Cabotegravir, the Long-Acting Integrase Strand Transfer Inhibitor, Potently Inhibits Human T-Cell Lymphotropic Virus Type 1 Transmission in vitro

Abstract

Human T-cell lymphotropic virus type 1 (HTLV-1) is a deltaretrovirus most prevalent in southwestern Japan, sub-Saharan Africa, Australia, South America, and the Caribbean. Latest figures approximate 10 million people worldwide to be infected with HTLV-1. This is likely a significant underestimation due to lack of screening in endemic areas and absence of seroconversion symptoms. The two primary diseases associated with HTLV-1 infection are adult T cell leukaemia-lymphoma, a malignant and, sometimes, aggressive cancer; and HTLV-1 associated myelopathy/tropical spastic paraparesis, a debilitating neurological degenerative disease. Unfortunately, despite the poor prognosis, there is currently no effective treatment for HTLV-1 infection. We previously showed that integrase strand transfer inhibitors (INSTIs) clinically used for human immunodeficiency virus type 1 (HIV-1) prophylaxis and treatment are also effective against HTLV-1 transmission in vitro. In 2021 a new INSTI, cabotegravir, was approved by the FDA for HIV-1 treatment. We thus set out to evaluate its efficacy against HTLV-1 infection in vitro. Strand transfer assays performed using recombinant HTLV-1 integrase treated with increasing concentrations of cabotegravir, effectively inhibited strand transfer activity, displaying an IC₅₀ of 77.8 ± 22.4 nM. Furthermore, cabotegravir blocked HTLV-1 transmission in tissue culture; we determined an EC₅₀ of 0.56 ± 0.26 nM, similar to bictegravir. Alu-PCR confirmed the block in integration. Thus, there are four INSTIs and one reverse transcriptase inhibitor approved by the FDA for HIV-1 treatment, that potently block HTLV-1 infection in vitro. This should strongly encourage the establishment of a new standard of HTLV-1 treatment - particularly for pre-exposure prophylaxis and prevention of mother-to-child transmission.

Keywords: HTLV-1; INSTI; MTCT; cabotegravir; integrase; pre-exposure prophylaxis; tenofovir disoproxil fumarate.

FIGURE 1

Inhibition of in vitro strand transfer activity of recombinant HTLV-1 IN by CAB. (A) Schematic illustrating the strand-transfer assay. Products of half-site integration co-migrate with open circular forms of DNA; concerted integration linearizes the supercoiled target DNA. (B) Representative gel shown used to quantify IN inhibition by CAB as shown in panel (C). Precipitated DNA samples were analysed on an agarose gel stained with ethidium bromide. Lane 1, negative control: no IN; lane 2: positive control, IN in the absence of drug. Lanes 3–12: in the presence of CAB; lane 3: 200 μM, lane 4: 20 μM, lane 5: 2 μM, lane 6: 634 nM, lane 7: 200 nM, lane 8: 63.4 nM, lane 9: 20 nM, lane 10: 2 nM, lane 11: 200 pM, and lane 12: 20 pM. Migration of DNA species in the gel is indicated on the right of the gel. S.c., supercoiled; o.c., open circular. The 1 kb DNA ladder (NEB, indicated on the left of the gel) was used as a reference. (C) Dose-response curve of CAB calculated based on the amount of concerted integration activity of HTLV-1 IN quantified by densitometry. Averages and standard deviations of three independent replicates are shown.

FIGURE 2

Cabotegravir potently blocks HTLV-1 infection and integration in tissue culture. (A) Infection was quantified by measuring the PVL of INSTI treated cells compared to DMSO treated cells arbitrarily set at 100%. Averages and standard deviations of four independent experiments are shown. (B) Integrated provirus of DMSO and 200 nM CAB (CAB) treated samples was quantified by Alu-qPCR and normalised to ALBUMIN numbers. Values are relative to DMSO control. Average and standard deviations of four independent experiments are shown; ^****p-value < 0.0001.