Repurposing Antidepressants and Phenothiazine Antipsychotics as Efflux Pump Inhibitors in Cancer and Infectious Diseases.

Multidrug resistance (MDR) is a major obstacle in the therapy of infectious diseases and cancer. One of the major mechanisms of MDR is the overexpression of efflux pumps (EPs) that are responsible for extruding antimicrobial and anticancer agents. EPs have additional roles of detoxification that may aid the development of bacterial infection and the progression of cancer. Therefore, targeting EPs may be an attractive strategy to treat bacterial infections and cancer. The development and discovery of a new drug require a long timeline and may come with high development costs. A potential alternative to reduce the time and costs of drug development is to repurpose already existing drugs. Antidepressants and antipsychotic agents are widely used in clinical practice in the treatment of psychiatric disorders and some somatic diseases. Antidepressants and antipsychotics have demonstrated various beneficial activities that may be utilized in the treatment of infections and cancer. This review aims to provide a brief overview of antibacterial and anticancer effects of selective serotonin reuptake inhibitors (SSRIs), tricyclic antidepressants (TCAs) and phenothiazine antipsychotics, while focusing on EPs. However, it should be noted that the antimicrobial activity of a traditionally non-antibiotic drug may have clinical implications regarding dysbiosis and bacterial MDR.

Low Ciprofloxacin Concentrations Select Multidrug-Resistant Mutants Overproducing Efflux Pumps in Clinical Isolates of Pseudomonas aeruginosa.

Low antibiotic concentrations present in natural environments are a severe and often neglected threat to public health. Even if they are present below their MICs, they may select for antibiotic-resistant pathogens. Notably, the minimal subinhibitory concentrations that select resistant bacteria, and define the respective sub-MIC selective windows, differ between antibiotics. The establishment of these selective concentrations is needed for risk-assessment studies regarding the presence of antibiotics in different habitats. Using short-term evolution experiments in a set of 12 Pseudomonas aeruginosa clinical isolates (including high-risk clones with ubiquitous distribution), we have determined that ciprofloxacin sub-MIC selective windows are strain specific and resistome dependent. Nonetheless, in all cases, clinically relevant multidrug-resistant (MDR) mutants emerged upon exposure to low ciprofloxacin concentrations, with these concentrations being below the levels reported in ciprofloxacin-polluted natural habitats where P. aeruginosa can be present. This feature expands the conditions and habitats where clinically relevant quinolone-resistant mutants can emerge. In addition, we established the lowest concentration threshold beyond which P. aeruginosa, regardless of the strain, becomes resistant to ciprofloxacin. Three days of exposure under this sub-MIC "risk concentration" led to the selection of MDR mutants that displayed resistance mechanisms usually ascribed to high selective pressures, i.e., the overproduction of the efflux pumps MexCD-OprJ and MexEF-OprN. From a One-Health viewpoint, these data stress the transcendent role of low drug concentrations, which can be encountered in natural ecosystems, in aggravating the antibiotic resistance problem, especially when it comes to pathogens of environmental origin. IMPORTANCE It has been established that antibiotic concentrations below MICs can select antibiotic-resistant pathogens, a feature of relevance for analyzing the role of nonclinical ecosystems in antibiotic resistance evolution. The range of concentrations where this selection occurs defines the sub-MIC selective window, whose width depends on the antibiotic. Herein, we have determined the ciprofloxacin sub-MIC selective windows of a set of Pseudomonas aeruginosa clinical isolates (including high-risk clones with worldwide distribution) and established the lowest concentration threshold, notably an amount reported to be present in natural ecosystems, beyond which this pathogen acquires resistance. Importantly, our results show that this ciprofloxacin sub-MIC selects for multidrug-resistant mutants overproducing clinically relevant efflux pumps. From a One-Health angle, this information supports that low antimicrobial concentrations, present in natural environments, may have a relevant role in worsening the antibiotic resistance crisis, particularly regarding pathogens with environmental niches, such as P. aeruginosa.

Antimicrobial, Anticancer and Multidrug-Resistant Reversing Activity of Novel Oxygen-, Sulfur- and Selenoflavones and Bioisosteric Analogues.

Multidrug resistance of cancer cells to cytotoxic drugs still remains a major obstacle to the success of chemotherapy in cancer treatment. The development of new drug candidates which may serve as P-glycoprotein (P-gp) efflux pump inhibitors is a promising strategy. Selenium analogues of natural products, such as flavonoids, offer an interesting motif from the perspective of drug design. Herein, we report the biological evaluation of novel hybrid compounds, bearing both the flavone core (compounds 1-3) or a bioisosteric analogue core (compounds 4-6) and the triflyl functional group against Gram-positive and Gram-negative bacteria, yeasts, nematodes, and human colonic adenocarcinoma cells. Results show that these flavones and analogues of flavones inhibited the activity of multidrug resistance (MDR) efflux pump ABCB1 (P-glycoprotein, P-gp). Moreover, the results of the rhodamine 123 accumulation assay demonstrated a dose-dependent inhibition of the abovementioned efflux pump. Three compounds (4, 5, and 6) exhibited potent inhibitory activity, much stronger than the positive control, verapamil. Thus, these chalcogen bioisosteric analogues of flavones become an interesting class of compounds which could be considered as P-gp efflux pump inhibitors in the therapy of MDR cancer. Moreover, all the compounds served as promising adjuvants in the cancer treatment, since they exhibited the P-gp efflux pump modulating activity.

N-Substituted piperazine derivatives as potential multitarget agents acting on histamine H3 receptor and cancer resistance proteins.

Taking into account that multidrug resistance (MDR) is the main cause for chemotherapeutic failure in cancer treatment, the ability of novel histamine H3 receptor ligands to reverse the cancer MDR was evaluated, using the ABCB1 efflux pump inhibition assay in mouse MDR T-lymphoma cells. The most active compounds displayed significant cytotoxic and antiproliferative effects as well as a very potent MDR efflux pump inhibitory action, 3-5-fold stronger than that of reference inhibitor verapamil. Although these compounds possess weak antagonistic properties against histamine H3 receptors, they are valuable pharmacological tools in the search for novel anticancer molecules. Furthermore, for the most active compounds, an insight into mechanisms of action using either, the luminescent Pgp-Glo™ Assay in vitro or docking studies to human Pgp, was performed.

Novel Inducers of the Expression of Multidrug Efflux Pumps That Trigger Pseudomonas aeruginosa Transient Antibiotic Resistance.

The study of the acquisition of antibiotic resistance (AR) has mainly focused on inherited processes, namely, mutations and acquisition of AR genes. However, inducible, noninheritable AR has received less attention, and most information in this field derives from the study of antibiotics as inducers of their associated resistance mechanisms. Less is known about nonantibiotic compounds or situations that can induce AR during infection. Multidrug resistance efflux pumps are a category of AR determinants characterized by the tight regulation of their expression. Their contribution to acquired AR relies in their overexpression. Here, we analyzed potential inducers of the expression of the chromosomally encoded Pseudomonas aeruginosa clinically relevant efflux pumps, MexCD-OprJ and MexAB-OprM. For this purpose, we developed a set of luxCDABE-based P. aeruginosa biosensor strains, which allows the high-throughput analysis of compounds able to modify the expression of these efflux pumps. Using these strains, we analyzed a set of 240 compounds present in Biolog phenotype microarrays. Several inducers of the expression of the genes that encode these efflux pumps were found. The study focused in dequalinium chloride, procaine, and atropine, compounds that can be found in clinical settings. Using real-time PCR, we confirmed that these compounds indeed induce the expression of the mexCD-oprJ operon. In addition, P. aeruginosa presents lower susceptibility to ciprofloxacin (a MexCD-OprJ substrate) when dequalinium chloride, procaine, or atropine are present. This study emphasizes the need to study compounds that can trigger transient AR during antibiotic treatment, a phenotype difficult to discover using classical susceptibility tests.

Non-antibiotics, Efflux Pumps and Drug Resistance of Gram-negative Rods.

Non-antibiotic medicinal products consist of drugs with diverse activity against bacteria. Many non-antibiotics demonstrate direct anti-bacterial activity against Gram-positive cocci. The activity observed against Gram-negative rods is much lower and non-antibiotics primarily from the following groups: non-steroidal anti-inflammatory drugs, cardiovascular and antidepressant medicinal products demonstrate this activity. It has been shown that the low activity of some non-antibiotics or the absence of activity against Gram-negative rods is related, among other things, to the extrusion of these compounds from bacterial cells by multi-drug resistance efflux pumps. Substrates for the resistance-nodulation-division efflux systems include the following non-antibiotics: salicylate, diclofenac, ibuprofen, mefenamic acid, naproxen, amitriptyline, alendronate sodium, nicergoline, and ticlopidine. In addition, interactions between non-antibiotics and multi-drug resistance efflux pumps have been observed. It has also been revealed that depending on the concentration, salicylate induces expression of multi-drug resistance efflux pumps in Escherichia coli, Salmonella enterica subsp. enterica serotype Typhimurium, and Burkholderia cenocepacia. However, salicylate does not affect the expression of the resistance-nodulation-division efflux systems in Stenotrophomonas maltophilia and Acinetobacter baumannii. Most importantly, there were no effects of medicinal products containing some non-antibiotic active substances, except salicylate, as substrates of multi-drug resistance efflux pumps, on the induction of Gram-negative rod resistance to quinolones.

Selenoesters and selenoanhydrides as novel multidrug resistance reversing agents: A confirmation study in a colon cancer MDR cell line.

Taking into account that multidrug resistance (MDR) is the main cause for chemotherapeutic failure in cancer treatment and as a continuation of our efforts to overcome this problem we report the evaluation of one cyclic selenoanhydride (1) and ten selenoesters (2-11) in MDR human colon adenocarcinoma Colo 320 cell line. The most potent derivatives (1, 9-11) inhibited the ABCB1 efflux pump much stronger than the reference compound verapamil. Particularly, the best one (9) was 4-fold more potent than verapamil at a 10-fold lower concentration. Furthermore, the evaluated derivatives exerted a potent and selective cytotoxic activity. In addition, they were strong apoptosis inducers as the four derivatives triggered apoptotic events in a 64-72% of the examined MDR Colo 320 human adenocarcinoma cells.

Identification of selenocompounds with promising properties to reverse cancer multidrug resistance.

In previous studies, 56 novel selenoesters and one cyclic selenoanhydride with chemopreventive, antiproliferative and cytotoxic activity were described. Herein, the selenoanhydride and selected selenoesters were evaluated for their ability to reverse the cancer multidrug resistance (MDR) using the ABCB1 efflux pump inhibition assay in mouse MDR T-lymphoma cells. Results showed that the selenoanhydride (1) and the selenoesters with ketone terminal fragments (9-11) exerted (1.7-3.6)-fold stronger efflux pump inhibitory action than the reference verapamil. In addition, those four derivatives triggered apoptotic events in more than 80% of the examined MDR mouse cells.