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The Human Immunodeficiency Virus (HIV) genome encodes three major structural proteins common to all retroviruses (Gag, Pol and Env), two regulatory proteins (Tat and Rev) that are essential for viral replication, and four accessory proteins (Nef, Vif, Vpu, Vpr). While accessory proteins were initially reported to be unnecessary for viral growth, their importance as virulence factors is now being more and more appreciated: they can dramatically alter the course and severity of viral infection, replication and disease progression. None of the HIV accessory proteins display enzymatic activity: they rather act altering cellular pathways via multiple protein-protein interactions with a number of host cell factors. All currently approved anti-HIV drugs target pol and env encoded proteins. Therefore, widening the molecular targets of HIV therapy by additionally targeting accessory proteins may expand treatment options, resulting in high impact effective new therapy. In this review we present the state of the art of compounds that target HIV accessory proteins. Most of the research has focused on the inhibition of specific accessory proteins/host cell partner interactions. Promising compounds have been found within different classes of molecules: small natural and synthetic molecules, peptides and proteins, oligonucleotides, in particular those used as RNA interference (RNAi) tools. With the assortment of compounds available, especially against Nef and Vif functions, the demonstration of the clinical efficacy of the new anti-HIV-1 drugs targeting accessory proteins is next challenge.

Background: The pyrimidine antimetabolite Gemcitabine (G) (2',2'-difluorodeoxycytidine) is used against several malignancies G exerts its antitumour effect mainly by incorporation of its triphosphate metabolite (dFdCTP) into DNA. Subsequently, DNA polymerase adds one additional deoxynucleotide and DNA synthesis is interrupted. The nuclear enzymes topoisomerase I and II (TPs) are critical for DNA function and cell survival; they control, maintain and modify DNA topology during both replication and translation of genetic materials. These enzymes induce cuts in one or both strands of DNA, allowing strands to pass through the nick and then rejoining the nicked strand of DNA. Anti-topoisomerase (TPs-inhibitors) drugs exist and are largely used in chemotherapy, however, most often blindly of the cancer TPs status., Aim: To understand the best association between G and TPs-inhibitors, we studied: (a) Topoisomerases I, II alpha and II beta mRNA expression in Peripheral Mononuclear Blood Cells (PBMCs) of patients with solid tumor, after 1, 2, 3, 4, 5, 6 h after treatment with Gemcitabine (G); b) in vivo expression of TPs genes after administration of Gemcitabine (a topoisomerases up-regulating drug) combined with the TPs inhibitors drugs (TID) Topotecan (T) and Etoposide (E), added to the culture beneath 1 h after TPD treatment. TPs mRNA expression was measured by quantitative real-time RT-PCR in PBMCs., Results: The administration of 1-h infused G is followed by a fast rise of TPs expression (P > 0.0001 Student's t test, paired data, each patient control of himself); TPs inhibitors, sequentially given after G, highly reduced the TPs rising (P > 0.0001)., Conclusions: G induces a TPs increase. A rationale might be available for combination chemotherapy (G plus TPs inhibitors). The study is ongoing to enroll further patients.

The transactivation responsive (TAR) RNA is the 5'-leader sequence of the HIV-1 mRNA genome and interacts with the Tat protein during transcription. Tat and the positive transcription elongation factor (P-TEFb) complex bind to TAR to promote efficient transcription of the full-length HIV genome. In the absence of the TAR.Tat.P-TEFb interaction, viral transcription is inefficient, which makes this RNA-protein complex an important target for therapeutic intervention of HIV replication. Inhibitors of HIV-1 transactivation mainly target: 1) TAR RNA, 2) Tat protein and 3) Tat.P-TEFb complex. 1) Compounds against TAR RNA are the most numerous: besides cationic peptides, which were initially developed, recent advances in TAR binding inhibitors include oligonucleotide based-agents and small molecules. Specific research efforts are currently underway to increase cellular uptake. 2) By targeting the Tat protein, both transactivation and other Tat-mediated intra/extracellular functions are affected. Various biopolymeric drugs are reported to effectively inhibit Tat activity. In addition, Tat-targeted antibodies have recently been developed. 3) Intracellular proteins have been discovered to disrupt Tat.P-TEFb interaction, raising the chance of inhibiting HIV-1 transcription via novel mechanisms.