Transient and Local Expression of Chemokine and Immune Checkpoint Traps To Treat Pancreatic Cancer

Abstract

Pancreatic tumors are known to be resistant to immunotherapy due to the extensive immune suppressive tumor microenvironment (TME). We hypothesized that CXCL12 and PD-L1 are two key molecules controlling the immunosuppressive TME. Fusion proteins, called traps, designed to bind with these two molecules with high affinity (Kd = 4.1 and 0.22 nM, respectively) were manufactured and tested for specific binding with the targets. Plasmid DNA encoding for each trap was formulated in nanoparticles and intravenously injected to mice bearing orthotopic pancreatic cancer. Expression of traps was mainly seen in the tumor, and secondarily, accumulations were primarily in the liver. Combination trap therapy shrunk the tumor and significantly prolonged the host survival. Either trap alone only brought in a partial therapeutic effect. We also found that CXCL12 trap allowed T-cell penetration into the tumor, and PD-L1 trap allowed the infiltrated T-cells to kill the tumor cells. Combo trap therapy also significantly reduced metastasis of the tumor cells to other organs. We conclude that the trap therapy significantly modified the immunosuppressive TME to allow the host immune system to kill the tumor cells. This can be an effective therapy in clinical settings.

Materials for Immunotherapy

“…Huang and co‐workers developed cationic liposome‐protamine‐HA nanoparticles to deliver siRNA to silence CD47 expression in solid tumors . Starting in 2017, the Huang group published a series of papers using a similar particle design (i.e., a liposome‐protamine‐DNA (LPD) nanoparticle) to deliver genes for various anticancer purposes, including those that encode for proteins that bind to (or trap): i) the immunosuppressive proteins PD‐L1 and C‐X‐C motif chemokine (CXCL)12, ii) the signaling protein Wnt family member 5A (Wnt5a), which has been implicated in inducing dendritic cell tolerance, iii) IL‐10, which is known to suppress dendritic cells from releasing IL‐12, to develop Th1 responses, iv) LPS, which relieved the immunosuppressive microenvironment and boosted anti‐PD‐L1 therapy against colorectal tumors, and v) CCR‐7, which is associated with the metastasis of breast cancer . The group also investigated the delivery of siRNA to silence high mobility group protein A1 (HMGA1), which is associated with immunosuppression .…”

Nanomaterials for cancer immunotherapy

“…The trimeric form of PD-L1 trap protein binds to mouse PD-L1 with a dissociation constant ( K d ) of 219 pM, a binding affinity more than a thousand times higher than that of monomeric PD-1 and PD-L1 (Fig. 7B) [171]. For local and transient expression of the PD-L1 trap protein, the optimized coding sequence for the monomeric trap was cloned into the expression vector pcDNA3.1, driven by a CMV promoter, and a strong signaling peptide from mouse serum albumin preproprotein was incorporated at the N-terminus to facilitate trap secretion from transfected cells after expression.…”

“…7C). This locally expressed PD-L1 blocker is promising in enhancing the therapeutic efficiency and reducing possible side effects of free anti-PD-L1 [171]. …”

“…Three injections of the LPD nanoparticles generated approximately 70% of TAFs as TRAIL-producing cells, and triggered apoptosis in the tumor cell nests adjacent to the TAFs [271]. Furthermore, when loading plasmids encoding CXCL12 fusion protein in the LPD nanoparticles, tumor-selective expression of CXCL12 trap protein resulted in subversion of the immunosuppressive TME in pancreatic cancer and effectively inhibited tumor growth [171]. …”

“…(C) Transient and local expression of His-tag labeled trap plasmid quantified by His-tag ELISA. Adapted with permission from ref [171]. Copyright (2017) American Chemical Society.…”