Inhibiting PI3 kinase-γ in both myeloid and plasma cells remodels the suppressive tumor microenvironment in desmoplastic tumors
Graphical abstract
Introduction
Pancreatic cancer is a malignant disease with a high mortality rate. The total number of deaths from pancreatic cancer is steadily increasing, with pancreatic cancer expected to be the second leading cause of cancer death in the USA by 2030 [45]. Historically, chemotherapy or radiotherapy did not reach satisfactory survival benefit in advanced pancreatic cancer. Recent studies have revealed that immunosuppression and inflammation are related to oncogenesis, as well as tumor development, invasion, and metastasis in pancreatic adenocarcinoma (PAC). Therefore, immunosuppression associated signaling, especially when it involves immune checkpoint and inflammation, has served as a novel treatment target for PAC. There is a highly immunosuppressive microenvironment regulated by immune cells, stromal cells, and mediators in PAC. This condition may result in its resistance to immune checkpoint therapy [24].
Tumor-associated macrophages and myeloid-derived suppressor cells (MDSC) are immunosuppressive, and a high ratio of suppressive cells to CD4+ and CD8+ T cells is related to poor survival of PAC patients [24]. MDSC levels are increased both in the circulation and in the microenvironment of PAC. Inhibition of MDSC in PAC is a potential method of cancer therapy [51]. Phosphoinositide-3-kinases (PI3Ks) pertain to signal transducing enzymes that play an important role in cancer and immunity. PI3K-γ signaling is especially pivotal for the function of myeloid cells, where it is downstream of G-protein coupled receptors (GPCRs) (e.g., chemokine receptors) and RAS [22,49,50]. For instance, murine syngeneic tumors grow slower when transplanted into immune-competent mice where PI3K-γ is genetically inactivated [25,50]. This growth reduction occurs because of the abrogation of tumor-associated myeloid cells that are known to promote an immune-suppressive tumor microenvironment (TME) that permits tumor growth [18,25,46,50]. In addition, MDSCs are associated with tumor regrowth after radiation or chemotherapy, and are known to lead to metastatic spread [8]. These preclinical studies highlight an important role for PI3K-γ in myeloid cell biology and suggest that PI3K-γ inhibition in MDSC may be effective at inhibiting tumor growth in a variety of settings.
IPI-549 can reduce the T-cell-suppressive activity of both murine and human myeloid-derived suppressor cells in vitro [6]. These findings indicate that IPI-549 increases antitumor immunity by remodeling the tumor-immune microenvironment via blockade of tumor-associated myeloid cells. In addition, the up-regulations of costimulatory and coinhibitory genes with IPI-549 treatment provides a mechanistic rationale for the observed combination activity with immune checkpoint inhibition. IPI-549 is currently in phase I development, both as a single agent and in combination with an anti-PD-1 antibody, in solid tumors [40].
B cells have been typical of positive regulators of humoral immune response and are characterized by their ability to terminally differentiate into antibody-secreting plasma cells [9,33]. B-cell inhibition of an immune response was first reported in 1974; spleen B-cells were found to impair delayed type hypersensitivity response in guinea pigs [30,41]. B cells are now regarded as an important ingredient of the immune suppression system. A potential therapeutic strategy for PAC would include targeted B-cell suppression [18,35,44,47].
Nanoparticles (NPs) can prolong the half-life of payloads in vivo and passively accumulate in the tumor regions via the enhanced permeability and retention (EPR) effect [19,39,57]. Numerous anti-tumor or immune-stimulating agents have been delivered by NPs [6,58]. For example, a Toll-like-receptor-7 agonist was encapsulated by poly(lactic-co-glycolic) acid (PLGA) [28]. In the current study, targeted IPI-549 NP was designed to improve the bioavailability and therapeutic activity. We hypothesized that tumor-targeted IPI-549 could reshape the tumor immune microenvironment and reverse its immune suppression more effectively than the oral dosage form.
Section snippets
Materials
IPI-549 was purchased from Chemietek (Indianapolis, IN, USA). Acid-terminated PLGA (lactide/glycolide (50:50)) was purchased from DURECT (Pelham, AL, USA). mPEG3500-NH2·HCl and tBOC-PEG3500-NH2·HCl were purchased from JenKem Technology USA, Inc. (Allen, TX). PLGA-PEG and PLGA-PEG-AEAA were synthesized according to our previous work, and the structures were confirmed by 1H NMR [20]. If not specifically mentioned, all other chemicals were purchased from Sigma-Aldrich (St. Louis, MO, USA).
Cell culture
The
PI3K-γ in B cells
During inflammation and cancer, PI3K-γ controls a critical switch between immune stimulation and suppression. Previous studies have shown that PI3K-γ is highly expressed in myeloid cells [29]. As shown in Fig. 1, we demonstrated that PI3K-γ was also highly expressed in B cells associated with both KPC pancreatic cancer and BPD6 melanoma models. Both tumor models contained extensive stroma structure (Fig. S1), which is typical of an immune-suppressive microenvironment [37]. BRAF mutation is very
Discussion
Breg cells produce large amounts of cytokines such as IL-10, TGF-β, and IL-35, which suppress the differentiation of pro-inflammatory lymphocytes, such as tumor necrosis factor α (TNF-α)-producing monocytes, IL-12-producing dendritic cells, Th17 cells, Th 1 cells, and cytotoxic CD8+ T cells [36,53,55]. Breg cells can also result in the differentiation of immune-suppressive T cells, Foxp3+ T cells, and T regulatory 1 (Tr1) cells [3,12]. According to previous studies [6,29], PI3K-γ is highly
Author contributions
XZ, LS and LH (Huang) designed the study. XZ, LS, QL and LH (Hou) performed experiments and analyzed the data. XZ, LS and LH (Huang) wrote the manuscript, with help of QL for revisions. QL designed the graphical abstract.
Acknowledgments
This work was supported by NIH grant CA198999 and Eshelman Institute for Innovation.
References (59)
- et al.
Tumor-derived granulocyte-macrophage colony-stimulating factor regulates myeloid inflammation and T cell immunity in pancreatic cancer
Cancer Cell
(2012) - et al.
Tumor-associated transforming growth factor-β and interleukin-10 contribute to a systemic Th2 immune phenotype in pancreatic carcinoma patients
Am. J. Pathol.
(1999) - et al.
Tumor microenvironment-responsive micelles for pinpointed intracellular release of doxorubicin and enhanced anti-cancer efficiency
Int. J. Pharm.
(2016) - et al.
Macrophage regulation of tumor responses to anticancer therapies
Cancer Cell
(2013) Activated pancreatic stellate cells sequester CD8+ T cells to reduce their infiltration of the juxtatumoral compartment of pancreatic ductal adenocarcinoma
Gastroenterology
(2013)- et al.
Nanoparticle containing insoluble drug for cancer therapy
Biotechnol. Adv.
(2014) - et al.
B-lymphocytes: how they develop and function
Blood
(2008) Interleukin-10-producing plasmablasts exert regulatory function in autoimmune inflammation
Immunity
(2014)- et al.
IL-35 promotes pancreas cancer growth through enhancement of proliferation and inhibition of apoptosis: evidence for a role as an autocrine growth factor
Cytokine
(2014) - et al.
Oncogenic Kras-induced GM-CSF production promotes the development of pancreatic neoplasia
Cancer Cell
(2012)