Preclinical and Clinical Binding Properties, Internalization Kinetics, and Clinicopathological Activity of Brentuximab Vedotin (SGN-35): A Novel Antibody Drug Conjugate for Anaplastic Large Cell Lymphoma and Classical Hodgkin Lymphoma
Authors: Fromm Jonathan R , McEarchern Julie A. , Kennedy Dana , Anju Thomas , Shustov Andrei R , Gopal Ajay K 
Published: October 2019

Abstract
Abstract 1789

Background:
Brentuximab vedotin (SGN-35) is a novel anti-CD30 antibody conjugated to the cytotoxic drug monomethyl auristatin E (MMAE) designed to selectively target and kill CD30 expressing neoplasms. This agent has demonstrated antitumor activity in classical Hodgkin lymphoma and CD30-positive T cell lymphoma, yet the binding properties, internalization kinetics, and clinicopathological findings have not been described in tumor specimens derived from treated patients. Therefore, we investigated the activity of SGN-35 on a patient with cutaneous manifestations of systemic ALK-negative anaplastic large cell lymphoma (ALCL), and correlated these results with studies of the activity of SGN-35 on cultured CD30-positive cells lines.

Methods and Results:
First, we confirmed (using flow cytometry) that SGN-35 and the anti-CD30 antibody clone BerH83 do not compete for binding to CD30. Next, in Karpas 299 (ALCL cell line) and KM-H2 (cell line derived from Hodgkin lymphoma) cells, we quantitatively monitored CD30 expression and cell-surface SGN-35 over time (measured as antigen binding capacity [ABC]/cell), demonstrating maximum antigen expression at 24–48 hours of incubation with 15 μg/ml SGN-35 followed by decrease at 120 hours, consistent with SGN-35-induced internalization (Table). Similar studies were performed on sequential tumor biopsies from a 68 year old male with a 5-year history of ALK-negative ALCL relapsing after 4 prior systemic regimens and radiation, now presenting with multiple pink ulcerated tumorous lesions on his lower extremities as well as bone and nodal involvement. H&E and anti-CD30 immunohistochemical stains of both pretreatment and 24 hrs post-treatment (after the first dose of SGN-35 (1.8mg/kg)-ClinicalTrials.gov identifier NCT01026415) skin punch biopsies showed a dense dermal infiltrate of large CD30-positive neoplastic cells. Biopsy at 48 hrs post-treatment demonstrated numerous apoptotic cells. Antigen density experiments on the patient biopsy specimens and clinical findings correlated with these morphologic results. CD30 antigen density was highest on the patient's cells pretreatment biopsy (1.01 × 105 ABC units/cell) and then decreased after 24 hrs (7.83 × 104 ABC units/cell) and 48 hrs (5.08 × 104 ABC units/cell). Bound SGN-35 was greatest at 24 hrs (2.26 × 103 ABC units/cell) and decreased at 48 hrs (1.40 × 103 ABC units/cell) (Table). The corresponding measured blood concentrations of SGN-35 at 24 hr, 48 hr, and 21 days were 10 μg/mL, 7 μg/mL, and 1 μg/mL, respectively. No CD30 positive cells were present in the day 21 biopsy, precluding evaluation of CD30 antigen density and bound SGN-35. Clinically, the size and prominence of the skin lesions were reduced at day 21 post treatment and biopsy at this time point showed no morphologic or immunohistochemical evidence of the neoplastic population (pathologic complete remission). After the second dose of SGN-35 the patient achieved an 81% reduction in all radiographically measurable lesions (partial response) and achieved a radiographic and cutaneous complete remission after the 5th infusion of this agent.

Conclusion:
These data are the first to suggest in both cell lines and patient-derived tissues that the internalization kinetics of SGN-35 is rapid with resultant reduction in CD30 expression within the first 48 hours and concurrent apoptosis induction within the targeted cells. While the measured SGN-35 occupancy of CD30 binding sites in the patient is lower than with the cell lines, these data highlight the potential antitumor activity of this agent. The results from the single patient need to be confirmed in a cohort of patients. Nevertheless, such results imply that even with subsaturating occupancy of CD30, thousands of molecules of SGN-35 (each with approximately 4 molecules of MMAE) are likely to be internalized by and potentially kill each targeted cell and may be sufficient to yield pathologic remissions and clinical activity.

Disclosures:
Fromm: Seattle Genetics: Research Funding. McEarchern:Seattle Genetics: Employment. Kennedy:Seattle Genetics: Employment. Shustov:Seattle Genetics: Research Funding; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees. Gopal:Seattle Genetics: Research Funding.