8.1. Inhibition of ACE2: MLN-4760
Briefly, one of the best candidates to treat COVID-19 patients, but not to prevent viral entry, is the small synthetic molecule MLN-4760 (specific ACE2 inhibitor, also known as C16, GL1001 or ORE1001, [113]) for the following reasons:(1) It has been shown to bind/inhibit ACE2 enzymatic activity even at low/acidic pH (pH 6.5, [115]) typical of hypercapnia (as it might occur in lungs of COVID-19 patients) when human ACE2 activity is maximal [79]; nevertheless, it retains its inhibitory effects on soluble ACE2 bound to spike proteins [24], indicating that it is able to bind and inhibit ACE2 activity regardless ACE2 binding to SARS-CoV-2 particles or to S1 fragments.
(2) No significant adverse effects were described upon its chronic administration neither alone nor in combination with ACE2 activators (while inhibiting their activating effects) nor after inducing functional impairment of ACE2 activity in rodent experiments in vivo [52,117,118,122,183,184] nor in a clinical Phase I trial in humans (http://oreholdings.com/wp-content/uploads/2013/06/09.10.09-425.pdf);
(3) Its administration by different route is well described in rodents and humans. In particular:(a) Chronic administration (about 4 weeks) of C-16/DLM-4760 in combination with ACE2 activating treatments was performed by daily intraperitoneal injection at a dose of 25mg/kg in distilled water (as a solution of 42 mg/mL) or 0.9% sterile saline (as a solution of 84 mg/mL using a 0.5-mL insulin syringe) freshly prepared [52,183,184].
(b) Alternatively, chronic administration (about 8 days) of GL1001/DLM-4760 disodium salt in combination with an ACE2 activating treatment was performed by subcutaneous injection (5mL/kg) containing up to a dose of 300 mg/kg, twice a day, formulated in a vehicle solution [15% 2-hydroxypropyl-β-cyclodextrin (HPBDC)/85% H2O] [122]. Subchronic doses of GL1001 indicate no adverse effects up to 1,000 mg/kg (see [122]).
(c) In humans ORE1001/GL1001/MLN-4760 was already proposed and tested in clinical trials. Its pharmaceutical indication was for digestive tract inflammations (Inflammatory bowel disease, gastritis and colitis) that are correlated with overexpression of ACE2. In a Phase I clinical testing up 14 days dosing, ORE1001 was well tolerated. Subjects received drug (dosing up to 2100 mg) with no side adverse effects reported. In particular, 47 subjects received single-dose from 2.1 to 2100 mg and 24 subjects received 14 day multiple doses from 50 mg to 1800 mg. All doses were well tolerated, with no significant side effects including blood pressure. Pharmacokinetics of orally administered capsules was consistent with once-daily dosing. (http://oreholdings.com/wp-content/uploads/2013/06/09.10.09-425.pdf). 300 mg (active drug) oral capsules were used in a Phase Ib/IIa clinical trial that was, however, abandoned. (https://clinicaltrials.gov/ct2/show/NCT01039597).
(d) Finally, MLN-4760 was also administered (2.5 mg/kg per day) by nasal inhalation for 2–3 days in lung-infected mice by Pseudomonas bacteria [185]. Interestingly, the report underscores the role played by local concentration of molecules (ACE2) in modulating lung inflammation and disease. For these reasons, in diseases involving respiratory tract, like SARS, inhalation treatment is preferable, even for the lower concentration (and hopefully lower toxicity) of MLN-4760 needed for this route of treatment administration.
Different routes of MLN-4760 treatment administration can be pursued depending on the hospital condition/expertise. In this exceptionally critical situation, it could be delivered to critical untreatable patients as a controlled “compassionate use”, in particular by inhalation. However, when, under hypoxic conditions, both arms of the RAS are upregulated, it might have a limited action and, by shifting the balance of ACE/ACE2 ratio in favour of ACE, might be even dangerous. Instead, specific inhibition of ACE2 enzymatic activity might effectively work in preventing the establishment of positive feedback loops in COVID-19 patients who are suffering from mild symptoms of the disease. MLN-4760 is sold by different companies, that, in case it works, could be encouraged to manufacture the molecule, actively contributing to face this global threat. On the other hand, the drug could be also synthesized in University chemistry labs because, to my knowledge, is no longer under patent restriction. MLN-4760, whose clinical development was abandoned after phase I trials (clinical name, ORE1001), is actually an interesting compound that could be useful for all patients in which a specific ACE2 upregulation is proven and associated to different (heart/lung/liver/intestine/kidney/immune system/blood/coagulation, etc.) pathological conditions related to ACE2 pathway downstream events, as it seems to occur in COVID-19 patients. Although in blood of normal subjects sACE2 activity is undetectable because its catalytic activity in human plasma is masked by an endogenous inhibitor [116] and chronic ACE2 activation may be deleterious, some patients might need of sACE2 activity to better face an acute pathological condition, therefore a careful monitoring of clinical parameters should be performed during patient treatment.