Introduction:: Pulmonary infectious diseases have rapidly gained widespread attention due to the devastating effects and mortality rates of the COVID-19 pandemic. As a result, many new therapeutics are being considered as possible additions to existing treatment regimens for both bacterial and viral lung infections. Unfortunately, many of these drugs exhibit poor pharmacokinetic (PK) properties and are thus cleared from the body too rapidly to be effective [1, 2]. We hypothesize that the incorporation of these therapeutic small molecules in a targeted polymer form, termed a “drugamer,” will improve PK profiles compared to native drugs and enhance efficacy in relevant disease models. To date, we have investigated this hypothesis by synthesizing, characterizing, and implementing drugamer therapy with small molecule payloads assigned to one of three categories for use in the lung: 1. antibiotics for treating bacterial infections, 2. antivirals for treating viral illnesses, and 3. small molecule agonists for stimulating the immune system. Notable outcomes supporting this hypothesis are discussed here.
Materials and Methods:: The three representative categories of drugamer discussed here are as follows: 1. Ciprofloxacin (cipro)-containing drugamers for treatment of bacterial lung infections; 2. Remdesivir (Rdv)-containing drugamers for treatment of COVID-19 and related viral lung infections; and 3. Small molecule agonists for stimulating the immune system. While the synthetic approaches for each drugamer varied depending on solubility of the parent drug, all drugamers contain mannose targeting moieties. Mannose is a water soluble moiety capable of binding the CD 206 receptor on alveolar macrophages, which targets the drugamers to the site of lung infection (Fig. 1). For all studies, animal procedures were conducted in accordance with IACUC approved protocols. Briefly, female C57BL/6 mice (Jackson Labs) were anesthetized with isoflurane. Mice were administered 50 μl intratracheal injections of various drugamers solubilized in PBS using a Penn Century Microsprayer as previously reported [3-5]. At various timepoints, mice were sacrificed by pentobarbital injection. A bronchoalveolar lavage (BAL) procedure was completed on the right lung and the left lung was harvested whole. Blood samples were collected by cardiac puncture. The following outcome measures were obtained: drugamer accumulation in whole lung was measured by IVIS imaging; drugamer and free drug PK profiles in blood, whole lung, and BAL cell pellets were measured by liquid chromatography mass spectroscopy; immune stimulation was measured by performing ELISAs to quantify cytokine secretion in lung cells; and finally, survival curves were generated by monitoring mice multiple times daily for changes in a panel of euthanasia criteria as outlined by the IACUC approved protocol.
Results, Conclusions, and Discussions:: Results: For the first category, cipro-containing drugamers demonstrated significant improvement in drugamer accumulation in the lung by varying mannose targeting moieties by discrete amounts. For the second category of drugamer, those containing antiviral agents for viral infections, we show an improved PK profile of Rdv in the drugamer form compared to the native drug itself when both are intratracheally administered. Finally, in the third category of small molecule immune stimulators, we show a significant increase in IFN-β production when mice are treated with a drugamer containing a small molecule immune agonist (Fig. 2).
Conclusions: Results of drugamers in category 1 show that distribution to target sites can be enhanced by using discrete targeting blocks within a polymer structure. Additionally, results from category 2 show that incorporating therapeutic agents along a polymer backbone targeted to CD 206 improves PK profiles of drugs within the alveolar macrophage. Finally, category 3 results demonstrate the ability of small molecule agonists to remain active when incorporated along a drugamer structure.
Discussions: Each of the aforementioned results highlights an advantage of the drugamer platform and demonstrates the utility of drugamers for therapeutic applications in the indicated area. Further research will expand upon synthetic approaches to achieving such structures and will investigate the efficacy of each drugamer in relevant models of murine lung infection.
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References (Optional): : [1] Guy, R. et al (2020). Science, 368(6493). [2] Singh et al. (2020). Pharmacol Rep, 72(6). [3] Das, D. et al (2017) Mol Pharm, 14(6). [4] Su, F. et al (2018). J. Control Release, 287. [5] Chavas, T. et al (2021). J Control Release, 330.
