Proteolytic resistance and biological activity of N-methylated analogs of [pGlu6] substance P6-11

Mass spectrometric characterization of crustacean hyperglycemic hormone precursor-related peptides (CPRPs) from the sinus gland of the crab, Cancer productus

Crustacean hyperglycemic hormone (CHH) precursor-related peptides (CPRPs) are produced during the proteolytic processing of CHH preprohormones. Currently, the physiological roles played by CPRPs are unknown. Due to their large size, direct mass spectrometric sequencing of intact CPRPs is difficult. Here, we describe a novel strategy for sequencing Cancer productus CPRPs directly from a tissue extract using nanoflow liquid chromatography coupled to quadrupole time-of-flight tandem mass spectrometry. Four novel CPRPs were characterized with the aid of MS/MS de novo sequencing of 27 truncated CPRP peptides. Extensive modifications (methionine oxidation and carboxy-terminal methylation) were identified in both the full-length and truncated peptides. To investigate the origin of the modifications and truncations, a full-length CPRP was synthesized and subjected to the same storage and extraction protocols used for the characterization of the native peptides. Here, some methionine oxidation was seen, however, no methylation or truncation was evident suggesting much of the chemical complexity seen in the native CPRPs is unlikely due to a sample preparation artifact. Collectively, our study represents the most complete characterization of CPRPs to date and provides a foundation for future investigation of CPRP function in C. productus.

Metabolism of the broad-spectrum neuropeptide growth factor antagonist: [D-Arg1, D-Phe5, D-Trp7,9, Leu11]-substance P

Broad-spectrum neuropeptide growth factor antagonists, such as [D-Arg1, D-Phe5, D-Trp7,9, Leu11]substance P (antagonist D) and [Arg6, D-Trp7,9, NmePhe8]substance P(6-11) (antagonist G), are currently being investigated as possible anti-tumour agents. These compounds are hoped to be effective against neuropeptide-driven cancers such as small-cell lung cancer. Antagonist D possesses a broader antagonistic spectrum than antagonist G and hence may be of greater therapeutic use. The in vitro metabolism of antagonist D has been characterised and the structures of two major metabolites have been elucidated by amino acid analysis and mass spectrometry. Metabolism was confined to the C-terminus where serine carboxypeptidase action produced [deamidated]-antagonist D (metabolite 1) and [des-Leu11]-antagonist D (metabolite 2) as the major metabolites. Biological characterisation of the metabolites demonstrated that these relatively minor changes in structure resulted in a loss of antagonist activity. These results provide some of the first structure-activity information on the factors that determine which neuropeptides these compounds inhibit and on the relative potency of that inhibition.

Pharmacokinetics, metabolism, tissue and tumour distribution of the neuropeptide growth factor antagonist [Arg6, D-Trp7,9, NmePhe8]- substance P(6-11) in nude mice bearing the H69 small-cell lung cancer xenograft

BACKGROUND

[Arg6, D-Trp7,9, NmePhe8]-Substance P (6-11) (codenamed antagonist G) represents the first board spectrum antagonist of a number of neuropeptides shown to act as growth factors in small-cell lung cancer (SCLC) and is shortly to enter clinical trials.

DESIGN

Pharmacokinetics, metabolism, tissue disposition have been studied in mice (nu/nu) bearing the NCI-H69 human SCLC xenograft after systemic drug adminstration at an active dose (45 mg/kg i.p.).

RESULTS

The peptide exhibited relatively long half life (28.9 min; clearance 45.6 ml/min/kg) and distributed widely (volume of distribution 1490 ml/kg). Marked accumulation of antagonist G (and its metabolites) was noted in the liver (AUC5278 micrograms/g x min) and to a lesser extent the spleen (AUC 930 micrograms/g x min) but only low levels appeared to cross the blood brain barrier (AUC in brain, 20 micrograms/g x min) or be taken up into the heart (AUC 101 micrograms/g x min). Tumour uptake was intermediate in value out of the 7 tissues studied (AUC 195 micrograms/g x min). Metabolism was restricted almost exclusively to the C terminal of the peptide producing 4 major products: M1, deamidated antagonist G; M2, Harg-DTrp-NmePhe-DTrp-Leu-OH, both of which retain growth factor antagonist activity; M3, a combination of oxidised antagonist G [Met11(O)] and oxidised deamidated antagoinst G; and M4, a combination of H-Arg-DTrp-NmePhe-DTrp-OH and H-DTrp-NmePhe-DTrp-Leu-OH. Extensive biotransformation to predominately M1 and M2 occurred in most tissues including the tumour where the parent peptide accounted for only 48.5% of the total.

CONCLUSION

Levels of antagonist G required to produce a small but significant effect on the growth of SCLC cell lines in vitro are in the region of 4-7 microM. Taking into account metabolites, a peak concentration of 4.1 microgram/g (4.3 microM) was achieved in the H69 xenograft. These studies reveal a favourable preclinical pharmacology profile for antagonist G and offer hope that anticancer activity may be achievable in man.

Processing of the neuropeptide growth factor antagonist [Arg6, D-Trp7.9, NmePhe8]-substance P (6-11) by a small cell lung cancer cell line (H69)

[Arg6, D-Trp7.9, NmePhe8]-substance P (6-11) (antagonist G) is a broad spectrum neuropeptide growth factor antagonist about to enter clinical trials as an anticancer drug. Its fate has been studied after incubation with two densities (5 x 10(4) cells/mL and 1 x 10(6) cells/mL) of the H69 small cell lung cancer cell line for up to 7 days at a concentration of 20 microM, corresponding to the IC50 for growth inhibition. HPLC analyses were conducted on cell pellets and media and in controls consisting of cell free media and water. Over 7 days in media containing cells a 70.4% reduction in parent peptide concentration occurred at the high density and a 44.1% reduction at low density. Despite this, there was a steady elevation in peptide associated with cells reaching a 189% increase by day 7. Oxidation of G at the C-terminal methionine residue occurred in all media studied indicative of a chemical process. The two major active metabolites of antagonist G (deamidated G and G minus Met11) were detected only in media in the presence of cells. These accumulated with time in media and cells together with oxidized products. These results reveal complex cellular pharmacology for antagonist G where H69 cells are increasingly exposed to 4 different peptide products rather than 1.

Metabolism of the anticancer peptide H-Arg-D-Trp-NmePhe-D-Trp-Leu-Met-NH2

H-Arg-D-Trp-NmePhe-D-Trp-Leu-Met-NH2 (Antagonist G) will be the first broad-spectrum neuropeptide antagonist to enter a phase I clinical trial. Its in vitro and in vivo metabolism has been extensively characterized. The major metabolites were identified and their structures elucidated by mass spectroscopy and amino acid analysis. Metabolism occurred almost exclusively at the C-terminus and was arrested by phenylmethylsulfonylfluoride, a known serine-protease inhibitor. Biological characterization of the metabolites demonstrated that the degradation of Antagonist G produces metabolites that retain neuropeptide antagonist properties.

Stability and in vitro metabolism of the mitogenic neuropeptide antagonists [D-Arg1,D-Phe5, D-Trp7,9, Leu11]-substance P and [Arg6, D-Trp7,9, MePhe8]-substance P (6-11) characterized by high-performance liquid chromatography

The substance P (SP) analogues [D-Arg1, D-Phe5, D-Trp7,9, Leu11]-SP and [Arg6, D-Trp7,9, MePhe8]-SP (6-11) (antagonists D and G, respectively) are under consideration as new anticancer drugs. In this report, the stability and in vitro metabolism of both antagonists in up to seven different media (water, 1 M acetic acid, human plasma, nude mouse liver and WX 322 human SCLC xenograft homogenized in either 1 M acetic acid or phosphate buffered saline (PBS), pH 7.4) have been characterized by both isocratic and gradient elution reversed-phase HPLC. Antagonist D was stable (never > 13% degradation over 24 h, at 37 degrees C) in water, 1 M acetic acid and plasma but was metabolized by PBS liver homogenates (10%, w/v) sequentially to two stable metabolites with a half life of 0.98 h at a concentration of 500 micrograms ml-1. The major pathway of degradation of antagonist G appeared to be C-terminal methionine oxidation (particularly in plasma) as well as hydrolysis, with even aqueous solutions being significantly affected at low concentrations of peptide (0.1 micrograms ml-1, half life 20.9 h at 37 degrees C). Stable metabolites of antagonist G were also detected in incubations with PBS liver homogenates (half life 1.53 h at 500 micrograms ml-1, 37 degrees C). Overall, the data presented indicate that the modifications made to SP have been relatively successful in preserving chemical and biological stability.