How Molecularly Imprinted Polymers can be Used for Diagnostic and Treatment of Tropical Diseases?

Molecularly imprinted polymers (MIPs) have been widely used in nanomedicine in the last few years. However, their use for diagnostic and treatment of tropical diseases is limited. Through this review, we aim to illustrate how MIPs were used to detect tropical disease and we show that they are not exploited enough in treatment. We finally show how MIPs could be used in the future in the treatment of tropical disease.


Introduction
Over the last two decades, biodegradable polymeric materials for biomedical applications have advanced significantly [1,2]. Biodegradable polymers have emerged as promising materials in therapeutic devices due to their biocompatibility, biodegradability, and minimal toxicity and they have been used for controlled/sustained drug release. As a result, natural or synthetic polymers able to encapsulate drugs is being studied for biomedical applications [3,4].
In this context, very recently molecularly imprinted polymers (MIPs) (Fig. 1) have been used to confer the in vivo targeting properties of nanoparticles [5]. MIPs are synthesized after the polymerization of a functional monomer in the presence of a molecule of interest (template) with a cross-linking agent. Then, the molecule is extracted and the polymer matrix contains tailor-made binding sites, perfectly complementary to the extracted molecule [6].
In contrast to therapeutic antibodies, the synthesis of MIPs is fast, economical and they are physically and chemically stable. Due to these remarkable properties, there is an increased interest concerning the use of MIPs in nanomedicine [7]. For example, MIPs have been employed by Cecchini et al. to target specific cells in Zebrafish embryos and by Koide et al. to inhibit in vivo the action of the human Vascular Endothelial Growth Factor [8]. Piletsky et al. developed an imprinted protein nanoparticle against Epidermal Growth Factor Receptor that can recognize cancer cells and passively deliver a drug [9].
Therapeutic antibodies that disrupt cell-cell adhesion mediated by dysregulated cadherins might be employed to treat cancer: in 2020, Haupt et al. published a solid-phase synthesis using an epitope, resulting in MIP nanoparticles able to selectively bind to cadherins [10]. The synthesized material proved more potent than commercially available antibodies to inhibit cell-cell adhesion and invasion of cancer.
Another potential new application of MIPs that has attracted considerable attention is drug-controlled release [11][12][13]. Although MIPs have not reached the clinical application yet, these materials have an enormous potential for creating satisfactory dosage forms.
However, up to now, no studies have been reported on the use of MIPs in the treatment of tropical diseases. In this review, we discuss the recent development of MIPs for medical applications related to tropical diseases and their improvement for their use in the treatment.

Infectious Diseases Specific to the Tropics
Tropical infectious diseases represent a real public health problem with effects in mortality and morbidity, imposing a heavy economic burden on the affected countries which are the world's poorest populations. The available drugs for many of these diseases are not satisfactory, and for some, there are few or no treatment options at all. That's why there is a huge need for new safe, specific, inexpensive and effective treatments.
The use of MIPs could be the solution to all these challenges. However, their use for diagnostic and treatment of tropical diseases is still limited. Through this review, we aim to illustrate how MIPs were used to detect tropical disease and we show that they are not exploited enough in treatment. This review discusses some of the challenges in developing MIPs to diagnose and treat these diseases and highlights recent progress.

Tropical Diseases (Not Neglected Tropical Diseases)
Tropical diseases are those diseases that occur exclusively in countries located between the Tropic of Cancer and the Tropic of Capricorn. It includes several illnesses that occur mainly in the tropics and subtropical regions (Asia, Central and Latin America, and Africa). The main reasons that infectious diseases spread in such regions are due to environmental, biological and social factors that support high levels of biodiversity of pathogens, vectors, and hosts [14][15][16]. Indeed, in practice, the term is often taken to refer to all diseases, caused by nutritional deficiencies or climatic conditions (such as heat, humidity, and altitude) [17]. The climate, lack of hygiene and difficult access to health care explain the proliferation of tropical diseases in these regions. Mosquitoes or certain flies are responsible of disease transmission. These are by far the most common vectors of disease. Indeed, most often, these insects carry the infectious agent (parasite, bacterium or virus) and then transmit it by subcutaneous blood exchange to humans and animals via their "bite" [18][19][20][21]. Vaccines are not available for any of the diseases, and many do not have cures.

Neglected Tropical Diseases (NTDs)
Neglected tropical diseases (NTDs) are a diverse group of diseases that affect more than a billion people of the world's population mostly in developing countries in tropical and subtropical areas of the world [22]. This group of diseases is intimately linked to poverty. Indeed, they thrive in areas where access to adequate sanitation, clean water and healthcare is limited, and people live in proximity with animals and infectious disease vectors, such as in remote and rural areas, informal settlements or conflict zones [23][24][25].
The NTDs called "neglected" are almost absent from the global health agenda. Even today, when the focus is on Universal Health Coverage, NTDs have very limited resources and are almost ignored by global funding agencies. NTDs are diseases of neglected populations that perpetuate a cycle of poor educational outcomes and limited professional opportunities.
In the early 2000s, the World Health Organization (WHO) had 17 NTDs in its portfolio, a diverse group of communicable diseases caused by a variety of pathogens including bacteria, parasites, helminths, protozoa or viruses and fungi. Since 2016, this list has been expanded with three groups of diseases to currently include 20 NTDs or groups of NTDs [26]. Those new NTDs include mycetoma, chromoblastomycosis and other deep mycoses; scabies and other ectoparasites; and snakebite envenoming ( Table 1).

MIPs Used for the Diagnosis of Tropical Diseases
The growing interest in biosensors from a general point of view is growing by the day and represents a global market of one billion dollars. They have achieved notoriety because of their many advantages. The system is composed of bioreceptors (enzymes, genetic material, antibodies, antigens, cells or tissues) immobilized on a transducer surface that can recognize the specific analyte (Fig. 2). Antibodies are the most commonly used. However, they are expensive, lack stability and their use are limited to physiological conditions. The transducer converts the response of the biological event into a quantifiable and measurable signal.  For most tropical diseases, the best diagnostic methods are costly and time consuming. Biosensors for diagnosing NTDs are therefore of crucial importance [27].
MIP sensors are the result of several researches due to their many advantages including their high affinity and selectivity, ease of preparation or their low costs which will greatly accelerate the diagnosis and consequently the treatment [27]. These materials can be synthesized easily in any laboratory in the world, without any specific equipment. Moreover, they are very stable and not soluble, important for the development of sensors.
In the literature, many researchers are interested in MIP electrochemical biosensors for tropical diseases such as typhoid, leprosy, meningitis but also for the detection of anti-malarial drugs [28][29][30][31]. Let's take as a first example, the case of typhoid, a deadly disease if not diagnosed in time [28]. Harijan et al. have therefore been interested in the development of an epitope (protein sequence) imprinted polymer to detect the typhoid bacterium in a specific way. The epitope sequence was predicted using immunoinformatic tools and the corresponding MIP was prepared by electropolymerization. The developed sensor was verified with unpaired peptides showing remarkable selectivity of the chosen epitope. The results showed that the MIP sensor responded to infected patients and showed no response to healthy patients [28].
The epitope imprinted polymer sensor technology has been developed by other researchers to detect other tropical diseases. Kushwaha et al. looked at the mycobacterium leprae bacterium responsible for leprosy with a sensor similar to the above. The piezoelectric electrochemical MIP film sensor used to detect the epitope of the engineered mycobacterium leprae exhibits excellent detection, with high sensitivity, affinity, stability and rapid recognition of the analyte. In addition, various epitope sequences and proteins were also examined for a MIP coated film showing selective adsorption towards the epitope sequence used in its manufacture.
The sensor showed good selectivity and selective recognition towards real blood samples of blood infected with mycobacterium leprae bacteria [29].
Gupta et al. paid particular attention to neisseria meningitidis, a bacterial pathogen causing bacterial meningitis. Their work aimed to propose a diagnostic tool for the detection of the bacterium using a protein imprinted polymer sensor developed on the gold surface of an electrode. The sensor specifically and selectively detects the protein associated with the epitope offering an easy and efficient diagnosis of this disease (Fig. 3) [30].
These preliminary results on epitope imprinted polymer sensors could open a new step towards reliable and costeffective medical diagnostics for healthcare.
In recent years, biosensing methods have undergone tremendous development offering promising candidates for future diagnostics. In the literature, various bioreceptors and transducers have been used for dengue virus detection [32,33]. The biosensor methods include amperometric, voltametric, impedimetric, potentiometric, nucleic acidbased and antibody-based biosensors [34]. Electrochemistry is one of the most sensitive and simple transduction techniques, allowing the miniaturization of devices. Arshad et al. focused on the molecularly imprinted polymer-based impedimetric sensor [34]. The screen-printed carbon electrode is modified with electrospun polysulfone nanofibers, then coated with dopamine while using NS1 (specific and sensitive biomarker of dengue virus infection) as a template during polymerization. Oxidative self-polymerization of dopamine ( Fig. 4) (2-(3,4-dihydroxyphenyl)ethylamine) on surfaces is a promising method to form thin polymer films by a single deposition process while controlling the film thickness [34].
Self-polymerization at room temperature allows to maintain the exact structure of the NS1 protein and to generate geometrically adapted printed sites for the specific detection of the target analyte. The MIP sensor unsurprisingly showed excellent analytical performance in terms of sensitivity and selectivity [34]. Table 2 summarizes the different monomers used for the fabrication of the MIP sensors mentioned above.
In addition, the applicability of the proposed methods for clinical diagnosis of viruses responsible for tropical diseases have demonstrated high accuracy. The ease and low cost of these MIP sensors allow their application for the detection of other analytes in different fields. Figure 5 shows the evolution of the number of publications related to MIP sensors (in blue) and the combination of MIP sensors for tropical diseases (in orange). It highlights that this theme is not very exploited due to the low number of publications.
It would be interesting to study this subject more closely as it could open new doors in the future concerning the diagnosis and treatment of tropical diseases.

Drug Delivery
The range of systems and approaches that can be used to improve drug delivery is growing and has important implications in the pharmaceutical industry. The development of new materials and technologies has reduced therapeutic side effects through enabled drug encapsulation and targeted delivery, prolonged blood circulation time and sustained or triggered drug delivery [35]. In recent years, MIP-based drug delivery systems have attracted attention because of their ability to improve loading and delivery of drugs and their stability in blood. However, only a few examples of these systems were reported for tropical disease applications (Table 3).
Zhang et al. developed the first synthesis of liquid crystalline molecularly imprinted polymers (LC-MIPs) coated multiwalled carbon nanotubes (MWCNTs) as an oral floating DDS [36]. The synthesis was achieved by functionalising MWCNTs with 9-vinylanthracene firstly, and then polymerization of LC-MIPs was performed on the surface of MWC-NTs using a monomer mixture of methacrylic acid, ethylene glycol dimethacrylate, and 4-methyl phenyl dicyclohexyl ethylene (LC monomer) using levofloxacin (LVF) as a model template (Fig. 6). LVF is a broad spectrum fluoroquinolone antibiotic, used for the treatment of tuberculosis and meningitis in combination with other antibiotics [37,38]. In vitro release experiments demonstrated that the LVF liberation   Juric and his coworkers reported the synthesis of cyclodextrin (CD) supramolecular hydrogels composed of molecularly imprinted with three antibiotics-rifampicin (RM), novobiocin (NB), and vancomycin (VA) [39]. They developed an affinity-based system that utilizes the unique properties of β-CD, a cyclic oligomer with a relatively  This leads to a guest-host complex with the antibiotics through various secondary molecular interactions such as hydrogen bonding, van der Waals bonding, and hydrophobic interactions. RM is used to treat a number of bacterial infections including tuberculosis and leprosy in combination with other antibiotics [40]. They studied the influence on drug loading, release kinetics, and antimicrobial activity. Both molecularly imprinted and non-imprinted CD-based hydrogels were successfully synthesized at room temperature in order to avoid denaturing the antibiotics and therefore the templates (Fig. 7). The delivery and drug loading studies by UV-Vis spectroscopy showed an increase in total drug-loading in its respective template impressed hydrogel without altering the therapeutic release window. Finally, the bioactivity assay confirmed that long-term stability and liberation of incorporated antibiotics was not compromised by molecularly imprinted hydrogels.
Some MIPs respond to environmental stimuli and can provide more controlled drug-delivery processes [41,42]. They have been developed with different external stimuliresponsivities including magnetic [43], pH- [44], thermo-, or/and photoresponsivity [45]. Mao et al. prepared pH-sensitive MIP nanospheres for improving antibacterial activity. They applied molecularly imprinted technology combined with a UV-initiated precipitation polymerization using vancomycin (VA) for the template (Fig. 8) [46]. VA is generally prescribed to combat severe infections caused by Staphylococcus aureus (S. aureus), it is very used for the treatment of hospital infections but also for respiratory infections, meningitis, tissue and skin infections. These MIPs exhibit a higher VA loading capacity, and a slower and long-term VA liberation than the corresponding NIPs. In addition, the MIPs were sensitive to pH values, i.e., a faster release rate and much higher release concentrations when the pH was decreased, which is desirable for suppressing bacterial infections. Furthermore, the VA-loaded MIPs demonstrated much Fig. 7 The preparation of CD supramolecular hydrogels. a Molecular imprinting CD scheme demonstrating how templating could result in geometrically higher affinities than a linear polymer. b Chemical synthesis of CD-Hexamethylene diisocyanate (HDI) networks [39]. Reproduced with permission from Wiley   Fig. 8 Imprinting mechanism for the drug delivery system of MIPs@VA [46]. Reproduced with permission from Elsevier higher antibacterial ratio for more than 90% to S. aureus. These results confirmed that these MIP nanospheres can be promising to achieve specific therapies such as preventing bacterial infections caused by tropical diseases.
Hence, MIPs emerge as a promising drug carrier mainly in the fields of sustained release, controlled release and targeted delivery system based on its distinct advantages. As described in this section, MIPs as drug delivery system applied to tropical diseases are still in its infancy, and more in-depth research needs to be undertaken to develop effective systems.

Biomimetic Nanomedicine
In the last few years, MIPs have been widely used for in vivo capture and neutralization of toxic substances because of their high target-recognition ability and good biocompatibility [47]. Moreover, some MIPs have been developed for their capability of strongly and selectively catching viruses, inhibiting enzymes, or sequestering proteins, which are highly promising as biomimetic nanomedicines [48,49]. To this day, any examples in the literature have been reported related to the use of MIPs to treat a tropical viral infection, but certain existing approaches could be optimized for pathogens found in tropical areas (Table 4).
In order to respond to the ever-increasing demand for new antiviral strategies, Sankarakumar and Tong described the use of MIPs as virus catchers to prevent viral infections [50]. This work successfully demonstrates the application of miniemulsion polymerization to surface imprinting of a model virus. The particles exhibited greater virucidal action than control particles when incubated with the template virus in the absence or presence of host cells E. coli. This work can provide a new application of such imprinted materials as an ideal antiviral agent for effective virus-capture and infection inhibition in tropical disease treatment.
Although not widely studied yet, MIPs may represent promising approaches to improve the diagnosis and treatment of the current Coronavirus Disease of 2019 (COVID-2019) as well as future pandemics [51]. Parisi et al. developed "monoclonal" antibody-based MIPs for recognition and binding to a specific sequence on the SARS-CoV-2 spike protein in order to block his function [52]. Indeed, Xu et al. have found that the spike virus protein has a relevant binding affinity to human angiotensin-converting enzyme 2 (ACE2), which is the corresponding receptor on the human respiratory epithelial cells (Fig. 9). They have obtained promising preliminary results, but further studies are needed. Specifically, these MIPs showed specific and selective binding affinity and detection of the target protein by electrophoresis. They also demonstrated a good hemocompatibility, which is a key requirement for a system designed for intravenous administration. Therefore, the developed MIPs could be potentially used as free-drug therapeutics in the treatment of 2019-nCoV infection as well as tropical infections. Additionally, when loaded with antiviral agents, they could block the virus protein and be used as targeted delivery of the loaded drug.
Owing to their efficiency in biological sensors, MIPs can potentially be employed in nanomedicine. However, as a first step, comprehensive analysis of their interaction with cells and biocompatibility tests must be conducted. Canforetta et al. reported the synthesis of bare and core-shell MIPs and evaluated their toxicity in different cell lines (HaCaT, MEFs, HT1080, and macrophages) and their internalization in cells [53]. They showed that bare and coating MIP nanoparticles are biocompatible and undergo cellular internalization, which is desired for cytoplasmic drug delivery applications. Furthermore, in vitro cytokine release studies demonstrated that macrophages were not activated in the presence of the MIPs. These results suggest that MIPs have great potential for in vivo studies. For example, Hoshino et al. developed MIPs to eliminate melittin (a peptide that is the principal component of bee venom) from the bloodstream of living mice [5]. The MIPs successfully cleared melittin, improving the survival rate of the mice over 24 h and reducing the toxic Precipitation polymerization Formation of a complex between the template and the functional monomers during the pre-polymerization step through noncovalent interactions Free-drug therapeutics in the treatment of 2019-nCoV infection [52] effects of the peptide. They demonstrated the potential of MIP nanoparticles for the selective recognition of molecules in vivo. These considerations highlight the potential of MIPs for in vitro and in vivo uses, and similar studies are likely to be developed in the future years.

Conclusion
Molecular imprinting systems have many promising biomedical applications, especially those requiring selective binding to a target. In this review, we report the most recent applications of MIPs and how this approach can be used as a powerful tool for the diagnosis and treatment of tropical diseases. In diagnosis, MIPs represent a promising sensing element due to its capacity to recognize targeted molecules with a high affinity, its low cost and stability. They are expected to grow rapidly in medical applications. In the future, they could be used directly by the patient who could test himself without any medical assistance which will revolutionize the healthcare industry. Huge progress has been achieved in the development of sensors but there are still several challenges. The most important one is that the sensitivity and selectivity need further improvements. Hence, more functional monomers need to be probed to enhance chemical recognition. However, the use of this approach presents many challenges and remains largely unexplored in the field of tropical diseases. This review should give novel ideas to researchers interested in the detection of tropical diseases as there is still a lot to develop. For the treatment of tropical diseases, few works, using MIPs, have been reported. As MIPs are used in nanomedicine since few years, especially in cancer treatment, its development for tropical diseases is only at an early stage. The main limitation to the use of MIPs in the treatment of tropical disease is mainly due to its biocompatibility. Hence, huge efforts should be devoted to the development of non toxic and biocompatible MIPs [53,56]. Hybrid MIP nanoparticles have emerged as a powerful material for controlled drug delivery because they can release drug by external stimuli. We recently developed an innovative MIP nanomaterial with magnetic delivery enabling active control over drug release using AMF [43,54,55]. Under AMF, the magnetic nanoparticles locally heat and the hydrogen bonding between the drug and the polymer is broken and the drug is released. Based on recent works using MIP or hybrid MIP nanoparticles for controlled drug release, their use for hydroxychloroquine release to treat malaria could be a novel treatment. These innovative MIPs offer the possibility to treat tropical diseases provided that they show any toxicity and are biodegradable. Funding This research received partial funding from ANR-21-CE09-0013, University Cancer Institute (UCI) and Siric Curamus Emergence.
Data availability statement Not applicable.

Conflicts of interest
The authors declare no conflict of interest. Nébéwia Griffete is Editorial Board Member of Chemistry Africa.

Institutional review board statement Not applicable.
Informed consent statement Not applicable. Fig. 9 Schematic representation of the interaction between "monoclonal" antibody-based MIPs and SARS-CoV-2 for the selective recognition and binding of the receptor binding domain (RBD) in order to block the function of the spike protein (Created with BioRender.com the 1st February 2022) [52]