Samuel Arnold

University of Washington Seattle | UW · Department of Medicine

Introduction: Cryptosporidiosis, the disease caused by parasitic infections with Cryptosporidium spp. can cause long-term adverse impacts and even death in malnourished children and immunocompromised patients. The only FDA-approved drug for treating cryptosporidiosis, nitazoxanide, has limited efficacy in the populations that are impacted most by...

Enteric infection with Shigella spp. can lead to symptoms ranging from acute watery diarrhea to sudden, severe dysentery. Approximately 212 000 diarrheal deaths annually are attributed to Shigella with a disproportionate impact in low-resource countries. The impact in under-resourced countries was illustrated by a reanalysis of the Global Enteric M...

This is a review of the development of bumped-kinase inhibitors (BKIs) for the therapy of One Health parasitic apicomplexan diseases. Many apicomplexan infections are shared between humans and livestock, such as cryptosporidiosis and toxoplasmosis, as well as livestock only diseases such as neosporosis. We have demonstrated proof-of-concept for BKI...

Shigellosis results from oral ingestion of the Gram-negative bacteria Shigella , and symptoms include severe diarrhea and dysentery. In the absence of vaccines, small molecule antibacterial drugs have provided treatment options for shigellosis. However, Shigella drug resistance is rapidly emerging, and Shigella strains with resistance to both third...

Background: We evaluated efficacy, pharmacokinetics (PK), and safety of clofazimine (CFZ) in HIV-infected patients with cryptosporidiosis. Methods: We performed a randomized, double-blind, placebo-controlled study. Primary outcomes in Part A were reduction in Cryptosporidium shedding, safety, and PK. Primary analysis was according to protocol (A...

In less than six months, COVID‐19 has spread from a marketplace in Wuhan, China to over 150 countries and territories of the world. Therapeutics are desperately needed to reduce the morbidity and mortality of this pandemic disease. It has been reported that hydroxychloroquine (HCQ) is active against SARS‐CoV‐2 in vitro, and this finding was quickly...

Bumped Kinase Inhibitors (BKIs), targeting Calcium-dependent Protein Kinase 1 (CDPK1) in apicomplexan parasites with a glycine gatekeeper, are promising new therapeutics for apicomplexan diseases. Here we will review advances, as well as challenges and lessons learned regarding efficacy, safety, and pharmacology, that have shaped our selection of p...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Encephalitozoon cuniculi is a unicellular, obligate intracellular eukaryotic parasite in the Microsporidia family and one of the agents responsible for microsporidosis infections in humans. Like most Microsporidia, the genome of E. cuniculi is markedly reduced and the organism contains mitochondria‐like organelles called mitosomes instead of mitoch...

Hollow fiber technology is a powerful tool for the culture of difficult-to-grow cells. Cryptosporidium parvum has a multistage sexual and asexual life cycle that has proved difficult to culture by conventional in vitro culture methods. Here, we describe a method utilizing a hollow fiber bioreactor for the continuous in vitro growth of C. parvum tha...

Shigella spp., the bacteria responsible for shigellosis, are one of the leading causes of diarrheal morbidity and mortality amongst children. There is a pressing need for the development of novel therapeutics, as resistance of Shigella to many currently used antibiotics is rapidly emerging. This paper describes the development of robust in vitro an...

Recent studies have illustrated the burden Cryptosporidium infection places on the lives of malnourished children and immunocompromised individuals. Treatment options remain limited and efforts to develop a new therapeutic are currently underway. However, there are unresolved questions about the ideal pharmacokinetic characteristics of new anti-Cry...

Bumped kinase inhibitors have been shown to be potent inhibitors of Toxoplasma gondii calcium dependent protein kinase 1. Pyrazolopyrimidine and 5-aminopyrazole-4-carboxamide scaffold-based BKIs are effective in acute and chronic experimental models of toxoplasmosis. Through further exploration of these two scaffolds and a new pyrrolopyrimidine sca...

Diarrhea is the second leading cause of death in children < 5 years globally and the parasite genus Cryptosporidium is a leading cause of that diarrhea. The global disease burden attributable to cryptosporidiosis is substantial and the only approved chemotherapeutic, nitazoxanide, has poor efficacy in HIV positive children. Chemotherapeutic develop...

Rubric for the evaluation of appetite, mentation, fecal consistency, and hydration. (DOCX)

Photograph of enrolled calves in confinement housing. (TIF)

Fluid therapy flow chart. Calculation of calf fluid deficit and volume to administer to maintain 5% dehydration. (TIF)

Recent reports highlighting the global significance of cryptosporidiosis among children have renewed efforts to develop control measures. We evaluated the efficacy of bumped kinase inhibitor (BKI) 1369 in the gnotobiotic piglet model of acute diarrhea caused by Cryptosporidium hominis , the species responsible for most human cases. Five day-treatme...

Improvements have been made to the safety and efficacy of bumped kinase inhibitors (BKIs), and they are advancing toward human and animal use for treatment of cryptosporidiosis. As the understanding of BKI pharmacodynamics for cryptosporidiosis therapy has increased, it has become clear that better compounds for efficacy do not necessarily require...

There is a substantial need for novel therapeutics to combat the widespread impact caused by Crytosporidium infection. However, there is a lack of knowledge on which drug pharmacokinetic characteristics are key to generate an in vivo response specifically if systemic drug exposure is crucial for in vivo efficacy. To identify which pharmacokinetic p...

Bumped kinase inhibitors (BKIs) of Cryptosporidium parvum calcium-dependent protein kinase 1 (CpCDPK1) are leading candidates for treatment of cryptosporidiosis diarrhea. Potential cardiotoxicity related to anti-human ether-à-go-go potassium channel (hERG) activity of the first generation anti-Cryptosporidium BKIs triggered further testing for effi...

Many life-cycle processes in parasites are regulated by protein phosphorylation. Hence, disruption of essential protein kinase function has been explored for therapy of parasitic diseases. However, the difficulty of inhibiting parasite protein kinases to the exclusion of host orthologues poses a practical challenge. A possible path around this diff...

Cryptosporidiosis, caused by the apicomplexan parasite Cryptosporidium parvum, is a diarrheal disease that has produced a large global burden in mortality and morbidity in humans and livestock. There are currently no consistently effective parasite-specific pharmaceuticals available for this disease. Bumped kinase inhibitors (BKIs) specific for par...

Perturbations in the vitamin A metabolism pathway could be a significant cause of male infertility, as well as a target towards the development of a male contraceptive, necessitating the need for a better understanding of how testicular retinoic acid (RA) concentrations are regulated. Quantitative analyses have recently demonstrated that RA is pres...

Protein quantification based on peptides using LC-MS/MS has emerged as a promising method to measure biomarkers, protein drugs and endogenous proteins. However, the best practices for selection, optimization and validation of the quantification peptides are not well established, and the influence of different matrices on protein digestion, peptide...

all-trans retinoic acid (atRA), the active metabolite of vitamin A, is an essential signaling molecule. Specifically the concentrations of atRA are spatiotemporally controlled in target tissues such as the liver and the testes. While the enzymes of the aldehyde dehydrogenase 1A family (ALDH1A) are believed to control the synthesis of atRA, a direct...

The asynchronous cyclic nature of spermatogenesis is essential for continual sperm production and is one of the hallmarks of mammalian male fertility. While various mRNA and protein localization studies have indirectly implicated changing retinoid levels along testis tubules, no quantitative evidence for these changes across the cycle of the semini...

Retinoic acid (RA), the active metabolite of Vitamin A, is required for spermatogenesis and many other biological processes. RA formation requires irreversible oxidation of retinal to RA by aldehyde dehydrogenase enzymes of the 1A family (ALDH1A). While ALDH1A1, ALDH1A2, and ALDH1A3 all form RA, the expression pattern and relative contribution of t...

The regulation of testicular retinoic acid synthesis is crucial for understanding its role in spermatogenesis. Bisdichloroacetyldiamines (BDADs) strongly inhibit spermatogenesis. We previously reported that one of these compounds, WIN 18,446, potently inhibited spermatogenesis in rabbits by inhibiting retinoic acid synthesis. To understand how WIN...

Objective To determine whether decreased testicular levels of enzymes necessary for retinoic acid biosynthesis were associated with male infertility, as retinoic acid is known to be necessary for spermatogenesis. Design Observational analysis of testicular tissue samples, sperm indices, and serum hormone concentrations. Setting Two infertility ce...

Substrates of a major drug-metabolizing enzyme CYP2D6 display increased elimination during pregnancy, but the underlying mechanisms are unknown in part due to a lack of experimental models. Here, we introduce CYP2D6-humanized (Tg-CYP2D6) mice as an animal model where hepatic CYP2D6 expression is increased during pregnancy. In the mouse livers, expr...

CYP2C22 was recently described as a retinoic acid-metabolizing cytochrome P450 (P450) enzyme whose transcription is induced by all-trans retinoic acid (atRA) in hepatoma cells (Qian, L et al (2010) J Lipid Res 51: 1781). We identified CYP2C22 as a putative nitric oxide (NO)-regulated protein in a proteomic screen, and raised specific polyclonal ant...

Intratesticular retinoic acid is necessary for spermatogenesis, but the relationship between intratesticular retinoic acid and sperm quality in man has not been studied. We hypothesized that intratesticular concentrations of retinoic acid would be lower in men with abnormal semen analyses compared to men with normal semen analyses. We recruited men...

Retinol (vitamin A) circulates at 1-4 μM concentration and is easily measured in serum. However, retinol is biologically inactive. Its metabolite, retinoic acid (RA), is believed to be responsible for biological effects of vitamin A, and hence the measurement of retinol concentrations is of limited value. A UHPLC-MS/MS method using isotope-labeled...

Lapatinib, a dual EGFR/HER2 kinase inhibitor, is approved for use in patients with trastuzumab-refractory HER2- overexpressing breast cancer. Increased PI3K signaling has been associated with resistance to trastuzumab, although its role in lapatinib resistance remains unclear. The purpose of the current study was to determine if PI3K/mTOR activity...

Decreased proliferation in a number of cell lines treated with all-trans Retinoic Acid (atRA) has been well documented[1], but the inhibition in proliferation is not seen in all cell lines, and the mechanism is not fully understood. It has been proposed that different expression profiles of nuclear receptors (RAR, PPAR) and soluble binding proteins...