Pravin R. Chaturvedi

Preclinical Profile of VX-950, a Potent, Selective, and Orally Bioavailable Inhibitor of Hepatitis C Virus NS3-4A Serine Protease

ABSTRACT VX-950 is a potent, selective, peptidomimetic inhibitor of the hepatitis C virus (HCV) NS3-4A serine protease, and it demonstrated excellent antiviral activity both in genotype 1b HCV replicon cells (50% inhibitory concentration [IC50] = 354 nM) and in human fetal hepatocytes infected with genotype 1a HCV-positive patient sera (IC50 = 280 nM). VX-950 forms a covalent but reversible complex with the genotype 1a HCV NS3-4A protease in a slow-on, slow-off process with a steady-state inhibition constant (Ki*) of 7 nM. Dissociation of the covalent enzyme-inhibitor complex of VX-950 and genotype 1a HCV protease has a half-life of almost an hour. A >4-log10 reduction in the HCV RNA levels was observed after a 2-week incubation of replicon cells with VX-950, with no rebound of viral RNA observed after withdrawal of the inhibitor. In several animal species, VX-950 exhibits a favorable pharmacokinetic profile with high exposure in the liver. In a recently developed HCV protease mouse model, VX-950 showed excellent inhibition of HCV NS3-4A protease activity in the liver. Therefore, the overall preclinical profile of VX-950 supports its candidacy as a novel oral therapy against hepatitis C.

Design principles for orally bioavailable drugs

Compound design is the hallmark of modern pharmaceutical research and development. Unfortunately, comprehensive and reliable guidelines for the introduction of favorable bioavailability properties into designed compounds remain elusive. Here, the authors discuss the limited set of design principles that address the problem of bioavailability, based on a retrospective analysis of orally bioavailable drugs. The roles of partition coefficient, molecular weight, carrier-mediated transport and conformational flexibility are evaluated. These properties are discussed as guiding principles only, and cannot be considered all-encompassing determinants of oral bioavailability.

A nonimmunosuppressant FKBP-12 ligand increases nerve regeneration

The immunosuppressant drugs FK506 and cyclosporin A inhibit T-cell proliferation via a common mechanism: calcineurin inhibition following binding to their respective binding proteins, the peptidyl prolyl isomerases FKBP-12 and cyclophilin A. In contrast, FK506, but not cyclosporin A, accelerates nerve regeneration. In the present study, we show that the potent FKBP-12 inhibitor V-10,367, which lacks the structural components of FK506 required for calcineurin inhibition, increases neurite outgrowth in SH-SY5Y neuroblastoma cells and speeds nerve regeneration in the rat sciatic nerve crush model. In SH-SY5Y cells, V-10,367 increased the lengths of neurite processes in a concentration-dependent (between 1 and 10 nM) fashion over time (up to 168 h). Daily subcutaneous injections of V-10,367 accelerated the onset of clinical signs of functional recovery in the hind feet compared to vehicle-treated control animals. Interdigit distances (between the first and fifth digits) measured on foot prints obtained during walking showed an increase in toe spread in V-10,367-treated rats compared to vehicle-treated controls. Electron microscopy demonstrated larger regenerating axons distal to the crush site in the sciatic nerve from V-10,367-treated rats. Quantitation of axonal areas in the soleus nerve revealed a shift to larger axonal calibers in V-10,367-treated rats (400 or 200 mg/kg/day); mean axonal areas were increased by 52 and 59%, respectively, compared to vehicle-treated controls. FKBP-12 ligands lacking calcineurin inhibitory activity represent a new class of potential drugs for the treatment of human peripheral nerve disorders.

The future of drug development: advancing clinical trial design

Declining pharmaceutical industry productivity is well recognized by drug developers, regulatory authorities and patient groups. A key part of the problem is that clinical studies are increasingly expensive, driven by the rising costs of conducting Phase II and III trials. It is therefore crucial to ensure that these phases of drug development are conducted more efficiently and cost-effectively, and that attrition rates are reduced. In this article, we argue that moving from the traditional clinical development approach based on sequential, distinct phases towards a more integrated view that uses adaptive design tools to increase flexibility and maximize the use of accumulated knowledge could have an important role in achieving these goals. Applications and examples of the use of these tools — such as Bayesian methodologies — in early- and late-stage drug development are discussed, as well as the advantages, challenges and barriers to their more widespread implementation.

Phase I and Pharmacokinetic Study of the Novel MDR1 and MRP1 Inhibitor Biricodar Administered Alone and in Combination With Doxorubicin

PURPOSE To evaluate the safety, tolerability, and pharmacokinetics of biricodar (VX-710), an inhibitor of P-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP1), alone and with doxorubicin in patients with advanced malignancies. The effect of VX-710 on the tissue distribution of (99m)Tc-sestamibi, a P-gp and MRP1 substrate, was also evaluated. PATIENTS AND METHODS Patients with solid malignancies refractory to standard therapy first received a 96-hour infusion of VX-710 alone at 20 to 160 mg/m(2)/h. After a 3-day washout, a second infusion of VX-710 was begun, on the second day of which doxorubicin 45 mg/m(2) was administered. Cycles were repeated every 21 to 28 days. (99m)Tc-sestamibi scans were performed before and during administration of VX-710 alone. RESULTS Of the 28 patients who enrolled, 25 patients were eligible for analysis. No dose-limiting toxicity (DLT) was observed in the nine assessable patients who received 120 mg/m(2)/h or less. Among seven patients receiving VX-710 160 mg/m(2)/h, two DLTs were seen: reversible CNS toxicity and febrile neutropenia. All other adverse events were mild to moderate and reversible. Plasma concentrations of VX-710 in patients who received at 120 and 160 mg/m(2)/h were two- to fourfold higher than concentrations required to fully reverse drug resistance in vitro. VX-710 exhibited linear pharmacokinetics with a harmonic mean half-life of 1.1 hours. VX-710 enhanced hepatic uptake and retention of (99m)Tc-sestamibi in all patients. CONCLUSION A 96-hour infusion of VX-710 at 120 mg/m(2)/h plus doxorubicin 45 mg/m(2) has acceptable toxicity in patients with refractory malignancies. The safety and pharmacokinetics of VX-710 plus doxorubicin warrant efficacy trials in malignancies expressing P-gp and/or MRP1.

Prediction of pharmacokinetic properties using experimental approaches during early drug discovery.

There has been a significant increase in the number of compounds synthesized in early drug-discovery programs with the advances in combinatorial chemistry and high-throughput biological screening efforts. Various in silico, in vitro and in situ approaches have been described in literature that achieve higher throughput pharmacokinetic screening. In silico methodologies have mainly attempted to quantify the prospects of oral absorption of compounds based upon their physico-chemical properties. There is a greater availability of in vitro and in situ approaches to screen compounds for intestinal permeability (as a surrogate for absorption) and metabolic stability (as a surrogate for clearance). More recent modifications of the in vitro and in situ approaches to assess the potential of absorption and metabolism have enabled a higher throughput and an ability to correlate better with in vivo pharmacokinetics of compounds.

Immunophilin ligands can prevent progressive dopaminergic degeneration in animal models of Parkinson's disease.

Slowing or halting the progressive dopaminergic (DA) degeneration in Parkinsons disease (PD) would delay the onset and development of motor symptoms, prolong the efficacy of pharmacotherapies and decrease drug‐induced side‐effects. We tested the potential of two orally administered novel immunophilin ligands to protect against DA degeneration in two animal models of PD. First, in an MPTP (N‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine) mouse model, we compared an immunophilin ligand (V‐10,367) documented to bind the immunophilin FKBP12 with V‐13,661, which does not bind FKBP12. Both molecules could prevent the loss of striatal DA innervation in a dose‐dependent fashion during 10 days of oral administration. Second, to determine whether an immunophilin ligand can protect against progressive and slow DA degeneration typical of PD, an intrastriatal 6‐hydroxydopamine‐infusion rat model was utilized. Oral treatment with the FKBP12‐binding immunophilin ligand began on the day of lesion and continued for 21 days. At this time point, post mortem analyses revealed that the treatment had prevented the progressive loss of DA innervation within the striatum and loss of DA neurons within the substantia nigra, related to functional outcome as measured by rotational behaviour. Notably, DA fibres extending into the area of striatal DA denervation were observed only in rats treated with the immunophilin ligand, indicating neuroprotection or sprouting of spared DA fibres. This is the first demonstration that immunophilin ligands can prevent a slow and progressive DA axonal degeneration and neuronal death in vivo. The effects of orally administered structurally related immunophilin ligands in acute and progressive models of DA degeneration are consistent with the idea that these compounds may have therapeutic value in PD.

Oral administration of a nonimmunosuppressant FKBP-12 ligand speeds nerve regeneration.

WE recently showed that s.c. injections of a nonimmunosuppressant FK506 binding protein-12 (FKBP-12) ligand (V-10,367) accelerates nerve regeneration in the rat sciatic nerve crush model. Here we examined the oral efficacy of this compound for speeding nerve regeneration. Rats receiving V-10,367 (5, 15 or 50 mg/kg/day) by oral gavage all demonstrated an increase in nerve regeneration compared to vehicle-treated controls. Functional recovery was observed earliest and axonal calibers of regenerating axons in the soleus nerve were largest in the 15 mg/kg group, mean axonal areas being increased by 66% compared to controls. Orally active nonimmunosuppressant FKBP-12 ligands may be useful for the treatment of human peripheral nerve disorders.

Practical Considerations for a Two-Stage Confirmatory Adaptive Clinical Trial Design and Its Implementation: ADVENT Trial

In this chapter, we provide the details of an innovative two-stage, seamless adaptive clinical trial called ADVENT. This trial was conducted as a “final phase 3” clinical trial to establish the safety and efficacy of a first-in-class antidiarrheal agent, crofelemer, for the symptomatic relief of diarrhea in HIV patients receiving anti-retroviral therapy. Given that this was a trial with two-stage design that included a dose selection, it was necessary to demonstrate the strong control of Type 1 error. This was accomplished with a close testing procedure applied to combination tests that utilized the inverse normal combination function. We developed a one-sided significance testing procedure that ensures strong control of the Type 1 error at level 0.025. Using appropriate statistical methodology for combining the results from the two stages, a statistically significant outcome was obtained for the primary efficacy endpoint and crofelemer received marketing approval based on the ADVENT trial. While the authors acknowledge the importance of statistical methodology required to analyze the data from the ADVENT trial, this chapter also provides significant details on the clinical and regulatory challenges that were demanded for the conduct of this innovative, two-stage, adaptive clinical trial.

Pharmacokinetics and Safety of Single Oral Doses of VX-366 (Isobutyramide) in Healthy Volunteers

VX‐366 (isobutyramide) is an orally available branched chain amide that may offer an alternative to current treatments for β‐hemoglobinopathy. A phase I, double‐blind, randomized, placebo‐controlled study was conducted to investigate four single oral doses of VX‐366 (1, 7, 14, or 28 grams or approximately 14, 100, 200 or 400 mg/kg) administered to four male volunteers each, with two other subjects in each group receiving a matching placebo. The total number of volunteers enrolled in this study was 24, with a mean age of 27 ± 6.4 years. VX‐366 was well tolerated at all dose levels studied, and peak plasma concentrations (Cmax) of 18.88 ± 1.02 μg/mL (0.2 mmol/L), 171.13 ± 32.13 μg/mL (2 mmol/L), 331.58 ± 35.48 μg/mL (3.8 mmol/L), and 538.83 ± 54.19 μg/mL (6 mmol/L) were achieved after the four respective doses. The half‐life (t1/2) of VX‐366 was more than 7 hours, and there was evidence of nonlinear pharmacokinetics. It is likely that nonrenal (metabolic) clearance plays a predominant role in elimination. Based on these data, VX‐366 given as a single daily dose of 100 to 150 mg/kg should be well tolerated and can be expected to result in peak plasma levels in excess of 170 μg/mL (2 mmol/L) and in trough plasma levels in excess of 40 μg/mL (0.5 mmol/L). These plasma levels exceed the concentrations previously shown to stimulate gamma globin synthesis both in vitro and in baboons.