Gausemycin Antibiotic Family Acts via Ca2+-Dependent Membrane Targeting

We report the molecular mechanism of action of gausemycins and the isolation of new members of the family, gausemycins C (1c), D (1d), E (1e), and F (1f), the minor components of the mixture. To elucidate the mechanism of action of gausemycins, we investigated the antimicrobial activity of the most active compounds, gausemycins A and B, in the presence of Ca2+, other metal ions, and phosphate. Gausemycins require a significantly higher Ca2+ concentration for maximum activity than daptomycin but lower than that required for malacidine and cadasides. Species-specific antimicrobial activity was found upon testing against a wide panel of Gram-positive bacteria. Membranoactivity of gausemycins was demonstrated upon their interactions with model lipid bilayers and micelles. The pore-forming ability was found to be dramatically dependent on the Ca2+ concentration and the membrane lipid composition. An NMR study of gausemycin B in zwitterionic and anionic micelles suggested the putative structure of the gausemycin/membrane complex and revealed the binding of Ca2+ by the macrocyclic domain of the antibiotic.

Gausemycins A,B: Cyclic Lipoglycopeptides from Streptomyces sp.*

We report a novel family of natural lipoglycopeptides produced by Streptomyces sp. INA-Ac-5812. Two major components of the mixture, named gausemycins A and B, were isolated, and their structures were elucidated. The compounds are cyclic peptides with a unique peptide core and several remarkable structural features, including unusual positions of d-amino acids, lack of the Ca²⁺ -binding Asp-X-Asp-Gly (DXDG) motif, tyrosine glycosylation with arabinose, presence of 2-amino-4-hydroxy-4-phenylbutyric acid (Ahpb) and chlorinated kynurenine (ClKyn), and N-acylation of the ornithine side chain. Gausemycins have pronounced activity against Gram-positive bacteria. Mechanistic studies highlight significant differences compared to known glyco- and lipopeptides. Gausemycins exhibit only slight Ca²⁺ -dependence of activity and induce no pore formation at low concentrations. Moreover, there is no detectable accumulation of cell wall biosynthesis precursors under treatment with gausemycins.

[Low-dose accelerated hyperfractionated radiotherapy for local control of chemoresistant Hodgkin's disease (a prospective randomized trial)]

The results are evaluated of the combined treatment of 154 patients with relapsed refractory Hodgkin's disease, which was conducted using standard dosage of conventional chemotherapy. Out of those, 117 with residual lesions were randomized to receive either focal radiotherapy (20-24 Gy) in accelerated hyperfractionation (1.3-1.5 Gy, twice a day, at 5-hr interval) or 38-40 Gy in standard fractionation. Local control persisted in 85-97% of irradiated sites (median follow-up of 24 months), irrespective of irradiation technique. TTD being lowered down to 20-24 Gy due to use of accelerated hyperfractionation, the frequency of late-onset radiation injuries of paramediastinal lung tissue was lower than in standard treatment, with a subsequently lower fraction of patients with stage II fibrosis.