Biophysical Mimicry of Lung Surfactant Protein B by Random Nylon-3 Copolymers

Abstract

Non-natural oligomers have recently shown promise as functional analogues of lung surfactant proteins B and C (SP-B and SP-C), two helical and amphiphilic proteins that are critical for normal respiration. The generation of non-natural mimics of SP-B and SP-C has previously been restricted to step-by-step, sequence-specific synthesis, which results in discrete oligomers that are intended to manifest specific structural attributes. Here we present an alternative approach to SP-B mimicry that is based on sequence-random copolymers containing cationic and lipophilic subunits. These materials, members of the nylon-3 family, are prepared by ring-opening polymerization of β-lactams. The best of the nylon-3 polymers display promising in vitro surfactant activities in a mixed lipid film. Pulsating bubble surfactometry data indicate that films containing the most surface-active polymers attain adsorptive and dynamic-cycling properties that surpass those of discrete peptides intended to mimic SP-B. Attachment of an N-terminal octadecanoyl unit to the nylon-3 copolymers – inspired by the post-translational modifications found in SP-C – affords further improvements by reducing the percent surface area compression to reach low minimum surface tension. Cytotoxic effects of the copolymers are diminished relative to that of an SP-B-derived peptide and a peptoid-based mimic. The current study provides evidence that sequence-random copolymers can mimic the in vitro surface-active behavior of lung surfactant proteins in a mixed lipid film. These findings raise the possibility that random copolymers might be useful for developing a lung surfactant replacement, which is an attractive prospect given that such polymers are easier to prepare than are sequence-specific oligomers.

Functionally Diverse Nylon-3 Copolymers from Readily Accessible β-Lactams

“…3 This synthetic advance allowed us to identify nylon-3 cationic/hydrophobic copolymers that display a variety of interesting biological activities. 4 However, the range of functional groups that can be incorporated into nylon-3 polymers via CSI-derived precursors remains limited. Here we expand the accessible side chain functionality to include carboxylic acids, thiols, hydroxyls and secondary amines, and we show that the resulting copolymers can display a variety of interesting behaviors.…”

“…8 Previously we have been able to place a single thiol group at one terminus of a nylon-3 chain, 4d,9 and we anticipated that β -lactam 10 or 11 would enable us to incorporate multiple thiol groups along the polymeric backbone. These β -lactams displayed little tendency toward homopolymerization, perhaps because of the bulky trityl protecting group.…”

“…4a,c,9,12 We used new β -lactams introduced above to explore the impact of the structure of the cationic subunit on the antibacterial activity of nylon-3 copolymers.…”

Biophysical investigation of the interfacial properties of cationic fluorocarbon/hydrocarbon hybrid surfactant: Mimicking the lung surfactant protein C

“…The molecular structure is decided by considering the structure-function relationship of the real mixture. Both hydrophobic proteins, SP-B and SP-C, are cationic and we propose that the cationic character of the new molecule is critical for the molecular level interaction, leading the similar behavior that is observed in the real mixture [2,21]. For that reason, in this study the molecular level interactions between FHCL and DPPC are presented at first to gain better understanding of the system.…”

“…For example, DPPC can be used as a lung expansion agent but will not be useful to capture all the necessary function. This is the driving force of the most study conducted nowadays to capture the selected properties of the real mixture by utilizing synthetic formulations [14,21]. In the study presented here it is aimed to create an understanding on the selected functions of lung surfactant that are associated with the SP-C protein and making simple connection of these with molecular level interaction of lipids with the designed surfactant molecule.…”