N-in-1 dosing pharmacokinetics in drug discovery: experience, theoretical and practical considerations.

N-in-1 (or cassette) dosing pharmacokinetics (PK) has been used in drug discovery for rapid assessment of PK properties of new chemical entities. However, because of potential for drug-drug interactions this procedure is still controversial. This study was to retrospectively evaluate the N-in-1 dosing approach in drug discovery with an emphasis on the potential for drug-drug interactions. The systemic clearance, volume of distribution, oral bioavailability, and renal excretion of the 31 lead compounds in rats, dogs or chimpanzees were significantly correlated between the N-in-1 dosing and discrete studies with r values of 0.69, 0.91, 0.53, and 0.83 (p < 0.005 for all), respectively. PK parameters for 11 quality control compounds which were involved in 194 N-in-1 studies for screening approximately 1000 compounds had coefficient of variations of less than 70%. The intrinsic microsomal clearances generated from the N-in-1 and discrete incubations were nearly identical (r = 0.97, p < 0.0001). The intrinsic clearances of quality control compound from the N-in-1 incubations were consistent with its discrete CL(int) estimate (cv: 5.4%). Therefore, N-in-1 dosing is a useful approach in drug discovery to quickly obtain initial PK estimates. Potential drug-drug interactions that result in confounding PK estimates do not occur as frequently as expected.

Discovery of a small molecule antagonist of the parathyroid hormone receptor by using an N-terminal parathyroid hormone peptide probe.

Once-daily s.c. administration of either human parathyroid hormone (PTH)-(1-84) or recombinant human PTH-(1-34) provides for dramatic increases in bone mass in women with postmenopausal osteoporosis. We initiated a program to discover orally bioavailable small molecule equivalents of these peptides. A traditional high-throughput screening approach using cAMP activation of the PTH/PTH-related peptide receptor (PPR) as a readout failed to provide any lead compounds. Accordingly, we designed a new screen for this receptor that used a modified N-terminal fragment of PTH as a probe for small molecule binding to the transmembrane region of the PPR, driven by the assumption that the pharmacological properties (agonist/antagonist) of compounds that bound to this putative signaling domain of the PPR could be altered by chemical modification. We developed DPC-AJ1951, a 14 amino acid peptide that acts as a potent agonist of the PPR, and characterized its activity in ex vivo and in vivo assays of bone resorption. In addition, we studied its ability to initiate gene transcription by using microarray technology. Together, these experiments indicated that the highly modified 14 amino acid peptide induces qualitatively similar biological responses to those produced by PTH-(1-34), albeit with lower potency relative to the parent peptide. Encouraged by these data, we performed a screen of a small compound collection by using DPC-AJ1951 as the ligand. These studies led to the identification of the benzoxazepinone SW106, a previously unrecognized small molecule antagonist for the PPR. The binding of SW106 to the PPR was rationalized by using a homology receptor model.

Potent P1' biphenylmethyl substituted aggrecanase inhibitors.

A series of cis-1(S)2(R)-amino-2-indanol based compounds with a biphenylmethyl group at the P1' position was found to be potent aggrecanase inhibitors. Both compounds 2j and 2n possessed very high aggrecanase affinity (IC(50)=1.5nM), and showed excellent selectivity over MMP-1 and MMP-9, with moderate selectivity against MMP-2.