Potent and prolonged acting cyclic lactam analogues of alpha-melanotropin: design based on molecular dynamics

Utilizing results from previous structure-activity relationships and theoretical studies of alpha-melanotropin (alpha-MSH, Ac-Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2) and its related superpotent analogues, Ac-[Nle4,D-Phe7]-alpha-MSH and Ac-[Cys4,Cys10]-alpha-MSH, we have designed a new class of alpha-MSH4-13 and alpha-MSH4-10 cyclic lactam fragment analogues of alpha-melanotropin. The cyclic peptides have the following general structures: Ac-[Nle4,Xxx5,D-Phe7,Yyy10,Gly11]-alpha-MSH4-13- NH2 and Ac-[Nle4,Xxx5,D-Phe7,Yyy10]-alpha-MSH4-10-NH2, where Xxx = Glu or Asp and Yyy = Lys, Orn, Dab, or Dpr. Formation of the lactam bridge between the side-chain groups Xxx and Yyy was performed either in solution or on a solid-phase support. Seven cyclic peptides were prepared and bioassayed for their melanotropic potency by using standard frog (Rana pipiens) and lizard (Anolis carolinensis) skin bioassays. Relative to alpha-MSH (relative potency = 1), the potencies of the cyclic peptides in the lizard skin bioassay were as follows: alpha-MSH (1); Ac-[Nle4,Glu5,D-Phe7,Lys10,Gly11]-alpha-MSH4-13- NH2 (6); Ac-[Nle4,Asp5,D-Phe7,Lys10,Gly11]-alpha-MSH4-13- NH2 (100); Ac-[Nle4,Glu5,D-Phe7,Lys10]-alpha-MSH4-10-NH2 (9); Ac-[Nle4,Asp5,D-Phe7,Lys10]-alpha-MSH4-10-NH2 (90); Ac-[Nle4,Asp5,D-Phe7,Orn10]-alpha-MSH4-10-NH2 (20); Ac-[Nle4,Asp5,D-Phe7,Dab10]-alpha-MSH4-10-NH2 (5); Ac-[Nle4,Asp5,D-Phe7,Dpr10]-alpha-MSH4-10-NH2 (5). Similar results were obtained in the frog skin bioassay, but the analogues were much less potent. Cyclic melanotropins with 23-membered rings exhibited 100-fold higher melanotropic potency than alpha-MSH with selectivity for the lizard melanocyte receptors over the frog melanocyte receptors. Increasing or decreasing the ring size of these cyclic melanotropins from 23 diminishes the biological potency of the resulting cyclic peptide. The 23- and 24-membered ring analogues showed prolonged (residual) biological activities in both biological assays, but the smaller ring systems (20, 21, 22) did not. These results provide new insights into the structural and conformational requirements of alpha-MSH and its analogues at two different types of pigment cell (melanocyte) receptors.     

A new, highly selective CCK-B receptor radioligand ([3H][N-methyl-Nle28,31]CCK26-33): evidence for CCK-B receptor heterogeneity

[N-methyl-Nle28,31]CCK26-33 (SNF 8702) is a nonsulfated cholecystokinin octapeptide analog that is highly selective for cholecystokinin-B (CCK-B) receptors. Inhibition studies using [125I] Bolton-Hunter-labeled CCK-8 show that SNF 8702 has over 4,000-fold greater affinity for CCK receptors in guinea pig cortex relative to those in guinea pig pancreas. SNF 8702 was tritium-labeled to a specific activity of 23.7 Ci/mmol and its binding properties characterized for guinea pig brain membrane preparations. [3H]SNF 8702 binds to a single site with high affinity (Kd = 0.69-0.90 nM) in guinea pig cortex, cerebellum, hippocampus and pons-medulla. Of these four tissues, the highest receptor density was measured in the cortex (86 fmol/mg of protein) and the lowest in the pons-medulla (22 fmol/mg of protein). In contrast to findings of single-site binding in some brain regions, evidence for CCK-B receptor heterogeneity is observed under other conditions. [3H]SNF 8702 binding to membranes prepared from whole guinea pig brain shows biphasic association kinetics at a concentration of 2.0 nM consistent with the presence of binding site heterogeneity. Binding site heterogeneity is consistently observed for [3H]SNF 8702 binding to guinea pig whole brain membranes in saturation studies where a high-affinity site (Kd = 0.31 nM) is distinguished from a low-affinity site (Kd = 3.3 nM). Binding site heterogeneity is also observed for the midbrain-thalamic region. CCK-B receptor heterogeneity is suggested by the effect of the guanyl nucleotide analogue, guanylyl-imidodiphosphate (Gpp(NH)p), on [3H]SNF 8702 binding to CCK-B receptors in the cerebellum.(ABSTRACT TRUNCATED AT 250 WORDS)     

Distribution and analgesia of [3H][D-Pen2, D-Pen5]enkephalin and two halogenated analogs after intravenous administration.

To improve pharmacological characteristics of the delta-selective, cyclic peptide [D-Pen2, D-Pen5]enkephalin (DPDPE), modification by halogenation at the Phe4 residue was undertaken. The present study was to determine the extent [3H]DPDPE, [3H][p-Cl-Phe4]DPDPE and [p-125IPhe4]DPDPE crosses the blood-brain barrier, elicits analgesia and to characterize selective organ distribution and stability after i.v. administration. A significantly greater percentage of total [3H][p-Cl-Phe4]DPDPE reached the brain after 10, 20 and 40 min as compared to [3H]DPDPE and both peptides were significantly displaced by pretreatment with naloxone or naltrindole. The amount of [3H]DPDPE detected in the brain was greater than that of [p-125IPhe4]DPDPE. Distribution results revealed large amounts of the administered peptides were sequestered rapidly in the gall bladder and secreted into the small intestine. Hot-plate antinociception tests 5 min after i.v. administration (30 and 60 mg/kg) revealed [p-Cl-Phe4]DPDPE to elicit a much greater analgesic effect as compared to DPDPE or [p-125IPhe4]DPDPE. These results provide evidence that [p-Cl-Phe4]DPDPE has a greater apparent distribution to the brain and has a greater effect on the antinociception threshold as tested on the hot-plate than DPDPE or [p-125IPhe4]DPDPE. Stability of unlabeled and tritiated DPDPE and [p-Cl-Phe4]DPDPE was determined both in vitro and in vivo; both unlabeled and tritiated DPDPE and [p-Cl-Phe4]DPDPE remain intact.     

Antidiarrheal properties of supraspinal mu and delta and peripheral mu, delta and kappa opioid receptors: inhibition of diarrhea without constipation

We evaluated the ability of mu [morphine, Tyr-Pro-N-MePhe-D-Pro-NH2 (PLO17)], delta (Tyr-D-Pen-Gly-Phe-D-Pen) (DPDPE) and kappa [U50,488H, (trans-3,4-dichloro-N-methyl-N-(2-(1-pyr-rolidinyl) cyclo-hexyl)benzeneacetamine)] opioid receptor selective agonists to inhibit diarrhea induced by castor oil (0.6 ml p.o.) in mice after supraspinal (i.c.v.) and peripheral (s.c.) administration. The antidiarrheal potency of each compound was compared to its analgesic and gastrointestinal antitransit potency when given by the same route of administration. When administered i.c.v., morphine, PLO17 and DPDPE inhibited diarrhea in a dose-related fashion. The mu agonists, morphine and PLO17, given i.c.v, inhibited diarrhea at doses much lower than those needed to produce analgesia or to inhibit gastrointestinal transit. DPDPE (i.c.v.) was equipotent in inhibiting diarrhea and in eliciting analgesia, but did not effect the rate of transit. U50,488H (i.c.v.) inhibited diarrhea only at extremely high doses which also caused profound postural-motor incapacitance. U50,488H given i.c.v. had no effect on transit at any dose. When given peripherally, morphine, PLO17, DPDPE and U50,488H all inhibited diarrhea in a dose-related fashion. All four compounds inhibited diarrhea at doses much below those needed to cause analgesia. Morphine s.c. and PLO17 s.c. both inhibited diarrhea at doses lower than those required to inhibit transit. DPDPE s.c. and U50,488H s.c. had no effect on transit at any dose. The antidiarrheal effects of i.c.v. morphine, i.c.v. PLO17 and i.c.v. DPDPE were antagonized by pretreatment with 1 microgram i.c.v. of naltrexone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Synergistic efficacy of the combination of ST-246 with CMX001 against orthopoxviruses

The combination of ST-246 and hexadecyloxypropyl-cidofovir or CMX001 was evaluated for synergistic activity in vitro against vaccinia virus and cowpox virus (CV) and in vivo against CV. In cell culture the combination was highly synergistic against both viruses, and the results suggested that combined treatment with these agents might offer superior efficacy in vivo. For animal models, ST-246 was administered orally with or without CMX001 to mice lethally infected with CV. Treatments began 1, 3, or 6 days postinfection using lower dosages than previously used for single-drug treatment. ST-246 was given at 10, 3, or 1 mg/kg of body weight with or without CMX001 at 3, 1, or 0.3 mg/kg to evaluate potential synergistic interactions. Treatment beginning 6 days post-viral inoculation with ST-246 alone only increased the mean day to death at 10 or 3 mg/kg but had no effect on survival. CMX001 alone also had no effect on survival. When the combination of the two drugs was begun 6 days after viral infection using various dosages of the two, a synergistic reduction in mortality was observed. No evidence of increased toxicity was noted with the combination either in vitro or in vivo. These results indicate that combinations of ST-246 and CMX001 are synergistic both in vitro and in vivo and suggest that combination therapy using ST-246 and CMX001 for treatment of orthopoxvirus disease in humans or animals may provide an additional benefit over the use of the two drugs by themselves.     

Opioid receptor selectivity of beta-endorphin in vitro and in vivo: mu, delta and epsilon receptors

The relative contributions of mu and delta opioid receptors in the response to Tyr-Gly-Gly-Phe-Met-Thr-Ser-Glu-Lys-Ser-Gln-Thr-Pro-Leu-Val-Thr-Leu-Phe- Lys-Asn - Ala-Ileu-Ileu-Lys-Asn-Ala-Tyr-Lys-Lys-Gly-Glu (B-endorphin) were assessed as reductions in B-endorphin potency in the presence of mu and delta receptor selective antagonists in the guinea pig ileum, mouse vas deferens, rat vas deferens and in analgesic and gastrointestinal transit time tests in mice. We used the nonselective antagonist naloxone, the mu antagonist D-Phe-Cys-Tyr-D-Trp-Lys-Thr-Pen-Thr-NH2 (CTP) and the delta antagonist N,N,diallyl-Tyr-Aib-Aib-Phe-Leu-OH (ICI 174,864) in each test system at concentrations that effectively antagonized the respective mu and delta agonists, Tyr-Pro-N-MePhe-D-Pro-NH2 and Tyr-D-Pen-Gly-Phe-D-Pen. In the guinea pig ileum, the inhibitory effects of 1 microM B-endorphin were blocked by 1 microM CTP and 1 microM naloxone, but not by 1 microM ICI 174,864. In the mouse vas deferens, B-endorphin (0.2 microM) was antagonized by 1 microM CTP, 1 microM ICI 174,864 and by 1 microM naloxone. In contrast, in the rat vas deferens, B-endorphin (0.01-1 microM) produced potent inhibitory actions that were blocked by 1 microM naloxone, but not by 1 microM-CTP or by 1 microM ICI 174,864. The mu agonist, Tyr-Pro-N-MePhe-D-Pro-NH2 (0.1-10 microM), like B-endorphin, also had inhibitory actions in the rat vas deferens, but its effects were blocked by 1 microM CTP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Antinociceptive activity of [beta-methyl-2', 6'-dimethyltyrosine(1)]-substituted cyclic [D-Pen(2), D-Pen(5)]Enkephalin and [D-Ala(2),Asp(4)]Deltorphin analogs

Research in our laboratories involves the development of selective opioid agonists and antagonists as: 1) pharmacological tools to elucidate the mechanisms of opioid antinociception, and 2) potential analgesics that possess therapeutic advantages over currently available drugs. We hypothesized that the selectivity of peptide agonists toward the opioid receptor types and subtypes is topographically dependent. The current results assess the antinociceptive activity and opioid receptor selectivity of a series of beta-methyl-2',6'-dimethyltyrosine (TMT)-substituted cyclic [D-Pen(2),D-Pen(5)]enkephalin (DPDPE) and [D-Ala(2), Asp(4)]deltorphin (DELT I) analogs. Compounds were injected via the intracerebroventricular route into male ICR mice, and antinociception was assessed using the 55 degrees C warm water tail-flick test. Antinociceptive A(50) values ranged from 0.35 to 17 nmol for the DELT I analogs and from 7.05 to >100 nmol for the DPDPE analogs. To test for receptor selectivity, mice were treated with selective mu- and delta-opioid antagonists. In general, mu [beta-funaltrexamine (beta-FNA)]- and delta(1) ([D-Ala(2),Leu(5), Cys(6)] enkephalin)-antagonists blocked the antinociceptive actions of [TMT(1)]DPDPE analogs, whereas the antinociceptive actions of [TMT(1)]DELT I analogs were more sensitive to antagonism by the delta(2)-selective antagonist [Cys(4)]deltorphin and the mu-antagonist beta-FNA. The antinociceptive actions of the [(2R, 3S)-TMT(1)]DELT I analog was suppressed by both [D-Ala(2),Leu(5), Cys(6)]enkephalin and beta-FNA. These results are in contrast to those found with the parent molecules DPDPE (primarily a delta(1) agonist) and DELT I (a mixed delta(1)/delta(2) agonist). These results demonstrate that topographical modification in position 1 of the DPDPE and DELT I peptides affects antinociceptive potency and opioid receptor selectivity.     

Light microscopic autoradiographic localization of delta opioid receptors in the rat brain using a highly selective bis-penicillamine cyclic enkephalin analog

Light microscopic autoradiography was used to visualize the neuroanatomical distribution of rat brain delta opioid receptors. Slide-mounted sections of rat brain were labeled with [3H]-[2-D-penicillamine, 5-D-penicillamine]enkephalin([3H]DPDPE), a highly selective delta opioid agonist. Saturation isotherms of [3H]DPDPE binding to thaw-mounted brain slices gave a maximal number of binding sites of 79.9 fmol/mg of protein and an apparent dissociation constant (Kd) of 6.3 nM. DPDPE and met-enkephalin inhibited [3H]DPDPE binding with high affinity (lC50 values of 6.3 and 13.8 nM, respectively). Putative mu opioid receptor selective ligands such as morphine sulfate, Tyr-D-Ala-Gly-NMePhe-Gyl-ol and [N-MePhe3, D-Pro4]morphiceptin (PL017) were less potent inhibitors of [3H]DPDPE binding. The rat brain areas containing the highest densities of receptors were the claustrum, basolateral amygdaloid nucleus, the caudate-putamen and nucleus accumbens, the external plexiform layer of the olfactory bulb and the olfactory tubercle. Moderate receptor density was characteristic of the hippocampal formation in which grains were seen over the molecular layer of the dentate gyrus and stratum oriens (CA1), and of the different layers of cerebral cortex. Generally, low density of binding was found over the thalamus and the septal nuclei. Low specific binding was also seen in the cerebellum, medulla oblongata and in the dorsal horn of the spinal cord. There was little specific [3H]DPDPE binding over the white matter areas.     

Treatment of Clinically Positive Cervical Lymph Nodes by Limited Local Node Excision and Adjuvant Radiotherapy in Melanoma Patients with Major Comorbidities

Introduction

When cervical lymph nodes are clinically positive for metastatic melanoma, surgeons may be hesitant to recommend a therapeutic complete lymph node dissection if the patient is elderly or has major comorbidities. A limited local node excision of the clinically positive nodes only, followed by adjuvant radiotherapy to the entire node field, may be an effective alternative in such patients.

Methods

All patients who had presented with a primary head and neck melanoma or an unknown primary site and had subsequently undergone limited local node excision and adjuvant radiotherapy for macroscopically involved cervical nodes between 1993 and 2010 at a tertiary referral center were selected for study.

Results

Twenty-eight patients were identified, with a median age of 78 years and a median of 2 major comorbidities. The 5-year regional control, disease-free survival, and overall survival rates were 69%, 44%, and 50%, respectively. At the time of data analysis, seven patients were alive without evidence of disease. Twenty-one patients had died: 11 of melanoma (4 with neck recurrence) and 10 of other causes (2 with neck recurrence).

Conclusions

Excision of clinically positive metastatic cervical lymph nodes followed by radiotherapy provides satisfactory regional disease control without risking serious morbidity or mortality in melanoma patients whose general condition is considered a contraindication for therapeutic complete lymph node dissection.