Harnessing the Power of CTLA4-FasL: Unraveling the Mechanism and Pre-Clinical Impact in Lymphoma Therapy

The fusion protein CTLA4-FasL, known as KAHR-102, is a stable homo-hexamer that targets both the B7 receptors (CD80 and CD86) on immune cells and the Fas-receptors (CD95) to induce apoptosis in cells expressing these receptors. This bi-functional drug is particularly effective against B cell lineage lymphoma cells, which commonly express both receptor types.

In the study, CTLA4-FasL demonstrated its efficacy in inducing apoptosis in highly resistant diffuse large B cell lymphoma (DLBCL) cell lines, such as LY 7, 19, and SUHDL-4. The drug showed potent inhibition of cell viability with an EC50 range of 0.02-0.06 nM and induced significant apoptosis as determined by the annexin-PI assay.

CTLA4-FasL was found to activate pro-apoptotic signals and inhibit anti-apoptotic pathways in cells with both B7 and Fas receptors. It also prevented the activation of the non-canonical NFkB pathway, which is crucial for its apoptotic effect. These effects were not observed in B7-negative cells or when B7 blocking antibodies were present.

In vivo, CTLA4-FasL significantly improved survival in both a BCL1 mouse model of systemic lymphoma and a human-to-mouse xenograft model when administered via four subcutaneous injections. The drug was found to be equally active on mouse and human cells.

Safety and tolerability were assessed in GLP toxicology studies in mice and cynomolgus monkeys. No significant anatomical pathology or adverse clinical symptoms were observed at the highest doses tested. Transient and dose-dependent leukopenia and elevated liver enzymes were noted in monkeys. Pharmacokinetic studies showed that the drug reached maximal plasma concentrations 4-6 hours post injection and had a half-life of about 2 hours in mice and 10-20 hours in monkeys.

In conclusion, CTLA4-FasL has been demonstrated as an effective treatment for B cell lymphoma in pre-clinical models, with transient leukopenia being the primary adverse effect observed in monkeys. A Phase I/IIa clinical trial for patients with lymphoma expressing both B7 and FasL on tumor cells is planned.