Oncolytic HSV Vectors and Anti-Tumor Immunity.

The therapeutic promise of oncolytic viruses (OVs) rests on their ability to both selectively kill tumor cells and induce anti-tumor immunity. The potential of tumors to be recognized and eliminated by an effective anti-tumor immune response has been spurred on by the discovery that immune checkpoint inhibition can overcome tumor-specific cytotoxic T cell (CTL) exhaustion and provide durable responses in multiple tumor indications. OV-mediated tumor destruction is now recognized as a powerful means to assist in the development of anti-tumor immunity for two important reasons: (i) OVs, through the elicitation of an anti-viral response and the production of type I interferon, are potent stimulators of inflammation and can be armed with transgenes to further enhance anti-tumor immune responses; and (ii) lytic activity can promote the release of tumor-associated antigens (TAAs) and tumor neoantigens that function as in situ tumor-specific vaccines to elicit adaptive immunity. Oncolytic herpes simplex viruses (oHSVs) are among the most widely studied OVs for the treatment of solid malignancies, and Amgen's oHSV Imlygic® for the treatment of melanoma is the only OV approved in major markets. Here we describe important biological features of HSV that make it an attractive OV, clinical experience with HSV-based vectors, and strategies to increase applicability to cancer treatment.

Seneca Valley virus replicons are packaged in trans and have the capacity to overcome the limitations of viral transgene expression.

Oncolytic viruses (OVs) promote the anti-tumor immune response as their replication, and the subsequent lysis of tumor cells, triggers the activation of immune-sensing pathways. Arming OVs by expressing transgenes with the potential to promote immune cell recruitment and activation is an attractive strategy to enhance OVs' therapeutic benefit. For picornaviruses, a family of OVs with clinical experience, the expression of a transgene is limited by multiple factors: genome physical packaging limits, high rates of recombination, and viral-mediated inhibition of transgene secretion. Here, we evaluated strategies for arming Seneca Valley virus (SVV) with relevant immunomodulatory transgenes. Specificially in the contex of arming SVV, we evaluated transgene maximum size and stabiltity, transgene secretion, and the impact of transgene inclusion on viral fitness. We find that SVV is not capable of expressing secreted payloads and has a transgene packaging capacity of ∼10% of viral genome size. To enable transgene expression, we developed SVV replicons with greater transgene size capacity and secretion capabilities. SVV replicons can be packaged in trans by virus in co-infected cells to express immunomodulatory transgenes in surrounding cells, thus providing a means to enhance the potential of this therapeutic to augment the anti-tumor immune response.

Development of intravenously administered synthetic RNA virus immunotherapy for the treatment of cancer.

The therapeutic effectiveness of oncolytic viruses (OVs) delivered intravenously is limited by the development of neutralizing antibody responses against the virus. To circumvent this limitation and to enable repeated systemic administration of OVs, here we develop Synthetic RNA viruses consisting of a viral RNA genome (vRNA) formulated within lipid nanoparticles. For two Synthetic RNA virus drug candidates, Seneca Valley virus (SVV) and Coxsackievirus A21, we demonstrate vRNA delivery and replication, virus assembly, spread and lysis of tumor cells leading to potent anti-tumor efficacy, even in the presence of OV neutralizing antibodies in the bloodstream. Synthetic-SVV replication in tumors promotes immune cell infiltration, remodeling of the tumor microenvironment, and enhances the activity of anti-PD-1 checkpoint inhibitor. In mouse and non-human primates, Synthetic-SVV is well tolerated reaching exposure well above the requirement for anti-tumor activity. Altogether, the Synthetic RNA virus platform provides an approach that enables repeat intravenous administration of viral immunotherapy.

ONCR-177, an Oncolytic HSV-1 Designed to Potently Activate Systemic Antitumor Immunity.

ONCR-177 is an engineered recombinant oncolytic herpes simplex virus (HSV) with complementary safety mechanisms, including tissue-specific miRNA attenuation and mutant UL37 to inhibit replication, neuropathic activity, and latency in normal cells. ONCR-177 is armed with five transgenes for IL12, FLT3LG (extracellular domain), CCL4, and antagonists to immune checkpoints PD-1 and CTLA-4. In vitro assays demonstrated that targeted miRNAs could efficiently suppress ONCR-177 replication and transgene expression, as could the HSV-1 standard-of-care therapy acyclovir. Although ONCR-177 was oncolytic across a panel of human cancer cell lines, including in the presence of type I IFN, replication was suppressed in human pluripotent stem cell-derived neurons, cardiomyocytes, and hepatocytes. Dendritic cells activated with ONCR-177 tumor lysates efficiently stimulated tumor antigen-specific CD8+ T-cell responses. In vivo, biodistribution analyses suggested that viral copy number and transgene expression peaked approximately 24 to 72 hours after injection and remained primarily within the injected tumor. Intratumoral administration of ONCR-177 mouse surrogate virus, mONCR-171, was efficacious across a panel of syngeneic bilateral mouse tumor models, resulting in partial or complete tumor regressions that translated into significant survival benefits and to the elicitation of a protective memory response. Antitumor effects correlated with local and distant intratumoral infiltration of several immune effector cell types, consistent with the proposed functions of the transgenes. The addition of systemic anti-PD-1 augmented the efficacy of mONCR-171, particularly for abscopal tumors. Based in part upon these preclinical results, ONCR-177 is being evaluated in patients with metastatic cancer (ONCR-177-101, NCT04348916).

Development of a new fully human anti-CD20 monoclonal antibody for the treatment of B-cell malignancies.

Despite the widespread use of rituximab, a chimeric monoclonal antibody with demonstrated efficacy in the treatment of non-Hodgkin's lymphomas, there is a recognized need to develop new agents with improved efficacy. Towards this end, using XenoMouse technology, a fully human IgG1 anti-CD20 monoclonal antibody was generated. This antibody, denoted mAb 1.5.3, evoked enhanced pro-apoptotic activity in vitro, as compared to rituximab, in the Ramos lymphoma cell line. Also, mAb 1.5.3 mediated both complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC) similar to rituximab in human B-lymphoma lines. Interestingly, mAb 1.5.3 demonstrated superior ADCC compared to rituiximab when FcgammaRIIIa F/F allotype donors were profiled and superior cytolytic activity across multiple human B-lymphoma and chronic B-cell leukemia lines in an in vitro whole blood assay. Furthermore, mAb 1.5.3 exhibited enhanced anti-tumor activity in Ramos, Daudi, and Namalwa tumour xenograft models. Lastly, mAb 1.5.3 produced a superior B-cell depletion profile in lymph node organs and bone marrow as compared to rituximab in a primate pharmacodynamic (PD) model. These findings underscore the potential of mAb 1.5.3 to exhibit improved clinical activity in the treatment of B-cell malignancies compared to rituximab.

Design of an Interferon-Resistant Oncolytic HSV-1 Incorporating Redundant Safety Modalities for Improved Tolerability.

Development of next-generation oncolytic viruses requires the design of vectors that are potently oncolytic, immunogenic in human tumors, and well tolerated in patients. Starting with a joint-region deleted herpes simplex virus 1 (HSV-1) to create large transgene capability, we retained a single copy of the ICP34.5 gene, introduced mutations in UL37 to inhibit retrograde axonal transport, and inserted cell-type-specific microRNA (miRNA) target cassettes in HSV-1 genes essential for replication or neurovirulence. Ten miRNA candidates highly expressed in normal tissues and with low or absent expression in malignancies were selected from a comprehensive profile of 800 miRNAs with an emphasis on protection of the nervous system. Among the genes essential for viral replication identified using a small interfering RNA (siRNA) screen, we selected ICP4, ICP27, and UL8 for miRNA attenuation where a single miRNA is sufficient to potently attenuate viral replication. Additionally, a neuron-specific miRNA target cassette was introduced to control ICP34.5 expression. This vector is resistant to type I interferon compared to ICP34.5-deleted oncolytic HSVs, and in cancer cell lines, the oncolytic activity of the modified vector is equivalent to its parental virus. In vivo, this vector potently inhibits tumor growth while being well tolerated, even at high intravenous doses, compared to parental wild-type HSV-1.

AZD7762, a novel checkpoint kinase inhibitor, drives checkpoint abrogation and potentiates DNA-targeted therapies.

Insights from cell cycle research have led to the hypothesis that tumors may be selectively sensitized to DNA-damaging agents resulting in improved antitumor activity and a wider therapeutic margin. The theory relies on the observation that the majority of tumors are deficient in the G1-DNA damage checkpoint pathway resulting in reliance on S and G2 checkpoints for DNA repair and cell survival. The S and G2 checkpoints are regulated by checkpoint kinase 1, a serine/threonine kinase that is activated in response to DNA damage; thus, inhibition of checkpoint kinase 1 signaling impairs DNA repair and increases tumor cell death. Normal tissues, however, have a functioning G1 checkpoint signaling pathway allowing for DNA repair and cell survival. Here, we describe the preclinical profile of AZD7762, a potent ATP-competitive checkpoint kinase inhibitor in clinical trials. AZD7762 has been profiled extensively in vitro and in vivo in combination with DNA-damaging agents and has been shown to potentiate response in several different settings where inhibition of checkpoint kinase results in the abrogation of DNA damage-induced cell cycle arrest. Dose-dependent potentiation of antitumor activity, when AZD7762 is administered in combination with DNA-damaging agents, has been observed in multiple xenograft models with several DNA-damaging agents, further supporting the potential of checkpoint kinase inhibitors to enhance the efficacy of both conventional chemotherapy and radiotherapy and increase patient response rates in a variety of settings.

Arming oHSV with ULBP3 drives abscopal immunity in lymphocyte-depleted glioblastoma.

Oncolytic viruses induce local tumor destruction and inflammation. Whether virotherapy can also overcome immunosuppression in noninfected tumor areas is under debate. To address this question, we have explored immunologic effects of oncolytic herpes simplex viruses (oHSVs) in a genetically engineered mouse model of isocitrate dehydrogenase (IDH) wild-type glioblastoma, the most common and most malignant primary brain tumor in adults. Our model recapitulates the genomics, the diffuse infiltrative growth pattern, and the extensive macrophage-dominant immunosuppression of human glioblastoma. Infection with an oHSV that was armed with a UL16-binding protein 3 (ULBP3) expression cassette inhibited distant tumor growth in the absence of viral spreading (abscopal effect) and yielded accumulation of activated macrophages and T cells. There was also abscopal synergism of oHSVULBP3 with anti-programmed cell death 1 (anti-PD-1) against distant, uninfected tumor areas; albeit consistent with clinical trials in patients with glioblastoma, monotherapy with anti-PD-1 was ineffective in our model. Arming oHSV with ULBP3 led to upregulation of antigen processing and presentation gene sets in myeloid cells. The cognate ULBP3 receptor NKG2D, however, is not present on myeloid cells, suggesting a noncanonical mechanism of action of ULBP3. Overall, the myeloid-dominant, anti-PD-1-sensitive abscopal effect of oHSVULBP3 warrants further investigation in patients with IDH wild-type glioblastoma.

A novel ex vivo high-throughput assay reveals antiproliferative effects of idelalisib and ibrutinib in chronic lymphocytic leukemia.

PI3Kδ (idelalisib) and BTK (ibrutinib) inhibitors have demonstrated significant clinical activity in chronic lymphocytic leukemia (CLL) interfering with the cross-talk between CLL cells and the lymph node microenviroment, yet their mechanism of action remains to be fully elucidated. Here, we developed an ex vivo model with the aim of reproducing the effects of the microenvironment that would help shed light on the in vivo mechanism of action of idelalisib and ibrutinib and predict their clinical efficacy in individual patients. First we explored the effects of various cell-extrinsic elements on CLL apoptosis and proliferation and found that the combination of CpG+IL2+HS5 stromal cell line + human serum +CLL plasma and erythrocyte fractions represented the best co-culture conditions to test the effects of the novel inhibitors. Then, using this assay, we investigated the impact of idelalisib and ibrutinib on both survival and proliferation in 30 CLL patients. While both drugs had a limited direct pro-apoptotic activity, a potent inhibition of proliferation was achieved at clinically achievable concentrations. Notably, up to 10% of CLL cells still proliferated even at the highest concentrations, likely mirroring the known difficulty to achieve complete responses in vivo. Altogether, this novel assay represents an appropriate ex vivo drug testing system to potentially predict the clinical response to novel inhibitors in particular by quantifying the antiproliferative effect.

PI3Kδ inhibitor idelalisib in combination with BTK inhibitor ONO/GS-4059 in diffuse large B cell lymphoma with acquired resistance to PI3Kδ and BTK inhibitors.

Activated B-cell-like diffuse large B-cell lymphoma relies on B-cell receptor signaling to drive proliferation and survival. Downstream of the B-cell receptor, the key signaling kinases Bruton's tyrosine kinase and phosphoinositide 3-kinase δ offer opportunities for therapeutic intervention by agents such as ibrutinib, ONO/GS-4059, and idelalisib. Combination therapy with such targeted agents could provide enhanced efficacy due to complimentary mechanisms of action. In this study, we describe both the additive interaction of and resistance mechanisms to idelalisib and ONO/GS-4059 in a model of activated B-cell-like diffuse large B-cell lymphoma. Significant tumor regression was observed with a combination of PI3Kδ and Bruton's tyrosine kinase inhibitors in the mouse TMD8 xenograft. Acquired resistance to idelalisib in the TMD8 cell line occurred by loss of phosphatase and tensin homolog and phosphoinositide 3-kinase pathway upregulation, but not by mutation of PIK3CD. Sensitivity to idelalisib could be restored by combining idelalisib and ONO/GS-4059. Further evaluation of targeted inhibitors revealed that the combination of idelalisib and the phosphoinositide-dependent kinase-1 inhibitor GSK2334470 or the AKT inhibitor MK-2206 could partially overcome resistance. Characterization of acquired Bruton's tyrosine kinase inhibitor resistance revealed a novel tumor necrosis factor alpha induced protein 3 mutation (TNFAIP3 Q143*), which led to a loss of A20 protein, and increased p-IκBα. The combination of idelalisib and ONO/GS-4059 partially restored sensitivity in this resistant line. Additionally, a mutation in Bruton's tyrosine kinase at C481F was identified as a mechanism of resistance. The combination activity observed with idelalisib and ONO/GS-4059, taken together with the ability to overcome resistance, could lead to a new therapeutic option in activated B-cell-like diffuse large B-cell lymphoma. A clinical trial is currently underway to evaluate the combination of idelalisib and ONO/GS-4059 (NCT02457598).

Idelalisib: First-in-Class PI3K Delta Inhibitor for the Treatment of Chronic Lymphocytic Leukemia, Small Lymphocytic Leukemia, and Follicular Lymphoma.

Idelalisib [Zydelig (Gilead Sciences, Inc.), also known as CAL-101 and GS-1101] was approved in 2014 in the United States and European Union for the treatment of three indolent B-cell neoplasms: relapsed/refractory chronic lymphocytic leukemia (CLL, in combination with rituximab), relapsed follicular lymphoma, and relapsed small lymphocytic lymphoma (as monotherapy). Furthermore, it was approved in the European Union as first-line therapy for poor-prognosis CLL with 17p deletions or TP53 mutations and in patients unsuitable for chemoimmunotherapy. Idelalisib is an orally bioavailable ATP-competitive kinase inhibitor that targets the PI3K p110 isoform δ (PI3Kδ) with high potency and selectivity. PI3Kδ is hyperactivated in B-cell malignancies and plays a pivotal role in the B-cell receptor pathway, a key oncogenic driver in B-cell malignancies. The near exclusive expression of the PI3Kδ isoform in hematopoietic cells and the selectivity of idelalisib for the PI3Kδ isoform are essential for its efficacy and tolerability, even in elderly patients unfit for chemotherapy. Idelalisib is the first PI3K inhibitor approved by the regulatory agencies; this approval will change the treatment landscape of indolent B-cell malignancies.

Effects of GABA agonists on body temperature regulation in GABA(B(1))-/- mice.

1. Activation of GABA(B) receptors evokes hypothermia in wildtype (GABA(B(1))+/+) but not in GABA(B) receptor knockout (GABA(B(1))-/-) mice. The aim of the present study was to determine the hypothermic and behavioural effects of the putative GABA(B) receptor agonist gamma-hydroxybutyrate (GHB), and of the GABA(A) receptor agonist muscimol. In addition, basal body temperature was determined in GABA(B(1))+/+, GABA(B(1))+/- and GABA(B(1))-/- mice. 2. GABA(B(1))-/- mice were generated by homologous recombination in embryonic stem cells. Correct gene targeting was assessed by Southern blotting, PCR and Western blotting. GABA(B) receptor-binding sites were quantified with radioligand binding. Measurement of body temperature was done using subcutaneous temperature-sensitive chips, and behavioural changes after drug administration were scored according to a semiquantitative scale. 3. GABA(B(1))-/- mice had a short lifespan, probably caused by generalised seizure activity. No histopathological or blood chemistry changes were seen, but the expression of GABA(B(2)) receptor protein was below the detection limit in brains from GABA(B(1))-/- mice, in the absence of changes in mRNA levels. 4. GABA(B) receptor-binding sites were absent in brain membranes from GABA(B(1))-/- mice. 5. GABA(B(1))-/- mice were hypothermic by approximately 1 degrees C compared to GABA(B(1))+/+ and GABA(B(1))+/- mice. 6. Injection of baclofen (9.6 mg kg-1) produced a large reduction in body temperature and behavioural effects in GABA(B(1))+/+ and in GABA(B(1))+/- mice, but GABA(B(1))-/- mice were unaffected. The same pattern was seen after administration of GHB (400 mg kg-1). The GABA(A) receptor agonist muscimol (2 mg kg-1), on the other hand, produced a more pronounced hypothermia in GABA(B(1))-/-mice. In GABA(B(1))+/+ and GABA(B(1))+/- mice, muscimol induced sedation and reduced locomotor activity. However, when given to GABA(B(1))-/- mice, muscimol triggered periods of intense jumping and wild running. 7. It is concluded that hypothermia should be added to the characteristics of the GABAB(1)-/-phenotype. Using this model, GHB was shown to be a selective GABAB receptor agonist. In addition, GABAB(1)-/- mice are hypersensitive to GABAA receptor stimulation, indicating that GABAB tone normally balances GABAA-mediated effects.

Preclinical evaluation of AMG 925, a FLT3/CDK4 dual kinase inhibitor for treating acute myeloid leukemia.

Acute myeloid leukemia (AML) remains a serious unmet medical need. Despite high remission rates with chemotherapy standard-of-care treatment, the disease eventually relapses in a major proportion of patients. Activating Fms-like tyrosine kinase 3 (FLT3) mutations are found in approximately 30% of patients with AML. Targeting FLT3 receptor tyrosine kinase has shown encouraging results in treating FLT3-mutated AML. Responses, however, are not sustained and acquired resistance has been a clinical challenge. Treatment options to overcome resistance are currently the focus of research. We report here the preclinical evaluation of AMG 925, a potent, selective, and bioavailable FLT3/cyclin-dependent kinase 4 (CDK4) dual kinase inhibitor. AMG 925 inhibited AML xenograft tumor growth by 96% to 99% without significant body weight loss. The antitumor activity of AMG 925 correlated with the inhibition of STAT5 and RB phosphorylation, the pharmacodynamic markers for inhibition of FLT3 and CDK4, respectively. In addition, AMG 925 was also found to inhibit FLT3 mutants (e.g., D835Y) that are resistant to the current FLT3 inhibitors (e.g., AC220 and sorafenib). CDK4 is a cyclin D-dependent kinase that plays an essential central role in regulating cell proliferation in response to external growth signals. A critical role of the CDK4-RB pathway in cancer development has been well established. CDK4-specific inhibitors are being developed for treating RB-positive cancer. AMG 925, which combines inhibition of two kinases essential for proliferation and survival of FLT3-mutated AML cells, may improve and prolong clinical responses.

Discovery of AMG 925, a FLT3 and CDK4 dual kinase inhibitor with preferential affinity for the activated state of FLT3.

We describe the structural optimization of a lead compound 1 that exhibits dual inhibitory activities against FLT3 and CDK4. A series of pyrido[4',3':4,5]pyrrolo[2,3-d]pyrimidine derivatives was synthesized, and SAR analysis, using cell-based assays, led to the discovery of 28 (AMG 925), a potent and orally bioavailable dual inhibitor of CDK4 and FLT3, including many FLT3 mutants reported to date. Compound 28 inhibits the proliferation of a panel of human tumor cell lines including Colo205 (Rb(+)) and U937 (FLT3(WT)) and induced cell death in MOLM13 (FLT3(ITD)) and even in MOLM13 (FLT3(ITD, D835Y)), which exhibits resistance to a number of FLT3 inhibitors currently under clinical development. At well-tolerated doses, compound 28 leads to significant growth inhibition of MOLM13 xenografts in nude mice, and the activity correlates with inhibition of STAT5 and Rb phosphorylation.

Peptibodies: A flexible alternative format to antibodies.

Peptibodies or peptide-Fc fusions are an attractive alternative therapeutic format to monoclonal antibodies. They consist of biologically active peptides grafted onto an Fc domain. This approach retains certain desirable features of antibodies, notably an increased apparent affinity through the avidity conferred by the dimerization of two Fcs and a long plasma residency time. Peptibodies can be made in E. coli using recombinant technology. The manufacturing process involves fermentation and downstream processing, including refolding and multiple column chromatographic steps, that result in overall yields and quality suitable for commercial development. Romiplostim, marketed under the brand name Nplate®, is the first peptibody to be approved by the United States Food and Drug Administration and the European Medicines Agency and is indicated for the treatment of immune thrombocytopenic purpura. AMG 386, a peptibody antagonist to angiopoietins 1 and 2, is being evaluated in Phase 3 clinical testing in combination with chemotherapy in women with ovarian cancer. AMG 819, a peptibody targeting nerve growth factor for pain has also progressed to clinical trials. These peptibodies illustrate the versatility of the modality.