Retrospective analysis of carcinogenicity assessments within FDA-notified GRAS determinations.

Frameworks have been developed to standardize the assessment of carcinogenic potential in the pharmaceutical and agrochemical industries, building upon decades of research. Carcinogenicity is also evaluated during the safety evaluation of food substances, using a comprehensive approach unique to each substance. To better understand these approaches, a retrospective assessment was conducted on the publicly available database of substances notified to the United States Food and Drug Administration (US FDA) as being Generally Recognized As Safe (GRAS). The data contained within these GRAS notifications (GRNs) were reviewed for the methods used to evaluate carcinogenic potential (genotoxicity studies, 2-year bioassays, other pre-clinical animal studies) to identify patterns that could provide an understanding of how this assessment has been conducted for different categories of food substances. While different approaches to the safety evaluation were required to adapt to the unique food substances, the data in all notifications supported the conclusion of safety. The evaluation of food substances for carcinogenic potential must consider all available data, including identifying the need for when more data must be generated to support an evaluation. Due to the complexity of substances used in food, ranging from defined chemical entities to minimally processed agricultural commodities to live microorganisms, the approach to conducting the safety evaluation of food substances must be able to adapt to the most relevant scientifically supported approach. This paper illustrates the data commonly used to support the safety of different types of food substances and proposes an approach familiar to other product sectors.

Leptomycin B alters the subcellular distribution of CRM1 (Exportin 1).

CRM1 (chromosome maintenance region 1, Exportin 1) binds to nuclear export signals and is required for nucleocytoplasmic transport of a large variety of proteins and RNP complexes. Leptomycin B (LMB), the first specific inhibitor of CRM1 identified, binds covalently to cysteine 528 in the nuclear export signal binding region of CRM1 leading to the inhibition of protein nuclear export. Although the biochemical mechanisms of action of CRM1 inhibitors such as LMB are well studied, the subcellular effects of inhibition on CRM1 are unknown. We have found that LMB causes CRM1 to redistribute from the nucleus to the cytoplasm in A549 cells. A significant decrease in nuclear CRM1 coupled with an increase in cytoplasmic CRM1 was sustained for up to 4 h, while there was no change in total CRM1 protein in fractionated cells. Cells expressing an LMB insensitive HA-tagged CRM1-C528S protein were unaffected by LMB treatment, whereas HA-tagged wildtype CRM1 redistributed from the nucleus to the cytoplasm with LMB treatment, similar to endogenous CRM1. GFP-tagged CRM1 protein microinjected into the cytoplasm of A549 cells distributed throughout the cell in untreated cells remained primarily cytoplasmic in LMB-treated cells. Upon nuclear microinjection, GFP-CRM1 translocated to and accumulated in the cytoplasm of LMB-treated cells. Thus, LMB binds to CRM1 and causes its redistribution to the cytoplasm by inhibiting its nuclear import. Decreasing the nuclear availability of CRM1 likely contributes to the accumulation of CRM1 cargo proteins in the nucleus, suggesting a new mechanism of action for LMB.