The mammalian Diaphanous-related (mDia) formins are cytoskeletal regulators that assemble and, in some cases, bundle filamentous actin (F-actin), as well as stabilize microtubules. The development of small molecule antagonists and agonists that interrogate mDia formin function has allowed us to investigate the roles of formins in disease states. A small molecule inhibitor of FH2 domain (SMIFH2) inhibits mDia-dependent actin dynamics and abrogates tumor cell migration and cell division in vitro and ex vivo tissue explants. mDia formin activation with small molecule intramimics IMM01/02 and mDia2-DAD peptides inhibited glioblastoma motility and invasion in vitro and ex vivo rat brain slices. However, SMIFH2, IMMs, and mDia2 DAD efficacy in vivo remains largely unexplored and potential toxicity across a range of developmental phenotypes has not been thoroughly characterized. In this study, we performed an in vivo screen of early life-stage toxicity in Danio rerio zebrafish embryos 2 days post-fertilization (dpf) in response to SMIFH2, IMM01/02, and mDia2 DAD. SMIFH2 at concentrations ≥5–10 μM induced significant defects in developing zebrafish, including shorter body lengths, tail curvature and defective tail cellularity, craniofacial malformations, pericardial edema, absent and/or compromised vasculature function and flow, depressed heart rates and increased mortality. Conversely, IMM and mDia2 DAD peptides were minimally toxic at concentrations up to 10–20 and 50 μM, respectively. SMIFH2's therapeutic potential may therefore be limited by its substantial in vivo toxicity at functional concentrations. mDia formin agonism with IMMs and mDia2 DADs may therefore be a more effective and less toxic anti-invasive therapeutic approach.

Despite the many years of extensive research using rodent models to study Alzheimer's disease (AD), no cure or disease halting drug exists. An increasing number of people are suffering from the disease and a therapeutic intervention is needed. Therefore, it is necessary to have complementary models to aid in the drug discovery. The zebrafish animal model is emerging as a valuable model for the investigation of AD and neurodegenerative drug discovery. The main genes involved in human AD have homologous counterparts in zebrafish and have conserved function. The basic brain structure of the zebrafish is also conserved when compared to the mammalian brain. Recently an AD model was established by administering okadaic acid to zebrafish. It was used to test the efficacy of a novel drug, lanthionine ketimine-5-ethyl ester, and to elucidate its mechanism of action. This demonstrated the ability of the okadaic acid-induced AD zebrafish model to be implemented in the drug discovery process for therapeutics against AD.