SUMMARY Background and purpose Ziconotide is a peptide that blocks N-type calcium channels and is anti-hyperalgesic after intrathecal delivery. We here characterize the spinal kinetics of intrathecal bolus and infused ziconotide in dog. Experimental approach Male beagle dogs (N = 5) were prepared with chronic intrathecal (IT) lumbar injection and cerebrospinal fluid (LCSF) sampling catheters connected to vest-mounted pumps. Each dog received: i) IT bolus ziconotide (10 µg + 1 µCi 3H-inulin), ii) IT infusion for 48 hr of ziconotide (1 µg/100 µL/hr), iii) IT infusion for 48 hr of ziconotide (5 µg/100 µL/hr), and iv) intravenous injection of ziconotide (0.1 mg/kg). After IT bolus, LCSF ziconotide and inulin showed an initial peak and biphasic (distribtution/elimination) clearance (ziconotide T1/2 α / ß = 0.14 and 1.77 hr, and inulin T1/2 α / ß = 0.16 and 3.88 hr, respectively). The LCSF: plasma ziconotide concentration ratio was 20,000: 1 at 30 min, and 30: 1 at 8 hr. IT infusion of 1 and then 5 µg/hr resulted in LCSF concentrations that peaked by 8 hr and remained stable at 343 and 1380 ng/mL, respectively, to the end of the 48-hr infusions. Terminal elimination T1/2 after termination of continuous infusion was 2.47 hr. Ziconotide LCSF: cisternal CSF: plasma concentration ratios after infusion of 1 µg/hr and 5 µg/hr were 1: 0.017: 0.001 and 1: 0.015: 0.003, respectively. IT infusion of ziconotide at 1 µg/hr inhibited thermal skin twitch by 24 hr, and produced modest trembling, ataxia, and decreased arousal. Effects continued through the 48-hr infusion period, increased in magnitude during the subsequent 5 µg/hr infusion periods, and disappeared after drug clearance. Conclusions and Implications After intrathecal bolus or infusion, ziconotide displays linear kinetics that are consistent with a hydrophilic molecule of approximately 2500 Da that is cleared slightly more rapidly than inulin from the LCSF. Behavioral effects were dose dependent and reversible.

Calcium channels are represented by at least 9 distinct genes (calcium channel classes A-I), corresponding to at least 5 functional and pharmacological "types" (L, N, P/Q, R and T). Selective L-, N-, and T-type channel antagonists are either in clinical use or in late stage clinical trials, while antagonists of P/Q channels are known to be toxic. No selective ligand has been identified for the R-type (class E), and its function and pharmacology are consequently, poorly understood. We review recent work on the discovery and initial characterization of SNX-482, the first known selective antagonist of R-type calcium channels. SNX-482 is a 41 residue acidic peptide with three disulfide bonds that has been isolated from the venom of the African tarantula, Hysterocrates gigas. In cell-based assays, it is a potent and selective inhibitor of the class E or R-type calcium channel. SNX-482 blocks some but not all native R-type currents: it blocks an R-type current in vertebrate neurohypophysis, but it does not block an R-type current in cerebellar granule cells. The peptide blocks oxytocin but not vasopressin release, suggesting a possible utility for SNX-482 as a neuroendocrine modulator. The peptide possesses antiseizure activity in several animal models of epilepsy, suggesting that class E antagonists may have pharmacological use in seizure disorders.

The effect of complement depletion with humanized cobra venom factor (CVF) on retinal lesion development/neovascularization was determined in a mouse model of wet age-related macular degeneration (AMD). Mice were treated with the humanized CVF protein HC3-1496 prior to, and once daily for 28 days after laser coagulation surgery of the retina. CVF transgenic mice exhibiting permanently low levels of serum complement activity and PBS-treated mice served as positive and negative controls, respectively. Fluorescein isothiocyanate (FITC)-dextran funduscopy after laser surgery indicated the presence of lesions in all mice that underwent laser surgery. In HC3-1496-treated mice as well as CVF transgenic mice smaller lesions were seen after 8 days. Measurement of lesion sizes by histopathological examination of eyes after 28 days revealed a significant reduction of lesion area and volume in both HC3-1496-treated animals and CVF transgenic animals compared to PBS-treated control animals. Systemic complement depletion with a complement depletor, such as the humanized CVF protein HC3-1496, represents a promising therapeutic concept for patients with wet AMD.

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