Background Irreversible inhibition of Bruton tyrosine kinase (Btk) by ibrutinib represents a significant therapeutic advance for chronic lymphocytic leukemia (CLL). However, ibrutinib also irreversibly inhibits alternative kinase targets, which potentially compromise its therapeutic index. Acalabrutinib (ACP-196) is a more selective irreversible Btk inhibitor specifically designed to improve upon the safety and efficacy of first generation Btk inhibitors. Methods Sixty-one patients with relapsed CLL were treated in a phase 1–2 multicenter study designed to assess the safety, efficacy, pharmacokinetics and pharmacodynamics of oral acalabrutinib. Patients were continuously treated with acalabrutinib 100 to 400 mg once daily in the dose-escalation portion of the study, and 100 mg twice daily in the expansion portion. Results Patient demographics include a median age of 62 years; median of 3 prior therapies; 31% del(17)(p13.1) and 75% unmutated immunoglobulin heavy chain variable genes. No dose-limiting toxicities occurred. The most common adverse events observed were headache (43%), diarrhea (39%) and increased weight (26%). Most adverse events were Grade 1–2. At a median follow-up of 14.3 months, the best overall response rate was 95%, including 85% partial response, 10% partial response with lymphocytosis and 5% stable disease. In patients with del(17)(p13.1), the best overall response was 100%. No cases of Richter’s transformation and only 1 CLL progression have occurred. Conclusions Acalabrutinib is a highly selective Btk inhibitor that provides effective and well tolerated treatment for patients with relapsed CLL, including those with del(17)(p13.1).

Chronic lymphocytic leukemia (CLL) is characterized by constitutive activation of the B-cell receptor (BCR) signaling pathway, but variable responsiveness of the BCR to antigen ligation. Bruton's tyrosine kinase (BTK) shows constitutive activity in CLL and is the target of irreversible inhibition by ibrutinib, an orally bioavailable kinase inhibitor that has shown outstanding activity in CLL. Early clinical results in CLL with other reversible and irreversible BTK inhibitors have been less promising, however, raising the question of whether BTK kinase activity is an important target of ibrutinib and also in CLL. To determine the role of BTK in CLL, we used patient samples and the Em-TCL1 (TCL1) transgenic mouse model of CLL, which results in spontaneous leukemia development. Inhibition of BTK in primary human CLL cells by small interfering RNA promotes apoptosis. Inhibition of BTK kinase activity through either targeted genetic inactivation or ibrutinib in the TCL1 mouse significantly delays the development of CLL, demonstrating that BTK is a critical kinase for CLL development and expansion and thus an important target of ibrutinib. Collectively, our data confirm the importance of kinase-functional BTK in CLL. (Blood. 2014; 123(8):1207-1213 IntroductionChronic lymphocytic leukemia (CLL) is a common adult leukemia that is currently incurable outside of stem cell transplantation. Although response to IgM ligation is variable, the B-cell receptor (BCR) signaling pathway is aberrantly active in this disease, with antigendependent 1,2 or -independent autonomous activation, 3 leading to constitutive activation of kinases inducing cell survival and proliferation. [4][5][6][7] One BCR pathway kinase that is uniformly overexpressed at the transcript level 8 and constitutively phosphorylated in CLL is Bruton's tyrosine kinase (BTK). Ibrutinib, an orally bioavailable irreversible inhibitor of BTK, has recently been shown to have outstanding clinical activity in CLL with extended durable remissions in both untreated and relapsed disease. 9 BTK is a critical mediator of B-lymphocyte signaling and development. Mutations in various domains are responsible for X-linked agammaglobulinemia, 10,11 a disorder characterized by developmental arrest of B cells and profound humoral immune deficiency in humans. A point mutation in the Pleckstrin homology domain is responsible for the milder X-linked immunodeficiency (XID) phenotype in the mouse, 12,13 which is characterized by reduced numbers of circulating B cells and reduced serum immunoglobulins. BTK is also a critical mediator in B-cell signaling. It is recruited to the membrane-bound signalosome in the early stages of B-cell activation, and, following phosphorylation by Syk and Lyn, participates in the phosphorylation of phospholipase C, gamma 2 (PLCg2), which leads to production of the second messengers diacylglycerol and inositol-1,4,5-triphosphate. This pathway is amplified in CLL and leads to prosurvival signals through its effects on phosphatidylinositol 3-kinase (PI3K), PL...

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous group of immature myeloid cells that expand in tumor bearing hosts in response to soluble factors produced by tumor and stromal cells. MDSC expansion has been linked to loss of immune effector cell function and reduced efficacy of immune-based cancer therapies, highlighting the MDSC population as an attractive therapeutic target. Ibrutinib, an irreversible inhibitor of Bruton’s tyrosine kinase (BTK) and IL2-inducible T-cell kinase (ITK), is in clinical use for the treatment of B cell malignancies. Here, we report that BTK is expressed by murine and human MDSCs, and that ibrutinib is able to inhibit BTK phosphorylation in these cells. Treatment of MDSCs with ibrutinib significantly impaired nitric oxide production and cell migration. In addition, ibrutinib inhibited in vitro generation of human MDSCs and reduced mRNA expression of indolamine 2,3-dioxygenase, an immunosuppressive factor. Treatment of mice bearing EMT6 mammary tumors with ibrutinib resulted in reduced frequency of MDSCs in both the spleen and tumor. Ibrutinib treatment also resulted in a significant reduction of MDSCs in wildtype mice bearing B16F10 melanoma tumors, but not in X-linked immunodeficiency mice (XID) harboring a BTK mutation, suggesting that BTK inhibition plays an important role in the observed reduction of MDSCs in vivo. Finally, ibrutinib significantly enhanced the efficacy of anti-PD-L1 (CD274) therapy in a murine breast cancer model. Together, these results demonstrate that ibrutinib modulates MDSC function and generation, revealing a potential strategy for enhancing immune-based therapies in solid malignancies.

Bromodomain and extra-terminal (BET) family proteins are key regulators of gene expression in cancer. Herein, we utilize BRD4 profiling to identify critical pathways involved in pathogenesis of chronic lymphocytic leukemia (CLL). BRD4 is overexpressed in CLL and is enriched proximal to genes upregulated or expressed in CLL with known functions in disease pathogenesis and progression. These genes, including key members of the B-cell receptor (BCR) signaling pathway, provide a rationale for this therapeutic approach to identify new targets in alternative types of cancer. Additionally, we describe PLX51107, a structurally distinct BET inhibitor with novel and pharmacologic properties that emulates or exceeds the efficacy of BCR signaling agents in preclinical models of CLL. Herein, the discovery of the involvement of BRD4 in the core CLL transcriptional program provides a compelling rationale for clinical investigation of PLX51107 as epigenetic therapy in CLL and application of BRD4 profiling in other cancers. To date, functional studies of BRD4 in CLL are lacking. Through integrated genomic, functional, and pharmacologic analyses, we uncover the existence of BRD4-regulated core CLL transcriptional programs and present preclinical proof-of-concept studies validating BET inhibition as an epigenetic approach to target BCR signaling in CLL. .

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Targeted inhibition of Bruton tyrosine kinase (BTK) with the irreversible inhibitor ibrutinib has improved outcomes for patients with hematologic malignancies, including chronic lymphocytic leukemia (CLL). Here, we describe preclinical investigations of ARQ 531, a potent, reversible inhibitor of BTK with additional activity against Src family kinases and kinases related to ERK signaling. We hypothesized that targeting additional kinases would improve global inhibition of signaling pathways, producing more robust responses. treatment of patient CLL cells with ARQ 531 decreases BTK-mediated functions including B-cell receptor (BCR) signaling, viability, migration, CD40 and CD86 expression, and NF-κB gene transcription., ARQ 531 was found to increase survival over ibrutinib in a murine Eμ-TCL1 engraftment model of CLL and a murine Eμ-MYC/TCL1 engraftment model resembling Richter transformation. Additionally, ARQ 531 inhibits CLL cell survival and suppresses BCR-mediated activation of C481S BTK and PLCγ2 mutants, which facilitate clinical resistance to ibrutinib. This study characterizes a rationally designed kinase inhibitor with efficacy in models recapitulating the most common mechanisms of acquired resistance to ibrutinib. Reversible BTK inhibition is a promising strategy to combat progressive CLL, and multikinase inhibition demonstrates superior efficacy to targeted ibrutinib therapy in the setting of Richter transformation. .

Purpose Acalabrutinib (ACP-196) is a novel, potent, and highly selective BTK inhibitor, which binds covalently to Cys481 in the ATP-binding pocket of BTK. We sought to evaluate the anti-tumor effects of acalabrutinib treatment in two established mouse models of chronic lymphocytic leukemia (CLL). Experimental Design Two distinct mouse models were used, the TCL1 adoptive transfer model where leukemic cells from Eμ-TCL1 transgenic mice are transplanted into C57BL/6 mice, and the human NSG primary CLL xenograft model. Mice received either vehicle or acalabrutinib formulated into the drinking water. Results Utilizing biochemical assays we demonstrate that acalabrutinib is a highly selective BTK inhibitor as compared to ibrutinib. In the human CLL NSG xenograft model, treatment with acalabrutinib demonstrated on-target effects including decreased phosphorylation of PLCγ2, ERK and significant inhibition of CLL cell proliferation. Further, tumor burden in the spleen of the mice treated with acalabrutinib was significantly decreased compared to vehicle treated mice. Similarly, in the TCL1 adoptive transfer model, decreased phosphorylation of BTK, PLCγ2 and S6 was observed. Most notably, treatment with acalabrutinib resulted in a significant increase in survival compared to mice receiving vehicle. Conclusions Treatment with acalabrutinib potently inhibits BTK in vivo, leading to on-target decreases in the activation of key signaling molecules (including BTK, PLCγ2, S6 and ERK). In two complementary mouse models of CLL acalabrutinib significantly reduced tumor burden and increased survival compared to vehicle treatment. Overall, acalabrutinib showed increased BTK selectivity compared to ibrutinib while demonstrating significant anti-tumor efficacy in vivo on par with ibrutinib.

DNA origami (DO) nanotechnology enables the construction of precise nanostructures capable of functionalization with small molecule drugs, nucleic acids, and proteins, suggesting a promising platform for biomedical applications. Despite the potential for drug and vaccine delivery, the impact of DO vehicles on immunogenicity in vivo is not well understood. Here, two DO vehicles, a flat triangle and a nanorod, at varying concentrations are evaluated in vitro and with a repeated dosing regimen administered at a high dose in vivo to study early and late immunogenicity. The studies show normal CD11b+ myeloid cell populations preferentially internalize DO in vitro. DO structures distribute well systemically in vivo, elicit a modest pro‐inflammatory immune response that diminishes over time and are nontoxic as shown by weight, histopathology, lack of cytokine storm, and a complete biochemistry panel at the day 10 end point. The results take critical steps to characterize the biological response to DO and suggest that DO vehicles represent a promising platform for drug delivery and vaccine development where immunogenicity should be a key consideration.