CRISPR/Cas9 disruption of EpCAM Exon 2 results in cell-surface expression of a truncated protein targeted by an EpCAM specific T cell engager

CRISPR/Cas9 gene-editing technology allows researchers to study protein function by specifically introducing double-stranded breaks in the gene of interest then analyze its subsequent loss in sensitive biological assays. To help characterize one of a series of highly potent, conditionally active, T cell engaging bispecific molecules called COBRA™, the human EpCAM gene was disrupted in HT29 cells using CRISPR/Cas9 and guide RNA targeting its Exon 2. Although a commercially available antibody indicated loss of cell-surface expression, the EpCAM targeting bispecific COBRA was still able to lyse these cells in a T cell dependent cellular cytotoxicity assay. RT-PCR sequence analysis of these cells showed a major alternative transcript generated after CRISPR/Cas9, with Exon 1 and 3 spliced together in-frame, skipping Exon 2 completely, to express a truncated cell-surface receptor recognized by the EpCAM-COBRA. Researchers who use CRISPR/Cas9 must be cognizant of this potential to express alternative versions of their proteins and use sensitive orthogonal detection methods to ensure complete gene disruption.

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CRISPR/Cas9 allows researchers to target gene disruption and analyze its loss of expression.

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After CRISPR/Cas9 targeting the EpCAM gene, no protein was detected after staining with a commercial antibody.

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An in-house EpCAM T-cell engager was able to lyse these supposedly EpCAM KO cells.

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cDNA analysis showed an alternative mRNA transcript arose after CRISPR/Cas9, creating a truncated version on the cell's surface.

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Scientists using CRISPR must be aware of the potential to make alternate forms and try other means to ensure no expression.

COBRA™: a highly potent conditionally active T cell engager engineered for the treatment of solid tumors

Conditionally active COBRA™ (COnditional Bispecific Redirected Activation) T cell engagers are engineered to overcome the limitations of inherently active first-generation T cell engagers, which are unable to discern between tumor and healthy tissues. Designed to be administered as prodrugs, COBRAs target cell surface antigens upon administration, but engage T cells only after they are activated within the tumor microenvironment (TME). This allows COBRAs to be preferentially turned on in tumors while safely remaining inactive in healthy tissue. Here, we describe the development of the COBRA design and the characterization of these conditionally active T cell engagers. Upon administration COBRAs are engineered to bind to tumor-associated antigens (TAAs) and serum albumin (to extend their half-life in circulation), but are inhibited from interacting with the T cell receptor complex signaling molecule CD3. In the TME, a matrix metalloproteinase (MMP)-mediated linker cleavage event occurs within the COBRA construct, which rearranges the molecule, allowing it to co-engage TAAs and CD3, thereby activating T cells against the tumor. COBRAs are conditionally activated through cleavage with MMP9, and once active are highly potent, displaying sub-pM EC₅₀s in T cell killing assays. Studies in tumor-bearing mice demonstrate COBRA administration completely regresses established solid tumor xenografts. These results strongly support the further characterization of the novel COBRA design in preclinical development studies.

TriTACs, a Novel Class of T-Cell-Engaging Protein Constructs Designed for the Treatment of Solid Tumors

T cells have a unique capability to eliminate cancer cells and fight malignancies. Cancer cells have adopted multiple immune evasion mechanisms aimed at inhibiting T cells. Dramatically improved patient outcomes have been achieved with therapies genetically reprogramming T cells, blocking T-cell inhibition by cancer cells, or transiently connecting T cells with cancer cells for redirected lysis. This last modality is based on antibody constructs that bind a surface antigen on cancer cells and an invariant component of the T-cell receptor. Although high response rates were observed with T-cell engagers specific for CD19, CD20, or BCMA in patients with hematologic cancers, the treatment of solid tumors has been less successful. Here, we developed and characterized a novel T-cell engager format, called TriTAC (for Trispecific T-cell Activating Construct). TriTACs are engineered with features to improve patient safety and solid tumor activity, including high stability, small size, flexible linkers, long serum half-life, and highly specific and potent redirected lysis. The present study establishes the structure/activity relationship of TriTACs and describes the development of HPN424, a PSMA- (FOLH1-) targeting TriTAC in clinical development for patients with metastatic castration-resistant prostate cancer.

Phase I Study of Enavatuzumab, a First-in-Class Humanized Monoclonal Antibody Targeting the TWEAK Receptor, in Patients with Advanced Solid Tumors

This phase I study evaluates the safety, MTD, pharmacokinetics (PK), pharmacodynamics, and preliminary anticancer activity of enavatuzumab, a humanized IgG1 antibody to the TWEAK receptor, in patients with advanced solid malignancies. Patients received escalating doses of enavatuzumab given intravenously over 60 minutes every 2 weeks. Blood was obtained for PK and biomarker assessment. Three patients were enrolled per dose level in a standard 3+3 design with response assessment by RECIST version 1.0, every 8 weeks. Thirty patients were enrolled at 6 dose levels ranging from 0.1 to 1.5 mg/kg. Dose-limiting toxicities included grade 4 (G4) lipase, G3 bilirubin, and G4 amylase elevations. There was no apparent correlation of liver or pancreatic enzyme elevation with drug exposure or the presence of liver metastases. Enavatuzumab exhibited a two-compartment linear PK model. Estimated systemic clearance was 23 to 33 mL/h with an elimination half-life of 7 to 18 days. The predicted target efficacious peak and trough concentrations occurred at 1.0 mg/kg following the second dose. There were no objective responses; 4 patients had stable disease. The MTD of enavatuzumab is 1.0 mg/kg i.v. every 2 weeks. Higher doses were not tolerated due to hepatopancreatic lab abnormalities. Further evaluation of the mechanisms of the liver and pancreatic enzyme toxicities is needed before embarking on further single-agent or combination strategies. Mol Cancer Ther; 17(1); 215-21. ©2017 AACR.

Predictive gene signature of response to the anti-TweakR mAb PDL192 in patient-derived breast cancer xenografts

Purpose

(1) To determine TweakR expression in human breast cancers (BC), (2) evaluate the antitumor effect of the anti-TweakR antibody PDL192, used alone or after chemotherapy-induced complete remission (CR), on patient-derived BC xenografts (PDX) and (3) define predictive markers of response.

Experimental Design

TweakR expression was analyzed by IHC on patients and PDXs BC samples. In vivo antitumor effect of PDL192 was evaluated on eight TweakR-positive BC PDXs alone or after complete remission induced by a combination of doxorubicin and cyclophosphamide. Using both responding and resistant PDX tumors after PDL192 administration, RT-QPCR were performed on a wide list of selected candidate genes to identify predictive markers of response.

Results

TweakR protein was expressed in about half of human BC samples. In vivo PDL192 treatment had significantly anti-tumor activity in 4 of 8 TweakR-positive BC PDXs, but no correlation between the expression level of the Tweak receptor and response to therapy was observed. PDL192 also significantly delayed tumor relapse after CR. Finally, an 8 gene signature was defined from sensitive and resistant PDXs.

Conclusions

PDL192 was highly efficient in some BC PDXs. We found 8 genes that were differentially expressed in responding and resistant tumors and could constitute a gene expression signature which would need to be extended to other xenograft models for confirmation. These data confirm the therapeutic potential of TweakR targeting in BC and the possibility of prospectively selecting patients who might benefit from therapy.

Nuclear Factor κB is Required for Tumor Growth Inhibition Mediated by Enavatuzumab (PDL192), a Humanized Monoclonal Antibody to TweakR

TweakR is a TNF receptor family member, whose natural ligand is the multifunctional cytokine TWEAK. The growth inhibitory activity observed following TweakR stimulation in certain cancer cell lines and the overexpression of TweakR in many solid tumor types led to the development of enavatuzumab (PDL192), a humanized IgG1 monoclonal antibody to TweakR. The purpose of this study was to determine the mechanism of action of enavatuzumab’s tumor growth inhibition and to provide insight into the biology behind TweakR as a cancer therapeutic target. A panel of 105 cancer lines was treated with enavatuzumab in vitro; and 29 cell lines of varying solid tumor backgrounds had >25% growth inhibition in response to the antibody. Treatment of sensitive cell lines with enavatuzumab resulted in the in vitro and in vivo (xenograft) activation of both classical (p50, p65) and non-classical (p52, RelB) NFκB pathways. Using NFκB DNA binding functional ELISAs and microarray analysis, we observed increased activation of NFκB subunits and NFκB-regulated genes in sensitive cells over that observed in resistant cell lines. Inhibiting NFκB subunits (p50, p65, RelB, p52) and upstream kinases (IKK1, IKK2) with siRNA and chemical inhibitors consistently blocked enavatuzumab’s activity. Furthermore, enavatuzumab treatment resulted in NFκB-dependent reduction in cell division as seen by the activation of the cell cycle inhibitor p21 both in vitro and in vivo. The finding that NFκB drives the growth inhibitory activity of enavatuzumab suggests that targeting TweakR with enavatuzumab may represent a novel cancer treatment strategy.

Expression of TweakR in breast cancer and preclinical activity of enavatuzumab, a humanized anti-TweakR mAb

Background

The receptor for the cytokine TWEAK (TweakR) is a cell surface member of the tumor necrosis factor receptor superfamily with diverse biological roles. TNFRSF family members are appealing therapeutic targets in oncology due to their aberrant expression and function in tumor cells. The goal of the current study was to examine the potential of TweakR as a therapeutic target in breast cancer.

Methods

Expression of TweakR in primary breast cancer tissues and metastases was characterized using immunohistochemistry. To determine the functional relevance of TweakR, breast cancer cell lines were treated in vitro and in vivo with enavatuzumab, a humanized mAb against TweakR.

Results

Overexpression of TweakR was observed in infiltrating tumors compared to normal adjacent breast tissues, and strong staining of TweakR was observed in all subtypes of invasive ductal breast cancer. In addition, a positive correlation of TweakR and HER2 expression and co-localization were observed, irrespective of ER status. TweakR expression was also observed in bone metastasis samples from primary breast cancer but rarely in benign tumors. Enavatuzumab inhibited the in vitro growth of TweakR-expressing breast cancer cell lines, and this activity was augmented by cross-linking the mAb. In addition, enavatuzumab significantly inhibited the in vivo growth of multiple breast cancer xenograft models including a model of metastasis.

Conclusions

TweakR is highly expressed in all subtypes of invasive ductal breast cancer, and enavatuzumab administration exhibited a dose-dependent inhibition of primary tumor growth and lung metastasis and enhanced the antitumor activity of several chemotherapy agents currently used to treat breast cancer. These data provide the rationale to evaluate enavatuzumab as a potential therapy for the treatment of breast cancer.

Electronic supplementary material

The online version of this article (doi:10.1007/s00432-012-1332-x) contains supplementary material, which is available to authorized users.

Abstract B17: PDL192, a humanized antibody to TweakR exhibits potent antitumor activity in pancreatic cancer models

Approximately 42,000 new cases of pancreatic cancer were diagnosed in the United States in 2009, and the 5-year survival rate for this disease is exceedingly low (approximately 5%). Given the lack of therapeutic success with current standards of care, new therapies are clearly needed to treat this disease. We have generated PDL192, a humanized IgG1 antibody to TweakR (Fn14, TNFRSF12A, CD266), a cell surface protein and member of the TNF receptor superfamily. PDL192 has been shown to exhibit antitumor activity in xenograft models on a range of solid tumor types via both direct tumor cell growth inhibition and by antibody-dependent cellular cytotoxicity. In this study, we explored the activity of PDL192 in pancreatic cancer models. Approximately 60% of primary pancreatic cancers express TweakR protein at high levels, as determined by immunohistochemistry. PDL192 exhibited potent anti-tumor activity in two cell line xenograft models, Panc1 and MiaPaCa2. PDL192 also exhibited significant anti-tumor activity against 3 of 6 primary tumor xenograft models derived from pancreatic patients. PDL192 was also tested in combination with gemcitabine, the most common treatment for pancreatic cancer patients. In the Panc1 and MiaPaCa2 xenograft models, the combination of PDL192 and gemcitabine exhibited more potent activity than either agent alone. In three of five primary tumor xenograft models tested, combining PDL192 and gemcitabine also resulted in greater anti-tumor activity than either agent alone. In one of the primary tumor models, where neither PDL192 nor gemcitabine alone exhibited significant anti-tumor activity, the combination completely inhibited tumor growth. The activity of PDL192 in multiple pancreatic xenograft models using both cell lines and primary tumors is supportive of the use of PDL192 for the treatment of pancreatic cancer. PDL192 is currently being evaluated in a phase1 safety study in patients with solid tumors.

Citation Information: Clin Cancer Res 2010;16(14 Suppl):B17.

Abstract B231: Targeting Her2+ ductal breast cancer with PDL192, a novel humanized anti-TweakR monoclonal antibody

TWEAK receptor (TweakR), also known as Fn14, is a cell surface protein and member of the tumor necrosis factor receptor superfamily. TNFRSF family members are appealing therapeutic targets due to their expression and function in tumor cells. The goal of the current study was to examine the potential of TweakR as a therapeutic target in various subtypes of breast cancer by 1) determining expression of TweakR using immunohistochemistry (IHC) and 2) treating cells derived from breast cancer in vitro and in vivo with PDL192, a novel, humanized anti-TweakR mAb. Overexpression of TweakR protein in breast cancer was confirmed by IHC on formalin fixed paraffin embedded (FFPE) tissues. TweakR was elevated in infiltrating tumors when compared with normal adjacent tissues. 30 to 40% of various subtypes of invasive ductal breast cancer samples stained highly for TweakR; however, fewer than 5% of lobular breast cancer samples had high levels of TweakR. In addition, a strong positive correlation of TweakR and Her2 expression was observed, irrespective of ER status. More than 60% of Her2+ invasive ductal cancer exhibited elevated levels of TweakR. Strong TweakR expression was also observed in bone metastasis samples from primary breast cancer but rarely in benign tumors, such as DCIS.

PDL192 inhibited the in vitro growth of various subtypes of TweakR-expressing breast cancer cell lines and this activity was augmented by crosslinking the mAb. In addition, PDL192 significantly inhibited the in vivo growth of a variant of the breast cancer xenograft model MDA-MB231 that exhibits metastatic potential. PDL192 administration exhibited a dose-dependent inhibition of primary tumor growth and lung metastasis and enhanced the anti-tumor activity of several chemotherapy agents currently used to treat breast cancer. These data provide the rationale to evaluate PDL192 as a potential therapy for the treatment of breast cancer. Currently, PDL192 is being tested in a phase I safety study for the treatment of patients with solid tumors.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B231.

c-mos and cdc2 cooperate in the translational activation of fibroblast growth factor receptor-1 during Xenopus oocyte maturation

During oocyte maturation in Xenopus, previously quiescent maternal mRNAs are translationally activated at specific times. We hypothesized that the translational recruitment of individual messages is triggered by particular cellular events and investigated the potential for known effectors of the meiotic cell cycle to activate the translation of the FGF receptor-1 (XFGFR) maternal mRNA. We found that both c-mos and cdc2 activate the translation of XFGFR. However, although oocytes matured by injection of recombinant cdc2/cyclin B translate normal levels of XFGFR protein, c-mos depletion reduces the level of XFGFR protein induced by cdc2/cyclin B injection. In oocytes blocked for cdc2 activity, injection of mos RNA induced low levels of XFGFR protein, independent of MAPK activity. Through the use of injected reporter RNAs, we show that the XFGFR 3' untranslated region inhibitory element is completely derepressed by cdc2 alone. In addition, we identified a new inhibitory element through which both mos and cdc2 activate translation. We found that cdc2 derepresses translation in the absence of polyadenylation, whereas mos requires poly(A) extension to activate XFGFR translation. Our results demonstrate that mos and cdc2, in addition to functioning as key regulators of the meiotic cell cycle, cooperate in the translational activation of a specific maternal mRNA during oocyte maturation.

Translational activation and cytoplasmic polyadenylation of FGF receptor-1 are independently regulated during Xenopus oocyte maturation

FGF signaling is critical for establishing the Xenopus laevis embryonic body plan and requires the expression of functional FGF receptor during early embryogenesis. FGF receptor-1 (XFGFR) maternal mRNA is present in immature oocytes, but the protein is not expressed until oocyte maturation. In this report we demonstrate that endogenous XFGFR translation begins just prior to germinal vesicle breakdown and that translation depends on completion of earlier meiotic events. We show that the previously identified XFGFR 3'UTR translation inhibitory element (TIE), which is necessary and sufficient for repressing translation in the immature oocyte, also regulates the onset of translation during oocyte maturation. In addition we demonstrate that cytoplasmic polyadenylation of XFGFR RNA is regulated independently of TIE-mediated translation and it not sufficient to activate the translation of XFGFR. These experiments reveal that polyadenylation and translational activation are separable events in this mRNA, each of which is timed and regulated independently.

The effect of vanadate on human kidney potassium dependent phosphatase

This study examined the effects of vanadate on the potassium dependent phosphatase activity present in purified human kidney microsomal (Na+ + K+)-adenosine triphosphatase. Vanadate anion inhibited the K+-dependent phosphatase at a K1 of 35 nM. This inhibition was noncompetitive with the substrate, p-nitrophenylphosphate. The inhibition by vanadate at 1 mM K+ was only 45% of the inhibition that was observed at 10 mM K+. Neither preincubation of the enzyme with vanadate, nor changing the pH of the assay from 8.2 to 7.2 had any effect on the K1 for vanadate. The inclusion of 2.5 mM isoproterenol, to complex the yanadate, reversed the inhibition, as did diluting the enzymatic reaction. Vanadate also inhibited the overall (Na+ + K+)-ATPase reaction at a K1 of 1.91 microM. This inhibition was also reversible upon inclusion of isoproterenol in the assay. Increasing the level of magnesium from 6 mM to 30 mM lowered the K1 of vanadate to 0.25 microM. The possible role of vanadate as a physiological mediator of (Na+ + k+)-atpase activity is discussed.