Exploring the Phenomenon of MNNG Dose-Dependent Death Polypharmacology

Abstract

Regulated cell death (RCD) is composed of several pathways that control cell fate. While each pathway is mechanistically distinct, these pathways have been shown to interact. Most of these interactions tend to be antagonistic, such that activation of one pathway blocks the subsequent activation of another pathway. This highlights that death pathways tend to be mutually exclusive. Thus, combining two cytotoxic drugs that activate different death pathways could result in less cell death than predicted, hampering therapeutic efficacy. As such, it is necessary to characterize which death pathways are activated by clinically relevant drugs, particularly for drug combination studies. However, studies of death pathway engagement are complicated by the fact that many drugs are capable of activating multiple RCD pathways. In order to improve annotations of RCD pathway activation by specific stimuli, we need to learn what features dictate which death pathway is activated. To study this phenomenon, we focused on characterizing RCD execution after treatment with methylnitronitrosoguanidine (MNNG), a DNA alkylating agent. MNNG is the canonical activator of parthanatos, an inflammatory form of RCD dependent on PARP-1 hyper-activation. We found that MNNG exhibits dose-dependent changes in death features, such as death onset time and death rate, indicative of a death mechanism change. As such we hypothesized that MNNG can induce multiple RCD pathways in a dose-dependent fashion. We found that this dose-dependent change in death features was generalizable to multiple cell lines. Moreover, we established that the phenotype was not due to PARP-trapping effects. Importantly, we uncovered that MNNG does induce a death mechanism switch. We found that MNNG is capable of inducing either parthanatos or apoptosis, depending on the dose. We also found evidence that the two death pathways induced by MNNG were mutually exclusive. And lastly, we established that the death mechanism switch was not due to altered mismatch repair (MMR). The information from this study could help to shed light on clinical outcomes from drug combination trials, specifically combinations with DNA damaging agents and PARP inhibitors.