European Journal of Pharmaceutics and Biopharmaceutics
Research paperDevelopment of a long-acting injectable formulation with nanoparticles of rilpivirine (TMC278) for HIV treatment
Introduction
In spite of major progress made in the past decade to inhibit the replication of HIV-1, thereby preventing the clinical presentation of AIDS, none of the currently available treatments for HIV infection can cure the infection [1], [2]. Also HAART, or highly active antiretroviral therapy consisting of at least three antiretroviral drugs, may fail following the development of viral resistance. Factors contributing to the incomplete suppression of HIV and to the development of resistance include insufficient drug potency, non-compliance, restricted tissue penetration, drug resistance and several host factors, such as host genetics [3], [4], [5], [6], [7]. Compliance during a life-long treatment is crucial, as establishing minimal inhibitory drug concentrations in the blood inhibits viral growth and the development of resistant strains [3], [5], [8], [9], [10].
A long-acting formulation of anti-HIV medication that generates sustained effective inhibitory concentrations with infrequent dosing may improve adherence to therapy. Next to facilitating maintenance of viral suppression following traditional anti-HIV therapy, a long-acting formulation, may serve as a practical opportunity for pre-exposure prophylaxis.
Long-acting formulations are well-accepted approaches for contraception and to treat psychiatric disorders [11], [12]. Most long-acting formulations are based on the active ingredient being incorporated in either an oil-based solution or suspension (such as haloperidol depot formulations), a microfine watery suspension (such as steroid depots) or a suitable matrix from which the active ingredient is slowly released (Risperidone Consta®) [11], [12]. The advent of nanotechnology, using suspensions of drug particles in the nanosize range, has provided opportunities to integrate poorly water- and oil-soluble molecules in long-acting injectable formulations: nanosizing allows to influence their release, while offering the advantage of higher mass packing (and thus higher dose) per volume and improved physical stability via use of more monodisperse material and one or more surfactants [13], [14].
TMC278 (rilpivirine) is a very poorly water- and oil-soluble diarylpyrimidine derivative and was chosen as a candidate for developing a long-acting therapeutic and prophylactic treatment for the following reasons: (1) as an NNRTI, it interferes early in the cycle of viral HIV replication, preventing the viral DNA synthesis and subsequent integration of the viral genome in the host’s DNA; (2) it is effective against a broad range of wild-type and HIV-mutant strains: its potent antiviral effect has been confirmed in a dose-finding study in treatment-naïve HIV patients [15], [16]; (3) TMC278 is well tolerated during long-term administration: in a 48-week study it was found to result in fewer neuropsychiatric and metabolic side effects than efavirenz [17], [18]. This paper describes some elementary pharmaceutical characteristics of TMC278 nanosuspensions prepared in an aqueous carrier and with average particle sizes targeted in the 200–800 nm range. In order to provide proof-of-concept of their long-acting release profile, a series of pharmacokinetic pilot experiments were performed in dogs and mice, thereby evaluating the impact of route of administration, chemical form, surfactant and average particle size.
Section snippets
Test compounds and formulations
The NNRTI rilpivirine (TMC278 (E)-4-[[4-[[4-(2-cyanoethenyl]-2,6-dimethylphenyl]-amino]-2-pyrimidinyl]-amino]-benzonitrile was isolated as the free base or its corresponding HCl salt. Both are stable crystalline polymorphic forms and are largely insoluble in water and oil (less than 2 × 10−5 mg/mL): the physical status is crystalline and solubility in water or in phosphate buffer at pH 7 is <0.1 mg/mL (Tibotec, data on file). Unless specified as TMC278.HCl salt, TMC278 refers in the text to its
Preliminary characterization of the nanosuspensions
Pharmaceutical formulation with the Elan’s NanoCrystal® technology proved that TMC278 could be nanosized. The particle size distributions of the targeted 200, 400 and 800 nm test-nanosuspensions of TMC278 base are given in Fig. 1. When measured with laser diffraction, the mean volume diameter was smaller than projected. For instance, in case of the 200 nm nanosuspensions with Vit-E TPGS, 10% of the particles were sized below 77 nm, 25% below 93 nm, 50% below 117 nm, 90% below 185 nm and 95% below 208
Discussion
With these studies, proof-of-concept was provided that:
- 1.
The antiretroviral TMC278 (rilpivirine) can be nanosized by wet milling to suitable formulations for parenteral application. The wet milling with zirconium beads in the presence of a non-ionic surfactant allowed the formulation of sufficiently stable, homogeneous and resuspendable nanosuspensions, suitable for testing as long-acting injections.
- 2.
Long-acting formulations of TMC278 can be developed, using nanotechnology by wet milling in
Acknowledgement
We thank Suzy Huijghebaert (HuginCR, BE-1310 La Hulpe Belgium) for her assistance in preparing the manuscript.
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