ROR1 targeting with the antibody-drug conjugate VLS-101 is effective in Richter syndrome patient-derived xenograft mouse models.

Richter syndrome (RS) represents the transformation of chronic lymphocytic leukemia (CLL), typically to an aggressive lymphoma. Treatment options for RS are limited and the disease is often fatal. Receptor tyrosine kinase-like orphan receptor 1 (ROR1) is expressed on CLL cells and other cancers but not on healthy adult tissues, making it an attractive, tumor-specific therapeutic target. VLS-101 is being developed as an antibody-drug conjugate (ADC) for therapy of ROR1-expressing (ROR1+) cancers. VLS-101 comprises UC-961 (a humanized immunoglobulin G1 monoclonal antibody that binds an extracellular epitope of human ROR1), a maleimidocaproyl-valine-citrulline-para-aminobenzoate linker, and the antimicrotubule cytotoxin monomethyl auristatin E (MMAE). VLS-101 binding to ROR1 results in rapid cellular internalization and delivery of MMAE to induce tumor cell death. We studied 4 RS patient-derived xenografts (RS-PDXs) with varying levels of ROR1 expression (11%, 32%, 85%, and 99% of cells). VLS-101 showed no efficacy in the lowest-expressing RS-PDX but induced complete remissions in those with higher levels of ROR1 expression. Responses were maintained during the posttherapy period, particularly after higher VLS-101 doses. In systemic ROR1+ RS-PDXs, VLS-101 dramatically decreased tumor burden in all RS-colonized tissues and significantly prolonged survival. Animals showed no adverse effects or weight loss. Our results confirm ROR1 as a target in RS and demonstrate the therapeutic potential of using an ADC directed toward ROR1 for the treatment of hematological cancers. A phase 1 clinical trial of VLS-101 (NCT03833180) is ongoing in patients with RS and other hematological malignancies.

The translational landscape of mTOR signalling steers cancer initiation and metastasis.

The mammalian target of rapamycin (mTOR) kinase is a master regulator of protein synthesis that couples nutrient sensing to cell growth and cancer. However, the downstream translationally regulated nodes of gene expression that may direct cancer development are poorly characterized. Using ribosome profiling, we uncover specialized translation of the prostate cancer genome by oncogenic mTOR signalling, revealing a remarkably specific repertoire of genes involved in cell proliferation, metabolism and invasion. We extend these findings by functionally characterizing a class of translationally controlled pro-invasion messenger RNAs that we show direct prostate cancer invasion and metastasis downstream of oncogenic mTOR signalling. Furthermore, we develop a clinically relevant ATP site inhibitor of mTOR, INK128, which reprograms this gene expression signature with therapeutic benefit for prostate cancer metastasis, for which there is presently no cure. Together, these findings extend our understanding of how the 'cancerous' translation machinery steers specific cancer cell behaviours, including metastasis, and may be therapeutically targeted.

Selective inhibition of phosphoinositide 3-kinase p110α preserves lymphocyte function.

Class IA phosphoinositide 3-kinase (PI3K) is essential for clonal expansion, differentiation, and effector function of B and T lymphocytes. The p110δ catalytic isoform of PI3K is highly expressed in lymphocytes and plays a prominent role in B and T cell responses. Another class IA PI3K catalytic isoform, p110α, is a promising drug target in cancer but little is known about its function in lymphocytes. Here we used highly selective inhibitors to probe the function of p110α in lymphocyte responses in vitro and in vivo. p110α inhibition partially reduced B cell receptor (BCR)-dependent AKT activation and proliferation, and diminished survival supported by the cytokines BAFF and IL-4. Selective p110δ inhibition suppressed B cell responses much more strongly, yet maximal suppression was achieved by targeting multiple PI3K isoforms. In mouse and human T cells, inhibition of single class IA isoforms had little effect on proliferation, whereas pan-class I inhibition did suppress T cell expansion. In mice, selective p110α inhibition using the investigational agent MLN1117 (previously known as INK1117) did not disrupt the marginal zone B cell compartment and did not block T cell-dependent germinal center formation. In contrast, the selective p110δ inhibitor IC87114 strongly suppressed germinal center formation and reduced marginal zone B cell numbers, similar to a pan-class I inhibitor. These findings show that although acute p110α inhibition partially diminishes AKT activation, selective p110α inhibitors are likely to be less immunosuppressive in vivo compared with p110δ or pan-class I inhibitors.

Targeting of mTORC1/2 by the mTOR kinase inhibitor PP242 induces apoptosis in AML cells under conditions mimicking the bone marrow microenvironment.

The interactions between the bone marrow (BM) microenvironment and acute myeloid leukemia (AML) is known to promote survival of AML cells. In this study, we used reverse phase-protein array (RPPA) technology to measure changes in multiple proteins induced by stroma in leukemic cells. We then investigated the potential of an mTOR kinase inhibitor, PP242, to disrupt leukemia/stroma interactions, and examined the effects of PP242 in vivo using a mouse model. Using RPPA, we confirmed that multiple survival signaling pathways, including the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR), were up-regulated in primary AML cells cocultured with stroma. PP242 effectively induced apoptosis in primary samples cultured with or without stroma. Mechanistically, PP242 attenuated the activities of mTORC1 and mTORC2, sequentially inhibited phosphorylated AKT, S6K, and 4EBP1, and concurrently suppressed chemokine receptor CXCR4 expression in primary leukemic cells and in stromal cells cultured alone or cocultured with leukemic cells. In the in vivo leukemia mouse model, PP242 inhibited mTOR signaling in leukemic cells and demonstrated a greater antileukemia effect than rapamycin. Our findings indicate that disrupting mTOR/AKT signaling with a selective mTOR kinase inhibitor can effectively target leukemic cells within the BM microenvironment.

Zilovertamab Vedotin Targeting of ROR1 as Therapy for Lymphoid Cancers.

BACKGROUND: Receptor tyrosine kinase-like orphan receptor 1 (ROR1) is an oncofetal protein present on many cancers. Zilovertamab vedotin (ZV) is an antibody­drug conjugate comprising a monoclonal antibody recognizing extracellular ROR1, a cleavable linker, and the anti-microtubule cytotoxin monomethyl auristatin E. METHODS: In this phase 1, first-in-human, dose-escalation study, we accrued patients with previously treated lymphoid cancers to receive ZV every 3 weeks until the occurrence of cancer progression or unacceptable toxicity had occurred. RESULTS: We enrolled 32 patients with tumor histologies of mantle cell lymphoma (MCL) (n=15), chronic lymphocytic leukemia (n=7), diffuse large B-cell lymphoma (DLBCL) (n=5), follicular lymphoma (n=3), Richter transformation lymphoma (n=1), or marginal zone lymphoma (n=1). Patients had received a median of four previous drug and/or cellular therapies. Starting dose levels were 0.5 (n=1), 1.0 (n=3), 1.5 (n=3), 2.25 (n=11), and 2.5 (n=14) mg per kg of body weight (mg/kg). Pharmacokinetic and pharmacodynamic data documented systemic ZV exposure and exposure-dependent ZV targeting of ROR1 on circulating tumor cells. As expected with an monomethyl auristatin E-containing antibody­drug conjugate, adverse events (AEs) included acute neutropenia and cumulative neuropathy resulting in a recommended ZV dosing regimen of 2.5 mg/kg every 3 weeks. No clinically concerning AEs occurred to suggest ROR1-mediated toxicities or nonspecific ZV binding to normal tissues. ZV induced objective tumor responses in 7 of 15 patients with MCL (47%; 4 partial and 3 complete) and in 3 of 5 patients with DLBCL (60%; 1 partial and 2 complete); objective tumor responses were not observed among patients with other tumor types. CONCLUSIONS: In heavily pretreated patients, ZV demonstrated no unexpected toxicities and showed evidence of antitumor activity, providing clinical proof of concept for selective targeting of ROR1 as a potential new approach to cancer therapy. (ClinicalTrials.gov number, NCT03833180.)

The antibody drug conjugate VLS-101 targeting ROR1 is effective in CAR T-resistant mantle cell lymphoma.

Mantle cell lymphoma (MCL) is a rare, aggressive and incurable subtype of non-Hodgkin's B-cell lymphoma. The principal barrier is frequent clinical relapse to multiple lines of therapies, including new FDA-approved biologics and cell therapy. Brexucabtagene autoleucel, the first and only FDA approved chimeric antigen receptor (CAR) T product in MCL, demonstrated unprecedented efficacy in overcoming resistance to Bruton's tyrosine kinase inhibitors. However, relapses have inevitably occurred and once relapsed these patients display a very poor clinical outcome. Currently, there is no optional therapy specifically designed for these patients. The development of tailored and more efficacious therapies is therefore critical and represents a new medical need. We found that while the receptor tyrosine kinase-like orphan receptor 1 (ROR1) is expressed across most of the MCL cells, it is significantly elevated in CAR T-relapsed MCL tumors. To see whether this aberrant ROR1 expression contributed to CAR T resistance, we targeted ROR1 using VLS-101, a monomethyl auristatin E conjugated anti-ROR1 antibody. VLS-101 showed potent anti-MCL activity in vitro in ROR1-expressing MCL cell lines and ex vivo in primary patient samples. Importantly, VLS-101 safely induced tumor regression in PDX models resistant to CAR T-cell therapy, ibrutinib and/or venetoclax. These data advocate for targeting ROR1 as a viable approach in the treatment of ROR1-positive MCL tumors, especially those with failure to prior therapies. These data also provide strong evidence for future enrollment of post-CD19 CAR T-cell relapsed MCL patients in a first in-human phase 1b VLS-101 trial. The upcoming testing in a clinical setting will provide important insights on this new therapeutic development aiming to overcome the CAR T resistance via targeting ROR1, which is a rising unmet clinical need in MCL.

The ETS Inhibitors YK-4-279 and TK-216 Are Novel Antilymphoma Agents.

PURPOSE: Transcription factors are commonly deregulated in cancer, and they have been widely considered as difficult to target due to their nonenzymatic mechanism of action. Altered expression levels of members of the ETS-transcription factors are often observed in many different tumors, including lymphomas. Here, we characterized two small molecules, YK-4-279 and its clinical derivative, TK-216, targeting ETS factors via blocking the protein-protein interaction with RNA helicases, for their antilymphoma activity. EXPERIMENTAL DESIGN: The study included preclinical in vitro activity screening on a large panel of cell lines, both as single agent and in combination; validation experiments on in vivo models; and transcriptome and coimmunoprecipitation experiments. RESULTS: YK-4-279 and TK-216 demonstrated an antitumor activity across several lymphoma cell lines, which we validated in vivo. We observed synergistic activity when YK-4-279 and TK-216 were combined with the BCL2 inhibitor venetoclax and with the immunomodulatory drug lenalidomide. YK-4-279 and TK-216 interfere with protein interactions of ETS family members SPIB, in activated B-cell-like type diffuse large B-cell lymphomas, and SPI1, in germinal center B-cell-type diffuse large B-cell lymphomas. CONCLUSIONS: The ETS inhibitor YK-4-279 and its clinical derivative TK-216 represent a new class of agents with in vitro and in vivo antitumor activity in lymphomas. Although their detailed mechanism of action needs to be fully defined, in DLBCL they might act by targeting subtype-specific essential transcription factors.

Structure-based Design of Pyridone-Aminal eFT508 Targeting Dysregulated Translation by Selective Mitogen-activated Protein Kinase Interacting Kinases 1 and 2 (MNK1/2) Inhibition.

Dysregulated translation of mRNA plays a major role in tumorigenesis. Mitogen-activated protein kinase interacting kinases (MNK)1/2 are key regulators of mRNA translation integrating signals from oncogenic and immune signaling pathways through phosphorylation of eIF4E and other mRNA binding proteins. Modulation of these key effector proteins regulates mRNA, which controls tumor/stromal cell signaling. Compound 23 (eFT508), an exquisitely selective, potent dual MNK1/2 inhibitor, was designed to assess the potential for control of oncogene signaling at the level of mRNA translation. The crystal structure-guided design leverages stereoelectronic interactions unique to MNK culminating in a novel pyridone-aminal structure described for the first time in the kinase literature. Compound 23 has potent in vivo antitumor activity in models of diffuse large cell B-cell lymphoma and solid tumors, suggesting that controlling dysregulated translation has real therapeutic potential. Compound 23 is currently being evaluated in Phase 2 clinical trials in solid tumors and lymphoma. Compound 23 is the first highly selective dual MNK inhibitor targeting dysregulated translation being assessed clinically.

MLN0128, a novel mTOR kinase inhibitor, disrupts survival signaling and triggers apoptosis in AML and AML stem/ progenitor cells.

mTOR activation leads to enhanced survival signaling in acute myeloid leukemia (AML) cells. The active-site mTOR inhibitors (asTORi) represent a promising new approach to targeting mTOR in AKT/mTOR signaling. MLN0128 is an orally-administered, second-generation asTORi, currently in clinical development. We examined the anti-leukemic effects and the mechanisms of action of MLN0128 in AML cell lines and primary samples, with a particular focus on its effect in AML stem/progenitor cells. MLN0128 inhibited cell proliferation and induced apoptosis in AML by attenuating the activity of mTOR complex 1 and 2. Using time-of-flight mass cytometry, we demonstrated that MLN0128 selectively targeted and functionally inhibited AML stem/progenitor cells with high AKT/mTOR signaling activity. Using the reverse-phase protein array technique, we measured expression and phosphorylation changes in response to MLN0128 in 151 proteins from 24 primary AML samples and identified several pro-survival pathways that antagonize MLN0128-induced cellular stress. A combined blockade of AKT/mTOR signaling and these pro-survival pathways facilitated AML cell killing. Our findings provide a rationale for the clinical use of MLN0128 to target AML and AML stem/progenitor cells, and support the use of combinatorial multi-targeted approaches in AML therapy.

MEK plus PI3K/mTORC1/2 Therapeutic Efficacy Is Impacted by TP53 Mutation in Preclinical Models of Colorectal Cancer.

PURPOSE: PI3K pathway activation occurs in concomitance with RAS/BRAF mutations in colorectal cancer, limiting the sensitivity to targeted therapies. Several clinical studies are being conducted to test the tolerability and clinical activity of dual MEK and PI3K pathway blockade in solid tumors. EXPERIMENTAL DESIGN: In the present study, we explored the efficacy of dual pathway blockade in colorectal cancer preclinical models harboring concomitant activation of the ERK and PI3K pathways. Moreover, we investigated if TP53 mutation affects the response to this therapy. RESULTS: Dual MEK and mTORC1/2 blockade resulted in synergistic antiproliferative effects in cell lines bearing alterations in KRAS/BRAF and PIK3CA/PTEN. Although the on-treatment cell-cycle effects were not affected by the TP53 status, a marked proapoptotic response to therapy was observed exclusively in wild-type TP53 colorectal cancer models. We further interrogated two independent panels of KRAS/BRAF- and PIK3CA/PTEN-altered cell line- and patient-derived tumor xenografts for the antitumor response toward this combination of agents. A combination response that resulted in substantial antitumor activity was exclusively observed among the wild-type TP53 models (two out of five, 40%), but there was no such response across the eight mutant TP53 models (0%). Interestingly, within a cohort of 14 patients with colorectal cancer treated with these agents for their metastatic disease, two patients with long-lasting responses (32 weeks) had TP53 wild-type tumors. CONCLUSIONS: Our data support that, in wild-type TP53 colorectal cancer cells with ERK and PI3K pathway alterations, MEK blockade results in potent p21 induction, preventing apoptosis to occur. In turn, mTORC1/2 inhibition blocks MEK inhibitor-mediated p21 induction, unleashing apoptosis. Clin Cancer Res; 21(24); 5499-510. ©2015 AACR.

PI3K-δ and PI3K-γ inhibition by IPI-145 abrogates immune responses and suppresses activity in autoimmune and inflammatory disease models.

Phosphoinositide-3 kinase (PI3K)-δ and PI3K-γ are preferentially expressed in immune cells, and inhibitors targeting these isoforms are hypothesized to have anti-inflammatory activity by affecting the adaptive and innate immune response. We report on a potent oral PI3K-δ and PI3K-γ inhibitor (IPI-145) and characterize this compound in biochemical, cellular, and in vivo assays. These studies demonstrate that IPI-145 exerts profound effects on adaptive and innate immunity by inhibiting B and T cell proliferation, blocking neutrophil migration, and inhibiting basophil activation. We explored the therapeutic value of combined PI3K-δ and PI3K-γ blockade, and IPI-145 showed potent activity in collagen-induced arthritis, ovalbumin-induced asthma, and systemic lupus erythematosus rodent models. These findings support the hypothesis that inhibition of immune function can be achieved through PI3K-δ and PI3K-γ blockade, potentially leading to significant therapeutic effects in multiple inflammatory, autoimmune, and hematologic diseases.

Dual mTORC1/2 and HER2 blockade results in antitumor activity in preclinical models of breast cancer resistant to anti-HER2 therapy.

PURPOSE: The PI3K/Akt/mTOR pathway is an attractive target in HER2-positive breast cancer that is refractory to anti-HER2 therapy. The hypothesis is that the suppression of this pathway results in sensitization to anti-HER2 agents. However, this combinatorial strategy has not been comprehensively tested in models of trastuzumab and lapatinib resistance. EXPERIMENTAL DESIGN: We analyzed in vitro cell viability and induction of apoptosis in five different cell lines resistant to trastuzumab and lapatinib. Inhibition of HER2/HER3 phosphorylation, PI3K/Akt/mTOR, and extracellular signal-regulated kinase (ERK) signaling pathways was evaluated by Western blotting. Tumor growth inhibition after treatment with lapatinib, INK-128, or the combination of both agents was evaluated in three different animal models: two cell-based xenograft models refractory to both trastuzumab and lapatinib and a xenograft derived from a patient who relapsed on trastuzumab-based therapy. RESULTS: The addition of lapatinib to INK-128 prevented both HER2 and HER3 phosphorylation induced by INK-128, resulting in inhibition of both PI3K/Akt/mTOR and ERK pathways. This dual blockade produced synergistic induction of cell death in five different HER2-positive cell lines resistant to trastuzumab and lapatinib. In vivo, both cell line-based and patient-derived xenografts showed exquisite sensitivity to the antitumor activity of the combination of lapatinib and INK-128, which resulted in durable tumor shrinkage and exhibited no signs of toxicity in these models. CONCLUSIONS: The simultaneous blockade of both PI3K/Akt/mTOR and ERK pathways obtained by combining lapatinib with INK-128 acts synergistically in inducing cell death and tumor regression in breast cancer models refractory to anti-HER2 therapy.

SGX523 is an exquisitely selective, ATP-competitive inhibitor of the MET receptor tyrosine kinase with antitumor activity in vivo.

The MET receptor tyrosine kinase has emerged as an important target for the development of novel cancer therapeutics. Activation of MET by mutation or gene amplification has been linked to kidney, gastric, and lung cancers. In other cancers, such as glioblastoma, autocrine activation of MET has been demonstrated. Several classes of ATP-competitive inhibitor have been described, which inhibit MET but also other kinases. Here, we describe SGX523, a novel, ATP-competitive kinase inhibitor remarkable for its exquisite selectivity for MET. SGX523 potently inhibited MET with an IC50 of 4 nmol/L and is >1,000-fold selective versus the >200-fold selectivity of other protein kinases tested in biochemical assays. Crystallographic study revealed that SGX523 stabilizes MET in a unique inactive conformation that is inaccessible to other protein kinases, suggesting an explanation for the selectivity. SGX523 inhibited MET-mediated signaling, cell proliferation, and cell migration at nanomolar concentrations but had no effect on signaling dependent on other protein kinases, including the closely related RON, even at micromolar concentrations. SGX523 inhibition of MET in vivo was associated with the dose-dependent inhibition of growth of tumor xenografts derived from human glioblastoma and lung and gastric cancers, confirming the dependence of these tumors on MET catalytic activity. Our results show that SGX523 is the most selective inhibitor of MET catalytic activity described to date and is thus a useful tool to investigate the role of MET kinase in cancer without the confounding effects of promiscuous protein kinase inhibition.