AcrB Trimer Stability and Efflux Activity, Insight from Mutagenesis Studies

The multidrug transporter AcrB in Escherichia coli exists and functions as a homo-trimer. The assembly process of obligate membrane protein oligomers, including AcrB, remains poorly understood. In a previous study, we have shown that individual AcrB subunit is capable of folding independently, suggesting that trimerization of AcrB follows a three-stage pathway in which monomers first fold, and then assemble. Here we destabilized the AcrB trimer through mutating a single Pro (P223) in the protruding loop of AcrB, which drastically reduced the protein activity. We replaced P223 separately with five residues, including Ala, Val, Tyr, Asn, and Gly, and found that AcrBP223G was the least active. Detailed characterization of AcrBP223G revealed that the protein existed as a well-folded monomer after purification, but formed a trimer in vivo. The function of the mutant could be partly restored through strengthening the stability of the trimer using an inter-subunit disulfide bond. Our results also suggested that the protruding loop is well structured during AcrB assembly with P223 served as a “wedge” close to the tip to stabilize the AcrB trimer structure. When this wedge is disrupted, the stability of the trimer is reduced, accompanied by a decrease of drug efflux activity

Safety and efficacy of low-dose sirolimus in the PIK3CA-Related Overgrowth Spectrum

Purpose PIK3CA-related overgrowth spectrum (PROS) encompasses a range of debilitating conditions defined by asymmetric overgrowth caused by mosaic activating PIK3CA variants. PIK3CA encodes the p110α catalytic subunit of phosphatidylinositol-3-kinase (PI3K), a critical transducer of growth factor signaling. As mTOR mediates the growth-promoting actions of PI3K, we hypothesized that the mTOR inhibitor sirolimus would slow pathological overgrowth. Methods Thirty-nine participants with PROS and progressive overgrowth were enrolled into open-label studies across three centers, and results were pooled. For the primary outcome, tissue volumes at affected and unaffected sites were measured by dual energy X-ray absorptiometry during 26 weeks of untreated run-in and 26 weeks of sirolimus therapy. Results Thirty participants completed the study. Sirolimus led to a change in mean percentage total tissue volume of –7.2% (SD 16.0, p = 0.04) at affected sites, but not at unaffected sites (+1.7%, SD 11.5, p = 0.48) (n = 23 evaluable). Twenty-eight of 39 (72%) participants had ≥1 adverse event related to sirolimus of which 37% were grade 3 or 4 in severity and 7/39 (18%) participants were withdrawn consequently. Conclusion This study suggests that low-dose sirolimus can modestly reduce overgrowth, but cautions that the side-effect profile is significant, mandating individualized risk–benefit evaluations for sirolimus treatment in PROS

Amongst eligible patients, age and comorbidity do not predict for dose-limiting toxicity from phase I chemotherapy." Cancer Chemotherapy & Pharmacology 65(4

Abstract Background There are no clear predictors clinicians can use to determine who is more likely to experience doselimiting toxicity (DLT) in phase I chemotherapy clinical trials. Many providers are reluctant to refer older adults to phase I trials because of concerns about the development of toxicity. The goal of this study was to identify clinical and nonclinical factors which were associated with the development of DLT in phase I studies. Methods Patients (pts) were included if they were treated at maximally tolerated dose (MTD) and above. Studies were included only if MTD was reached. Data collected included age, comorbidity (Cumulative Illness Rating Score-Geriatrics), labs at enrollment, height, weight, performance status, cancer type, duration of diagnosis, prior treatment, drug level, smoking status, marital status, mean income, percent of population high school educated as determined by ZIP code, and distance to the phase I trial hospital. Those who did and did not have DLT were compared by bivariate and then multivariate analysis. Results A total of 242 charts were reviewed from 24 cytotoxic chemotherapy studies, and 27 diVerent types of cancer were represented. On bivariate analysis, mean age, household income (higher), weight, body surface area, dose of drug, alkaline phosphatase, hemoglobin, and LDH were signiWcantly associated with DLT (P < 0.05). CIRS-G score was not associated with DLT. In multivariate analysis, dose level (P = 0.004) and distance from the phase I trial hospital (P = 0.04) were still signiWcant predictors of DLT. Age did not predict for severity of DLT. Conclusions Age and comorbidity did not predict for development of DLT in phase I chemotherapy trials. Many of these pts were very Wt, with relatively low CIRS-G scores, so the impact of comorbidity may not have been fully evaluated. Several social and clinical factors may predict for development of DLT. A prospective study is being planned to conWrm these results