Radiation Therapy Exacerbates Tumor-Promoting Innervation and Nerve Signaling in Rectal Cancer

PURPOSE

Many solid tumors present with perineural invasion (PNI), and innervation correlates with worsened prognosis. The effects that commonly administered therapies such as radiation therapy (RT) have on PNI status remain unknown. We investigated the contribution of RT on the nervous system and elucidated the implications that increased nerve signaling can have on tumor burden using our previously developed orthotopic murine model of rectal cancer (RC) and our targeted and clinically relevant short-course RT (SCRT) regimen.

METHODS

Medical charts for patients with RC treated at the Wilmot Cancer Institute were obtained and PNI status was analyzed. Human data were accompanied by an orthotopic murine model of RC. Briefly, luciferase-expressing murine colon-38 (MC38-luc) tumor cells were injected orthotopically into the rectal wall of C57BL6 mice. Targeted SCRT (5 gray (Gy) per fraction for 5 consecutive fractions) was administered to the tumor. Intratumoral innervation was determined by immunohistochemistry (IHC), local norepinephrine (NE) concentration was quantified by enzyme-linked immunosorbent assay (ELISA), and β2-adrenergic receptor (B2AR) expression was assessed by flow cytometry. Chronic NE signaling was mirrored by daily isoproterenol treatment, and the effect on tumor burden was determined by overall survival, presence of metastatic lesions, and tumor size. Isoproterenol signaling was inhibited by administration of propranolol.

RESULTS

Human RC patients with PNI have decreased overall survival compared with patients without PNI. In our mouse model, SCRT induced the expression of genes involved in neurogenesis, increased local NE secretion, and upregulated B2AR expression. Treating mice with isoproterenol resulted in decreased overall survival, increased rate of metastasis, and reduced SCRT efficacy. Interestingly, the isoproterenol-induced decrease in SCRT efficacy could be abrogated by blocking the BAR through the use of propranolol, suggesting a direct role of BAR stimulation on impairing SCRT responses.

CONCLUSIONS

Our results indicate that while SCRT is a valuable treatment, it is accompanied by adverse effects on the nervous system that may impede the efficacy of therapy and promote tumor burden. Therefore, we could speculate that therapies aimed at targeting this signaling cascade or impairing nerve growth in combination with SCRT may prove beneficial in future cancer treatment.

The divergent role of the GM-CSF/GM-CSFR signaling pathway in cholangiocarcinoma and pancreatic ductal adenocarcinoma

736

Background: The granulocyte-macrophage colony-stimulating factor ligand and receptor (GM-CSF/GM-CSFR) pathway plays a multifaceted role in the setting of cancer, exerting an anti-tumorigenic or pro-tumorigenic effect depending on GM-CSF expression. In previous work, we and others have shown increased GM-CSF expression to correlate with poor prognosis in patients with cholangiocarcinoma (CCA) and pancreatic ductal adenocarcinoma (PDAC). We also demonstrated how GM-CSF neutralization leads to reduced tumor size in murine CCA models, in part due to inhibition of alternative macrophage polarization. Here, we explore the impact of blocking GM-CSFR signaling in CCA and PDAC, two immunologically cold tumors with poor prognoses. Methods: Immunohistochemistry (IHC) and digital quantification of staining was performed on tissue from a human PDAC and CCA databank. Murine F4/80+ bone marrow-derived macrophages were cultured in tumor-conditioned media (TCM) derived from PDAC (KP2) or CCA (URCCA4.3) cell lines, with and without anti-GM-CSFR antibody. Quantitative real time PCR (qRT-PCR) analysis was performed for gene expression. URCCA4.3 and a luciferase-labeled PDAC (KCKO) cell line were orthotopically implanted into Bc/BIL3 knockout (KO) mice which lack GM-CSFR and C57BL/6 mice. Mice implanted with URCCA4.3 were enrolled into vehicle or gemcitabine treatment groups. Mice implanted with KCKO were untreated. Tumor growth was monitored by ultrasonography or bioluminescence imaging. Results: Digital analysis of IHC staining for GM-CSFR in human PDAC tumors revealed low expression to be associated with improved overall survival (OS) and greater number of days to recurrence, while high levels were associated with worse OS and fewer days to recurrence (p<0.01). In addition, human CCA specimens had greater GM-CSFR expression compared to normal uninvolved liver (p<0.01). qRT-PCR analysis of RNA from bone marrow-derived macrophages exposed to either CCA or PDAC TCM demonstrated lower expression of genes associated with alternative macrophage polarization ( Arg1, Cd274, Pdcd1lg2) and chronic inflammation ( Ccl2, Ccl17, Irf4) (all p<0.01) in response to GM-CSFR blockade. GM-CSFR KO mice implanted with URCCA4.3 demonstrated no differences in tumor growth with or without chemotherapy, compared to wild-type controls. Similarly, KO mice implanted with an immunogenic PDAC cell line (KCKO) had no differences in tumor size compared to wild-type controls. Conclusions: GM-CSFR expression is prognostic in the setting of PDAC and elevated in human CCA compared to normal liver. In vitro, GM-CSFR blockade downregulated pro-tumor genes associated with immunosuppression and inflammation. However, complete disruption of GM-CSFR signaling reversed the efficacy generated with GM-CSF ligand neutralization, suggesting some signaling is required for inducing anti-tumor immune responses.

Abstract PO025: GM-CSF neutralization enhances the efficacy of chemotherapy in an orthotopic murine model of cholangiocarcinoma

Introduction: With current effective treatments in cholangiocarcinoma (CCA) lacking, we expounded on our prior work highlighting the critical role of the granulocyte-macrophage-colony stimulating factor ligand/receptor (GM-CSF/GM-CSFRα) signaling pathway by evaluating GM-CSF neutralization combined with first-line chemotherapy in a novel murine model of CCA. Methods: Resected CCA specimens were used to construct a human tissue macro-array. Immunohistochemistry (IHC) staining for GM-CSFRα and digital quantification of staining intensity was performed. A novel syngeneic CCA cell line derived from spontaneous murine CCA from LSL-KrasG12D; Tp53Flox/Flox −; Alb-Cre (KPPC) mice was surgically injected into the left hepatic lobes of C57BL/6J mice. Disease onset and extent of progression was monitored over time using ultrasonography (US) in groups of mice enrolled into treatment with vehicle, gemcitabine, anti-GM-CSF, and gemcitabine plus anti-GM-CSF. Mice were sacrificed at predetermined endpoints for flow cytometry analysis. Results: IHC analysis and digital quantification of resected human tumors demonstrated that CCA expresses significantly higher levels of GM-CSFRα (p&lt;0.01) compared to uninvolved normal liver. Mice injected with a novel syngeneic CCA cell line expressing high levels of GM-CSF protein uniformly developed tumors fourteen days after orthotopic implantation. Histopathological evaluation of orthotopic CCA tumors demonstrated faithful recapitulation of both spontaneous murine and human disease with marked development of malignant biliary ductal epithelium (CK7), desmoplastic stroma (Sirius red, trichrome), and prominent inflammatory leukocytic infiltrate (CD45). Flow cytometry analysis of end-stage orthotopically implanted tumors demonstrated a progressive expansion of myeloid cells (70.7% CD11b+) compared to CD8+ (0.8%) and CD4+ (2.0%) T cells, indicative of a highly immunosuppressive tumor immune microenvironment. Combination therapy with GM-CSF neutralization and chemotherapy significantly reduced tumor size as screened via US compared to vehicle (p&lt;0.0001), anti-GM-CSF (p&lt;0.01), and chemotherapy alone (p&lt;0.01). In addition, combination therapy reduced the rate of tumor growth compared to each of the three other treatment groups (all p&lt;0.0001). Finally, tumor weights were significantly reduced in the combination therapy group versus the vehicle (p&lt;0.0001), anti-GM-CSF (p&lt;0.001), and chemotherapy alone (p&lt;0.05) cohorts. Conclusion: Human CCA demonstrates elevated levels of GM-CSFRα compared to normal liver. Neutralization of GM-CSF in combination with chemotherapy reduced tumor growth and weight in a novel murine model of CCA. Targeting the GM-CSF/GM-CSFRα pathway represents an innovative means of improving tumor control in CCA.

Citation Format: Yatee A Dave, Paul R Burchard, Nicholas A Ullman, Mary Georger, Luis I Ruffolo, Brian A Belt, David C Linehan. GM-CSF neutralization enhances the efficacy of chemotherapy in an orthotopic murine model of cholangiocarcinoma [abstract]. In: Proceedings of the AACR Special Conference: Advances in the Pathogenesis and Molecular Therapies of Liver Cancer; 2022 May 5-8; Boston, MA. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(17_Suppl):Abstract nr PO025.

Abstract PO024: Combination therapy with PXS-5505 improves chemotherapeutic efficacy and reduces myeloid immune suppression in murine cholangiocarcinoma – a novel therapeutic strategy for clinical translation

Introduction: Despite growing prevalence, 5-year survival for cholangiocarcinoma remains poor due to an immunosuppressive fibroinflammatory stroma, featuring abundant collagen and cancer-associated fibroblasts. Lysyl oxidases (LOX) consist of 5 secreted enzymes that catalyze collagen cross-linking, resulting in increased tumor stroma density and facilitate immune evasion. Here, we present our findings of pan-LOX inhibition with a novel orally dosed agent (PXS-5505) in a murine model of CCA. Methods: Immunohistochemistry (IHC) analysis was performed on a human tissue macro-array of CCA. Mice that develop spontaneous CCA (KPPC) or orthotopically injected with a syngeneic cell line derived from a KPPC tumor were screened for disease onset and progression with ultrasonography (U/S). Groups of KPPC mice or mice bearing orthotopic tumors were enrolled into treatment cohorts of chemotherapy with or without PXS-5505 to evaluate survival and to perform fixed time point studies with treated tumors including assessment of intratumoral interstitial fluid pressure (IFP), IHC analysis of tumor markers, chemotherapy drug perfusion into tumors by mass spectrometry, and flow cytometry analysis of tumor single cell suspensions for stromal and immune cell populations. Results: IHC analysis demonstrated significantly elevated LOX expression in both human and KPPC CCA (p&lt;0.0001 and p=0.0025, respectively) compared to normal liver controls. High LOX expression was associated with worse disease-free (p=0.02) and overall (p=0.03) survival in resected human CCA specimens. KPPC mice treated with the combination of chemotherapy plus PXS-5505 demonstrated delayed tumor growth (p&lt;0.0001) and ascites onset (p=0.005) with improved survival (median 77 vs. 59 days, p=0.001) compared to chemotherapy alone. In addition, combination therapy reduced IFP (p=0.002) and was associated with increased mean blood vessel area (p&lt;0.0001) and increased concentration of intratumoral chemotherapy levels (p=0.02) compared to chemotherapy alone. Subsequent IHC revealed increased cell death through cleaved caspase-3 (p=0.0003) and damage-associated molecular pattern (DAMP) release through HMGB1 (p=0.0004). Flow cytometry analysis of tumors treated with combination therapy demonstrated reduced prevalence of tumor-infiltrating monocytic and granulocytic myeloid-derived suppressor cell populations (p=0.002 and p=0.01, respectively) and tumor associated macrophages (TAMs; p=0.02). There were increased CD4+ (p=0.01) T-cells with a reduced proportion of Treg+CD4+ (p&lt;0.0001) T-cells. The ratio of CD8:Treg was significantly elevated in the combination therapy cohort (p=0.001) and depletion of T-cells in orthotopic tumors abrogated the improved survival with combination therapy. Conclusions: LOX is elevated in human CCA and its expression correlates with prognosis following resection. Combination therapy with PXS-5505 delays tumor progression and improves survival in murine CCA models. Thus, chemotherapy combined with PXS-5505 represents a novel therapeutic strategy for treating CCA.

Citation Format: Paul R Burchard, Luis I Ruffolo, Nicholas A Ullman, Yatee Dave, Benjamin Dale, Mary Georger, Rachel Jewell, Nabeel Badri, Brian A Belt, David C Linehan, Roberto Hernandez-Alejandro. Combination therapy with PXS-5505 improves chemotherapeutic efficacy and reduces myeloid immune suppression in murine cholangiocarcinoma – a novel therapeutic strategy for clinical translation [abstract]. In: Proceedings of the AACR Special Conference: Advances in the Pathogenesis and Molecular Therapies of Liver Cancer; 2022 May 5-8; Boston, MA. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(17_Suppl):Abstract nr PO024.

Immunologic Strategies in Pancreatic Cancer: Making Cold Tumors Hot

The rising incidence and persistent dismal 5-year overall survival of pancreatic ductal adenocarcinoma (PDAC) highlight the need for new effective systemic therapies. Immunotherapy has shown significant benefits in solid organ tumors, but has thus far been disappointing in the treatment of PDAC. There have been several promising preclinical studies, but translation into the clinic has proved to be challenging. This is likely a result of PDAC's complex immunosuppressive tumor microenvironment that acts to insulate the tumor against an effective cytotoxic immune response. Here, we summarize the mechanisms of immunosuppression within the PDAC tumor microenvironment and provide an up-to-date review of completed and ongoing clinical trials using various immunotherapy strategies.

GM-CSF drives myelopoiesis, recruitment and polarisation of tumour-associated macrophages in cholangiocarcinoma and systemic blockade facilitates antitumour immunity

OBJECTIVE

Intrahepatic cholangiocarcinoma (iCCA) is rising in incidence, and at present, there are limited effective systemic therapies. iCCA tumours are infiltrated by stromal cells, with high prevalence of suppressive myeloid populations including tumour-associated macrophages (TAMs) and myeloid-derived suppressor cells (MDSCs). Here, we show that tumour-derived granulocyte-macrophage colony-stimulating factor (GM-CSF) and the host bone marrow is central for monopoiesis and potentiation of TAMs, and abrogation of this signalling axis facilitates antitumour immunity in a novel model of iCCA.

METHODS

Blood and tumours were analysed from iCCA patients and controls. Treatment and correlative studies were performed in mice with autochthonous and established orthotopic iCCA tumours treated with anti-GM-CSF monoclonal antibody.

RESULTS

Systemic elevation in circulating myeloid cells correlates with poor prognosis in patients with iCCA, and patients who undergo resection have a worse overall survival if tumours are more infiltrated with CD68+ TAMs. Mice with spontaneous iCCA demonstrate significant elevation of monocytic myeloid cells in the tumour microenvironment and immune compartments, and tumours overexpress GM-CSF. Blockade of GM-CSF with a monoclonal antibody decreased tumour growth and spread. Mice bearing orthotopic tumours treated with anti-GM-CSF demonstrate repolarisation of immunosuppressive TAMs and MDSCs, facilitating T cell response and tumour regression. GM-CSF blockade dampened inflammatory gene networks in tumours and TAMs. Human tumours with decreased GM-CSF expression exhibit improved overall survival after resection.

CONCLUSIONS

iCCA uses the GM-CSF-bone marrow axis to establish an immunosuppressive tumour microenvironment. Blockade of the GM-CSF axis promotes antitumour T cell immunity.

A phase I study to evaluate the safety and tolerability of SX-682 in combination with PD-1 inhibitor as maintenance therapy for unresectable pancreatic adenocarcinoma

TPS631

Background: Survival outcomes for advanced pancreatic ductal adenocarcinoma (PDAC) remain dismal despite improvements in systemic therapy regimens developed over the past decade. In addition, current first-line therapies result in cumulative cytopenias and neuropathy, highlighting the need for more effective, less toxic maintenance treatment strategies. There are currently no standard approved maintenance treatments for patients with PDAC not associated with BRCA or DNA-repair mutations. Pre-clinical data suggest a potential synergistic effect of combining blockade of CXC chemokine receptors (CXCR) with immunotherapy or chemotherapy in pancreatic cancer1,2. We are currently conducting a Phase I study (NCT04477343) evaluating SX-682, an oral CXCR1/2 inhibitor, and Nivolumab as maintenance treatment for advanced PDAC. Methods: This is an open-label, dose escalation Phase I clinical trial evaluating the combination of SX-682 and Nivolumab. Patients must have histologically confirmed unresectable PDAC and have completed at least 16 weeks of first-line chemotherapy with disease stability or treatment response at time of enrollment. Radiographically measurable disease must be present per iRECIST criteria. Patients receive a 3-week run-in phase of twice-daily dosing of SX-682, followed by combination of twice-daily dosed SX-682 and every 2-week Nivolumab (240 mg IV). Dose finding of SX-682 is performed using Bayesian optimal interval (BOIN) design to determine the maximum tolerated dose (MTD) when combined with Nivolumab. Pre-treatment and one on treatment (Day 28-35) biopsies are required for enrollment to evaluate change in tumor microenvironment immune cell composition by single cell-RNA sequencing, flow cytometry, RNA RT-qPCR, and IHC. The primary endpoint is to determine MTD; the key secondary endpoint is progression-free survival (PFS), defined as the time from enrollment to progression via iRECIST criteria or death. Nine of a planned 20 patients have been enrolled. Dose-level 1 (SX-682 50 mg BID) completed enrollment without dose-limiting toxicity (DLT). Dose-level 2, which commenced in June 2021, (SX-682 100 mg BID) is without DLTs, but has not completed enrollment at time of abstract submission.

Nywening TM, Belt BA, Cullinan DR, et al. Targeting both tumour-associated CXCR2(+) neutrophils and CCR2(+) macrophages disrupts myeloid recruitment and improves chemotherapeutic responses in pancreatic ductal adenocarcinoma. 1) Gut. 2018;67(6):1112-1123.

Steele CW, Karim SA, Leach JDG, et al. CXCR2 Inhibition Profoundly Suppresses Metastases and Augments Immunotherapy in Pancreatic Ductal Adenocarcinoma. 2) Cancer Cell. 2016;29(6):832-845. Clinical trial information: NCT04477343.

The impact of CA 19-9 on survival in patients with clinical stage I pancreatic cancer

606

Background: Standard of care for early-stage resectable pancreatic cancer (PC) includes a combination of surgical resection and chemotherapy. Frequently, CA 19-9 is used as a biomarker to monitor treatment effect and has prognostic significance. We evaluated the impact of CA 19-9 on overall survival (OS) in patients with clinical stage I PC (cT1N0 and cT2N0) utilizing the National Cancer Database (NCDB). Methods: The NCDB was queried between 2010 and 2014 to identify patients with clinical stage I PC. Patients who had missing or undocumented CA 19-9 value at diagnosis were excluded. Demographic and clinical characteristics were analyzed. Patients were stratified into two cohorts based on the CA 19-9 value at diagnosis – CA 19-9 < 98 U/mL and CA 19-9 > 98 U/mL. Univariable and multivariable analyses were performed, and variables associated with OS were identified. Kaplan-Meier survival curves were computed to compare the OS between the two cohorts. Results: A total of 12,480 patients met our inclusion criteria. A majority of patients were female (51.9%), white (84.4%), with a median age of 70 years. Nearly, half the patients received care in an academic/research program (49.5%). A majority of patients had tumors located in the head of the pancreas (71.9%), and received single-agent (35.1%) or multiagent (22.9%) chemotherapy. Over half the patients (6505 patients, 52.1%) had a CA 19-9 value > 98 U/mL. A CA 19-9 value > 98 U/mL in patients predicted a significantly shorter median OS of 12.1 months compared to 19.4 months in patients with a CA 19-9 < 98 U/mL, p<0.0001 (Table). The 5-year OS rate was 9.9% in patients with a CA 19-9 value of > 98 U/mL compared to a 5-year OS rate of 18.1% for patients with a CA 19-9 value < 98 U/mL. On multivariable analysis, CA 19-9 > 98 compared to CA 19-9 < 98 (HR 1.53, p<0.001) and black race compared to white race (HR 1.10, p<0.001) was associated with worse survival, whereas tumor location in the body and tail compared to the head (HR 0.82, p<0.001), single-agent (HR 0.55, p<0.001) and multiagent (HR 0.55, p<0.001) chemotherapy compared to no chemotherapy, independently predicted improved OS. Conclusions: This is the first National Cancer Database study to demonstrate the prognostic value of CA 19-9 in patients with clinical stage I pancreatic cancer, with a value < 98 U/mL predicting improved survival. Clinical stage I pancreatic cancer patients appear to derive a significant benefit from chemotherapy, including single and multiagent chemotherapy, irrespective of the CA 19-9 value.[Table: see text]

Association of suboptimal lymph node yield with inferior survival in resected stage 1 colon cancer patients

3601

Background: A minimum of 12 lymph nodes are required during colectomy to accurately stage colon cancer. Prior studies in stage II colon cancer patients demonstrate association of inadequate lymph node examination (LNE) with worse overall survival (OS). No large-scale analogous studies related to LNE have been completed in stage I colon cancer patients. We evaluated patients with stage I colon cancer to determine the association between lymph node yield and OS. Methods: We reviewed the National Cancer Database between 2004-2015 to identify patients with pathologic stage I colon cancer (pT1N0 or pT2N0) who underwent definitive surgical resection. Patients who received radiation therapy or had missing values were excluded. Clinical and demographic characteristics were analyzed. Based on LNE, patients were stratified into 4 cohorts (LNE, 0-5, 6-11, 12-19, 20+) and 2 cohorts (0-11, 12+). Univariable and multivariable analyses were performed to identify variables associated with OS. Kaplan-Meier survival curves were computed to compare the cohorts. Results: We included 81,909 patients for analyses. Median age at diagnosis was 69. A majority were female (51.1%), white (83.8%), received care in a community cancer program (59.5%), and had a Charlson-Deyo score of 0 (66.6%). Only 0.7% of patients had a margin positive resection with a 2.5cm median tumor size. Patients were similarly split between pT1 and pT2. Suboptimal LNE was noted in 27.8% of patients. Patients with LNE were distributed - 10.7% (0-5), 17.1% (6-11), 43.4% (12-19) and 28.9% (20+). Postoperative 30-day mortality was 1.9%. 521 (0.7%) received systemic therapy. Ten-year survival in patients with 0-5 LNE was 52.8% compared to 60.1% with 20+ LNE. On multivariable analyses, patients aged ≥ 69, male sex, increasing tumor size (quartile), pT2 staging and a higher Charlson-Deyo score independently predicted worse OS (p < 0.001). LNE categories were significantly associated with OS (p < 0.001) (Table). On regrouping into 0-11 and 12+ LNE groups, 0-11 LNE group predicted worse OS (HR 1.22, p < 0.001). On multivariable analysis, the above variables continued to show similar association with OS (p < 0.001). Conclusions: Our study demonstrates that lymph node yield is associated with overall survival in patients with stage 1 colon cancer undergoing surgical resection. Furthermore, patients with suboptimal lymph node yield are associated with an inferior overall survival compared to those with optimal lymph node yield. Moreover, this study finds that a large number of patients ( > 25%) continue to have suboptimal lymph node yields. Future efforts should focus on improving the lymph node yield with optimal efforts by the surgeon and pathologist. Future studies should examine the role of systemic therapy in patients with inadequate lymph node yield.[Table: see text]

Antibody blockade of semaphorin 4D to sensitize pancreatic cancer to immune checkpoint blockade

26

Background: Pancreatic ductal adenocarcinoma (PDAC) carries a dismal prognosis, and will soon become the second leading cause of cancer mortality. Unfortunately, T-cell directed immunotherapies have failed to demonstrate efficacy in PDAC. These failures may in part be mediated by an immunosuppressive tumor microenvironment (TME). Semaphorin 4D (Sema4D) is a glycoprotein which binds its cognate receptors Plexin B1/B2. Here we present our work in blocking Sema4D in a murine model of PDAC. Methods: C57b/6 mice were orthotopically injected with PDAC line (KP2) derived from KRASG12D,TP53Flox/Wt;P48-Cre autochthonous tumors and confirmed for disease by ultrasound. Mice were treated with FOLFIRINOX (5-FU, Irinotecan, Oxaliplatin, weekly), immune checkpoint blockade (ICB) (anti-PD1, anti-CTLA-4 mAbs bi-weekly), and anti-Sema4D mAB (bi-weekly). Human and mouse circulating and tumor infiltrating leukocytes were interrogated through flow cytometry (FACS) for immune subset and expression of Sema4D and Plexin receptors. Archived human PDAC tissues were assessed through quantitative immunohistochemistry (IHC) for presence of Sema4D positive infiltrate. Results: Both FACS and IHC analysis of human PDAC specimens confirm the presence and increased prevalence over normal pancreata of Sema4D lymphocytes and Plexin B1/B2 expressing tumor associated macrophages (TAMs). KP2 orthotopically injected mice exhibited longer survival when treated with the triple combination of FOLFIRINOX, ICB, and anti-Sema4D antibody, compared to FOLFIRINOX alone, FOLFIRINOX plus ICB, or FOLFIRINOX plus anti-Sema4D antibody (P < 0.02). Flow cytometric analysis of anti-Sema4D and ICB treated murine tumors show a doubling of penetration by CD 8+ effector T cells within tumors compared to control groups (P = 0.03). A loss in Sema4D fluorescence signal via FACS in tumor-infiltrating CD3+ leukocytes was observed in mice treated with anti-SEMA4D, confirming penetration and target blockade within the TME. Conclusions: Sema4D and Plexin B1/B2 leukocytes penetrate human PDAC tumors, and treatment with Sema4D blocking antibody improved response to ICB in combination with standard of care FOLFIRINOX in preclinical murine studies.

CXCR1/2 blockade to enhance response to immune checkpoint inhibition in an aggressive orthotopic pancreatic adenocarcinoma model

19

Background: Pancreatic adenocarcinoma (PDAC) is the fourth leading cause of cancer related deaths, with the incidence expected to rise in the coming years. Despite conventional chemotherapy and advances in immune checkpoint blockade, 5 year survival remains a dismal 8%. Intratumoral accumulation of granulocytic myeloid derived suppressor cells (G-MDSC) pose a significant barrier to treatment as they contribute to immune evasion by PDAC and correlate with poor prognosis. The ELR+ CXC chemokine receptors CXCR1 and CXCR2 (CXCR1/2) contribute to peripheral neutrophil migration into tissues and have been implicated in tumor mediated G-MDSC recruitment to the tumor microenvironment. Here we present our findings using an orally dosed CXCR1/2 inhibitor, SX-682, in an orthotopic PDAC model. Methods: C57BL/6 mice underwent orthotopic injections with KP2 cells. Mice were randomized into five groups (Table) receiving three weeks of FOLFIRINOX with combinations of SX-682 and/or checkpoint inhibition (anti-PD1/anti-CTLA4). FOLFIRINOX was dosed weekly for three weeks. Checkpoint inhibition was administered twice weekly. Chow weights were monitored for consumption of SX-682. Results: The simultaneous administration of FOLFIRINOX with SX-682 combined with checkpoint inhibition (triple therapy) resulted in a significant increase in survival compared to other groups (p = 0.0001). Notably, there was a significant increase in survival with triple therapy versus FOLFIRINOX plus checkpoint alone (p = 0.0259). Median survival of the triple therapy group was 42.5 days, compared to 37 days with checkpoint inhibition (p = <0.05). There were no differences in chow consumption between the control and medicated chow groups. Conclusions: CXCR1/2 blockade combined with immune checkpoint inhibition and first line chemotherapy significantly enhanced survival in our PDAC mouse model. Thus, CXCR1/2 inhibition with SX-682 represents a promising target for clinical intervention in PDAC. [Table: see text]

Association of CXCR2+ granulocytic myeloid derived suppressor cells with the development of cholangiocarcinoma: A possible target for intervention

565

Background: Cholangiocarcinoma (CCA) is the second most common primary liver malignancy, with increasing incidence. Currently, surgical resection offers the only chance for cure, however the prognosis remains poor in part due to high rates of unresectability, recurrence, and poor response to conventional therapy. Thus, new systemic therapies represent an unmet medical need. Few preclinical models exist for identifying and testing new targeted or immune based therapies. Here we present our findings of the immune infiltrate in human CCA tumor microenvironment (TME) and a spontaneous murine model that faithfully recapitulates human disease. Methods: Histology and immunohistochemistry (IHC) staining was performed on human CCA and adjacent normal liver. Mice with targeted hepatic Kras activation and loss of p53 (KPPC) spontaneously develop CCA. KPPC hepatic tumors and normal livers from littermate controls underwent histological and gene expression studies. Flow cytometric analysis was performed on bone marrow, spleen, peripheral blood, CCA tumors and normal littermate livers. Results: Digital IHC quantification of archival human CCA specimens demonstrated elevated levels of CD15+CXCR2+ granulocytic myeloid derived suppressor cells (G-MDSC) compared to adjacent normal liver (p = < 0.05). In addition, the CXCR2 ligand, CXCL5, was significantly elevated in CCA tumors compared to adjacent normal liver. In KPPC mice, flow cytometric analysis of hepatic tumors showed an abundance of CD45+ leukocytes comprised of immunosuppressive G-MDSC vs normal littermate controls (p = 0.0007) which recapitulates human disease. qRT-PCR demonstrated significantly increased expression of G-csf, Csf1, Cxcl1, Cxcl2, and Cxcl5 (p = < 0.0001) in CCA KPPC tumors compared to normal livers. Accordingly, granulocytes in KPPC mice were elevated in both the bone marrow and blood compared to normal littermate controls. Conclusions: These data suggest CCA co-opts the ELR+ cytokine/CXCR2 axes to mobilize and recruit immunosuppressive G-MDSC to the TME. Targeted therapy against tumor infiltrating neutrophils can be tested in this pre-clinical model to inform clinical translation.