Linear low-dose extrapolation for noncancer health effects is the exception, not the rule

The nature of the exposure-response relationship has a profound influence on risk analyses. Several arguments have been proffered as to why all exposure-response relationships for both cancer and noncarcinogenic end-points should be assumed to be linear at low doses. We focused on three arguments that have been put forth for noncarcinogens. First, the general “additivity-to-background” argument proposes that if an agent enhances an already existing disease-causing process, then even small exposures increase disease incidence in a linear manner. This only holds if it is related to a specific mode of action that has nonuniversal properties—properties that would not be expected for most noncancer effects. Second, the “heterogeneity in the population” argument states that variations in sensitivity among members ofthe target population tend to “flatten out and linearize” the exposure-response curve, but this actually only tends to broaden, not linearize, the dose-response relationship. Third, it has been argued that a review of epidemiological evidence shows linear or no-threshold effects at low exposures in humans, despite nonlinear exposure-response in the experimental dose range in animal testing for similar endpoints. It is more likely that this is attributable to exposure measurement error rather than a true non-threshold association. Assuming that every chemical is toxic at high exposures and linear at low exposures does not comport to modern-day scientific knowledge of biology. There is no compelling evidence-based justification for a general low-exposure linearity; rather, case-specific mechanistic arguments are needed

Evaluation of Therapeutics for Advanced-Stage Heart Failure and Other Severely-Debilitating or Life-Threatening Diseases

Severely-debilitating or life-threatening (SDLT) diseases include conditions in which life expectancy is short or quality of life is greatly diminished despite available therapies. As such, the medical context for SDLT diseases is comparable to advanced cancer and the benefit vs. risk assessment and development of SDLT disease therapeutics should be similar to that of advanced cancer therapeutics. A streamlined development approach would allow patients with SDLT conditions earlier access to therapeutics and increase the speed of progression through development. In addition, this will likely increase the SDLT disease therapeutic pipeline, directly benefiting patients and reducing the economic and societal burden of SDLT conditions. Using advanced-stage heart failure (HF) as an example that illustrates the concepts applicable to other SDLT indications, this article proposes a streamlined development paradigm for SDLT disease therapeutics and recommends development of aligned global regulatory guidance