Target engagement and intracellular delivery of mono- and bivalent LDL receptor-binding peptide-cargo conjugates: Implications for the rational design of new targeted drug therapies.

Targeted delivery to specific tissues and subcellular compartments is of paramount importance to optimize therapeutic or diagnostic interventions while minimizing side-effects. Using recently identified LDL receptor (LDLR) -targeting small synthetic peptide-vectors conjugated to model cargos of different nature and size, we investigated in LDLR-expressing cells the impact of vector-cargo molecular engineering and coupling valency, as well as the cellular exposure duration on their target engagement and intracellular trafficking and delivery profiles. All vector-cargo conjugates evaluated were found to be delivered to late compartments together with the natural ligand LDL, although to varying extents and with different kinetics. Partial recycling together with the LDLR was also consistently observed. Under continuous cellular exposure, the extent of intracellular vector-cargo delivery primarily relies on their endosomal unloading potential. In this condition, the highest intracellular delivery potential was observed with a monovalent conjugate displaying a rather high LDLR dissociation rate. On the contrary, under transient cellular exposure followed by chase, low dissociation-rate bivalent conjugates revealed a higher intracellular delivery potential than the monovalent conjugate. This was shown to rely on their ability to undergo multiple endocytosis-recycling rounds, with limited release in the ligand-free medium. The absence of reciprocal competition with the natural ligand LDL on their respective intracellular trafficking was also demonstrated, which is essential in terms of potential safety liabilities. These results demonstrate that not only molecular engineering of new therapeutic conjugates of interest, but also the cellular exposure mode used during in vitro evaluations are critical to anticipate and optimize their delivery potential.

[Nuclear import of the genome from the human immunodeficiency virus type 1]. / Import nucléaire du matériel génétique du virus de l'immunodéficience humaine de type 1.

HIV and other lentiviruses have the ability to replicate in non-dividing cells, such as macrophages and quiescent T lymphocytes, which represent major target cells during the course of infection. After virus entry, the viral genomic RNA is reverse transcribed into a linear double-strand DNA. This viral DNA associates with viral and host cell proteins into the so-called pre-integration complex (PIC). In contrast to oncoretroviruses which require nuclear envelope disintegration during mitosis to integrate their genome into host chromosomes, lentiviruses, such as HIV, have evolved an active strategy to import their own genome through the envelope of the interphasic nucleus. In this review, we will discuss on the most recent developments reported in the literature regarding the cellular and molecular bases that govern the intra-cytoplasmic routing and the translocation of the HIV-1 genome into the nuclear compartment, two crucial steps of the viral life cycle that are still poorly understood.