Combinatorial efficacy of entospletinib and chemotherapy in patient-derived xenograft models of infant acute lymphoblastic leukemia

Abstract

Survival of infants with KMT2A-rearranged acute lymphoblastic leukemia (ALL) remains dismal despite intensive chemotherapy. We observed constitutive phosphorylation of spleen tyrosine kinase (SYK) and associated signaling proteins in infant ALL patient-derived xenograft (PDX) model specimens and hypothesized that the SYK inhibitor entospletinib would inhibit signaling and cell growth in vitro and leukemia proliferation in vivo. We further predicted that combined entospletinib and chemotherapy could augment anti-leukemia effects. Basal kinase signaling activation and HOXA9/MEIS1 expression differed among KMT2A-rearranged (KMT2A-AFF1 [n=4], KMT2A-MLLT3 [n=1], KMT2A-MLLT1 [n=4]) and non-KMT2A-rearranged [n=3] ALL specimens and stratified by genetic subgroup. Incubation of KMT2A-rearranged ALL cells in vitro with entospletinib inhibited methylcellulose colony formation and SYK pathway signaling in a dose-dependent manner. In vivo inhibition of leukemia proliferation with entospletinib monotherapy was observed in RAS-wild-type KMT2A-AFF1, KMT2A-MLLT3, and KMT2A-MLLT1 ALL PDX models with enhanced activity in combination with vincristine chemotherapy in several models. Surprisingly, entospletinib did not decrease leukemia burden in two KMT2A-AFF1 PDX models with NRAS or KRAS mutations, suggesting potential RAS-mediated resistance to SYK inhibition. As hypothesized, superior inhibition of ALL proliferation was observed in KMT2A-AFF1 PDX models treated with entospletinib and the MEK inhibitor selumetinib versus vehicle or inhibitor monotherapies (p<0.05). In summary, constitutive activation of SYK and associated signaling occurs in KMT2A-rearranged ALL with in vitro and in vivo sensitivity to entospletinib. Combination therapy with vincristine or selumetinib further enhanced treatment effects of SYK inhibition. Clinical study of entospletinib and chemotherapy or other kinase inhibitors in patients with KMT2A-rearranged leukemias may be warranted.

Activated interleukin-7 receptor signaling drives B-cell acute lymphoblastic leukemia in mice

“…While technically challenging, it will also be important to determine whether this BCR-like program is active in aIL7Rexpressing progenitors prior to overt disease development, or whether this phenomenon is a feature of transformation and/or secondary mutation acquisition. Regardless, consistent with recent data in CRLF2rearranged Ph-like ALL 85 and KMT2A-rearranged infant B-ALL 96 , our results suggest that targeting this BCR-like program with Syk inhibitors (in parallel with other pathway agents) could potentially provide therapeutic benefit for aIL7R leukemias in vivo in preclinical models and in patients.…”

An open‐label phase 2 trial of entospletinib in indolent non‐Hodgkin lymphoma and mantle cell lymphoma

“…The relatively low response rate as a single agent suggests that entospletinib should be investigated in combination with other agents. In vitro and in vivo studies show synergistic activity with vincristine in a broad panel of NHL cell lines (Axelrod et al , ) and a model of acute lymphoblastic leukaemia (Loftus et al , ). Syk inhibition may also reduce resistance to venetoclax, a BCL2 inhibitor, through downregulation of Mcl1 (Bojarczuk et al , ).…”

Oncogene-independent BCR-like signaling adaptation confers drug resistance in Ph-like ALL

“…Our new data further extend this observation, as we demonstrate that dexamethasone strongly represses ruxolitinib-induced changes in B cell development and BCR signaling genes. Strikingly, dexamethasone together with ruxolitinib and idelalisib fully inhibited STAT5, PI3K, and ERK signaling and eliminated Ph-like ALL cells in vitro and in vivo in comparison with drug monotherapies or into secondary or tertiary recipient NSG mice for experimental studies described herein (4,14,15,66). After flow cytometric confirmation of more than 1% CD45 + CD19 + (and CD10 + and TSLPR + for CRLF2-R Ph-like) human ALL in peripheral blood of well-engrafted mice, animals were randomized to treatment with indicated combinations of (a) oral (p.o.)…”