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. 2015 Apr 28;4(4):e237.
doi: 10.1038/mtna.2015.11.

Targeting the PD-1/PD-L1 Immune Evasion Axis With DNA Aptamers as a Novel Therapeutic Strategy for the Treatment of Disseminated Cancers

Aaron Prodeus  1 , Aws Abdul-Wahid  2 , Nicholas W Fischer  1 , Eric H-B Huang  2 , Marzena Cydzik  2 , Jean Gariépy  3
Affiliations

Targeting the PD-1/PD-L1 Immune Evasion Axis With DNA Aptamers as a Novel Therapeutic Strategy for the Treatment of Disseminated Cancers

Aaron Prodeus et al. Mol Ther Nucleic Acids. .

Abstract

Blocking the immunoinhibitory PD-1:PD-L1 pathway using monoclonal antibodies has led to dramatic clinical responses by reversing tumor immune evasion and provoking robust and durable antitumor responses. Anti-PD-1 antibodies have now been approved for the treatment of melanoma, and are being clinically tested in a number of other tumor types as both a monotherapy and as part of combination regimens. Here, we report the development of DNA aptamers as synthetic, nonimmunogenic antibody mimics, which bind specifically to the murine extracellular domain of PD-1 and block the PD-1:PD-L1 interaction. One such aptamer, MP7, functionally inhibits the PD-L1-mediated suppression of IL-2 secretion in primary T-cells. A PEGylated form of MP7 retains the ability to block the PD-1:PD-L1 interaction, and significantly suppresses the growth of PD-L1+ colon carcinoma cells in vivo with a potency equivalent to an antagonistic anti-PD-1 antibody. Importantly, the anti-PD-1 DNA aptamer treatment was not associated with off-target TLR-9-related immune responses. Due to the inherent advantages of aptamers including their lack of immunogenicity, low cost, long shelf life, and ease of synthesis, PD-1 antagonistic aptamers may represent an attractive alternative over antibody-based anti PD-1 therapeutics.

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Figures

Figure 1
Figure 1
Secondary structure and binding affinities of highly enriched anti-PD-1 aptamer sequences MP5 and MP7. Mfold secondary structure predictions of the top two enriched aptamer sequences MP5 (a) and MP7 (b) identified by next-generation sequencing after five rounds of SELEX toward mPD-1.FcHIS. (c,d) Concentration-dependent binding of 32P-labeled aptamers MP5 (c) and MP7 (d) to mPD-1.FcHIS captured in a nitrocellulose filter binding assay. Filled symbols represent the % DNA bound of the full-length aptamer at each mPD-1.FcHIS concentration while empty symbols represent the % DNA Bound of the respective reverse complement of each aptamer used as a negative binding control.
Figure 2
Figure 2
Specificity of anti-PD-1 aptamers MP5 and MP7 towards the mPD-1 extracellular domain. (a) Ribbon structure overlays highlighting similarities between the mouse (blue) and human (gray) PD-1 extracellular IgV-like domain. (b) Aligned primary sequences emphasizing homology between the extracellular regions of mouse (PDB ID: 1NPU) and human (PDB ID: 3RRQ) PD-1 (refs. ,). Gray highlights represent conserved primary sequences. (c) Surface plasmon resonance binding responses of mPD-1.FcHIS, hPD-1.Fc, an irrelevant Fc control, histidine-tagged rCEA-N domain, and mPD-L1.Fc toward immobilized MP5 (filled bars) or MP7 (empty bars). Histograms represent mean binding response of duplicate injections ± SD.
Figure 3
Figure 3
Anti-PD-1 DNA aptamer MP7 antagonizes PD-1/PD-L1 mediated suppression of IL-2 secretion in vitro. (a) IL-2 ELISPOT assay to compare the effects of PD-L1.Fc or an isotype matched control Fc on the IL-2 secretion by splenocytes stimulated with anti-CD3 antibody. PD-L1.Fc (15 µg/ml) reduced IL-2 SFU by 51% as compared to the Fc control. Each bar represents the mean SFU/2 × 105 cells from at least three replicate wells ± SEM. **P < 0.05 relative to anti-CD3 + Fc-control group. (b) Phosphate-buffered saline, cSeq, anti-PD-1 aptamers (250 nmol/l) or an antagonistic anti-PD-1 antibody (RMPI-14 mAb, 125 nmol/l) were added to splenocytes in wells coated with anti-CD3 + PD-L1.Fc to monitor the blockage of PD-L1-mediated suppression of IL-2 secretion. Bars represent % Blockage of PD-L1 suppressed IL-2 Secretion where the IL-2 spot forming units (SFU) in wells without aptamer/antibody are set to 0% and IL-2 SFU in wells supplemented with anti-PD-1 blocking antibody are set to 100% as anti-PD-1 antibody restored IL-2 secretion to levels 20% above that of anti-CD3 stimulation alone. Each histogram bar represents the mean value ± SEM (n = 5). NS, not significant.
Figure 4
Figure 4
PEGylated MP7 directly blocks PD-1/PD-L1 binding. (a) Reaction scheme of aptamer conjugation to a 40 kDa polyethylene glycol (PEG) at the 5' termini. (b) The ability of PEGylated anti-PD-1 aptamers (PEG-MP5, PEG-MP7), PEG-cSeq, RPMI-14 mAb, or an isotype matched IgG control to inhibit the binding of soluble mPD-1.FcHIS to plate bound mPD-L1.Fc was determined using a competitive enzyme-linked immunosorbent assay utilizing an anti-HIS-HRP conjugated antibody. Each histogram bar represents the mean % of PD-1 blocked from binding PD-L1 ± SD (n = 3).
Figure 5
Figure 5
PEGylated MP7 suppresses growth of disseminated PD-L1+ colon carcinoma MC38.CEA cells in vivo. (a) Flow cytometry analysis of MC38.CEA cells costained with FITC-conjugated anti-CEA antibody and APC-conjugated anti-PD-L1 antibody confirming low basal PD-L1 expression which is upregulated by IFNγ stimulation (500 units/ml, 24 hours). (b) Experimental outline of in vivo tumor model. MC38.CEA cells were injected i.p. into groups of C57Bl/6 mice (n = 5; day 0) and animals were subsequently treated with either RMPI-14 mAb, an isotype matched IgG (Isotype), PEG-MP7 or PEG-cSeq on days 1,3,5, and 7. (c) Photographs highlighting tumor nodules found in the intraperitoneal cavity of treated or control mice upon necropsy at day-21 post-tumor implantation. The total number of tumor nodules in each animal (d) and their cumulative tumor volume (e) was quantified upon necropsy to evaluate the antitumor effect of each PD-1:PD-L1 blocking reagent.
Figure 6
Figure 6
Anti-PD-1 aptamer PEG-MP7 is not cytotoxic and enhances tumor-specific T-cell responses in vivo without induction of a TLR9-mediated innate immune response. (a) Cell viability assay was quantified using (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) (MTS) dye after a 24-hour incubation of MC38.CEA cells with 5 µmol/l of PEG-MP7, PEG-cSeq, MP7, or 8M urea. Bars represent the mean OD490 nm ± SD from replicate wells. ***P < 0.001. Aptamer-induced TLR-9 signaling was assayed by injection of PEG-cSeq, PEG-MP7, PBS, or a control CpG ODN into naive C57Bl/6 mice (n = 3) and 3 hours later the sera levels of TNFα (b) and IL-6 (c) were quantified by ELISA. Only injection of the CpG ODN yielded signal above the lower limit of detection (dotted line). Each symbol represents the average cytokine levels from each individual animal measured in duplicate.
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