Pharmacokinetics of trastuzumab deruxtecan (T-DXd), a novel anti-HER2 antibody-drug conjugate, in HER2-positive tumour-bearing mice.

Trastuzumab deruxtecan (T-DXd, DS-8201a) is an antibody-drug conjugate (ADC), comprising an anti-HER2 antibody (Ab) at a drug-to-Ab ratio of 7-8 with the topoisomerase I inhibitor DXd. In this study, we investigated the pharmacokinetics (PK), biodistribution, catabolism, and excretion profiles of T-DXd in HER2-positive tumour-bearing mice.Following intravenous (iv) administration of T-DXd, the PK profiles of T-DXd and total Ab (the sum of conjugated and unconjugated Ab) were almost similar, indicating that the linker is stable during circulation. Biodistribution studies using radiolabelled T-DXd demonstrated tumour-specific distribution and long-term retention. DXd was the main catabolite released from T-DXd in tumours, with exposure levels at least five times higher than those in normal tissues and seven times higher than those achieved by non-targeted control ADC. Following iv administration of DXd, it was rapidly cleared from the circulation (T1/2; 1.35 h) and excreted mainly through faeces as its intact form.The PK profiles reveal that T-DXd effectively delivers the expected payload, DXd, to tumours, while minimising payload exposure to the systemic circulation and normal tissues. The released DXd is rapidly cleared from systemic circulation, presumably via the bile with negligible metabolism, and excreted through the faeces.

Observation of Clinically Relevant Drug Interaction in Chimeric Mice with Humanized Livers: The Case of Valproic Acid and Carbapenem Antibiotics.

BACKGROUND AND OBJECTIVE: Human in vitro and dog in vitro/in vivo researches indicate that the drug-drug interaction (DDI) of decreased plasma valproic acid (VPA) concentration by co-administration of carbapenem antibiotics is caused by inhibition of acylpeptide hydrolase (APEH)-mediated VPA acylglucuronide (VPA-G) hydrolysis by carbapenems. In this study, we investigated VPA disposition and APEH activities in TK-NOG chimeric mice, whose livers were highly replaced with human hepatocytes, to evaluate the utility of this animal model and the clinical relevance of the DDI mechanism. METHODS: VPA and VPA-G concentrations in plasma, urinary excretion of VPA-G and APEH activity in humanized livers were measured after co-administration of VPA with meropenem (MEPM) to chimeric mice. RESULTS: After co-administration with MEPM to the chimeric mice, plasma VPA concentration more rapidly decreased than without the co-administration. An increase in plasma AUC and urinary excretion of VPA-G was also observed. APEH activity in humanized livers was strongly inhibited even at 24 h after co-administration of MEPM to the chimeric mice. CONCLUSION: The DDI of VPA with carbapenems was successfully observed in chimeric mice with humanized livers. The DDI was caused by long-lasting inhibition of hepatic APEH-mediated VPA-G hydrolysis by carbapenems, which strongly supports the APEH-mediated mechanism of the clinical DDI. This is the first example showing the usefulness of chimeric mice with humanized livers for evaluation of a DDI via non-cytochrome P450 enzyme.

In vivo inhibition of acylpeptide hydrolase by carbapenem antibiotics causes the decrease of plasma concentration of valproic acid in dogs.

1. Our previous in vitro studies suggest that inhibition of the acylpeptide hydrolase (APEH) activity as valproic acid glucuronide (VPA-G) hydrolase by carbapenems in human liver cytosol is a key process for clinical drug-drug interaction (DDI) of valproic acid (VPA) with carbapenems. Here, we investigated whether in vivo DDI of VPA with meropenem (MEPM) was caused via inhibition of APEH in dogs. 2. More rapid decrease of plasma VPA levels and increased urinary excretion of VPA-G were observed after co-administration with MEPM compared with those after without co-administration, whereas the plasma level and bile excretion of VPA-G showed no change. 3. Dog VPA-G hydrolase activity, inhibited by carbapenems, was mainly located in cytosol from both the liver and kidney. APEH-immunodepleted cytosols lacked VPA-G hydrolase activity. Hepatic and renal APEH activity was negligible even at 24 h after dosing of MEPM to a dog. 4. In conclusion, DDI of VPA with carbapenems in dogs is caused by long-lasting inhibition of APEH-mediated VPA-G hydrolysis by carbapenems, which could explain the delayed recovery of plasma VPA levels to the therapeutic window even after discontinuation of carbapenems in humans.

Systematic research of peptide spacers controlling drug release from macromolecular prodrug system, carboxymethyldextran polyalcohol-peptide-drug conjugates.

The primary purpose of this study was to comprehensively delineate specificity of the peptide spacer sequence to tumor-expressed proteases for the design of macromolecular carrier-peptide spacer-drug conjugate system. 225 conjugates of carboxymethyldextran polyalcohol (CM-Dex-PA) as water-soluble carrier and a dansyl derivative (N-(4-aminobutyl)-5-(dimethylamino)-1-naphthalenesulfonamide, DNS) as the model drug linked with different tetrapeptide spacers (Gly-Gly-P(2)-P(1), P(2), P(1): Ala, Asn, Gly, Cit, Gln, Ile, Leu, Met, Phe, Pro, Ser, Thr, Trp, Tyr, and Val) were combinatorially synthesized. First, the drug release assay of all of the fluorogenic model conjugates was performed in murine Meth A solid tumor homogenates. The drug release rate was higher with conjugates having hydrophobic amino acids at P(2). It was also found that conjugates with Asn release the drug rapidly and, in contrast, those with Pro does not. Second, we selected three peptide spacers (Gly-Gly-Phe-Gly, Gly-Gly-Ile-Gly, Gly-Gly-Pro-Leu), which release only DNS at different rates, and applied them to doxorubicin (DXR) conjugates. These three DXR conjugates were used for investigating relationships with drug release, pharmacokinetics, and antitumor activity against Meth A bearing mice of these conjugates. The release of DXR from the conjugates corresponded well with that of DNS conjugates in tumor homogenates. CM-Dex-PA-Gly-Gly-Phe-Gly-DXR and CM-Dex-PA-Gly-Gly-Ile-Gly-DXR indicated strong antitumor activity, with the comparable pharmacokinetic profile of released DXR in tumor. Taken with the fact that the drug release rate in tumor homogenates was approximately 10-fold different between these two DXR conjugates, it is likely that cellular uptake of the conjugate would be rate-limiting, rather than the drug release process under the in vivo situation. However, much weaker antitumor activity was observed with CM-Dex-PA-Gly-Gly-Pro-Leu-DXR, of which the drug release was extremely slow.

Relationship between drug release of DE-310, macromolecular prodrug of DX-8951f, and cathepsins activity in several tumors.

DE-310 is composed of the topoisomerase-I inhibitor DX-8951 (exatecan) and carboxymethyldextran polyalcohol (CM-Dex-PA) carrier, which are covalently linked via peptidyl spacer (Gly-Gly-Phe-Gly). In this study, we investigated relationship between the cathepsin activity and the drug release of DE-310 by use of human liver origin cathepsin (B, L and H) and tumor cells (murine tumor cells (Meth A and M5076), and human tumor cells (HCT116, A549, PC-12, T98G, and HL-60)). Preliminary studies indicated that human liver cathepsin B produced Glycyl DX-8951 (G-DX-8951) from DE-310 more preferentially than DX-8951, whereas human liver cathepsin L produced DX-8951 preferentially. Release of drugs from DE-310 and cathepsin activities were measured in tumor cell types. The release of both DX-8951 and G-DX-8951 from DE-310 correlated well with cathepsin B activity of tumor cells. The release of DX-8951 was weakly, but not significantly, correlated with cathepsin L activity. In M5076 (high cathepsin activity) or Meth A (low cathepsin activity) xenograft models, the levels of DX-8951 and G-DX-8951 in M5076 were higher than in Meth A after single intravenous administration of DE-310. Our findings suggest that cathepsin B is primarily responsible for drug release from DE-310 in tumor.

Hyperthermia-enhanced tumor accumulation and antitumor efficacy of a doxorubicin-conjugate with a novel macromolecular carrier system in mice with non-small cell lung cancer.

A novel drug delivery system (DDS) compound was formed by binding doxorubicin hydrochloride (DXR) to the macromolecular carrier carboxymethyldextran polyalcohol (CM-Dex-PA) via the peptidyl spacer (GGFG: Gly-Gly-Phe-Gly). Its use in a murine tumor model confirmed that the DDS (CM-Dex-PA-GGFG-DXR) was retained in the blood and distributed in tumor tissue. The combined use of hyperthermia (HT: 41-42 degrees C for 40 min) and DXR-conjugate (5, 10 or 20 mg/kg i.v.) on tumor accumulation and efficacy was investigated in a murine model of non-small cell lung cancer. Tumor size was measured and the tumor inhibition rate (IR) was calculated. The mean tumor concentration of conjugated DXR in the DXR-conjugate group was 9.40 microg/g compared with 19.04 microg/g in the DXR-conjugate + HT group (p=0.0008). The antitumor efficacy of the DXR-conjugate was significantly enhanced in the groups receiving the combination therapy (p=0.0039, p=0.0250). Significant differences were found between the groups given DXR and those given DXR-conjugate (p=0.0492, p=0.0104). The results demonstrate that the antitumor efficacy of DXR-conjugate is significantly superior to that of DXR alone and the combined use of DXR-conjugate and HT increases the drug's concentration in the tumor, with significant enhancement of antitumor efficacy.

Quantitative acid hydrolysis of DE-310, a macromolecular carrier system for the camptothecin analog DX-8951f.

DE-310 is a novel macromolecular prodrug of the topoisomerase-I inhibitor DX-8951. DX-8951 is covalently linked to carboxymethyl dextran polyalcohol (CM-Dex-PA) via a Gly-Gly-Phe-Gly (GGFG) tetrapeptide spacer. The present study was conducted to identify the portions of DX-8951 linked to DE-310, as well as to quantify the number of DX-8951 molecules associated with DE-310. Two different structures terminated with either glycolaldehyde (CM-GA-GGFG-DX-8951) or glycerol (CM-Glr-GGFG-DX-8951) are obtained when the polymer backbone is fragmented with 1 M HCl. The two products, i.e., CM-GA-GGFG-DX-8951 and CM-Glr-GGFG-DX-8951, indicate linkage of GGFG-DX-8951 with carboxymethyl (CM) group at C-2 and C-4 position of the glucose units, respectively. In the present study, CM-GA-GGFG-DX-8951 was reduced to CM-ethyleneglycol (EG)-GGFG-DX-8951 in order to improve stability prior to HPLC analysis. Hydrolysis results revealed that the amount of CM-GA-GGFG-DX-8951 liberated was 84.7 nmol/mg DE-310 and the amount of CM-Glr-GGFG-DX-8951 was 71.8 nmol/mg DE-310. Considering the ratio of generation between CM-GA-GGFG-DX8951 and CM-Glr-GGFG-DX8951, it suggested that slightly larger amount of GGFG-DX-8951 was linked to carboxymethyl groups at the C-2 position of glucose units in DE-310. The sum of the amounts of CM-GA-GGFG-DX-8951 and CM-Glr-GGFG-DX-8951 agrees well with the amount of G-DX-8951 produced from DE-310 by alpha-chymotrypsin treatment (157.5 nmol/mg DE-310). The data indicate that the established hydrolysis give a quantitative evaluation of the DX-8951 linked to DE-310.

A possible mechanism for the long-lasting antitumor effect of the macromolecular conjugate DE-310: mediation by cellular uptake and drug release of its active camptothecin analog DX-8951.

DE-310, a new macromolecular prodrug, was designed to enhance the pharmacological profiles of a novel camptothecin analog (DX-8951f), and a single treatment with DE-310 exhibits a similar or greater therapeutic effect than do optimally scheduled multiple administrations of DX-8951f in several types of tumors. In this study, the drug-release mechanism by which DE-310 excites antitumor activity was investigated in Meth A cells, a malignant ascites model of murine fibrosarcoma. A single i.v. injection of DE-310 at the maximum tolerated dose (MTD) prolonged survival of Meth A-bearing mice by 300%. DX-8951 and glycyl-8951 (G-DX-8951), enzymatic cleavage products of DE-310, were detected in serum and ascites fluid, and also in the culture medium of Meth A ascites cells incubated in vitro with DE-310. The total amounts of DX-8951, G-DX-8951, and conjugated DX-8951 in Meth A tumor cells were three times higher than that in macrophages. Furthermore, DX-8951-related fluorescence was observed in Meth A ascites cells obtained from Meth A-bearing mice that had received DE-310 or CM-Dex-PA-DX-8951 that does not release free DX-8951. DX-8951-related fluorescence was also observed at the site of lysosomes in cells incubated in vitro with DE-310 at 37 degrees C, but not in those incubated at 4 degrees C. Drugs were released from DE-310 by cysteine proteinase prepared from Meth A tumor tissue. These results suggest that the mechanism by which DX-8951 is released from DE-310 in vivo is involved in the process of uptake of DE-310 into tumor or macrophages, digestion by intracellular lysosomal cysteine proteinase, and subsequent secretion of the drugs.