Predicting Cerdulatinib Therapeutic Concentrations in Patients with Relapsed/Refractory B Cell Malignancies Using Preclinical Models and Clinical PK/PD and Tumor Response Correlates

Background: Preclinical data and early clinical studies demonstrate a reliance on B cell antigen receptor (BCR) signaling and/or cytokine-induced JAK/STAT signaling for survival of subsets of B cell malignancies. Increased serum concentrations of several cytokines are observed in CLL and NHL and predict a more aggressive disease progression (Yan, X. J., et al, 2011; Mahadevan, D., et al, 2009; el Far. M., et al, 2004; Lai, R., et al, 2002; Fayed, L., et al, 2001). The source of these cytokines may be derived from the tumor itself in an autocrine stimulation fashion, or from non-tumor leukocytes which have mounted an ineffective immune response within the tumor microenvironment. Experimentally, IL4 has been shown to promote the survival of CLL B cells in culture and protect them from death by treatment with fludarabine and chlorambucil (Steele, A.J., et al, 2010). The mechanism underlying this survival support appears to be cytokine-induced up-regulation of BCL2 family members (Castejon, R., et al, 1999; Jewell, A.P., et al, 1994; Panayiotidis, P., et al, 1993; Dancescu, M., et al, 1992). Combined SYK/JAK inhibition may therefore represent a powerful strategy to treat B cell malignancies. Cerdulatinib is a reversible ATP competitive inhibitor of SYK, JAK1, JAK3, and TYK2 that is currently in clinical development for the treatment of relapsed/refractory B cell lymphoma and leukemia. We review here cerdulatinib preclinical and clinical pharmacodynamic/pharmacokinetic relationships to tumor response in treated patients.

Methods: Inhibition of SYK- and JAK-dependent and independent signaling was determined by intracellular phospho-flow following stimulation of human whole blood with various agonists against BCR and cytokine receptors. Anti-tumor activities of cerdulatinib and other selective inhibitors of BCR and JAK/STAT pathways were evaluated in fourteen DLBCL cell lines by CellTiter Glo, caspase 3 induction, and cell cycle arrest. In vivo anti-inflammatory activity of cerdulatinib was determined using the rat collagen induced arthritis model. The effective concentrations pre-clinically were compared to cerdulatinib-induced SYK and JAK inhibition, anti-inflammatory activity, and anti-tumor activity following oral dosing in relapsed/refractory CLL and NHL patients.

Results: Cerdulatinib demonstrated broad anti-tumor activity in DLBCL cell lines, relative to other targeted agents. In a panel of 14 cell lines representing both ABC and GCB subtypes, 9 underwent apoptosis and an additional 2 underwent cell cycle arrest. Cooperative effects of SYK and JAK inhibition were observed in 4 of the cell lines, whereas 3 cell lines were sensitive to SYK but not JAK inhibition, and 1 cell line was sensitive to JAK but not SYK inhibition. Three of the 14 cell lines were resistant to cerdulatinib. Apoptosis was induced in the majority of DLBCL cell lines at 2 µM (achieved at clinical doses ≥40 mg). In healthy whole blood ex vivo spiking experiments, cerdulatinib selectively inhibited BCR/SYK and cytokine (IL2, IL4, IL6) JAK/STAT signaling with IC₅₀'s ranging from 0.2-0.9 µM (achieved at clinical doses of 15 mg-40 mg). Inflammation and joint destruction in the rat collagen-induced arthritis model was arrested at 0.3 µM average plasma concentration (achieved at clinical doses ≥30 mg). In cancer patients receiving cerdulatinib once daily, plasma concentrations above 2 µM have been safely achieved, while maintaining steady-state Cmin of ~1 µM. Following oral dosing in patients, SYK and JAK pathways were inhibited with similar potency as was observed in healthy volunteer ex vivo spiking experiments with >90% inhibition of SYK and JAK safely achieved for multiple cycles of therapy. Tumor response as measured by CT scan strongly correlated with percent inhibition of SYK and JAK signaling in patient-derived whole blood, and percent inhibition of serum markers of inflammation (e.g., β2M, CRP, IL10, VCAM1, sTNFR, CCL3).

Conclusion: Once daily oral dosing of cerdulatinib at 40-65 mg achieves steady-state plasma concentrations in the 1-2µM range (trough to peak), which is sufficient to block SYK/JAK signaling, inflammatory mechanisms, and affect tumor viability both in DLBCL cell lines and in patients. We conclude that these exposure levels are sufficient to begin testing the clinical potential of cerdulatinib. We will begin enrolling phase Ib/IIa expansion cohorts this year.