Acinetobacter baumannii is a major nosocomial pathogen which frequently develops multidrug resistance by acquisition of antibiotic resistance genes and overexpression of intrinsic efflux systems, such as the RND efflux pumps AdeABC and AdeIJK. A third RND system was characterized by studying spontaneous mutants BM4663 and BM4664, which were selected in the presence of chloramphenicol and norfloxacin, respectively, from the AdeABC-and AdeIJK-defective derivative A. baumannii BM4652. They exhibited enhanced resistance to fluoroquinolones, tetracycline-tigecycline, chloramphenicol, clindamycin, trimethoprim, sulfamethoxazole, sodium dodecyl sulfate, and dyes such as ethidium bromide, safranin O, and acridine orange. Comparison of transcriptomes of mutants with that of their parental strain, using a microarray technology, demonstrated the overexpression of three genes that encoded an RND efflux system, named AdeFGH. Inactivation of AdeFGH in BM4664 restored an antibiotic susceptibility profile identical to that of BM4652, indicating that AdeFGH was cryptic in BM4652 and responsible for multidrug resistance in its mutants. RNA analysis demonstrated that the three genes were cotranscribed. The adeFGH operon was found in 36 out of 40 A. baumannii clinical isolates, but none of the 22 isolates tested overexpressed the pump genes. Spontaneous MDR mutant BM4684, overexpressing adeFGH, was obtained from clinical isolate BM4587, indicating that adeFGH can be overexpressed in a strain harboring adeABC-adeIJK. An open reading frame, coding a LysR-type transcriptional regulator, named adeL, was located upstream from the adeFGH operon and transcribed in the opposite direction. Mutations in adeL were found in the three adeFGH-overexpressing mutants, suggesting that they were responsible for overexpression of AdeFGH.

Resistance-nodulation-division efflux system AdeIJK contributes to intrinsic resistance to various drug classes in Acinetobacter baumannii. By whole-genome sequencing, we have identified in clinical isolate BM4587 the adeN gene, located 813 kbp upstream from adeIJK, which encodes a TetR transcriptional regulator. In one-step mutant BM4666 overexpressing adeIJK, the deletion of cytosine 582 (C 582 ) in the 3= portion of this gene was responsible for a frameshift mutation resulting in the deletion of the seven C-terminal residues. trans-Complementation of this BM4587 derivative with a plasmid expressing adeN restored antibiotic susceptibility to the host associated with the loss of adeJ overexpression. The inactivation of adeN in BM4587 led to a diminished susceptibility to antibiotics that are substrates for AdeIJK and to a 5-fold increase in adeJ expression. Taken together, these results indicate that AdeN represses AdeIJK expression. Quantitative reverse transcription-PCR (qRT-PCR) demonstrated that AdeN is constitutively expressed in BM4587 and does not regulate its own expression. Deletion of cytosine 582 and a 394-bp deletion of the 3= part of adeN were found in independent one-step adeIJK-overexpressing mutants selected from clinical isolates BM4667 and BM4651, respectively. The corresponding alterations were located in the ␣9 helix, which is known to be involved in dimerization, a process essential for the activity of TetR regulators. The adeN gene was detected in all of the 30 A. baumannii strains tested and in Acinetobacter calcoaceticus, Acinetobacter nosocomialis, and Acinetobacter pittii.

vomiting (25%), and fatigue (23%). Most AEs were Grade (G) 1-2. The G3 treatment-related AEs were rash (6 pts), fatigue (1 pt), decreased appetite (1 pt), dehydration (1 pt), pruritus (1 pt), and face edema (1 pt). In particular, no G3 treatment-related gastrointestinal toxicity or liver enzyme elevation has been reported. To date, 24 ALKþ NSCLC pts treated at doses 200 mg are evaluable for response; partial response (PR) was achieved in 16 pts (67%) and stable disease (SD) in 3 pts (13%). In the crizotinib-naïve pts (n¼8), responses were observed in 6 pts (75%) and SD in 1 pt (13%). In the 12 pts with prior crizotinib but no other ALK TKI, 10 pts (83%) achieved PR and 1 (8%) SD. CNS responses have been observed in both crizotinib naïve and crizotinib resistant pts. The median duration of treatment in the 24 evaluable ALKþ pts is 23.8þ weeks, with the longest being 112þ weeks. Conclusion: X-396 is well-tolerated and induces responses in both crizotinib-naïve and crizotinib-resistant ALKþ NSCLC pts, as well as patients with CNS lesions. Enrollment is ongoing in the expansion cohorts.