No abstract

Overexpression of P‐glycoprotein (P‐gp) contributes to the multidrug resistance (MDR) phenotype found in many cancer cells. P‐gp has been identified as a promising molecular target, although attempts to find successful therapies to counteract its function as a drug efflux pump have largely failed to date. Apart from its role in drug efflux, P‐gp may have other cellular functions such as being involved in apoptosis, and is found in various locations in the cell. Its expression is highly regulated, namely by microRNAs (miRNAs or miRs). In addition, P‐gp may regulate the expression of miRs in the cell. Furthermore, both P‐gp and miRs may be found in microvesicles or exosomes and may be transported to neighboring, drug‐sensitive cells. Here, we review this current issue together with recent evidence of this network of interactions between P‐gp and miRs.

No abstract

Mitoxantrone (MTX) is a pharmaceutical drug used in the treatment of several cancers and refractory multiple sclerosis (MS). Despite its therapeutic value, adverse effects may be severe, namely the frequently reported cardiotoxicity, whose mechanisms need further research. This work aimed to assess if inflammation or oxidative stress-related pathways participate in the cardiotoxicity of MTX, using the mouse as an animal model, at two different age periods (infant or adult mice) using two therapeutic relevant cumulative doses. Histopathology findings showed that MTX caused higher cardiac toxicity in adults. In MTX-treated adults, at the highest dose, noradrenaline cardiac levels decreased, whereas at the lowest cumulative dose, protein carbonylation increased and the expression of nuclear factor kappa B (NF-κB) p65 subunit and of M1 macrophage marker increased. Moreover, MTX-treated adult mice had enhanced expression of NF-κB p52 and tumour necrosis factor (TNF-α), while decreasing interleukin-6 (IL-6). Moreover, while catalase expression significantly increased in both adult and infant mice treated with the lowest MTX cumulative dose, the expression of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and glutathione peroxidase only significantly increased in infant animals. Nevertheless, the ratio of GAPDH to ATP synthase subunit beta decreased in adult animals. In conclusion, clinically relevant doses of MTX caused dissimilar responses in adult and infant mice, being that inflammation may be an important trigger to MTX-induced cardiotoxicity.

Curcumin (1) is a secondary metabolite of turmeric, derived from Curcuma longa L. and was shown to have many biological activities. One of the most interesting properties of curcumin (1) is the antitumour activity allied with the ability to act as a multidrug resistance (MDR) modulator. Several curcumin derivatives have been synthesized with the purpose of discovering more information about the mechanisms of action, to establish structure-activity relationships (SAR), and to overcome pharmacokinetic problems. Over the past few decades, more potent and more stable curcumin derivatives have emerged with potential as drug candidates. Some important SAR studies pointed out that the unstable α,β-unsaturated diketone linker present in curcumin (1) may not be necessary for the antitumour activity; generally, shorter linkers result in more potent compounds than curcumin (1); the type of substituents and their substitution pattern are crucial regarding the biological activities of interest. Overall, the structure of curcumin (1) may represent an important basis for the development of more effective therapeutic agents, particularly in chemotherapy, as reflected by ongoing clinical trials. This article aims to review the synthesis and biological activities of curcumin (1) and derivatives, highlighting the MDR modulation properties of curcumin (1), since these effects makes this natural product a promising lead compound for the development of new anticancer drugs.