Potent Preclinical Activity of Ponatinib in Germinal Center B-Cell-like Diffuse Large B-Cell Lymphoma (GCB-DLBCL) Models

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IntroductionDiffuse large B-cell lymphoma (DLBCL), the most common type of Non-Hodgkin lymphoma (NHL), comprises 2 major molecular subtypes: germinal center B-cell-like (GCB) and activated B cell-like (ABC). Although standard therapy (rituximab+ chemotherapy [R-CHOP]) is effective in most patients (pts), a significant proportion do not achieve durable remissions. Treatment of relapsed and refractory DLBCL pts with targeted therapy, such as the BTK inhibitor ibrutinib, has shown some promise; however, responses are mostly restricted to the ABC subtype. Treatment options for pts with relapsed/refractory GCB, outside of stem cell transplantation, are especially limited.Ponatinib is a potent pan-BCR-ABL inhibitor approved for pts with refractory or T315I+ chronic myeloid leukemia or Ph+ acute lymphoblastic leukemia. Initial characterization of the in vitro kinase activity of ponatinib demonstrated substantial activity against a number of additional oncogenic kinases, including KIT, RET, FLT3, and members of the FGFR, PDGFR, and SRC families. To obtain a broad, unbiased, assessment of the anti-proliferative effects of ponatinib, we screened a panel of 246 human tumor cell lines. Based on the novel finding that a GCB-DLBCL cell line was amongst those inhibited most potently by ponatinib, we conducted studies to further characterize the activity of ponatinib in NHL, and GCB-DLBCL in particular.ResultsA broad cell-based screen identified a small subset of cell lines (18/246; 7%) whose growth was potently inhibited by ponatinib (GI50<42 nM). A majority of these lines express activated variants of previously validated targets of ponatinib: ABL (N=5, GI50 <0.3 nM), FLT3 (N=1, GI50 1 nM), FGFR2 (N=2, GI50s 5-29 nM), and PDGFRα (N=1, 14 nM). In addition, ponatinib potently inhibited growth of the GCB-DLBCL cell line DoHH2 (GI50 8 nM). The cellular activity of ponatinib was next examined in a larger set of NHL cell lines enriched for the GCB subtype (Table 1). Ponatinib only exhibited modest activity (GI50 46-119 nM) against 2 mantle cell lymphoma (MCL) lines, but potently inhibited growth (GI50≤10 nM) of the one Burkitt's lymphoma (BL) line tested (Daudi). Most notably, ponatinib also potently inhibited growth of 5/9 GCB cell lines. In contrast, none of the GCB lines showed sensitivity to ibrutinib (GI50s >100 nM). Finally, we evaluated the in vivo potency of ponatinib in mice implanted with the GCB cell lines exhibiting the greatest (SU-DHL-4) and weakest (SU-DHL-10) in vitro sensitivity to ponatinib, using dosing regimens previously shown to be active in BCR-ABL models predictive of efficacy in patients. Once-daily oral administration of ponatinib resulted in a dose-dependent inhibition of SU-DHL-4 tumor growth, with 10 mg/kg inducing 78% tumor regression, and 30 mg/kg rapidly inducing complete regression that was maintained in all mice for an additional 2 weeks after ponatinib dosing was stopped. In contrast, ponatinib had much more modest effects on SU-DHL-10 tumors with 30 mg/kg only inhibiting tumor growth by 39%.ConclusionPonatinib has promising in vitro and in vivo activity against a substantial subset of GCB-DLBCL models tested, with potency similar to that observed in BCR-ABL models. These results provide support for evaluating ponatinib in GCB-DLBCL pts who have failed prior therapy. Studies to further characterize the molecular basis for the activity of ponatinib in NHL are ongoing.Table 1In vitro drug activity in 12 NHL cell linesCell lineTypePonatinib GI50 (nM)Ibrutinib GI50 (nM)SU-DHL-4GCB DLBCL1.3313DoHH2GCB DLBCL2.5114PfeifferGCB DLBCL62,074SU-DHL-6GCB DLBCL9.81,041WSU-NHLGCB DLBCL101,672FarageGCB DLBCL511,409U-2932GCB DLBCL79>10,000RLGCB DLBCL2126,939SU-DHL-10GCB DLBCL2382,827DaudiBL2.94,319MinoMCL46>10,000Jeko-1MCL1194,781GI50: the concentration that causes 50% growth inhibition. DisclosuresGozgit:ARIAD Pharmaceuticals Inc.: Employment, Other: Full-time Employee & Shareholder (self-managed). Song:ARIAD Pharmaceuticals Inc.: Employment, Other: Full-time Employee & Shareholder (self-managed). Wardwell:ARIAD Pharmaceuticals Inc.: Employment, Other: Full-time Employee & Shareholder (self-managed). Nadworny:ARIAD Pharmaceuticals Inc.: Employment, Other: Full-time Employee & Shareholder (self-managed). Ning:ARIAD Pharmaceuticals Inc.: Employment, Other: Full-time Employee & Shareholder (self-managed). Rivera:ARIAD Pharmaceuticals Inc.: Employment, Other: Full-time Employee & Shareholder (self-managed).