Abstract: Cabotegravir (GSK1265744) is a potent integrase strand transfer inhibitor (INSTI) developed for the treatment and prevention of HIV-1 infection. Formulated as both a daily oral tablet and a long-acting injectable nanosuspension, cabotegravir addresses the critical challenge of daily adherence to antiretroviral therapy. Clinical trials have demonstrated its non-inferiority when co-administered with rilpivirine for HIV maintenance therapy and its superiority over daily oral regimens for pre-exposure prophylaxis (PrEP). While its long pharmacokinetic half-life enables monthly or bi-monthly dosing, it also introduces challenges such as a prolonged pharmacokinetic tail that may risk resistance if therapy is interrupted. This review synthesizes current literature on the pharmacological activity, molecular mechanism, structure-activity relationship, limitations, and future perspectives of cabotegravir in HIV management.
1. Introduction
The advent of highly active antiretroviral therapy (HAART) has drastically improved the lifespan and quality of life for people living with HIV [2]. However, strict adherence to daily oral regimens remains a significant barrier to maintaining viral suppression, preventing drug resistance, and reducing transmission risks [1][2]. To overcome pill fatigue and adherence challenges, long-acting injectable antiretrovirals have emerged as a paradigm-shifting strategy [9].
Cabotegravir (GSK1265744) is a novel, potent integrase strand transfer inhibitor (INSTI) developed for both the treatment and prevention of HIV-1 [1]. Its unique physicochemical properties have enabled its formulation as a long-acting nanosuspension capable of maintaining therapeutic drug concentrations for extended periods following intramuscular or subcutaneous injection [2]. This review explores the pharmacological and clinical profile of cabotegravir, highlighting its role in modern HIV antiretroviral therapy.
2. Pharmacological Activity
Cabotegravir exhibits subnanomolar antiviral activity, with an in vitro half-maximal inhibitory concentration (IC50) of 0.22 to 0.34 nmol/L against HIV-1 strains [1][3]. It is highly protein-bound (>99.8%) to serum albumin, resulting in a protein-adjusted 90% inhibitory concentration (PA-IC90) of 166 ng/mL and a volume of distribution of 12.3 L [1][4]. The drug is primarily metabolized by uridine diphosphate glucuronosyltransferase (UGT) 1A1, with a minor contribution from UGT1A9, and is eliminated mainly in the feces [2][4][13]. It does not significantly induce or inhibit the cytochrome P450 (CYP450) pathway, minimizing the risk of severe drug-drug interactions [2].
Following intramuscular injection of the long-acting nanosuspension, cabotegravir demonstrates an absorption-limited apparent terminal half-life of 21 to 50 days [1][3]. This prolonged half-life is driven by the slow absorption rate of the drug from the nanoparticle depot in the tissue rather than a change in systemic elimination [3]. Clinically, cabotegravir is co-administered with the non-nucleoside reverse transcriptase inhibitor (NNRTI) rilpivirine for HIV treatment. Phase III trials (ATLAS and FLAIR) demonstrated that monthly or bi-monthly injections of cabotegravir and rilpivirine are non-inferior to daily oral standard-of-care regimens in maintaining virologic suppression [4][9]. For pre-exposure prophylaxis (PrEP), the HPTN-083 and HPTN-084 trials showed that long-acting cabotegravir administered every 8 weeks was superior to daily oral tenofovir disoproxil fumarate/emtricitabine (TDF/FTC) in preventing HIV acquisition in diverse populations [5][9].
3. Molecular Mechanism of Action
Cabotegravir functions as an integrase strand transfer inhibitor (INSTI) [2]. It exerts its antiviral effect by binding to the active site of the HIV integrase enzyme, a critical metalloenzyme required for viral replication [4]. By blocking the strand transfer step of viral complementary DNA (cDNA) integration into the host cell genome, cabotegravir effectively halts the HIV replication cycle [1][4]. Its efficacy is closely related to maintaining trough concentrations (Ctrough) above the therapeutic threshold [4].
4. Structure-Activity Relationship (SAR)
Cabotegravir is a carbamoyl pyridone analogue and shares structural similarities with the earlier INSTI, dolutegravir [2][5]. Its chemical structure was specifically optimized to possess a high melting point and very low aqueous solubility (<10 mg/mL) [1][4]. These intrinsic physicochemical properties are essential for its formulation into a sterile, long-acting injectable nanosuspension, where the active drug is milled to a median particle size of 200 nm and suspended at a high concentration (200 mg/mL) [1][3].
From a resistance perspective, cabotegravir possesses a high genetic barrier to resistance. Single coding mutations are generally insufficient to significantly reduce its potency [5]. In vitro studies indicate that moderate to high-level resistance (>100-fold to >1000-fold reduction in susceptibility) requires specific combinations of mutations in the integrase gene, such as T97A/G140S/G148H, with or without E138A [5]. These structural features ensure that cabotegravir remains active against many viral strains, although cross-resistance with other INSTIs can occur if multiple key mutations accumulate [5].
5. Current Limitations
Despite its clinical success, the use of long-acting cabotegravir presents several limitations. The most frequently reported adverse events are injection site reactions (ISRs), including pain, erythema, and nodule formation, which occur in a majority of patients following intramuscular administration [1][3][6]. Additionally, the drug's prolonged pharmacokinetic "tail"—where sub-therapeutic concentrations can remain detectable in plasma for 52 weeks or longer after the final injection—poses a significant risk for the emergence of drug-resistant HIV strains if therapy is discontinued or doses are missed without bridging with oral antiretrovirals [4][5].
Logistical and implementation challenges also exist. The current formulation requires administration via a Z-track intramuscular injection into the gluteal muscle by a healthcare professional, necessitating regular clinic visits [7][9]. Furthermore, while cabotegravir has a low potential for drug-drug interactions, it is a mild inhibitor of the renal transporters OAT1 and OAT3, which may require caution when co-administered with narrow therapeutic index drugs like methotrexate [2][4].
6. Future Perspectives
Future developments aim to streamline the administration and accessibility of long-acting cabotegravir. While initial protocols required a 4-week oral lead-in phase to assess tolerability, recent data suggest that a "direct-to-injection" approach is safe and effective, potentially simplifying treatment initiation [7][9]. Studies are also exploring alternative injection sites, such as the vastus lateralis (thigh muscle), to improve patient convenience and privacy [9].
In the realm of novel combinations, cabotegravir is being investigated alongside broadly neutralizing antibodies (bNAbs), such as VRC07-523LS, to create new long-acting regimens with different mechanisms of action [7]. Furthermore, expanding access to long-acting cabotegravir for PrEP in low- and middle-income countries (LMICs) remains a global health priority, supported by recent World Health Organization (WHO) guidelines advocating for its use in HIV prevention [11][12]. Continued research into implementation strategies, including pharmacy-based administration, will be crucial for maximizing the public health impact of this innovative therapy [9].
