FDA Approves Antibody Drug Conjugate ZYNLONTA® for Large B-Cell Lymphoma

SUMMARY: The FDA on April 23, 2021 granted accelerated approval to ZYNLONTA® (Loncastuximab tesirine-lpyl ), a CD19-directed antibody and alkylating agent conjugate, for adult patients with Relapsed or Refractory Large B-Cell Lymphoma after two or more lines of systemic therapy, including Diffuse Large B-Cell Lymphoma (DLBCL) not otherwise specified, DLBCL arising from Low Grade Lymphoma, and High Grade B-Cell Lymphoma.

The American Cancer Society estimates that in 2021, about 81,560 people will be diagnosed with Non Hodgkin Lymphoma (NHL) in the United States and about 20,720 individuals will die of this disease. Diffuse Large B-Cell Lymphoma (DLBCL) is the most common of the aggressive Non-Hodgkin lymphoma’s in the United States, and the incidence has steadily increased 3-4% each year. More than half of patients are 65 or older at the time of diagnosis and the incidence is likely to increase with the aging of the American population. The etiology of Diffuse Large B-Cell Lymphoma is unknown. Contributing risk factors include immunosuppression (AIDS, transplantation setting, autoimmune diseases), UltraViolet radiation, pesticides, hair dyes, and diet. DLBCL is a neoplasm of large B cells and the most common chromosome abnormality involves alterations of the BCL-6 gene at the 3q27 locus, which is critical for germinal center formation. Two major molecular subtypes of DLBCL arising from different genetic mechanisms have been identified, using gene expression profiling: Germinal Center B-Cell-like (GCB) and Activated B-Cell-like (ABC). Patients in the GCB subgroup have a higher five year survival rate, independent of clinical IPI (International Prognostic Index) risk score, whereas patients in the ABC subgroup have a significantly worse outcome. Regardless, R-CHOP regimen (RITUXAN®-Rituximab, Cyclophosphamide, Doxorubicin, Vincristine, and Prednisone), given every 21 days, for 6 cycles, delivered with curative intent, is the current standard of care for patients of all ages, with newly diagnosed DLBCL, regardless of molecular subtype. Approximately 30-40% of patients experience disease progression or relapse, during the first 2 years and attempts to improve on R-CHOP regimen have not been successful. For patients who fail first line therapy, outcomes are poor, worsening with each line of therapy, and the chance for cure or long term disease-free survival diminishes. There is a significant unmet need for patients with Relapsed/Refractory DLBCL.

ZYNLONTA® is a CD19-directed Antibody Drug Conjugate comprised of a humanized anti-CD19 antibody, conjugated through a linker to a potent pyrrolobenzodiazepine (PBD) dimer toxin. Once bound to a CD19-expressing cell, ZYNLONTA® is internalized by the cell following which the toxic payload is released. The potent toxin then binds irreversibly to DNA to create highly potent interstrand cross-links that block DNA strand separation, thereby disrupting essential DNA metabolic processes such as replication and ultimately resulting in cell death. CD19 is a clinically validated target for the treatment of B-cell malignancies.

The present FDA approval of ZYNLONTA® was based on LOTIS-2, which is an open-label, single arm trial in which 145 adult patients who had Relapsed or Refractory DLBCL or High Grade B-Cell Lymphoma were included. This study included transplant eligible and ineligible patients, patients with double or triplet-hit lymphoma, and patients who previously received stem cell transplant or CD 19-targeted CAR-T cell therapy. Patients received ZYNLONTA® 0.15 mg/kg every 3 weeks for 2 cycles, then 0.075 mg/kg every 3 weeks for subsequent cycles. Treatment was continued until progressive disease or unacceptable toxicity. Enrolled patients had at least two prior systemic regimens. The main efficacy outcome measure was Overall Response Rate (ORR). Pre-specified analyses of ORR and Duration of Response (DoR) by demographic and clinical characteristics were performed, and ORR was assessed by independent reviewer according to the Lugano response criteria.

The ORR was 48.3% with a Complete Response Rate of 24.1%. The Partial Response (PR) rate was 24.1%. Patients had a median time to response of 1.3 months and the median Duration of Response for the 70 responders was 10.3 months (inclusive of patients who were censored). The most common Grade 3 or higher treatment-related adverse events included neutropenia with a low incidence of febrile neutropenia, thrombocytopenia, Gamma-Glutamyl Transferase increase, and anemia.

The authors concluded that ZYNLONTA® had substantial single-agent antitumor activity in patients with Relapsed/Refractory Diffuse Large B-Cell Lymphoma, with encouraging and durable responses noted in patients with high-risk characteristics.

Efficacy and Safety of Loncastuximab Tesirine (ADCT-402) in Relapsed/Refractory Diffuse Large B-Cell Lymphoma. Caimi PF, Ai WZ, Alderuccio JP, et al. Presented at the 62nd ASH Annual Meeting and Exposition, December 5-8,2020. Abstract#1183