N, N-diethyl-2-[4-(phenylmethyl)phenoxy] ethanamine (DPPE), a chemopotentiating and cytoprotective agent in clinical trials : interaction with histamine at cytochrome P450 3A4 and other isozymes that metabolize antineoplastic drugs

• Published in: Cancer chemotherapy and pharmacology 2000, Vol.45 (4), p.298-304
• Main Authors: BRANDES, L. J, QUEEN, G. M, LABELLA, F. S
• Format: Article
• Language: English
• Subjects: Adjuvants, Pharmaceutic - metabolism; Adjuvants, Pharmaceutic - pharmacology; Animals; Antineoplastic agents; Antineoplastic Agents - metabolism; Antineoplastic Agents - pharmacology; Biological and medical sciences; Cell Survival - drug effects; Chromatography, Thin Layer; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme System - metabolism; General aspects; Histamine - metabolism; In Vitro Techniques; Indicators and Reagents; Isoenzymes - metabolism; Male; Medical sciences; Microsomes, Liver - metabolism; Mixed Function Oxygenases - metabolism; Pharmacology. Drug treatments; Phenyl Ethers - metabolism; Phenyl Ethers - pharmacology; Rats; Rats, Sprague-Dawley; Spectrophotometry, Ultraviolet; Testosterone - metabolism
• ISSN: 0344-5704; 1432-0843
• DOI: 10.1007/s002800050044

N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine HCl (DPPE), an intracellular histamine (HA) antagonist with chemopotentiating and cytoprotective properties, is currently in phase 2 and 3 clinical trials in breast and prostate cancer. DPPE modulates growth at in vitro concentrations that antagonize HA binding to cytochromes P450 in rat liver microsomes. HA inhibits P450 metabolism of some drugs. Recent in vitro studies in human colon cancer cells have linked DPPE enhancement of paclitaxel, doxorubicin and vinblastine cytotoxicity to inhibition of the P-glycoprotein (P-gp) pump. Many substrates of P-gp are also substrates of CYP3A4, a P450 isozyme that metabolizes a variety of antineoplastic agents and is highly expressed in some malignant tissues. Therefore, we assessed whether (a) DPPE and HA interact at CYP3A4 and other P450 human isozymes, and (b) DPPE inhibits the catalytic activity of CYP3A4. Using spectral analysis, we measured DPPE and HA binding to insect microsomes that express human P450 isozymes 1A1, 2B6, 2D6 or 3A4. Employing thin-layer chromatography, we assessed the metabolism of DPPE by each isozyme and DPPE inhibition of testosterone metabolism by CYP3A4 and by rat liver microsomes. (1) DPPE evoked "type I" (substrate site binding) absorbance-difference spectra with CYP2D6 (K(S) = 4.1 +/- 0.4 microM), CYP3A4 (K(S) = 31 +/- 15 microM) and CYP1A1 (K(S) = 40 +/- 9 microM), but not with CYP2B6. (2) In correspondence with the binding studies, DPPE was metabolized by CYP2D6, CYP3A4 and CYP1A1; no metabolism occurred with CYP2B6. (3) HA evoked "type II" (heme iron binding) absorbance-difference spectra with all four isozymes, with K(S) values in the range 80-600 microM. DPPE inhibited HA (600 microM) binding to CYP2D6 (IC50 = 4 microM, 95% CI= 1.8-8.9 microM) and CYP1A1 (IC50 = 135 microM: 95% CI = 100-177 microM), but stimulated HA (500 and 1000 microM) binding to CYP3A4 (EC50 = 155 microM, 95% CI = 104-231 microM). DPPE did not affect HA binding to CYP2B6. (4) DPPE inhibited the metabolism of testosterone by CYP3A4. The concentration/effect curve was biphasic: DPPE inhibited metabolism by 30% at the first site (IC50 = 3 microM, 95% CI = 0.5-25.5 microM), and an additional 70% inhibition occurred at the second site (IC50 = 350 microM, 95% CI = 215-570 microM). A similar result was observed with rat liver microsomes. DPPE is a substrate for CYP3A4, CYP2D6 and CYP1A1, but not CYP2B6. DPPE inhibits testosterone metabolism by interacting at two site