Considerations from an International Regulatory and Pharmaceutical Industry (IQ MPS Affiliate) Workshop on the Standardization of Complex In Vitro Models in Drug Development

In May 2022, there is an International Regulatory and Pharmaceutical Industry (Innovation and Quality [IQ] Microphysiological Systems [MPS] Affiliate) Workshop on the standardization of complex in vitro models (CIVMs) in drug development. This manuscript summarizes the discussions and conclusions of this joint workshop organized and executed by the IQ MPS Affiliate and the United States Food and Drug Administration (FDA). A key objective of the workshop is to facilitate discussions around opportunities and/or needs for standardization of MPS and chart potential pathways to increase model utilization in the context of regulatory decision making. Participation in the workshop included 200 attendees from the FDA, IQ MPS Affiliate, and 26 global regulatory organizations and affiliated parties representing Europe, Japan, and Canada. It is agreed that understanding global perspectives regarding the readiness of CIVM/MPS models for regulatory decision making and potential pathways to gaining acceptance is useful to align on globally. The obstacles are currently too great to develop standards for every context of use (COU). Instead, it is suggested that a more tractable approach may be to think of broadly applicable standards that can be applied regardless of COU and/or organ system. Considerations and next steps for this effort are described.

Perspectives on the evaluation and adoption of complex in vitro models in drug development: Workshop with the FDA and the pharmaceutical industry (IQ MPS Affiliate)

Complex in vitro models (CIVM) offer the potential to improve pharmaceutical clinical drug attrition due to safety and/ or efficacy concerns. For this technology to have an impact, the establishment of robust characterization and qualifi­cation plans constructed around specific contexts of use (COU) is required. This article covers the output from a workshop between the Food and Drug Administration (FDA) and Innovation and Quality Microphysiological Systems (IQ MPS) Affiliate. The intent of the workshop was to understand how CIVM technologies are currently being applied by pharma­ceutical companies during drug development and are being tested at the FDA through various case studies in order to identify hurdles (real or perceived) to the adoption of microphysiological systems (MPS) technologies, and to address evaluation/qualification pathways for these technologies. Output from the workshop includes the alignment on a working definition of MPS, a detailed description of the eleven CIVM case studies presented at the workshop, in-depth analysis, and key take aways from breakout sessions on ADME (absorption, distribution, metabolism, and excretion), pharmacology, and safety that covered topics such as qualification and performance criteria, species differences and concordance, and how industry can overcome barriers to regulatory submission of CIVM data. In conclusion, IQ MPS Affiliate and FDA scientists were able to build a general consensus on the need for animal CIVMs for preclinical species to better determine species concordance. Furthermore, there was acceptance that CIVM technologies for use in ADME, pharmacology and safety assessment will require qualification, which will vary depending on the specific COU.

Recommended Guidelines for Developing, Qualifying, and Implementing Complex In Vitro Models (CIVMs) for Drug Discovery

The pharmaceutical industry is continuing to face high research and development (R&D) costs and low overall success rates of clinical compounds during drug development. There is an increasing demand for development and validation of healthy or disease-relevant and physiological human cellular models that can be implemented in early-stage discovery, thereby shifting attrition of future therapeutics to a point in discovery at which the costs are significantly lower. There needs to be a paradigm shift in the early drug discovery phase (which is lengthy and costly), away from simplistic cellular models that show an inability to effectively and efficiently reproduce healthy or human disease-relevant states to steer target and compound selection for safety, pharmacology, and efficacy questions. This perspective article covers the various stages of early drug discovery from target identification (ID) and validation to the hit/lead discovery phase, lead optimization, and preclinical safety. We outline key aspects that should be considered when developing, qualifying, and implementing complex in vitro models (CIVMs) during these phases, because criteria such as cell types (e.g., cell lines, primary cells, stem cells, and tissue), platform (e.g., spheroids, scaffolds or hydrogels, organoids, microphysiological systems, and bioprinting), throughput, automation, and single and multiplexing endpoints will vary. The article emphasizes the need to adequately qualify these CIVMs such that they are suitable for various applications (e.g., context of use) of drug discovery and translational research. The article ends looking to the future, in which there is an increase in combining computational modeling, artificial intelligence and machine learning (AI/ML), and CIVMs.

Three-dimensional lung tumor microenvironment modulates therapeutic compound responsiveness in vitro--implication for drug development

Three-dimensional (3D) cell culture is gaining acceptance in response to the need for cellular models that better mimic physiologic tissues. Spheroids are one such 3D model where clusters of cells will undergo self-assembly to form viable, 3D tumor-like structures. However, to date little is known about how spheroid biology compares to that of the more traditional and widely utilized 2D monolayer cultures. Therefore, the goal of this study was to characterize the phenotypic and functional differences between lung tumor cells grown as 2D monolayer cultures, versus cells grown as 3D spheroids. Eight lung tumor cell lines, displaying varying levels of epidermal growth factor receptor (EGFR) and cMET protein expression, were used to develop a 3D spheroid cell culture model using low attachment U-bottom plates. The 3D spheroids were compared with cells grown in monolayer for 1) EGFR and cMET receptor expression, as determined by flow cytometry, 2) EGFR and cMET phosphorylation by MSD assay, and 3) cell proliferation in response to epidermal growth factor (EGF) and hepatocyte growth factor (HGF). In addition, drug responsiveness to EGFR and cMET inhibitors (Erlotinib, Crizotinib, Cetuximab [Erbitux] and Onartuzumab [MetMab]) was evaluated by measuring the extent of cell proliferation and migration. Data showed that EGFR and cMET expression is reduced at day four of untreated spheroid culture compared to monolayer. Basal phosphorylation of EGFR and cMET was higher in spheroids compared to monolayer cultures. Spheroids showed reduced EGFR and cMET phosphorylation when stimulated with ligand compared to 2D cultures. Spheroids showed an altered cell proliferation response to HGF, as well as to EGFR and cMET inhibitors, compared to monolayer cultures. Finally, spheroid cultures showed exceptional utility in a cell migration assay. Overall, the 3D spheroid culture changed the cellular response to drugs and growth factors and may more accurately mimic the natural tumor microenvironment.

Chemokine (C-C motif) ligand 2 mediates direct and indirect fibrotic responses in human and murine cultured fibrocytes

Background

Fibrocytes are a population of circulating bone-marrow-derived cells that express surface markers for leukocytes and mesenchymal cells, and are capable of differentiating into myofibroblasts. They have been observed at sites of active fibrosis and increased circulating numbers correlate with mortality in idiopathic pulmonary fibrosis (IPF). Inhibition of chemokine (C-C motif) receptor 2 (CCR2) during experimental models of lung fibrosis reduces lung collagen deposition, as well as reducing lung fibrocyte accumulation. The aim of the present study was to determine whether human and mouse fibrocytes express functional CCR2.

Results

Following optimized and identical human and murine fibrocyte isolation, both cell sources were shown to be positive for CCR2 by flow cytometry and this expression colocalized with collagen I and CD45. Human blood fibrocytes stimulated with the CCR2 ligand chemokine (C-C motif) ligand 2 (CCL2), demonstrated increased proliferation (P < 0.005) and differentiation into myofibroblasts (P < 0.001), as well as a chemotactic response (P < 0.05). Murine fibrocytes also responded to CCR2 stimulation, with CCL12 being more potent than CCL2.

Conclusions

This study directly compares the functional responses of human and murine fibrocytes to CCR2 ligands, and following comparable isolation techniques. We have shown comparable biological effects, strengthening the translatability of the murine models to human disease with respect to targeting the CCR2 axis to ameliorate disease in IPF patients.

Morphological Analysis and Lentiviral Transduction of Fetal Monkey Bone Marrow-Derived Mesenchymal Stem Cells

We explored the transduction kinetics of HIV-1-derived lentiviral vectors containing the CMV, EF1alpha, or PGK promoter expressing EGFP in fetal rhesus monkey bone marrow-derived mesenchymal stem cells (rhMSC). Studies included the effects of transduction (MOI 0-100) on growth, cell cycle, and differentiation toward an osteogenic lineage. Flow cytometric analysis indicated an approximate 8- to 10-fold greater quantity of EGFP-expressing rhMSC when cells were transduced with the CMV or EF1alpha promoter compared to PGK, although quantitative PCR revealed no differences at the DNA level. The CMV promoter initially expressed 10- to 100-fold higher levels of EGFP compared to EF1alpha or PGK, respectively, at increasing MOI, although a significant decline in transgene expression was observed posttransduction and with advancing passage (P < 0.01), whereas a significant increase in the level of expression was observed over time with the EF1alpha promoter. At an MOI of 100, a transient arrest at the S phase of the cell cycle was observed for both vector constructs. Transduced rhMSC differentiated toward an osteogenic lineage comparable to untransduced rhMSC and showed equivalent levels of alkaline phosphatase activity. These findings suggest that the SIN HIV-1-derived lentiviral vectors used in these studies can efficiently transduce rhMSC in vitro (CMV > EF1alpha > PGK) without inhibiting differentiation potential, although the cell cycle was transiently altered at high MOI

Variable maternal nutrition and growth hormone treatment in the second quarter of pregnancy in pigs alter semitendinosus muscle in adolescent progeny

Maternal nutrition and growth hormone (GH) treatment during early- to mid-pregnancy can each alter the subsequent growth and differentiation of muscle in progeny. We have investigated the effects of varying maternal nutrition and maternal treatment with porcine (p) GH during the second quarter of pregnancy in gilts on semitendinosus muscle cross-sectional area and fibre composition of progeny, and relationships between maternal and progeny measures and progeny muscularity. Fifty-three Large White x Landrace gilts, pregnant to Large White x Duroc boars, were fed either 2.2 kg (about 35 % ad libitum intake) or 3.0 kg commercial ration (13.5 MJ digestible energy, 150 g crude protein (N x 6.25)/kg DM)/d and injected with 0, 4 or 8 mg pGH/d from day 25 to 50 of pregnancy, then all were fed 2.2 kg/d for the remainder of pregnancy. The higher maternal feed allowance from day 25 to 50 of pregnancy increased the densities of total and secondary fibres and the secondary:primary fibre ratio in semitendinosus muscles of their female progeny at 61 d of age postnatally. The densities of secondary and total muscle fibres in semitendinosus muscles of progeny were predicted by maternal weight before treatment and maternal plasma insulin-like growth factor-II during treatment. Maternal pGH treatment from day 25 to day 50 of pregnancy did not alter fibre densities, but increased the cross-sectional area of the semitendinosus muscle; this may be partially explained by increased maternal plasma glucose. Thus, maternal nutrition and pGH treatment during the second quarter of pregnancy in pigs independently alter muscle characteristics in progeny.

Fetal and maternal outcome after administration of tenofovir to gravid rhesus monkeys (Macaca mulatta)

Tenofovir has been shown to cross the placenta in quantities sufficient to sustain reductions in viral load in simian immunodeficiency virus (SIV)-infected fetal monkeys. With chronic exposure (30 mg/kg), however, significant bone-related toxicity has been shown in approximately 25% of infants studied. Further investigations were conducted to determine whether the bone-related toxicity observed was initiated during fetal life. Gravid rhesus monkeys (n = 4) were administered tenofovir subcutaneously once daily from 20 to 150 days of gestation (30 mg/kg; term: 165 +/- 10 days). Fetuses were monitored sonographically, and maternal and fetal blood and urine samples were collected to assess hematologic parameters, clinical chemistry, insulin-like growth factor (IGF) levels, and bone biomarkers. Fetuses were delivered by hysterotomy near term for necropsy and evaluation of bone-related mechanical properties. Results of these studies have shown 1) normal fetal development, although overall body weights and crown-rump lengths were less than those for age-matched controls (p < or = .03); 2) a significant reduction in circulating IGF-I (p <.001); 3) a small reduction in fetal bone porosity (p < or = .03); and 4) transient alterations in maternal body weights and bone-related biomarkers during the treatment period. The results of these studies suggest that chronic fetal exposure to tenofovir at the maternal dose of 30 mg/kg throughout gestation can alter select fetal parameters and transiently affect maternal bone biomarkers.

Lentiviral vector gene transfer into fetal rhesus monkeys (Macaca mulatta): lung-targeting approaches

We previously reported the efficiency of gene transfer in fetal monkeys using retroviral vectors and an intraperitoneal (IP) approach. Here, we explored intrapulmonary administration to determine whether gene transfer can be limited to the developing lung. The HIV-1-derived lentiviral vector (VSV-G pseudotyped; 1 x 10(7) infectious particles/fetus), using the enhanced green fluorescent protein (EGFP) as a reporter, was directly injected into fetal lung with ultrasound guidance (n=4; 55 or 70 days gestation; term 165+/-10 days). Fetuses were monitored sonographically, fetal/maternal blood samples collected during gestation, and four of four healthy newborns were delivered at term. All lung lobes were positive for the transgene (< or = 1%) when assessed by PCR, and transgene expression was observed by direct fluorescence microscopy and flow cytometry. The results of this study show the following: (1) successful gene transfer in fetal monkeys using an intrapulmonary approach; (2) less transduction of non-pulmonary tissues with gene transfer at 70 days gestation compared with 55 days gestation or use of an IP approach; (3) that the pulmonary epithelium was EGFP-positive by immunohistochemistry; and (4) no evidence of transplacental transport of vector sequences or antibody responses in the dams. The results of these investigations indicate the efficiency of fetal gene transfer by intrapulmonary delivery, and emphasize the importance of the fetal monkey as a preclinical model system for exploring in utero genetic treatment strategies for pulmonary disorders.