Eradication of tumors and development of anti-cancer immunity using STINGa targeted by pHLIP

Abstract

Despite significant progress in the development of novel STING agonists (STINGa), applications appear to be challenged by the low efficiency and poor selectivity of these agents. A pH Low Insertion Peptide (pHLIP) extends the lifetime of a STINGa in the blood and targets it to acidic cancer-associated fibroblasts (CAFs), tumor-associated macrophages (TAMs), myeloid derived suppressor cells (mMDSCs) and dendritic cells (DCs). CAFs constitute 25% of all live cells within CT26 tumors, and M2-type TAMs and mMDSCs are the most abundant among the immune cells. The resulting activation of cytokines within the tumor microenvironment (TME) triggers the eradication of small (100 mm3) and large (400-700 mm3) CT26 tumors in mice after a single dose of pHLIP-STINGa. The tumor stroma was destroyed (the number of CAFs was reduced by 98%), intratumoral hemorrhage developed, and the level of acidity within the TME was reduced. Further, no tumors developed in 20 out of 25 tumor-free mice re-challenged by an additional injection of cancer cells. The therapeutic effect on CT26 tumors was insignificant in nude mice, lacking T-cells. Thus, targeted delivery of STINGa to tumor stroma and TAMs induces activation of signaling, potentially resulting in the recruitment and infiltration of T-cells, which gain access to the tumor core. The cytotoxic activity of T-cells is not impaired by an acidic environment and immune memory is developed.

Aiming the magic bullet: targeted delivery of imaging and therapeutic agents to solid tumors by pHLIP peptides

“…Acidic regions targeted by pHLIP were not restricted to hypoxic areas. Highly proliferative, invasive regions at the tumor-stroma interface are very well marked by pHLIP peptides ( Rohani et al, 2019 ; Gillies, 2021 ; Moshnikova et al, 2022a ). Within the TME, cancer cells, CAFs, TAMs and mMDSC are marked by pHLIP ( Sahraei et al, 2019 ; Moshnikova et al, 2022a ; Visca et al, 2022 ).…”

“…Highly proliferative, invasive regions at the tumor-stroma interface are very well marked by pHLIP peptides ( Rohani et al, 2019 ; Gillies, 2021 ; Moshnikova et al, 2022a ). Within the TME, cancer cells, CAFs, TAMs and mMDSC are marked by pHLIP ( Sahraei et al, 2019 ; Moshnikova et al, 2022a ; Visca et al, 2022 ). In addition to primary tumors, satellites near the primary tumor, pre-metastatic niche and micro-metastases in distant organs have been shown to be well targeted by pHLIP peptides ( Segala et al, 2009 ; Reshetnyak et al, 2011 ; Cruz-Monserrate et al, 2014 ; Adochite et al, 2016 ; Rohani et al, 2019 ; Crawford et al, 2020 ; Gillies, 2021 ; Matsui et al, 2023 ).…”

“…Importantly, the fluorescence of pHLIP-ICG is enhanced about 20-fold when tethered to a cellular membrane when compared with the emission of pHLIP-ICG in aqueous solution ( Golijanin et al, 2016 ; Roberts et al, 2019 ; Crawford et al, 2020 ). pHLIP-ICG was used to image tumors in various mouse tumor models ( Crawford et al, 2020 ; Moshnikova et al, 2022a ; Visca et al, 2022 ) and ex-vivo in human bladder and upper urinary tract specimens using different clinical instruments including da Vinci ( Golijanin et al, 2016 ) and Stryker endoscopic systems ( Brito et al, 2020 ; Moshnikova et al, 2022b ). Compared to white light, NIR fluorescence pHLIP-ICG imaging evaluation had a higher sensitivity of 98% vs. 81% in the detection of malignant lesions in human bladders ( Moshnikova et al, 2022b ).…”

“…Reprogramming of M2-type TAMs (M2-TAMs) toward an M1 phenotype, suppression of CAFs and mMDSCs, as well as activation of dendritic cells (DCs) to train T cells are advantageous, while activation of T cells is associated with the development of pro-apoptotic signals. pHLIP was able to accomplish a number of desirable tasks in the delivery of STINGa: i) pHLIP-STINGa extended the lifetime of a STINGa in the blood; ii) > 70% of CAFs and M2-TAMs, and >50% of mMDSCs and DCs within TME were targeted by pHLIP-STINGa, resulting in activation of cytokines within the TME; iii) the tumor stroma was destroyed (the number of CAFs was reduced by 98%), triggering intratumoral hemorrhage, which led to an increase of pH within the TME ( Moshnikova et al, 2022a ). As a result, a single dose of pHLIP-STINGa administered either by intravenous or intraperitoneal injection eradicated tumors in 18 out of 20 mice, and tumors were not developed upon a re-challenge by an additional injection of cancer cells (90 days after a single dose of pHLIP-STINGa).…”

Biosynthesized tumor acidity and MMP dual-responsive plant toxin gelonin for robust cancer therapy

“…Importantly, the pHLIP-based delivery modality takes advantage of the acidic tumor environment, and it does not rely on the expression level of tumor-specific antigens. 32 Therefore, pHLIP can serve as a powerful vehicle for highly effective delivery of a broad range of theranostic cargoes including magnetite nanoparticles, 33,34 STING agonist, 35 peptide nucleic acids, [36][37][38] enhanced green fluorescent protein (EGFP) 39 and pleiotropic cytokine interleukin-2 (IL-2). 40 Recently, a doubleswitch pHLIP system has been developed for selective enrichment of circulating tumor microenvironment-derived extracellular vesicles (cTME-EVs).…”