In vitro metabolism of a new cardioprotective agent, KR-33028 in the human liver microsomes and cryopreserved human hepatocytes

KR-33028, a potent inhibitor of the Na+/H+ exchanger NHE1, suppresses metastatic potential of triple-negative breast cancer cells

Hyper-activation of the Na⁺/H⁺ exchanger NHE1 occurs at the onset of oncogenic transformation and plays a critical role in breast cancer carcinogenesis. Dysregulation of NHE1 activity results in intracellular alkalinization and the acidification of the extracellular tumor microenvironment that promotes metastasis. Hence, the use of chemical inhibitors of NHE1 as chemotherapeutic agents is an alluring prospect. We previously demonstrated that two structurally different NHE1 inhibitors, EMD87580 [(2-methyl-4,5-di-(methylsulfonyl)-benzoyl)-guanidine], and HMA [5-(N,N-hexamethylene)-amiloride], were effective as co-adjuvants to potentiate paclitaxel-mediated cytotoxic chemotherapy in triple-negative breast cancer (TNBC) cells. Both these drugs, however, had reduced or minimal anti-cancer effects when used alone. Here, we tested KR-33028 (4-cyano (benzo[b]thiophene-2-carbonyl)guanidine), a potent and selective inhibitor of NHE1, to determine its efficacy in inhibition of metastatic potential of TNBC cells. In highly invasive MDA-MB-231, moderately invasive MDA-MB-468, and lowly invasive Hs578T TNBC cells, KR-33028 considerably reduced rates of cell migration and anchorage-independent colony growth. Invasion of MDA-MB-231 and MDA-MB-468 cells through extracellular matrix was also dramatically decreased in response to KR-33028. We further tested the effect of KR-33028 on MDA-MB-231 cells lacking NHE1 expression (231koNHE1); no differences were observed between untreated control and KR-33028-treated 231koNHE1 cells. Taken together, our results highlight the in vitro efficacy of KR-33028-mediated NHE1 inhibition on limiting cellular functions that are predictive of metastasis in vivo. We suggest that targeting NHE1 in the development of novel chemotherapeutics could be highly effective in combatting triple-negative breast cancer and that KR-33028 is potentially useful in prevention of metastasis.

Dose-dependent pharmacokinetics of a new Na+/H+ exchanger inhibitor KR-33028 in rats

The dose-dependency of the pharmacokinetics of a new Na(+)/H(+) exchanger inhibitor, KR-33028 was evaluated in rats after intravenous and oral administration. After intravenous administration of KR-33028 (1, 5, 10 and 20mg/kg doses), the systemic clearance (Cl) was reduced and AUC was nonlinearly increased as a function of dose. The volume of distribution (V(ss)), however, remained unchanged as the dose was increased, which was consistent with unaltered plasma protein binding in vitro (unbound fraction = 0.09-0.12). Upon oral administration (2, 10 and 20mg/kg doses), KR-33028 was rapidly absorbed, and this was consistent with high Caco-2 P(app) values found in vitro. There were nonlinear increases in AUC and C(max), and the absolute oral bioavailability (F) was significantly increased as the dose was increased (F = 23.3%, 40.7% and 78.2% for 2, 10 and 20mg/kg doses, respectively). The extent of urinary excretion was low for both intravenous (0.5-0.7%) and oral (0.2-0.8%) doses. The reduced systemic clearance and increased oral bioavailability at high doses appears to be due to a saturable first-pass metabolism.

Determination of a selective Na+/H+ exchanger inhibitor, 4-cyano(benzo[b]thiophene-2-carbonyl)guanidine (KR-33028) in rat plasma by liquid chromatography–tandem mass spectrometry

A liquid chromatography-tandem mass spectrometric (LC/MS/MS) method was developed for the determination of a selective Na(+)/H(+) exchanger inhibitor 4-cyano(benzo[b]thiophene-2-carbonyl)guanidine (KR-33028) in rat plasma. KR-33028 and the internal standard, linezolid, were extracted from rat plasma with ethyl acetate at neutral pH. The analytes were separated on an XBridge C(18) column with a mixture of methanol-0.1% formic acid (35:65, v/v) as mobile phase and detected using an electrospray ionization tandem mass spectrometry in the multiple-reaction-monitoring mode. The standard curve was linear (r = 0.9998) over the concentration range of 2.0-1000 ng/mL. The coefficients of variation of intra- and inter-assay were 1.3-6.8% and the relative error was 0.8-5.0%. The recoveries of KR-33028 and linezolid were 70.5 and 84.6%, respectively. The lower limit of quantification for KR-33028 was 2.0 ng/mL using 50 microL plasma sample. This method was successfully applied to the pharmacokinetic study of KR-33028 in rats.

Characterization of the cytochrome P450 enzymes involved in the metabolism of a new cardioprotective agent KR-33028

KR-33028 (N-[4-cyano-benzo[b]thiophene-2-carbonyl]guanidine) is a new cardioprotective agent for preventing ischemia-reperfusion injury. This study was performed to characterize the cytochrome P450 (CYP) enzymes that are involved in the metabolism of KR-33028. Hydroxylation (5-hydroxy- and 7-hydroxy-KR-33028) is major pathways for the metabolism of KR-33028 in human liver microsomes. Among the nine c-DNA expressed CYP isoforms tested, KR-33028 was 5-hydroxylated by CYP3A4 and 7-hydroxylated by CYP1A2, CYP3A4, and CYP2C19. These findings were supported by the combination of chemical inhibition studies in human liver microsomes and correlation analysis. Furafylline and ketoconazole potently inhibited hydroxylation of KR-33028 in human liver microsomes. Correlation analysis between the known CYP enzyme activities and the rates of the formation of 5-hydroxy- and 7-hydroxy-KR-33028 in the 16 human liver microsomes has showed significant correlations with CYP3A4-mediated midazolam 1'-hydroxylation and CYP1A2-mediated phenacetin O-deethylation, respectively. A 7-hydroxy-KR-33028 formation is also weakly correlated with CYP3A4-mediated midazolam 1'-hydroxylation. The kinetics of the major biotransformation of KR-33028 were studied: CYP3A4 mediated the formation of 5-hydroxy-KR-33028 from KR-33028 with Cl(int)=0.22microl/min/pmol CYP. The intrinsic clearance for 7-hydroxy-KR-33028 formation by CYP1A2, CYP2C19, and CYP3A4 were 0.26, 0.19, and 0.03microl/min/pmol CYP, respectively. Taken together, these results provide evidence that CYP3A4 and CYP1A2 are the major isoforms responsible for the hydroxy metabolites formation from KR-33028.

STEREOSELECTIVE METABOLISM OF ENDOSULFAN BY HUMAN LIVER MICROSOMES AND HUMAN CYTOCHROME P450 ISOFORMS

Endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,3,4-benzo(e)dioxathiepin-3-oxide) is a broad-spectrum chlorinated cyclodiene insecticide. This study was performed to elucidate the stereoselective metabolism of endosulfan in human liver microsomes and to characterize the cytochrome P450 (P450) enzymes that are involved in the metabolism of endosulfan. Human liver microsomal incubation of endosulfan in the presence of NADPH resulted in the formation of the toxic metabolite, endosulfan sulfate. The intrinsic clearances (CL(int)) of endosulfan sulfate from beta-endosulfan were 3.5-fold higher than those from alpha-endosulfan, suggesting that beta-endosulfan would be cleared more rapidly than alpha-endosulfan. Correlation analysis between the known P450 enzyme activities and the rate of the formation of endosulfan sulfate in the 14 human liver microsomes showed that alpha-endosulfan metabolism is significantly correlated with CYP2B6-mediated bupropion hydroxylation and CYP3A-mediated midazolam hydroxylation, and that beta-endosulfan metabolism is correlated with CYP3A activity. The P450 isoform-selective inhibition study in human liver microsomes and the incubation study of cDNA-expressed enzymes also demonstrated that the stereoselective sulfonation of alpha-endosulfan is mediated by CYP2B6, CYP3A4, and CYP3A5, and that that of beta-endosulfan is transformed by CYP3A4 and CYP3A5. The total CL(int) values of endosulfan sulfate formation catalyzed by CYP3A4 and CYP3A5 were consistently higher for beta-endosulfan than for the alpha-form (CL(int) of 0.67 versus 10.46 microl/min/pmol P450, respectively). CYP2B6 enantioselectively metabolizes alpha-endosulfan, but not beta-endosulfan. These findings suggest that the CYP2B6 and CYP3A enzymes are major enzymes contributing to the stereoselective disposition of endosulfan.