Abstract 4049: TIDAL-01: A selected TIL process that enriches for neoantigen reactive TIL in solid tumors

Background: Tumor infiltrating lymphocyte (TIL) therapy is capable of mediating durable complete responses in melanoma. While solid tumors such as colorectal cancer (CRC), non-small cell lung cancer (NSCLC), ovarian and breast have been shown to contain neoantigen reactive TIL, the success of bulk TIL therapy in these tumors has been limited. Enhancing tumor reactivity through the selective expansion of neoantigen-reactive subpopulations, has demonstrated success in cancers outside of melanoma underscoring the potential of a neoantigen selected TIL approach in indications with lower tumor mutational burdens. Here we demonstrate that the TIDAL-01 process, which utilizes tumor-specific mutation containing peptides to select neoantigen reactive TIL produces TIL products significantly enriched in neoantigen reactivity.

Methods: Fresh tumors were cut into fragments or dissociated and cultured in a primary expansion (preREP). Antigen presenting cells (APCs) were isolated and expanded from patient matched blood. Whole exome and RNA sequencing was performed on tumor tissue and autologous PBMCs and used to predict and prioritize neoantigen mutations. Peptides encoding the mutations were synthesized, loaded onto APCs and co-cultured with autologous TIL. Neoantigen reactive TIL were selected by fluorescence activated cell sorting (FACS), based on the upregulation of the activation markers CD134 and CD137 and expanded with a rapid expansion protocol (REP). Bulk and unselected TIL were expanded alongside for comparison. Neoantigen reactivity was quantified and deconvoluted by cytokine secretion, degranulation, upregulation of CD134/CD137 by flow and when practical, killing of autologous tumor cell lines or organoids.

Results: Successful TIL expansion was achieved in 31/34 (91%) tumors (14/17 CRC, 10/10 NSCLC, 3/3 ovarian and 3/3 melanoma) using both tumor fragments and dissociated tumors. CRC tumors accounted for half of the samples (17/34), and the tumor mutational burden within these samples varied substantially, ranging from 229 to 5436 mutations. Upregulation of CD134 and CD137 and increased IFN-γ production was observed in all samples upon co-culture with peptide loaded APCs. Peptide restimulation and deconvolution revealed that the TIDAL-01 process is capable of enriching for both CD4 and CD8 reactivities. Selected TIL products produced up to 50x more IFN-γ, TNF-α and Granzyme B than bulk TIL and at least 2x higher levels of degranulation, indicative of greater killing potential.

Conclusions: TIL from metastatic CRC, melanoma, NSCLC and ovarian tumors were successfully expanded from the majority of patients. Co-culture of TIL and peptide loaded APCs followed by FACS significantly enriched for neoantigen reactivity compared to bulk TIL, demonstrating the potential of the TIDAL-01 process to produce selected TIL products for the treatment of non-melanoma tumors.

Citation Format: Larissa A. Pikor, Antoine Bernard, Nathalie Brassard, Anna Fritzsche, Anna Kluew, Zachary K. Jilesen, Jake Nikota, Rohan Bareja, Christian Laing, David F. Stojdl, TJ Langer, Stewart Abbot, Barbara Sennino, Simon Turcotte. TIDAL-01: A selected TIL process that enriches for neoantigen reactive TIL in solid tumors. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4049.

Non-viral precision T cell receptor replacement for personalized cell therapy

T cell receptors (TCRs) enable T cells to specifically recognize mutations in cancer cells1-3. Here we developed a clinical-grade approach based on CRISPR-Cas9 non-viral precision genome-editing to simultaneously knockout the two endogenous TCR genes TRAC (which encodes TCRα) and TRBC (which encodes TCRβ). We also inserted into the TRAC locus two chains of a neoantigen-specific TCR (neoTCR) isolated from circulating T cells of patients. The neoTCRs were isolated using a personalized library of soluble predicted neoantigen-HLA capture reagents. Sixteen patients with different refractory solid cancers received up to three distinct neoTCR transgenic cell products. Each product expressed a patient-specific neoTCR and was administered in a cell-dose-escalation, first-in-human phase I clinical trial ( NCT03970382 ). One patient had grade 1 cytokine release syndrome and one patient had grade 3 encephalitis. All participants had the expected side effects from the lymphodepleting chemotherapy. Five patients had stable disease and the other eleven had disease progression as the best response on the therapy. neoTCR transgenic T cells were detected in tumour biopsy samples after infusion at frequencies higher than the native TCRs before infusion. This study demonstrates the feasibility of isolating and cloning multiple TCRs that recognize mutational neoantigens. Moreover, simultaneous knockout of the endogenous TCR and knock-in of neoTCRs using single-step, non-viral precision genome-editing are achieved. The manufacture of neoTCR engineered T cells at clinical grade, the safety of infusing up to three gene-edited neoTCR T cell products and the ability of the transgenic T cells to traffic to the tumours of patients are also demonstrated.

Neoantigen-targeted CD8+ T cell responses with PD-1 blockade therapy

Neoantigens are peptides derived from non-synonymous mutations presented by human leukocyte antigens (HLAs), which are recognized by antitumour T cells1-14. The large HLA allele diversity and limiting clinical samples have restricted the study of the landscape of neoantigen-targeted T cell responses in patients over their treatment course. Here we applied recently developed technologies15-17 to capture neoantigen-specific T cells from blood and tumours from patients with metastatic melanoma with or without response to anti-programmed death receptor 1 (PD-1) immunotherapy. We generated personalized libraries of neoantigen-HLA capture reagents to single-cell isolate the T cells and clone their T cell receptors (neoTCRs). Multiple T cells with different neoTCR sequences (T cell clonotypes) recognized a limited number of mutations in samples from seven patients with long-lasting clinical responses. These neoTCR clonotypes were recurrently detected over time in the blood and tumour. Samples from four patients with no response to anti-PD-1 also demonstrated neoantigen-specific T cell responses in the blood and tumour to a restricted number of mutations with lower TCR polyclonality and were not recurrently detected in sequential samples. Reconstitution of the neoTCRs in donor T cells using non-viral CRISPR-Cas9 gene editing demonstrated specific recognition and cytotoxicity to patient-matched melanoma cell lines. Thus, effective anti-PD-1 immunotherapy is associated with the presence of polyclonal CD8+ T cells in the tumour and blood specific for a limited number of immunodominant mutations, which are recurrently recognized over time.

Abstract 2757: Correlates of peptide-HLA manufacturing success, TCR capture and neoTCR trafficking from patients using the PACTImmune࣪ Database

PACT Pharma uses a state-of-the-art approach to predict and validate neoepitopes (neoEs) and their cognate T cell receptors (neoTCRs) by capturing neoE-specific T cells from peripheral blood. This neoTCR discovery and validation process is being applied in a clinical trial (NCT03970382) evaluating personalized neoTCR-T cell therapy in solid tumors. The PACTImmune Database (PIDB) accumulates extensive pre-, on- and post-treatment data related to this trial. Here we present PIDB data on the prediction of peptide-HLA manufacturing success, as well as correlates of success of neoTCR capture and neoTCR T cell tumor trafficking, all of which have direct applications for prospective patient enrollment and treatment.

The PIDB contains distinct data sets on our neoTCR platform that we examined for predictive capabilities for three distinct applications. The first application was predicting manufacturing success rates of our single chain trimer (comPACT) which consists of the predicted neoE peptide together with B2M and the HLA heavy chain. Using multiple linear regression (MLR), we built a model predicting success rates of comPACT protein manufacturing (defined as comPACT protein yields >detection threshold) and compared it to prediction based solely on expressed tumor mutation burden (eTMB). Using univariate analysis, we compared variables between patients with 3 neoTCRs selected versus those with 0 neoTCRs. Finally, using principal component analysis (PCA) we evaluated if the PIDB neoantigen and TCR characteristics correlate with neoTCR T cell trafficking in patients (n=4) dosed with neoTCR T cells. Trafficking was determined by sequencing (neoTCR specific reads) and in some cases, IHC/RNAScope imaging of post-dosing biopsies.

MLR analysis of comPACT protein expression data resulted in significant improvement in comPACT manufacturing success rate predictions (R2=0.66, P<<0.001). These predictions were better than using eTMB alone (R2=0.33, P<<0.001). Patients with 3 neoTCRs selected had a significantly higher number of comPACTs and mutations covered by those comPACTs as compared to 0 neoTCR patients (P=0.004 and 0.002, respectively). All four patients demonstrated trafficking of neoTCR products into the tumor in post-dosing biopsies. Based on TCR characteristics PCA showed separation between tumor trafficking and non-trafficking TCRs (data pending).

Application of PIDB data improves predictions of peptide-HLA manufacturing success, identifies differences between patients with 3 and no neoTCR products and provides insights into trafficking TCR characteristics, which in turn enables us to optimize our neoTCR selection strategy for patients with solid cancers. PIDB thus represents a significant & maturing dataset for patient-specific tumor immunogenicity in solid cancers and provides opportunities to optimize personalized neoTCR T cell treatment.

Citation Format: Eric W. Stawiski, Vinnu Bhardwaj, Jyoti Mathur, Eva Huang, Olivier Dalmas, Zheng Pan, Cliff Wang, James Heath, Barbara Sennino, Mark Frohlich, Arati Rao, Stefanie Mandl. Correlates of peptide-HLA manufacturing success, TCR capture and neoTCR trafficking from patients using the PACTImmune࣪ Database [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2757.

Abstract 563: Circulating tumor-specific T cells preferentially recognize patient-specific mutational neoantigens and infrequently recognize shared cancer driver mutations

Background: Due to a lack of prior technologies able to generate a landscape analysis of mutational neoantigen-HLA class I complex T cell recognition, it is unclear how the frequency of T cell receptors (TCR) against patient-specific mutations compares to shared oncogenic mutations.

Methods: We used the imPACT Isolation Technology®, which allows the selective capture of cancer-specific CD8 T cells from the blood of cancer patients at frequencies as low as 1 in 300K CD8 T cells. This TCR isolation platform is based on whole exome sequencing of a tumor and paired normal tissue control for the identification of non-synonymous mutations, including mutations in cancer driver genes (e.g., p53, KRAS, PI3KCA or HRAS). Bioinformatic algorithms were used to predict potential HLA-binding neoantigens (neoAg) in context of the patient’s HLA class I haplotype. A library of multimerized and barcoded predicted neoAg peptide-HLA molecules were generated to interrogate patient CD8 T cells. The paired αβ-TCR sequences were derived from the single cell sorted T cells. TCRs from antigen experienced CD8 T cell were functionally validated by generating T cells expressing neoTCRs, using non-viral precision gene editing to insert the transgenic TCR chains into the endogenous TRAC locus. We previously showed that all (40/40) TCRs isolated using this approach, reacted to patient-matched cancer cell lines (Puig Saus et al. AACR 2020).

Results: Neoantigen-specific T cells isolated from the peripheral blood of 243 patients with melanoma, bladder, endometrial, ovarian, colorectal, head and neck, urothelial and breast cancers were analyzed For each patient, an average of 352 neoAg-HLA capture complexes were predicted. Across all patients 58,058 neoAg-HLA complexes were manufactured, spanning 8,804 unique mutations. Among these, only about 2% represented known oncogene driver mutations. The predicted peptide-HLA binding affinity for cancer driver mutations was significantly lower (P<0.001) compared to patient-specific neoAg. Remarkably, functional characterization of 206 TCRs showed that most TCRs (93.7%) recognized patient-specific neoAg. Despite the low percentage of neoAg-HLA capture complexes covering oncogene driver mutations (~ 2%), 6.3% of TCRs (13) targeted known cancer driver proteins. Primary human T cells were then engineered to express each TCR. TCR T cells became functionally activated only when exposed to the cognate antigen, irrespective of whether they target neoAg or cancer driver mutations, confirming the high degree of specificity of the isolated TCRs.

Conclusion: A landscape analysis of neoAg-specific TCRs recognizing mutations in cancer has revealed that most T cells recognizing neoantigen-HLA complexes are specific for private mutations in each cancer, though low frequencies of TCR targeting driver mutations can still be identified.

Citation Format: Barbara Sennino, Jyoti Mathur, Eva Huang, Andrew Conroy, Marc Ting, Benjamin Yuen, Zheng Pan, Eric Stawiski, Stefanie Mandl. Circulating tumor-specific T cells preferentially recognize patient-specific mutational neoantigens and infrequently recognize shared cancer driver mutations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 563.

Abstract 2829: Non-viral precision genome engineering enables personalized adoptive neoTCR T cell therapy for cancer including multiple additional edits that improve the activity of neoTCR T cells by enhancing CD4 T cell antigen sensitivity and conferring resistance to TGFβ

Personalized autologous TCR-T cell therapies targeting neoepitopes (neoE) derived from tumor-specific mutations are a compelling approach for the treatment of patients with solid tumors. Using the ultra-sensitive imPACT Isolation Technology®, antigen-experienced, neoE-specific CD8 T cells are captured from the blood of patients with solid cancers followed by cloning of the cognate, neoE-specific, MHC class I-restricted T cell receptors (neoTCRs). DNA-mediated (non-viral) precision genome engineering technology is then used to engineer autologous CD8 and CD4 T cells to express the neoTCR. We have further built upon this platform to modify neoTCR-T cells to address potential sources for tumor immune evasion.

The versatility of this single-step gene editing platform is demonstrated here by the presentation of a neoTCR T cell product with knockout of endogenous TCRα and TCRβ and the simultaneous expression of a neoTCR with CD8 co-receptor (CD8coR) from the same expression cassette along with knockout of TGFβ receptor 2 (TGFBR2). We have previously shown that CD8coR expression augments the activity of CD4 T cells engineered to express MHC class I restricted neoTCRs, by increasing CD4 neoTCR T cell helper and effector function. TGFβ is known to promote tumor growth, metastasis, and epithelial to mesenchymal transition (EMT) and to inhibit effector immune responses while promoting fibrosis and the differentiation of inhibitory cell types such as regulatory T cells. TGFβ is expressed by many tumor types and high TGFβ expression is associated with worse prognosis for several cancer subtypes including colorectal, lung and glioblastoma. TGFBR2 is a critical mediator of TGFβ signaling, resulting in potent, inhibitory effects on T cell function.

Our data show that simultaneous ablation of TGFBR2 signaling and expression of CD8coR was achieved with high efficiency, resulting in fully functional CD8 and CD4 neoTCR-T cells. Deletion of TGFBR2 with or without CD8coR expression, together with the expression of a neoE-targeted TCR preserved T cell effector function in the presence of inhibitory concentrations of TGFβ. Importantly, the combination of TGFBR2 knockout and CD8coR expression resulted in additive benefits, providing proof-of-concept for modifying two orthogonal features to improve neoTCR T cell function. Altogether, these results demonstrate the applicability of this versatile, precision genome engineering platform technology to yield enhanced, next-generation neoTCR-T cell therapies to expand the potential for clinical benefit in persons with solid cancers.

Citation Format: Charles W. Tran, Kayla Lee, Bhamini Purandare, James Byers, Michael M. Dubreuil, William Lu, Michal Mass, Kyle Jacoby, Stefanie J. Mandl, Barbara Sennino. Non-viral precision genome engineering enables personalized adoptive neoTCR T cell therapy for cancer including multiple additional edits that improve the activity of neoTCR T cells by enhancing CD4 T cell antigen sensitivity and conferring resistance to TGFβ [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2829.

Abstract 1526: Single-step precision genome engineering platform enables versatile generation of personalized (neoTCR) adoptive cell therapy T cells with supplementary anti-tumor attributes

Personalized autologous TCR-T cell therapies targeting neoE-specific neoepitopes (NeoE) derived from tumor-exclusive mutations are a compelling approach for the treatment of patients with solid tumors. Using the ultra-sensitive imPACT Isolation Technology®, antigen-experienced neoE-specific CD8 T cells are captured from the blood of patients with solid cancers followed by cloning of the cognate neoepitope-specific HLA class I-restricted T cell receptors (HLA-I neoTCRs). Using DNA-mediated (non-viral) precision genome engineering technology, fresh CD8 and CD4 T cells from the same patient with cancer are engineered to express the HLA-I neoTCR. We have further innovated this platform of precision genome engineering to confer neoTCR-T cells with supplementary gene edits to address the array of potential sources for tumor immune evasion. Two examples of the versatility of this single step gene editing platform are described in this study: 1) concurrent expression of a CD8 co-receptor (CD8coR) to augment activity of CD4 T cells engineered with lower affinity HLA-I neoTCRs; and 2) simultaneous disruption of TET2 expression in T cells, which has previously been reported to positively affect T cell differentiation and persistence. The data shows that these simultaneous supplemental gene modifications were achieved with high efficiency, resulting in fully functional CD8 and CD4 neoTCR-T cells. Surface expression of CD8coR together with the neoE-targeted TCR increased T cell effector function and antigen-specific tumor cell killing. NeoTCR-T cells with concomitant deletion of TET2-expression exhibited enhanced cytotoxicity against neoantigen-expressing tumor cells. Together, these results demonstrate the applicability of this versatile precision genome engineering platform technology to yield enhanced next generation neoTCR-T cell therapies to expand the potential for clinical benefit in treating persons with solid cancers.

Citation Format: Michael M. Dubreuil, Charles W. Tran, Bhamini Purandare, William Lu, James Byers, Michal Mass, Kyle Jacoby, Barbara Sennino, Alex Franzusoff, Stefanie J. Mandl. Single-step precision genome engineering platform enables versatile generation of personalized (neoTCR) adoptive cell therapy T cells with supplementary anti-tumor attributes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1526.

Abstract 2177: Tumor neoantigen profiling with validated patient-specific TCR characterization to improve neoepitope prediction

PACT Pharma has developed an ultra-sensitive approach to validate predicted neoantigens and the cognate T cell receptors (neoTCRs) from tumor specific somatic mutations by capturing neoantigen-specific T cells from peripheral blood. This process is used in clinical trials (NCT03970382) of personalized neoTCR-T therapy for persons with solid cancers.

Using the state of the art prediction pipeline and screening process, more than one hundred twenty neoantigens were predicted from 5 type of solid cancers that were validated by characterizing cognate T cells and their close to 200 unique TCRs captured from the blood of the same individual. These validated neoepitopes of 8 to 11 amino acids represent broad HLA class I coverage with >30 alleles to date. Our analysis revealed that mutations can occur in all positions within the epitopes. Epitope immunogenicity is potentially affected by different mechanisms including mutation position, agretopicity, as well as HLA interacting positions and/or by interactions between mutated residues and its cognate TCRs. It was observed that these validated neoepitopes comprise broad ranges of predicted HLA binding affinities, stability, and neoantigen expression levels. The analysis presented here offers insights to enable machine learning to advance rules for epitope selection and prioritization that may be important for immunological approaches to address a broad range of diseases, including cancer.

Citation Format: Zheng Pan, Olivier Dalmas, Songming Peng, Kyle Jacoby, Barbara Sennino, Yan Ma, Chad Smith, Amin Momin, Allison Xu, Katharine Heeringa, Jonathan Johnston, Duo An, Boi Quach, William Lu, Diana Nguyen, Andrew Conroy, Bhamini Purandare, Eva Huang, Eric Stawiski, Alex Franzusoff, Stefanie Mandl. Tumor neoantigen profiling with validated patient-specific TCR characterization to improve neoepitope prediction [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2177.

Abstract 2192: Non-viral genome engineering method allows highly efficient, single-step removal and precise insertion of multiple large genes

Recent advances in gene editing have enabled the targeted engineering of primary cells to insert entire transgenes without the use of viral vectors. Using these methods, novel genes can be inserted in a seamless manner into the specified genomic locus, realizing the goal of precise targeted genomic modifications. Non-viral modification of primary cells holds potential to significantly reduce costs and time needed for the generation of therapeutic cell products. It has also allowed the generation of personalized cell therapies involving patient-specific manufacturing of DNA constructs, such as for the developed of patient-derived, neoepitope-specific TCR-T cells.

Proof-of-concept experiments have shown that non-viral genome engineering methods can integrate small genetic elements such as GFP, while the delivery of larger therapeutically relevant payloads at high efficiency has previously been challenging. Here we describe a proprietary single-step, DNA-mediated method developed for seamlessly engineering fully natural neoepitope-specific TCRs (neoTCR) into the endogenous TCR locus of primary human T cells at high efficiencies (i.e. >50% gene editing efficiency). This method allows the delivery of the two genes comprising the neoTCR without the need for selection necessitated by less efficient approaches.

To further evaluate this approach, fresh human donor T cells were engineered to express the patient-specific neoTCR plus two additional gene products, CD8α and CD8β (i.e. precise genome engineering of four ectopic genes). The data shows that these modifications were made at high efficiency, resulting in fully functional CD8 and CD4 T cells. Surface expression of CD8 coreceptor together with the neoE-targeted TCR increased T cell signaling sensitivity of the engineered neoTCR-T cells by 10-100 fold.

The potential for off-target cleavage or unexpected genomic outcomes was assessed using multiple methods, including a newly developed primary T cell GUIDE-seq assay. Despite multi-locus editing, no evidence of off-target insertion or unexpected genomic rearrangements were observed.

In summary, these results demonstrate the applicability of a single step, highly efficient method for manufacturing fresh human T cells into neoTCR-T cell therapies, engineered with multiple functionalities. This proprietary precision genome engineering technology supports the on-going Phase 1 clinical trial of personalized autologous, NeoTCR-P1 engineered T cell therapies for patients with solid tumors (NCT03970382).

Citation Format: Kyle Jacoby, William Lu, Diana Nguyen, Barbara Sennino, Andrew Conroy, Bhamini Purandare, Alex Franzusoff, Stefanie Mandl. Non-viral genome engineering method allows highly efficient, single-step removal and precise insertion of multiple large genes [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2192.

Abstract NG11: Landscape analysis of neoepitope-specific T-cell responses to immunotherapy

In infectious disease, polyclonal T cell responses against immunodominant epitopes drive successful immune responses. In cancer, neoepitopes (neoE) derived from non-synonymous mutations, similarly to the immunodominant epitopes in viral infections, are potentially highly immunogenic because the T cells recognizing these antigens are not subjected to the mechanisms of tolerance. Indeed, early studies support that neoE derived from non-synonymous mutations are the primary target of T cell responses induced by immune checkpoint blockade therapy and have been successfully targeted by adoptively transferred T cell therapies (ACT) in multiple cancer histologies. However, there is limited knowledge on the immunodominance and evolution of neoE's, or the clonality of the T cell responses against these neoE. Furthermore, little is known regarding the correlation between the presence and expansion of neoE-specific T cells and the clinical response to immunotherapy in patients. To characterize the neoE-specific T cell responses induced after immunotherapy, we collected peripheral blood mononuclear cells (PBMCs) over time (longitudinally) and established expanded tumor infiltrating lymphocyte cultures (TILs) and autologous tumor cell lines from the patient's tumor biopsies. We performed whole exome and RNA sequencing of the tumor and normal tissue controls for the computational prediction and ranking of patient-specific neoEs. We then generated a library of capture reagents consisting of the patient HLA class I molecules loaded with predicted neoE (Peng et al. AACR 2019) and isolated neoE-specific T cells from the patients' PBMC or TIL samples. Once isolated, the paired neoE-specific TCR alpha and beta chains (neoTCR) were obtained by single cell sequencing. For functional characterization of the neoTCRs, healthy donor primary human T cells were modified to express the neoTCR using CRISPR-based, non-viral precision genome engineering by replacing the endogenous TCR with the respective neoTCR (Jacoby et al., AACR 2019, Sennino et al., AACR 2019). These gene-edited T cells were then used in co-culture experiments with the patient autologous cell lines. We analyzed T cell responses in three patients (PT1, PT2, and PT3) with metastatic melanoma receiving immunotherapy. PT1 had a fast and durable anti-tumor response to anti-PD-1 therapy. Sequencing identified 2556 somatic coding mutations. A library of 243 neoE-specific pMHC capture reagents across 3 HLA types, HLA-A*03:01, A*24:01, and C*12:03 was generated and used for screening of PBMCs or TILs derived from multiple longitudinal time points. Several hundred neoE-specific T cells were isolated. Importantly, this neoE-specific T cell response was comprised of 17 different neoE-specific T cells clones targeting only 5 different HLA-neoE complexes supporting the immunodominance hypothesis. On the other hand, PT2 and PT3 showed marginal responses to immunotherapy. Patient two progressed after being treated with anti-PD1. This patient had 24 somatic coding mutations. Seventeen neoE-HLA reagents across 3 HLAs, B*35:03, C*12:03, and C*08:01 were generated and used to capture neoE-specific T cells from TILs and PBMCs. While 14 different TCRs targeting 7 HLA-neoE complexes were identified from expanded TILs, no neoE-reactive T cells were captured from the peripheral blood. PT3 presented with progressive disease after being treated with local TVEC. This patient had 61 somatic coding mutations; 78 neoE-specific pHLA capture reagents covering HLA-A*02:01, A*03:01, B*07:02, C*05:01, and C*07:02 were generated and used to screen for neoE-specific T cells in the patient's TIL and PBMCs. In contrast to PT2, 2 different neoTCRs targeting the same HLA-neoE complexes were isolated from PBMCs, but none from TILs. To further characterize the T cell responses from patients that responded or did not respond to immunotherapy, we generated 18 separate T cell products, each expressing a different neoTCR isolated from PT1, PT2 and PT3. For PT1, we characterized 14 different neoTCRs specific for neoE's in the mutated IL8, PUM1 and TPP2 genes. All 14 T cell products displayed specific cytotoxicity against the matched autologous melanoma cell line established from a biopsy of patient one (50-75% tumor growth inhibition compared to melanoma cell line growth in co-culture with a mismatched control TCR, 96 hour assay using a product to target ratio (P:T) of 1:1, p < 0.000001 for each comparison). No cytotoxic effect against an unmatched human melanoma cell line was observed. Furthermore, neoE TCR T cells upregulated 4-1BB and OX-40, secreted IFNγ, IL-2, TNFα, and IL6, and induced T cell proliferation and degranulation. Again, no unspecific T cell activation was observed when T cells were co-cultured with unmatched targets. Interestingly, precision genome engineered T cell products expressing neoTCRs identified from patients that did not respond to therapy (PT2 and PT3), also potently killed autologous tumor cells. Four neoTCRs were studied (2 TCR for PT2 and 2 TCRs for PT3), and three of them showed specific cytotoxicity against the matched autologous melanoma cell line (50-100% tumor growth inhibition compared to melanoma cell line growth in co-culture with a mismatched control TCR, 96 hour assay using P:T 5:1, p < 0.05 for each comparison). Additionally, upon co-culture with the matched melanoma cell line, but not against an unmatched melanoma cell line control, neoE TCR T cells upregulated 4-1BB and OX-40, secreted IFNγ, IL-2, TNFα, and IL6, and induced T cell proliferation and degranulation. These data demonstrate that even patients that did not respond to immunotherapy harbor neoTCRs that, when expressed in ‘fresh' T cells, are able to kill the autologous tumor cell lines. Using newly developed techniques to isolate and capture neoE-specific single T cells, as well as non-viral gene editing, we isolated and characterized neoE-specific T cells that can recognize the cancer cells and induce an anti-tumor response. We also studied the neoE immunodominance and TCR clonality over time of the natural T cell repertoire that induce anti-tumor responses to ICB therapy. Our results show that in a patient with a good response to anti-PD-1, there is a polyclonal response that targets a limited number of neoE-HLA complexes (2% of the neoE tested in the case of patient one) highlighting the immunodominance of these epitopes. Interestingly, different T cell clonotypes targeting the same mutations evolve over time, suggesting functional differences amongst the TCRs. In addition, our results demonstrate that even patients that did not respond to these therapies harbor neoE-specific T cells, as we were able to isolate neoE-specific T cells that recognized and killed patient-derived cancer cells. This suggests that even in patients that do not respond to immunotherapy, neoE-specific TCRs can be isolated and could be potentially used for personalized ACT. Finally, our results also show how non-viral precision genome engineering can successfully redirect T cells to neoE-expressing tumors, enabling the personalized ACT.

Citation Format: Cristina Puig-Saus, Barbara Sennino, Bhamini Purandare, Duo An, Boi Quach, Songming Peng, Huiming Xia, Sidi Zhao, Zheng Pan, Yan Ma, Justin Saco, Sameeha Jilani, Christine Shieh, Katharine Heeringa, Olivier Dalmas, Robert Moot, Diana Nguyen, William Lu, Kyle Jacoby, Andrew Conroy, Jasreet Hundal, Malachi Griffith, Stefanie Mandl, Alex Franzusoff, Antoni Ribas. Landscape analysis of neoepitope-specific T-cell responses to immunotherapy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr NG11.

Abstract 1435: An ultra-sensitive and high-throughput technology (imPACT) for the identification and isolation of intrinsic and emergent neoepitope-specific T cells from the peripheral blood and TILs of cancer patients

T cells capable of targeting neoepitopes (neoE) from tumor-specific mutations hold the potential to uniquely recognize and kill tumor cells. However, most cancer patients fail to mount a sufficient intrinsic T cell immune response to translate into clinical benefit. PACT Pharma has developed an ultra-sensitive and high-throughput technology (imPACT) for identifying and isolating neoE-specific T cells from peripheral blood. Whole exome sequencing of tumors and computational prediction identify patient-specific neoepitopes resulting from tumor-specific mutations. We then interrogate patient blood for neoE-specific T cells using human leukocyte antigen (HLA) protein-based reagents comprising a spectrum of human HLAs, thus enabling the evaluation of >99% of all individuals with cancer. We have identified and isolated neoE-specific T cells from the peripheral blood of >80% treatment-naive patients with bladder and colorectal cancers, melanoma and other solid tumors. Primary human T cells engineered with T cell receptor sequences (TCRs) cloned from the imPACT-isolated T cells gain the ability to kill cognate neoE-presenting tumor cells, thereby also confirming the specificity of the isolated TCR sequences to bind to the neoE target. This approach is also amenable to the longitudinal analysis of patients undergoing treatment for their cancers, to characterize the neoE-specific T cell populations likely to confer clinical benefit. In summary, the imPACT technology efficiently discovers potentially meaningful intrinsic neoE-specific TCRs from patients, enabling the development of personalized neoTCR-T cell therapies for the eradication of solid tumors.

Citation Format: Songming Peng, Boi Quach, Duo An, Salemiz Sandoval, Robert Bao, Zheng Pan, Michael Bethune, Olivier Dalmas, Michael Yi, Corey Meadows, Katherine Heeringa, Linlin Guo, Benjamin yuen, John Sorfleet, Kyle Jacoby, Robert Moot, William Lu, Diana Nguyen, Barbara Sennino, Andrew Conroy, Bhamini Purandare, Adam Litterman, Stefanie Mandl, Alex Franzusoff. An ultra-sensitive and high-throughput technology (imPACT) for the identification and isolation of intrinsic and emergent neoepitope-specific T cells from the peripheral blood and TILs of cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1435.

Abstract 4783: Highly efficient, non-viral precision genome engineering for the generation of personalized neoepitope-specific adoptive T cell therapies

Methods used to engineer cells for adoptive cell therapies (ACT) utilizing receptors that are constant across many patients (CAR or shared Ag TCRs) typically rely on Lenti-, retro-, or adeno-associated virus to deliver specificity-altering sequences to T cells. However, for personalized therapies such as the generation of neoepitope-specific TCR T cell therapies, use of viral vectors is not feasible due to long manufacturing timelines and prohibitive per-patient costs. PACT Pharma has developed a highly efficient, DNA-mediated (non-viral) proprietary precision genome engineering approach to engineer neoepitope-specific primary human T cells. This method can be widely utilized to generate T cells at research scale, as well as for ex vivo manufacturing.

Briefly, genomes of individual primary human CD8 and CD4 T cells are engineered with site-specific nucleases in a single-step transfection process to yield efficient, targeted replacement of the endogenous TCR with the therapeutic neoTCR sequences. In this way, the expression of the endogenous TCR is abolished ensuring natural expression and regulation of the inserted neoTCR. The precision of neoTCR-T cell genome engineering was evaluated by Targeted Locus Amplification (TLA) for off-target integration hot spots or translocations, and by next generation sequencing based off-target cleavage assays and found to lack evidence of unintended outcomes.

Engineered neoepitope-specific T cells are highly functional as demonstrated by antigen-specific proliferation, killing and cytokine production. Phenotype and detailed functional characterization of PACTs neoTCR-P1 T cells were performed and are described in a separate abstract.

PACT’s precision genome engineering approach enables highly efficient generation of bespoke NeoTCR T cells for personalized adoptive cell therapy for patients with solid tumors. Furthermore, PACT precision genome engineering method is not restricted to the use in T cells and has also been applied successfully to other primary cell types, including natural killer and hematopoietic stem cells.

Citation Format: Kyle Jacoby, Robert Moot, William Lu, Diana Nguyen, Barbara Sennino, Andrew Conroy, Bhamini Purandare, Adam J. Litterman, Fabrizia Urbinati, Susan P. Foy, Theresa Hunter, Albert Tai, Michael T. Bethune, Songming Peng, Olivier Dalmas, Alex Franzusoff, Stefanie J. Mandl. Highly efficient, non-viral precision genome engineering for the generation of personalized neoepitope-specific adoptive T cell therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4783.

Abstract B005: FPT155, a novel therapeutic CD80-Fc fusion protein with potent antitumor activity in preclinical models

Optimal activation of T cells requires both antigen-specific signaling and induction of costimulatory pathways. Costimulatory pathways are upregulated by foreign antigenic challenge but are not active in the normal immune state, thus maintaining peripheral tolerance to self-antigens. The absence of costimulatory signaling may likewise play a role in tolerance to cancer cells. Five Prime has developed a CD80 (B7.1) extracellular domain (ECD)-Fc fusion protein (FPT155) as a costimulatory molecule that can stimulate T-cell activation and break tumor immune tolerance. In vitro studies show that FPT155 induces T-cell activation and cytokine production via CD28. FPT155 activity requires T-cell receptor engagement, which indicates that FPT155 is not a CD28 “superagonist” that can drive T-cell activation independently of antigenic stimulation. To investigate the impact of CD80-Fc in preclinical models, we generated murine FPT155 (mFPT155), a surrogate fusion protein, composed of the mouse CD80 ECD fused with the murine Fc region of IgG2a. mFPT155 is well tolerated in mice and has potent efficacy in syngeneic tumor models, including the induction of complete tumor regression in the CT26 model. mFPT155 promotes the infiltration of T cells into the tumor core and increases the effector T:Treg ratio, thus inducing a favorable microenvironment for an effective antitumor immune response. Furthermore, combination of mFPT155 and anti-PD1 therapy leads to stronger antitumor efficacy compared to either therapy alone. Together these results indicate that mFPT155 is a potent T-cell costimulator with strong antitumor activity in mouse tumor models. We are currently performing IND-enabling studies and plan to initiate a clinical study with FPT155 in 2018.

Citation Format: Susannah D. Barbee, Barbara Sennino, Jacqueline De La Torre, Monica Macal, Quinn Walker, Marc R. Jabon, Amanda Chen, David A. Busha, Margaret Best, Kristen L. Pierce, Luis Borges, Kevin P. Baker, Thomas Brennan. FPT155, a novel therapeutic CD80-Fc fusion protein with potent antitumor activity in preclinical models [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B005.

Amplification of Oncolytic Vaccinia Virus Widespread Tumor Cell Killing by Sunitinib through Multiple Mechanisms

Oncolytic viruses pose many questions in their use in cancer therapy. In this study, we assessed the potential of mpJX-594 (mouse-prototype JX-594), a replication-competent vaccinia virus administered by intravenous injection, to target the tumor vasculature, produce immune activation and tumor cell killing more widespread than the infection, and suppress invasion and metastasis. These actions were examined in RIP-Tag2 transgenic mice with pancreatic neuroendocrine tumors that developed spontaneously and progressed as in humans. mpJX-594 initially infected tumor vascular endothelial cells, leading to vascular pruning and prolonged leakage in tumors but not in normal organs; parallel effects were observed in U87 gliomas. Viral infection spread to tumor cells, where tumor cell killing was much more widespread than the infection. Widespread tumor cell killing at 5 days was prevented by depletion of CD8⁺ T lymphocytes and did not require GM-CSF, as mpJX-594 variants that expressed human, mouse, or no GM-CSF produced equivalent amounts of killing. The antivascular, antitumor, and antimetastatic effects of mpJX-594 were amplified by concurrent or sequential administration of sunitinib, a multitargeted receptor tyrosine kinase inhibitor. These effects were not mimicked by selective inhibition of VEGFR2 despite equivalent vascular pruning, but were accompanied by suppression of regulatory T cells and greater influx of activated CD8⁺ T cells. Together, our results showed that mpJX-594 targets tumor blood vessels, spreads secondarily to tumor cells, and produces widespread CD8⁺ T-cell-dependent tumor cell killing in primary tumors and metastases, and that these effects can be amplified by coadministration of sunitinib.Significance: These findings reveal multiple unrecognized features of the antitumor properties of oncolytic vaccinia viruses, all of which can be amplified by the multitargeted kinase inhibitor sunitinib. Cancer Res; 78(4); 922-37. ©2017 AACR.

Abstract 1599: Antibody-based inhibition of CSF-1R as a component of combination immunotherapy in preclinical models

The colony stimulating factor 1 receptor (CSF-1R) signaling pathway promotes tumor progression via the recruitment, differentiation, and survival of immuno-suppressive tumor-associated macrophages (TAMs). FivePrime has developed cabiralizumab (FPA008), an IgG4 antibody against CSF-1R that blocks the ability of both CSF-1 and IL-34 to bind and activate this receptor, thereby modulating the immune response to tumorigenesis. In order to investigate the impact of CSF-1R signaling inhibition in preclinical models, we generated a surrogate antibody, cmFPA008, which targets mouse CSF-1R and demonstrates equivalent affinity and ligand-blocking ability as FPA008. Utilizing a combination of flow cytometry and immunofluorescence analyses, we have identified alterations in the tumor microenvironment that occur upon CSF-1R inhibition, including significant reduction of immunosuppressive TAMs and an increase in tumor PD-L1 expression. Interestingly, we observe a transient increase in CD8+ T cell number and activation upon TAM depletion, followed by a subsequent increase in MDSC populations that corresponds with reduction of the CD8+ T cell numbers. Moreover, we have used murine syngeneic tumor models to examine the anti-tumor impact of CSF-1R inhibition in combination with other immuno-oncology agents. Our results show that, when added to PD-1/PD-L1 blockade, cmFPA008 can significantly enhance anti-tumor efficacy. We are currently exploring the effects of combining cmFPA008-induced TAM depletion with additional immuno-oncology agents, including T cell agonists. Our preclinical results demonstrate that inhibition of the CSF-1R pathway can combine with various immuno-oncology agents with distinct mechanisms of action. FivePrime has initiated a clinical trial in collaboration with Bristol-Myers Squibb (BMS) to investigate the use of cabiralizumab in combination with nivolumab (anti-PD-1, OPDIVO®) in six different tumor types.

Citation Format: David I. Bellovin, Nebiyu Wondyfraw, Barbara Sennino, Quinn Walker, Susan Johnson, Anita Levin, Emma Masteller, Susannah D. Barbee, Robert Sikorski, Tom Brennan. Antibody-based inhibition of CSF-1R as a component of combination immunotherapy in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1599. doi:10.1158/1538-7445.AM2017-1599

Abstract 1407: FPA144, a therapeutic monoclonal antibody targeting the FGFR2b receptor, promotes antibody dependent cell-mediated cytotoxicity and stimulates sensitivity to PD-1 in the 4T1 syngeneic tumor model

Five Prime Therapeutics, Inc. has developed an FGFR2b-specific humanized monoclonal antibody, FPA144, to treat patients with cancer bearing overexpression of the FGFR2b receptor, and is currently in clinical trials as a single agent for gastric cancer (NCT02318329). FGFR2 gene amplification and FGFR2b overexpression occur in approximately 5% of gastric cancers and are associated with a poor prognosis in gastric cancer patients. In addition to blocking ligand binding and inducing FGFR2b internalization, FPA144 is glycoengineered for enhanced antibody-dependent cell-mediated cytotoxicity (ADCC). We have shown previously that FPA144 can produce complete and durable tumor growth inhibition in FGFR2b-over-expressing and FGFR2-amplified gastric cancer xenografts in immune-compromised mice (Gemo et al., Poster 5446, AACR 2014). In order to understand the contribution of the immune system to the mechanisms of action of FPA144, we evaluated the anti-tumor effects and immune cell recruitment of FPA144 in the 4T1 model of cancer in immune-competent mice. Although this model expresses FGFR2b, it is not FGFR2 amplified. Therapeutic treatment with FPA144 in the orthotopic 4T1 model resulted in a reduction in tumor burden (33%, P<0.001) and concomitant recruitment of NK cells to the site of tumor implantation, while a modified antibody lacking Fc effector function neither inhibited tumor growth nor lead to the recruitment of NK cells. Together these data support a potential role for ADCC as a mechanism of FPA144 tumor growth inhibition. In addition, treatment with FPA144 increased PD-L1 expressing cells within the tumor microenvironment, providing a strong rationale that FPA144 may combine effectively with PD-1 blockade for additional tumor growth inhibition. PD-1 blockade by the RPM1-14 antibody did not inhibit tumor growth as a single agent in the 4T1 model. Treatment with RPM1-14 in combination with FPA144, however, inhibited tumor growth by 49% (P<0.001), demonstrating an additive benefit of combination therapy. Overall, these data suggest that the enhanced ADCC activity of FPA144 may be critical for anti-tumor efficacy in tumors that have modest expression of FGFR2b. In addition, FPA144 may reprogram the tumor micro-environment in a way that primes the tumor for additional anti-tumor activity when combined with PD-1 blockade.

Citation Format: Janine Powers, Servando Palencia, Susan Foy, Barbara Sennino, Toni Rose Hidalgo, Abigael Gemo, Thomas Brennan, Kisten Pierce. FPA144, a therapeutic monoclonal antibody targeting the FGFR2b receptor, promotes antibody dependent cell-mediated cytotoxicity and stimulates sensitivity to PD-1 in the 4T1 syngeneic tumor model. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1407.

Abstract LB-234: Poxvirus-based active immunotherapy synergizes with PD-1 plus LAG-3 immune checkpoint inhibition to enhance antitumor efficacy in preclinical models

Treatment with poxvirus-based active immunotherapies shows evidence of robust immune responses against a variety of tumor-associated antigens in preclinical and clinical studies. Poxvirus-based immunotherapies in development include PSA-targeted PROSTVAC, now in Phase 3 clinical development; CV-301 (targeting CEA and MUC-1); as well as MVA-BN-HER2 and MVA-BN-Brachyury (targeting HER-2 and the transcription factor Brachyury, respectively). Evidence of robust and productive anti-tumor efficacy in preclinical models was accompanied by treatment-emergent infiltration of tumors by activated cytotoxic CD8 T cells producing high amounts of IFNγ.

Treatment with immune checkpoint inhibitors such as anti-PD-1 antibodies is showing significant clinical benefit by re-activating dormant tumor-specific T cells. Furthermore, preclinical studies have shown further synergistic efficacy by combining PD-1 blockade with inhibition of LAG-3, which acts independently of PD-1 to modulate T cell function. We hypothesized that poxvirus-based active immunotherapy may provide even greater improvements to patient outcome when used in combination with immune checkpoint blockade, by inducing new productive tumor-specific responses. This may be especially important in patients lacking an endogenous T cell response against their tumors.

In therapeutic CT26-HER2 solid and metastatic tumor models, mice were administered MVA-BN-HER2 immunotherapy alone or in combination with anti-PD-1 and/or anti-LAG-3 antibodies. Synergistic benefit for anti-tumor efficacy was observed when combining MVA-BN-HER2 immunotherapy with anti-PD-1 alone, while combination with anti-LAG-3 alone had little effect. Notably, a further enhancement occurred when MVA-BN-HER2 immunotherapy was combined with PD-1 and LAG-3 blockade as shown by complete tumor regression in 20/20 mice. Subsequent rejection of HER-2 negative tumors 6 months after the original challenge revealed that immune responses were durable and included antigen spread to additional tumor antigens.

Flow cytometric analysis demonstrated that tumor infiltrating lymphocytes (TILs) in untreated tumors were PD-1hi and LAG-3+, a more exhausted phenotype. Poxvirus-based immunotherapy led to the induction of activated TILs characterized by low to mid-levels of PD-1 expression. While PD-1 blockade prevented binding to PD-L1 it also caused an increase in LAG-3 expression on T cells. Together these data provide further rationale for why combination therapy of poxvirus-based immunotherapy with inhibition of PD-1 plus LAG-3 resulted in synergistic efficacy in preclinical tumor models.

Overall these data demonstrate that combining complementary immune-based therapies such as poxvirus-based active immunotherapy and PD-1 plus LAG-3 immune checkpoint blockade result in synergistic anti-tumor efficacy.

Citation Format: Barbara Sennino, Susan P. Foy, Ryan B. Rountree, Tracy dela Cruz, Evan J. Gordon, Veronica Xavier, Felicia Kemp, Alex Franzusoff, James Breitmeyer, Stefanie J. Mandl. Poxvirus-based active immunotherapy synergizes with PD-1 plus LAG-3 immune checkpoint inhibition to enhance antitumor efficacy in preclinical models. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-234. doi:10.1158/1538-7445.AM2015-LB-234

Abstract 296: Synergistic actions of oncolytic vaccinia virus and sunitinib on pancreatic neuroendocrine tumors in RIP-Tag2 mice

Pexa-Vec (JX-594) is an engineered oncolytic vaccinia virus that lacks thymidine kinase and expresses human granulocyte-macrophage colony stimulating factor. In addition to having oncolytic effects on tumor cells and promoting an immune response, Pexa-Vec has been found to cause rapid reduction of tumor blood flow in preclinical models and in clinical trials. The angiogenesis inhibitor sunitinib reduces tumor vascularity and can augment the activity of vesicular stomatitis virus by suppressing two interferon-induced anti-viral host proteins, RNA-dependent protein kinase and ribonuclease L.

We explored the interaction of mpJX-594, a mouse-adapted version of Pexa-Vec, and sunitinib. The mouse-adapted version, mpJX-594, was engineered from Western Reserve strain vaccinia virus by deletion of thymidine kinase and addition of human GM-CSF, yellow fluorescent protein, and luciferase genes. The effects of mpJX-594 or sunitinib given individually on pancreatic neuroendocrine tumors in RIP-Tag2 mice were compared to those of the two agents given together. Treatment with mpJX-594 alone reduced tumor vascularity and induced widespread apoptosis in the tumors. After treatment with sunitinib alone, tumor vascularity was decreased, but apoptosis was much less than after mpJX-594 alone. When mpJX-594 was given together with sunitinib, the amount of viral infection in tumors, assessed by vaccinia immunoreactivity, was much more than after mpJX-594 alone. Vaccinia staining was detected in most of the tumor blood vessels and in large patches of tumor cells. The reduction of tumor vascularity and amount of apoptosis were greater after both agents than after either of them given alone.

To determine whether mpJX-594 increased the efficacy of sunitinib in tumors or vice versa, we examined the effects of sequential administration, where mpJX-594 or sunitinib was given first and then followed 5 days later by the other. In both cases, the reduction in tumor vascularity after sequential treatment was greater than after either agent given alone. When sunitinib was given first, tumor vascularity was less throughout tumors, and the surviving vessels appeared more normal. By comparison, when mpJX-594 was given before sunitinib, the tumor vasculature was greatly reduced in some regions and less so in others, and the remaining blood vessels were abnormal. Apoptotic cells were much more numerous and widespread when mpJX-594 preceded sunitinib than after either agent given alone. In contrast, when sunitinib was given first, tumor apoptosis was greater than after sunitinib alone but not after mpJX-594 alone.

Together these findings indicate that mpJX-594 amplifies the anti-vascular and anti-tumor effects of sunitinib and vice versa in RIP-Tag2 pancreatic neuroendocrine tumors, regardless of the sequence of administration, but the magnitude of the changes differs according to the sequence of administration.

Citation Format: Corry E. McDonald, Barbara Sennino, Brian J. Schriver, John C. Bell, David H. Kirn, Caroline J. Breitbach, Donald M. McDonald. Synergistic actions of oncolytic vaccinia virus and sunitinib on pancreatic neuroendocrine tumors in RIP-Tag2 mice. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 296. doi:10.1158/1538-7445.AM2015-296

Magnetic resonance imaging of stem cell apoptosis in arthritic joints with a caspase activatable contrast agent

About 43 million individuals in the U.S. encounter cartilage injuries due to trauma or osteoarthritis, leading to joint pain and functional disability. Matrix-associated stem cell implants (MASI) represent a promising approach for repair of cartilage defects. However, limited survival of MASI creates a significant bottleneck for successful cartilage regeneration outcomes and functional reconstitution. We report an approach for noninvasive detection of stem cell apoptosis with magnetic resonance imaging (MRI), based on a caspase-3-sensitive nanoaggregation MRI probe (C-SNAM). C-SNAM self-assembles into nanoparticles after hydrolysis by caspase-3, leading to 90% amplification of (1)H MR signal and prolonged in vivo retention. Following intra-articular injection, C-SNAM causes significant MR signal enhancement in apoptotic MASI compared to viable MASI. Our results indicate that C-SNAM functions as an imaging probe for stem cell apoptosis in MASI. This concept could be applied to a broad range of cell transplants and target sites.

Combination strategy targeting VEGF and HGF/c-met in human renal cell carcinoma models

Alternative pathways to the VEGF, such as hepatocyte growth factor or HGF/c-met, are emerging as key players in tumor angiogenesis and resistance to anti-VEGF therapies. The aim of this study was to assess the effects of a combination strategy targeting the VEGF and c-met pathways in clear cell renal cell carcinoma (ccRCC) models. Male SCID mice (8/group) were implanted with 786-O tumor pieces and treated with either a selective VEGF receptor tyrosine kinase inhibitor, axitinib (36 mg/kg, 2×/day); a c-met inhibitor, crizotinib (25 mg/kg, 1×/day); or combination. We further tested this drug combination in a human ccRCC patient-derived xenograft, RP-R-01, in both VEGF-targeted therapy-sensitive and -resistant models. To evaluate the resistant phenotype, we established an RP-R-01 sunitinib-resistant model by continuous sunitinib treatment (60 mg/kg, 1×/day) of RP-R-01-bearing mice. Treatment with single-agent crizotinib reduced tumor vascularization but failed to inhibit tumor growth in either model, despite also a significant increase of c-met expression and phosphorylation in the sunitinib-resistant tumors. In contrast, axitinib treatment was effective in inhibiting angiogenesis and tumor growth in both models, with its antitumor effect significantly increased by the combined treatment with crizotinib, independently from c-met expression. Combination treatment also induced prolonged survival and significant tumor growth inhibition in the 786-O human RCC model. Overall, our results support the rationale for the clinical testing of combined VEGF and HGF/c-met pathway blockade in the treatment of ccRCC, both in first- and second-line setting.

Iron administration before stem cell harvest enables MR imaging tracking after transplantation

PURPOSE

To determine whether intravenous ferumoxytol can be used to effectively label mesenchymal stem cells (MSCs) in vivo and can be used for tracking of stem cell transplants.

MATERIALS AND METHODS

This study was approved by the institutional animal care and use committee. Sprague-Dawley rats (6-8 weeks old) were injected with ferumoxytol 48 hours prior to extraction of MSCs from bone marrow. Ferumoxytol uptake by these MSCs was evaluated with fluorescence, confocal, and electron microscopy and compared with results of traditional ex vivo-labeling procedures. The in vivo-labeled cells were subsequently transplanted in osteochondral defects of 14 knees of seven athymic rats and were evaluated with magnetic resonance (MR) imaging up to 4 weeks after transplantation. T2 relaxation times of in vivo-labeled MSC transplants and unlabeled control transplants were compared by using t tests. MR data were correlated with histopathologic results.

RESULTS

In vivo-labeled MSCs demonstrated significantly higher ferumoxytol uptake compared with ex vivo-labeled cells. With electron microscopy, iron oxide nanoparticles were localized in secondary lysosomes. In vivo-labeled cells demonstrated significant T2 shortening effects in vitro and in vivo when they were compared with unlabeled control cells (T2 in vivo, 15.4 vs 24.4 msec; P < .05) and could be tracked in osteochondral defects for 4 weeks. Histologic examination confirmed the presence of iron in labeled transplants and defect remodeling.

CONCLUSION

Intravenous ferumoxytol can be used to effectively label MSCs in vivo and can be used for tracking of stem cell transplants with MR imaging. This method eliminates risks of contamination and biologic alteration of MSCs associated with ex vivo-labeling procedures.

Abstract 2841: Widespread endothelial cell infection and tumor cell apoptosis after intravenous injection of oncolytic vaccinia virus JX-594 into RIP-Tag2 mice

Replication-competent oncolytic viruses are being developed as a promising strategy for treating certain types of cancer. JX-594 is an oncolytic vaccinia virus that lacks thymidine kinase and expresses human granulocyte-macrophage colony stimulating factor (hGM-CSF). Replication of JX-594 is promoted by EGFR/Ras pathway signaling in cancer cells. In addition to having direct oncolytic effects on tumor cells and recruiting an immune response, JX-594 has been found to cause rapid reduction of tumor blood flow in preclinical models and in clinical trials. To understand the mechanism of this vascular effect, we injected mouse-adapted JX-594 vaccinia virus (mJX-594, on Western Reserve backbone and expressing hGM-CSF) intravenously into RIP-Tag2 transgenic mice and examined the pancreatic neuroendocrine tumors at 6 hours or 1, 2, or 5 days after injection. Dot-like vaccinia immunoreactivity was widespread in endothelial cells of tumor vessels at 6 hours. Scattered endothelial cells had intense staining. Vaccinia immunoreactivity in tumor blood vessels was still widespread at 1 day, but at 5 days, most tumor vessels were narrowed, some appeared fragmented, and tumor vascularity was reduced by 40%. Normalization of tumor vessels, as observed after inhibition of VEGF signaling, was not found at any time examined. Intratumoral hypoxia was evident as diffuse regions of pimonidazole staining at 6 hours. Pimonidazole staining increased from 1 to 5 days, and was especially strong in regions of vascular pruning. Extravascular vaccinia immunoreactivity was located in scattered cells at 1 day and increased with time. At 5 days, most tumors had large patches of vaccinia-positive cells. This staining was not present in the surrounding normal acinar pancreas. Apoptotic cells stained for activated caspase-3 were scattered throughout tumors at 6 hours. Most of these apoptotic cells were endothelial cells. Apoptotic tumor cells were sparse at 6 hours, but at 5 days apoptotic cells were 23-fold more numerous than at baseline and even more widespread than vaccinia immunoreactivity, and tumors tended to be smaller than corresponding controls. These findings are consistent with oncolytic virus mJX-594 causing rapid infection of tumor vascular endothelial cells in RIP-Tag2 mice. Endothelial cell infection is followed by regression of tumor blood vessels, exaggeration of intratumoral hypoxia, and oncolytic actions on tumor cells that lead to widespread tumor cell apoptosis.

Citation Format: Barbara Sennino, Brian J. Schriver, Caroline J. Breitbach, Naomi De Silva, John C. Bell, David H. Kirn, Donald M. McDonald. Widespread endothelial cell infection and tumor cell apoptosis after intravenous injection of oncolytic vaccinia virus JX-594 into RIP-Tag2 mice. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2841. doi:10.1158/1538-7445.AM2013-2841

Inhibition of c-Met reduces lymphatic metastasis in RIP-Tag2 transgenic mice

Inhibition of VEGF signaling can promote lymph node metastasis in preclinical models, but the mechanism is not fully understood, and successful methods of prevention have not been found. Signaling of hepatocyte growth factor (HGF) and its receptor c-Met can promote the growth of lymphatics and metastasis of some tumors. We sought to explore the contributions of c-Met signaling to lymph node metastasis after inhibition of VEGF signaling. In particular, we examined whether c-Met is upregulated in lymphatics in or near pancreatic neuroendocrine tumors in RIP-Tag2 transgenic mice and whether lymph node metastasis can be reduced by concurrent inhibition of VEGF and c-Met signaling. Inhibition of VEGF signaling by anti-VEGF antibody or sunitinib in mice from the age of 14 to 17 weeks was accompanied by more intratumoral lymphatics, more tumor cells inside lymphatics, and more lymph node metastases. Under these conditions, lymphatic endothelial cells, like tumor cells, had strong immunoreactivity for c-Met and phospho-c-Met. c-Met blockade by the selective inhibitor, PF-04217903, significantly reduced metastasis to local lymph nodes. Together, these results indicate that inhibition of VEGF signaling in RIP-Tag2 mice upregulates c-Met expression in lymphatic endothelial cells, increases the number of intratumoral lymphatics and number of tumor cells within lymphatics, and promotes metastasis to local lymph nodes. Prevention of lymph node metastasis by PF-04217903 in this setting implicates c-Met signaling in tumor cell spread to lymph nodes.

Identification of pY654-β-catenin as a critical co-factor in hypoxia-inducible factor-1α signaling and tumor responses to hypoxia

Hypoxia is linked to epithelial-mesenchymal transition (EMT) and tumor progression in numerous carcinomas. Responses to hypoxia are thought to operate via hypoxia-inducible factors (HIFs), but the importance of co-factors that regulate HIF signaling within tumors is not well understood. Here, we elucidate a signaling pathway that physically and functionally couples tyrosine phosphorylation of β-catenin to HIF1α signaling and HIF1α-mediated tumor EMT. Primary human lung adenocarcinomas accumulate pY654-β-catenin and HIF1α. All pY654-β-catenin, and only the tyrosine phosphorylated form, was found complexed with HIF1α and active Src, both within the human tumors and in lung tumor cell lines exposed to hypoxia. Phosphorylation of Y654, generated by hypoxia mediated, reactive oxygen species (ROS)-dependent Src kinase activation, was required for β-catenin to interact with HIF1α and Src, to promote HIF1α transcriptional activity, and for hypoxia-induced EMT. Mice bearing hypoxic pancreatic islet adenomas, generated by treatment with anti-vascular endothelial growth factor antibodies, accumulate HIF1α/pY654-β-catenin complexes and develop an invasive phenotype. Concurrent administration of the ROS inhibitor N-acetylcysteine abrogated β-catenin/HIF pathway activity and restored adenoma architecture. Collectively, the findings implicate accumulation of pY654-β-catenin specifically complexed to HIF1α and Src kinase as critically involved in HIF1α signaling and tumor invasion. The findings also suggest that targeting ROS-dependent aspects of the pY654-β-catenin/ HIF1α pathway may attenuate untoward biological effects of anti-angiogenic agents and tumor hypoxia.

MR imaging features of gadofluorine-labeled matrix-associated stem cell implants in cartilage defects

Objectives

The purpose of our study was to assess the chondrogenic potential and the MR signal effects of GadofluorineM-Cy labeled matrix associated stem cell implants (MASI) in pig knee specimen.

Materials and Methods

Human mesenchymal stem cells (hMSCs) were labeled with the micelle-based contrast agent GadofluorineM-Cy. Ferucarbotran-labeled hMSCs, non-labeled hMSCs and scaffold only served as controls. Chondrogenic differentiation was induced and gene expression and histologic evaluation were performed. The proportions of spindle-shaped vs. round cells of chondrogenic pellets were compared between experimental groups using the Fisher's exact test. Labeled and unlabeled hMSCs and chondrocytes in scaffolds were implanted into cartilage defects of porcine femoral condyles and underwent MR imaging with T1- and T2-weighted SE and GE sequences. Contrast-to-noise ratios (CNR) between implants and adjacent cartilage were determined and analyzed for significant differences between different experimental groups using the Kruskal-Wallis test. Significance was assigned for p<0.017, considering a Bonferroni correction for multiple comparisons.

Results

Collagen type II gene expression levels were not significantly different between different groups (p>0.017). However, hMSC differentiation into chondrocytes was superior for unlabeled and GadofluorineM-Cy-labeled cells compared with Ferucarbotran-labeled cells, as evidenced by a significantly higher proportion of spindle cells in chondrogenic pellets (p<0.05). GadofluorineM-Cy-labeled hMSCs and chondrocytes showed a positive signal effect on T1-weighted images and a negative signal effect on T2-weighted images while Ferucarbotran-labeled cells provided a negative signal effect on all sequences. CNR data for both GadofluorineM-Cy-labeled and Ferucarbotran-labeled hMSCs were significantly different compared to unlabeled control cells on T1-weighted SE and T2*-weighted MR images (p<0.017).

Conclusion

hMSCs can be labeled by simple incubation with GadofluorineM-Cy. The labeled cells provide significant MR signal effects and less impaired chondrogenesis compared to Ferucarbotran-labeled hMSCs. Thus, GadoflurineM-Cy might represent an alternative MR cell marker to Ferucarbotran, which is not distributed any more in Europe or North America.

Controlling escape from angiogenesis inhibitors

Selective inhibition of vascular endothelial growth factor (VEGF) increases the efficacy of chemotherapy and has beneficial effects on multiple advanced cancers, but response is often limited and the disease eventually progresses. Changes in the tumour microenvironment--hypoxia among them--that result from vascular pruning, suppressed angiogenesis and other consequences of VEGF inhibition can promote escape and tumour progression. New therapeutic approaches that target pathways that are involved in the escape mechanisms add the benefits of blocking tumour progression to those of slowing tumour growth by inhibiting angiogenesis.

Magnetic resonance imaging of ferumoxide-labeled mesenchymal stem cells in cartilage defects: in vitro and in vivo investigations

The purpose of this study was to (1) compare three different techniques for ferumoxide labeling of mesenchymal stem cells (MSCs), (2) evaluate if ferumoxide labeling allows in vivo tracking of matrix-associated stem cell implants (MASIs) in an animal model, and (3) compare the magnetic resonance imaging (MRI) characteristics of ferumoxide-labeled viable and apoptotic MSCs. MSCs labeled with ferumoxide by simple incubation, protamine transfection, or Lipofectin transfection were evaluated with MRI and histopathology. Ferumoxide-labeled and unlabeled viable and apoptotic MSCs in osteochondral defects of rat knee joints were evaluated over 12 weeks with MRI. Signal to noise ratios (SNRs) of viable and apoptotic labeled MASIs were tested for significant differences using t-tests. A simple incubation labeling protocol demonstrated the best compromise between significant magnetic resonance signal effects and preserved cell viability and potential for immediate clinical translation. Labeled viable and apoptotic MASIs did not show significant differences in SNR. Labeled viable but not apoptotic MSCs demonstrated an increasing area of T2 signal loss over time, which correlated to stem cell proliferation at the transplantation site. Histopathology confirmed successful engraftment of viable MSCs. The engraftment of iron oxide-labeled MASIs by simple incubation can be monitored over several weeks with MRI. Viable and apoptotic MASIs can be distinguished via imaging signs of cell proliferation at the transplantation site.

Abstract SY41-02: Tumor cell effects of vascular reprogramming: Contributions of c-MET and VEGF

Intratumoral hypoxia is associated with greater risk of metastasis and less favorable prognosis. Hypoxia increases the expression in tumor cells of c-MET, the tyrosine kinase receptor for hepatocyte growth factor, through HIF-1α binding sites on the c-MET promoter. Activation of c-MET promotes tumor cell proliferation, motility, and invasion and is associated with tumor aggressiveness. Intratumoral hypoxia is increased by vascular pruning produced by angiogenesis inhibitors that block VEGF signaling.

We asked whether selective VEGF inhibition, which exaggerates intratumoral hypoxia and activates c-MET, is sufficient to increase tumor invasiveness and metastasis and whether selective inhibition c-MET is sufficient to block these effects. We found that treatment of pancreatic neuroendocrine tumors in RIP-Tag2 mice with a neutralizing anti-VEGF antibody or with the tyrosine kinase inhibitor sunitinib reduced tumor burden. Both treatments also increased intratumoral hypoxia, expression and activation of c-MET, tumor invasion into the exocrine pancreas, and metastasis to the liver. Increased intratumoral hypoxia was documented by increased HIF-1α and staining for pimonidazole, carbonic anhydrase-IX, and Glut1 in tumor cells. Treatment with either agent for only a week was accompanied by increased expression of c-MET mRNA and corresponding increases in c-MET protein and c-MET phosphorylation in tumor cells. Exposure to hypoxia also increased c-MET phosphorylation in freshly isolated RIP-Tag2 tumor cells in vitro. With these findings, the selective anti-VEGF antibody #AF-493-NA was added to the list, which already includes sunitinib, anti-VEGFR-2 antibody (DC101), and genetic deletion of VEGF, of interventions reported to promote tumor invasion and metastasis in preclinical models.

To test the involvement of c-MET in the exaggerated tumor aggressiveness, we used three complementary approaches to block c-MET signaling. The first used the tyrosine kinase inhibitor PF-04217903 because of its high selectivity for c-MET. The second used PF-02341066 (crizotinib), a tyrosine kinase inhibitor that has high potency against c-MET but also blocks anaplastic lymphoma kinase (ALK). The third used the tyrosine kinase inhibitor XL184 (cabozantinib), which simultaneously blocks c-MET and VEGFR among other receptor tyrosine kinases.

We found that RIP-Tag2 tumors treated with either PF-04217903 or PF-02341066 from age 14 to 17 weeks were about the same size as vehicle-treated controls but were less invasive and had fewer metastases. After this treatment, the tumors had a smoother contour, a distinctive ball-like shape, and less invasion into the exocrine pancreas. Liver metastases were significantly smaller and less numerous. Inhibition of c-MET and VEGF together, by administration of PF-04217903 or PF-02341066 together with anti-VEGF antibody or sunitinib, slowed tumor growth and had even more potent effects on invasion and metastasis than found with either c-MET inhibitor used alone. These findings in RIP-Tag2 tumors were corroborated by parallel experiments on orthotopic Panc-1 pancreatic adenocarcinomas. Expression of c-MET and invasiveness of Panc-1 tumors were increased by treatment with sunitinib, and the increase was blocked by concurrent administration of PF-04217903. XL184 given as a single agent reduced tumor invasion and metastasis in RIP-Tag2 mice as much as the drug combinations. The similarity of effects of XL184 on tumor invasion and metastasis to those of selective inhibitors given together argues for c-MET and VEGFR being relevant targets of XL184, although additional involvement of inhibition of AXL, KIT, RET or other targets cannot be excluded for this multi-targeted agent.

To test whether concurrent inhibition of c-MET and VEGF signaling can reverse tumor invasion, we compared tumors in RIP-Tag2 mice treated for 3 weeks with tumors in onset controls at age 14 weeks. The amount of invasion found after treatment with PF-042107903 plus sunitinib or with XL184 given alone was less than in onset controls. Similarly, the metastatic burden in the liver was less after XL184 for 3 weeks than in onset controls. Overall, the experiments revealed that, consistent with published reports, inhibition of VEGF signaling by function-blocking antibody or sunitinib causes vascular pruning and slowing of tumor growth but also increases invasion and metastasis in these preclinical models. The findings fit with a mechanism involving vascular pruning, intratumoral hypoxia, HIF-1α accumulation, and activation of c-MET in tumor cells. Invasion and metastasis that accompany VEGF inhibition can be blocked by concurrent inhibition of c-MET. PF-04217903 and PF-02341066 have similar efficacy in this regard when either is given together with anti-VEGF antibody or sunitinib. Inhibition of both c-MET and VEGF signaling by XL184 has potent anti-angiogenic activity and reduces tumor growth while also reducing invasion and metastasis. The findings indicate that tumor invasion and metastasis can be reduced along with tumor growth by blocking c-MET and VEGF signaling together to offset the consequences of intratumoral hypoxia resulting from angiogenesis inhibition and vascular pruning.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr SY41-02. doi:1538-7445.AM2012-SY41-02

Abstract 1378: Concurrent inhibition of c-Met and VEGF signaling suppresses tumor invasion in orthotopic Panc-1 pancreatic carcinomas in mice

Multiple factors can contribute to evasive resistance that develops during treatment with angiogenesis inhibitors that target the vascular endothelial growth factor (VEGF) pathway. Evidence from studies of neuroendocrine tumors in RIP-Tag2 transgenic mice indicates that hypoxia-induced activation of pro-invasive pathways involving the receptor for hepatocyte growth factor, c-Met, can participate. The present study sought to determine whether this mechanism also applies to other types of tumors. Our approach was to ask whether growth and invasiveness of Panc-1 pancreatic adenocarcinomas implanted orthotopically in nude mice were reduced by inhibition of c-Met during concurrent treatment with an angiogenesis inhibitor for 3 weeks. Panc-1 tumors in mice treated with the angiogenesis inhibitor sunitinib, a tyrosine kinase inhibitor that blocks VEGFR and related receptors, had a 75% reduction in vascularity and grew more slowly than controls but had twice as much of intratumoral hypoxia, assessed by pimonidazole staining. Unlike the faint c-Met immunoreactivity in most tumor cells of vehicle-treated Panc-1 tumors, c-Met staining was stronger in tumor cells after treatment with sunitinib. Tumors in mice treated with the selective c-Met inhibitor PF-04217903 alone had little change in tumor vascularity or intratumoral hypoxia and grew faster than those treated with sunitinib. However, tumors treated with sunitinib plus PF-04217903 together grew more slowly than after sunitinib alone but had similar amounts of vascular pruning and hypoxia. Tumor invasiveness, reflected by amylase-positive acinar cells of the exocrine pancreas located within tumors, was exaggerated after sunitinib treatment but, importantly, was significantly less in tumors treated with sunitinib plus PF-04217903. These findings indicate that sunitinib used alone reduced the growth of Panc-1 tumors but increased intratumoral hypoxia, c-Met expression, and local invasion into the surrounding normal pancreas. By comparison, sunitinib administered concurrently with the c-Met inhibitor PF-04217903 resulted in further slowing of tumor growth and less tumor invasiveness.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1378. doi:1538-7445.AM2012-1378

Abstract LB-315: Suppression of tumor invasion and metastasis by inhibition of c-MET and VEGF signaling together

Treatment with inhibitors that block vascular endothelial growth factor (VEGF) signaling can make tumors more aggressive in preclinical models. The mechanism underlying this form of resistance is not fully understood, but vascular pruning, intratumoral hypoxia, and increased expression of c-MET, the tyrosine kinase receptor for hepatocyte growth factor (HGF), could be contributing factors. We found that treatment of pancreatic neuroendocrine tumors in RIP-Tag2 mice with a neutralizing anti-VEGF antibody or with sunitinib, a receptor tyrosine kinase inhibitor that blocks VEGFR and related receptors, reduced tumor burden and vascularity but increased intratumoral hypoxia, HIF-1alpha, and expression and activation of c-MET. Invasion into the exocrine pancreas and metastasis to the liver also increased. Importantly, administration of either of two c-MET inhibitors, PF-04217903 or crizotinib (PF-02341066), together with anti-VEGF therapy reduced tumor growth and vascularity and also significantly decreased local invasion and liver metastasis. Similar benefits were found after treatment with cabozantinib (XL184), a multitargeted tyrosine kinase inhibitor that simultaneously blocks c-MET and VEGF receptors. Together, these results indicate that inhibition of VEGF signaling can promote vascular pruning, intratumoral hypoxia, HIF-1alpha accumulation, and activation of c-MET. Concurrent inhibition of c-MET and VEGF signaling not only can slow tumor growth but also can reduce invasion and metastasis. Inhibition of c-MET and VEGF signaling pathways together combines the favorable tumor growth-slowing effects of inhibiting angiogenesis with suppression of invasion and metastasis, despite the intratumoral hypoxia due to vascular pruning.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-315. doi:1538-7445.AM2012-LB-315

Suppression of tumor invasion and metastasis by concurrent inhibition of c-Met and VEGF signaling in pancreatic neuroendocrine tumors

Invasion and metastasis increase after the inhibition of VEGF signaling in some preclinical tumor models. In the present study we asked whether selective VEGF inhibition is sufficient to increase invasion and metastasis and whether selective c-Met inhibition is sufficient to block this effect. Treatment of pancreatic neuroendocrine tumors in RIP-Tag2 mice with a neutralizing anti-VEGF antibody reduced tumor burden but increased tumor hypoxia, hypoxia-inducible factor-1α, and c-Met activation and also increased invasion and metastasis. However, invasion and metastasis were reduced by concurrent inhibition of c-Met by PF-04217903 or PF-02341066 (crizotinib). A similar benefit was found in orthotopic Panc-1 pancreatic carcinomas treated with sunitinib plus PF-04217903 and in RIP-Tag2 tumors treated with XL184 (cabozantinib), which simultaneously blocks VEGF and c-Met signaling. These findings document that invasion and metastasis are promoted by selective inhibition of VEGF signaling and can be reduced by the concurrent inhibition of c-Met.

SIGNIFICANCE

This report examines the mechanism of increased tumor aggressiveness after anti-VEGF therapy and presents evidence for roles of vascular pruning, hypoxia, and c-Met activation. The results show that simultaneous inhibition of c-Met and VEGF signaling not only slows tumor growth but also reduces invasion and metastasis.

Increased vascular delivery and efficacy of chemotherapy after inhibition of platelet-derived growth factor-B

Inhibition of platelet-derived growth factor-B (PDGF-B) has multiple effects on tumors, including loss of pericytes, regression of some vessels, normalization of other vessels, and reduction of interstitial pressure. PDGF-B inhibition also increases the efficacy of cancer therapeutics, but the role on tumor vessel efficiency and drug delivery is unclear. We sought to determine whether inhibition of PDGF-B signaling can increase delivery and efficacy of cyclophosphamide in Lewis lung carcinomas or RIP-Tag2 tumors. PDGF-B blockade in Lewis lung carcinoma tumors by the DNA aptamer AX102 for 14 days increased the number of perfused tumor vessels marked by lectin in the bloodstream by 50%. AX102 also increased the width of sleeves of viable tumor cells around blood vessels by 66%, increased tumor cell proliferation by 90%, and increased intratumoral delivery of Hoechst 33342 by 78%. A low dose of cyclophosphamide (20 mg/kg) reduced tumor cell proliferation by 31% when combined with AX102 but not when given alone. Synergy of cyclophosphamide and AX102 on tumor cell proliferation also was found in RIP-Tag2 tumors. Similarly, the PDGF receptor signaling inhibitor imatinib increased delivery of cyclophosphamide and reduced tumor burden in RIP-Tag2 mice, without evidence of tumor cell sensitization to chemotherapy. Together, these findings indicate that inhibition of PDGF-B signaling promotes the delivery and efficacy of chemotherapeutic agents by increasing the efficiency of tumor blood vessels.

Labeling human mesenchymal stem cells with fluorescent contrast agents: the biological impact

Purpose

This study aims to determine the effect of human mesenchymal stem cell (hMSC) labeling with the fluorescent dye DiD and the iron oxide nanoparticle ferucarbotran on chondrogenesis.

Procedures

hMSCs were labeled with DiD alone or with DiD and ferucarbotran (DiD/ferucarbotran). hMSCs underwent confocal microscopy, optical imaging (OI), and magnetic resonance (MR) imaging. Chondrogenesis was induced by transforming growth factor-b and confirmed by histopathology and glycosaminoglycan (GAG) production. Data of labeled and unlabeled hMSCs were compared with a t test.

Results

Cellular uptake of DiD and ferucarbotran was confirmed with confocal microscopy. DiD labeling caused a significant fluorescence on OI, and ferucarbotran labeling caused a significant T2* effect on MR images. Compared to nonlabeled controls, progenies of labeled MSCs exhibited similar chondrocyte morphology after chondrogenic differentiation, but the labeled cells demonstrated significantly reduced GAG production (p < 0.05).

Conclusion

DiD and DiD/ferucarbotran labeling of hMSC does not interfere with cell viability or morphologic differentiation into chondrocytes, but labeled cells exhibit significantly less GAG production compared to unlabeled cells.

VEGF and c-Met blockade amplify angiogenesis inhibition in pancreatic islet cancer

Angiogenesis inhibitors that block VEGF receptor (VEGFR) signaling slow the growth of many types of tumors, but eventually the disease progresses. Multiple strategies are being explored to improve efficacy by concurrent inhibition of other functionally relevant receptor tyrosine kinases (RTK). XL880 (foretinib, GSK1363089) and XL184 (cabozantinib) are small-molecule inhibitors that potently block multiple RTKs, including VEGFR and the receptor of hepatocyte growth factor c-Met, which can drive tumor invasion and metastasis. This study compared the cellular effects of XL880 and XL184 with those of an RTK inhibitor (XL999) that blocks VEGFR but not c-Met. Treatment of RIP-Tag2 mice with XL999 resulted in 43% reduction in vascularity of spontaneous pancreatic islet tumors over 7 days, but treatment with XL880 or XL184 eliminated approximately 80% of the tumor vasculature, reduced pericytes and empty basement membrane sleeves, caused widespread intratumoral hypoxia and tumor cell apoptosis, and slowed regrowth of the tumor vasculature after drug withdrawal. Importantly, XL880 and XL184 also decreased invasiveness of primary tumors and reduced metastasis. Overall, these findings indicate that inhibition of c-Met and functionally related kinases amplifies the effects of VEGFR blockade and leads to rapid, robust, and progressive regression of tumor vasculature, increased intratumoral hypoxia and apoptosis, and reduced tumor invasiveness and metastasis.

Abstract 377: Inhibition of c-Met and VEGFR by XL184 reduces tumor invasiveness and metastasis and prolongs survival of RIP-Tag2 transgenic mice

Recent studies have shown that inhibition of VEGF signaling can promote tumor invasiveness and metastasis in some preclinical models. The mechanism underlying the increased aggressiveness is not fully understood but activation of the hepatocyte growth factor/c-Met pathway may be a factor. We addressed this mechanism by determining whether inhibition of VEGFR and c-Met together can reduce tumor growth and invasiveness and improve host survival. Our approach was to compare the effects of a tyrosine kinase inhibitor, XL184 (BMS-907351), which blocks VEGFR and c-Met, with the effects of an antibody that selectively blocks mouse VEGF. After treatment of pancreatic islet cell tumors in 14-week-old RIP-Tag2 mice withanti-mouse VEGF antibody for 3 weeks, the tumors were smaller (tumor area 4.3 ± 0.8 mm2 in antibody group versus 17.3 ± 6.5 mm2 in vehicle group, P &lt; 0.05) but had greater expression of c-Met. Tumors treated with anti-VEGF antibody also had more irregular borders, indicative of invasion of the surrounding acinar pancreas (invasion index 18.9 versus 12.7 in vehicle group, P &lt; 0.05), and more abundant liver metastases (metastases 2.73 ± 1.83 /mm2 versus 0.45 ± 0.12 /mm2 in vehicle group, P &lt; 0.05). By comparison, mice treated with XL184 not only had smaller tumors (tumor area 0.7 ± 0.1 mm2, P &lt; 0.05) than in the other groups but also had less invasive tumors (invasion index 4.5, P &lt; 0.05), and lacked liver metastases. All mice treated with XL184 from 14 weeks of age survived until 20 weeks (n = 6), but none treated with vehicle (n = 14) or anti-VEGF antibody (n = 8) reached that end point. These results show that selective inactivation of VEGF reduces tumor growth but leads to greater invasiveness and metastasis in the RIP-Tag2 model. However, inhibition of VEGFR and c-Met by XL184 not only slows tumor growth but also decreases tumor invasiveness and liver metastasis and prolongs host survival.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 377.

An optical imaging method to monitor stem cell migration in a model of immune-mediated arthritis

The objective of this work is to establish an optical imaging technique that would enable monitoring of the integration of mesenchymal stem cells (MSC) in arthritic joints. Our approach is based on first developing a labeling technique of MSC with the fluorescent dye DiD followed by tracking the cell migration kinetics from the spatial distribution of the DiD fluorescence in optical images (OI). The experimental approach involves first the in vitro OI of MSC labeled with DiD accompanied by fluorescence microscopy measurements to establish localization of the signal within the cells. Thereafter, DiD-labeled MSC were injected into polyarthritic, athymic rats and the signal localization within the experimental animals was monitored over several days. The experimental results indicate that DiD integrated into the cell membrane. DiD-labeled MSC localization in the arthritic ankle joints was observed with OI indicating that this method can be applied to monitor MSC in arthritic joints.

Correlative dynamic contrast MRI and microscopic assessments of tumor vascularity in RIP-Tag2 transgenic mice

The purpose of this study was to define the feasibility of dynamic contrast-enhanced magnetic resonance imaging (MRI) to estimate the vascular density and leakiness of spontaneous islet cell tumors in RIP-Tag2 transgenic mice. Dynamic T(1)-weighted spoiled gradient echo (SPGR) imaging at 2.0 T was performed in 17 RIP-Tag2 mice using a prototype blood pool macromolecular contrast medium (MMCM), albumin-(Gd-DTPA)(35). Kinetic analysis of the dynamic enhancement responses based on a two-compartment model was used to estimate fractional plasma volume (fPV) and the coefficient of endothelial permeability (K(PS)) for each tumor. The MRI estimate of fPV was correlated on a tumor-by-tumor basis with corresponding microscopic measurements of vascular density. The fPV assays by MMCM-enhanced imaging ranged from 2.4%-14.1% of tissue volume. Individual tumor fPV values correlated significantly (r = 0.79, P < 0.001) with the corresponding microscopic estimates of vascularity consisting of the combined area densities of lectin-perfused microvessels plus erythrocyte-stained blood lakes. A biotinylated derivative of the albumin-based MMCM confirmed extravasation of the contrast agent from some tumor blood vessels and accumulation in 25% of blood lakes. The K(PS) values ranged from 0 (no detectable leak) to 0.356 mL/min/100 cm(3). Dynamic MMCM-enhanced MRI is feasible in RIP-Tag2 pancreatic tumors, yielding estimates of vascular permeability and microscopically validated measurements of vascular richness.

The influence of ferucarbotran on the chondrogenesis of human mesenchymal stem cells

For in vivo applications of magnetically labeled stem cells, biological effects of the labeling procedure have to be precluded. This study evaluates the effect of different ferucarbotran cell labeling protocols on chondrogenic differentiation of human mesenchymal stem cells (hMSC) as well as their implications for MR imaging. hMSC were labeled with ferucarbotran using various protocols: cells were labeled with 100 microg Fe/ml for 4 and 18 h and additional samples were cultured for 6 or 12 days after the 18 h labeling. Supplementary samples were labeled by transfection with protamine sulfate. Iron uptake was quantified by ICP-spectrometry and labeled cells were investigated by transmission electron microscopy and by immunostaining for ferucarbotran. The differentiation potential of labeled cells was compared with unlabeled controls by staining with Alcian blue and Hematoxylin and Eosin, then quantified by measurements of glucosaminoglycans (GAG). Contrast agent effect at 3 T was investigated on days 1 and 14 of chondrogenic differentiation by measuring signal-to-noise ratios on T(2)-SE and T(2)*-GE sequences. Iron uptake was significant for all labeling protocols (p < 0.05). The uptake was highest after transfection with protamine sulfate (25.65 +/- 3.96 pg/cell) and lowest at an incubation time of 4 h without transfection (3.21 +/- 0.21 pg/cell). While chondrogenic differentiation was decreased using all labeling protocols, the decrease in GAG synthesis was not significant after labeling for 4 h without transfection. After labeling by simple incubation, chondrogenesis was found to be dose-dependent. MR imaging showed markedly lower SNR values of all labeled cells compared with the unlabeled controls. This contrast agent effect persisted for 14 days and the duration of differentiation. Magnetic labeling of hMSC with ferucarbotran inhibits chondrogenesis in a dose-dependent manner when using simple incubation techniques. When decreasing the incubation time to 4 h, inhibition of chondrogenesis was not significant.

[Effects of MRI-assayed microvascular permeability on the accumulation of vinorelbine in xenograft tumors]

PURPOSE

To determine the effects of MRI-assayed vascular leakiness on the delivery of macromolecular therapeutics to tumors.

MATERIALS AND METHODS

MDA-MB 435 tumors, subcutaneously implanted into nude rats were treated with a single dose of bevacizumab at levels of 0.1 mg (n = 5) or 1.0 mg (n = 10) or received saline (control animals, n = 8). After 24 hours, albumin-(Gd-DTPA) (30)-enhanced MRI was performed. Just prior to MRI, the cytotoxic drug vinorelbine was administered intravenously. Upon completion of the MR experiment, tumor vinorelbine concentrations were quantified by high performance liquid chromatography (HPLC). Vascular leakiness (K (PS)) was calculated based on the MRI data using a pharmacokinetic model.

RESULTS

K (PS) was calculated as 3.70 +/- 1.12 (control tumors), 1.95 +/- 0.70 (0.1 mg group) and 0.75 +/- 0.46 microl min (-1)cm (-3) (1.0 mg group). K (PS) was significantly higher in the control group compared to the 1.0 mg bevacizumab group. Vinorelbine concentrations were measured as 409.4 +/- 109.7 (control tumors), 387.5 +/- 47.5 (0.1 mg group) and 250.7 +/- 71.9 (1.0 mg group). These differences were not significant. A moderate and significant correlation was found between K (PS) and Vinorelbine concentrations in tumors (r = 0.49, p < 0.05).

CONCLUSION

MRI-assayed K (PS) based on dynamic MRI enhanced by albumin-(Gd-DTPA) (30) correlated significantly with vinorelbine accumulation in experimental xenograft tumors under angiogenesis inhibition. Thus, the MRI technique applied in our study could potentially help to predict accumulation of macromolecular cytotoxic drugs and to optimize individual therapeutic regimes in tumors.

Relaxation effects of ferucarbotran-labeled mesenchymal stem cells at 1.5T and 3T: discrimination of viable from lysed cells

Human mesenchymal stem cells (hMSCs) were labeled with Ferucarbotran by simple incubation and cultured for up to 14 d. Iron content was determined by spectrometry and the intracellular localization of the contrast agent uptake was studied by electron and confocal microscopy. At various time points after labeling, ranging from 1 to 14 d, samples with viable or lysed labeled hMSCs, as well as nonlabeled controls, underwent MRI. Spin-echo (SE) and gradient-echo (GE) sequences with multiple TRs and TEs were used at 1.5T and 3T on a clinical scanner. Spectrometry showed an initial iron oxide uptake of 7.08 pg per cell. Microscopy studies revealed lysosomal compartmentalization. Contrast agent effects of hMSCs were persistent for up to 14 d after labeling. A marked difference in the T(2) effect of compartmentalized iron oxides compared to free iron oxides was found on T(2)-weighted sequences, but not on T(2)*-weighted sequences. The observed differences may be explained by the loss of compartmentalization of iron oxide particles, the uniformity of distribution, and the subsequent increase in dephasing of protons on SE images. These results show that viable cells with compartmentalized iron oxides may-in principle-be distinguished from lysed cells or released iron oxides.

Cellular source and amount of vascular endothelial growth factor and platelet-derived growth factor in tumors determine response to angiogenesis inhibitors

Vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), and their receptors are important targets in cancer therapy based on angiogenesis inhibition. However, it is unclear whether inhibition of VEGF and PDGF together is more effective than inhibition of either one alone. Here, we used two contrasting tumor models to compare the effects of inhibiting VEGF or PDGF alone, by adenovirally generated soluble receptors, to the effects of inhibiting both together. In RIP-Tag2 tumors, VEGF and PDGF inhibition together reduced tumor vascularity and abundance of pericytes. However, VEGF inhibition reduced tumor vascularity without decreasing pericyte density, and PDGF inhibition reduced pericytes without reducing tumor vascularity. By contrast, in Lewis lung carcinomas (LLC), inhibition of VEGF or PDGF reduced blood vessels and pericytes to the same extent as did inhibition of both together. Similar results were obtained using tyrosine kinase inhibitors AG-013736 and imatinib. In LLC, VEGF expression was largely restricted to pericytes and PDGF was largely restricted to endothelial cells, but, in RIP-Tag2 tumors, expression of both growth factors was more widespread and significantly greater than in LLC. These findings suggest that inhibition of PDGF in LLC reduced pericytes, and then tumor vessels regressed because pericytes were the main source of VEGF. The vasculature of RIP-Tag2 tumors, in which most VEGF is from tumor cells, was more resistant to PDGF inhibition. The findings emphasize the interdependence of pericytes and endothelial cells in tumors and the importance of tumor phenotype in determining the cellular effects of VEGF and PDGF inhibitors on tumor vessels.

Vascular permeability during antiangiogenesis treatment: MR imaging assay results as biomarker for subsequent tumor growth in rats

PURPOSE

To prospectively evaluate in rats the acute change in tumor vascular leakiness (K(PS)) assayed at magnetic resonance (MR) imaging after a single dose of the angiogenesis inhibitor bevacizumab as a predictive biomarker of tumor growth response after a prolonged treatment course.

MATERIALS AND METHODS

Institutional animal care and use committee approval was obtained. Seventeen female rats with implanted human breast cancers underwent dynamic albumin-(Gd-DTPA)(30)-enhanced MR imaging followed by an initial dose of bevacizumab or saline (as a control). Treatment was continued every 3rd day, for a total of four doses at five possible dose levels: 0 mg bevacizumab (n = 4 [control rats]), 0.1 mg bevacizumab (n = 3), 0.25 mg bevacizumab (n = 2), 0.5 mg bevacizumab (n = 5), and 1.0 mg bevacizumab (n = 3). A second MR imaging examination was performed 24 hours after the initial dose to enable calculation of the acute change in MR imaging-assayed leakiness, or Delta K(PS). This acute change in K(PS) at MR imaging was correlated with tumor growth response for each cancer at the completion of the 11-day treatment course. For statistical analyses, an unpaired two-tailed t test, analysis of variance, and linear regression analyses were used.

RESULTS

The MR imaging-assayed change in tumor microvascular leakiness, tested as a potential biomarker, correlated strongly with tumor growth rate (R(2) = 0.74, P < .001). K(PS) and tumor growth decreased significantly in all bevacizumab-treated cancers compared with these values in control group cancers (P < .05).

CONCLUSION

The MR imaging-assayed acute change in vascular leakiness after a single dose of bevacizumab was an early, measurable predictive biomarker of tumor angiogenesis treatment response.

Sequential loss of tumor vessel pericytes and endothelial cells after inhibition of platelet-derived growth factor B by selective aptamer AX102

Inhibition of platelet derived growth factor (PDGF) can increase the efficacy of other cancer therapeutics, but the cellular mechanism is incompletely understood. We examined the cellular effects on tumor vasculature of a novel DNA oligonucleotide aptamer (AX102) that selectively binds PDGF-B. Treatment with AX102 led to progressive reduction of pericytes, identified by PDGF receptor beta, NG2, desmin, or alpha-smooth muscle actin immunoreactivity, in Lewis lung carcinomas. The decrease ranged from 35% at 2 days, 63% at 7 days, to 85% at 28 days. Most tumor vessels that lacked pericytes at 7 days subsequently regressed. Overall tumor vascularity decreased 79% over 28 days, without a corresponding decrease in tumor size. Regression of pericytes and endothelial cells led to empty basement membrane sleeves, which were visible at 7 days, but only 54% remained at 28 days. PDGF-B inhibition had a less pronounced effect on pancreatic islet tumors in RIP-Tag2 transgenic mice, where pericytes decreased 47%, vascularity decreased 38%, and basement membrane sleeves decreased 21% over 28 days. Taken together, these findings show that inhibition of PDGF-B signaling can lead to regression of tumor vessels, but the magnitude is tumor specific and does not necessarily retard tumor growth. Loss of pericytes in tumors is an expected direct consequence of PDGF-B blockade, but reduced tumor vascularity is likely to be secondary to pericyte regression.

Cell labeling with the positive MR contrast agent Gadofluorine M

The purpose of this study was to label human monocytes with Gadofluorine M by simple incubation for subsequent cell depiction at 1.5 and 3 T. Gadofluorine M displays a high r(1) relaxivity and is spontaneously phagocytosed by macrophages. Human monocytes were incubated with Gadofluorine M-Cy at varying concentrations and incubation times and underwent MR imaging at 1.5 and 3 T at increasing time intervals after the labeling procedure. R1-relaxation rates and r1 relaxivities of the labeled cells and non-labeled controls were determined. Cellular contrast agent uptake was examined by fluorescence microscopy and quantified by ICP-AES. Efficient cell labeling was achieved after incubation of the cells with 25 mM Gd Gadofluorine M for 12 h, resulting in a maximal uptake of 0.3 fmol Gd/cell without impairment of cell viability. Fluorescence microscopy confirmed internalization of the fluorescent contrast agent by monocytes. The r1 relaxivity of the labeled cells was 137 mM(-1)s(-1) at 1.5 T and 80.46 mM(-1)s(-1) at 3 T. Imaging studies showed stable labeling for at least 7 days. Human monocytes can be effectively labeled for MR imaging with Gadofluorine M. Potential in vivo cell-tracking applications include targeting of inflammatory processes with Gadofluorine-labeled leukocytes or monitoring of stem cell therapies for the treatment of arthritis.