Chimeric Antigen Receptor-T Cell and Oncolytic Viral Therapies for Gastric Cancer and Peritoneal Carcinomatosis of Gastric Origin: Path to Improving Combination Strategies

Precision immune oncology capitalizes on identifying and targeting tumor-specific antigens to enhance anti-tumor immunity and improve the treatment outcomes of solid tumors. Gastric cancer (GC) is a molecularly heterogeneous disease where monoclonal antibodies against human epidermal growth factor receptor 2 (HER2), vascular endothelial growth factor (VEGF), and programmed cell death 1 (PD-1) combined with systemic chemotherapy have improved survival in patients with unresectable or metastatic GC. However, intratumoral molecular heterogeneity, variable molecular target expression, and loss of target expression have limited antibody use and the durability of response. Often immunogenically "cold" and diffusely spread throughout the peritoneum, GC peritoneal carcinomatosis (PC) is a particularly challenging, treatment-refractory entity for current systemic strategies. More adaptable immunotherapeutic approaches, such as oncolytic viruses (OVs) and chimeric antigen receptor (CAR) T cells, have emerged as promising GC and GCPC treatments that circumvent these challenges. In this study, we provide an up-to-date review of the pre-clinical and clinical efficacy of CAR T cell therapy for key primary antigen targets and provide a translational overview of the types, modifications, and mechanisms for OVs used against GC and GCPC. Finally, we present a novel, summary-based discussion on the potential synergistic interplay between OVs and CAR T cells to treat GCPC.

Expansion of endogenous T cells in CSF of pediatric CNS tumor patients undergoing locoregional delivery of IL13R〿2-targeting CAR T cells: an interim analysis

Outcomes for pediatric brain tumor patients remain poor, and there is optimism that chimeric antigen receptor (CAR) T cell therapy can improve prognosis. Here, we present interim results from the first six pediatric patients treated on an ongoing phase I clinical trial (NCT04510051) of IL13BBζ-CAR T cells delivered weekly into the lateral cerebral ventricles, identifying clonal expansion of endogenous CAR-negative CD8+ T cells in the cerebrospinal fluid (CSF) over time. Additionally, of the five patients evaluable for disease response, three experienced transient radiographic and/or clinical benefit not meeting protocol criteria for response. The first three patients received CAR T cells alone; later patients received lymphodepletion before the first infusion. There were no dose limiting toxicities (DLTs). Aside from expected cytopenias in patients receiving lymphodepletion, serious adverse events possibly attributed to CAR T cell infusion were limited to one episode of headache and one of liver enzyme elevation. One patient withdrew from treatment during the DLT period due to a Grade 3 catheter-related infection and was not evaluable for disease response, although this was not attributed to CAR T cell infusion. Importantly, scRNA- and scTCR-sequence analyses provided insights into CAR T cell interaction with the endogenous immune system. In particular, clonally expanded endogenous CAR- T cells were recovered from the CSF, but not the peripheral blood, of patients who received intraventricular IL13BBζ-CAR T cell therapy. Additionally, although immune infiltrates in CSF and post-therapy tumor did not generally correlate, a fraction of expanded T cell receptors (TCRs) was seen to overlap between CSF and tumor. This has important implications for what samples are collected on these trials and how they are analyzed. These initial findings provide support for continued investigation into locoregionally-delivered IL13BBζ-CAR T cells for children with brain tumors.

Development of the oncolytic virus, CF33, and its derivatives for peritoneal-directed treatment of gastric cancer peritoneal metastases

BACKGROUND

Gastric cancer (GC) that metastasizes to the peritoneum is fatal. CF33 and its genetically modified derivatives show cancer selectivity and oncolytic potency against various solid tumors. CF33-hNIS and CF33-hNIS-antiPDL1 have entered phase I trials for intratumoral and intravenous treatments of unresectable solid tumors (NCT05346484) and triple-negative breast cancer (NCT05081492). Here, we investigated the antitumor activity of CF33-oncolytic viruses (OVs) against GC and CF33-hNIS-antiPDL1 in the intraperitoneal (IP) treatment of GC peritoneal metastases (GCPM).

METHODS

We infected six human GC cell lines AGS, MKN-45, MKN-74, KATO III, SNU-1, and SNU-16 with CF33, CF33-GFP, or CF33-hNIS-antiPDL1 at various multiplicities of infection (0.01, 0.1, 1.0, and 10.0), and performed viral proliferation and cytotoxicity assays. We used immunofluorescence imaging and flow cytometric analysis to verify virus-encoded gene expression. We evaluated the antitumor activity of CF33-hNIS-antiPDL1 following IP treatment (3×105 pfu × 3 doses) in an SNU-16 human tumor xenograft model using non-invasive bioluminescence imaging.

RESULTS

CF33-OVs showed dose-dependent infection, replication, and killing of both diffuse and intestinal subtypes of human GC cell lines. Immunofluorescence imaging showed virus-encoded GFP, hNIS, and anti-PD-L1 antibody scFv expression in CF33-OV-infected GC cells. We confirmed GC cell surface PD-L1 blockade by virus-encoded anti-PD-L1 scFv using flow cytometry. In the xenograft model, CF33-hNIS-antiPDL1 (IP; 3×105 pfu × 3 doses) treatment significantly reduced peritoneal tumors (p<0.0001), decreased amount of ascites (62.5% PBS vs 25% CF33-hNIS-antiPDL1) and prolonged animal survival. At day 91, seven out of eight mice were alive in the virus-treated group versus one out of eight in the control group (p<0.01).

CONCLUSIONS

Our results show that CF33-OVs can deliver functional proteins and demonstrate effective antitumor activity in GCPM models when delivered intraperitoneally. These preclinical results will inform the design of future peritoneal-directed therapy in GCPM patients.

Development of a novel chimeric oncolytic viral platform, CF33 and its derivatives, for peritoneal-directed CF33-OV treatment of gastric cancer peritoneal carcinomatosis

428

Background: Peritoneal carcinomatosis (PC) is a deadly end-stage manifestation of gastric cancer (GC). CF33, a chimeric oncolytic virus, and its genetically modified derivatives have shown exclusive cancer selectivity and oncolytic potency against various solid tumors. Intravenous and intratumoral CF33-hNIS and CF33-hNIS-antiPDL1 have entered phase I trials to treat triple-negative breast cancer and unresectable solid tumors. Here, we investigated the antitumor activities of CF33-OVs against GCPC. Methods: We infected six GC cell lines, including both intestinal-type (AGS and MKN-74) and diffuse-type (KATO III, MKN-45, SNU-1, and SNU-16) with CF33, CF33-GFP, or CF33-hNIS-antiPDL1 at various multiplicities (MOI 0.01, 0.1, 1.0 and 10.0) to examine viral proliferation and cytotoxicity by using standard plaque assay and cell proliferation assay. We performed immunofluorescence imaging and flow cytometric analysis to verify virus-encoded gene expression and blockade of PD-L1 binding by virus-encoded anti-PD-L1 scFv. A mouse model of peritoneal dissemination xenograft of SNU-16-ffluc cells was set up to evaluate the antitumor activity of intraperitoneal (IP) CF33-hNIS-antiPDL1 treatment (3x105 pfu x 3 doses). Results: CF33-OVs showed dose-dependent infection, replication, and killing of human GC cell lines. Immunofluorescence imaging showed virus-encoded GFP, hNIS, and anti-PD-L1 scFv expression in CF33-OV-infected GC cells. GC cell surface PD-L1 binding was blocked by virus-encoded anti-PD-L1 scFv. In the xenograft model, IP CF33-hNIS-antiPDL1 treatment significantly reduced peritoneal tumors (p<0.0001), decreased amount of ascites (62.5% PBS vs. 25% CF33-hNIS-antiPLD1), and prolonged animal survival (p<0.01). Conclusions: CF33-OVs demonstrate effective antitumor activity and can deliver functional proteins in vitro and in vivo. CF33-hNIS-antiPDL1 treatment induced sustained regression of GCPC and prolonged survival. These promising preclinical results support peritoneal-directed strategies with CF33-hNIS-antiPDL1 in GCPC patients.

Abstract 588: Regional administration of IL-12 endowed CAR T cells effectively targets systemic disease

While chimeric antigen receptor (CAR) T cell therapy has shown impressive clinical efficacy for hematological malignancies, efficacy remains limited for solid tumors due in large part to the immunosuppressive tumor microenvironment. Tumor-associated glycoprotein 72 (TAG72) is an aberrantly glycosylated protein overexpressed on ovarian cancer and is an exciting target for CAR T cell immunotherapy. Our lab previously developed a second-generation TAG72 CAR T cell product and showed its potency against TAG72-expressing ovarian tumor cells both in vitro and in preclinical mouse models. We report here further modification of our TAG72 CAR T cells, with incorporation of interleukin-12 (IL-12) and interleukin-15 (IL-15), and evaluate the therapeutic benefits in peritoneal ovarian tumor models.

In this preclinical study, we build upon our earlier work with in vitro and in vivo evaluation of 9 different second-generation TAG72 CAR constructs varying in single-chain variable fragment, extracellular spacer, transmembrane, and intracellular co-stimulatory domains. We then engineer CAR T cells with two types of cytokines - IL-12 and IL-15 - and put these engineered cells against challenging in vivo tumor models.

Through in vitro and in vivo studies, we identified the most optimal construct with which we aim to evaluate in a phase 1 clinical trial targeting TAG72-positive ovarian cancer in early 2022. Despite thorough optimizations to the CAR backbone, CAR T cells can be additionally engineered for improved anti-tumor response. Therefore, we further engineered CAR T cells with IL-12 or IL-15 production that greatly improved the effectiveness of TAG72-CAR T cells in difficult-to-treat in vivo tumor models. We observed that modification of CAR T cells with IL-15 displayed toxicity when regionally delivered in vivo, yet introduction of IL-12 not only demonstrated safe and superior therapeutic responses, but also allowed the regional administration of CAR T cells to address systemic disease. We are now expanding these findings by evaluating these therapies using syngeneic immunocompetent mouse tumor models.

The tumor microenvironment (TME) harbors various factors that thwart the killing of tumor cells by CAR T cells. Thus, CAR T cells will likely require further engineering to overcome this barrier. We show that amplifying cytokine pathways is one way to overcome the TME and improve the efficacy of CAR T cell therapy for solid tumors.

Citation Format: Hee Jun Lee, Saul Priceman. Regional administration of IL-12 endowed CAR T cells effectively targets systemic disease [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 588.

A phase 1, first-in-human (FIH) study of the anti-HER2 CAR macrophage CT-0508 in subjects with HER2 overexpressing solid tumors

2533

Background: Most solid tumors are resistant to immunotherapy. In pre-clinical studies, CAR-M infiltrate tumors, phagocytose tumor cells, activate the tumor micro environment (TME), recruit T cells, and present tumor antigens to T cells leading to robust anti-tumor immunity. CT-0508 is a first in class CAR-M, comprised of autologous monocyte derived macrophages expressing an anti-HER2 CAR. Here we present preliminary clinical results from the CT-0508 Phase 1 FIH study. Methods: This multi-center, open-label study is evaluating CT-0508’s safety, tolerability, and manufacturing feasibility in 18 participants (pts) with advanced solid tumors overexpressing HER2 who have progressed on prior therapies. Monocytes are isolated from mobilized apheresis products, differentiated into macrophages and engineered with an anti-HER2 CAR. Group 1 pts (n = 9) receive a fractionated dose (D1, D3, D5) and Group 2 pts (n = 9) receive the full dose on D1. CT-0508 is administered without preparative chemotherapy (bridging is permitted). Serial blood samples, 1 pre and 2 post-treatment biopsies are collected to investigate safety, pharmacokinetics and mechanism of action. Results: Seven pts (4F/3M), median age 64 (49-73), have been treated [breast (2), esophageal (2), cholangiocarcinoma, ovarian and parotid gland cancers]. A median of 3 (2-10) prior lines of therapy have been administered, most pts (85.7%) received prior anti HER2 therapy. CT-0508 was successfully manufactured with high viability, purity and CAR expression, and was well tolerated with no dose limiting toxicities or AEs leading to discontinuation or dose modification. Two related SAEs were reported in the same pt (Grade 1 CRS, hospitalized for monitoring and Grade 2 infusion reaction, resolved within 1h). Three other pts had Grade 1-2 CRS; resolved within 4d with no use of tocilizumab needed. There were no major organ toxicities and no on-target off-tumor toxicities. Post-infusion cytokines were transiently elevated in most pts and were self-limiting. Among the 4 pts who reached week 8, the best overall response was stable disease (n = 3) and 1 pt progressed, with a median follow up of 8w. CT-0508 rapidly egressed from peripheral blood. CT-0508 CAR mRNA was detected in all tumor biopsies of the first 2 pts. CT-0508 activated the TME, with increased myeloid cell activation, T cell infiltration, activation and proliferation. TCR sequencing demonstrated peripherally expanding T cells enriched for tumor infiltrating lymphocyte clones, suggesting expansion of tumor reactive T cells. Correlative data from additional pts will be presented. Conclusions: In 7 pts, CT-0508 was safe and feasible to manufacture. Early correlative data demonstrate trafficking, TME modulation, and potential induction of anti-tumor T cell immunity. The study is actively enrolling. Clinical trial information: NCT04660929.

A phase 1, first-in-human (FIH) study of adenovirally transduced autologous macrophages engineered to contain an anti-HER2 chimeric antigen receptor (CAR) in participants with HER2 overexpressing solid tumors

TPS2677

Background: Adoptive T cell therapies have led to remarkable advances among patients with hematologic malignancies, but have had less success in those with solid tumors. Macrophages are actively recruited and abundantly present in the solid tumor microenvironment (sTME). Tumor associated macrophages are predominantly immunosuppressive and support tumor growth (M2), while a subset of proinflammatory macrophages enhance anti-tumor immunogenicity (M1). M1 macrophage function can be augmented by CAR expression to selectively recognize and phagocytose antigen overexpressing cancer cells. Moreover, CAR macrophages can reprogram the sTME and present neoantigens to T cells, leading to epitope spreading and anti-tumor immune memory. Human Epidermal Growth Factor Receptor 2 (HER2) overexpression promotes tumorigenesis in many solid tumors (Table). CT-0508 is a cell product comprised of autologous monocyte-derived proinflammatory macrophages expressing an anti-HER2 CAR. Pre-clinical studies have shown that CT-0508 induced targeted cancer cell phagocytosis while sparing normal cells, decreased tumor burden, prolonged survival, and were safe and effective in a semi-immunocompetent mouse model of human HER2 overexpressing ovarian cancer. Methods: This Phase 1, FIH study is evaluating safety, tolerability, cell manufacturing feasibility, trafficking, and preliminary evidence of efficacy of investigational product CT-0508 in 18 participants (pt) with locally advanced (unresectable) or metastatic solid tumors overexpressing HER2. Pt previously treated with available therapies, including anti-HER2 therapies, as indicated, and subsequent progression are permitted. Filgrastim is used to mobilize autologous hematopoietic progenitor cells for monocyte collection by apheresis. CT-0508 is manufactured, prepared, and cryopreserved from mobilized peripheral blood monocytes. Group 1 pt (n=9) receive CT-0508 infusion split over D1, 3, and 5. A Safety Review Committee will review dose limiting toxicities. Group 2 pt (n=9) will receive the full CT-0508 infusion on D1. Pre- and post-treatment biopsies and blood samples will be collected to investigate correlates of safety (immunogenicity), trafficking (RNA scope), CT-0508 persistence in blood and in the tumor, target antigen engagement, TME modulation (single cell RNA sequencing), immune response (TCR sequencing) and others. Radiographic imaging is also being conducted to assess preliminary tumor activity. Clinical trial information: NCT04660929. [Table: see text]

Phase 1 study of PSCA-targeted chimeric antigen receptor (CAR) T cell therapy for metastatic castration-resistant prostate cancer (mCRPC)

91

Background: Chimeric antigen receptor (CAR)-engineered T cell therapies are being pursued for the treatment of mCRPC. Prostate Stem Cell Antigen (PSCA) is highly expressed on the surface membrane in mCRPC and with limited expression on normal tissues. We undertook a phase 1, first-in-human study of a PSCA-targeted 4-1BB-co-stimulated CAR T cell therapy in mCRPC. Methods: CAR T cells were manufactured at City of Hope’s cGMP facility. The trial followed the Target equivalence range design with an equivalence range of.20-.35 and too toxic level of 0.51 following participants in cohorts of 3. The plan was to begin at a dose of 100 million (M) without lymphodepletion (LD) chemotherapy consisting of fludarabine and cyclophosphamide, then add LD to 100M prior to dose escalation to maximum 600M. Patients (pts) were required to have disease progression after at least 1 androgen receptor targeted therapy but there was no limit on prior chemotherapy or other treatments. Primary objective is to define the dose limiting toxicity (DLT) and recommended phase 2 dose as well as to describe preliminary bioactivity and efficacy. Correlative studies include MRI for target bone lesion response, CAR T cell persistence, circulating tumor cells, and serum cytokines. Results: 12 pts have been treated to date, median age 68 (42-72). Three pts were treated at the 100M dose with no DLTs. In the 100M plus LD dose level there 2 pts experienced DLT of grade 3 cystitis non-infective and fatigue. The protocol was amended to reduce the LD dose to 300 mg/m2 cyclophosphamide D1-3 and intensify monitoring with early intervention for cystitis. No DLT occurred in 3 pts treated in the modified LD 100M cohort. Cytokine release syndrome (CRS), DLTs and best response by RECIST are presented by dose level in the table. PSA declines (one >90%) were seen as well as radiographic improvement, though RECIST response was limited to stable disease (SD) by concurrent bone metastases. Correlative studies indicated bioactivity of PSCA-CAR T cells. Conclusions: PSCA-CAR T cell therapy is feasible in pts with mCRPC with DLT of cystitis, and shows preliminary anti-tumor effect at a dose of 100M plus LD. Dose escalation to 300M may proceed. Clinical trial information: NCT03873805. [Table: see text]

224 M2 macrophage-mediated immune suppression of chimeric antigen receptor T cells via PD-L1 signaling in prostate cancer

Background

The immune suppressive tumor microenvironment (TME) that inhibits T cell infiltration, survival, and anti-tumor activity has posed a major challenge for developing effective immunotherapies for solid tumors. Chimeric antigen receptor T cell therapy has shown unprecedented clinical response in treating patients with hematological malignancies, and intense investigation is underway to achieve similar responses with solid tumors. Immunologically cold tumors, including prostate cancers, are often infiltrated with abundant macrophages, and infiltration of M2 macrophages correlates with metastasis and poor prognosis.

Methods

To model this in vitro, we utilized a novel co-culture system with tumor cells, prostate stem cell antigen (PSCA)-directed CAR T cells, and polarized macrophages. To investigate the TME in vivo, we took advantage of ”humanized” MISTRG mice, which are immunocompromised mice with knocked-in human genes that support human hematopoiesis and efficient tumor-infiltration of myeloid cell populations. Humanized MISTRG mice were intratibially engrafted with LAPC9 tumor cells to model bone metastatic disease.

Results

We observed significant hampering of PSCA-CAR T cell activity in vitro with the presence of M2 macrophages, but not M1 macrophages, coinciding with a robust induction of PD-L1 in both tumor cells and macrophages. We also observed PD-L1 expression in tumor-associated macrophages infiltrating tumors following PSCA-CAR T cell therapy in the humanized mice. Anti-PD-L1 monoclonal antibodies in combination with CAR-T cell therapy altered phenotype and survival of M2 macrophages, resulting in improved anti-tumor activity of PSCA-CAR T cells in the presence of M2 macrophages.

Conclusions

Recently, immune checkpoint (IC) blockade (ICB) has been utilized in combination with chimeric antigen receptor (CAR) T cell therapy, with the notion that induction of immune responses with CAR T cells may instigate checkpoint pathways in immunologically cold tumors that would otherwise not respond to ICB. This study gives insights to a mechanism by which CAR T cells and ICB work in synergy to modulate immune landscape of immunologically cold tumors, and our ongoing studies will continue to elucidate the TME-mediated immunosuppression of CAR T cell therapy.

126 Regional administration of IL-12 endowed CAR T cells effectively targets systemic disease

Background

While chimeric antigen receptor (CAR) T cell therapy has shown impressive clinical efficacy for hematological malignancies,1 efficacy remains limited for solid tumors due in large part to the immunosuppressive tumor microenvironment.2 Tumor-associated glycoprotein 72 (TAG72) is an aberrantly glycosylated protein overexpressed on ovarian cancer3 and is an exciting target for CAR T cell immunotherapy. Our lab previously developed a second-generation TAG72 CAR T cell product and showed its potency against TAG72-expressing ovarian tumor cells both in vitro and in preclinical mouse models.4 We report here further modification of our TAG72 CAR T cells, with incorporation of interleukin-12 (IL-12) and interleukin-15 (IL-15), and evaluate the therapeutic benefits in peritoneal ovarian tumor models.

Methods

In this preclinical study, we build upon our earlier work with in vitro and in vivo evaluation of 9 different second-generation TAG72 CAR constructs varying in single-chain variable fragment, extracellular spacer, transmembrane, and intracellular co-stimulatory domains. We then engineer CAR T cells with two types of cytokines – IL-12 and IL-15 – and put these engineered cells against challenging in vivo tumor models.

Results

Through in vitro and in vivo studies, we identify the most optimal construct with which we aim to evaluate in a phase 1 clinical trial targeting TAG72-positive ovarian cancer in 2021. Despite thorough optimizations to the CAR backbone, CAR T cells can be additionally engineered for improved anti-tumor response. Therefore, we further engineered CAR T cells with IL-12 or IL-15 production that greatly improves the effectiveness of TAG72-CAR T cells in difficult-to-treat in vivo tumor models. We observed that modification of CAR T cells with IL-15 displayed toxicity when regionally delivered in vivo, yet introduction of IL-12 not only demonstrated safe and superior therapeutic responses, but also allowed the regional administration of CAR T cells to address systemic disease. We are now expanding these findings by evaluating these therapies using syngeneic immunocompetent mouse tumor models.

Conclusions

The tumor microenvironment (TME) harbors various factors that thwart the killing of tumor cells by CAR T cells. Thus, CAR T cells will likely require further engineering to overcome this barrier. We show that amplifying cytokine pathways is one way to overcome the TME and improve the efficacy of CAR T cell therapy for solid tumors.

References

Maude SL, Teachey DT, Porter DL, Grupp SA. CD19-targeted chimeric antigen receptor T-cell therapy for acute lymphoblastic leukemia. Blood 2015 Jun 25;125(26):4017–23.

Priceman SJ, Forman SJ, Brown CE. Smart CARs engineered for cancer immunotherapy. Curr Opin Oncol 2015 Nov;27(6):466–74.

Chauhan SC, Vinayek N, Maher DM, Bell MC, Dunham KA, Koch MD, Lio Y, Jaggi M. Combined Staining of TAG-72, MUC1, and CA125 Improves Labeling Sensitivity in Ovarian Cancer: Antigens for Multi-targeted Antibody-guided Therapy. J Histochem Cytochem 2007 Aug;55(8):867–75.

Murad JP, Kozlowska AK, Lee HJ, Ramamurthy M, Chang WC, Yazaki P, Colcher D, Shively J, Cristea M, Forman SJ, Priceman SJ. Effective Targeting of TAG72+ Peritoneal Ovarian Tumors via Regional Delivery of CAR-Engineered T Cells. Front Immunol 2018 Nov 19;9:2268.

A phase I study to evaluate PSCA-targeting chimeric antigen receptor (CAR)-T cells for patients with PSCA+ metastatic castration-resistant prostate cancer (mCRPC)

TPS250

Background: Although treatment options have improved, mCRPC remains highly lethal. Immunotherapy holds potential for durable remissions but not yet in mCRPC. CAR-T cell therapy has yielded cure for patients with refractory hematologic malignancies, and shows promise in solid tumors. Identifying and targeting the optimal antigen will be key to successful translation in solid tumors. Prostate stem cell antigen (PSCA) is highly expressed on prostate cancer cells, especially metastatic foci, and has limited expression on normal tissues. City of Hope has developed a second-generation PSCA CAR-T cell therapy containing an intracellular 4-1BB co-stimulatory domain (PSCA-BBζ) for first-in-human testing in men with mCRPC refractory to standard therapy (NCT03873805). Methods: The toxicity equivalence range (TEQR) design of Blanchard and Longmate will be used to evaluate select doses of PSCA-BBζ cells and determine the maximum tolerated dose (MTD). Doses include Cohort 1 = 100 million (M) CAR-T x 1 alone; Cohort 1b = 100M CAR-T x1 after lymphodepletion; Cohort 2 = 300M after lymphodepletion; Cohort 3 = 600M after lymphodepletion. 12 subjects will be accrued at the MTD. Eligibility: mCRPC treated with either abiraterone, enzalutamide or both; prior chemotherapy and/or radium223 allowed but not mandated. Tumor tissue, primary or metastatic, must stain positive for PSCA by IHC (Abcam 15168) and biopsy is repeated 28 days post infusion. Endpoints: Primary: all toxicities and dose-limiting toxicities defined as grade 3+ toxicity with attribution of possibly related or above, except CRS grade 3 resolved to < grade 2 within 72 hours or grade 3 encephalopathy resolved to baseline within 28 days. Secondary: persistence/expansion of CAR-T, response (soft tissue by RECIST, bone by PCWG3 criteria). Correlative studies include blood (immunophenotyping, cytokines, circulating tumor cell enumeration and PSCA expression), MRI (enhancement/diffusion changes in target lesions) and metastatic core biopsies (PSCA expression and local immune phenotype changes). Progress: 4 subjects have successfully manufactured PSCA-BBζ T cells; 1 completed treatment. Clinical trial information: NCT03873805.

STAT3 Activation-Induced Fatty Acid Oxidation in CD8+ T Effector Cells Is Critical for Obesity-Promoted Breast Tumor Growth

Although obesity is known to be critical for cancer development, how obesity negatively impacts antitumor immune responses remains largely unknown. Here, we show that increased fatty acid oxidation (FAO) driven by activated STAT3 in CD8+ T effector cells is critical for obesity-associated breast tumor progression. Ablating T cell Stat3 or treatment with an FAO inhibitor in obese mice spontaneously developing breast tumor reduces FAO, increases glycolysis and CD8+ T effector cell functions, leading to inhibition of breast tumor development. Moreover, PD-1 ligation in CD8+ T cells activates STAT3 to increase FAO, inhibiting CD8+ T effector cell glycolysis and functions. Finally, leptin enriched in mammary adipocytes and fat tissues downregulates CD8+ T cell effector functions through activating STAT3-FAO and inhibiting glycolysis. We identify a critical role of increased oxidation of fatty acids driven by leptin and PD-1 through STAT3 in inhibiting CD8+ T effector cell glycolysis and in promoting obesity-associated breast tumorigenesis.

Abstract 4981: Extracellular spacer and co-stimulatory domains define target sensitivity and persistence of CAR T cells for the treatment of PSCA+ bone metastatic prostate cancer

Advancing chimeric antigen receptor (CAR)-engineered adoptive T cells for the treatment of solid cancers is a major focus in the field of immunotherapy, given impressive recent clinical responses in hematological malignancies. Prostate cancer should be amenable to CAR-based immunotherapy given that several tumor antigens, including prostate stem-cell antigen (PSCA), are widely over-expressed in metastatic disease. The selectivity of CARs for solid cancers is crucial, however, due to the absence of truly restricted tumor antigen expression and potential safety concerns with “on-target off-tumor” activity. Here, we show that optimized co-stimulatory signaling and extracellular spacer domains are essential in defining a CAR’s selectivity towards tumor cells that over-express the target antigen. The 4-1BB co-stimulatory domain in PSCA-CARs confers enhanced tumor selectivity with dampened yet dose-responsive cytokine production, reduced T cell exhaustion phenotype, and equivalent tumor killing ability compared to PSCA-CARs containing the CD28 co-stimulatory domain. CARs containing a short extracellular spacer demonstrate the most selective killing of high PSCA-expressing tumors but are unable to produce the inflammatory cytokines important for a complete anti-tumor response. We show that longer extracellular spacers in PSCA-CARs are necessary for both tumor killing and cytokine production. PSCA-CARs exhibit robust in vivo anti-tumor activity in subcutaneous and orthotopic bone-metastatic patient-derived prostate cancer xenograft models, and 4-1BB-containing CARs show superior persistence in controlling metastatic disease compared with CD28-containing CARs. Our study demonstrates the critical impact of CAR components in defining an optimized tumor-selective CAR T cell, and also highlights the importance of clinically relevant animal models in developing effective solid cancer CAR T cell therapies.

Citation Format: Kelly Kennewick, Dileshni Tilakawardane, Ethan Gerdts, John Murad, Anthony Park, Brook Jeang, Yukiko Yamaguchi, Stephen J. Forman, Saul Priceman. Extracellular spacer and co-stimulatory domains define target sensitivity and persistence of CAR T cells for the treatment of PSCA+ bone metastatic prostate cancer [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 4981. doi:10.1158/1538-7445.AM2017-4981

Chimeric antigen receptors with mutated IgG4 Fc spacer avoid fc receptor binding and improve T cell persistence and antitumor efficacy

The success of adoptive therapy using chimeric antigen receptor (CAR)-expressing T cells partly depends on optimal CAR design. CARs frequently incorporate a spacer/linker region based on the constant region of either IgG1 or IgG4 to connect extracellular ligand-binding with intracellular signaling domains. Here, we evaluated the potential for the IgG4-Fc linker to result in off-target interactions with Fc gamma receptors (FcγRs). As proof-of-principle, we focused on a CD19-specific scFv-IgG4-CD28-zeta CAR and found that, in contrast to CAR-negative cells, CAR+ T cells bound soluble FcγRs in vitro and did not engraft in NSG mice. We hypothesized that mutations to avoid FcγR binding would improve CAR+ T cell engraftment and antitumor efficacy. Thus, we generated CD19-specific CARs with IgG4-Fc spacers that had either been mutated at two sites (L235E; N297Q) within the CH2 region (CD19R(EQ)) or incorporated a CH2 deletion (CD19Rch2Δ). These mutations reduced binding to soluble FcγRs without altering the ability of the CAR to mediate antigen-specific lysis. Importantly, CD19R(EQ) and CD19Rch2Δ T cells exhibited improved persistence and more potent CD19-specific antilymphoma efficacy in NSG mice. Together, these studies suggest that optimal CAR function may require the elimination of cellular FcγR interactions to improve T cell persistence and antitumor responses.

CSF1R signaling blockade stanches tumor-infiltrating myeloid cells and improves the efficacy of radiotherapy in prostate cancer

Radiotherapy is used to treat many types of cancer, but many treated patients relapse with local tumor recurrence. Tumor-infiltrating myeloid cells (TIM), including CD11b (ITGAM)(+)F4/80 (EMR1)+ tumor-associated macrophages (TAM), and CD11b(+)Gr-1 (LY6G)+ myeloid-derived suppressor cells (MDSC), respond to cancer-related stresses and play critical roles in promoting tumor angiogenesis, tissue remodeling, and immunosuppression. In this report, we used a prostate cancer model to investigate the effects of irradiation on TAMs and MDSCs in tumor-bearing animals. Unexpectedly, when primary tumor sites were irradiated, we observed a systemic increase of MDSCs in spleen, lung, lymph nodes, and peripheral blood. Cytokine analysis showed that the macrophage colony-stimulating factor CSF1 increased by two-fold in irradiated tumors. Enhanced macrophage migration induced by conditioned media from irradiated tumor cells was completely blocked by a selective inhibitor of CSF1R. These findings were confirmed in patients with prostate cancer, where serum levels of CSF1 increased after radiotherapy. Mechanistic investigations revealed the recruitment of the DNA damage-induced kinase ABL1 into cell nuclei where it bound the CSF1 gene promoter and enhanced CSF1 gene transcription. When added to radiotherapy, a selective inhibitor of CSF1R suppressed tumor growth more effectively than irradiation alone. Our results highlight the importance of CSF1/CSF1R signaling in the recruitment of TIMs that can limit the efficacy of radiotherapy. Furthermore, they suggest that CSF1 inhibitors should be evaluated in clinical trials in combination with radiotherapy as a strategy to improve outcomes.

Mitogen-activated protein kinase phosphatase-1 deficiency decreases atherosclerosis in apolipoprotein E null mice by reducing monocyte chemoattractant protein-1 levels

RATIONALE

We previously reported that mitogen-activated protein kinase phosphatase-1 (MKP-1) expression is necessary for oxidized phospholipids to induce monocyte chemoattractant protein-1 (MCP-1) secretion by human aortic endothelial cells. We also reported that inhibition of tyrosine phosphatases including MKP-1 ameliorated atherosclerotic lesions in mouse models of atherosclerosis.

OBJECTIVE

This study was conducted to further investigate the specific role of MKP-1 in atherogenesis.

METHODS AND RESULTS

We generated MKP-1(-/-)/apoE(-/-) double-knockout mice. At 24weeks of age, the size, macrophage and dendritic cell content of atherosclerotic lesions of the aortic root were significantly lower ( approximately -41% for lesions and macrophages, and approximately -78% for dendritic cells) in MKP-1(-/-)/apoE(-/-) mice when compared with apoE(-/-) mice. Total cholesterol (-18.4%, p=0.045) and very low-density lipoprotein (VLDL)/low-density lipoprotein (LDL) cholesterol (-20.0%, p=0.052) levels were decreased in MKP-1(-/-)/apoE(-/-) mice. Serum from MKP-1(-/-)/apoE(-/-) mice contained significantly lower levels of MCP-1 and possessed significantly reduced capability to induce monocyte migration in vitro. Moreover, peritoneal macrophages isolated from MKP-1(-/-)/apoE(-/-) mice produced significantly lower levels of MCP-1 when compared to peritoneal macrophages from apoE(-/-) mice. Furthermore, MKP-1(-/-)/apoE(-/-) mice had significantly reduced serum hydroxyeicosatetraenoic acids (HETEs) levels, which have been reported to induce MCP-1 levels.

CONCLUSIONS

Our results demonstrate that MKP-1 deficiency significantly decreases atherosclerotic lesion development in mice, in part, by affecting MCP-1 levels in the circulation and MCP-1 production by macrophages. MKP-1 may serve as a potential therapeutic target for the treatment of atherosclerotic disease.

A novel intracellular protein delivery platform based on single-protein nanocapsules

An average cell contains thousands of proteins that participate in normal cellular functions, and most diseases are somehow related to the malfunctioning of one or more of these proteins. Protein therapy, which delivers proteins into the cell to replace the dysfunctional protein, is considered the most direct and safe approach for treating disease. However, the effectiveness of this method has been limited by its low delivery efficiency and poor stability against proteases in the cell, which digest the protein. Here, we show a novel delivery platform based on nanocapsules consisting of a protein core and a thin permeable polymeric shell that can be engineered to either degrade or remain stable at different pHs. Non-degradable capsules show long-term stability, whereas the degradable ones break down their shells, enabling the core protein to be active once inside the cells. Multiple proteins can be delivered to cells with high efficiency while maintaining low toxicity, suggesting potential applications in imaging, therapy and cosmetics fields.