Pharmacokinetics of the protease inhibitor KNI-272 in plasma and cerebrospinal fluid in nonhuman primates after intravenous dosing and in human immunodeficiency virus-infected children after intravenous and oral dosing

Pseudoprolines as stereoelectronically tunable proline isosteres

The cyclic structure of proline (Pro) confers unique conformational properties on this natural amino acid that influences polypeptide structure and function. Pseudoprolines are a family of Pro isosteres that incorporate a heteroatom, most prominently oxygen or sulfur but also silicon and selenium, to replace the C_β or C_γ carbon atom of the pyrrolidine ring. These readily synthetically accessible structural motifs can facilitate facile molecular editing in a fashion that allows modulation of the amide bond topology of dipeptide elements and influence over ring pucker. While the properties of pseudoprolines have been exploited most prominently in the design of oligopeptide analogues, they have potential application in the design and optimization of small molecules. In this Digest, we summarize the physicochemical properties of pseudoprolines and illustrate their potential in drug discovery by surveying examples of applications in the design of bioactive molecules.

Current Status and Perspectives of Protease Inhibitors and Their Combination with Nanosized Drug Delivery Systems for Targeted Cancer Therapy

In cancer treatments, many natural and synthetic products have been examined; among them, protease inhibitors are promising candidates for anti-cancer agents. Since dysregulated proteolytic activities can contribute to tumor development and metastasis, antagonization of proteases with tailored inhibitors is an encouraging approach. Although adverse effects of early designs of these inhibitors disappeared after the introduction of next-generation agents, most of the proposed inhibitors did not pass the early stages of clinical trials due to their nonspecific toxicity and lack of pharmacological effects. Therefore, new applications that modulate proteases more specifically and serve their programmed way of administration are highly appreciated. In this context, nanosized drug delivery systems have attracted much attention because preliminary studies have demonstrated that the therapeutic capacity of inhibitors has been improved significantly with encapsulated formulation as compared to their free forms. Here, we address this issue and discuss the current application and future clinical prospects of this potential combination towards targeted protease-based cancer therapy.

A phase I trial of the pharmacokinetics, toxicity, and activity of KNI-272, an inhibitor of HIV-1 protease, in patients with AIDS or symptomatic HIV infection

The pharmacokinetics, toxicity, and activity of KNI-272, a transition state inhibitor of HIV-1 protease, was assessed in a phase I trial. After an initial phase in which the pharmacokinetics were assessed, 37 patients with AIDS or symptomatic HIV infection and 100-400 CD4 cells/mm3 were entered in an escalating dose study. KNI-272 was administered four times daily for up to 12 weeks. Oral bioavailability ranged from 22 to 55% and was not appreciably different in the fasting and post-prandial state. The dose limiting toxicity was hepatic transaminase elevation; this could be reduced by escalating the dose over 4 weeks. When administered this way, the maximum tolerated oral dose was 40 mg/kg per day. At the highest two tolerated doses (26.4 and 40 mg/kg per day), there was some evidence of an anti-HIV effect with median decreases of 0.2-0.3 log10 copies/ml plasma HIV RNA; these decreases persisted through 7-8 weeks of treatment. There was an upward trend in the CD4 count at the 40 mg/kg per day dose but not at other doses. Additional studies focused on approaches to improve the therapeutic index of KNI-272 may be warranted.