Assessment of sustained efficacy and resistance emergence under human-simulated exposure of cefiderocol against Acinetobacter baumannii using in vitro chemostat and in vivo murine infection models

Objectives

This study evaluated the sustained kill and potential for resistance development of Acinetobacter baumannii exposed to human-simulated exposure of cefiderocol over 72 h in in vitro and in vivo infection models.

Methods

Seven A. baumannii isolates with cefiderocol MICs of 0.12-2 mg/L were tested. The sustained bactericidal activity compared with the initial inoculum and the resistance appearance over 72 h treatment were evaluated in both an in vitro chemostat and an in vivo murine thigh infection model under the human-simulated exposure of cefiderocol (2 g every 8 h as 3 h infusion).

Results

In the in vitro model, regrowth was observed against all seven tested isolates and resistance emergence (>2 dilution MIC increase) was observed in five test isolates. Conversely, sustained killing over 72 h and no resistance emergence were observed in six of seven tested isolates in vivo. The mechanism of one resistant isolate that appeared only in the in vitro chemostat studies was a mutation in the tonB-exbB-exbD region, which contributes to the energy transduction on the iron transporters. The resistance acquisition mechanisms of other isolates have not been identified.

Conclusions

The discrepancy in the sustained efficacy and resistance emergence between in vitro and in vivo models was observed for A. baumannii. Although the resistance mechanisms in vitro have not been fully identified, sustained efficacy without resistance emergence was observed in vivo for six of seven isolates. These studies reveal the in vivo bactericidal activity and the low potential for development of resistance among A. baumannii evaluated under human-simulated exposures.

Escherichia coli strains possessing a four amino acid YRIN insertion in PBP3 identified as part of the SIDERO-WT-2014 surveillance study

Background

In addition to carbapenemases, dissemination of recently reported Escherichia coli lineages possessing a four amino acid insertion in PBP3 (encoded by ftsI) that confers reduced susceptibility to PBP3-targeted β-lactams, such as ceftazidime, can pose a threat of antimicrobial resistance.

Objectives

To evaluate genotypic and phenotypic characteristics of E. coli possessing the mutated PBP3 collected during SIDERO-WT-2014 surveillance.

Methods

A subset of 65 E. coli clinical isolates with MICs ≥2 mg/L for ceftazidime/avibactam, ceftolozane/tazobactam or cefiderocol, among a total of 1529 isolates from the multinational surveillance study, were subjected to gene analysis and antimicrobial susceptibility testing. Isogenic PBP3 mutants were constructed to confirm experimentally an impact on antimicrobial susceptibility.

Results

Eleven strains possessing a YRIN-inserted PBP3 were identified, consisting of nine strains collected from the same hospital in Turkey (ST1284) and one each from the USA and Italy (ST361). Strains associated with each ST lineage possessed similar genetic backgrounds including β-lactamase genotypes; all nine strains from Turkey carried CMY-42, OXA-1 and the OXA-181 carbapenemase (five strains additionally carried CTX-M-15 ESBL), whereas the two other strains carried CMY-42 and TEM-1, indicating dissemination driven by selective pressure. The presence of the YRIN insertion contributed to reduced susceptibility to aztreonam, ceftazidime, cefepime and ceftolozane/tazobactam, although the strains remained susceptible to ceftazidime/avibactam despite relatively high MICs.

Conclusions

E. coli strains of both ST1284 and ST361 lineages, possessing YRIN-inserted PBP3, are disseminating in several regions. The YRIN insertion in PBP3 occurred with multiple β-lactamases, which indicates frequent cross-resistance to other β-lactams.

Reduced susceptibility mechanism to cefiderocol, a siderophore cephalosporin, among clinical isolates from a global surveillance programme (SIDERO-WT-2014)

OBJECTIVE

To investigate possible mechanistic factors to explain cefiderocol (CFDC) non-susceptibility, we characterized 38 clinical isolates with a CFDC minimum inhibitory concentration (MIC) of >4μg/mL from a multi-national surveillance study.

METHODS

The MIC measurement in the presence of β-lactamase inhibitors and whole genome sequencing were performed.

RESULTS

The MIC decrease of CFDC by β-lactamase inhibitors was observed against all of the test isolates. Among the 38 isolates, NDM and PER genes were observed in 5 and 25 isolates, respectively. No other β-lactamases responsible for high MIC were identified in the other eight isolates. The MIC of CDFC against Escherichia coli isogenic strains introduced with NDM and PER β-lactamase increased by ≥16-fold, suggesting the contribution of NDM and PER to the non-susceptibility to CFDC. Against NDM producers, a ≥8-fold MIC increase was observed only when both serine- and metallo-type β-lactamase inhibitors were added. In addition, many of the PER or NDM producers remained susceptible to CFDC. These results suggested that the presence of only NDM or PER would not lead to non-susceptibility to CFDC and that multiple factors would be related to CFDC resistance.

CONCLUSION

Multiple factors including NDM and PER could be related to reduced susceptibility to CFDC.

Abstract 372: VGF is functionally responsible for chemotherapy resistance in non-small cell lung cancer

Despite the success of immune checkpoint therapy, most non-small cell lung cancer (NSCLC) patients still receive conventional chemotherapy. Overcoming chemotherapy resistance by identifying specific targets should improve cancer treatment and patient survival. In this study, we examined a prospective chemotherapy-resistant subpopulation in NCI-H1975 NSCLC cells and identified a novel target, neurosecretory protein VGF (VGF). Using flow cytometry, we first analyzed the expression profile of cancer stem cell markers in 100 cancer cell lines and found that NCI-H1975 cells could be divided into three subpopulations, CD44-low (CD44-L), CD44-middle (CD44-M) and CD44-high cells based on the expression pattern of CD44. CD44-M cells account for less than 5% of the NCI-H1975 cells under normal conditions, but only this subpopulation can proliferate in vitro and in vivo after treatment with cytotoxic agents, such as paclitaxel, pemetrexed and 5-fluorouracil. Affymetrix microarray analysis revealed that VGF is specifically expressed in CD44-M cells and we hypothesized that VGF would play a critical role in chemotherapy resistance. We next employed patient-derived xenograft (PDX) models of NSCLC to confirm this hypothesis with human clinical samples. NOD/SCID mice were subcutaneously transplanted with PDX and treated with either vehicle or paclitaxel (12 mg/kg, Q3Dx3, i.v.). VGF immunohistochemistry on resected PDX revealed that the number of VGF-expressing cells increased 5.6-fold in the paclitaxel-treated group compared to the vehicle control. We also performed VGF immunohistochemistry on NSCLC surgical specimens which were obtained from 127 patients, consisting of 42 neoadjuvant chemotherapy treated cases and 85 non-treated cases. The frequency of VGF-expressing specimens was higher in neoadjuvant chemotherapy treated cases (50%) than non-treated cases (18%). These results suggest that VGF-expressing tumor subpopulation is paclitaxel-resistant even in clinical settings. We also analyzed the molecular functions of VGF. Knockdown of VGF expression by siRNAs could signifıcantly suppress paclitaxel resistance in CD44-M cells. On the other hand, overexpression of VGF could significantly induce paclitaxel resistance in CD44-L cells. These results suggest that VGF is functionally responsible for chemotherapy resistance in NSCLC patients and combined administration of an anti-VGF drug and chemotherapy could be effective for preventing cancer recurrence and prolonging cancer free survival.

Citation Format: Wataru Nogami, Yumi Tona, Soichi Tofukuji, Yoshino Ishioka, Mitsunobu Matsumoto, Hajime Yamada, Kenji Kuwabara, Hidekazu Tanaka, Shigeki Adachi, Yoko Yamamoto, Ryu Kanzaki, Soichiro Funaki, Yasushi Shintani, Meinoshin Okumura, Taisei Nomura. VGF is functionally responsible for chemotherapy resistance in non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 372.

696. Mechanism of Cefiderocol high MIC mutants obtained in non-clinical FoR studies

Background

Cefiderocol (S-649266, CFDC) is a novel siderophore cephalosporin with activity against a wide variety of Gram-negative bacteria including carbapenem-resistant strains. We previously reported that CFDC is efficiently transported into Pseudomonas aeruginosa via iron transporter PiuA. In this study, we examined frequency of resistance of P. aeruginosa to CFDC, and investigated the resistance mechanisms of appeared colonies.

Methods

Frequency of resistance (FoR) was determined by plating an overnight culture of P. aeruginosa PAO1 on Mueller–Hinton Agar containing 4× or 10×MIC of CFDC or ceftazidime (CAZ). Appeared colonies were analyzed by whole-genome sequencing (WGS) to identify genomic mutations. The mRNA expression was determined by real-time RT-PCR, and pyoverdine production was determined by MALDI-TOF/MS and expression of outer membrane protein was analyzed by SDS–PAGE and proteomic analysis.

Results

The FoR to CFDC was 2.9 × 10^–8 and <7.1 × 10^–8, which were lower than those to CAZ (3.1 × 10^–7 and 3.4 × 10^–8) in the conditions of 4× and 10×MIC, respectively. MIC of CFDC against CFDC-derived mutant increased from 0.5 μg/mL (MIC against PAO1) to 2 μg/mL, and MICs of CAZ did not increase. In the case of CAZ-derived mutant, MICs of CAZ increased from 1 μg/mL (MIC against PAO1) to 16 μg/mL or higher, though MIC of CFDC did not increase, suggesting no cross-resistance between CFDC and CAZ. WGS identified mutations in upstream regions of pvdS (pvdS mutant), which regulates pyoverdine synthesis, or fecI (fecI mutant), which regulates the synthesis of iron transporter FecA contributing to the transport of iron citrate. The pvdS expression and pyoverdine production in the pvdS mutant were more than 4- and 6-fold higher than those in PAO1, respectively. The expression of fecA in the fecI mutant was more than ninefold higher than that in PAO1.

Conclusion

The MIC increase of CFDC against P. aeruginosa occurred due to the mutation of iron transporter-related genes. The resistance acquisition risks should be low as the frequency of resistance to CFDC was lower and the MIC increase of CFDC against the mutants was smaller than that of CAZ. In addition, no cross-resistance between CFDC and CAZ was observed.

Disclosures

A. Ito, Shionogi & Co., Ltd.: Employee, Salary. T. Nishikawa, Shionogi & Co., Ltd.: Employee, Salary. R. Ishii, Shionogi & Co., Ltd.: Employee, Salary. M. Kuroiwa, Shionogi & Co., Ltd.: Employee, Salary. Y. Ishioka, Shionogi & Co., Ltd.: Employee, Salary. N. Kurihara, Shionogi & Co., Ltd.: Employee, Salary. I. Sakikawa, Shionogi & Co., Ltd.: Employee, Salary. T. Ota, Shionogi & Co., Ltd.: Employee, Salary. M. Rokushima, Shionogi & Co., Ltd.: Employee, Salary. M. Tsuji, SHIONOGI & CO., LTD.: Employee, Salary. T. Sato, SHIONOGI & CO., LTD.: Employee, Salary. Y. Yamano, SHIONOGI & CO., LTD.: Employee, Salary.