Spatiotemporal Synergy

Reverse-engineering co-transport to prevent spatiotemporal decoupling of synergistic antibiotics

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The Problem

Synergistic antibiotic combinations are discovered under idealized conditions: both drugs present simultaneously, at fixed concentrations, in a homogeneous liquid. In the infected lung, none of these assumptions hold. Drugs arrive at different rates, are cleared on different timescales, and must traverse spatially heterogeneous barriers — mucus, biofilm matrix, necrotic tissue — that selectively filter based on physicochemical identity.

The result is spatiotemporal decoupling: two drugs that are synergistic in a test tube may never achieve the overlapping concentrations, at the same place, at the same time, that synergy requires. The combination fails not because the mechanism is wrong, but because the delivery environment uncouples it.

Our Approach

We reframe antimicrobial synergy as a system property — not just a drug-pair attribute — that can be preserved or broken by the transport environment. Our approach has three components:

Schematic of colistin and niclosamide mechanisms of resistance and synergy in Gram-negative bacteria, showing how membrane charge and permeability govern drug fate.
Colistin and niclosamide exploit complementary mechanisms at the Gram-negative membrane, but transport constraints in vivo can uncouple the co-exposure window that synergy requires.

Mapping the co-exposure window. Using physiologically informed in vitro platforms that incorporate realistic mucus barriers, dynamic drug clearance, and spatial heterogeneity, we define the concentration–time window within which synergy is maintained. We showed that for niclosamide–colistin, mucin selectively impairs niclosamide diffusion while colistin passes freely, creating a spatial mismatch that abolishes synergy even when both drugs are administered simultaneously. Removing niclosamide after just two hours — mimicking its rapid pulmonary clearance — eliminated the combination’s advantage entirely.

Mucin selectively impairs niclosamide diffusion while colistin passes freely, demonstrating how standard assays miss barrier-driven spatial decoupling of drug synergy.
Mucin selectively impairs niclosamide diffusion while colistin passes freely — standard synergy assays miss this barrier-driven spatial decoupling entirely.

Engineering particles that enforce co-transport. Once we know what the co-exposure window requires, we design formulations that deliver it. We developed a strategy where colistin serves a dual role: it is both the synergistic antibiotic partner and the surface-active excipient that stabilizes niclosamide microcrystals during antisolvent precipitation. The resulting spray-dried composite particles co-localize both drugs in a single respirable particle — crystalline niclosamide cores embedded in an amorphous colistin shell — achieving excipient-free, high-drug-loading inhalation powders.

Graphical abstract showing colistin-stabilized antisolvent precipitation strategy for engineering niclosamide-colistin composite inhalation powders.
Colistin-stabilized antisolvent precipitation enables engineering of microcrystalline niclosamide into inhalable composite powders — one drug serves simultaneously as the synergistic partner and the crystallization excipient.
Scanning electron micrograph of spray-dried niclosamide-colistin composite particles showing wrinkled, collapsed morphology.
Spray-dried niclosamide–colistin composite particles. The wrinkled, collapsed morphology reflects the interplay between shell formation kinetics and internal solvent evaporation during particle engineering.

Validating in physiologically relevant models. In a murine lung infection model, intratracheal delivery of the co-processed particles reduced pulmonary bacterial burden to levels comparable to systemic ceftazidime — demonstrating that the formulation preserves therapeutic activity when delivered to the lung.

Selected Publications