The identification of adjuvants to improve vaccination efficacy is a major unmet need. One approach is to augment the functionality of dendritic cells (DCs) by using Toll-like receptor-9 (TLR9) agonists such as cytosine-phosphate-guanine oligodeoxynucleotides (CpG ODNs) as adjuvants. Another approach is adjuvant selection based on production of bioactive interleukin-12 (IL-12). We report a D-peptide isomer, designated D-15800, that induces monocyte differentiation to the DC phenotype in vitro and more effectively stimulates IL-12p70 production upon T cell receptor (TCR) activation than the L-isomer. In the absence of TCR activation and either IL-12p70 or interleukin-2 production, only D-15800 activates CD4+ T and natural killer cells. In the presence of CpG ODN, D-15800 synergistically enhances production of interferon-alpha (IFN-α). Taken together with its biostability in human serum and depot retention upon injection, co-delivery of D-15800 with TLR9 agonists could serve to improve vaccine efficacy.

Cancers and autoimmune diseases commonly co-exist and immune checkpoint inhibitor therapy (ICI) exacerbates autoimmune pathologies. We recently described a lipidic peptide, designated IK14004, that promotes expansion of immunosuppressive T regulatory (Treg) cells and uncouples interleukin-2 from interferon-gamma production while activating CD8+ T cells. Herein, we report IK14004-mediated inhibition of Lewis lung cancer (LLC) growth and re-invigoration of splenocyte-derived exhausted CD4+ T cells. In human immune cells from healthy donors, IK14004 modulates expression of the T cell receptor α/β subunits, induces Type I IFN expression, stimulates natural killer (NK) cells to express NKG2D/NKp44 receptors and enhances K562 cytotoxicity. In both T and NK cells, IK14004 alters the IL-12 receptor β1/β2 chain ratio to favour IL-12p70 binding. Taken together, this novel peptide offers an opportunity to gain further insight into the complexity of ICI immunotherapy so that autoimmune responses may be minimised without promoting tumour evasion from the immune system.

Ultraviolet radiation (UVR) induces immunosuppression and DNA damage, both of which contribute to the rising global incidence of skin cancer including melanoma. Nucleotide excision repair, which is activated upon UVR-induced DNA damage, is linked to expression of interleukin-12 (IL-12) which serves to limit immunosuppression and augment the DNA repair process. Herein, we report an immunomodulating peptide, designated IK14800, that not only elicits secretion of IL-12, interleukin-2 (IL-2) and interferon-gamma (IFN-γ) but also reduces DNA damage in the skin following exposure to UVR. Combined with re-invigoration of exhausted CD4+ T cells, inhibition of UVR-induced MMP-1 release and suppression of B16F10 melanoma metastases, IK14800 offers an opportunity to gain further insight into mechanisms underlying the development and progression of skin cancers.

Whilst the advent of Immune Checkpoint Blockade has revolutionized the management of cancer, a significant proportion of patients have limited or absent response to these therapies. A key cause of this immune insensitivity is the hostile solid tumor microenvironment (TME) dominated by immunosuppressive myeloid cells. We previously identified the acid sensing G protein coupled receptor (GPCR), GPR65, as a primary determinant of these suppressive cells. In mice, genetic deletion of Gpr65 or oral administration of small molecule GPR65 inhibitors in vivo causes a profound repolarization of immunosuppressive tumor associated macrophages, an increase in infiltrating effector cells and potent anti tumor effects in syngeneic models. In TCGA data, across all tumors, patients homozygous for a hypomorphic coding variant in GPR65 (I231L) show increased overall survival, providing compelling genetic evidence of the clinical potential of GPR65 inhibition. To further explore the translational potential of GPR65 we employed a range of techniques to define the human biology of this receptor in different contexts. At the mechanistic level, single cell RNA sequencing (scRNAseq) of human PBMCs obtained from healthy donors demonstrated a pronounced effect of low pH on the myeloid compartment, with a clear polarization of these cells toward an immunosuppressive character and modulation of GPR65 expression. In parallel, pharmacological inhibition of GPR65 in human monocyte derived macrophages exposed to low pH demonstrated that equivalent gene expression changes are primarily due to GPR65 activation. To examine the relevance of these findings to the intact acidic human TME, we performed studies in fresh primary human tumor histocultures from clear cell renal cell carcinoma (ccRCC) patients with immunohistochemically confirmed high macrophage infiltration and carbonic anhydrase 9 (CA9) expression. In these cultures, GPR65 inhibition caused a dose dependent suppression of a geneset closely overlapping with that modulated by GPR65 in primary macrophages. Furthermore, we observed a marked decrease in immune suppressive IL10 secretion with coincident elevation of specific proinflammatory chemokines. Consistent with these findings, in vivo administration of a small molecule GPR65 inhibitor elicited similar changes in human CA9 expressing RCC PDX tumors implanted in myeloid boosted CD34+ stem cell engrafted NCG mice. In summary, inhibition of GPR65 provides a unique and genetically validated approach to favorably modify the immunosupressive TME with features highly conserved between mouse and human contexts. We propose that GPR65 inhibition holds significant clinical promise, with specific evidence around ccRCC as a potential standout indication. Citation Format: Barbara Cipriani, Alastair Corbin, David Miller, Alan Naylor, Faraz Khan, Gavin Milne, Barbara Young, Rupert Satchell, Sourav Sarkar, Mussa Quareshy, Anastasia Nika, Preeti Singh, Gavin Knox, Darryl Turner, Satish Sankaran, Nandini Pal Basak, Toszka Bohn, Tobia Bopp, Surya Koturan, Bo Sun, Benjamin Fairfax, Tom McCarthy, Stuart Hughes. The translational biology of small molecule GPR65 inhibitors: shared effects between mouse models and human primary tumors highlight the unique transformative potential of targeting a genetically validated innate immune checkpoint [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 668.

Background An important facet of the hostile tumor microenvironment (TME) and a recognized driver of cancer immunosuppression is extracellular acidification which results from the glycolytic nature of rapidly proliferating cancer cells. Pathios identified GPR65, a pH-sensing G protein-coupled receptor (GPCR), as the primary sensor of this acidity in human immune cells. Activation of GPR65 is particularly pronounced in macrophages where it leads to the downregulation of key chemokines and anti-tumorigenic cytokines, and the upregulation of pro-tumorigenic wound repair and remodeling factors. In dendritic cells GPR65 signaling suppresses antigen presentation pathways, whereas in T cells and natural killer cells it leads to the suppression of chemokine receptors required for effective tumor homing. Consequently, acid sensing by GPR65 can explain tumor resistance to current immunotherapies. Validating the relevance of this target in immuno-oncology, cancer patients homozygous for the hypomorphic GPR65 variant (I231L) exhibit profoundly improved survival compared to patients with other genotypes. Methods Pathios has developed PTT-4256, a first-in-class small molecule inhibitor of GPR65. The in vitro efficacy of PTT-4256 under low pH conditions was determined by cAMP screening, gene expression and cytokine release profiling of primary immune populations. Anti-tumor activity was assessed using the MC38 and B16.F10 syngeneic mouse models, whilst immunomodulatory effects in MC38 tumor-infiltrating leukocytes were profiled by targeted RNAseq. Notably, PTT-4256 is markedly more potent at human GPR65 versus the mouse receptor. To determine its full potential in patients and to develop an accurate prediction of efficacious human exposure, we employed a range of approaches including molecular pharmacology, site-directed mutagenesis, PK/PD modelling, and genetically engineered mice. Results PTT-4256 fully counteracts the low pH-driven immunosuppressive transcriptional program in human and murine immune cells and restores the secretion of key pro-inflammatory cytokines and chemokines in macrophages. PTT-4256 displays an excellent oral PK profile across species and elicits significant monotherapy efficacy in MC38 and B16.F10 mouse models. Through molecular modelling and site-directed mutagenesis we identified three key residues that explained the difference in potency of PTT-4256 between mouse and human GPR65. Incorporating these residues in a transgenic knock-in mouse fully restored human pharmacology in vitro and provided an important translational platform. Conclusions GPR65 is a key checkpoint on tumor-infiltrating immune cells that links the chronically acidic TME to tumor-promoting immunosuppression. The GPR65 inhibitor PTT-4256 restores anti-tumor immunity and demonstrates pronounced single-agent efficacy in mice, and is therefore being advanced towards clinical development. Ethics Approval Protocols or procedures involving the care and use of animals in studies in China were reviewed and approved by the Institutional Animal Care and Use Committee of Crown Bioscience. During studies, the care and use of animals was conducted in accordance with the regulation of the Association for Assessment and Accreditation of Laboratory Animal Care. Studies involving the welfare and use of animals within the UK complied with the UK Animals Scientific Procedures Act 1986 (ASPA) in line with Directive 2010/63/EU of the European Parliament and Council of 22/September/2010 on the protection of animals used for scientific purposes and UK Home Office guidance on the implementation of the Act and applicable codes of practice for the care and housing of laboratory animals.

Background High frequencies of Tumor Associated Macrophages (TAMs) are related to poor patient prognosis. The Tumor Microenvironment (TME) is characterised by resource scarcity, toxic metabolic by-products, and low pH, together creating an immunosuppressive environment which polarises TAMs towards a pro-tumorigenic state. Methods We identified the proton-sensing G-Protein-Coupled Receptor 65 (GPR65) as a key determinant of low-pH-induced immunosuppression in human cancers, specifically via modulating TAM phenotype in response to the acidic TME. The importance of GPR65 in human cancers is highlighted by three key findings: (1) cancer patients homozygous for the hypomorphic I231L variant exhibit a pronounced survival benefit, (2) GPR65 and downstream pathway genes are highly expressed in innate immune cells from all human solid tumors when assessed by single cell RNA sequencing, and (3) low pH treatment of macrophages in vitro leads to a marked suppression of inflammatory genes and an upregulation of a tissue repair signature. Results We have identified potent and selective small-molecule antagonists of human GPR65 that inhibit the low pH-induced accumulation of cAMP in recombinant cell systems and primary human macrophages with single-digit nanomolar potencies. These compounds dose-dependently prevent the low pH-driven suppression of inflammatory cytokine and chemokine genes and counteract the upregulation of pro-tumorigenic and tissue repair genes in both human and mouse macrophages. Oral administration of our exemplar compound PTT-3213 in subcutaneous MC38 tumor-bearing mice caused gene expression changes consistent with those observed in primary macrophages in vitro, indicative of a dramatic impact on the TME. Weekly dosing of PTT-3213 significantly reduced MC38 Tumor Volume (TV) compared to vehicle (46%). This monotherapy activity was comparable to bi-weekly administration of anti-PD1, whilst combination of PTT-3213 and anti-PD-1 led to a more pronounced curtailment of TV vs vehicle-treated animals (61%). In accordance with the increased expression of chemokine genes, PTT-3213 monotherapy in MC38-bearing mice markedly elevated the frequency of tumor-infiltrating NK cells (up to 22-fold). There was also an increase in the CD8+/CD4+ T cell ratio which attained statistical significance in combination with anti-PD-1. Conclusions Taken together, we have identified GPR65 as a key innate immune checkpoint and therapeutic target in solid tumors and propose that macrophage conditioning via GPR65 inhibition may provide an efficacious strategy to counteract the immunosuppressive action of the acidic TME on TAMs in patients. Ethics Approval Protocols or procedures involving the care and use of animals in studies in China were reviewed and approved by the Institutional Animal Care and Use Committee of Crown Bioscience. During studies, the care and use of animals was conducted in accordance with the regulation of the Association for Assessment and Accreditation of Laboratory Animal Care Studies involving the welfare and use of animals within the UK complied with the UK Animals Scientific Procedures Act 1986 (ASPA) in line with Directive 2010/63/EU of the European Parliament and Council of 22/September/2010 on the protection of animals used for scientific purposes and UK Home Office guidance on the implementation of the Act and applicable codes of practice for the care and housing of laboratory animals.

T cell-dendritic cell (DC) interactions contribute to reciprocal stimulation leading to DC maturation that results in production of interleukin-12 (IL-12) and interferon-gamma (IFN-γ). Both cytokines have been implicated in autoimmune diseases while being necessary for effective immune responses against foreign antigens. We describe a lipidic peptide, designated IK14004, that modifies crosstalk between T cells and DCs resulting in suppression of IL-12p40/IFN-γ production. T cell production of interleukin-2 (IL-2) and IFN-γ is uncoupled and IL-12p70 production is enhanced. IK14004 induces expression of activating co-receptors in CD8+ T cells and increases the proportion of Foxp3-expressing CD4+ T regulatory cells. The potential for IK14004 to impact on signalling pathways required to achieve a balanced immune response upon stimulation of DCs and T cells is highlighted. This novel compound provides an opportunity to gain further insights into the complexity of T cell-DC interactions relevant to autoimmunity associated with malignancies and may have therapeutic benefit.