Correction to: Use of Physiologically Based Pharmacokinetic (PBPK) Modeling for Predicting Drug-Food Interactions: an Industry Perspective

An Erratum to this paper has been published: https://doi.org/10.1208/s12248-020-00535-z.

Use of Physiologically Based Pharmacokinetic (PBPK) Modeling for Predicting Drug-Food Interactions: an Industry Perspective

The effect of food on pharmacokinetic properties of drugs is a commonly observed occurrence affecting about 40% of orally administered drugs. Within the pharmaceutical industry, significant resources are invested to predict and characterize a clinically relevant food effect. Here, the predictive performance of physiologically based pharmacokinetic (PBPK) food effect models was assessed via de novo mechanistic absorption models for 30 compounds using controlled, pre-defined in vitro, and modeling methodology. Compounds for which absorption was known to be limited by intestinal transporters were excluded in this analysis. A decision tree for model verification and optimization was followed, leading to high, moderate, or low food effect prediction confidence. High (within 0.8- to 1.25-fold) to moderate confidence (within 0.5- to 2-fold) was achieved for most of the compounds (15 and 8, respectively). While for 7 compounds, prediction confidence was found to be low (> 2-fold). There was no clear difference in prediction success for positive or negative food effects and no clear relationship to the BCS category of tested drug molecules. However, an association could be demonstrated when the food effect was mainly related to changes in the gastrointestinal luminal fluids or physiology, including fluid volume, motility, pH, micellar entrapment, and bile salts. Considering these findings, it is recommended that appropriately verified mechanistic PBPK modeling can be leveraged with high to moderate confidence as a key approach to predicting potential food effect, especially related to mechanisms highlighted here.

An Eye Opener: Lessons Learnt in Retinoblastoma Awareness and Screening Program

Background: Retinoblastoma is most common intraocular malignancy of infancy. Globally screening is recommended for ‘at risk’ children. Despite knowing this, Indian Cancer Society undertook general screening at behest of a corporate donor. Scenario in India is challenging as children at rural, urban slums are not routinely screened for any of eye disease. ICS implemented the pilot project among underprivileged children with primary aim of spreading awareness and improve the ocular health. Though expected outcome was zero retinoblastoma suspect cases; based on past projects it was expected that other eye conditions like squint, cataract etc. would be identified in a few. Aim: To screen 4500 children below 4 years of age at Indian rural and suburban slum areas. To create awareness about retinoblastoma and other eye conditions in community. Methods: Locations were identified where literacy, awareness, immunization coverage were low. Partners were selected a team of experts (ocular oncologists, pediatric ophthalmologists, optometrists, paramedical staff) were deployed for implementation. For awareness, all parents coming for the immunization, Aaganwadis and preschools etc. were given a talk on the importance of child eye screening and various disease which can be detected and prevented through simple eye examination. Special community level programs planned to create awareness about retinoblastoma and early childhood eye screening. Brochures and pamphlets were to be given in the vernacular language of the region. Screening for retinoblastoma was planned in 2 phases, those found to have positive red reflex in stage 1 are subjected to dilation, after obtaining consent from the parents. Proformas were filled in and treatment was given as per the pediatric eye disease identified. Results: In 5 months 2450 children were screened, at tribal area and in suburban slum areas. Awareness sessions were conducted for 348 mothers in batches at the tribal area and similarly for mothers and teachers at Anganwadi, schools. None of the parents/teachers were aware about cancer of eye. A thorough eye check-up was done based on the suggestions of the American Association of Pediatric eye diseases and special attention was given to tests such as Bruckners test. Number of children suspected of retinoblastoma was nil, however, 6% children were found to have other eye conditions such as congenital cataract, corneal opacity, refractive errors, squints and ptosis in the tribal area and project is ongoing in suburban area. Treatment was given as per the protocol for same. Conclusion: Screening for retinoblastoma for not at risk children is not recommended. Main aim for implementing retinoblastoma awareness program is to integrate it with immunization or nutritional program in India. This would ensure standardized ocular care. Challenges are numerous, such as lack of infrastructure, poor literacy rates, low income levels. Yet, innovative strategies are needed for better impact of awareness programs.

Modulating nasal mucosal permeation using metabolic saturation and enzyme inhibition techniques

OBJECTIVE

Presystemic elimination resulting from local enzymatic degradation can play a key role in limiting the bioavailability of intranasally administered drugs. The aim of this study was to evaluate the transfer of a metabolically susceptible drug across the nasal mucosa to illustrate the relative contributions of drug diffusivity and metabolic susceptibility on overall nasal mucosal permeation and to understand the effects of changes in enzymatic activity on the transfer across nasal epithelial and submucosal tissues.

METHODS

The concentration-dependent permeation of melatonin, a CYP450 substrate, across excised bovine nasal olfactory and respiratory explants was studied along with quantifying the extent of melatonin 6-hydroxylation. Microsomal preparations were also used to determine the kinetic parameters for melatonin to 6-hydroxymelatonin biotransformation.

KEY FINDINGS

Enzyme saturation at higher melatonin concentrations and inclusion of a CYP450 inhibitor both resulted in the significant increase in melatonin permeation across the nasal mucosa.

CONCLUSIONS

Metabolic loss of melatonin during nasal permeation demonstrates CYP450 activity in the nasal epithelium and submucosal tissues. The extent of biotransformation of melatonin during its transport across the nasal mucosal explants suggests that, although the nasal route bypasses hepatic first-pass metabolism, nasal bioavailability can be significantly influenced by mucosal enzymatic activity.

Gene expression and immunochemical localization of major cytochrome P450 drug-metabolizing enzymes in bovine nasal olfactory and respiratory mucosa

Despite tremendous advancement in the characterization of nasal enzyme expression, knowledge of the role of the nasal mucosa in the metabolism of xenobiotics is still inadequate, primarily due to the limited availability of in vitro models for nasal metabolism screening studies. An extensive knowledge of the oxidative and conjugative metabolizing capacity of the cattle (Bos taurus) olfactory and respiratory mucosa can aid in efficient use of these tissues for pre-clinical investigations of the biotransformation and toxicity of therapeutic agents following nasal administration or inhalation. Cows are also exposed to a variety of airborne pollutants and pesticides during their lifetime, the metabolism of which can have profound toxicological and ecological consequences. The aim of the present study was to characterize cytochrome P450 (CYP) enzyme expression in the bovine nasal mucosa. Amplification of the specific genes through RT-PCR confirmed expression of several CYP enzymes in bovine hepatic and nasal tissues. The results demonstrate that bovine nasal olfactory and respiratory mucosal and liver tissues express similar populations, families, and distributions of CYP enzymes, as has been previously reported with other species, including humans. Bovine ex vivo tissues can serve as a readily available reference tissue to elucidate preclinical toxico-kinetic effects resulting from exposure to substances in the environment or following drug administration.

Simian virus 40 small-t does not transactivate RNA polymerase II promoters in virus infections

Transcriptional stimulatory properties of virus-encoded transactivators appear to be critical for viral gene expression and may be linked to cellular transformation in certain cases. Recently, the simian virus 40 (SV40) 17-kDa small-t antigen was shown to stimulate transcription of polymerase II and III genes in transient transfection assays. In experiments performed in our laboratory, two of the polymerase II promoters of the adenovirus genome, namely, the EII-early and EIII promoters, were transactivation, we examined the transient transfection assays. To further elucidate the mechanism of this transactivation, we examined the ability of small-t to transactivate the adenovirus type 5 EII-early and EIII promoters in CV-1 cells under conditions in which the small-t gene or the reporter genes were introduced into the cells through transfection and other routes. In one approach, we used established CV-1 cell lines which constitutively express the small-t gene, and study of the EII-early promoter was afforded by infection of an EIA-negative adenovirus type 5 variant. For the second approach, a recombinant adenovirus was constructed in which small-t was expressed from a replication origin-negative SV40 early promoter in the EIA region of an adenovirus vector (Ad-SV-t). The effect of small-t on adenovirus EII-early and EIII promoter expression was studied in coinfection or single-infection experiments. In both cases, transcription of the adenovirus early promoters was not stimulated by small-t. These and other results indicate that transactivation of polymerase II promoters by small-t occurs only when the target gene is in a transiently transfected state. Thus, small-t-mediated transactivation of polymerase II promoters is dependent on the type of assay system used and may be mechanistically different from that of the widely studied EIA.

Mutational analysis of simian virus 40 small-t antigen

Several point mutations in the simian virus 40 (SV40) small-t antigen have been analyzed for their effects on protein stability, transformation, transactivation, and binding of two cellular proteins. All mutations which affected cysteine residues in two cysteine clusters produced highly unstable small-t antigens. Four point mutations outside these clusters and one in-frame deletion mutant, dl890, produced stable proteins but reduced transformation efficiency. These were able to transactivate the EII promoter and bind the cellular proteins, suggesting that these activities are not sufficient for small-t-mediated enhancement of transformation.