Nanoparticles Incorporating a Fluorescence Turn-on Reporter for Real-Time Drug Release Monitoring, a Chemoenhancer and a Stealth Agent: Poseidon’s Trident against Cancer?

The rate and extent
of drug release under physiological conditions
is a key factor influencing the therapeutic activity of a formulation.
Real-time detection of drug release by conventional pharmacokinetics
approaches is confounded by low sensitivity, particularly in the case
of tissue-targeted novel drug delivery systems, where low concentrations
of the drug reach systemic circulation. We present a novel fluorescence
turn-on platform for real-time monitoring of drug release from nanoparticles
based on reversible fluorescence quenching in fluorescein esters.
Fluorescein-conjugated carbon nanotubes (CNTs) were esterified with
methotrexate in solution and solid phase, followed by supramolecular
functionalization with a chemoenhancer (suramin) or/and a stealth
agent (dextran sulfate). Suramin was found to increase the cytotoxicity
of methotrexate in A549 cells. On the other hand, dextran sulfate
exhibited no effect on cytotoxicity or cellular uptake of CNTs by
A549 cells, while a decrease in cellular uptake of CNTs and cytotoxicity
of methotrexate was observed in macrophages (RAW 264.7 cells). Similar
results were also obtained when CNTs were replaced with graphene.
Docking studies revealed that the conjugates are not internalized
by folate receptors/transporters. Further, docking and molecular dynamics
studies revealed the conjugates do not exhibit affinity toward the
methotrexate target, dihydrofolate reductase. Molecular dynamics studies
also revealed that distinct features of dextran-CNT and suramin-CNT
interactions, characterized by π–π interactions
between CNTs and dextran/suramin. Our study provides a simple, cost-effective,
and scalable method for the synthesis of nanoparticles conferred with
the ability to monitor drug release in real-time. This method could
also be extended to other drugs and other types of nanoparticles.