Synergistic Activity of Repurposed Peptide Drug Glatiramer Acetate with Tobramycin against Cystic Fibrosis Pseudomonas aeruginosa

Pseudomonas aeruginosa is the most common pathogen infecting the lungs of people with cystic fibrosis (CF), causing both acute and chronic infections. Intrinsic and acquired antibiotic resistance, coupled with the physical barriers resulting from desiccated CF sputum, allow P. aeruginosa to colonize and persist in spite of antibiotic treatment. As well as the specific difficulties in eradicating P. aeruginosa from CF lungs, P. aeruginosa is also subject to the wider, global issue of antimicrobial resistance. Glatiramer acetate (GA) is a peptide drug, used in the treatment of multiple sclerosis (MS), which has been shown to have moderate antipseudomonal activity. Other antimicrobial peptides (AMPs) have been shown to be antibiotic resistance breakers, potentiating the activities of antibiotics when given in combination, restoring and/or enhancing antibiotic efficacy. Growth, viability, MIC determinations, and synergy analysis showed that GA improved the efficacy of tobramycin (TOB) against reference strains of P. aeruginosa, reducing TOB MICs and synergizing with the aminoglycoside. This was also the case for clinical strains from people with CF. GA significantly reduced the MIC50 of TOB for viable cells from 1.69 mg/L (95% confidence interval [CI], 0.26 to 8.97) to 0.62 mg/L (95% CI, 0.15 to 3.94; P = 0.002) and the MIC90 for viable cells from 7.00 mg/L (95% CI, 1.18 to 26.50) to 2.20 mg/L (95% CI, 0.99 to 15.03; P = 0.001), compared to results with TOB only. Investigation of mechanisms of GA activity showed that GA resulted in significant disruption of outer membranes, depolarization of cytoplasmic membranes, and permeabilization of P. aeruginosa and was the only agent tested (including cationic AMPs) to significantly affect all three mechanisms. IMPORTANCE The antimicrobial resistance crisis urgently requires solutions to the lost efficacy of antibiotics. The repurposing of drugs already in clinical use, with strong safety profiles, as antibiotic adjuvants to restore the efficacy of antibiotics is an important avenue to alleviating the resistance crisis. This research shows that a clinically used drug from outside infection treatment, glatiramer acetate, reduces the concentration of tobramycin required to be effective in treating Pseudomonas aeruginosa, based on analyses of both reference and clinical respiratory isolates from people with cystic fibrosis. The two agents acted synergistically against P. aeruginosa, being more effective combined in vitro than predicted for their combination. As a peptide drug, glatiramer acetate functions similarly to many antimicrobial peptides, interacting with and disrupting the P. aeruginosa cell wall and permeabilizing bacterial cells, thereby allowing tobramycin to work. Our findings demonstrate that glatiramer acetate is a strong candidate for repurposing as an antibiotic resistance breaker of pathogenic P. aeruginosa.

Abstract P5-09-02: Cell culture models to study mechanisms for endocrine resistant breast cancer, new treatment options and new biomarkers

Introduction: Estrogen is the main driver of growth of the majority of breast cancers and many patients benefit from endocrine therapy. However, both innate and acquired resistance is a major problem. In order to study resistance mechanisms and to explore targeted treatment options for endocrine resistant breast cancer, we have developed in vitro cell culture models based on the estrogen receptor (ER) positive and estrogen responsive human breast cancer cell lines MCF-7 and T47D.

Methods: Panels of MCF-7 and T47D sublines with acquired resistant to tamoxifen, fulvestrant and aromatase inhibitors were established by selection of colonies surviving long term treatment. Long-term estrogen deprived (LTED) MCF-7/S9 cells were developed by step-wise serum reduction until transfer to serum-free medium. The endocrine resistant sublines were analysed with respect to expression and function of the ER and the HER system, with respect to response to 195 kinase inhibitors and to second-line endocrine therapy.

Results: ER expression was reduced in tamoxifen and fulvestrant resistant MCF-7 sublines, unchanged in tamoxifen resistant T47D sublines, whereas fulvestrant resistant T47D sublines were ER negative. In general, ER was functional in the resistant MCF-7 cells. Both tamoxifen and fulvestrant resistant MCF-7 sublines expressed increased level of HER1, the activated form of HER3 and activated ERK1/2, whereas HER4 was severely decreased. In fulvestrant resistant T47D sublines, HER1 and HER4 expression were decreased whereas HER2 expression was highly upregulated. The kinase inhibitor screen disclosed HER receptors as common hits in the tamoxifen and fulvestrant resistant MCF-7 sublines. Regarding T47D, c-Src and Aurora were common hits for tamoxifen and fulvestrant resistant sublines. Tamoxifen resistant MCF-7 and T47D sublines were severely growth inhibited by ER knockdown with either siRNA or fulvestrant, but complete growth arrest required combined treatment with e.g ERK1/2 inhibitor. LTED MCF-7 cells were resistant to aromatase inhibitor treatment and sensitive to both tamoxifen and fulvestrant.

Conclusions: In our large panels of MCF-7 and T47D derived endocrine resistant sublines, it was a general finding that ER is the main driver of growth of tamoxifen resistant tumor cells, and also of growth of LTED MCF-7 cells. The ER down modulator fulvestrant inhibited growth of tamoxifen resistant sublines but complete growth arrest required combined treatment with e.g. a kinase inhibitor targeting the activated growth promoting pathways in the resistant cells. In fulvestrant resistant sublines, ER played only a minor role in MCF-7 sublines and no role in T47D sublines. The HER system played a major role in fulvestrant resistant MCF-7 cells, whereas Aurora B and c-Src were new candidate targets for fulvestrant resistant T47D cells. These cell culture models reflect clinical findings and will be available for collaborative studies, e.g. to discover new predictive markers to select targeted therapy for resistant tumors.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-09-02.

Development of intestinal mucosal immunity in fetal life and the first postnatal months

Nine premature infants who were either stillborn or who died shortly after delivery (gestational age, 24-32 wk), eight full-term infants who died during the first 3 postnatal wk, and four infants who died in the postneonatal period were studied by immunohistochemistry for duodenal expression of secretory component (SC) and epithelial HLA class I and II determinants and for the presence of IgA-, IgM-, and IgG-producing immunocytes. Only small amounts of SC appeared before the 29th gestational wk, but thereafter it increased rapidly; 1 wk after birth, SC showed an adult distribution pattern. Epithelial class I was expressed throughout the period investigated, whereas class II (HLA-DR) determinants were absent on the duodenal villi until 1 wk after birth. HLA-DP and -DQ were not expressed by the epithelium. No IgA immunocytes were seen before 1 wk after birth, whereas a few IgM- and IgG-producing cells were present throughout the period studied. The intense epithelial HLA-DR expression from the 2nd postnatal wk, along with SC and the appearance of IgA immunocytes, suggests that the intestinal immune system is modulated in response to environmental factors shortly after birth.