Airway tryptase levels inform the lack of clinical efficacy of the tryptase inhibitor MTPS9579A in asthma.

BACKGROUND: Tryptase, a mast cell protease, has been identified as a potential therapeutic target in managing patients with refractory asthma. We assessed the efficacy, safety, pharmacokinetics, and pharmacodynamics of MTPS9579A, an anti-tryptase antibody, in a phase 2a randomized trial for patients with uncontrolled asthma and a phase 1c trial to understand activity within the lower respiratory tract. METHODS: Phase 2a patients (n = 134) received 1800 mg MTPS9579A or placebo intravenously every 4 weeks for 48 weeks. The primary endpoint was time to the first composite exacerbation event. Phase 1c patients (n = 27) received one intravenous dose of 300 or 1800 mg MTPS9579A or placebo. Both trials measured MTPS9579A concentrations and effects on tryptase in serum and nasal lining fluid; phase 1c also analyzed bronchial lining fluid. RESULTS: MTPS9579A did not meet the primary endpoint (hazard ratio = 0.90; 95% CI: 0.55-1.47; p = 0.6835); exacerbation rates in the placebo group were low. Serum and nasal MTPS9579A pharmacokinetics and tryptase levels were consistent with data from healthy volunteers. However, in phase 1c patients, compared to nasal levels, MTPS9579A bronchial concentrations were 6.8-fold lower, and bronchial active and total tryptase levels were higher (119-fold and 30-fold, respectively). Pharmacokinetic/pharmacodynamic modeling predicted intravenous doses of 3800 mg every 4 weeks would be necessary to achieve 95% active tryptase inhibition from baseline. CONCLUSIONS: The MTPS9579A dose tested in the phase 2a study was insufficient to inhibit tryptase in bronchial lining fluid, likely contributing to the observed lack of efficacy.

Complex In Vitro Model Characterization for Context of Use in Toxicologic Pathology: Use Cases by Collaborative Teams of Biologists, Bioengineers, and Pathologists.

Complex in vitro models (CIVMs) offer the potential to increase the clinical relevance of preclinical efficacy and toxicity assessments and reduce the reliance on animals in drug development. The European Society of Toxicologic Pathology (ESTP) and Society for Toxicologic Pathology (STP) are collaborating to highlight the role of pathologists in the development and use of CIVM. Pathologists are trained in comparative animal medicine which enhances their understanding of mechanisms of human and animal diseases, thus allowing them to bridge between animal models and humans. This skill set is important for CIVM development, validation, and data interpretation. Ideally, diverse teams of scientists, including engineers, biologists, pathologists, and others, should collaboratively develop and characterize novel CIVM, and collectively assess their precise use cases (context of use). Implementing a morphological CIVM evaluation should be essential in this process. This requires robust histological technique workflows, image analysis techniques, and needs correlation with translational biomarkers. In this review, we demonstrate how such tissue technologies and analytics support the development and use of CIVM for drug efficacy and safety evaluations. We encourage the scientific community to explore similar options for their projects and to engage with health authorities on the use of CIVM in benefit-risk assessment.

Common and Not-So-Common Pathologic Findings of the Gastrointestinal Tract of Rhesus and Cynomolgus Macaques.

Rhesus and cynomolgus macaques are the most frequently used nonhuman primate (NHP) species for biomedical research and toxicology studies of novel therapeutics. In recent years, there has been a shortage of laboratory macaques due to a variety of competing factors. This was most recently exacerbated by the surge in NHP research required to address the severe acute respiratory syndrome (SARS)-coronavirus 2 pandemic. Continued support of these important studies has required the use of more varied cohorts of macaques, including animals with different origins, increased exposure to naturally occurring pathogens, and a wider age range. Diarrhea and diseases of the gastrointestinal tract are the most frequently occurring spontaneous findings in macaques of all origins and ages. The purpose of this review is to alert pathologists and scientists involved in NHP research to these findings and their impact on animal health and study endpoints, which may otherwise confound the interpretation of data generated using macaques.

Disruption of IRE1α through its kinase domain attenuates multiple myeloma.

Multiple myeloma (MM) arises from malignant immunoglobulin (Ig)-secreting plasma cells and remains an incurable, often lethal disease despite therapeutic advances. The unfolded-protein response sensor IRE1α supports protein secretion by deploying a kinase-endoribonuclease module to activate the transcription factor XBP1s. MM cells may co-opt the IRE1α-XBP1s pathway; however, the validity of IRE1α as a potential MM therapeutic target is controversial. Genetic disruption of IRE1α or XBP1s, or pharmacologic IRE1α kinase inhibition, attenuated subcutaneous or orthometastatic growth of MM tumors in mice and augmented efficacy of two established frontline antimyeloma agents, bortezomib and lenalidomide. Mechanistically, IRE1α perturbation inhibited expression of key components of the endoplasmic reticulum-associated degradation machinery, as well as secretion of Ig light chains and of cytokines and chemokines known to promote MM growth. Selective IRE1α kinase inhibition reduced viability of CD138+ plasma cells while sparing CD138- cells derived from bone marrows of newly diagnosed or posttreatment-relapsed MM patients, in both US- and European Union-based cohorts. Effective IRE1α inhibition preserved glucose-induced insulin secretion by pancreatic microislets and viability of primary hepatocytes in vitro, as well as normal tissue homeostasis in mice. These results establish a strong rationale for developing kinase-directed inhibitors of IRE1α for MM therapy.

Inflammation of a Posterior Ciliary Artery in a Naive Cynomolgus Macaque.

This brief communication describes a previously unreported background lesion in the eye of a naive cynomolgus macaque. Inflammation of a posterior ciliary artery was, in this case, morphologically similar to vascular inflammation of other tissues described in naive cynomolgus macaques. However, the available literature does not describe this lesion at this anatomical site. The affected animal did not present with any abnormal clinical signs and ophthalmological examinations were within normal limits. Toxicologic pathologists should be aware of this finding in order to help differentiate it from a test item-related finding.

Tolerability Assessment of Formulation pH in New Zealand White Rabbits Following Intravitreal Administration.

Development of intravitreal drugs presents several challenges due to the delicate ocular environment and volume constraints of what can be safely administered in the eye. Formulation development of intravitreally administered drugs may necessitate the use of nonphysiological pH in order to accommodate manufacturing processes or achieve favorable drug properties. Clinical and nonclinical data show that intravitreal drugs formulated in the pH 5.5 to 7.4 range are well tolerated. The aim of this study was to provide ocular toxicity data for formulations in the pH 4.0 to 5.5 range following intravitreal administration in New Zealand White rabbits. This range was evaluated as part of formulation development for an intravitreal drug that necessitated the use of pH outside the available tolerability data for formulations. Toxicity was assessed by ophthalmic examinations, intraocular pressure (IOP) measurement, clinical observations, body weights, and microscopic analysis of ocular tissue. Histidine chloride pH 5.0 to 5.5 and acetate chloride pH 4.0 to 5.0 solutions were well tolerated, and no test article-related ocular inflammation, IOP changes, or gross or microscopic findings were observed in any eye. The data presented here add to the knowledge of pH ranges that can be explored for intravitreal drug formulation development.

Fab-Nanolipoprotein Conjugate Causes Vitreous Opacity and Cataracts Following a Single Intravitreal Administration in New Zealand White Rabbits.

One strategy employed to prolong the ocular half-life of large molecule therapeutics is via covalent attachment to a carrier, resulting in an increase in size thereby slowing their clearance from the eye. Rabbit antigen-binding fragment conjugated to nanolipoprotein (RabFab-NLP) is a novel conjugate intended to prolong ocular half-life through an increase in hydrodynamic radius compared to Fab alone (∼12 vs ∼3 nm). Nanolipoproteins are mimetics of endogenous high-density lipoproteins and consist of lipids and apolipoproteins (ApoE422k), both biologically derived materials. The objective of this study was to evaluate the ocular toxicity and toxicokinetics of RabFab-NLP after a single intravitreal administration in New Zealand White rabbits. Serum toxicokinetic data suggested a significant increase in ocular residence time of RabFab-NLP compared to RabFab alone. Ophthalmic examinations showed that RabFab-NLP caused vitreous and lens opacities as early as day 3 and day 8 postdose, respectively, which persisted for the entire study duration to day 30. The RabFab-NLP-related microscopic findings were present in the lens, vitreous cavity, and/or optic nerve head. Based on the observed ocular toxicity, a single intravitreal dose of 1.3 mg/eye RabFab-NLP was not tolerated and caused vitreous opacity and cataracts in rabbit eyes.

Retinal and Lens Degeneration in New Zealand White Rabbits Administered Intravitreal TSG-6 Link Domain-Rabbit FAb Fusion Proteins.

Fusion of biologic therapeutics to hyaluronic acid binding proteins, such as the link domain (LD) of Tumor necrosis factor (TNF)-Stimulated Gene-6 (TSG-6), is expected to increase vitreous residence time following intravitreal injection and provide for long-acting delivery. The toxicity of a single intravitreal dose of free TSG-6-LD and fusion proteins of TSG-6-LD and a nonbinding rabbit antibody fragment (RabFab) were assessed in New Zealand White rabbits. Animals administered free TSG-6-LD exhibited extensive lens opacities and variable retinal vascular attenuation, correlated with microscopic findings of lens and retinal degeneration. Similar but less severe findings were present in animals dosed with the RabFab-TSG-6-LD fusion proteins. In-life ocular inflammation was noted in all animals from 7-days postdose and was associated with high anti-RabFab antibody titers in animals administered fusion proteins. Inflammation and retinal degeneration were multifocally associated with evidence of retinal detachment, and hypertrophy and migration of vimentin, glial fibrillary acidic protein, and glutamine synthetase positive Müller cells to the outer nuclear layer. Further assessment of alternative hyaluronic acid binding protein fusions should consider the potential for retinal degeneration and enhanced immune responses early in development.

An anti-CD3/anti-CLL-1 bispecific antibody for the treatment of acute myeloid leukemia.

Acute myeloid leukemia (AML) is a major unmet medical need. Most patients have poor long-term survival, and treatment has not significantly changed in 40 years. Recently, bispecific antibodies that redirect the cytotoxic activity of effector T cells by binding to CD3, the signaling component of the T-cell receptor, and a tumor target have shown clinical activity. Notably, blinatumomab is approved to treat relapsed/refractory acute lymphoid leukemia. Here we describe the design, discovery, pharmacologic activity, pharmacokinetics, and safety of a CD3 T cell-dependent bispecific (TDB) full-length human IgG1 therapeutic antibody targeting CLL-1 that could potentially be used in humans to treat AML. CLL-1 is prevalent in AML and, unlike other targets such as CD33 and CD123, is not expressed on hematopoietic stem cells providing potential hematopoietic recovery. We selected a high-affinity monkey cross-reactive anti-CLL-1 arm and tested several anti-CD3 arms that varied in affinity, and determined that the high-affinity CD3 arms were up to 100-fold more potent in vitro. However, in mouse models, the efficacy differences were less pronounced, probably because of prolonged exposure to TDB found with lower-affinity CD3 TDBs. In monkeys, assessment of safety and target cell depletion by the high- and low-affinity TDBs revealed that only the low-affinity CD3/CLL1 TDB was well tolerated and able to deplete target cells. Our data suggest that an appropriately engineered CLL-1 TDB could be effective in the treatment of AML.

Idiopathic Colitis in Rhesus Macaques Is Associated With Dysbiosis, Abundant Enterochromaffin Cells and Altered T-Cell Cytokine Expression.

Idiopathic chronic diarrhea (ICD) is a common ailment affecting captive rhesus macaques ( Macaca mulatta). ICD cases are characterized by diarrhea in the absence of commonly identified diarrheal pathogens and multiple recurrences even after supportive therapy. Histologically, the disease is characterized by lymphoplasmacytic colitis. We identified 35 rhesus macaques euthanized for ICD during a 7-month period and described demographic, clinical, histologic, and immunologic commonalities. We found a trend of historic Campylobacter spp. and trichomonad infections. Furthermore, rhesus macaques with ICD demonstrated loss of normal colonic adherent bacterium, identified in this study as Helicobacter macacae; increased abundance of Pentatrichomonas hominis; and increased frequency of colonic serotonin-positive enterochromaffin cells. Interestingly, colonic and ileal T-helper cells of animals with ICD manifested decreased capacity for expression of certain cytokines, in particular interleukin (IL)-4 and IL-13. These data further describe a common ailment and suggest new avenues to identify complex interactions involved in the etiology of recurring diarrhea in young rhesus macaques.

Characterization of the xenobiotic response of Caenorhabditis elegans to the anthelmintic drug albendazole and the identification of novel drug glucoside metabolites.

Knowledge of how anthelmintics are metabolized and excreted in nematodes is an integral part of understanding the factors that determine their potency, spectrum of activity and for investigating mechanisms of resistance. Although there is remarkably little information on these processes in nematodes, it is often suggested that they are of minimal importance for the major anthelmintic drugs. Consequently, we have investigated how the model nematode Caenorhabditis elegans responds to and metabolizes albendazole, one of the most important anthelmintic drugs for human and animal use. Using a mutant strain lacking the ß-tubulin drug target to minimize generalized stress responses, we show that the transcriptional response is dominated by genes encoding XMEs (xenobiotic-metabolizing enzymes), particularly cytochrome P450s and UGTs (UDP-glucuronosyl transferases). The most highly induced genes are predominantly expressed in the worm intestine, supporting their role in drug metabolism. HPLC-MS/MS revealed the production of two novel glucoside metabolites in C. elegans identifying a major difference in the biotransformation of this drug between nematodes and mammals. This is the first demonstration of metabolism of a therapeutic anthelmintic in C. elegans and provides a framework for its use to functionally investigate nematode anthelmintic metabolism.

An integrated approach for characterizing immunogenic responses toward a bispecific antibody.

Bispecific antibodies (bsAbs) recognize and bind two different targets or two epitopes of the same antigen, making them an attractive diagnostic and treatment modality. Compared to the production of conventional bivalent monospecific antibodies, bsAbs require greater engineering and manufacturing. Therefore, bsAbs are more likely to differ from endogenous immunoglobulins and contain new epitopes that can increase immunogenic risk. Anti-A/B is a bsAb designed using a 'knobs-into-holes' (KIH) format. Anti-A/B exhibited an unexpectedly high immunogenicity in both preclinical and clinical studies, resulting in early termination of clinical development. Here, we used an integrated approach that combined in silico analysis, in vitro assays, and an in vivo study in non-human primates to characterize anti-A/B immunogenicity. Our findings indicated that the immunogenicity is associated with epitopes in the anti-B arm and not with mutations engineered through the KIH process. Our results showed the value of this integrated approach for performing immunogenicity risk assessment during clinical candidate selection to effectively mitigate risks during bsAb development.

In Vivo Assessment of Antibody-Dependent Enhancement of Influenza B Infection.

A theoretical safety concern proposed in the influenza literature is that therapeutic antiviral antibodies could have the potential for antibody-dependent enhancement (ADE) of infection and disease. ADE may occur when virus-specific antibodies at subtherapeutic, nonneutralizing concentrations facilitate virus uptake and, in some cases, enhance replication, which can lead to an exacerbation of virus-mediated disease. Alternatively, ADE may occur due to antibody-dependent complement activation exacerbating virus-mediated disease in the absence of increased replication. As a result of this theoretical safety concern, safety assessment of anti-influenza antibodies may include an in vivo evaluation of ADE of infection and/or disease. These studies were conducted to investigate the potential of MHAB5553A, a broadly specific, neutralizing therapeutic anti-influenza B antibody, to elicit ADE of infection and disease in mouse models of influenza B infection. In parallel studies, female DBA/2J mice were infected with either influenza B/Victoria/504/2000 or influenza B/Brisbane/60/2008 representing distinct lineages. Assessment of ADE was based on an integration of results from multiple endpoints, including infectious lung viral titers and genomes, body weight, mortality, lung weight, and histopathology. In these studies, the high dose of 15 mg/kg MHAB5553A resulted in substantial attenuation of influenza pneumonia, with more modest effects at 1.5 mg/kg; whereas MHAB5553A treatment at 0.15 or 0.015 mg/kg was generally comparable to vehicle-treated controls. Our results demonstrate that MHAB5553A across a broad range of doses did not enhance primary influenza B infection or disease in this model, and represent a nonclinical de-risking of the ADE potential with this antibody.

Preclinical pharmacokinetics and pharmacodynamics of DCLL9718A: An antibody-drug conjugate for the treatment of acute myeloid leukemia.

Few treatment options are available for acute myeloid leukemia (AML) patients. DCLL9718A is an antibody-drug conjugate that targets C-type lectin-like molecule-1 (CLL-1). This receptor is prevalent on monocytes, neutrophils, and AML blast cells, and unlike CD33, is not expressed on hematopoietic stem cells, thus providing possible hematopoietic recovery. DCLL9718A comprises an anti-CLL-1 IgG1 antibody (MCLL0517A) linked to a pyrrolobenzodiazepine (PBD) dimer payload, via a cleavable disulfide-labile linker. Here, we characterize the in vitro and in vivo stability, the pharmacokinetics (PK) and pharmacodynamics (PD) of DCLL9718A and MCLL0517A in rodents and cynomolgus monkeys. Three key PK analytes were measured in these studies: total antibody, antibody-conjugated PBD dimer and unconjugated PBD dimer. In vitro, DCLL9718A, was stable with most (> 80%) of the PBD dimer payload remaining conjugated to the antibody over 96 hours. This was recapitulated in vivo with antibody-conjugated PBD dimer clearance estimates similar to DCLL9718A total antibody clearance. Both DCLL9718A and MCLL0517A showed linear PK in the non-binding rodent species, and non-linear PK in cynomolgus monkeys, a binding species. The PK data indicated minimal impact of conjugation on the disposition of DCLL9718A total antibody. Finally, in cynomolgus monkey, MCLL0517A showed target engagement at all doses tested (0.5 and 20 mg/kg) as measured by receptor occupancy, and DCLL9718A (at doses of 0.05, 0.1 and 0.2 mg/kg) showed strong PD activity as evidenced by notable reduction in monocytes and neutrophils.

The cytochrome P450 family in the parasitic nematode Haemonchus contortus.

Haemonchus contortus, a highly pathogenic and economically important parasitic nematode of sheep, is particularly adept at developing resistance to the anthelmintic drugs used in its treatment and control. The basis of anthelmintic resistance is poorly understood for many commonly used drugs with most research being focused on mechanisms involving drug targets or drug efflux. Altered or increased drug metabolism is a possible mechanism that has yet to receive much attention despite the clear role of xenobiotic metabolism in pesticide resistance in insects. The cytochrome P450s (CYPs) are a large family of drug-metabolising enzymes present in almost all living organisms, but for many years thought to be absent from parasitic nematodes. In this paper, we describe the CYP sequences encoded in the H. contortus genome and compare their expression in different parasite life-stages, sexes and tissues. We developed a novel real-time PCR approach based on partially assembled CYP sequences "tags" and confirmed findings in the subsequent draft genome with RNA-seq. Constitutive expression was highest in larval stages for the majority of CYPs, although higher expression was detected in the adult male or female for a small subset of genes. Many CYPs were expressed in the worm intestine. A number of H. contortus genes share high identity with Caenorhabditis elegans CYPs and the similarity in their expression profiles supports their classification as putative orthologues. Notably, H. contortus appears to lack the dramatic CYP subfamily expansions seen in C. elegans and other species, which are typical of CYPs with exogenous roles. However, a small group of H. contortus genes cluster with the C. elegans CYP34 and CYP35 subfamilies and may represent candidate xenobiotic metabolising genes in the parasite.

The Influence of Dietary Fat Source on Life Span in Calorie Restricted Mice.

Calorie restriction (CR) without malnutrition extends life span in several animal models. It has been proposed that a decrease in the amount of polyunsaturated fatty acids (PUFAs), and especially n-3 fatty acids, in membrane phospholipids may contribute to life span extension with CR. Phospholipid PUFAs are sensitive to dietary fatty acid composition, and thus, the purpose of this study was to determine the influence of dietary lipids on life span in CR mice. C57BL/6J mice were assigned to four groups (a 5% CR control group and three 40% CR groups) and fed diets with soybean oil (high in n-6 PUFAs), fish oil (high in n-3 PUFAs), or lard (high in saturated and monounsaturated fatty acids) as the primary lipid source. Life span was increased (p < .05) in all CR groups compared to the Control mice. Life span was also increased (p < .05) in the CR lard mice compared to animals consuming either the CR fish or soybean oil diets. These results indicate that dietary lipid composition can influence life span in mice on CR, and suggest that a diet containing a low proportion of PUFAs and high proportion of monounsaturated and saturated fats may maximize life span in animals maintained on CR.

The influence of Shc proteins on life span in mice.

The signaling molecule p66Shc is often described as a longevity protein. This conclusion is based on a single life span study that used a small number of mice. The purpose of the present studies was to measure life span in a sufficient number of mice to determine if longevity is altered in mice with decreased Shc levels (ShcKO). Studies were completed at UC Davis and the European Institute of Oncology (EIO). At UC Davis, male C57BL/6J WT and ShcKO mice were fed 5% or 40% calorie-restricted (CR) diets. In the 5% CR group, there was no difference in survival curves between genotypes. There was also no difference between genotypes in prevalence of neoplasms or other measures of end-of-life pathology. At 40% calorie restriction group, 70th percentile survival was increased in ShcKO, while there were no differences between genotypes in median or subsequent life span measures. At EIO, there was no increase in life span in ShcKO male or female mice on C57BL/6J, 129Sv, or hybrid C57BL/6J-129Sv backgrounds. These studies indicate that p66Shc is not a longevity protein. However, additional studies are needed to determine the extent to which Shc proteins may influence the onset and severity of specific age-related diseases.

Metastatic hepatocellular carcinoma in a juvenile rhesus macaque (Macaca mulatta).

Neoplasia in juvenile (younger than 5 y) rhesus macaques has been estimated to represent only approximately 1.4% of all occurrences of spontaneous neoplasia. Here we report an unusual case of a 3.75-y-old primiparous female rhesus macaque that was euthanized due to poor prognosis associated with progressive anemia, marked hepatomegaly, and radiographic evidence of meta- static neoplasia. Postmortem examination revealed an invasive, hemorrhagic hepatic mass that effaced approximately 70% of the liver parenchyma and had evidence of metastatic spread to multiple abdominal organs, the lungs, and the pituitary gland. Neoplastic polygonal cells lined large necrohemorrhagic cavities and exhibited marked anisocytosis and anisokaryosis, with frequent multinucleate cells. There was no desmoplasia associated with the primary neoplasm or metastases. Immunohistochemical studies revealed the neoplastic cells to be diffusely reactive with pancytokeratin, cytokeratin 7, and cytokeratin 8/18 antibodies and rarely reactive with carcinoembryonic antigen antibodies. The cells did not react with vimentin, S100, CD31, or factor VIII antibodies. Tumor morphology and immunophenotype led to the diagnosis of anaplastic hepatocellular carcinoma. This report represents the first known case of metastatic liver neoplasia in a rhesus macaque. The young age of this animal and the aggressive nature of the neoplasm are highly unusual and reminiscent of adolescent onset hepatocellular carcinoma in humans.

Fatal hepatic tetratrichomoniasis in a juvenile Waldrapp ibis (Geronticus eremita).

Waldrapp ibis (Geronticus eremita) are a critically endangered species, and there are currently more birds in captivity than in the wild. A juvenile, male Waldrapp ibis housed in a mixed-species exhibit was found dead with no premonitory signs. Necropsy revealed extensive necrotizing hepatitis associated with numerous pleomorphic protozoa that were immunohistochemically reactive with antibodies raised against Tritrichomonas foetus, a parasite of cattle. Electron microscopy confirmed the organisms as members of family Trichomonadidae, and sequence analysis of the first ribosomal internal transcribed spacer region (ITS1), 5.8S ribosomal RNA, and ITS2 regions indicated high genetic similarity (96-97%) to members of the Tetratrichomonas gallinarum complex. The animal was born in captivity, and no introductions in this exhibit had occurred since 2009. Other Waldrapp ibis that had contact with the infected male were negative for flagellate infections by fecal examination, thus cross-species transmission is proposed as the source of infection. The host range of the T. gallinarum complex is very large and although the pathogenicity of its members, especially for wild birds, is controversial, these parasites should be considered as a possible cause of acute mortality in Waldrapp ibis. In addition, immunohistochemistry with T. foetus antibodies and molecular diagnostics may be useful tools for preventative veterinary care of endangered bird populations. A greater understanding of the ecology and pathogenesis of this pathogen may also be vital for screening subclinical captive populations and existing wild populations prior to reintroduction efforts.

The transcriptional response of Caenorhabditis elegans to Ivermectin exposure identifies novel genes involved in the response to reduced food intake.

We have examined the transcriptional response of Caenorhabditis elegans following exposure to the anthelmintic drug ivermectin (IVM) using whole genome microarrays and real-time QPCR. Our original aim was to identify candidate molecules involved in IVM metabolism and/or excretion. For this reason the IVM tolerant strain, DA1316, was used to minimise transcriptomic changes related to the phenotype of drug exposure. However, unlike equivalent work with benzimidazole drugs, very few of the induced genes were members of xenobiotic metabolising enzyme families. Instead, the transcriptional response was dominated by genes associated with fat mobilization and fatty acid metabolism including catalase, esterase, and fatty acid CoA synthetase genes. This is consistent with the reduction in pharyngeal pumping, and consequential reduction in food intake, upon exposure of DA1316 worms to IVM. Genes with the highest fold change in response to IVM exposure, cyp-37B1, mtl-1 and scl-2, were comparably up-regulated in response to short-term food withdrawal (4 hr) independent of IVM exposure, and GFP reporter constructs confirm their expression in tissues associated with fat storage (intestine and hypodermis). These experiments have serendipitously identified novel genes involved in an early response of C. elegans to reduced food intake and may provide insight into similar processes in higher organisms.