Human CD19 antigen is a 95-kDa type I membrane glycoprotein in the immunoglobulin superfamily whose expression is limited to the various stages of B-cell development and differentiation and is maintained in the majority of B-cell malignancies, including leukemias and non-Hodgkin lymphomas of B-cell origin. Coupled with its differential and favorable expression profile, CD19 has rapid internalization kinetics and is not shed into the circulation, making it an ideal target for the development of antibody-drug conjugates (ADCs) to treat B-cell malignancies. ADCT-402 (loncastuximab tesirine) is a novel CD19-targeted ADC delivering SG3199, a highly cytotoxic DNA minor groove interstrand crosslinking pyrrolobenzodiazepine (PDB) dimer warhead. It showed potent and highly targeted in vitro cytotoxicity in CD19-expressing human cell lines. ADCT-402 was specifically bound, internalized, and trafficked to lysosomes in CD19-expressing cells and, following release of the PBD warhead, resulted in formation of DNA crosslinks that persisted for 36 hours. Bystander killing of CD19 cells by ADCT-402 was also observed. In vivo, single doses of ADCT-402 resulted in highly potent, dose-dependent antitumor activity in several subcutaneous and disseminated human tumor models with marked superiority to comparator ADCs delivering tubulin inhibitors. Dose-dependent DNA crosslinks and γ-H2AX DNA damage response were measured in tumors by 24 hours after single dose administration, whereas matched peripheral blood mononuclear cells showed no evidence of DNA damage. Pharmacokinetic analysis in rat and cynomolgus monkey showed excellent stability and tolerability of ADCT-402 in vivo. Together, these impressive data were used to support the clinical testing of this novel ADC in patients with CD19-expressing B-cell malignancies.

Synthetic pyrrolobenzodiazepine (PBD) dimers, where two PBD monomers are linked through their aromatic A-ring phenolic C8-positions via a flexible propyldioxy tether, are highly efficient DNA minor groove cross-linking agents with potent cytotoxicity. PBD dimer SG3199 is the released warhead component of the antibody-drug conjugate (ADC) payload tesirine (SG3249), currently being evaluated in several ADC clinical trials. SG3199 was potently cytotoxic against a panel of human solid tumour and haematological cancer cell lines with a mean GI50 of 151.5 pM. Cells defective in DNA repair protein ERCC1 or homologous recombination repair showed increased sensitivity to SG3199 and the drug was only moderately susceptible to multidrug resistance mechanisms. SG3199 was highly efficient at producing DNA interstrand cross-links in naked linear plasmid DNA and dose-dependent cross-linking was observed in cells. Cross-links formed rapidly in cells and persisted over 36 hours. Following intravenous (iv) administration to rats SG3199 showed a very rapid clearance with a half life as short as 8 minutes. These combined properties of cytotoxic potency, rapid formation and persistence of DNA interstrand cross-links and very short half-life contribute to the emerging success of SG3199 as a warhead in clinical stage ADCs.

Toxicokinetic analysis is an essential part of nonclinical drug development. Advances in bioanalytical techniques have opened up the potential to use smaller sample volumes (microsamples) to assess drug exposure in blood, plasma and/or serum. Microsampling can increase the amount of nonclinical safety information available, improve its validity by linking toxic effects to drug exposure in individual animals and represents the most significant opportunity to reduce animal use in toxicology studies in the short term. In May 2013, a workshop was held with 80 delegates from 33 companies with the aim of sharing information and knowledge on microsampling technologies. This article covers the discussions at the workshop, current practice in the industry, regulatory experiences and the future direction of microsampling across drug development.

Embryonic (before the end of organogenesis) exposure was assessed in one molecule each in rabbit, rat, and mouse, but detectable levels were present only in rodents. In rodents, fetal levels remained relatively constant from gestation day (GD) 16 and 17 until the end of gestation, while maternal levels decreased or remained constant in rat and decreased in mice. In rabbits, following a last dose on GD 19, fetal levels increased markedly in late gestation while maternal levels decreased. In the cynomolgus monkey, fetal levels increased substantially from GD 50 to 100 and were maintained relatively constant through parturition (approximately GD 165). Based on available data of both the monkey and rabbit, IgG1 molecules appeared to transfer more readily than other isotypes in late gestation. Across all species, there was no differential transfer based on pharmacologic target being soluble or membrane bound. Within each species there was a correlation between maternal and fetal exposure, suggesting it may be possible to predict fetal exposures from maternal exposure data. These nonclinical data (both temporal and quantitative aspects) are discussed in a comparative context relative to our understanding of IgG placental transfer in humans.

BACKGROUND. Hypophosphatasia (HPP) is a rare genetic disorder resulting in variable alterations of bone formation and mineralization that are caused by mutations in the ALPL gene, encoding the tissue-nonspecific alkaline phosphatase (ALP) enzyme. METHODS.In this phase IIA open-label, single-center, intra-patient, dose-escalating study, adult patients with HPP received 3 ascending intravenous doses of 5, 10, and 20 mg/kg BPS804, a fully human anti-sclerostin monoclonal antibody, on days 1, 15, and 29, respectively. Patients were followed for 16 weeks after the last dose. We assessed the pharmacodynamics, pharmacokinetics, preliminary efficacy, and safety of BPS804 administrations at specified intervals during treatment and follow-up. RESULTS.Eight patients (mean age 47.8 years) were enrolled in the study (6 females, 2 males). BPS804 treatment increased mean ALP and bone-specific ALP enzymatic activity between days 2 and 29. Transient increases in the bone formation markers procollagen type-I N-terminal propeptide (PINP), osteocalcin, and parathyroid hormone as well as a transient decrease in the bone resorption marker C-telopeptide of type I collagen (CTX-1) were observed. Lumbar spine bone mineral density showed a mean increase by day 85 and at end of study. Treatment-associated adverse events were mild and transient.CONCLUSION. BPS804 treatment was well tolerated and resulted in increases in bone formation biomarkers and bone mineral density, suggesting that sclerostin inhibition could be applied to enhance bone mineral density, stability, and regeneration in non-life-threatening clinical situations in adults with HPP. TRIAL REGISTRATION. Clinicaltrials.gov NCT01406977. FUNDING.