safe, and well tolerated by most patient populations, including those with chronic diseases or 20 immunocompromised status. HCQ is a weak diprotic base that can pass through the lipid cell 21 membrane and preferentially concentrate in acidic cytoplasmic vesicles. HCQ is being 22 studied to prevent and treat coronavirus disease 2019 , possibly via blocking the 23 interactions between virus and angiotensin-converting enzyme-2 (ACE-2) receptor as well as 24 sialic acids receptor and has shown potential in vitro (1, 2) and preliminary clinical results (3, 25 4). As of Jul 8, 2020, a total of 232 studies involves HCQ use among 2478 clinical trials for 26 COVID-19 registered with the clinicaltrials.gov. 27
However, the effective in vivo levels as well as the optimal dosing regimen of HCQ for 28 treating COVID-19 remains unclear. The in vitro EC 50 values (0.72 to 17.31 µM) proposed 29 for optimized dosing regimens are based on extracellular drug concentration (1, 2). A higher 30 lung (intracellular) concentration to predict the in vivo antiviral efficacy was suggested (5). 31
The HCQ concentration (6.7 µg/mL) required to clear 100% of SARS-CoV-2 in vitro might 32 not be achievable with the currently proposed oral dosing regimen of 800 mg HCQ sulfate 33 orally daily, followed by a maintenance dose of 400 mg given daily for 4 days (2, 6). Further, 34 a high cumulative doses of HCQ may raise concerns of systemic toxicity, including cardiotoxicity (7). 36
An alternative strategy is needed to bridge the gap between in vitro and clinical use of a 37 potentially effective agent in the context of COVID-19 pandemic. A drug delivery directly to 38 the respiratory tracts while minimizing the systemic exposure is a desirable alternative (5). In 39 this report, a proof-of-concept study was conducted to evaluate the systemic 40 pharmacokinetics (PK) profiles and tissue distribution following a single dose of inhalable 41 liposomal HCQ in a rat model and compared to that of unformulated HCQ through 42 intravenous (IV) delivery. 43 significantly more HCQ disposition (Fig. 1A) and longer half-life in lung was observed 46 compared to that those of HCQ by either IV or IT administration (37.5 hours vs. 15.2 hours 47 and 17.7 hours for HCQ-IV and HCQ-IT, respectively) (Table 1) . Notably, even at 72 hours 48 post-dose, liposomal HCQ-IT had 77-fold (to HCQ-IV) and 43-fold (to HCQ-IT) higher 49 HCQ concentrations in lung. A single dose of 0.284 mg liposomal HCQ-IT achieved 129.4 50 g/g in C max and 4193.2 h*g/g in AUC 0-72 and showed overall greater lung exposure with 51 29-fold in C max and 35-fold in AUC 0-72 compared to HCQ-IV with normalized dose ( Table  52 2). 53 HCQ pharmacokinetics in blood and heart. With IV administration, HCQ showed 54 similar PK profile and systemic exposures as HCQ-IT in overall, including C max and AUC 55 ( Fig. 1B and Table 1 ). On the contrary, liposomal HCQ-IT showed significantly lower 56 systemic exposure in blood with only around 20% of C max and 74% of AUC 0-72 after 57
normalizing dose compared to HCQ-IV ( Table 2 ). As observed in blood, liposomal HCQ-IT 58 showed significantly lower exposure in the heart from 0.25 hours to 24 hours ( Fig. 1C and 59 Table 1 ). With normalized dose, liposomal HCQ-IT yielded only 24% of C max and 58% of 60 sustained release in the lung was observed by targeted delivery of inhalable liposomal HCQ, 64 suggesting a potential treatment strategy for COVID-19 pulmonary disease. Fan et al. and 65 others have suggested that significantly higher lung (intracellular) concentrations relative to 66 the in vitro EC 50 would be required to achieve in vivo antiviral efficacy SARS-CoV-2 (5, 6). 67
Also, it has been proposed that the prediction of in vivo efficacy should be driven primarily 68 by high lung HCQ concentrations for treatment of viral pneumonia instead of HCQ blood 69 exposure (6). Given the current dosing regimen for oral HCQ is unlikely to produce an 70 antiviral effect, FDA recently revoked the emergency use authorization (EUA) to use HCQ to 71 treat COVID-19 in certain hospitalized patients and WHO also stopped the HCQ arm of the 72 COVID-19 Solidarity Trial. Here our findings supported the feasibility of alternative targeted 73 delivery of HCQ to the lungs with potentially effective antiviral levels while minimizing the 74 systemic exposure. 75
The aerosolized delivery of therapeutic drugs to the lower respiratory tract has been 76 applied for the treatment of various lung infectious and inflammatory disorders. For example, 77 aerosolized HCQ (AHCQ) has been applied in clinical trials for asthma and showed well 78 tolerance without significant toxicity after 21 days of dosing (8). In the current study, it is unformulated HCQ directly to trachea, indicating unformulated HCQ is possibly to be 81 retained in lung only transiently and distributed rapidly from lung to systemic circulation. 82
The results suggest a sustained release formulation of HCQ, like inhalable liposomal HCQ 83 demonstrated here might be able to provide preferentially higher concentrations in the lung 84 than an aerosolized, non-liposomal HCQ formulation. 85
It was demonstrated that the inhalable liposomal formulation could provide efficient 86 aerosolized delivery of liposomal drugs to lung and increase drug exposure in airways and 87 lung with lower doses than used for systemic administration (9). For instance, ARIKAYCE ® , 88 an inhalable liposomal amikacin has been developed and accelerated approved by FDA in 89 2018 for treating Mycobacterium avium complex lung disease (10). As shown in this 90
proof-of-concept study, the inhalable liposomal HCQ did increase exposure in the lung with 91 extended residence time compared to systemically administered HCQ. Notably, the 92 significantly increased lung exposure at normalized dose suggested the lung HCQ 93 concentration with in vivo antiviral efficacy could be achieved at a relatively lower dose of 94 inhalable liposomal HCQ than that of oral regimens with loading dose initiation (11). 95
In addition to prolonging the residence time and increasing the exposure in lung, 96 significantly lower effective dose with less dosing frequency of inhalable liposomal HCQ might also reduce systemic exposure and potential adverse events. One of the well-known 98 side effects of HCQ in the treatment of rheumatological disorders is cardiotoxicity, including 99 abnormal heart rhythms such as QTc interval prolongation and ventricular tachycardia, a 100 dangerously rapid heart rate (12). In recent study, among 84 COVID-19 patients who 101 received HCQ and azithromycin at NYU's Langone Medical Center, 11% of them had 102 prolonged QT intervals to be considered at high risk of arrhythmia (13). The present study 103
showed liposomal HCQ-IT not only reduced systemic exposure but also decreased heart 104 tissue distribution of HCQ compared to HCQ-IV. It suggested inhalable liposomal HCQ at a 105 significantly lower effective dose should possess less cardiotoxicity concerns than 106 conventional oral HCQ tablets. 107
While there is no commercially available aerosolized formulation of HCQ, a recent 108 empirical study of inhaled HCQ aerosols at 4 mg per day over one week found it was well 109 tolerated without significant adverse events (14). This further supports the rationale of 110 applying inhalable liposomal HCQ with direct lung targeting in COVID-19 infection/disease 111 prevention and treatment. 112
A limitation of the current study is that the pharmacokinetics of liposomal HCQ were 113 evaluated in a rat model using IT instillation to mimic the intended inhalation administration. 114 the IT instilled microsprayed-droplets. Furthermore, it is suggested the aerosol-generating 116 procedure (nebulization) on patients with known or suspected COVID-19 should be 117 performed cautiously given that SARS-CoV-2 is highly contagious through the respiratory 118 route 119 (https://www.cdc.gov/coronavirus/2019-ncov/hcp/infection-control-recommendations.html) 120
(15). Therefore, we have developed a disposable closed-loop system connected to the 121 nebulizer to maximize the targeted delivery of inhaled liposomal HCQ while minimize the 122 spreading and contaminating the air and environment (data not shown). 123
In conclusion, this study in a rat model demonstrate the desirable pharmacokinetics of 124 inhalable liposomal HCQ in vivo. It supports the working hypothesis that inhalable liposomal 125 HCQ might serve as a potential treatment option for the delivery of HCQ for COVID-19 126 pulmonary disease by achieving targeted antiviral levels with less frequent dosing and at a 127 relatively lower dose. 128
Company, Ltd., Taiwan. It is composed of HCQ encapsulated in liposomes with mean Blood was collected from jugular veins at scheduled sampling time points into 155 collection tubes with K 2 EDTA as the anticoagulant and stored at -80°C until analysis. After 156 blood draw, each animal was perfused with 2 mM K 2 EDTA/saline solution before lungs and 157 hearts were removed, weighed and stored at -80°C. 158
Bioanalysis and PK calculation. Blood samples were mixed well with acetonitrile with 159 0.1% formic acid for protein precipitation. The supernatant was dried by nitrogen and 160 reconstituted with 30% acetonitrile with 0.1% formic acid containing internal standard (IS) 161 prior to injection into a liquid chromatography-tandem mass spectrometer (LC-MS/MS). 162
For lung and heart samples, tissue/organ was homogenized with 50% methanol with 0.1% 163 formic acid. The tissue/organ homogenate was added with IS and mixed well with acetonitrile with 0.1% formic acid for protein precipitation. The resulting sample solution 165 was mixed well with 0.1% formic acid to final 30% acetonitrile with 0.1% formic acid prior 166 to injection into a LC-MS/MS. 167
Concentrations of HCQ in blood and tissue/organ samples were determined by 168
Sciex Triple Quad 5500. The ACQUITY BEH C18 column (2.1×50 mm) was selected for 170 sample separation with gradient elution consist of 0.1% formic acid in water (mobile phase 171 A) and acetonitrile containing 0.1% formic acid (mobile phase B) at 0.4 mL/min flow rate. 172
Total run time was 4.5 minutes and the column oven was set at 40°C. The mass 173 spectrometer was set up in MRM mode to monitor the transition 336 → 247 for HCQ. The 174 linear range of the assay is 0.5-500 ng/mL, 0.5-500 ng/mL and 20-10,000 ng/mL for blood, 175 heart and lung assay, respectively. PK parameters of HCQ were calculated by a 176 non-compartmental method using Phoenix ® WinNonlin ® (version 8.0). Sparse sampling 177 computation was applied for the calculation of PK parameters in tissue/organ. 178 Statistical Analysis. Two-sample t tests were used to assess differences in concentration 179 between liposomal HCQ-IT and HCQ-IV. P < 0.05 is considered significant. in 0.25 to 4 hours. * P < 0.05; ** P < 0.01; *** P < 0.001; ns P > 0.05 compared to HCQ-I V.