A year-long extended release nanoformulated cabotegravir prodrug.

Long-acting cabotegravir (CAB) extends antiretroviral drug administration from daily to monthly. However, dosing volumes, injection site reactions and health-care oversight are obstacles towards a broad usage. The creation of poloxamer-coated hydrophobic and lipophilic CAB prodrugs with controlled hydrolysis and tissue penetrance can overcome these obstacles. To such ends, fatty acid ester CAB nanocrystal prodrugs with 14, 18 and 22 added carbon chains were encased in biocompatible surfactants named NMCAB, NM2CAB and NM3CAB and tested for drug release, activation, cytotoxicity, antiretroviral activities, pharmacokinetics and biodistribution. Pharmacokinetics studies, performed in mice and rhesus macaques, with the lead 18-carbon ester chain NM2CAB, showed plasma CAB levels above the protein-adjusted 90% inhibitory concentration for up to a year. NM2CAB, compared with NMCAB and NM3CAB, demonstrated a prolonged drug release, plasma circulation time and tissue drug concentrations after a single 45 mg per kg body weight intramuscular injection. These prodrug modifications could substantially improve CAB's effectiveness.

The transition to dolutegravir and other new antiretrovirals in low-income and middle-income countries: what are the issues?

: There are currently approximately 16 million people taking NNRTI-based first-line treatment in low-income and middle-income countries. Most of these patients are using the combination of tenofovir (TDF), lamivudine (3TC) and efavirenz (EFV). The integrase inhibitor dolutegravir (DTG) has shown an improved safety profile compared with EFV in randomized studies. DTG also has a high barrier to development of drug resistance. New co-formulated tablets with TDF/3TC/DTG are being introduced into LMICs, for a median price of $75 per person-year. The prodrug of TDF, tenofovir alafenamide (TAF) is cheaper to manufacture than TDF. A combined pill with TAF/3TC/DTG is also being launched in LMICs, at a similar low price. However, the clinical development programmes for DTG and TAF did not include extensive analysis of several key populations: pregnant women, people with HIV-tuberculosis (TB) coinfection taking rifampicin-based treatment, and treatment-naive or pretreated patients with NRTI drug resistance. An observational study in Botswana has shown an increased risk of neural tube defects when dolutegravir is used in early pregnancy. In LMICs, only 50% of patients have access to regular viral load testing, and genotypic resistance testing is rarely performed. There is currently no clinical data to support switching patients from TDF/3TC/EFV directly to TDF/3TC/DTG if their viral load is either detectable or unknown. New clinical trials and observational studies will be needed to better understand the consequences of this switch of treatment in LMICs. Clinical trials of new antiretrovirals in key populations should be conducted earlier in their development. This will ensure that new treatments can be introduced into LMICs soon after their launch in high-income countries.

Development of a Novel Formulation That Improves Preclinical Bioavailability of Tenofovir Disoproxil Fumarate.

Tenofovir disoproxil fumarate (TDF), the bisphosphonate ester prodrug of tenofovir (TFV), has poor bioavailability due to intestinal degradation and efflux transport. Reformulation using U.S. Food and Drug Administration-approved esterase and efflux inhibitors to increase oral bioavailability could provide lower dose alternatives and reduce costs for patients with HIV in resource-limited settings. Inhibition of mucosal and intracellular esterases was studied in human and rat intestinal extracts (S9), where TDF was protected by the carboxylesterase inhibitor bis-para-nitrophenylphosphate, the ester mix EM1, and the generally recognized-as-safe (GRAS) excipient propylparaben. Permeability studies using Madin-Darby canine kidney and Caco-2 cell monolayers demonstrated that TDF was a substrate for the permeability glycoprotein with permeability glycoprotein inhibitors reducing basolateral to apical transport of TDF. These studies also showed that transport was increased by esterase inhibitors. TDF, TFV, and tenofovir monophosphonate ester transport across Caco-2 monolayers with esterase and efflux inhibitors revealed a maximum 38.7-fold increase in apical to basolateral TDF transport with the potent non-GRAS combination of EM1 and GF120918. Transport was increased 22.8-fold by the GRAS excipients, propylparaben, and d-a-tocopheryl polyethylene glycol 1000 succinate (a vitamin E derivative). TFV pharmacokinetics in rats following oral administration of TDF and GRAS esterase and efflux inhibitors confirmed enhanced bioavailability. Area under the curve increased 1.5- to 2.1-fold with various combinations of parabens and d-a-tocopheryl polyethylene glycol 1000 succinate. This significant inhibition of TDF hydrolysis and efflux in vivo exhibits the potential to safely increase TDF bioavailability in humans.

In vitro screening for molecules that affect virus capsid assembly (and other protein association reactions).

Protein self-assembly is critical for numerous biological processes. Yet, assembly is rarely targeted by therapeutic agents, in part because it is hard to identify molecules that interfere with protein-protein interactions. Here, we describe a simple fluorescence-based screen for self-association and its application to the assembly of hepatitis B virus capsids. These data are analyzed to identify kinetic and thermodynamic effects--both of which are critical for the viral lifecycle and for understanding the mechanism of assembly effectors. Suggestions are made for modification of this protocol so that it can be applied to other self-assembling systems. With manual pipetting, setting up a plate takes about 2 h, the initial reading takes 1 h and the end point reading the following day takes about 5 min.