Comparison of cisplatin-induced anti-tumor response in CT26 syngeneic tumors of three BALB/c substrains

Background To determine whether the background of BALB/c substrains affects the response to anti-tumor drugs, we measured for alterations in tumor growth, histopathological structure of the tumor, and expressions of tumor-related proteins in three BALB/c substrains derived from different sources (BALB/cKorl, BALB/cA and BALB/cB), after exposure to varying concentrations of cisplatin (0.1, 1 and 5 mg/kg). Results Cisplatin treatment induced similar responses for body and organ weights, serum analyzing factors, and blood analyzing factors in all BALB/c substrains with CT26 syngeneic tumor. Few differences were detected in the volume and histopathological structure of the CT26 tumor. Growth inhibition of CT26 tumors after exposure to cisplatin was greater in the BALB/cB substrain than BALB/cKorl and BALB/cA substrains, and a similar pattern was observed in the histopathological structure of tumors. However, the expression levels of other tumor-related factors, including Ki67, p27, p53, Bcl-2-associated X protein (Bax), B-cell lymphoma 2 (Bcl-2), caspase-3 (Cas-3), matrix metallopeptidase 2 (MMP2) and vascular endothelial growth factor (VEGF) proteins, were constantly maintained in the tumors of all three substrains after cisplatin treatment. A similar decrease pattern was observed for the expressions of inflammatory cytokines, including interleukin (IL)-1β, IL-6 and IL-10, in the CT26 tumors of the three BALB/c substrains. Conclusions Taken together, results of the present study indicate that the genetic background of the three BALB/c substrains has no major effect on the therapeutic responsiveness of cisplatin, except growth and histopathology of the CT26 syngeneic tumor.

Tumor-immune profiling of CT-26 and Colon 26 syngeneic mouse models reveals mechanism of anti-PD-1 response

Background Immune checkpoint blockade (ICB) therapies have changed the paradigm of cancer therapies. However, anti-tumor response of the ICB is insufficient for many patients and limited to specific tumor types. Despite many preclinical and clinical studies to understand the mechanism of anti-tumor efficacy of ICB, the mechanism is not completely understood. Harnessing preclinical tumor models is one way to understand the mechanism of treatment response. Methods In order to delineate the mechanisms of anti-tumor activity of ICB in preclinical syngeneic tumor models, we selected two syngeneic murine colorectal cancer models based on in vivo screening for sensitivity with anti-PD-1 therapy. We performed tumor-immune profiling of the two models to identify the potential mechanism for anti-PD-1 response. Results We performed in vivo screening for anti-PD-1 therapy across 23 syngeneic tumor models and found that CT-26 and Colon 26, which are murine colorectal carcinoma derived from BALB/c mice, showed different sensitivity to anti-PD-1. CT-26 tumor mice were more sensitive to the anti-PD-1 antibody than Colon 26, while both models show similarly sensitivity to anti-CTLA4 antibody. Immune-profiling showed that CT-26 tumor tissue was infiltrated with more immune cells than Colon 26. Genomic/transcriptomic analyses highlighted thatWnt pathway was one of the potential differences between CT-26 and Colon 26, showing Wnt activity was higher in Colon 26 than CT-26. . Conclusions CT-26 and Colon 26 syngeneic tumor models showed different sensitivity to anti-PD-1 therapy, although both tumor cells are murine colorectal carcinoma cell lines from BALB/c strain. By characterizing the mouse cells lines and tumor-immune context in the tumor tissues with comprehensive analysis approaches, we found that CT-26 showed “hot tumor” profile with more infiltrated immune cells than Colon 26. Further pathway analyses enable us to propose a hypothesis that Wnt pathway could be one of the major factors to differentiate CT-26 from Colon 26 model and link to anti-PD-1 response. Our approach to focus on preclinical tumor models with similar genetic background but different sensitivity to anti-PD-1 therapy would contribute to illustrating the potential mechanism of anti-PD-1 response and to generating a novel concept to synergize current anti-PD-1 therapies for cancer patients.

186 Development of KSQ-001, an engineered TIL (eTIL) therapy for solid tumors through CRISPR/Cas9-mediated editing of SOCS1

BackgroundAdoptive cell therapy with ex vivo expanded tumor infiltrating lymphocytes (TIL) offers a potentially curative treatment for cancer. However, the immunosuppressive tumor microenvironment limits the effectiveness of TIL therapy. To address this medical need, we used our Immune-CRISPRomics® Platform to perform a series of genome-wide CRISPR/Cas9 screens to identify targets enhancing the ability of T cells to infiltrate and kill solid tumors in an in vivo setting. These screens identified SOCS1 as a top target that restrains T cell anti-tumor immunity. Based on these findings, we developed KSQ-001, an engineered TIL (eTIL) therapy created via CRISPR/Cas9-mediated editing of SOCS1 for the treatment of solid tumors.MethodsGenome-wide CRISPR/Cas9 screens were conducted in in vitro primary human T cells and TIL cultures and in in vivo primary mouse OT1 and PMEL-TCR-Tg T cells in syngeneic tumor models. The efficacy of surrogate murine KSQ-001 (mKSQ-001), in which the SOCS1 gene is inactivated by CRISPR/Cas9 in OT1 or PMEL-TCR-Tg T cells, was evaluated in both the B16-Ova and CRC-gp100 syngeneic tumor models, with memory formation and efficacy evaluated both in the presence and absence of cyclophosphamide-mediated lymphodepletion. KSQ-001 was manufactured from human TIL using SOCS1-targeting sgRNAs selected for therapeutic use based on potency and selectivity, with KSQ-001 characterized for in vitro function and in vivo anti-tumor efficacy.ResultsUpon adoptive transfer of a single dose into solid tumor-bearing hosts, mKSQ-001 was found to robustly enhance anti-tumor efficacy and eradicate tumors in 7/10 mice in the PD1-sensitive OT1/B16-Ova model and to drive responses in the PD-1 refractory PMEL/CRC-gp100 syngeneic tumor model. mKSQ-001 also showed a ten-fold increase in anti-tumor potency in vivo compared to unengineered T-cell product and established durable anti-tumor memory by persisting in the form of T central memory cells detectable at high frequency in the peripheral blood of complete responder mice. In the setting of lymphodepletion, mKSQ-001 also displayed heightened anti-tumor potency, accumulation, and memory formation in comparison to inactivation of PD-1. Importantly, human KSQ-001 displayed a transcriptional signature indicative of increased anti-tumor function, produced increased amounts of pro-inflammatory cytokines, exhibited a hypersensitivity to IL-12 signaling, and demonstrated increased anti-tumor function both in vitro and in vivo solid tumor models.ConclusionsBased on insights from our Immune-CRISPRomics® platform and demonstrated efficacy across multiple preclinical tumor models, we have developed KSQ-001, a novel eTIL therapy. These preclinical data support clinical testing of KSQ-001 in a variety of solid tumor indications.

721 Intratumoral immunotherapy with aluminum hydroxide-tethered IL-12 induces potent local and systemic immunity with minimal toxicity

BackgroundInterleukin-12 (IL-12) is a potent pro-inflammatory cytokine that promotes Th1 skewing, IFNγ expression, T- and NK-cell activation, and antigen presentation. In animal models, IL-12 can elicit robust anti-tumor responses through activation of both innate and adaptive immunity. However, clinical translation of IL-12 has been hindered by significant immune-related toxicity when delivered systemically, necessitating low doses that are often insufficient for efficacy. Intratumoral (IT) administration can expand the therapeutic window of IL-12 by increasing the local tumor concentration relative to systemic exposure but is in turn limited by rapid vascular and lymphatic clearance of injected drug from the tumor and corresponding systemic accumulation. Here we describe an approach to locally retain intratumorally administered IL-12 by complexing it to the common vaccine adjuvant aluminum hydroxide (alum) through a novel phosphopeptide linkage.MethodsSingle-chain murine IL-12 (mIL12) was genetically fused at its c-terminus to a short alum-binding peptide (ABP) that is specifically phosphorylated on multiple serines when co-expressed with the kinase Fam20C. Phosphorylated mIL12-ABP proteins were complexed with a 10x mass excess of aluminum hydroxide through a naturally occurring ligand exchange reaction between the phosphoserines in the ABP and surface hydroxyl groups on alum. mIL12-ABP/alum complexes were characterized for in vitro potency and in vivo efficacy in multiple syngeneic tumor models including MC38, CT26, A20, 4T1, and B16F10 following IT administration. Immune analyses and re-challenge experiments are in progress.Results mIL12-ABP is phosphorylated on multiple sites when co-expressed with Fam20C and is stably retained on aluminum hydroxide in vitro under elution conditions containing phosphate and serum. Alum-bound mIL12-ABP remains active in cellular assays with a 3–4 fold increase in EC50 compared to free protein. Following intratumoral administration, the mIL12-ABP/alum complexes have significantly extended tumor retention compared to unmodified mIL12, leading to potent local immune activation for >1 week. One or two doses of IT administered mIL12-ABP/alum is sufficient to induce robust monotherapy efficacy in diverse syngeneic tumor models including cold tumors resistant to checkpoint blockade and other immunotherapies. Locally administered mIL12-ABP/alum is further able to prime a systemic immune response leading to efficacy against non-injected tumors and spontaneous metastases. Doses required for optimal efficacy are well tolerated in mice with no significant weight loss or other evidence of systemic toxicity.ConclusionsAnkyra's platform is a differentiated approach to expand the therapeutic window of IL-12 and other cytokine drugs by enhancing tumor retention following IT administration.

876 Intratumoral administration and local retention of IL-2/IL-12 fusion proteins drive a potent systemic anti-tumor immune response

BackgroundIL-2 and IL-12 synergistically trigger the stimulation and proliferation of T and NK cells to mediate anti-tumor immunity. Although aldesleukin, a high-dose IL-2 intravenous (IV) infusion regimen, has been approved for the treatment of melanoma and renal cell carcinoma, adoption has been hindered by frequent grade 3 and 4 severe adverse events. No IL-12 therapy has been approved yet due to toxicity. Cullinan Amber is developing a fusion protein that uniquely combines in one polypeptide both IL-2 and IL-12 with a collagen-binding domain to reduce toxicity and increase efficacy following intra-tumoral (IT) administration via retention in the tumor microenvironment.MethodsProteins were expressed in HEK293 cells. Collagen binding was measured by ELISA. IL-2 and IL-12 bioactivity was evaluated by CTLL-2 proliferation and HEK-Blue IL-12 reporter cells. In vivo studies were conducted in B16F10, MC38, and CT26 syngeneic tumor models. Systemic Amber construct concentrations were determined by ELISA.Results”Amber” constructs, comprised of IL-2, IL-12, and a collagen-binding domain, were produced and confirmed to retain bioactivity. B16F10 tumor-bearing mice injected with Amber IT had systemic Amber levels <5% as compared to mice administered the same dose IV. When IL-2/IL-12 fusion proteins lacking a collagen-binding domain were injected IT in B16F10-bearing mice, 60% of mice needed to be euthanized due to severe body weight loss, while Amber-treated mice did not lose body weight. In the checkpoint-refractory B16F10 and MC38 models, Amber demonstrated 95% tumor growth inhibition (figure 1a) and 100% CRs (figure 1b), respectively. 90% of the mice cured of their primary MC38 tumors were protected from re-challenge (figure 1b). Notably, 70% CRs were observed in the MC38 model even after a single-dose treatment of Amber. Similar data was obtained in the CT26 model. Amber treatment of mice bearing large 500 mm3 MC38 tumors resulted in dramatic tumor shrinkage (figure 1c). In mice bearing two MC38 tumors, only one of which was treated IT, 100% of treated tumors and 90% of distal untreated tumors were eliminated when Amber was combined with an anti-PD1 antibody (figure 1d), demonstrating a robust abscopal response.Abstract 876 Figure 1Efficacy of amber constructs in syngeneic tumor modelsConclusionsThe use of collagen-binding domains for tumor retention enables the safe and effective delivery of IL-2 and IL-12 in a single multifunctional molecule. Taken together, the preclinical data suggests that Amber constructs may show robust single-agent activity in clinical trials against checkpoint-refractory tumors with minimal toxicity, as well as the potential to significantly deepen anti-tumor responses in combination with checkpoint inhibitor therapy.

765 The first-in-class small molecule TREX1 inhibitor CPI-381 demonstrates type I IFN induction and sensitization of tumors to immune checkpoint blockade

BackgroundTREX1 is an exonuclease that functions as a negative regulator of innate immunity. TREX1 controls dsDNA sensing in tumor and immune cells by preventing aberrant dsDNA buildup that triggers STING-mediated Type 1 Interferon (IFN) induction leading to priming of the adaptive immune system. Loss of function mutations in TREX1 and genetic ablation of trex1 in mice lead to induction of IFNbeta-driven autoimmunity. Thus, TREX1 is a promising target to elicit IFN-mediated anti-tumor immunity.MethodsTo characterize TREX1 inhibitors we developed cell-based assays utilizing human HCT116 carcinoma and THP-1 monocytic Dual reporter cell lines to monitor IRF activity. Activation of cGAS was assessed by measuring cGAMP levels in B16F10 melanoma cells. The potency of TREX1 inhibitors in primary human dendritic cells (DC)s was analyzed by measuring IFNbeta induction by exogenous dsDNA. Analysis of tumor growth inhibition following TREX1 inhibitor treatment was conducted in mouse syngeneic tumor models. TREX1 activity was assessed by measuring degradation of a custom dsDNA substrate.ResultsWe report here the development of a small molecule TREX1 inhibitor, CPI-381, with nanomolar cellular potency, which translated into a robust induction of IRF reporter activity. We observed a significant increase in cGAMP production in B16F10 cells transfected with DNA in the presence of CPI-381, suggesting that CPI-381-mediated inhibition of TREX1 leads to the activation of dsDNA sensors, such as cGAS. Treatment of THP-1 cells with CPI-381 induced the expression of several key ISG involved in innate immunity. Moreover, inhibition of TREX1 with CPI-381 phenocopied the effect of TREX1 genetic deletion in primary human DCs by upregulating IFNbeta. To evaluate whether TREX1 negatively regulates IFNbeta production in syngeneic tumor models, we knocked down trex1 in B16F10, MB49, MC38, and CT26 murine cells. Accumulation of cytosolic dsDNA resulted in a substantial increase in IFNbeta secretion by all four TREX1-KO cell lines.In vivo efficacy studies with CPI-381 demonstrated reduced tumor growth in the MC38 syngeneic tumor model either alone or in combination with anti-PD1. We observed a reduction of TREX1 activity in CPI-381 treated tumors, confirming an inverse relationship between TREX1 intra-tumor activity and tumor growth, and efficient target engagement after systemic (oral) delivery.ConclusionsWe have developed a first-in-class, potent TREX1 inhibitor demonstrating excellent in vitro and in vivo potency via enhancement of cytosolic dsDNA sensing and induction of IFNbeta in cancer and immune cells. CPI-381-induced tumor-intrinsic TREX1 inhibition elicits antitumor immunity as a single agent and increases response to immune checkpoint blockade via mechanisms downstream of TREX1 that activate type I IFN signaling.Ethics ApprovalAll animal work was approved and conducted under the oversight of the Charles River Accelerator and Development Lab (CRADL, Cambridge, MA) Institutional Animal Care and Use Committee (protocol # 2021-1258).