Precluding the progression of metastasis with early diagnosis of triple-negative breast cancer remains challenging due to lack of targeting specificity with poor diagnostic potential. Herein, an amphipathic chitosan-based targeted nanomicellar theranostics (30-45 nm) comprising doxorubicin-superparamagnetic iron oxide nanoparticles complexes (89.23%) with lower critical micelle concentration (0.1 μg/mL) were developed. Micelles exhibit concentration-based contrast enhancement in MRI (r2 6.27 mM s) and hyperthermia rather than thermal-ablation. This theranostics delivers doxorubicin under alternating magnetic field (480 kHz) and at endosomal pH (pH 5.2) while showing stability at pH 7.4. Anti-αβ integrin antibody conjugation onto PEGylated micelles (62.3%) enhances micellar internalization into drug-resistant MDA-MB-231 after 1 h and magnetizes the cells after 6 h over that with nonconjugated micelles. Immigration of MDA-MB-231 and 4T1 cells retards after 24 h, while significant reduction of mitochondrial membrane potential is observed under hyperthermia. Intratumoral administration of nanomicelles in 4T1 orthotopic spontaneous metastasis model demonstrated antitumor and fibrosis mediated caging effect with simultaneous enhancement of MRI-T contrast.

Antibiotics like colistin are the last resort to deal with infections by carbapenem-resistant Enterobacteriaceae (CREB). Resistance to colistin severely restricts therapeutic options. To tackle this dire situation, urgent measures to restore colistin sensitivity are needed. in this study, whole-genome sequencing of colistin-resistant E. coli strain was performed and the genome analysis revealed that the strain belonged to the sequence type ST405. Multiple mutations were observed in genes implicated in colistin resistance, especially those related to the L-Ara-4-N pathway but mgrB was unmutated and mcr1-9 genes were missing. MarR inhibitor salicylate was used to re-sensitize this strain to colistin, which increased the negative charge on the cell surface especially in colistin resistant E. coli (U3790 strain) and thereby facilitated a decrease in colistin MIC by 8 fold. It is indeed well known that MarR inhibition by salicylate triggers the expression of AcrAB efflux pumps through MarA. So, in order to fully restore colistin sensitivity, a potent efflux pump inhibitor (BC1), identified earlier by this group was employed. The combination of colistin with both salicylate and BC1 caused a remarkable 6 log reduction in cell counts of U3790 in time-kill assay. Infection of muscle tissue of zebrafish with U3790 followed by various treatments showed that the combination of colistin + salicylate + BC1 was highly effective in reducing bioburden in infected muscle tissue by 4 log fold. Thus, our study shows that a combination of MarR inhibitor to enhance colistin binding and efflux pump inhibitor to reduce colistin extrusion was highly effective in restoring colistin sensitivity in colistin-resistant clinical isolate of E. coli in vitro and in vivo. Antimicrobial resistance (AMR) poses a grave threat to public health and is attributed as the third major cause of mortality worldwide. Rise in infections caused by multidrug-resistant (MDR) pathogens prompted WHO to declare a list of 12 priority AMR pathogens in 2017, of which, carbapenem-resistant Enterobacteriaceae (Escherichia coli, Klebsiella spp, Serratia spp, Proteus spp) fall under critical priority group 1. Due to rising AMR menace, new antimicrobial agents or resistance modulatory agents to curtail AMR are urgently required. Recently, WHO has released its first report on AMR surveillance, which reveals an alarming trend of widespread dissemination of resistant traits among microbes globally, wherein resistance to commonly used antibiotics were found to range from 0-82% 2. Carbapenem-resistant Enterobacteriaceae (CREB) is becoming resistant to almost all antibiotics and its clinical outcomes are also poor 3,4. Among Enterobacteriaceae, Escherichia coli tops the list in causing a wide range of clinical infections due to their high prevalence, multidrug resistance and most importantly, rapid acquisition/ transfer of resistance traits by horizontal gene transfer 5,6. Colistin is a drug of last resort for CREBs 7. Colistin resistance implies a pan drug resistant state, with...

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Colistin resistance in Enterobacteriaceae especially Klebsiella pneumoniae and Escherichia coli is driving the evolution of pan drug resistant strains. Screening a library of 13 plant nutraceuticals led to the identification of acetyl shikonin and ursolic acid, which exhibited synergy with colistin against extremely drug resistant (XDR) clinical strains of E. coli (U3790) and K. pneumoniae (BC936). Ursolic acid caused a significant colistin MIC reversal of 16-fold in U3790 and 4-fold in BC936 strains. Ursolic acid also potentiated the bactericidal effect of colistin against both U3790 and BC936 by causing ~ 4 to 4.5 log fold decline in CFU of both clinical isolates in a time kill assay. At 2× minimum effective concentration, ursolic acid was non-toxic to zebrafish as evidenced by brain and liver enzyme profiles and by histopathology studies. In combination with colistin, ursolic acid reduced bacterial bioburden of U3790/BC936 by 1–1.58 log fold from the infected muscle tissue of zebrafish. Mechanistic explorations via studies on real time efflux, membrane potential and intracellular accumulation of dansyl chloride tagged colistin revealed that colistin efflux is inhibited by ursolic acid. In addition, ursolic acid also enhanced outer membrane permeability which probably facilitates colistin’s attack on outer and inner membranes. Our study shows that ursolic acid synergizes with colistin by inhibiting colistin efflux in Enterobacteriaceae that helps to curtail colistin resistant Enterobacteriaceae . Electronic supplementary material The online version of this article (10.1186/s13568-019-0750-4) contains supplementary material, which is available to authorized users.

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