Anticancer Effects of Mesothelin-Targeted Immunotoxin Therapy Are Regulated by Tyrosine Kinase DDR1

Discoidin Domain Receptor Tyrosine Kinase 1 (DDR1) Is a Novel Therapeutic Target in Liposarcoma: A Tissue Microarray Study

BACKGROUND

Liposarcoma is the most commonly diagnosed subtype of soft tissue sarcoma. As these tumors often arise near vital organs and neurovascular structures, complete resection can be challenging; consequently, recurrence rates are high. Additionally, available chemotherapeutic agents have shown limited benefit and substantial toxicities. There is, therefore, a clear and unmet need for novel therapeutics for liposarcoma. Discoidin domain receptor tyrosine kinase 1 (DDR1) is involved in adhesion, proliferation, differentiation, migration, and metastasis in several cancers. However, the expression and clinical importance of DDR1 in liposarcoma are unknown.

QUESTIONS/PURPOSES

The purposes of this study were to assess (1) the expression, (2) the association between DDR1 and survival, and (3) the functional roles of DDR1 in liposarcoma.

METHODS

The correlation between DDR1 expression in tumor tissues and clinicopathological features and survival was assessed via immunohistochemical staining of a liposarcoma tissue microarray. It contained 53 samples from 42 patients with liposarcoma and 11 patients with lipoma. The association between DDR1 and survival in liposarcoma was analyzed by Kaplan-Meier plots and log-rank tests. The DDR1 knockout liposarcoma cell lines were generated by CRISPR-Cas9 technology. The DDR1-specific and highly selective DDR1 inhibitor 7RH was applied to determine the impact of DDR1 expression on liposarcoma cell growth and proliferation. In addition, the effect of DDR1 inhibition on liposarcoma growth was further accessed in a three-dimensional cell culture model to mimic DDR1 effects in vivo.

RESULTS

The results demonstrate elevated expression of DDR1 in all liposarcoma subtypes relative to benign lipomas. Specifically, high DDR1 expression was seen in 55% (23 of 42) of liposarcomas and no benign lipomas. However, DDR1 expression was not found to be associated with poor survival in patients with liposarcoma. DDR1 knockout or treatment of 7RH showed decreased liposarcoma cell growth and proliferation.

CONCLUSION

DDR1 is aberrantly expressed in liposarcoma, and it contributes to several markers of oncogenesis in these tumors.

CLINICAL RELEVANCE

This work supports DDR1 as a promising therapeutic target in liposarcoma.

Mechanisms of Resistance to Immunotoxins Containing Pseudomonas Exotoxin A in Cancer Therapy

Immunotoxins are a class of targeted cancer therapeutics in which a toxin such as Pseudomonas exotoxin A (PE) is linked to an antibody or cytokine to direct the toxin to a target on cancer cells. While a variety of PE-based immunotoxins have been developed and a few have demonstrated promising clinical and preclinical results, cancer cells frequently have or develop resistance to these immunotoxins. This review presents our current understanding of the mechanism of action of PE-based immunotoxins and discusses cellular mechanisms of resistance that interfere with various steps of the pathway. These steps include binding of the immunotoxin to the target antigen, internalization, intracellular processing and trafficking to reach the cytosol, inhibition of protein synthesis through ADP-ribosylation of elongation factor 2 (EF2), and induction of apoptosis. Combination therapies that increase immunotoxin action and overcome specific mechanisms of resistance are also reviewed.

Mesothelin-Targeted Recombinant Immunotoxins for Solid Tumors

Mesothelin (MSLN) is a cell surface glycoprotein normally expressed only on serosal surfaces, and not found in the parenchyma of vital organs. Many solid tumors also express MSLN, including mesothelioma and pancreatic adenocarcinoma. Due to this favorable expression profile, MSLN represents a viable target for directed anti-neoplastic therapies, such as recombinant immunotoxins (iToxs). Pre-clinical testing of MSLN-targeted iTox’s has yielded a strong body of evidence for activity against a number of solid tumors. This has led to multiple clinical trials, testing the safety and efficacy of the clinical leads SS1P and LMB-100. While promising clinical results have been observed, neutralizing anti-drug antibody (ADA) formation presents a major challenge to overcome in the therapeutic development process. Additionally, on-target, off-tumor toxicity from serositis and non-specific capillary leak syndrome (CLS) also limits the dose, and therefore, impact anti-tumor activity. This review summarizes existing pre-clinical and clinical data on MSLN-targeted iTox’s. In addition, we address the potential future directions of research to enhance the activity of these anti-tumor agents.

Discoidin Domain Receptors, DDR1b and DDR2, Promote Tumour Growth within Collagen but DDR1b Suppresses Experimental Lung Metastasis in HT1080 Xenografts

The Discoidin Domain Receptors (DDRs) constitute a unique set of receptor tyrosine kinases that signal in response to collagen. Using an inducible expression system in human HT1080 fibrosarcoma cells, we investigated the role of DDR1b and DDR2 on primary tumour growth and experimental lung metastases. Neither DDR1b nor DDR2 expression altered tumour growth at the primary site. However, implantation of DDR1b- or DDR2-expressing HT1080 cells with collagen I significantly accelerated tumour growth rate, an effect that could not be observed with collagen I in the absence of DDR induction. Interestingly, DDR1b, but not DDR2, completely hindered the ability of HT1080 cells to form lung colonies after intravenous inoculation, suggesting a differential role for DDR1b in primary tumour growth and lung colonization. Analyses of tumour extracts revealed specific alterations in Hippo pathway core components, as a function of DDR and collagen expression, that were associated with stimulation of tumour growth by DDRs and collagen I. Collectively, these findings identified divergent effects of DDRs on primary tumour growth and experimental lung metastasis in the HT1080 xenograft model and highlight the critical role of fibrillar collagen and DDRs in supporting the growth of tumours thriving within a collagen-rich stroma.

The Role of Mesothelin as a Diagnostic and Therapeutic Target in Pancreatic Ductal Adenocarcinoma: A Comprehensive Review

Mesothelin is a tumor differentiation antigen, which is highly expressed in several solid neoplasms, including pancreatic cancer. Its selective expression on malignant cells and on only a limited number of healthy tissues has made it an interesting candidate for investigation as a diagnostic and prognostic biomarker and as a therapeutic target. Based on a strong preclinical rationale, a number of therapeutic agents targeting mesothelin have entered clinical trials, including immunotoxins, monoclonal antibodies, antibody-drug conjugates, cancer vaccines, and adoptive T cell therapies with chimeric antigen receptors. In pancreatic cancer, mesothelin has been investigated mainly to address two unmet issues: the urgent need for new laboratory techniques for early tumor detection and the lack of successfully targetable oncogenic alterations for patients' treatment. In this review, we describe the clinicopathological significance of mesothelin expression in pancreatic cancer initiation and progression, we summarize available studies evaluating mesothelin as a potential diagnostic and prognostic biomarker in this disease, and we discuss current evidence and future perspectives of preclinical and clinical studies testing mesothelin as a molecular target for pancreatic cancer treatment.

Mesothelin as a biomarker for targeted therapy

CAR-T cell therapy targeting CD19 has achieved remarkable success in the treatment of B cell malignancies, while various solid malignancies are still refractory for lack of suitable target. In recent years, a large number of studies have sought to find suitable targets with low “on target, off tumor” concern for the treatment of solid tumors. Mesothelin (MSLN), a tumor-associated antigen broadly overexpressed on various malignant tumor cells, while its expression is generally limited to normal mesothelial cells, is an attractive candidate for targeted therapy. Strategies targeting MSLN, including antibody-based drugs, vaccines and CAR-T therapies, have been assessed in a large number of preclinical investigations and clinical trials. In particular, the development of CAR-T therapy has shown great promise as a treatment for various types of cancers. The safety, efficacy, doses, and pharmacokinetics of relevant strategies have been evaluated in many clinical trials. This review is intended to provide a brief overview of the characteristics of mesothelin and the development of strategies targeting MSLN for solid tumors. Further, we discussed the challenges and proposed potential strategies to improve the efficacy of MSLN targeted immunotherapy.

Paclitaxel synergizes with exposure time adjusted CD22-targeting immunotoxins against B-cell malignancies

CD22-targeted recombinant immunotoxins (rIT) are active in hairy cell leukemia or acute lymphoblastic leukemia (ALL), but not in mantle cell lymphoma (MCL) patients. The goal was to enhance rIT efficacy in vivo and to define a strong combination treatment. Activity of Moxetumomab pasudotox (Moxe) and LR combined with paclitaxel was tested against MCL cell lines in vitro and as bolus doses or continuous infusion in xenograft models. In the KOPN-8 ALL xenograft, Moxe or paclitaxel alone was active, but all mice died from leukemia; when combined, 60% of the mice achieved a sustained complete remission. Against MCL cells in vitro, LR was more active than Moxe and the cells had to be exposed to rIT for more than 24 hours for them to die. To maintain high blood levels in vivo, LR was administered continuously by 7-day pumps achieving a well-tolerated steady plasma concentration of 45 ng/ml. In JeKo-1 xenografts, continuously administered LR was 14-fold more active than bolus doses and the combination with paclitaxel additionally improved responses by 135-fold. Maintaining high rIT-plasma levels greatly improves responses in the JeKo-1 model and paclitaxel substantially enhances bolus and continuously infused rIT, supporting a clinical evaluation against B-cell malignancies.

"Stealth dissemination" of macrophage-tumor cell fusions cultured from blood of patients with pancreatic ductal adenocarcinoma

Here we describe isolation and characterization of macrophage-tumor cell fusions (MTFs) from the blood of pancreatic ductal adenocarcinoma (PDAC) patients. The MTFs were generally aneuploidy, and immunophenotypic characterizations showed that the MTFs express markers characteristic of PDAC and stem cells, as well as M2-polarized macrophages. Single cell RNASeq analyses showed that the MTFs express many transcripts implicated in cancer progression, LINE1 retrotransposons, and very high levels of several long non-coding transcripts involved in metastasis (such as MALAT1). When cultured MTFs were transplanted orthotopically into mouse pancreas, they grew as obvious well-differentiated islands of cells, but they also disseminated widely throughout multiple tissues in "stealth" fashion. They were found distributed throughout multiple organs at 4, 8, or 12 weeks after transplantation (including liver, spleen, lung), occurring as single cells or small groups of cells, without formation of obvious tumors or any apparent progression over the 4 to 12 week period. We suggest that MTFs form continually during PDAC development, and that they disseminate early in cancer progression, forming "niches" at distant sites for subsequent colonization by metastasis-initiating cells.

Inhibition of Discoidin Domain Receptor 1 Reduces Collagen-mediated Tumorigenicity in Pancreatic Ductal Adenocarcinoma

The extracellular matrix (ECM), a principal component of pancreatic ductal adenocarcinoma (PDA), is rich in fibrillar collagens that facilitate tumor cell survival and chemoresistance. Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase that specifically binds fibrillar collagens and has been implicated in promoting cell proliferation, migration, adhesion, ECM remodeling, and response to growth factors. We found that collagen-induced activation of DDR1 stimulated protumorigenic signaling through protein tyrosine kinase 2 (PYK2) and pseudopodium-enriched atypical kinase 1 (PEAK1) in pancreatic cancer cells. Pharmacologic inhibition of DDR1 with an ATP-competitive orally available small-molecule kinase inhibitor (7rh) abrogated collagen-induced DDR1 signaling in pancreatic tumor cells and consequently reduced colony formation and migration. Furthermore, the inhibition of DDR1 with 7rh showed striking efficacy in combination with chemotherapy in orthotopic xenografts and autochthonous pancreatic tumors where it significantly reduced DDR1 activation and downstream signaling, reduced primary tumor burden, and improved chemoresponse. These data demonstrate that targeting collagen signaling in conjunction with conventional cytotoxic chemotherapy has the potential to improve outcome for pancreatic cancer patients. Mol Cancer Ther; 16(11); 2473-85. ©2017 AACR.

Suppression of Tobacco Carcinogen-Induced Lung Tumorigenesis by Aerosol-Delivered Glycerol Propoxylate Triacrylate-Spermine Copolymer/Short Hairpin Rab25 RNA Complexes in Female A/J Mice

BACKGROUND

Rab25, a member of Rab family of small guanosine triphosphatase, is associated with progression of various types of human cancers, including lung cancer, the leading cause of cancer-associated deaths around the globe.

METHODS

In this study, we report the gene therapeutic effect of short hairpin Rab25 RNA (shRab25) on 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumorigenesis in female A/J mice. Initially, mice (6 weeks old) were injected with single dose of NNK (2 mg/0.1 mL saline/mouse) by intraperitoneal injection to induce the tumor. Eight weeks later, shRab25 was complexed with glycerol propoxylate triacrylate-spermine (GPT-SPE) copolymer and delivered into tobacco-induced lung cancer models through a nose-only inhalation system twice a week for 2 months.

RESULTS

GPT-SPE/shRab25 largely decreased the tobacco-induced tumor numbers and tumor volume in the lungs compared to GPT-SPE- or GPT-SPE/shScr-delivered groups. Remarkably, aerosol-delivered GPT-SPE/shRab25 significantly decreased the expression level of Rab25 and other prominent apoptosis-related proteins in female A/J mice. The apoptosis in these mice was determined by detecting the expression level of Bcl-2, proliferating cell nuclear antigen, Bax, and further confirmed by TUNEL assay.

CONCLUSIONS

Our results strongly confirm the tumorigenic role of Rab25 in tobacco carcinogen-induced lung cancer and hence demonstrate aerosol delivery of shRab25 as a therapeutic target for lung cancer treatment.

WEE1 inhibition targets cell cycle checkpoints for triple negative breast cancers to overcome cisplatin resistance

Cisplatin is one of the most commonly used therapeutic drugs for cancer therapy, yet prolonged cisplatin treatment frequently results in drug resistance. To enhance therapeutic effect of cisplatin, we conducted a high throughput screening using a kinase library containing 704 kinases against triple negative breast cancer (TNBC) cells. We demonstrated that cisplatin activates ATR, CHK1 and WEE1, which shut down DNA replication and attenuate cisplatin induced-lethality. WEE1 inhibition sensitizes TNBCs and cisplatin resistant cancer cells to cisplatin-induced lethality, because it not only impairs DNA replication checkpoint more profoundly than inhibition of ATR or CHK1, but also defects G2-M cell cycle checkpoint. Finally, we demonstrated that combined cisplatin treatment and WEE1 inhibition synergistically inhibits xenograft cancer growth accompanied by markedly reduced expression of TNBC signature genes. Thus targeting DNA replication and G2-M cell cycle checkpoint simultaneously by cisplatin and WEE1 inhibition is promising for TNBCs treatment, and for overcoming their cisplatin resistance.

Up-regulation of N-cadherin by Collagen I-activated Discoidin Domain Receptor 1 in Pancreatic Cancer Requires the Adaptor Molecule Shc1

Pancreatic ductal adenocarcinomas are highly malignant cancers characterized by extensive invasion into surrounding tissues, metastasis to distant organs, and a limited response to therapy. A main feature of pancreatic ductal adenocarcinomas is desmoplasia, which leads to extensive deposition of collagen I. We have demonstrated that collagen I can induce epithelial-mesenchymal transition (EMT) in pancreatic cancer cells. A hallmark of EMT is an increase in the expression of the mesenchymal cadherin N-cadherin. Previously we showed up-regulation of N-cadherin promotes tumor cell invasion and that collagen I-induced EMT is mediated by two collagen receptors, α2β1-integrin and discoidin domain receptor 1 (DDR1). DDR1 is a receptor-tyrosine kinase widely expressed during embryonic development and in many adult tissues and is also highly expressed in many different cancers. In the signaling pathway initiated by collagen, we have shown proline-rich tyrosine kinase 2 (Pyk2) is downstream of DDR1. In this study we found isoform b of DDR1 is responsible for collagen I-induced up-regulation of N-cadherin and tyrosine 513 of DDR1b is necessary. Knocking down Shc1, which binds to tyrosine 513 of DDR1b via its PTB (phosphotyrosine binding) domain, eliminates the up-regulation of N-cadherin. The signaling does not require a functional SH2 domain or the tyrosine residues commonly phosphorylated in Shc1 but is mediated by the interaction between a short segment of the central domain of Shc1 and the proline-rich region of Pyk2. Taken together, these data illustrate DDR1b, but not DDR1a, mediates collagen I-induced N-cadherin up-regulation, and Shc1 is involved in this process by coupling to both DDR1 and Pyk2.

Chemical Screens Identify Drugs that Enhance or Mitigate Cellular Responses to Antibody-Toxin Fusion Proteins

The intersection of small molecular weight drugs and antibody-based therapeutics is rarely studied in large scale. Both types of agents are currently part of the cancer armamentarium. However, very little is known about how to combine them in optimal ways. Immunotoxins are antibody-toxin gene fusion proteins engineered to target cancer cells via antibody binding to surface antigens. For fusion proteins derived from Pseudomonas exotoxin (PE), potency relies on the enzymatic domain of the toxin which catalyzes the ADP-ribosylation of EF2 causing inhibition of protein synthesis leading to cell death. Candidate immunotoxins have demonstrated clear value in clinical trials but generally have not been curative as single agents. Therefore we undertook three screens to discover effective combinations that could act synergistically. From the MIPE-3 library of compounds we identified various enhancers of immunotoxin action and at least one major class of inhibitor. Follow-up experiments confirmed the screening data and suggested that immunotoxins when administered with everolimus or nilotinib exhibit favorable combinatory activity and would be candidates for preclinical development. Mechanistic studies revealed that everolimus-immunotoxin combinations acted synergistically on elements of the protein synthetic machinery, including S61 kinase and 4E-BP1 of the mTORC1 pathway. Conversely, PARP inhibitors antagonized immunotoxins and also blocked the toxicity due to native ADP-ribosylating toxins. Thus, our goal of investigating a chemical library was justified based on the identification of several approved compounds that could be developed preclinically as ‘enhancers’ and at least one class of mitigator to be avoided.

Tyrosine Kinase Signaling in Clear Cell and Papillary Renal Cell Carcinoma Revealed by Mass Spectrometry-Based Phosphotyrosine Proteomics

PURPOSE

Targeted therapies in renal cell carcinoma (RCC) are limited by acquired resistance. Novel therapeutic targets are needed to combat resistance and, ideally, target the unique biology of RCC subtypes.

EXPERIMENTAL DESIGN

Tyrosine kinases provide critical oncogenic signaling and their inhibition has significantly impacted cancer care. To describe a landscape of tyrosine kinase activity in RCC that could inform novel therapeutic strategies, we performed a mass spectrometry-based system-wide survey of tyrosine phosphorylation in 10 RCC cell lines as well as 15 clear cell and 15 papillary RCC human tumors. To prioritize identified tyrosine kinases for further analysis, a 63 tyrosine kinase inhibitor (TKI) drug screen was performed.

RESULTS

Among the cell lines, 28 unique tyrosine phosphosites were identified across 19 kinases and phosphatases including EGFR, MET, JAK2, and FAK in nearly all samples. Multiple FAK TKIs decreased cell viability by at least 50% and inhibited RCC cell line adhesion, invasion, and proliferation. Among the tumors, 49 unique tyrosine phosphosites were identified across 44 kinases and phosphatases. FAK pY576/7 was found in all tumors and many cell lines, whereas DDR1 pY792/6 was preferentially enriched in the papillary RCC tumors. Both tyrosine kinases are capable of transmitting signals from the extracellular matrix and emerged as novel RCC therapeutic targets.

CONCLUSIONS

Tyrosine kinase profiling informs novel therapeutic strategies in RCC and highlights the unique biology among kidney cancer subtypes. Clin Cancer Res; 22(22); 5605-16. ©2016 AACR.