Angiotensin I-converting enzyme (ACE) has two homologous active NH 2 -and COOH-terminal domains and displays activity toward a broad range of substrates. The tetrapeptide N -acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) has been shown to be hydrolyzed in vitro by ACE and to be a preferential substrate for its NH 2 -terminal active site. This peptide is a regulatory factor of hematopoiesis which reversibly prevents the recruitment of pluripotent hematopoietic stem cells and normal early progenitors into S-phase. We found that a single oral dose of 50 mg of the ACE inhibitor, captopril, when administered to eight healthy subjects in a double-blind, crossover, placebo-controlled study, massively increased the plasma level of Ac-SDKP.

Doxorubicin (DXR) incorporated into biodegradable acrylate nanoparticles such as polyisohexylcyanoacrylate (PIHCA) has been shown to increase DXR cytotoxicity and reduce cardiotoxicity by modifying tissue distribution in preclinical studies. We have conducted a phase I clinical trial of DXR-PIHCA in 21 patients with refractory solid tumors (10 male, 11 female, median age: 53 years, median PS: 1, prior free-DXR therapy: 7 patients). A total of 32 courses at 28 day intervals were administered at 6 dose levels (15, 30, 45, 60, 75 and 90 mg/m2). The drug was given as a 10 minute IV infusion on day 1 to the first 5 patients: 2 of them presented a grade 2 allergic reaction (W.H.O. criteria) during infusion, which was rapidly reversible once drug administration was discontinued. Subsequently, in the other 16 patients, the administration was modified to a 60 minute i.v. perfusion diluted in 250 cc of Dextrose 5%: only 1 patient presented the same allergic reaction. Grade 2 fever and vomiting occurred in 9 patients and 7 patients respectively during the first 24 h after treatment. There was no cardiac toxicity among the 18 evaluable patients. Grade 3 or 4 hematologic toxicity occurred at the 75 and 90 mg/m2 dose level. The dose limiting toxicity was neutropenia. The maximum tolerated dose was 90 mg/m2 and the recommended phase II dose was 75 mg/m2. A pharmacokinetic evaluation of DXR-PIHCA was conducted in 3 patients each at a different dose level (60, 60 and 75 mg/m2) and was compared with free DXR given to the same patients in the same conditions.

The acute administration of the angiotensin-converting enzyme (ACE) inhibitor captopril to healthy subjects transiently increases 5.5-fold the plasma levels of a natural stem-cell regulator, N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP). The aim of this study was to measure plasma Ac-SDKP levels during chronic treatment with all types of ACE inhibitors and to assess its relevance as a marker of ACE inhibition. Plasma levels of Ac-SDKP were blindly determined in age- and sex-matched hypertensive patients either treated (ACEI group, n=27) or not (non-ACEI group, n=23) with an ACE inhibitor for more than 1 month. Geometric mean [range] of plasma Ac-SDKP levels were significantly higher in the ACEI group (3.78 [1.48 to 14.5] pmol/mL) than in the non-ACEI group, with no overlap between the groups (0.75 [0.36 to 1.22] pmol/mL, P<.0001). The measurement of Ac-SDKP in plasma discriminated all the patients of the ACEI group, whereas the simultaneous determination of either in vitro (using hippuryl-histidine-leucine as substrate) or in vivo (angiotensin II/angiotensin I ratio) ACE activity failed to identify nine and five cases, respectively. We conclude that Ac-SDKP accumulates in plasma during chronic ACE inhibitor treatment. The long-term consequences of Ac-SDKP accumulation are unknown. The reliability of plasma Ac-SDKP measurement makes it the best marker of chronic ACE inhibition, which can help to verify patients' compliance to ACE inhibitor treatment.