22 July 2021
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A biosimilar mucus model to evaluate the diffusion of drugs for more efficient cystic fibrosis therapies
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n
Ionic binding Hydrophobic interaction H-bonding Disulfide bondings-s
s-s
s-s
N
C
Pro-Thr-Ser (PTS) domain Non-PTS region with Von Willebrand domains
O-linked oligosaccharide N-linked oligosaccharide
Cystine rich domain
Cystine knot N-Acetyl-D-neuraminic acid (sialic acid)
Drug able to diffuse through mucus layer Drug subjected to steric barrier
Drug subjected to interactional barrier Drug directly bound to mucin
Drug bound to other mucus components Bacteria
CFTR defect
Normal
airways Airways affectedby cystic fibrosis
A BIOSIMILAR MUCUS MODEL TO EVALUATE THE DIFFUSION OF DRUGS FOR
MORE EFFICIENT CYSTIC FIBROSIS THERAPIES
Cosmin Butnarasu,
aMaura Vallaro,
aDaniela Pacheco,
bPaola Petrini,
bLivia Visai
cand Sonja Visentin
aa
Dipartimento di Biotecnologie Molecolari e Scienze per la Salute, Università degli Studi di Torino, 10125, Italia
b
Dipartimento di Chimica, Materiali e Ingegneria Chimica, Politecnico di Milano, 20133, Italia
c
Dipartimento di Medicina Molecolare, Università degli Studi di Pavia, 27100, Italia
E-mail:
cosminstefan.butnarasu@unito.it
INTRODUCTION
The mucosal surfaces of the human body are covered with a thin mucus layer. From a structural and compositional point of view, mucus is a semi-permeable hydrogel with heterogeneous composition, and its primary function is to protect the underlying epithelium from environmental noxious agents such as air pollutants or bacteria. The barrier properties of mucus are principally due to mucins, which are the mainly expressed glycoproteins within mucus [1].
However, mucus can equally act as a barrier for drug delivery especially in those diseases characterized by mucus hypersecretion with altered chemical and structural features such as bronchial asthma, chronic obstructive pulmonary disease (COPD) and cystic fibrosis (CF).
CF is a chronical life-limiting autosomal recessive pathological condition caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene which encode for a cAMP-regulated epithelial chloride channel (Figure 1, [2-3]). Most of the health problems (pulmonary and gastrointestinal) experienced by CF patients arise from the overproduction of the thick mucus. Even if there is no cure for CF, in the last 4 decades life expectancy of cystic fibrosis patients has improved significantly. The principal treatments involve mucolytics, bronchodilators, anti-inflammatory agents and inhaled antibiotics. Actually, only few mutation-specific drugs (ivacaftor, lumacaftor, tezacaftor) can treat the disease by acting on the underlying defect.
Since mucin is the mainly expressed glycoprotein within mucus, the protein-drug interaction may have an important role on the drug pharmacokinetics as a strong bind with mucin may results in a reduced drug absorption, hence a low drug efficacy. The determination of the extent of the interaction between the dataset drugs with a mucin solution was measured using two spectrophotometric methods. UV-VIS absorption and fluorescence spectra of
mucin upon increasing concentration of drugs were recorded. KA and KD constants were
calculated by using the Stern-Volmer equation (Figure 3).
Alginate/mucin hydrogels were developed taking advantage of the internal crosslinking
mechanism of alginate in the presence of CaCO3. Rheological parameters such as the elastic
or
storage modulus
(G’) and the viscous orloss modulus
(G’’) of the biosimilar mucus werestudied in order to obtain values as similar as possible to the values of the pathological mucus. Stability analysis was also conducted to acquire, using both water and PBS, at 25 ºC, changes on weight percentage and volumetric increase.
AIMS
MUCIN-ANTIMICROBIC DRUGS INTERACTION
MUCUS MODEL
RESULTS
The biosimilar mucus model is a fast and economic tool suitable for high throughput screening purposes indeed, it can be employed on parallel artificial
membrane permeability assays (PAMPA) in order
to evaluate the diffusion of drugs (Figure 5).
KA (M-1 104) KD (M 10-5) Aztreonam 2,26 4,42 Ceftazidime 2,63 3,80 CFTR(inh)-172 4,99 2,00 Levofloxacin 2,78 3,59 Rifampicin - -Tobramycin - -Ampicillin - -REFERENCES
[1] M. Boegh and H. M. Nielsen, “Mucus as a barrier to drug delivery - Understanding and mimicking the barrier properties,” [2] www.organiclifestylemagazine.com/nutritional-support-for-cystic-fibrosis
[3] Robbins Basic Pathology,” 10th Editi., 2018, pp. 250–254.
[4] X. Murgia, B. Loretz, O. Hartwig, M. Hittinger, and C. M. Lehr, “The role of mucus on drug transport and its potential to affect therapeutic outcomes,” [5] https://chemicalize.com
MUCIN + Drug KA MUCIN-Drug
KD
The orally taken systemic drugs must pass through the gastrointestinal mucus barrier, whereas inhaled drugs must pass through airway mucus and their pulmonary deposition to reach their targets. Due to the wide variety of functional groups present in the mucin structure (Figure 2a), many interactions can be established with molecules of hydrophilic as well as hydrophobic nature
[4] and association (KA) and dissociation (KD) can be obtained (Figure 2b).
Therefore, the design of effective cystic fibrosis drugs must take into account the interaction of the potential candidates with mucin, and the diffusion across the mucus layer. The need to characterize drug behavior in a rapid, simple and reproducible manner has urged the development of airway mucus models. In this work, we investigate the affinity of some drugs to mucin and an airway mucus model composed by alginate and mucin, which aim to model both composition and rheological properties of the pathologic CF-mucus, is developed.
(Figure 1)
(Figure 2a)
Pro-Thr-Ser (PTS) domain
Non-PTS region with Von Willebrand domains O-linked oligosaccharide
N-linked oligosaccharide Cystine rich domain
Cystine knot
N-Acetyl-D-neuraminic acid (sialic acid)
!" ! = $%& ' + 1 Stern-Volmer equation 320 360 400 440 480 0.00 0.05 0.10 0.15 0 2×106 4×106 6×106 8×106 1×107 λ (nm) Abs Intensity 300 350 400 450 0 2×106 4×106 6×106 8×106 1×107 λ (nm) Intensity 240 300 360 420 480 0.0 0.2 0.4 0.6 λ (nm) Abs CFTR(inh)-172 0 1×100 2×100 3×100 0.9 1.0 1.1 1.2 1.3 [Ceftazidime] (M) F0 /F Y = 49902*X + 1 FRET Fluorescence
UV-Vis However, the study
of the only mucin-drug interaction is incomplete (Figure 4) Aztreonam Ampicillin Beta-lactam antibiotics Levofloxacin Fluoroquinolone Rifampicin Ansamycin Ceftazidime Cephalosporin Tobramycin Aminoglycoside Inhibitor of CFTR protein (Figure 3)
PAMPA
Mucus gel was dropped off onto the artificial membrane in the donor compartment of the
PAMPA in order to mimic the mucosal surfaces. A defined concentration of drug was added in the donor compartment and after 5 hours the rate of drug diffusion was determined by measuring drug’s concentration in the acceptor compartment.
(Figure 4)
(Figure 5) (Figure 2b)
CONCLUSIONS
(Table 1)
Even though some of the antibiotics herein
investigated (ceftazidime, aztreonam,
levofloxacin) can interact with mucin, the order
of magnitude of KA is quite low (Table 1) while
tobramycin showed no affinity to mucin. All these data could in part explain why these antimicrobial drugs are the most employed antibiotics in CF. The low affinity of the tested drugs could be in part explained by their high hydrophilicity. However, in order to obtain a structure-affinity relationship a broader database should be investigated. Propranolol CFTR Ampicillin Ceftazidime 0 2×10-5 4×10-5 6×10-5 Permeability Mucus free Mucus
Results of PAMPA test
Highly permeable drug
Low permeable drugs
CFTR(inh)-172LevofloxacinCeftazidimeAztreonam
0 2×104 4×104 6×104 Ka 0.94 - 4,0 - 6,2 LogD7.4 - 0.51 (Figure 6)
Ceftazidime, aztreonam, CFTR(inh)-172 and levofloxacin showed to interact with mucin whereas no interaction was detected in presence of rifampicin, tobramycin and ampicillin. The values of association constant are all in the same order of magnitude. Contrary to what was expected, the charge of the molecule seems to play not such a fundamental role upon interaction with mucin, in fact positively charged molecules at pH 7.4, such as tobramycin, have no interaction, whereas negatively charged drugs such as CFTR(inh)-172 or aztreonam can interact. This suggest that the binding to mucin could not be due only to electrostatic interactions but other factors as lipophilicity or H-bonding may play an important role. All the tested drugs have high hydrophilicity, in fact the
values of logD7.4 are all negative (except for CFTR(inh)-172 and rifampicin). CFTR(inh)-172 which has exhibited the higher affinity is also the most hydrophobic at pH 7.4. The biosimilar mucus was
employed also in PAMPA test, and the permeability of some drugs was measured in absence and in presence of mucus. Compared to a highly permeable compound (propranolol) the drugs we tested are low permeable already in absence of mucus and consequently the permeability is less influenced by mucus if compared to propranolol (Figure 6).
