Summary: Anthracycline antibiotics (ANT), such as doxorubicin or daunorubicin, are a class of anticancer drugs that are widely used in oncology. Although highly effective in cancer therapy, their usefulness is greatly limited by their cardiotoxicity. Possible mechanisms of ANT cardiotoxicity include their conversion to secondary alcohol metabolites (i.e. doxorubicinol, daunorubicinol) catalyzed by carbonyl reductases (CBR) and aldo-keto reductases (AKR). These metabolites are suspected to be more cardiotoxic than their parent compounds. Moreover, overexpression of ANT-reducing enzymes (CBR and AKR) are found in many ANT-resistant cancers. The secondary metabolites show decreased cytotoxic properties and are more susceptible to ABC-mediated efflux than their parent compounds; thus, metabolite formation is considered one of the mechanisms of cancer resistance. Inhibitors of CBR and AKR were found to reduce the cardiotoxicity of ANT and the resistance of cancer cells, and therefore are being investigated as prospective cardioprotective and chemosensitizing drug candidates. In this review, the significance of a two-electron reduction of ANT, including daunorubicin, epirubicin, idarubicin, valrubicin, amrubicin, aclarubicin, and especially doxorubicin, is described with respect to toxicity and efficacy of therapy. Additionally, CBR and AKR inhibitors, including monoHER, curcumin, (−)-epigallocatechin gallate, resveratrol, berberine or pixantrone, and their modulating effect on the activity of ANT is characterized and discussed as potential mechanism of action for novel therapeutics in cancer treatment.

Background: The phosphodiesterase 10 (PDE10) family, identified in 1999, is mainly expressed in the brain, particularly in the striatum, within the medium spiny neurons, nucleus accumbens, and olfactory tubercle. Inhibitors of PDE10 (PDE10-Is) are a conceptually rational subject for medicinal chemistry with potential use in the treatment of psychiatric and neurodegenerative diseases. Objective: This review is based on peer-reviewed published articles, and summarizes the cellular and molecular biology of PDE10 as a rational target for psychiatric and neurodegenerative drug discovery. Here, we present the classification of PDE10-Is from a medicinal chemistry point of view across a wide range of different, drug-like chemotypes starting from theophylline and caffeine analogs, papaverine and dimethoxy catechol type PDE10-Is, TP-10, MP-10, MP-10/papaverine/quinazoline series inhibitors, and ending with the newest inhibitors obtained from fragment-based lead discovery (FBLD). The authors have collated recent research on inhibition of PDE10A as a promising therapeutic strategy for psychiatric and neurodegenerative diseases, based on its efficacy in animal models of schizophrenia, Parkinson’s, Huntington’s, and Alzheimer’s diseases. This review also presents pharmacological data on PDE10-Is as possible therapeutics for the treatment of cognitive deficits, obesity and depression. Moreover, it summarizes the current strategies for PDE10-Is drug discovery based on the results of clinical trials. The authors also present the latest studies on crystal structures of PDE10 complexes with novel inhibitors.