Preclinical development of EXT608, an investigational parathyroid hormone derivative with extended half-life for the treatment of hypoparathyroidism.

Hypoparathyroidism, a deficiency of parathyroid hormone (PTH), results in hypocalcemia, hyperphosphatemia, and hypercalciuria. The disease is poorly controlled by calcium and vitamin D supplements or native PTH(1-84) replacement therapy. A version of PTH is being developed using D-VITylation technology, whereby vitamin D is conjugated to a therapeutic peptide, which confers a long plasma half-life by virtue of binding to the abundant vitamin D binding protein (DBP). D-VITylation of PTH caused no reduction in activity at the PTHR1 receptor, and resulted in a plasma elimination half-life of 7-15 h in rats and 24-32 h in cynomolgus monkeys. Analysis of steady-state pharmacokinetics as a function of dose showed flat profiles with smaller peak:trough ratios at low doses, indicative of slower subcutaneous absorption. In thyroparathyroidectomized (TPTx) rats, PTH(1-34)-vitamin D conjugates restored serum calcium and phosphate levels into the normal range over the 24 h dosing period, and increased bone turnover markers and reduced bone mineral density. Urinary calcium was initially elevated, but normalized by the end of treatment on day 27. In healthy monkeys, a single dose of PTH(1-34)-vitamin D conjugates elevated serum calcium levels above the normal range for a period of 24-48 h while simultaneously reducing urinary calcium. Therefore, the lead compound, EXT608, is a promising candidate as a therapeutic that can truly mimic the endogenous activity of PTH and warrants further study in patients with hypoparathyroidism.

EXT418, a novel long-acting ghrelin, mitigates Lewis lung carcinoma induced cachexia in mice.

BACKGROUND: Ghrelin is a potential therapy for cachexia due to its orexigenic properties and anabolic effects on muscle and fat. However, its clinical use is limited by the short half-life of active (acylated) ghrelin (~11 min in humans). EXT418 is a novel long-acting, constitutively active ghrelin analog created by covalently linking it to a vitamin D derivative. Here, we evaluated the effects and mechanisms of action of EXT418 on Lewis lung carcinoma (LLC)-induced cachexia in mice. METHODS: Male C57BL/6J mice (5- to 7-month-old) were implanted with 1 × 106 heat-killed (HK) or live LLC cells. When the tumour was palpable, mice were injected with vehicle (T + V) or EXT418 daily (T + 418 Daily, 0.25 mg/kg/day) or every other day (T + 418 EOD, 0.5 mg/kg/EOD) for up to 14 days, whereas HK-treated mice were given vehicle (HK + V). Subsets of T + 418 Daily or EOD-treated mice were pair-fed to the T + V group. Body composition and grip strength were evaluated before tumour implantation and at the end of the experiment. Molecular markers were probed in muscles upon termination. RESULTS: In tumour-bearing mice, administration of EXT418 daily or EOD partially prevented weight loss (T + V vs. T + 418 Daily, P = 0.030; and vs. T + 418 EOD, P = 0.020). Similar effects were observed in whole body fat and lean body mass. Grip strength in tumour-bearing mice was improved by EXT418 daily (P = 0.010) or EOD (P = 0.008) administration compared with vehicle-treated mice. These effects of EXT418 on weight and grip strength were partially independent of food intake. EXT418 daily administration also improved type IIA (P = 0.015), IIB (P = 0.037) and IIX (P = 0.050) fibre cross-sectional area (CSA) in tibialis anterior (TA) and EXT418 EOD improved CSA of IIB fibres in red gastrocnemius (GAS; P = 0.005). In skeletal muscles, tumour-induced increases in atrogenes Fbxo32 and Trim63 were ameliorated by EXT418 treatments (TA and GAS/plantaris, PL), which were independent of food intake. EXT418 administration decreased expression of the mitophagy marker Bnip3 (GAS/PL; P ≤ 0.010). Similar effects of EXT418 EOD were observed in p62 (GAS/PL; P = 0.039). In addition, EXT418 treatments ameliorated the tumour-induced elevation in muscle Il6 transcript levels (TA and GAS/PL), independently of food intake. Il-6 transcript levels in adipose tissue and circulating IL-10 were elevated in response to the tumour but these increases were not significant with EXT418 administration. Tumour mass was not altered by EXT418. CONCLUSIONS: EXT418 mitigates LLC-induced cachexia by attenuating skeletal muscle inflammation, proteolysis, and mitophagy, without affecting tumour mass and partially independent of food intake.

D-VITylation: Harnessing the biology of vitamin D to improve the pharmacokinetic properties of peptides and small proteins.

Peptides have great potential to be potent and specific therapeutics, yet their small size leads to rapid glomerular filtration, which severely limits therapeutic applications. Although conjugation of small proteins to large polymers typically results in longer residence times, these conjugates often have a significant loss of biological activity due to steric hindrance. Here, we improve the pharmacokinetics (PK) of peptide therapeutics by harnessing the biology of vitamin D. Attachment of a small vitamin D-based molecule (D-VITylation) protects the conjugated peptide or protein from renal clearance by virtue of reversible binding to the serum-circulating vitamin D binding protein (DBP), without compromising bioactivity. Varying the conjugation site on vitamin D affects the binding to DBP, with higher affinity corresponding to a longer plasma half-life. We also demonstrate the important contribution of the peptide to the overall PK, likely due to alternative clearance mechanisms such as protease degradation and receptor-mediated cellular uptake. With a Fab antibody fragment, for which these alternate clearance mechanisms are not significant, D-VITylation increases the half-life of elimination from 14 to 61 h in rats. The PK profile in minipigs and projected lifetime in humans suggest that D-VITylation is a viable strategy to achieve once-weekly dosing of peptide therapeutics in humans.

Complete genome sequence analysis of Seneca Valley virus-001, a novel oncolytic picornavirus.

The complete genome sequence of Seneca Valley virus-001 (SVV-001), a small RNA virus, was determined and was shown to have typical picornavirus features. The 7280 nt long genome was predicted to contain a 5' untranslated region (UTR) of 666 nt, followed by a single long open reading frame consisting of 6543 nt, which encodes a 2181 aa polyprotein. This polyprotein could potentially be cleaved into 12 polypeptides in the standard picornavirus L-4-3-4 layout. A 3' UTR of 71 nt was followed by a poly(A) tail of unknown length. Comparisons with other picornaviruses showed that the P1, 2C, 3C and 3D polypeptides of SVV-001 were related most closely to those of the cardioviruses, although they were not related as closely to those of encephalomyocarditis virus and Theiler's murine encephalomyelitis virus as the latter were to each other. Most other regions of the polyprotein differed considerably from those of all other known picornaviruses. SVV-001 contains elements of an internal ribosome entry site reminiscent of that found in hepatitis C virus and a number of genetically diverse picornaviruses. SVV-001 is a novel picornavirus and it is proposed that it be classified as the prototype species in a novel genus named 'Senecavirus'.

Seneca Valley virus, a systemically deliverable oncolytic picornavirus, and the treatment of neuroendocrine cancers.

BACKGROUND: Numerous clinical trials have demonstrated that oncolytic viruses can elicit antitumor responses when they are administered directly into localized cancers. However, the treatment of metastatic disease with oncolytic viruses has been challenging due to the inactivation of viruses by components of human blood and/or to inadequate tumor selectivity. METHODS: We determined the cytolytic potential and selectivity of Seneca Valley Virus-001 (SVV-001), a newly discovered native picornavirus, in neuroendocrine and pediatric tumor cell lines and normal cells. Suitability of the virus for intravenous delivery in humans was assessed by blood inactivation assays. Safety was evaluated in vivo using an immune-competent mouse model, and efficacy was evaluated in vivo in athymic mice bearing tumors derived from human small-cell lung cancer and retinoblastoma cell lines. RESULTS: Cell lines derived from small-cell lung cancers and solid pediatric cancers were at least 10,000-fold more sensitive to the cytolytic activity of SVV-001 than were any of the adult normal human cells tested. Viral infectivity was not inhibited by human blood components. Intravenous doses up to 1 x 10(14) virus particles (vp) per kg were well tolerated, and no dose-limiting toxicity was observed in immune-competent mice. A single intravenous dose of 1 x 10(8) vp per kg into athymic mice bearing preestablished small-cell lung or retinoblastoma tumors resulted in complete, durable responses in ten of ten and five of eight mice, respectively. CONCLUSIONS: SVV-001 has potent cytolytic activity and high selectivity for tumor cell lines having neuroendocrine properties versus adult normal cells. Systemically administered SVV-001 has potential for the treatment of metastatic neuroendocrine cancers.