Lucien, Fabrice

Pre-analytical variability significantly impacts the reproducibility of liquid biopsy research, which is critical for precision medicine and biomedical research. This report highlights the challenges and variability in the pre-analytical processes of liquid biopsies, especially regarding extracellular vesicles (EVs), which are crucial for diagnostics in oncology. The MIBlood-EV initiative aims to standardize the reporting of pre-analytical variables and the quality control of plasma and serum samples to enhance reproducibility in EV research. By providing a comprehensive and flexible reporting framework, MIBlood-EV seeks to improve the reliability of EV studies and facilitate the development of evidence-based protocols, ultimately advancing the field of liquid biopsy research.

Abstract Purpose: Metastatic castration-resistant prostate cancer (mCRPC) resistant to androgen receptor signaling inhibitors (ARSI) is often lethal. Liquid biopsy biomarkers for this deadly form of disease remain under investigation, and underpinning mechanisms remain ill-understood. Experimental Design: We applied targeted cell-free DNA (cfDNA) sequencing to 126 patients with mCRPC from three academic cancer centers and separately performed genome-wide cfDNA methylation sequencing on 43 plasma samples collected prior to the initiation of first-line ARSI treatment. To analyze the genome-wide sequencing data, we performed nucleosome positioning and differential methylated region analysis. We additionally analyzed single-cell and bulk RNA sequencing data from 14 and 80 patients with mCRPC, respectively, to develop and validate a stem-like signature, which we inferred from cfDNA. Results: Targeted cfDNA sequencing detected AR/enhancer alterations prior to first-line ARSIs that correlated with significantly worse progression-free survival (P = 0.01; HR = 2.12) and overall survival (P = 0.02; HR = 2.48). Plasma methylome analysis revealed that AR/enhancer lethal mCRPC patients have significantly higher promoter-level hypomethylation than AR/enhancer wild-type mCRPC patients (P < 0.0001). Moreover, gene ontology and CytoTRACE analysis of nucleosomally more accessible transcription factors in cfDNA revealed enrichment for stemness-associated transcription factors in patients with lethal mCRPC. The resulting stemness signature was then validated in a completely held-out cohort of 80 patients with mCRPC profiled by tumor RNA sequencing. Conclusions: We analyzed a total of 220 patients with mCRPC, validated the importance of cell-free AR/enhancer alterations as a prognostic biomarker in lethal mCRPC, and showed that the underlying mechanism for lethality involves reprogramming developmental states toward increased stemness. See related commentary by Nawfal et al., p. 7

CD36 expression in both immune and non-immune cells is known to be directly involved in cancer metastasis. Extracellular vesicles (EVs) secreted by malignant melanocytes play a vital role in developing tumor-promoting microenvironments, but it is unclear whether this is mediated through CD36. To understand the role of CD36 in melanoma, we first analyzed the SKCM dataset for clinical prognosis, evaluated the percentage of CD36 in lymphatic fluid-derived EVs (LEVs), and tested whether melanoma-derived EVs increase CD36 expression and induce M2-macrophage-like characteristics. Furthermore, we performed a multiplex immunofluorescence (MxIF) imaging analysis to evaluate the CD36 expression and its colocalization with various other cells in the lymph node (LN) of patients and control subjects. Our findings show that cutaneous melanoma patients have a worse clinical prognosis with high CD36 levels, and a higher percentage of CD36 in total LEVs were found at baseline in melanoma patients compared to control. We also found that monocytic and endothelial cells treated with melanoma EVs expressed more CD36 than untreated cells. Furthermore, melanoma-derived EVs can regulate immunosuppressive macrophage-like characteristics by upregulating CD36. The spatial imaging data show that cells in tumor-involved sentinel LNs exhibit a higher probability of CD36 expression than cells from control LNs, but this was not statistically significant. Conclusively, our findings demonstrated that CD36 plays a vital role in controlling the immunosuppressive microenvironment in the LN, which can promote the formation of a protumorigenic niche.

Liver fibrosis is characterized by the activation of perivascular hepatic stellate cells (HSCs), the release of fibrogenic nanosized extracellular vesicles (EVs), and increased HSC glycolysis. Nevertheless, how glycolysis in HSCs coordinates fibrosis amplification through tissue zone-specific pathways remains elusive. Here, we demonstrate that HSC-specific genetic inhibition of glycolysis reduced liver fibrosis. Moreover, spatial transcriptomics revealed a fibrosis-mediated up-regulation of EV-related pathways in the liver pericentral zone, which was abrogated by glycolysis genetic inhibition. Mechanistically, glycolysis in HSCs up-regulated the expression of EV-related genes such as Ras-related protein Rab-31 ( RAB31 ) by enhancing histone 3 lysine 9 acetylation on the promoter region, which increased EV release. Functionally, these glycolysis-dependent EVs increased fibrotic gene expression in recipient HSC. Furthermore, EVs derived from glycolysis-deficient mice abrogated liver fibrosis amplification in contrast to glycolysis-competent mouse EVs. In summary, glycolysis in HSCs amplifies liver fibrosis by promoting fibrogenic EV release in the hepatic pericentral zone, which represents a potential therapeutic target.

2565 Background: Mesothelin (MSLN) is overexpressed in mesothelioma and other solid tumors making it the focus of multiple targeted therapies, including antibody drug conjugates (ADCs), T cell receptor (TCR) fusion constructs, and chimeric antigen receptor T-cell (CAR-T) products. However, the clinical efficacy of these treatments remains limited. We hypothesize that soluble MSLN (sMSLN) in the plasma binds to MSLN-targeted therapies before reaching the tumor. Our study aimed to evaluate the effects of sMSLN on a MSLN-targeting antibody, anetumab, and explore methods to reduce sMSLN. Methods: Exploratory analysis in NCT03126630: sMSLN testing was performed on blood samples from participants enrolled in NCT03126630 at the Molecular Targets Core Lab, National Cancer Institute. The median was used to categorize high and low levels of sMSLN. Survival was estimated with the Kaplan-Meier method and compared between groups with the log rank test. Anetumab immunoprecipitation: Anetumab was covalently coupled to Dynabeads at 5 µg per mg of beads to immunoprecipitate MSLN from two plasma samples. Assays were performed in duplicate. Therapeutics plasma exchange (TPE):Whole blood samples were collected before and after one plasma volume of TPE with albumin as the replacement fluid in patients undergoing routine TPE for various medical conditions, such as autoimmune diseases and hyperviscosity syndromes. Plasma levels of sMSLN were measured with an ELISA assay in matched pre- and post-TPE plasma samples. Results: We obtained sMSLN levels from 40 patients enrolled in NCT03126630. For patients treated with both anetumab ravtansine and pembrolizumab, median progression free survival (PFS) was shorter in the high sMSLN group (5 months) vs the low sMSLN group (12 months). For patients treated with pembrolizumab alone, PFS was similar for patients with high and low sMSLN (4 vs 3.4 months). Anetumab significantly reduced the concentration of sMSLN in plasma samples as detected by MSLN ELISA (p<0.05), demonstrating that sMSLN can bind to and sequester anetumab. Next, we evaluated TPE as a mechanism to reduce sMSLN. We obtained pre- and post-TPE plasma samples from 15 patients undergoing routine TPE for various medical conditions. TPE consistently reduced sMSLN (p<0.05) with an average decrease of 43.6% or 15.4 ng/mL. Conclusions: We found that high sMSLN levels are associated with shorter PFS for anetumab ravtansine, but not pembrolizumab. Additionally, anetumab binds to sMSLN in the plasma, which suggests that sMSLN can sequester anti-MSLN antibodies and may limit the efficacy of MSLN-targeted therapies. High levels of sMSLN could potentially be used as a biomarker to select which patients should not receive MSLN-targeting therapies. Furthermore, our results indicate that sMSLN reduction is feasible with TPE. Decreasing sMSLN could restore the activity of MSLN-targeted therapies.

Abstract Background: Although targeting myeloid cells has become one of the next generation targets for cancer immunotherapy, there is a lack of therapeutic tools to specifically target these cells. Our group has developed a novel humanized PD-L1-targeting antibody, H1A, that induces PD-L1 degradation via blockade of PD-L1 and CMTM6, therefore limiting PD-L1 intrinsic signaling while also preventing interactions with PD-1. In the immune cell compartment, CMTM6 expression is restricted to myeloid cells, making these cells the primary target of H1A. Recently, we unexpectedly found that targeting intrinsic PD-L1 in myeloid cells via H1A resulted in increased release of CCL2 from myeloid cells. In this study, we examined the role of CCL2/CCR2 signaling in CD8 T cell function using human peripheral blood-derived immune cells and evaluated the therapeutic potential of H1A antibody using our humanized PD-L1/PD-1 mouse model. Methods: Human PBMCs derived from healthy donors were treated with H1A or Atezolizumab, a blocking PD-L1 antibody, followed by mass cytometry and flow cytometry to evaluate immune cell phenotype and functional states. PD-L1 expressing myeloid cells isolated from human PBMCs were treated with H1A or Atezolizumab and assessed for CCL2 secretion using multiplex immunoassays. CCL2 production and transcription were confirmed by flow cytometry and single-cell RNA-sequencing. CCR2 blockade was used on human PBMCs to evaluate the effects of CCL2/CCR2 signaling on T cell function alongside H1A treatment. Finally, in vivo antitumor activity of H1A and Atezolizumab were compared in two humanized PD-L1 tumor models. Results: H1A reduced the frequency of regulatory T cells and increased effector T cells, in whole PBMCs upon global T cell activation with anti-CD3/CD28. H1A enhanced the secretion and production of CCL2 from myeloid cells, which was confirmed at a transcript level. CCR2 blockade diminished CD8 T cells’ ability to differentiate into effector cells in H1A treated PBMCs. H1A demonstrated comparable therapeutic effects with Atezolizumab in treatment of immunogenic and ICI-responsive mouse tumor MC38, which is CD8 T cell-dependent, but showed superior therapeutic effects in treatment of ICI-insensitive mouse tumor E0771 compared to Atezolizumab. Both treatments elicited durable memory specific immune responses upon E0771 tumor rechallenge. Conclusion: H1A demonstrated a superior antitumor activity compared to Atezolizumab in our preclinical models via a new mechanism by which H1A caused degradation of intrinsic PD-L1 in myeloid cells. This causes more release of CCL2 to improve T cell function via CCR2 upon T cell activation. Thus, H1A is emerging as a new immunotherapy tool to target PD-L1/CMTM6 in myeloid cells for treatment of cancers that are refractory to current immune checkpoint inhibitor therapy. Citation Format: Michelle Alexandria Hsu, Xin Liu, Ying Li, Whitney Barham, Kevin Pavelko, Jake Hirdler, Fabrice Lucien, Haidong Dong. Targeting PD-L1/CMTM6 in myeloid cells results in elevated release of CCL2 to improve CD8 T cell-mediated antitumor response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2664.

Upamostat is an orally available small-molecule serine protease inhibitor that is a highly potent inhibitor of trypsin 1, trypsin 2, trypsin 3 (PRSS1/2/3), and the urokinase-type plasminogen activator (uPA). These enzymes are expressed in many cancers, especially during tissue remodeling and subsequent tumor cell invasion. Opaganib (ABC294640), a novel, orally available small molecule is a selective inhibitor of the phosphorylation of sphingosine to sphingosine-1-phosphate (S-1-P) by sphingosine kinase 2 (SPHK2). Both sphingosine kinase 1 (SPHK1) and SPHK2 are known to regulate the proliferation-inducing compound S-1-P. However, SPHK2 is more critical in cancer pathogenesis. The goal of this project was to investigate the potential antitumor effects of upamostat and opaganib, individually and in combination, on cholangiocarcinoma (CCA) xenografts in nude mice. PAX165, a patient-derived xenograft (PDX) from a surgically resected CCA, expresses substantial levels of SPHK2, PRSS1, PRSS2, and PRSS3. Four groups of 18 mice each were treated with upamostat, opaganib, both, or vehicle. Mouse weights and PAX165 tumor volumes were measured. Tumor volumes in the upamostat, opaganib, and upamostat plus opaganib groups were significantly decreased compared to the control group.

695 Background: Small cell carcinoma of the bladder (SCCB) is a rare variant of bladder cancer with limited data informing prognosis. We present a novel prognostic model for disease specific survival (DSS) for patients with non-metastatic (M0) SCCB, derived from the Surveillance, Epidemiology and End Results (SEER) database. Methods: The SEER database (18 registries/November 2020) was queried with the ICD-10 topography codes C67.0-C67.9 (bladder), and the morphologic code 8041 (SCCB). Eligible patients (adults, histologic confirmation, available follow-up/staging data, M0) were randomly divided into a training (TC) and a validation cohort (VC) (7:3 ratio). Variables significantly associated with DSS were identified with multivariate Cox regression and backwards stepwise conditional approach and inserted in the model. Points were assigned to each variable based on the formula: Probability of an event at time t=S0(t)exp(β1x1, β2x2...), (β = regression coefficients, x = observed covariate values, S0(t) = survival function). Cumulative risk points were assigned to each patient and three distinct risk categories for DSS were constructed. Harrel’s C-statistic with bootstrap resampling was used for internal (TC) and external (VC) validation. Model performance was compared to the AJCC 8th edition (likelihood ratio test -LRT). Results: A total of 1039 patients were included (739 TC, 300 VC). No statistically significant differences in baseline characteristics/survival outcomes were identified between TC and VC. Age (years), T/N stage, radical cystectomy, chemotherapy, and radiation were significant variables inserted in the multivariate model (table). Patients were stratified to three risk groups (low, intermediate, high) based on the total cumulative risk points collected. Median DSS was NR (95%CI; NR, NR), 25 (95% CI; 18-32) and 9 months (95% CI; 7-11) for the low, intermediate, and high-risk category, log-rank p<.001. Harrel's C-statistic for the model was 0.70 (95%CI;0.67-0.73) in the TC and 0.66 (95%CI; 0.61-0.71) in the VC. In comparison, C-statistic for the AJCC 8th edition was 0.56 (95% CI; 0.52-0.59) and 0.53 (95% CI; 0.51 to 0.57), respectively. The LRT demonstrated superior performance of the model compared to AJCC (p<.001). Conclusions: We present a novel prognostic model for DSS in patients with locoregional SCCB composed of variables readily available in daily practice, which may serve as a useful tool for individualized risk assessment of patients with this rare malignancy. Further validation in prospective studies/clinical trials is warranted. [Table: see text]

458 Background: Immune checkpoint inhibitors (ICI) targeting PD-1/PD-L1 axis has revolutionized the therapeutic landscape of patients with advanced and locally advanced renal cell carcinoma (RCC). However, complete response rates remain low and there is a need for novel therapeutic options for ICI-resistant and refractory RCC. Our group has generated a novel humanized anti-PD-L1 antibody, called H1A, that induces PD-L1 degradation preventing not only its interaction with PD-1 but also inhibiting pro-tumorigenic intracellular signaling. In this study, we compared the antitumor activity of H1A with FDA-approved ICI using patient-derived immune cells and humanized mouse tumor models. Methods: In vivo antitumor activity of H1A and atezolizumab (ATZ) was compared in three humanized PD-1/PD-L1 mouse tumor models with different immunogenicity (E0771:high, MC38:moderate, B16-F10:poor). Peripheral blood mononuclear cells (PBMC) were isolated from 14 RCC patients undergoing with nephrectomy. PBMC were treated with H1A, nivolumab (NIV), atezolizumab (ATZ) and pembrolizumab (PEM) to evaluate their efficacy in inducing tumor cell death in an ex-vivo cytotoxicity assay. Mass cytometry was employed to determine the impact of H1A and atezolizumab on the PBMC profile. Results: MC38 tumors showed moderate response to both H1A and ATZ which was abrogated by CD8 T cell depletion. In E0771 tumors, higher percentage of complete responders was observed with H1A compared to ATZ and E0771 rechallenge revealed memory antitumor immunity with complete rejection of tumors. Patient-derived PBMC treated with H1A showed superior tumor cell killing compared to NIV, PEM and ATZ (p<0.01). While H1A treatment of PBMC induced expansion of effector NK and CD8 T cells (GZMB+ T-bet+), ATZ treatment led to enrichment of Tregs (CD25+,Foxp3+) expressing inhibitory markers PD-1 and LAG-3. Conclusions: H1A demonstrated superior antitumor activity compared to FDA-approved ICI which lays the ground for clinical testing of H1A as a next-generation immune checkpoint inhibitor for the treatment of renal cell carcinoma.

381 Background: Venous tumor thrombus (VTT) is associated with worse oncologic outcomes in clear cell renal cell carcinoma (ccRCC). It is unknown if VTT and pulmonary embolism (PE) predispose patients to pulmonary metastasis. Methods: We queried our institutional registry for ccRCC patients undergoing radical nephrectomy (1970-2019). Cox proportional hazards regression models, adjusting for factors associated with ccRCC progression, were used to determine if VTT and PE were associated with pulmonary metastasis. Results: Of 3,410 patients studied, 1,025 (30%) had VTT, and patients with VTT were more likely to present with pulmonary metastasis at nephrectomy (20% vs 7%, p<0.001). Within the VTT subset, level of VTT was not significantly associated with pulmonary metastasis at nephrectomy (p=0.3). For all patients who had metastatic disease at nephrectomy (n=643), pulmonary metastasis was more common in those with VTT versus those without VTT (68% vs 51%, p<0.001). Excluding patients with pulmonary metastasis at nephrectomy, on multivariable analysis, VTT remained associated with post-nephrectomy pulmonary metastasis (hazard ratio (HR) 1.31, p<0.001) without a notable difference in HRs between renal vein (1.27) and caval (1.38) VTT. Presence of PE in the setting of VTT was associated with increased pulmonary metastasis post-nephrectomy (HR 2.31, p<0.001). Conclusions: VTT is associated with disproportionately increased pulmonary metastasis at presentation and post-nephrectomy in ccRCC patients. Further, the presence of PE at nephrectomy for VTT was associated with increased pulmonary metastasis post-nephrectomy. These results support a metastatic predilection of ccRCC with VTT to the lungs.