A phase Ib study evaluating the recommended phase II dose, safety, tolerability, and efficacy of mivavotinib in combination with nivolumab in advanced solid tumors.

Mivavotinib (TAK-659/CB-659), a dual SYK/FLT3 inhibitor, reduced immunosuppressive immune cell populations and suppressed tumor growth in combination with anti-PD-1 therapy in cancer models. This dose-escalation/expansion study investigated the safety, pharmacokinetics, pharmacodynamics, and preliminary efficacy of mivavotinib plus nivolumab in patients with advanced solid tumors. Patients received oral mivavotinib 60-100 mg once-daily plus intravenous nivolumab 3 mg/kg on days 1 and 15 in 28-day cycles until disease progression or unacceptable toxicity. The dose-escalation phase evaluated the recommended phase II dose (RP2D; primary endpoint). The expansion phase evaluated overall response rate (primary end point) at the RP2D in patients with triple-negative breast cancer (TNBC). During dose-escalation (n = 24), two dose-limiting toxicities (grade 4 lipase increased and grade 3 pyrexia) occurred in patients who received mivavotinib 80 mg and 100 mg, respectively. The determined RP2D was once-daily mivavotinib 80 mg plus nivolumab 3 mg/kg. The expansion phase was terminated at ~50% enrollment (n = 17) after failing to meet an ad hoc efficacy futility threshold. Among all 41 patients, common treatment-emergent adverse events (TEAEs) included dyspnea (48.8%), aspartate aminotransferase increased, and pyrexia (46.3% each). Common grade ≥3 TEAEs were hypophosphatemia and anemia (26.8% each). Mivavotinib plasma exposure was generally dose-proportional (60-100 mg). One patient had a partial response. Mivavotinib 80 mg plus nivolumab 3 mg/kg was well tolerated with no new safety signals beyond those of single-agent mivavotinib or nivolumab. Low response rates highlight the challenges of treating unresponsive tumor types, such as TNBC, with this combination and immunotherapies in general. TRIAL REGISTRATION ID: NCT02834247.

A phase Ib trial of mivavotinib (TAK-659), a dual SYK/FLT3 inhibitor, in patients with relapsed/refractory acute myeloid leukemia.

Mivavotinib (TAK-659) is an investigational type 1 tyrosine kinase inhibitor with dual activity against spleen tyrosine kinase (SYK) and FMS-like tyrosine kinase 3 (FLT3). We conducted a phase Ib study to investigate the safety, tolerability, and efficacy of mivavotinib in patients with refractory and/or relapsed (R/R) acute myeloid leukemia (AML). Both daily (QD) and twice daily (BID) dosing regimens were evaluated. A total of 43 patients were enrolled, and there were 5 complete responses (4 with incomplete count recovery). In the QD dosing regimen, the maximum tolerated dose (MTD) was not reached up to 160 mg QD per protocol; 140 mg QD was identified as the recommended phase II dose. In the BID dosing regimen, the MTD was 60 mg BID. Thirty patients (70%) experienced a bleeding event on study; the majority were grades 1 or 2, were resolved without mivavotinib modification, and were not considered related to study treatment. Eleven patients (26%) experienced grade ≥3 bleeding events, which were observed most frequently with the 80 mg BID dose. We conducted platelet aggregation studies to investigate the potential role of mivavotinib-mediated SYK inhibition on platelet function. The bleeding events observed may have been the result of several confounding factors, including AML disease status, associated thrombocytopenia, and high doses of mivavotinib. Overall, these findings indicate that the activity of mivavotinib in R/R AML is modest. Furthermore, any future clinical investigation of this agent should be undertaken with caution, particularly in thrombocytopenic patients, due to the potential bleeding risk of SYK inhibition. ClinicalTrials.gov: NCT02323113.

Tumor cell SYK expression modulates the tumor immune microenvironment composition in human cancer via TNF-α dependent signaling.

BACKGROUND: The expression of SYK in cancer cells has been associated with both tumor promoting and tumor suppressive effects. Despite being proposed as anticancer therapeutic target, the possible role of SYK in modulating local adaptive antitumor immune responses remains uncertain. Using detailed analysis of primary human tumors and in vitro models, we reveal the immunomodulatory effect of SYK protein in human solid cancer. METHODS: We spatially mapped SYK kinase in tumor cells, stromal cells and tumor-infiltrating leukocytes (TILs) in 808 primary non-small cell lung carcinomas (NSCLCs) from two cohorts and in 374 breast carcinomas (BCs) from two independent cohorts. We established the associations of localized SYK with clinicopathologic variables and outcomes. The immunomodulatory role of SYK on tumor cells was assessed using in vitro cytokine stimulation, transcriptomic analysis and selective SYK blockade using a small molecule inhibitor. Functional responses were assessed using cocultures of tumor cells with peripheral blood lymphocytes. T cell responses in baseline and post-treatment biopsies from patients with BC treated with a SYK inhibitor in a phase I clinical trial were also studied. RESULTS: Elevated tumor cell or leukocyte SYK expression was associated with high CD4+ and CD8+ TILs and better outcome in both NSCLC and BC. Tumor cell SYK was associated with oncogenic driver mutations in EGFR or KRAS in lung adenocarcinomas and with triple negative phenotype in BC. In cultured tumor cells, SYK was upregulated by TNFα and required for the TNFα-induced proinflammatory responses and T cell activation. SYK blockade after nivolumab in a phase I clinical trial including three patients with advanced triple negative BC reduced TILs and T cell proliferation. Our work establishes the proinflammatory function of tumor cell SYK in lung and breast cancer. SYK signaling in cultured tumor cells is required for T cell activation and SYK blockade limits adaptive antitumor immune responses and tumor rejection in patients with cancer. CONCLUSIONS: Together, our results establish the immunomodulatory role of SYK expression in human solid tumors. This information could be used to develop novel biomarkers and/or therapeutic strategies.

Activation of Tumor-Cell STING Primes NK-Cell Therapy.

Activation of the stimulator of interferon genes (STING) pathway promotes antitumor immunity but STING agonists have yet to achieve clinical success. Increased understanding of the mechanism of action of STING agonists in human tumors is key to developing therapeutic combinations that activate effective innate antitumor immunity. Here, we report that malignant pleural mesothelioma cells robustly express STING and are responsive to STING agonist treatment ex vivo. Using dynamic single-cell RNA sequencing of explants treated with a STING agonist, we observed CXCR3 chemokine activation primarily in tumor cells and cancer-associated fibroblasts, as well as T-cell cytotoxicity. In contrast, primary natural killer (NK) cells resisted STING agonist-induced cytotoxicity. STING agonists enhanced migration and killing of NK cells and mesothelin-targeted chimeric antigen receptor (CAR)-NK cells, improving therapeutic activity in patient-derived organotypic tumor spheroids. These studies reveal the fundamental importance of using human tumor samples to assess innate and cellular immune therapies. By functionally profiling mesothelioma tumor explants with elevated STING expression in tumor cells, we uncovered distinct consequences of STING agonist treatment in humans that support testing combining STING agonists with NK and CAR-NK cell therapies.

Convergent synthesis of hydrophilic monomethyl dolastatin 10 based drug linkers for antibody-drug conjugation.

We report a modular approach to synthesize maleimido group containing hydrophilic dolastatin 10 (Dol10) derivatives as drug-linkers for the syntheses of antibody-drug conjugates (ADCs). Discrete polyethylene glycol (PEG) moieties of different chain lengths were introduced as part of the linker to impart hydrophilicity to these drug linkers. The synthesis process involved construction of PEG maleimido derivatives of the tetrapeptide intermediate (N-methylvaline-valine-dolaisoleucine-dolaproine), which were subsequently coupled with dolaphenine to generate the desired drug linkers. The synthetic method reported in this manuscript circumvents the use of highly cytotoxic Dol10 in its native form. By using trastuzumab (Herceptin®) as the antibody we have synthesized Dol10 containing ADCs. The presence of a discrete PEG chain in the drug linkers resulted in ADCs free from aggregation. The effect of PEG chain length on the biological activities of these Dol10 containing ADCs was investigated by in vitro cytotoxicity assays. ADCs containing PEG6 and PEG8 spacers exhibited the highest level of in vitro anti-proliferative activity against HER2-positive (SK-BR-3) human tumor cells. ADCs derived from Herceptin® and PEG8-Dol10, at a dose of 10 mg kg-1, effectively delayed the tumor growth and prolonged the survival time in mice bearing human ovarian SKOV-3 xenografts.

Design, Synthesis, and in†vitro Evaluation of Multivalent Drug Linkers for High-Drug-Load Antibody-Drug Conjugates.

A series of novel multivalent drug linkers (MDLs) containing cytotoxic agents were synthesized and conjugated to antibodies to yield highly potent antibody-drug conjugates (ADCs) with drug/antibody ratios (DARs) higher than those typically reported in the literature (10 vs. ≈4). These MDLs contain two copies of a cytotoxic agent attached to biocompatible scaffolds composed of a branched peptide core and discrete polyethylene glycol (PEG) chains to enhance solubility and decrease aggregation. These drug linkers produced well-defined ADCs, whose DARs could be accurately determined by LC-MS. Using this approach, ADCs with significantly lower aggregation and higher DAR than those of conventional drug linker design were obtained with highly hydrophobic cytotoxic agents such as monomethyldolastatin 10 (MMAD). The in vitro potencies of the MDL-derived conjugates matched that of ADCs of similar DAR with conventional linkers, and the potency increased proportionally with drug loading. This approach may provide a means to prepare highly potent ADCs from a broader range of drugs, including those with lower cytotoxicity or poor solubility, which otherwise limits their use for antibody-drug conjugates. This may also provide a means to further improve the potency achievable with cytotoxins currently used in ADCs.

A Robust Multiplex Mass Spectrometric Assay for Screening Small-Molecule Inhibitors of CD73 with Diverse Inhibition Modalities.

CD73/Ecto-5'-nucleotidase is a membrane-tethered ecto-enzyme that works in tandem with CD39 to convert extracellular adenosine triphosphate (ATP) into adenosine. CD73 is highly expressed on various types of cancer cells and on infiltrating suppressive immune cells, leading to an elevated concentration of adenosine in the tumor microenvironment, which elicits a strong immunosuppressive effect. In preclinical studies, targeting CD73 with anti-CD73 antibody results in favorable antitumor effects. Despite initial studies using antibodies, inhibition of CD73 catalytic activity using small-molecule inhibitors may be more effective in lowering extracellular adenosine due to better tumor penetration and distribution. To screen small-molecule libraries, we explored multiple approaches, including colorimetric and fluorescent biochemical assays, and due to some limitations with these assays, we developed a mass spectrometry (MS)-based assay. Only the MS-based assay offers the sensitivity and dynamic range required for screening small-molecule libraries at a substrate concentration close to the Km value of substrate and for evaluating the mode of binding of screening hits. To achieve a throughput suitable for high-throughput screening (HTS), we developed a RapidFire-tandem mass spectrometry (RF-MS/MS)-based multiplex assay. This assay allowed a large diverse compound library to be screened at a speed of 1536 reactions per 40-50 min.

PET with the 89Zr-labeled transforming growth factor-ß antibody fresolimumab in tumor models.

UNLABELLED: Transforming growth factor-ß (TGF-ß) promotes cancer invasion and metastasis and is therefore a potential drug target for cancer treatment. Fresolimumab, which neutralizes all mammalian active isoforms of TGF-ß, was radiolabeled with (89)Zr for PET to analyze TGF-ß expression, antibody tumor uptake, and organ distribution. METHODS: (89)Zr was conjugated to fresolimumab using the chelator N-succinyldesferrioxamine-B-tetrafluorphenol. (89)Zr-fresolimumab was analyzed for conjugation ratio, aggregation, radiochemical purity, stability, and immunoreactivity. (89)Zr-fresolimumab tumor uptake and organ distribution were assessed using 3 protein doses (10, 50, and 100 µg) and compared with (111)In-IgG in a human TGF-ß-transfected Chinese hamster ovary xenograft model, human breast cancer MDA-MB-231 xenograft, and metastatic model. Latent and active TGF-ß1 expression was analyzed in tissue homogenates with enzyme-linked immunosorbent assay. RESULTS: (89)Zr was labeled to fresolimumab with high specific activity (>1 GBq/mg), high yield, and high purity. In vitro validation of (89)Zr-fresolimumab showed a fully preserved immunoreactivity and long (>1 wk) stability in solution and in human serum. In vivo validation showed an (89)Zr-fresolimumab distribution similar to IgG in most organs, except for a higher uptake in the liver in all mice and higher kidney uptake in the 10-µg group. (89)Zr-fresolimumab induced no toxicity in mice; it accumulated in primary tumors and metastases in a manner similar to IgG. Both latent and active TGF-ß was detected in tumor homogenates, whereas only latent TGF-ß could be detected in liver homogenates. Remarkably high (89)Zr-fresolimumab uptake was seen in sites of tumor ulceration and in scar tissue, processes in which TGF-ß is known to be highly active. CONCLUSION: Fresolimumab tumor uptake and organ distribution can be visualized and quantified with (89)Zr-fresolimumab PET. This technique will be used to guide further clinical development of fresolimumab and could possibly identify patients most likely to benefit.

Transforming growth factor-beta regulates house dust mite-induced allergic airway inflammation but not airway remodeling.

RATIONALE: It is now believed that both chronic airway inflammation and remodeling contribute significantly to airway dysfunction and clinical symptoms in allergic asthma. Transforming growth factor (TGF)-beta is a powerful regulator of both the tissue repair and inflammatory responses, and numerous experimental and clinical studies suggest that it may play an integral role in the pathogenesis of asthma. OBJECTIVES: We investigated the role of TGF-beta in the regulation of allergic airway inflammation and remodeling using a mouse model of house dust mite (HDM)-induced chronic allergic airway disease. METHODS: We have previously shown that intranasal administration of an HDM extract (5 d/wk for 5 wk) elicits robust Th2-polarized airway inflammation and remodeling that is associated with increased airway hyperreactivity. Here, Balb/c mice were similarly exposed to HDM and concurrently treated with a pan-specific TGF-beta neutralizing antibody. MEASUREMENTS AND MAIN RESULTS: We observed that anti-TGF-beta treatment in the context of either continuous or intermittent HDM exposure had no effect on the development of HDM-induced airway remodeling. To further confirm these findings, we also subjected SMAD3 knockout mice to 5 weeks of HDM and observed that knockout mice developed airway remodeling to the same extent as HDM-exposed littermate controls. Notably, TGF-beta neutralization exacerbated the eosinophilic infiltrate and led to increased airway hyperreactivity. CONCLUSIONS: Collectively, these data suggest that TGF-beta regulates HDM-induced chronic airway inflammation but not remodeling, and furthermore, caution against the use of therapeutic strategies aimed at interfering with TGF-beta activity in the treatment of this disease.

Regulated interaction of the Fanconi anemia protein, FANCD2, with chromatin.

DNA damage activates the monoubiquitination of the Fanconi anemia (FA) protein, FANCD2, resulting in the assembly of FANCD2 nuclear foci. In the current study, we characterize structural features of FANCD2 required for this intranuclear translocation. We have previously identified 2 normal mRNA splice variants of FANCD2, one containing exon 44 sequence at the 3' end (FANCD2-44) and one containing exon 43 sequence (FANCD2-43). The 2 predicted FANCD2 proteins differ in their carboxy terminal 24 amino acids. In stably transfected FANCD2(-/-) fibroblasts, FANCD2-44 and FANCD2-43 proteins were monoubiquitinated on K561. Only FANCD2-44 corrected the mitomycin C (MMC) sensitivity of the transfected cells. We find that monoubiquitinated FANCD2-44 was translocated from the soluble nuclear compartment into chromatin. A mutant form of FANCD2-44 (FANCD2-K561R) was not monoubiquitinated and failed to bind chromatin. A truncated FANCD2 protein (Exon44-T), lacking the carboxy terminal 24 amino acids encoded by exon 44 but retaining K561, and another mutant FANCD2 protein, with a single amino acid substitution at a conserved residue within the C-terminal 24 amino acids (D1428A), were monoubiquitinated. Both mutants were targeted to chromatin but failed to correct MMC sensitivity. Taken together, our results indicate that monoubiquitination of FANCD2 regulates chromatin binding and that D1428 within the carboxy terminal acidic sequence encoded by exon 44 is independently required for functional complementation of FA-D2 cells. We hypothesize that the carboxy terminus of FANCD2-44 plays a critical role in sensing or repairing DNA damage.

Regulation of the Fanconi anemia pathway by monoubiquitination.

Fanconi anemia (FA) is an autosomal recessive cancer susceptibility syndrome characterized by multiple congenital anomalies, bone marrow failure, and cellular sensitivity to mitomycin C (MMC). To date, six FA genes have been cloned, and the encoded proteins function in a novel pathway. The FA pathway is required for the normal cellular response to DNA damage. Following DNA damage, the pathway is activated, leading to monoubiquitination of the FA protein, FANCD2, and its targeting to subnuclear foci. Disruption of the FA pathway results in the absence of FANCD2 nuclear foci, leading to the cellular and clinical abnormalities of FA. Here, we review the recent studies describing the regulated monoubiquitination of the FANCD2 protein and discuss the interaction of the FA pathway with other DNA damage response pathways.

S-phase-specific interaction of the Fanconi anemia protein, FANCD2, with BRCA1 and RAD51.

Fanconi anemia (FA) is a human autosomal recessive cancer susceptibility disorder characterized by cellular sensitivity to mitomycin C and defective cell-cycle progression. Six FA genes (corresponding to subtypes A, C, D2, E, F, and G) have been cloned, and the encoded FA proteins interact in a common pathway. DNA damage activates this pathway, leading to monoubiquitination of the downstream FANCD2 protein and targeting to nuclear foci containing BRCA1. In the current study, we demonstrate that FANCD2 also undergoes monoubiquitination during S phase of the cell cycle. Monoubiquitinated FANCD2 colocalizes with BRCA1 and RAD51 in S-phase-specific nuclear foci. Monoubiquitination of FANCD2 is required for normal cell-cycle progression following cellular exposure to mitomycin C. Our data indicate that the monoubiquitination of FANCD2 is highly regulated, and they suggest that FANCD2/BRCA1 complexes and FANCD2/RAD51 complexes participate in an S-phase-specific cellular process, such as DNA repair by homologous recombination.

Convergence of the fanconi anemia and ataxia telangiectasia signaling pathways.

Fanconi anemia (FA) and ataxia telangiectasia (AT) are clinically distinct autosomal recessive disorders characterized by spontaneous chromosome breakage and hematological cancers. FA cells are hypersensitive to mitomycin C (MMC), while AT cells are hypersensitive to ionizing radiation (IR). Here, we identify the Fanconi anemia protein, FANCD2, as a link between the FA and ATM damage response pathways. ATM phosphorylates FANCD2 on serine 222 in vitro. This site is also phosphorylated in vivo in an ATM-dependent manner following IR. Phosphorylation of FANCD2 is required for activation of an S phase checkpoint. The ATM-dependent phosphorylation of FANCD2 on S222 and the FA pathway-dependent monoubiquitination of FANCD2 on K561 are independent posttranslational modifications regulating discrete cellular signaling pathways. Biallelic disruption of FANCD2 results in both MMC and IR hypersensitivity.