Safety, tolerability, pharmacokinetics, and antimalarial efficacy of a novel Plasmodium falciparum ATP4 inhibitor SJ733: a first-in-human and induced blood-stage malaria phase 1a/b trial

BACKGROUND

(+)-SJ000557733 (SJ733) is a novel, orally bioavailable inhibitor of Plasmodium falciparum ATP4. In this first-in-human and induced blood-stage malaria phase 1a/b trial, we investigated the safety, tolerability, pharmacokinetics, and antimalarial activity of SJ733 in humans.

METHODS

The phase 1a was a single-centre, dose-escalation, first-in-human study of SJ733 allowing modifications to dose increments and dose-cohort size on the basis of safety and pharmacokinetic results. The phase 1a took place at St Jude Children's Research Hospital and at the University of Tennessee Clinical Research Center (Memphis, TN, USA). Enrolment in more than one non-consecutive dose cohort was allowed with at least 14 days required between doses. Participants were fasted in seven dose cohorts and fed in one 600 mg dose cohort. Single ascending doses of SJ733 (75, 150, 300, 600, 900, or 1200 mg) were administered to participants, who were followed up for 14 days after SJ733 dosing. Phase 1a primary endpoints were safety, tolerability, and pharmacokinetics of SJ733, and identification of an SJ733 dose to test in the induced blood-stage malaria model. The phase 1b was a single-centre, open-label, volunteer infection study using the induced blood-stage malaria model in which fasted participants were intravenously infected with blood-stage P falciparum and subsequently treated with a single dose of SJ733. Phase 1b took place at Q-Pharm (Herston, QLD, Australia) and was initiated only after phase 1a showed that exposure exceeding the threshold minimum exposure could be safely achieved in humans. Participants were inoculated on day 0 with P falciparum-infected human erythrocytes (around 2800 parasites in the 150 mg dose cohort and around 2300 parasites in the 600 mg dose cohort), and parasitaemia was monitored before malaria inoculation, after inoculation, immediately before SJ733 dosing, and then post-dose. Participants were treated with SJ733 within 24 h of reaching 5000 parasites per mL or at a clinical score higher than 6. Phase 1b primary endpoints were calculation of a parasite reduction ratio (PRR₄₈) and parasite clearance half-life, and safety and tolerability of SJ733 (incidence, severity, and drug-relatedness of adverse events). In both phases of the trial, SJ733 hydrochloride salt was formulated as a powder blend in capsules containing 75 mg or 300 mg for oral administration. Healthy men and women (of non-childbearing potential) aged 18-55 years were eligible for both studies. Both studies are registered with ClinicalTrials.gov (NCT02661373 for the phase 1a and NCT02867059 for the phase 1b).

FINDINGS

In the phase 1a, 23 healthy participants were enrolled and received one to three non-consecutive doses of SJ733 between March 14 and Dec 7, 2016. SJ733 was safe and well tolerated at all doses and in fasted and fed conditions. 119 adverse events were recorded: 54 (45%) were unrelated, 63 (53%) unlikely to be related, and two (2%) possibly related to SJ733. In the phase 1b, 17 malaria-naive, healthy participants were enrolled. Seven participants in the 150 mg dose cohort were inoculated and dosed with SJ733. Eight participants in the 600 mg dose cohort were inoculated, but two participants could not be dosed with SJ733. Two additional participants were subsequently inoculated and dosed with SJ733. SJ733 exposure increased proportional to the dose through to the 600 mg dose, then was saturable at higher doses. Fasted participants receiving 600 mg exceeded the target area under the concentration curve extrapolated to infinity (AUC_0-∞) of 13 000 μg × h/L (median AUC_0-∞ 24 283 [IQR 16 135-31 311] μg × h/L, median terminal half-life 17·4 h [IQR 16·1-24·0], and median timepoint at which peak plasma concentration is reached 1·0 h [0·6-1·3]), and this dose was tested in the phase 1b. All 15 participants dosed with SJ733 had at least one adverse event. Of the 172 adverse events recorded, 128 (74%) were mild. The only adverse event attributed to SJ733 was mild bilateral foot paraesthesia that lasted 3·75 h and resolved spontaneously. The most common adverse events were related to malaria. Based on parasite clearance half-life, the derived log₁₀PRR₄₈ and corresponding parasite clearance half-lives were 2·2 (95% CI 2·0-2·5) and 6·47 h (95% CI 5·88-7·18) for 150 mg, and 4·1 (3·7-4·4) and 3·56 h (3·29-3·88) for 600 mg.

INTERPRETATION

The favourable pharmacokinetic, tolerability, and safety profile of SJ733, and rapid antiparasitic effect support its development as a fast-acting component of combination antimalarial therapy.

FUNDING

Global Health Innovative Technology Fund, Medicines for Malaria Venture, and the American Lebanese Syrian Associated Charities.

Neuropathogenesis of Japanese encephalitis in a primate model

Background

Japanese encephalitis (JE) is a major cause of mortality and morbidity for which there is no treatment. In addition to direct viral cytopathology, the inflammatory response is postulated to contribute to the pathogenesis. Our goal was to determine the contribution of bystander effects and inflammatory mediators to neuronal cell death.

Methodology/Principal Findings

Material from a macaque model was used to characterize the inflammatory response and cytopathic effects of JE virus (JEV). Intranasal JEV infection induced a non-suppurative encephalitis, dominated by perivascular, infiltrates of mostly T cells, alongside endothelial cell activation, vascular damage and blood brain barrier (BBB) leakage; in the adjacent parenchyma there was macrophage infiltration, astrocyte and microglia activation. JEV antigen was mostly in neurons, but there was no correlation between intensity of viral infection and degree of inflammatory response. Apoptotic cell death occurred in both infected and non-infected neurons. Interferon-α, which is a microglial activator, was also expressed by both. Tumour Necrosis Factor-α, inducible nitric oxide synthase and nitrotyrosine were expressed by microglial cells, astrocytes and macrophages. The same cells expressed matrix metalloproteinase (MMP)-2 whilst MMP-9 was expressed by neurons.

Conclusions/Significance

The results are consistent with JEV inducing neuronal apoptotic death and release of cytokines that initiate microglial activation and release of pro-inflammatory and apoptotic mediators with subsequent apoptotic death of both infected and uninfected neurons. Activation of astrocytes, microglial and endothelial cells likely contributes to inflammatory cell recruitment and BBB breakdown. It appears that neuronal apoptotic death and activation of microglial cells and astrocytes play a crucial role in the pathogenesis of JE.

Japanese encephalitis (JE) is one of the most important causes of viral encephalitis worldwide, with no specific antiviral treatment available. Despite some recent successes with widespread vaccination, JE will likely remain an important public health problem; because the virus is mosquito-borne and has natural animal hosts, it will never be eradicated. We have little understanding of what determines the severity and outcome of infection. Data from human post mortem studies is very limited because of cultural constraints on autopsies in areas where JE occurs. Circumstantial evidence suggests that in addition to cytopathology caused directly by infection of neurons, there may be bystander cell death of non-infected neurons, caused by an excessive inflammatory response. Our study used archived brain samples from a prior challenge study in a validated macaque model of JE. We stained for the presence of JEV antigen, apoptosis, and pro-inflammatory markers in affected areas, such as the thalamus and brainstem. We show that bystander neuronal cell death is important, and elucidate the inflammatory and apoptotic mechanisms underlying it. Currently there is no proven efficacious therapy for most viral infections of the central nervous system, including JE. Novel strategies for treating such infections are urgently needed. Our findings suggest new anti-inflammatory and anti-apoptotic therapeutic approaches may be useful in treating this debilitating disease.

Brunner's gland lesions in rats induced by a vascular endothelial growth factor receptor inhibitor

Vascular endothelial growth factor (VEGF) receptor tyrosine kinase (RTK) inhibitors are reported to cause reversible mucosal hyperplasia (adenosis) in the duodenum of rats; however, the pathogenesis is not fully elucidated. Using lenvatinib, a VEGF RTK inhibitor, we characterized the histologic time course of this duodenal change in rats. At 4 weeks, there was degeneration and necrosis of Brunner's gland epithelium accompanied by neutrophil infiltration around the affected glands. At 13 weeks, the inflammation was more extensive, and Brunner's gland epithelium was attenuated and flattened and was accompanied by reactive hyperplasia of duodenal epithelium. At 26 weeks, the changes became more severe and chronic and characterized by marked cystic dilation, which extended to the external muscular layer. These dilated glands exhibited morphological characteristics of duodenal crypt epithelium, suggestive of replacement of disappeared Brunner's glands by regenerative duodenal crypt epithelial cells. Similar changes were not present in similar time course studies in dog and monkey studies, suggesting that this is a rodent- or species-specific change. Based on the temporal progression of Brunner's gland lesion, we identify degeneration and necrosis of the Brunner's glands as the primary change leading to inflammation, cystic dilatation, and regeneration with cells that are morphologically suggestive of duodenal crypt epithelium.

Correlation of protection against Japanese encephalitis virus and JE vaccine (IXIARO(®)) induced neutralizing antibody titers

Immune sera from volunteers vaccinated in a blinded Phase 3 clinical trial with JE-VAX(®) and a new Japanese encephalitis virus (JEV) vaccine (IC51 or IXIARO), were tested for the ability to protect mice against lethal JEV challenge. Sera from IXIARO vaccinated subjects were pooled into four batches based on neutralizing antibody measured by plaque reduction neutralization test (PRNT(50) titer): high (∼200), medium (∼40-50), low (∼20) and negative (<10). Pooled sera from JE-VAX(®) vaccinated subjects (PRNT(50) titer∼55) and pooled JEV antibody negative pre-vaccination sera were used as controls. Groups of ten 6- to 7-week-old female ICR mice were injected intraperitoneally with 0.5 ml of each serum pool diluted 1:2 or 1:10, challenged approximately 18 h later with a lethal dose of either JEV strain SA14 (genotype III) or strain KE-093 (genotype I) and observed for 21 days. All mice in the non-immune serum groups developed clinical signs consistent with JEV infection or died, whereas high titer sera from both IXIARO and JE-VAX(®) sera protected 90-100% of the animals. Statistical tests showed similar protection against both JEV strains SA14 and KE-093 and protection correlated with the anti-JEV antibody titer of IXIARO sera as measured by PRNT(50). Ex vivo neutralizing antibody titers showed that almost all mice with a titer of 10 or greater were fully protected. In a separate study, analysis of geometric mean titers (GMTs) of the groups of mice vaccinated with different doses of IXIARO and challenged with JEV SA14 provided additional evidence that titers≥10 were protective.