutation Subtype in Pancreatic Ductal Adenocarcinoma: Does It Influence Prognosis or Stage of Disease at Presentation?

Background: KRAS G12D mutation subtype is present in over 40% of pancreatic ductal adenocarcinoma (PDAC), one of the leading global causes of cancer death. This retrospective cohort study aims to investigate whether detection of the KRAS G12D mutation subtype in PDAC patients is a determinant of prognosis across all stages of disease. Methods: We reviewed the medical records of 231 patients presenting with PDAC at a large tertiary hospital, and compared survival using the Kaplan Meier, log-rank test and Cox proportional hazards regression model. Results: KRAS G12D mutation subtype was not significantly associated with poorer survival compared across the whole population of PDAC patients (p = 0.107; HR 1.293 95% CI (0.946-1.767)). However, KRAS G12D patients who were resectable had a shorter median survival time of 356 days compared to all other genotypes (median survival 810 days) (p = 0.019; HR 1.991 95% CI (1.121-3.537)). Conclusions: KRAS G12D patients who were resectable at diagnosis had shorter survival compared to all other PDAC patients. These data suggest that KRAS G12D may be a clinically useful prognostic biomarker of PDAC.

Assessing compound binding to the Eg5 motor domain using a thermal shift assay.

Eg5 is a kinesin whose inhibition leads to cycle arrest during mitosis, making it a potential therapeutic target in cancers. Circular dichroism and isothermal titration calorimetry of our pyrrolotriazine-4-one series of inhibitors with Eg5 motor domain revealed enhanced binding in the presence of adenosine 5'-diphosphate (ADP). Using this information, we studied the interaction of this series with ADP-Eg5 complexes using a thermal shift assay. We measured up to a 7 degrees C increase in the thermal melting (T(m)) of Eg5 for an inhibitor that produced IC(50) values of 60 and 130 nM in microtubule-dependent adenosine triphosphatase (ATPase) and cell-based cytotoxicity assays, respectively. In general, the inhibitor potency of the pyrrolotriazine-4-one series in in vitro biological assays correlated with the magnitude of the thermal stability enhancement of ADP-Eg5. The thermal shift assay also confirmed direct binding of Eg5 inhibitors identified in a high-throughput screen and demonstrated that the thermal shift assay is applicable to a range of chemotypes and can be useful in evaluating both potent (nM) and relatively weakly binding (microM) leads. Overall, the thermal shift assay was found to be an excellent biophysical method for evaluating direct binding of a large number of compounds to Eg5, and it complemented the catalytic assay screens by providing an alternative determination of inhibitor potency.

The discovery of macrocyclic XIAP antagonists from a DNA-programmed chemistry library, and their optimization to give lead compounds with in vivo antitumor activity.

Affinity selection screening of macrocycle libraries derived from DNA-programmed chemistry identified XIAP BIR2 and BIR3 domain inhibitors that displace bound pro-apoptotic caspases. X-ray cocrystal structures of key compounds with XIAP BIR2 suggested potency-enhancing structural modifications. Optimization of dimeric macrocycles with similar affinity for both domains were potent pro-apoptotic agents in cancer cell lines and efficacious in shrinking tumors in a mouse xenograft model.

Inhibitors of human mitotic kinesin Eg5: characterization of the 4-phenyl-tetrahydroisoquinoline lead series.

In a high-throughput screening effort, a series of tetrahydroisoquinolines was identified as modest inhibitors of human Eg5. A medicinal chemistry optimization effort led to the identification of R-4-(3-hydroxyphenyl)-N,N-7,8-tetramethyl-3,4-dihydroisoquinoline-2(1H)-carboxamide (32a) as a potent inhibitor of human Eg5 (ATPase IC50 104 nM) with good anti-proliferative activity in A2780 cells (IC50 234 nM).

Synthesis and SAR of pyrrolotriazine-4-one based Eg5 inhibitors.

Synthesis and SAR of substituted pyrrolotriazine-4-one analogues as Eg5 inhibitors are described. Many of these analogues displayed potent inhibitory activities in the Eg5 ATPase and A2780 cell proliferation assays. In addition, pyrrolotriazine-4-one analogue 26 demonstrated in vivo efficacy in an iv P388 murine leukemia model. Both NMR and X-ray crystallographic studies revealed that these analogues bind to an allosteric site on the Eg5 protein.

Omalizumab, an anti-IgE antibody, in the treatment of adults and adolescents with perennial allergic rhinitis.

BACKGROUND: Treatment with omalizumab, an anti-IgE antibody, improves symptoms and quality of life in patients with seasonal allergic rhinitis but has not previously been investigated in patients with perennial symptoms. OBJECTIVE: To investigate the efficacy, safety, and tolerability of omalizumab in the treatment of perennial allergic rhinitis (PAR). METHODS: Two hundred eighty-nine patients (aged 12 to 70 years) with moderate-to-severe symptomatic PAR were randomized to 16 weeks' double-blind subcutaneous treatment with either placebo (n = 145) or omalizumab (at least 0.016 mg/kg/IgE [IU/mL] per 4 weeks; n = 144). The primary efficacy variable was the mean daily nasal severity score, as determined from patient daily diary cards. Secondary efficacy variables included use of rescue antihistamine, rhinoconjunctivitis-specific quality of life (RQoL), and patients' evaluation of treatment efficacy. Safety and tolerability were evaluated from adverse event reports and laboratory safety parameters. RESULTS: Throughout 16 weeks of treatment, the mean daily nasal severity score was significantly lower in omalizumab-treated patients than with placebo (P < 0.001). The improvement in symptoms when taking omalizumab was paralleled by a reduction in use of rescue antihistamine (P < or = 0.005 overall) and improved RQoL relative to placebo. Patients' evaluation of treatment efficacy significantly favored omalizumab over placebo (P = 0.001). Omalizumab therapy was well tolerated. There were no safety concerns. CONCLUSIONS: Omalizumab was safe and well tolerated in the treatment of patients with PAR, providing effective control of symptoms and improved RQoL while simultaneously minimizing reliance on rescue antihistamines.

Phosphodiesterase 7A-deficient mice have functional T cells.

Phosphodiesterases (PDEs) are enzymes which hydrolyze the cyclic nucleotide second messengers, cAMP and cGMP. In leukocytes, PDEs are responsible for depletion of cAMP which broadly suppresses cell functions and cellular responses to many activation stimuli. PDE7A has been proposed to be essential for T lymphocyte activation based on its induction during cell activation and the suppression of proliferation and IL-2 production observed following inhibition of PDE7A expression using a PDE7A antisense oligonucleotide. These observations have led to the suggestion that selective PDE7 inhibitors could be useful in the treatment of T cell-mediated autoimmune diseases. In the present report, we have used targeted gene disruption to examine the role PDE7A plays in T cell activation. In our studies, PDE7A knockout mice (PDE7A(-/-)) showed no deficiencies in T cell proliferation or Th1- and Th2-cytokine production driven by CD3 and CD28 costimulation. Unexpectedly, the Ab response to the T cell-dependent Ag, keyhole limpet hemocyanin, in the PDE7A(-/-) mice was found to be significantly elevated. The results from our studies strongly support the notion that PDE7A is not essential for T cell activation.