The Promise of Long-Acting Antiretroviral Therapies: From Need to Manufacture

Abstract

Antiretroviral therapy has transformed human immunodeficiency virus infections from certain death to a manageable chronic disease. Achieving strict adherence to drug regimens that limit toxicities and viral resistance is an achievable goal. Success is defined by halting viral transmission and by continuous viral restriction. A step towards improving treatment outcomes is in long-acting antiretrovirals. While early results remain encouraging there remain opportunities for improvement. These rest, in part, on the required large drug dosing volumes, local injection-site reactions, and frequency of injections. Thus, implantable devices and long-acting parenteral prodrugs have emerged which may provide more effective clinical outcomes. The recent successes in transforming native antiretrovirals into lipophilic and hydrophobic prodrugs stabilized into biocompatible surfactants can positively affect both. Formulating antiretroviral prodrugs demonstrates improvements in cell and tissue targeting, in drug-dosing intervals, and in the administered volumes of nanosuspensions. As such, the newer formulations also hold the potential to suppress viral loads beyond more conventional therapies with the ultimate goal of HIV-1 elimination when combined with other modalities.

Keywords: good manufacturing practices; human immunodeficiency virus type one (HIV-1); implantable devices; long-acting slow effective release antiretroviral therapy; regimen adherence; viral reservoirs.

Figure 1.

Generating long-acting slow effective release antiretroviral therapy (LASER ART). The plates serve to review each of the delivery schemes now either developed or being actively researched for oral, device-linked or parenteral administrations. (A) Schematic illustration of nanoformulated native drug (nanoART) or long acting slow effective release ART (LASER ART) as defined by hydrophobic lipophilic prodrugs. Nanocrystals are developed of ARVs (for example, dolutegravir). Surfactant-stabilized nanocrystals are prepared by high-pressure homogenization or wet milling. Cell-based assays are used to screen drug potency, cytotoxicity, uptake, retention, release and efficacy. The top performing formulations are then moved forward for safety, pharmacokinetic and pharmacodynamics assessments. (B) The prodrug concept and LASER ART nanocrystal formation, particle uptake, intracellular prodrug release and slow hydrolysis to extend the apparent half-life of the drug. The ARVs are modified to improve drug potency, enhance cell membrane permeability and facilitate encapsulation into LASER ART nanocrystals that are rapidly taken up by cells and distributed into lymphoid tissues. (C) Examples of extended release oral ARV formulations in preclinical development include capsules, tablets, thin films and suspensions. The ARVs are embedded in a matrix system that controls drug release. (D) pH sensitive microparticles and devices are being leveraged to control release of ART after oral administration. (E) Subcutaneous implantable devices, vaginal rings, films and gels loaded with ARVs are at various stages of preclinical development to provide sustained release of ART for HIV-1 treatment and prevention.

Figure 2.

Theranostic multimodal nanoparticles predict drug delivery to infectious tissue sites. (A) Theranostic particles are made with multifunctional capabilities for delivery to virus infected, inflamed or after organ injuries. The schematic illustration denoted the surface targeting and internal drug, nucleic acid and or imaging payloads that form the backbone of the nanoparticle. (B) Following parenteral injection biodistribution is seen in each of the listed tissues with preference in HIV-1 infected lymphoid organs, brain and the reticuloendothelial system but not excluding the kidney, bone, muscle, heart and skin amongst others. (C) The multifunctionality of the particles with metal, isotope and fluorescence encasements, particle distribution can be monitored by bioimaging. These include, but are not limited to, single photon emission computed tomography-computerized tomography (SPECT/CT), confocal microscopy and magnetic resonance imaging (MRI) “amongst others” to track biodistributions. (D) Diagnostic and therapeutic payloads contained within the theranostic particles reach their cell and tissue destinations at levels reflecting extent of disease, infection, inflammation or degeneration (in red) then ameliorate the disease process or restrict/eliminate infection. The bioimaging of the particles can then define time, place and drug levels in real time enabling delivery the therapeutics that combat disease events. All together these methods provide real-time particle tracking, biodistribution and treatment of disease (in green).

Figure 3.

Current good manufacturing practices (cGMP). The Nebraska Nanomedicine Production Plant (NNPP) reflects standards set forth by the USA Food and Drug Administration (FDA). The facility is compliant with cGMP guidelines. Formulation development involves standard protocols for preclinical screening, particle purification, a range of stability tests, optimization of nanoparticle production and in-depth characterizations. These are first conducted using good laboratory practices and defined cross observational protocols. When cGMP dictates FDA compliant product scale-up, lyophilization and sterilization. These lead to the production of therapies for human use in clinical trials.

Figure 4.. Developmental testing of prodrug formulations.

Design for chemical modifications of native ARV is forged into go no go “clock” criteria. CAB is given as an example. CAB was first transformed into a lipophilic hydrophobic prodrug. The transformation was screened by prodrug hydrolysis with plasma esterases during timed-incubations. Assessment of half-maximal effective concentration or EC50 reflective of drug potency was made for antiretroviral responses halfway between baseline and maximum based exposures. The native drug and prodrug with or without nanoencasements were tested for uptake, release, retention and antiretroviral activities in primary human CD4+ T cells and macrophages. Bioanalytical testing was conducted that included prodrug stability over time, temperature and pH. Measures of drug and prodrug levels inside and released from cells were performed. In the subsequent evaluation nanoformulated prodrug was subjected to PK testing and tissue biodistribution in rodents then followed by parallel assessments in rhesus macaques. This then proceeded to full GLP guideline testing for product use and considered by a complete drug toxicology profile evaluation as is the pre-clinical PD testing evaluations for pre-exposure prophylaxis. Ongoing works includes serial tittered viral exposure through vaginal or rectal routes. Investigational new drug enabling, FDA approval and GMP production will precede the first in human testing (phase I clinical trial).