Jonathan B. Mitchem

Targeting Tumor-Infiltrating Macrophages Decreases Tumor-Initiating Cells, Relieves Immunosuppression, and Improves Chemotherapeutic Responses

Tumor-infiltrating immune cells can promote chemoresistance and metastatic spread in aggressive tumors. Consequently, the type and quality of immune responses present in the neoplastic stroma are highly predictive of patient outcome in several cancer types. In addition to host immune responses, intrinsic tumor cell activities that mimic stem cell properties have been linked to chemoresistance, metastatic dissemination, and the induction of immune suppression. Cancer stem cells are far from a static cell population; rather, their presence seems to be controlled by highly dynamic processes that are dependent on cues from the tumor stroma. However, the impact immune responses have on tumor stem cell differentiation or expansion is not well understood. In this study, we show that targeting tumor-infiltrating macrophages (TAM) and inflammatory monocytes by inhibiting either the myeloid cell receptors colony-stimulating factor-1 receptor (CSF1R) or chemokine (C-C motif) receptor 2 (CCR2) decreases the number of tumor-initiating cells (TIC) in pancreatic tumors. Targeting CCR2 or CSF1R improves chemotherapeutic efficacy, inhibits metastasis, and increases antitumor T-cell responses. Tumor-educated macrophages also directly enhanced the tumor-initiating capacity of pancreatic tumor cells by activating the transcription factor STAT3, thereby facilitating macrophage-mediated suppression of CD8(+) T lymphocytes. Together, our findings show how targeting TAMs can effectively overcome therapeutic resistance mediated by TICs.

Inflammatory Monocyte Mobilization Decreases Patient Survival in Pancreatic Cancer: A Role for Targeting the CCL2/CCR2 Axis

Purpose: To determine the role of the CCL2/CCR2 axis and inflammatory monocytes (CCR2+/CD14+) as immunotherapeutic targets in the treatment of pancreatic cancer. Experimental Design: Survival analysis was conducted to determine if the prevalence of preoperative blood monocytes correlates with survival in patients with pancreatic cancer following tumor resection. Inflammatory monocyte prevalence in the blood and bone marrow of patients with pancreatic cancer and controls was compared. The immunosuppressive properties of inflammatory monocytes and macrophages in the blood and tumors, respectively, of patients with pancreatic cancer were assessed. CCL2 expression by human pancreatic cancer tumors was compared with normal pancreas. A novel CCR2 inhibitor (PF-04136309) was tested in an orthotopic model of murine pancreatic cancer. Results: Monocyte prevalence in the peripheral blood correlates inversely with survival, and low monocyte prevalence is an independent predictor of increased survival in patients with pancreatic cancer with resected tumors. Inflammatory monocytes are increased in the blood and decreased in the bone marrow of patients with pancreatic cancer compared with controls. An increased ratio of inflammatory monocytes in the blood versus the bone marrow is a novel predictor of decreased patient survival following tumor resection. Human pancreatic cancer produces CCL2, and immunosuppressive CCR2+ macrophages infiltrate these tumors. Patients with tumors that exhibit high CCL2 expression/low CD8 T-cell infiltrate have significantly decreased survival. In mice, CCR2 blockade depletes inflammatory monocytes and macrophages from the primary tumor and premetastatic liver resulting in enhanced antitumor immunity, decreased tumor growth, and reduced metastasis. Conclusions: Inflammatory monocyte recruitment is critical to pancreatic cancer progression, and targeting CCR2 may be an effective immunotherapeutic strategy in this disease. Clin Cancer Res; 19(13); 3404–15. ©2013 AACR.

Pancreatic adenocarcinoma induces bone marrow mobilization of myeloid-derived suppressor cells which promote primary tumor growth

PurposeMyeloid-derived suppressor cells (MDSC) are a heterogeneous population of immunosuppressive cells that are upregulated in cancer. Little is known about the prevalence and importance of MDSC in pancreas adenocarcinoma (PA).Experimental designPeripheral blood, bone marrow, and tumor samples were collected from pancreatic cancer patients, analyzed for MDSC (CD15+CD11b+) by flow cytometry and compared to cancer-free controls. The suppressive capacity of MDSC (CD11b+Gr-1+) and the effectiveness of MDSC depletion were assessed in C57BL/6 mice inoculated with Pan02, a murine PA, and treated with placebo or zoledronic acid, a potent aminobisphosphonate previously shown to target MDSC. The tumor microenvironment was analyzed for MDSC (Gr1+CD11b+), effector T cells, and tumor cytokine levels.ResultsPatients with PA demonstrated increased frequency of MDSC in the bone marrow and peripheral circulation which correlated with disease stage. Normal pancreas tissue showed no MDSC infiltrate, while human tumors avidly recruited MDSC. Murine tumors similarly recruited MDSC that suppressed CD8+ T cells in vitro and accelerated tumor growth in vivo. Treatment with zoledronic acid impaired intratumoral MDSC accumulation resulting in delayed tumor growth rate, prolonged median survival, and increased recruitment of T cells to the tumor. This was associated with a more robust type 1 response with increased levels of IFN-γ and decreased levels of IL-10.ConclusionsMDSC are important mediators of tumor-induced immunosuppression in pancreatic cancer. Inhibiting MDSC accumulation with zoledronic acid improves the host anti-tumor response in animal studies suggesting that efforts to block MDSC may represent a novel treatment strategy for pancreatic cancer.

Induction of Th17 Cells in the Tumor Microenvironment Improves Survival in a Murine Model of Pancreatic Cancer

An important mechanism by which pancreatic cancer avoids antitumor immunity is by recruiting regulatory T cells (Tregs) to the tumor microenvironment. Recent studies suggest that suppressor Tregs and effector Th17 cells share a common lineage and differentiate based on the presence of certain cytokines in the microenvironment. Because IL-6 in the presence of TGF-β has been shown to inhibit Treg development and induce Th17 cells, we hypothesized that altering the tumor cytokine environment could induce Th17 and reverse tumor-associated immune suppression. Pan02 murine pancreatic tumor cells that secrete TGF-β were transduced with the gene encoding IL-6. C57BL/6 mice were injected s.c. with wild-type (WT), empty vector (EV), or IL-6–transduced Pan02 cells (IL-6 Pan02) to investigate the impact of IL-6 secretion in the tumor microenvironment. Mice bearing IL-6 Pan02 tumors demonstrated significant delay in tumor growth and better overall median survival compared with mice bearing WT or EV Pan02 tumors. Immunohistochemical analysis demonstrated an increase in Th17 cells (CD4+IL-23R+ cells and CD4+IL-17+ cells) in tumors of the IL-6 Pan02 group compared with WT or EV Pan02 tumors. The upregulation of IL-17–secreting CD4+ tumor-infiltrating lymphocytes was substantiated at the cellular level by flow cytometry and ELISPOT assay and mRNA level for retinoic acid-related orphan receptor γt and IL-23R by RT-PCR. Thus, the addition of IL-6 to the tumor microenvironment skews the balance toward Th17 cells in a murine model of pancreatic cancer. The delayed tumor growth and improved survival suggests that induction of Th17 in the tumor microenvironment produces an antitumor effect.

Long-term results of resection of adenocarcinoma of the body and tail of the pancreas using radical antegrade modular pancreatosplenectomy procedure.

BACKGROUND The radical antegrade modular pancreatosplenectomy (RAMPS) procedure is a modification of standard distal pancreatosplenectomy. It was designed to provide the operative approach developed for cancers of the head of the pancreas to cancers of the body and tail of the pancreas, particularly with respect to the extent of node dissection and emphasis on obtaining microscopically negative tangential margins. The purpose of this report is to provide long-term survival results. STUDY DESIGN Forty-seven patients had RAMPS between 1999 and 2008. The decision to perform anterior vs posterior RAMPS was based on the position of the tumor as assessed by preoperative computed tomograms. Patients were entered in a prospective database and followed at intervals. RESULTS Thirty-two patients had anterior RAMPS and 15 had posterior RAMPS. Twenty-four patients had resection of 33 organs in addition to the left adrenal gland in the posterior RAMPS. Specimens were inked in the operating room. Mean tumor size was 4.4 cm. Negative tangential margins were obtained in 89% of specimens. Overall, the R0 rate was 81%. Mean lymph node count was 18. There were no 30-day or in-hospital mortalities. Mean and median follow-up times of living patients were 44.4 and 26.4 months. Median survival was 26 months and 5-year overall actuarial survival was 35.5%. The actual survival of 23 patients whose surgery was performed more than 5 years before the time of analysis was 30.4%. CONCLUSIONS RAMPS is associated with high negative tangential margin rates and very satisfactory survival rates for this aggressive tumor.

Tumor-induced STAT3 activation in monocytic myeloid-derived suppressor cells enhances stemness and mesenchymal properties in human pancreatic cancer

Pancreatic cancer (PC) mobilizes myeloid cells from the bone marrow to the tumor where they promote tumor growth and proliferation. Cancer stem cells (CSCs) are a population of tumor cells that are responsible for tumor initiation. Aldehyde dehydrogenase-1 activity in PC identifies CSCs, and its activity has been correlated with poor overall prognosis in human PC. Myeloid cells have been shown to impact tumor stemness, but the impact of immunosuppressive tumor-infiltrating granulocytic and monocytic myeloid-derived suppressor cells (Mo-MDSC) on ALDH1Bright CSCs and epithelial to mesenchymal transition is not well understood. In this study, we demonstrate that Mo-MDSC (CD11b+/Gr1+/Ly6G−/Ly6Chi) significantly increase the frequency of ALDH1Bright CSCs in a mouse model of PC. Additionally, there was significant upregulation of genes associated with epithelial to mesenchymal transition. We also found that human PC converts CD14+ peripheral blood monocytes into Mo-MDSC (CD14+/HLA-DRlow/−) in vitro, and this transformation is dependent on the activation of the STAT3 pathway. In turn, these Mo-MDSC increase the frequency of ALDH1Bright CSCs and promote mesenchymal features of tumor cells. Finally, blockade of STAT3 activation reversed the increase in ALDH1Bright CSCs. These data suggest that the PC tumor microenvironment transforms monocytes to Mo-MDSC by STAT3 activation, and these cells increase the frequency of ALDH1Bright CSCs. Therefore, targeting STAT3 activation may be an effective therapeutic strategy in targeting CSCs in PC.

Myeloid-Derived Suppressor Cells: General Characteristics and Relevance to Clinical Management of Pancreatic Cancer

Recent studies describe a heterogeneous population of cells of the myeloid lineage, termed myeloid derived suppressor cells (MDSC), which are observed with increased prevalence in the peripheral blood and tumor microenvironment of cancer patients, including pancreatic cancer. Accumulation of MDSC in the peripheral circulation has been related to extent of disease, and correlates with stage. MDSC have primarily been implicated in promoting tumor growth by suppressing antitumor immunity. There is also compelling evidence MDSC are also involved in angiogenesis and metastatic spread. Two main subsets of MDSC have been identified in cancer patients: a monocytic subset, characterized by expression of CD14, and a granulocytic subset characterized by expression of CD15. Both subsets of MDSC actively suppress host immunity through a variety of mechanisms including production of reactive oxygen species and arginase. Just as in humans, accumulation of monocytic and granulocytic MDSC has been noted in the bone marrow, spleen, peripheral circulation, and tumors of tumor bearing mice. Successful targeting of MDSC in mice is associated with improved immune responses, delayed tumor growth, improved survival, and increased efficacy of vaccine therapy. By further elucidating mechanisms of MDSC recruitment and maintenance in the tumor environment, strategies could be developed to reverse immune tolerance to tumor. We discuss here what is currently known about MDSC as well as some potential strategies targeting MDSC in the context of our work on pancreatic cancer and recent literature. Due to the number of new reports on MDSC, the most pertinent ones have been selected.

The novel sigma-2 receptor ligand SW43 stabilizes pancreas cancer progression in combination with gemcitabine

BackgroundSigma-2 receptors are over-expressed in proliferating cancer cells, making an attractive target for the targeted treatment of pancreatic cancer. In this study, we investigated the role of the novel sigma-2 receptor ligand SW43 to induce apoptosis and augment standard chemotherapy.ResultsThe binding affinity for sigma-2 ligands is high in pancreas cancer, and they induce apoptosis with a rank order of SV119 < SW43 < SRM in vitro. Combining these compounds with gemcitabine further increased apoptosis and decreased viability. Our in vivo model showed that sigma-2 ligand treatment decreased tumor volume to the same extent as gemcitabine. However, SW43 combination treatment with gemcitabine was superior to the other compounds and resulted in stabilization of tumor volume during treatment, with minimal toxicities.ConclusionsThis study shows that the sigma-2 ligand SW43 has the greatest capacity to augment gemcitabine in a pre-clinical model of pancreas cancer and has provided us with the rationale to move this compound forward with clinical investigations for patients with pancreatic cancer.

Impact of neoadjuvant chemotherapy on rate of tissue expander/implant loss and progression to successful breast reconstruction following mastectomy

PURPOSE We examined the frequency and causes of tissue expander (TE) and permanent implant (PI) reconstruction failure in patients undergoing neoadjuvant chemotherapy. METHODS AND MATERIALS Charts were reviewed from 120 patients with clinical stage II/III breast cancer enrolled between 2004 and 2007 into a prospective clinical trial of neoadjuvant chemotherapy. Patient demographics, tobacco use, radiation treatment, and data relating to the loss of TE, as well as progression to PI and PI loss, were collected. RESULTS Of 120 patients, 61 underwent 75 mastectomies. Twenty-six patients had 34 TEs placed at the time of mastectomy. Eleven (32%) TEs required removal prior to definitive reconstruction. Fourteen (41%) TEs successfully progressed to PI exchange. Four of the PIs required removal. TE loss occurred most frequently due to infection and extrusion. Radiation, smoking history, or elevated body mass index (BMI) did not significantly affect reconstruction loss. CONCLUSION Thirty-eight percent of immediate TEs or PI placements at the time of mastectomy failed to progress to definitive reconstruction in patients receiving neoadjuvant therapy, suggesting that reconstruction with TEs or PI reconstruction should be used cautiously in this patient population.

A single-institution review of 157 patients presenting with benign and malignant tumors of the ampulla of Vater: Management and outcomes

BACKGROUND Although benign ampullary tumors are removed endoscopically, due to their potential to progress to malignant disease, the favored treatment for adenocarcinoma is pancreaticoduodenectomy. We reviewed our institutions experience in order to identify which patients were at highest risk of disease progression following surgical resection, as well as evaluate whether localized T1 tumors are best treated by pancreaticoduodenectomy. METHODS We retrospectively reviewed 157 patients who presented with an ampullary mass, from 2001 to 2010, and identified 51 with benign adenoma and 106 with adenocarcinoma. RESULTS Patients with malignant tumors most often presented with larger tumors and jaundice, which alone was predictive of survival (OR = 67). Forty-five percent of patients with pathologically confirmed T1 tumors had positive lymph nodes and median survival was modest at 60 months. Lymph node involvement was predictive of recurrence and decreased survival. CONCLUSION Patients with malignant tumors often present with jaundice and larger tumors. These findings should warrant suspicion for cancer and expedited preoperative workup. Based on our finding that nearly half the patients with T1 tumors had positive lymph nodes, we recommend pancreaticoduodenectomy for any patient with biopsy proven adenocarcinoma who is a suitable candidate for surgery.