Gentamicin C2a

Gentamicin is a broad-spectrum aminoglycoside antibiotic widely used to treat life-threatening bacterial infections. The gentamicin C complex consists of gentamicin C1, gentamicin C1a, and epimers gentamicin C2 and gentamicin C2a. At present there is a generally accepted pathway of gentamicin biosynthesis, except for detailed understanding of the epimerization process involving gentamicins C2 and C2a. Here we have investigated the biosynthesis of these epimers. JI-20B-an intermediate in the gentamicin biosynthetic pathway-and its epimer JI-20Ba were generated by in-frame deletion within genP, which encodes a phosphotransferase that catalyzes the first step of 3',4'-bisdehydroxylation in gentamicin biosynthesis. GenB1 and GenB2 are aminotransferases with different substrate specificities and enantioselectivities. JI-20Ba, containing a 6'S chiral amine, a precursor of gentamicin C2a, was synthesized from G418 by GenQ/GenB1 through sequential oxidation/transamination at C-6'. GenQ/GenB2 catalyzed the synthesis of JI-20B, containing a 6'R chiral amine, a precursor of gentamicin C2, from G418. GenB2 catalyzed the epimerization of JI-20Ba/JI-20B and of gentamicins C2a/C2.

Background:Many pediatric cancer centers still use Gentamicin as first line combination treatment in patients with fever and neutropenia. Since 2011, our center has implemented a dosing regimen with 250 mg/m2BSA (max. 10 mg/kg, max. 400 mg) as a single daily infusion according to the German guideline.Patients and methods:In this prospective audit (February 2011 to December 2019), 105 Gentamicin treatment cycles were analyzed in 66 pediatric cancer patients, focusing on adherence to the dosing regimen and the drug monitoring results.Results:Adherence to the dosing regimen was high (89%). In 64% of all cycles, the Cmax(drawn 1 h after the 2nddose) reached the target of 10-20 µg/ml. Cmaxsignificantly correlated with dosing in mg/m2BSA (p=0,007), but not with dosing in mg/kg (p=0,366). Age below 6 years did not influence these results. The Gentamicin Ctrough(drawn 8-10 h after the second dose) was < 2 µg/ml in 93% of all cycles without any dose correlation. None of the patients experienced Gentamicin-associated nephrotoxicity.Discussion and conclusion:This prospective audit of single daily infusion Gentamicin in pediatric cancer patients without impaired renal function elicits the feasibility and safety of the dosing regimen in mg/m2BSA according to the German guideline. Since indications for first-line gentamicin are limited, a multicenter prospective study would be advantageous to confirm these observations.

Gentamicin is a potent broad-spectrum aminoglycoside antibiotic whose use is hampered by ototoxic side-effects. Hospital gentamicin is a mixture of five gentamicin C-subtypes and several impurities of various ranges of nonexact concentrations. We developed a purification strategy enabling assaying of individual C-subtypes and impurities for ototoxicity and antimicrobial activity. We found that C-subtypes displayed broad and potent in vitro antimicrobial activities comparable to the hospital gentamicin mixture. In contrast, they showed different degrees of ototoxicity in cochlear explants, with gentamicin C2b being the least and gentamicin C2 the most ototoxic. Structure-activity relationships identified sites in the C4'-C6' region on ring I that reduced ototoxicity while preserving antimicrobial activity, thus identifying targets for future drug design and mechanisms for hair cell toxicity. Structure-activity relationship data suggested and electrophysiological data showed that the C-subtypes both bind and permeate the hair cell mechanotransducer channel, with the stronger the binding the less ototoxic the compound. Finally, both individual and reformulated mixtures of C-subtypes demonstrated decreased ototoxicity while maintaining antimicrobial activity, thereby serving as a proof-of-concept of drug reformulation to minimizing ototoxicity of gentamicin in patients.