Recent developments in HIV protease inhibitor research

Indazole as a Privileged Scaffold: The Derivatives and their Therapeutic Applications

BACKGROUND

Heterocyclic compounds, also called heterocycles, are a major class of organic chemical compound that plays a vital role in the metabolism of all living cells. The heterocyclic compound, indazole, has attracted more attention in recent years and is widely present in numerous commercially available drugs. Indazole-containing derivatives, representing one of the most important heterocycles in drug molecules, are endowed with a broad range of biological properties.

METHODS

A literature search was conducted in PubMed, Google Scholar and Web of Science regarding articles related to indazole and its therapeutic application.

RESULTS

The mechanism and structure-activity relationship of indazole and its derivatives were described. Based on their versatile biological activities, the compounds were divided into six groups: anti-inflammatory, antibacterial, anti-HIV, antiarrhythmic, antifungal and antitumour. At least 43 indazole-based therapeutic agents were found to be used in clinical application or clinical trials.

CONCLUSION

This review is a guide for pharmacologists who are in search of valid preclinical/clinical drug compounds where the progress of approved marketed drugs containing indazole scaffold is examined from 1966 to the present day. Future direction involves more diverse bioactive moieties with indazole scaffold and greater insights into its mechanism.

Structure-based discovery of Tipranavir disodium (PNU-140690E): a potent, orally bioavailable, nonpeptidic HIV protease inhibitor

Efforts to develop therapeutically relevant HIV protease inhibitors as medicinal agents in confronting the AIDS crisis have been aided by the wealth of fundamental information acquired during related drug discovery campaigns against other aspartyl proteases. This knowledge base was brought to full force with the broad screening identification of small, nonpeptidic, inhibitory molecules as templates for chemical elaboration. Significantly, the ability to collect crystallographic data on the inhibitor-enzyme complexes in a rapid fashion afforded the opportunity for a structure-based approach to drug discovery. Iterative cycles of synthesis, biological testing, and structural information gathering followed by prudent design modifications afforded compounds suitable for clinical evaluation. Displaying high enzymatic inhibition (Ki = 8 pM), potent in vitro antiviral cell culture activity (IC90 = 100 nM), and a useful pharmacokinetic profile, PNU-140690E (Tipranavir disodium) has entered into clinical studies. Promising results from these early trials supported further evaluation of this compound in HIV-infected individuals. PNU-140690E is currently under extensive clinical study.

New anti-HIV derivatives: synthesis and antiviral evaluation

A small focused library of 18 compounds incorporating the motif 1,3-(N,N'-dibenzyl)diamino-2-propanol has been synthesized, using adapted synthetic methodologies. These series of compounds were evaluated for their in vitro anti-HIV activity on infected MT4 cells (syncytium formation observation). Some of the new synthesized compounds show potent anti-HIV activities. EC50 values for compounds (31, 40, 34, 37 and 46) range from 0.1 to 1 microM. In order to determine at which level these new derivatives interfere with the HIV replicative cycle, inhibition assays on recombinant HIV protease and HIV integrase have been performed. None of the compounds were found active on these two enzymatic targets. Experiments are in progress in order to identify their biological target within the HIV replicative cycle.

Probing the role of interfacial residues in a dimerization inhibitor of HIV-1 protease

The importance of each side chain of a cross-linked interfacial peptide inhibitor of HIV-1 protease was evaluated using an alanine scanning approach. Whereas the parent inhibitor has an IC50 value of 350 nM, values for the mutations reported here range from 280-9200 nM. The relative importance or each residue was thus assigned and correlated to the solvent accessible surface area (SASA) exposed upon mutation.

Pharmacokinetic interactions between HIV-protease inhibitors in rats

The interactions of four HIV-protease inhibitors, ritonavir (RIT), saquinavir (SAQ), indinavir (IND) and nelfinavir (NEL), were examined by in vitro metabolic studies using rat liver microsomal fractions. The substrate concentrations employed were 0.75 approximately 12 microM, and the inhibitor concentrations were 2.5 approximately 60 microM. The metabolic clearance rates of SAQ, NEL and IND as determined by V(max)/K(m) were 170.9+/-10.9, 126.0+/-4.4 and 73.0+/-2.0 microL/min/mg protein, respectively. RIT was a potent inhibitor of the other three protease inhibitors, and the inhibition constants (K(i)) were 1.64 microM for SAQ, 0.95 microM for IND and 1. 01 microM for NEL. NEL was the second strongest inhibitor with a K(i) for NEL inhibition of IND metabolism of 2.14 microM. IND was the third strongest inhibitor with K(i)s of 2.76 microM for inhibition of NEL and 3.55 microM for inhibition of SAQ. As SAQ has the highest metabolic clearance rate, the K(i) for the SAQ inhibition of IND metabolism was high, 9.50 microM. Based on these in vitro results, drug interactions between NEL and IND or RIT were studied after oral administration to rats where the dose of each drug was 20 mg/kg. The C(max) and AUC of NEL were increased 3.6- and 8.5-fold by the co-administration with RIT. However, in contrast to co-administration of NEL and RIT, the effect of IND on the pharmacokinetics of NEL was negligible and the t(1/2) of NEL was not significantly increased by IND. Therefore, the combination of NEL and IND is recommended as a combination therapy for AIDS patients.

Design and synthesis of novel conformationally restricted HIV protease inhibitors

A set of HIV protease inhibitors represented by compound 2 has previously been described. Structural and conformational analysis of this compound suggested that conformational restriction of the P1/P2 portion of the molecule could lead to a novel set of potent protease inhibitors. Thus, probe compounds 3-7 were designed, synthesized, and found to be potent inhibitors of HIV protease.

Design, synthesis, and conformational analysis of a novel series of HIV protease inhibitors

A combination of structure-based design and both solution, and solid-phase synthesis were utilized to derive a potent (nM) series of HIV-1 protease inhibitors bearing a structurally novel backbone. Detailed structural analysis of several inhibitors prepared in this series has suggested that rigidification of the P1/P2 region of this class of molecules may result in compounds with improved potency.

Design and selection of DMP 850 and DMP 851: the next generation of cyclic urea HIV protease inhibitors

BACKGROUND

Recent clinical trials have demonstrated that HIV protease inhibitors are useful in the treatment of AIDS. It is necessary, however, to use HIV protease inhibitors in combination with other antiviral agents to inhibit the development of resistance. The daunting ability of the virus to rapidly generate resistant mutants suggests that there is an ongoing need for new HIV protease inhibitors with superior pharmacokinetic and efficacy profiles. In our attempts to design and select improved cyclic urea HIV protease inhibitors, we have simultaneously optimized potency, resistance profile, protein binding and oral bioavailability.

RESULTS

We have discovered that nonsymmetrical cyclic ureas containing a 3-aminoindazole P2 group are potent inhibitors of HIV protease with excellent oral bioavailability. Furthermore, the 3-aminoindazole group forms four hydrogen bonds with the enzyme and imparts a good resistance profile. The nonsymmetrical 3-aminoindazoles DMP 850 and DMP 851 were selected as our next generation of cyclic urea HIV protease inhibitors because they achieve 8 h trough blood levels in dog, with a 10 mg/kg dose, at or above the protein-binding-adjusted IC90 value for the worst single mutant--that containing the Ile84-->Val mutation.

CONCLUSIONS

In selecting our next generation of cyclic urea HIV protease inhibitors, we established a rigorous set of criteria designed to maximize chances for a sustained antiviral effect in HIV-infected individuals. As DMP 850 and DMP 851 provide plasma levels of free drug that are sufficient to inhibit wild-type HIV and several mutant forms of HIV, they could show improved ability to decrease viral load for clinically significant time periods. The ultimate success of DMP 850 and DMP 851 in clinical trials might depend on achieving or exceeding the oral bioavailability seen in dog.

Non-peptidic HIV protease inhibitors: C2-symmetry-based design of bis-sulfonamide dihydropyrones

Potent, non-peptidic, dihydropyrone sulfonamide HIV protease inhibitors have been previously described. Crystallographic analysis of dihydropyrone sulfonamide inhibitor/HIV protease complexes suggested incorporation of a second, C2 symmetry-related sulfonamide group. Selected bis-sulfonamide dihydropyrone analogues display high HIV protease inhibitory activity.

Potent cyclic urea HIV protease inhibitors with 3-aminoindazole P2/P2' groups

Cyclic ureas containing 3-aminoindazole P2/P2' groups are extremely potent inhibitors of HIV protease. The parent 3-aminoindazole 6 showed a Ki < 0.01 nM but poor translation of enzyme activity to antiviral activity was observed. A series of 3-alkylaminoindazoles revealed that translation improved with increasing lipophilicity. An X-ray crystal structure of 6 bound to HIV protease was obtained.