Paul Hales

Hydrolysis of Biological Peptides by Human Angiotensin-converting Enzyme-related Carboxypeptidase

Human angiotensin-converting enzyme-related carboxypeptidase (ACE2) is a zinc metalloprotease whose closest homolog is angiotensin I-converting enzyme. To begin to elucidate the physiological role of ACE2, ACE2 was purified, and its catalytic activity was characterized. ACE2 proteolytic activity has a pH optimum of 6.5 and is enhanced by monovalent anions, which is consistent with the activity of ACE. ACE2 activity is increased ∼10-fold by Cl− and F− but is unaffected by Br−. ACE2 was screened for hydrolytic activity against a panel of 126 biological peptides, using liquid chromatography-mass spectrometry detection. Eleven of the peptides were hydrolyzed by ACE2, and in each case, the proteolytic activity resulted in removal of the C-terminal residue only. ACE2 hydrolyzes three of the peptides with high catalytic efficiency: angiotensin II (1-8) (k cat/K m = 1.9 × 106 m −1 s−1), apelin-13 (k cat/K m = 2.1 × 106 m −1s−1), and dynorphin A 1–13 (k cat/K m = 3.1 × 106 m −1 s−1). The ACE2 catalytic efficiency is 400-fold higher with angiotensin II (1-8) as a substrate than with angiotensin I (1-10). ACE2 also efficiently hydrolyzes des-Arg9-bradykinin (k cat/K m = 1.3 × 105 m −1 s−1), but it does not hydrolyze bradykinin. An alignment of the ACE2 peptide substrates reveals a consensus sequence of: Pro-X (1–3 residues)-Pro-Hydrophobic, where hydrolysis occurs between proline and the hydrophobic amino acid.

Evaluation of the Proteasome Inhibitor MLN9708 in Preclinical Models of Human Cancer

The proteasome was validated as an oncology target following the clinical success of VELCADE (bortezomib) for injection for the treatment of multiple myeloma and recurring mantle cell lymphoma. Consequently, several groups are pursuing the development of additional small-molecule proteasome inhibitors for both hematologic and solid tumor indications. Here, we describe MLN9708, a selective, orally bioavailable, second-generation proteasome inhibitor that is in phase I clinical development. MLN9708 has a shorter proteasome dissociation half-life and improved pharmacokinetics, pharmacodynamics, and antitumor activity compared with bortezomib. MLN9708 has a larger blood volume distribution at steady state, and analysis of 20S proteasome inhibition and markers of the unfolded protein response confirmed that MLN9708 has greater pharmacodynamic effects in tissues than bortezomib. MLN9708 showed activity in both solid tumor and hematologic preclinical xenograft models, and we found a correlation between greater pharmacodynamic responses and improved antitumor activity. Moreover, antitumor activity was shown via multiple dosing routes, including oral gavage. Taken together, these data support the clinical development of MLN9708 for both hematologic and solid tumor indications.

Heart block, ventricular tachycardia, and sudden death in ACE2 transgenic mice with downregulated connexins

Angiotensin converting enzyme related carboxypeptidase (ACE2) is a recently discovered homolog of angiotensin converting enzyme with tissue-restricted expression, including heart, and the capacity to cleave angiotensin peptides. We tested the hypothesis that cardiac ACE2 activity contributes to features of ventricular remodeling associated with the renin-angiotensin system by generating transgenic mice with increased cardiac ACE2 expression. These animals had a high incidence of sudden death that correlated with transgene expression levels. Detailed electrophysiology revealed severe, progressive conduction and rhythm disturbances with sustained ventricular tachycardia and terminal ventricular fibrillation. The gap junction proteins connexin40 and connexin43 were downregulated in the transgenic hearts, indicating that ACE2-mediated gap junction remodeling may account for the observed electrophysiologic disturbances. Spontaneous downregulation of the ACE2 transgene in surviving older animals correlated with restoration of nearly normal conduction, rhythm, and connexin expression.

Characterization of a new series of non-covalent proteasome inhibitors with exquisite potency and selectivity for the 20S β5-subunit

The mammalian 26S proteasome is a 2500 kDa multi-catalytic complex involved in intracellular protein degradation. We describe the synthesis and properties of a novel series of non-covalent di-peptide inhibitors of the proteasome used on a capped tri-peptide that was first identified by high-throughput screening of a library of approx. 350000 compounds for inhibitors of the ubiquitin–proteasome system in cells. We show that these compounds are entirely selective for the β5 (chymotrypsin-like) site over the β1 (caspase-like) and β2 (trypsin-like) sites of the 20S core particle of the proteasome, and over a panel of less closely related proteases. Compound optimization, guided by X-ray crystallography of the liganded 20S core particle, confirmed their non-covalent binding mode and provided a structural basis for their enhanced in vitro and cellular potencies. We demonstrate that such compounds show low nanomolar IC50 values for the human 20S β5 site in vitro, and that pharmacological inhibition of this site in cells is sufficient to potently inhibit the degradation of a tetra-ubiquitin–luciferase reporter, activation of NFκB (nuclear factor κB) in response to TNF-α (tumour necrosis factor-α) and the proliferation of cancer cells. Finally, we identified capped di-peptides that show differential selectivity for the β5 site of the constitutively expressed proteasome and immunoproteasome in vitro and in B-cell lymphomas. Collectively, these studies describe the synthesis, activity and binding mode of a new series of non-covalent proteasome inhibitors with unprecedented potency and selectivity for the β5 site, and which can discriminate between the constitutive proteasome and immunoproteasome in vitro and in cells.The mammalian 26S proteasome is a 2500 kDa multi-catalytic complex involved in intracellular protein degradation. We describe the synthesis and properties of a novel series of non-covalent di-peptide inhibitors of the proteasome based [corrected] on a capped tri-peptide that was first identified by high-throughput screening of a library of approx. 350000 compounds for inhibitors of the ubiquitin-proteasome system in cells. We show that these compounds are entirely selective for the beta5 (chymotrypsin-like) site over the beta1 (caspase-like) and beta2 (trypsin-like) sites of the 20S core particle of the proteasome, and over a panel of less closely related proteases. Compound optimization, guided by X-ray crystallography of the liganded 20S core particle, confirmed their non-covalent binding mode and provided a structural basis for their enhanced in vitro and cellular potencies. We demonstrate that such compounds show low nanomolar IC50 values for the human 20S beta5 site in vitro, and that pharmacological inhibition of this site in cells is sufficient to potently inhibit the degradation of a tetra-ubiquitin-luciferase reporter, activation of NFkappaB (nuclear factor kappaB) in response to TNF-alpha (tumour necrosis factor-alpha) and the proliferation of cancer cells. Finally, we identified capped di-peptides that show differential selectivity for the beta5 site of the constitutively expressed proteasome and immunoproteasome in vitro and in B-cell lymphomas. Collectively, these studies describe the synthesis, activity and binding mode of a new series of non-covalent proteasome inhibitors with unprecedented potency and selectivity for the beta5 site, and which can discriminate between the constitutive proteasome and immunoproteasome in vitro and in cells.

Genome-Wide siRNA Screen for Modulators of Cell Death Induced by Proteasome Inhibitor Bortezomib

Multiple pathways have been proposed to explain how proteasome inhibition induces cell death, but mechanisms remain unclear. To approach this issue, we performed a genome-wide siRNA screen to evaluate the genetic determinants that confer sensitivity to bortezomib (Velcade (R); PS-341). This screen identified 100 genes whose knockdown affected lethality to bortezomib and to a structurally diverse set of other proteasome inhibitors. A comparison of three cell lines revealed that 39 of 100 genes were commonly linked to cell death. We causally linked bortezomib-induced cell death to the accumulation of ASF1B, Myc, ODC1, Noxa, BNIP3, Gadd45alpha, p-SMC1A, SREBF1, and p53. Our results suggest that proteasome inhibition promotes cell death primarily by dysregulating Myc and polyamines, interfering with protein translation, and disrupting essential DNA damage repair pathways, leading to programmed cell death.

Antitumor activity of the investigational proteasome inhibitor MLN9708 in mouse models of B-cell and plasma cell malignancies.

Purpose: The clinical success of the first-in-class proteasome inhibitor bortezomib (VELCADE) has validated the proteasome as a therapeutic target for treating human cancers. MLN9708 is an investigational proteasome inhibitor that, compared with bortezomib, has improved pharmacokinetics, pharmacodynamics, and antitumor activity in preclinical studies. Here, we focused on evaluating the in vivo activity of MLN2238 (the biologically active form of MLN9708) in a variety of mouse models of hematologic malignancies, including tumor xenograft models derived from a human lymphoma cell line and primary human lymphoma tissue, and genetically engineered mouse (GEM) models of plasma cell malignancies (PCM). Experimental Design: Both cell line–derived OCI-Ly10 and primary human lymphoma–derived PHTX22L xenograft models of diffuse large B-cell lymphoma were used to evaluate the pharmacodynamics and antitumor effects of MLN2238 and bortezomib. The iMycCα/Bcl-XL GEM model was used to assess their effects on de novo PCM and overall survival. The newly developed DP54-Luc–disseminated model of iMycCα/Bcl-XL was used to determine antitumor activity and effects on osteolytic bone disease. Results: MLN2238 has an improved pharmacodynamic profile and antitumor activity compared with bortezomib in both OCI-Ly10 and PHTX22L models. Although both MLN2238 and bortezomib prolonged overall survival, reduced splenomegaly, and attenuated IgG2a levels in the iMycCα/Bcl-XL GEM model, only MLN2238 alleviated osteolytic bone disease in the DP54-Luc model. Conclusions: Our results clearly showed the antitumor activity of MLN2238 in a variety of mouse models of B-cell lymphoma and PCM, supporting its clinical development. MLN9708 is being evaluated in multiple phase I and I/II trials. Clin Cancer Res; 17(23); 7313–23. ©2011 AACR.

Optimization of a series of dipeptides with a P3 threonine residue as non-covalent inhibitors of the chymotrypsin-like activity of the human 20S proteasome.

Starting from a tripeptide screening hit, a series of dipeptide inhibitors of the proteasome with Thr as the P3 residue has been optimized with the aid of crystal structures in complex with the β-5/6 active site of y20S. Derivative 25, (β5 IC(50)=7.4 nM) inhibits only the chymotryptic activity of the proteasome, shows cellular activity against targets in the UPS, and inhibits proliferation.

Identification of Potent and Selective Non-covalent Inhibitors of the Plasmodium falciparum Proteasome

We have identified short N,C-capped peptides that selectively inhibit the proteasome of the malaria-causing pathogen Plasmodium falciparum. These compounds are highly potent in culture with no toxicity in host cells. One cyclic biphenyl ether compound inhibited intraerythrocytic growth of P. falciparum with an IC50 of 35 nM, and we show that even a pulse treatment with this cyclic peptide induced parasite death due to proteasome inhibition. These compounds represent promising new antimalarial agents that target the essential proteasomal machinery of the parasite without toxicity toward the host.

Optimization of a series of dipeptides with a P3 β-neopentyl asparagine residue as non-covalent inhibitors of the chymotrypsin-like activity of human 20S proteasome

Inhibition of the proteasome by covalent inhibitors is a clinically proven anti-cancer therapy. We report here that dipeptides with a P3 neopentyl Asn residue are potent, reversible, non-covalent inhibitors selective for the chymotryptic activity of the 20S proteasome in vitro and in cells. The X-ray structure of compound 20 in complex with yeast 20S reveals the importance of hydrophobic bonding interactions of the neopentyl group within the S3 binding pocket of the 20S β5 sub-unit. Four compounds show comparable potencies to boronic acid inhibitors in a panel of assays.

Abstract C99: Beyond bortezomib: Development of Millennium's next-generation proteasome inhibitors.

Bortezomib (Velcade®) is a proteasome inhibitor that has been approved by the U.S. Food and Drug Administration for the treatment of patients with multiple myeloma or relapsed mantle cell lymphoma. It is currently available in more than 90 countries worldwide. The molecule is an N-capped dipeptidyl boronic acid and its molecular mechanism involves slow-tight binding to the chymotrypsin-like (β5) sites of the 26S proteasome. In the development of Millennium9s next generation inhibitors, we have investigated several parameters affecting the drug9s activity in biological systems. These include tissue proteasome concentration, blood/plasma partitioning and the kinetics of proteasome inhibition in cultured cells. We find that the abundance of the proteasome (approx. 1–5 μM β5 active site concentration) in cells and tissues together with the slow rate of dissociation of bortezomib from the proteasome (110 min. half-life) led to partitioning of the inhibitor in red blood cells, thereby limiting its distribution to potential sites of therapeutic action. Based on the hypothesis that more rapid dissociation from the proteasome should improve tissue distribution, we have developed an investigational, dipeptidyl boronic acid proteasome inhibitor (MLN9708). MLN9708 displays comparable potency (i.e. similar Ki) to bortezomib for the β5 site of the proteasome but a shorter (18 min.) half-life of dissociation. This affects rapid recovery of proteasome activity in tissue culture cells upon washout of the drug as well as reduced blood/plasma partitioning in mice, supporting the hypothesis that a more rapid equilibrium proteasome inhibitor can improve tissue distribution. MLN9708 is currently in phase 1 clinical trials. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C99.