Method to generate highly stable D-amino acid analogs of bioactive helical peptides using a mirror image of the entire PDB

Biologics are a rapidly growing class of therapeutics with many advantages over traditional small molecule drugs. A major obstacle to their development is that proteins and peptides are easily destroyed by proteases and, thus, typically have prohibitively short half-lives in human gut, plasma, and cells. One of the most effective ways to prevent degradation is to engineer analogs from dextrorotary (D)-amino acids, with up to 105-fold improvements in potency reported. We here propose a general peptide-engineering platform that overcomes limitations of previous methods. By creating a mirror image of every structure in the Protein Data Bank (PDB), we generate a database of ∼2.8 million D-peptides. To obtain a D-analog of a given peptide, we search the (D)-PDB for similar configurations of its critical-"hotspot"-residues. As a proof of concept, we apply our method to two peptides that are Food and Drug Administration approved as therapeutics for diabetes and osteoporosis, respectively. We obtain D-analogs that activate the GLP1 and PTH1 receptors with the same efficacy as their natural counterparts and show greatly increased half-life.

In vivo demonstration that parathyroid hormone and parathyroid hormone-related protein stimulate expression by osteoblasts of interleukin-6 and leukemia inhibitory factor

We have previously reported that parathyroid hormone (PTH) and PTH related protein (PTHrP) stimulate expression of interleukin-6 (IL-6) and leukemia inhibitory factor (LIF) in osteoblasts in vitro. In the current study, we have developed a model of hormone injection into the subcutaneous space overlying mouse parietal bones to demonstrate that similar processes occur in osteoblasts in vivo. Specifically, PTH and PTHrP rapidly and transiently induce expression of the mRNAs encoding IL-6 and LIF. The effects are dose-dependent, with a maximal stimulation of approximately 50-fold for each cytokine. Although PTH and PTHrP activate both adenyl cyclase and phospholipase C-dependent signal transduction pathways, stimulation of IL-6 and LIF depends on adenyl cyclase since it is not reproduced by PTH(3-34), a partial agonist that only activates phospholipase C. These results confirm our previous in vitro studies and support the hypothesis that IL-6 and/or LIF are physiologically important mediators of at least some of the actions of PTH and PTHrP.

A new strategy for modulating chemotherapy-induced alopecia, using PTH/PTHrP receptor agonist and antagonist

Parathyroid hormone (PTH) related peptide (PTHrP) and the PTH/PTHrP receptor (PTH/PTHrP-R) show prominent cutaneous expression, where this signaling system may exert important paracrine and/or autocrine functions, such as in hair growth control. Chemotherapy-induced alopecia - one of the fundamental unsolved problems of clinical oncology - is driven in part by defined abnormalities in hair follicle cycling. We have therefore explored the therapeutic potential of a PTH/PTHrP-R agonist and two PTH/PTHrP-R antagonists in a mouse model of cyclophosphamide-induced alopecia. Intraperitoneal administration of the agonist PTH(1-34) or the antagonists PTH(7-34) and PTHrP(7-34) significantly altered the follicular response to cyclophosphamide in vivo. PTH(7-34) and PTHrP(7-34) shifted it towards a mild form of "dystrophic anagen", associated with a significant reduction in apoptotic (TUNEL+) hair bulb cells, thus mitigating the degree of follicle damage and retarding the onset of cyclophosphamide-induced alopecia. PTH(1-34), in contrast, forced hair follicles into "dystrophic catagen", associated with enhanced intrafollicular apoptosis. We had previously shown that an induced shift in the follicular damage-response towards "dystrophic catagen" mitigates cyclophosphamide-induced alopecia, whereas a shift towards "dystrophic catagen" initially enhanced the hair loss, yet subsequently promoted accelerated hair follicle recovery. Therefore, this study in an established animal model of chemotherapy-induced alopecia, which closely mimics human chemotherapy-induced alopecia, strongly encourages the exploration of PTH/PTHrP-R agonists and antagonists as novel therapeutic agents in chemotherapy-induced alopecia.

Differential regulation of receptor-stimulated cyclic adenosine monophosphate production by polyvalent cations in MC3T3-E1 osteoblasts

Extracellular cations have paradoxical trophic and toxic effects on osteoblast function. In an effort to explain these divergent actions, we investigated in MC3T3-E1 osteoblasts if polyvalent cations differentially modulate the agonist-stimulated cyclic adenosine monophosphate (cAMP) pathway, an important regulator of osteoblastic function. We found that a panel of cations, including gadolinium, aluminum, calcium, and neomycin, inhibited prostaglandin E1 (PGE)-stimulated cAMP accumulation but paradoxically potentiated parathyroid hormone (PTH)-stimulated cAMP production. In contrast, these cations had no effect on forskolin- or cholera toxin-induced increases in cAMP, suggesting actions proximal to adenylate cyclase and possible modulation of receptor interactions with G proteins. Phorbol 12-myristate 13-acetated (PMA) mimicked the effects of cations on PGE1- and PTH-stimulated cAMP accumulation in MC3T3-E1 cells, respectively, diminishing and augmenting the responses. Moreover, down-regulation of protein kinase C (PKC) by overnight treatment with PMA prevented gadolinium (Gd3+) from attenuating PGE1- and enhancing PTH-stimulated cAMP production, indicating involvement of PKC-dependent pathways. Cations, however, activated signal transduction pathways not coupled to phosphatidylinositol-specific phospholipase C (PI-PLC), since there was no corresponding increase in inositol phosphate formation or intracellular calcium concentrations. In addition, pertussis toxin treatment failed to prevent Gd(3+)-mediated suppression of PGE1-stimulated cAMP, suggesting actions independent of Gm. Thus, polyvalent cations may either stimulate or inhibit hormone-mediated cAMP accumulation in osteoblasts. These differential actions provide a potential explanation for the paradoxical trophic and toxic effects of cations on osteoblast function that occur in vivo under different hormonal conditions.

Identification of determinants of inverse agonism in a constitutively active parathyroid hormone/parathyroid hormone-related peptide receptor by photoaffinity cross-linking and mutational analysis

We have investigated receptor structural components responsible for ligand-dependent inverse agonism in a constitutively active mutant of the human parathyroid hormone (PTH)/parathyroid hormone-related peptide (PTHrP) receptor type 1 (hP1R). This mutant receptor, hP1R-H223R (hP1R(CAM-HR)), was originally identified in Jansen's chondrodysplasia and is altered in transmembrane domain (TM) 2. We utilized the PTHrP analog, [Bpa(2),Ile(5),Trp(23),Tyr(36)]PTHrP-(1-36)-amide (Bpa(2)-PTHrP-(1-36)), which has valine 2 replaced by p-benzoyl-l-phenylalanine (Bpa); this substitution renders the peptide a photoreactive inverse agonist at hP1R(CAM-HR). This analog cross-linked to hP1R(CAM-HR) at two contiguous receptor regions as follows: the principal cross-link site (site A) was between receptor residues Pro(415)-Met(441), spanning the TM6/extracellular loop three boundary; the second cross-link site (site B) was within the TM4/TM5 region. Within the site A interval, substitution of Met(425) to Leu converted Bpa(2)-PTHrP-(1-36) from an inverse agonist to a weak partial agonist; this conversion was accompanied by a relative shift of cross-linking from site A to site B. The functional effect of the M425L mutation was specific for Bpa(2)-containing analogs, as inverse agonism of Bpa(2)-PTH-(1-34) was similarly eliminated, whereas inverse agonism of [Leu(11),d-Trp(12)]PTHrP-(5-36) was not affected. Overall, our data indicate that interactions between residue 2 of the ligand and the extracellular end of TM6 of the hP1R play an important role in modulating the conversion between active and inactive receptor states.

Conformational studies of mono- and bicyclic parathyroid hormone-related protein-derived agonists

Parathyroid hormone-related protein (PTHrP) is expressed in a wide variety of cells where it acts as an autocrine and/or paracrine factor involved in regulation of cellular growth, differentiation, and embryonic development. It may also play a physiological endocrine role in calcium transport across the placenta or during lactation. The N-terminal portion, PTHrP-(1-34), retains all the calciotropic parathyroid hormone-like activity and is a lead structure for the design of novel, bone anabolic agents for the treatment of bone disorders such as osteoporosis. To characterize the putative bioactive conformation, we have carried out a detailed structural analysis of a series of three conformationally constrained PTHrP-(1-34)-based mono- and bicyclic lactam-containing biologically active analogs: (III) The conformational properties were studied by circular dichroisim, nuclear magnetic resonance spectroscopy, distance geometry calculations, and molecular dynamic simulations in water/trifluoroethanol (TFE) mixtures. The helical content in water of both monocyclic analogs I and II is approximately 22%; that of the bicyclic analog III is approximately 40%. In 30% TFE, all analogs reached a maximal helical content of 80%, corresponding to 26 or 27 residues out of 34 in a helical conformation. High-resolution structures obtained with 50:50 TFE/water revealed that all three analogs display two helical domains and a hinge region around Gly12-Lys13. The highly potent mono- and bicyclic agonists I and III display a second hinge around Arg19-Arg20 which is shifted to Ser14-Asp17 in the weakly potent monocyclic agonist II. We suggest that the presence and localization of discrete hinges in the sequence together with the high propensity for helicity of the C-terminal sequence and the enhancement of helical nucleation at the N-terminal sequence are essential for generating a PTH/PTHrP receptor-compatible bioactive conformation.

Discovery of a small molecule antagonist of the parathyroid hormone receptor by using an N-terminal parathyroid hormone peptide probe

Once-daily s.c. administration of either human parathyroid hormone (PTH)-(1-84) or recombinant human PTH-(1-34) provides for dramatic increases in bone mass in women with postmenopausal osteoporosis. We initiated a program to discover orally bioavailable small molecule equivalents of these peptides. A traditional high-throughput screening approach using cAMP activation of the PTH/PTH-related peptide receptor (PPR) as a readout failed to provide any lead compounds. Accordingly, we designed a new screen for this receptor that used a modified N-terminal fragment of PTH as a probe for small molecule binding to the transmembrane region of the PPR, driven by the assumption that the pharmacological properties (agonist/antagonist) of compounds that bound to this putative signaling domain of the PPR could be altered by chemical modification. We developed DPC-AJ1951, a 14 amino acid peptide that acts as a potent agonist of the PPR, and characterized its activity in ex vivo and in vivo assays of bone resorption. In addition, we studied its ability to initiate gene transcription by using microarray technology. Together, these experiments indicated that the highly modified 14 amino acid peptide induces qualitatively similar biological responses to those produced by PTH-(1-34), albeit with lower potency relative to the parent peptide. Encouraged by these data, we performed a screen of a small compound collection by using DPC-AJ1951 as the ligand. These studies led to the identification of the benzoxazepinone SW106, a previously unrecognized small molecule antagonist for the PPR. The binding of SW106 to the PPR was rationalized by using a homology receptor model.

Evaluation in vivo of a potent parathyroid hormone antagonist: [Nle8,18,D-Trp12,Tyr34]bPTH(7-34)NH2

In an effort to design and select potent parathyroid hormone (PTH) antagonists suitable for clinical utility, a PTH analog was evaluated in vivo in an animal model to assess its properties in preparation for human studies. The previously described PTH antagonist, [Nle8,18,D-Trp12,Tyr34]bPTH(7-34)NH2, which is highly active in vitro, was documented in these studies to be an effective antagonist of the PTH-stimulated calcemic response in vivo. In thyroparathyroidectomized (TPTX) rats, the efficacy of the antagonist was demonstrated to be dose-dependent. Inhibition was demonstrated when intravenous administration of antagonist started 1 h prior to coinfusion with the PTH agonist [Nle8,18,Tyr34]bPTH(1-34)NH2. Maximal inhibition by antagonist (an 84% decline in serum calcium levels compared with agonist alone) of the calcemic response was observed when a 200-fold molar excess of antagonist (12 nmol/h) was administered. At dose ratios of antagonist:agonist as low as 10:1, a 40-50% inhibition of PTH-stimulated calcemic response is evident, provided a longer (2 h) lead time for antagonist infusion is allowed. Based on these and related studies, the antagonist [Nle8,18,D-Trp12,Tyr34]bPTH(7-34)NH2 has displayed sufficient potency to obtain approval from the appropriate institutional and regulatory agencies for clinical trials in hypercalcemic states of parathyroid and tumor origin.

Therapy for Alopecia Areata in Mice by Stimulating the Hair Cycle with Parathyroid Hormone Agonists Linked to a Collagen-Binding Domain

Alopecia areata is a common disorder in which autoimmune destruction of hair follicles results in patchy hair loss. Currently there is no adequate therapy, although immune modulator therapies are currently in development. Parathyroid hormone (PTH) is a hair cycle stimulator which shows promise in treating various forms of alopecia, although its short half-life limits its clinical use. PTH-CBD is a PTH analog which binds collagen, prolonging retention in skin. We tested effects of PTH-CBD in C3H/HeJ-engrafted mice, the animal model for alopecia areata, on hair growth and found that a significant proportion of animals had reduced hair loss (PTH-CBD: 13/21, 62% vs.

CONTROL

3/10, 30%; P<0.01). Histological analysis showed no change in immune response, but there was increased number of anagen hair follicles and increased production of beta-catenin, a factor which initiates the anagen phase of the hair cycle. PTH-CBD thus shows promise as a therapy for alopecia areata, either alone or in conjunction with immune modulation therapy.

Therapy for alopecia areata in mice using parathyroid hormone agonists and antagonists, linked to a collagen-binding domain

Alopecia areata is a common form of hair loss in which autoimmune-mediated destruction of hair follicles causes patchy hair loss, for which there is no adequate therapy. Parathyroid hormone (PTH) induces the hair cycle and promotes hair growth. PTH-CBD is a fusion protein of PTH and a bacterial collagen-binding domain (CBD), leading to targeted delivery to and retention in the skin collagen. We tested the effects of a single dose of PTH-CBD (low or high dose) on an animal model for alopecia areata, the C3H/HeJ engrafted mouse. In all the treated animals, there was a rapid (1-4 days) increase in hair growth, with sustained effects observed over a 2-month period (7/10 total treated mice<40% hair loss based on gray scale analysis, vs. 2/5 in vehicle control animals). Histological examination revealed massive stimulation of anagen VI hair follicles in treated animals despite an ongoing immune response. PTH-CBD thus shows promise as a therapy for alopecia areata, likely in conjunction with a mild immune suppressant, such as hydrocortisone cream.

Zinc(II)-mediated enhancement of the agonist activity of histidine-substituted parathyroid hormone(1-14) analogues

Previous studies on parathyroid hormone (PTH)(1-14) revealed that residues (1-9) played a dominant role in stimulating PTH-1 receptor-mediated increases in cAMP formation. In the present study, we examined the effects of installing a metal-binding motif in the (10-14) region of rat PTH(1-14) on the peptide's agonist activity. We found that substitution of histidine for the native asparagine at position 10 of PTH(1-14) provided a peptide that was approx. 8-fold more potent as an agonist in the presence of divalent zinc salts than it was in the absence of the metal. This enhancement in potency was dependent on the native histidine at position 14, the concentration of Zn(II) utilized, and did not occur with other divalent metal ions. The zinc-activated [His(10)]-PTH(1-14) peptide was blocked by a classical PTH-1 receptor antagonist, PTHrP(7-36), and did not activate the PTH-2 receptor. The zinc-mediated enhancing effect did not require the large N-terminal extracellular domain of the PTH-1 receptor. Although we were able to demonstrate that [His(10)]-PTH(1-14) binds Zn(II) using (1)H-NMR, our spectroscopic studies (circular dichroism and nuclear magnetic resonance) were not consistent with the notion that zinc enhanced the activity of [His(10)]-PTH(1-14) simply by inducing a helical structure in the 10-14 region. Rather, the data suggest that the enhancement in cAMP potency arises from the formation of a ternary complex between [His(10)]-PTH(1-14), a zinc atom, and the extracellular loop/transmembrane domain region of the PTH-1 receptor.

Expression and characterization of a recombinant human parathyroid hormone partial agonist with antagonistic properties: Gly-hPTH(-1-->+84)

We have produced and characterized a hPTH analogue with an amino-terminal extension of glycine, Gly-hPTH(-1-->+84) (denoted Gly-hPTH). The hormone analogue was synthesized in E. coli strain BJ5183 transformed with the expression plasmid pKKPTH, extracted from the bacterial pellet and purified by reverse-phase high performance liquid chromatography. Its chemical nature, as determined by amino acid composition analysis, N-terminal amino acid analysis, and mass spectrometry, showed the 9480-Da Gly-hPTH as the predominant species. Because f-Met-Gly-hPTH was the expected form encoded by the plasmid construct, the results indicate that the f-Met residue was efficiently removed from the precurser form. The following functional characteristics of Gly-hPTH were demonstrated. 1) In cells transfected with the human PTH/PTHrP receptor, the receptor binding affinity was reduced threefold compared to the authentic hPTH(1-84) produced by Saccharomyces cerevisiae (apparent Kds: 8.4 and 2.7 nM, respectively). 2) Using the same cells, Gly-hPTH showed 27-fold reduced potency compared to hPTH(1-84) in stimulating intracellular cAMP production (EC50: 32 and 1.2 nM, respectively). 3) Gly-hPTH demonstrated antagonist activity by reducing hPTH-induced cAMP production by 33 +/- 5% (mean +/- SD) when tested at a 1:1 molar ratio. In these studies the recombinant authentic hPTH(1-84) was used as standard for comparisons, and it showed an equal receptor binding affinity and cAMP production as the chemically synthesized peptide [Nle8,18,Tyr34]bovinePTH(1-34)-NH2.

PREOS NPS (Allelix/Nycomed)

NPS Allelix and Nycomed are developing PREOS, an injectable recombinant human parathyroid hormone, for the potential treatment of osteoporosis. In May 2005, NPS filed a market authorization application for PREOS in the US which was accepted for review in July 2005.

MBX 2109, A Once-Weekly Parathyroid Hormone Replacement Therapy Prodrug: Phase 1, First-In-Human, Randomized Trial

CONTEXT

Hypoparathyroidism denotes parathyroid hormone (PTH) deficiency and impaired mineral metabolism. MBX 2109, a novel prodrug yielding a biologically active PTH peptide agonist (PTH[1-32], extended by a fatty acylated Lys33), is being developed as a long-acting, once-weekly PTH replacement therapy.

OBJECTIVE

Here, we report the safety, pharmacokinetics (PK), and pharmacodynamics (PD) of MBX 2109 in healthy volunteers.

METHODS

This phase 1, randomized, double-blind, placebo-controlled, multiple ascending-dose study (NCT05158335) enrolled healthy adults, who were randomly assigned 4:1 to receive MBX 2109 (200, 400, 600, and 900 μg; n = 8) or placebo (n = 2) by subcutaneous administration once weekly for 4 doses (days 1, 8, 15, and 22). The primary end point was safety and tolerability. Key secondary end points were PK and PD.

RESULTS

Overall, 40 participants (MBX 2109 n = 32, placebo n = 8) were randomly assigned (mean age, 43.3 years; 22.5% female). Treatment-emergent adverse events (TEAEs) occurred in 50% to 88% of MBX 2109 groups and in 25% of placebo participants. In the MBX 2109 groups, no severe or serious TEAEs were observed. Injection-site reaction was the most common treatment-related TEAE. The half-lives were 79 to 95 hours for MBX 2109 and 184 to 213 hours for the fatty-acylated biologically active PTH peptide, which showed dose- and time-dependent exposure increases.

CONCLUSION

The sustained-action PTH prodrug MBX 2109 was well tolerated with no unexpected, off-target safety issues. The long half-life and flat exposure profile of MBX 2109's biologically active PTH agonist supports once-weekly administration. MBX 2109 doses were identified for future studies.