No consensus strategies exist for prognosticating metastatic castration-resistant prostate cancer (mCRPC). Circulating tumor DNA fraction (ctDNA%) is increasingly reported by commercial and laboratory tests but its utility for risk stratification is unclear. Here, we intersect ctDNA%, treatment outcomes, and clinical characteristics across 738 plasma samples from 491 male mCRPC patients from two randomized multicentre phase II trials and a prospective province-wide blood biobanking program. ctDNA% correlates with serum and radiographic metrics of disease burden and is highest in patients with liver metastases. ctDNA% strongly predicts overall survival, progression-free survival, and treatment response independent of therapeutic context and outperformed established prognostic clinical factors. Recognizing that ctDNA-based biomarker genotyping is limited by low ctDNA% in some patients, we leverage the relationship between clinical prognostic factors and ctDNA% to develop a clinically-interpretable machine-learning tool that predicts whether a patient has sufficient ctDNA% for informative ctDNA genotyping (available online: https://www.ctDNA.org). Our results affirm ctDNA% as an actionable tool for patient risk stratification and provide a practical framework for optimized biomarker testing.

Glucocorticoid drugs are widely used to treat immune-related diseases, but their use is limited by side effects and by resistance, which especially occurs in macrophage-dominated diseases. In order to improve glucocorticoid therapies, more research is required into the mechanisms of glucocorticoid action. In the present study, we have used a zebrafish model for inflammation to study glucocorticoid effects on the innate immune response. In zebrafish larvae, the migration of neutrophils towards a site of injury is inhibited upon glucocorticoid treatment, whereas migration of macrophages is glucocorticoid resistant. We show that wounding-induced increases in the expression of genes that encode neutrophil-specific chemoattractants (Il8 and Cxcl18b) are attenuated by the synthetic glucocorticoid beclomethasone, but that beclomethasone does not attenuate the induction of the genes encoding Ccl2 and Cxcl11aa, which are required for macrophage recruitment. RNA sequencing on FACS-sorted macrophages shows that the vast majority of the wounding-induced transcriptional changes in these cells are inhibited by beclomethasone, whereas only a small subset is glucocorticoid-insensitive. As a result, beclomethasone decreases the number of macrophages that differentiate towards a pro-inflammatory (M1) phenotype, which we demonstrated using a tnfa:eGFP-F reporter line and analysis of macrophage morphology. We conclude that differentiation and migration of macrophages are regulated independently, and that glucocorticoids leave the chemotactic migration of macrophages unaffected, but exert their anti-inflammatory effect on these cells by inhibiting their differentiation to an M1 phenotype. The resistance of macrophage-dominated diseases to glucocorticoid therapy can therefore not be attributed to an intrinsic insensitivity of macrophages to glucocorticoids.

Background T-cell mediated immunotherapy brought clinical success for many cancer patients. Nonetheless, downregulation of MHC class I antigen presentation, frequently occurring in solid cancers, limits the efficacy of these therapies. Unraveling the mechanisms underlying this type of immune escape is therefore of great importance. We here investigated the immunological effects of metabolic stress in cancer cells as a result of nutrient deprivation. Methods TC1 and B16F10 tumor cell lines were cultured under oxygen- and glucose-deprivation conditions that mimicked the tumor microenvironment of solid tumors. Presentation of peptide antigens by MHC class I molecules was measured by flow cytometry and via activation of tumor-specific CD8 T cell clones. The proficiency of the IFNy-STAT1 pathway was investigated by Western blots on phosphorylated proteins, transfection of constitutive active STAT1 constructs and qPCR of downstream targets. Kinase inhibitors for PI3K were used to examine its role in IFNy receptor signal transduction. Results Combination of oxygen- and glucose-deprivation resulted in decreased presentation of MHC class I antigens on cancer cells, even in the presence of the stimulatory cytokine IFNy. This unresponsiveness to IFNy was the result of failure to phosphorylate the signal transducer STAT1. Forced expression of constitutive active STAT1 fully rescued the MHC class I presentation. Furthermore, oxygen- and glucose-deprivation increased PI3K activity in tumor cells. Pharmacological inhibition of this pathway not only restored signal transduction through IFNy-STAT1 but also improved MHC class I presentation. Importantly, PI3K inhibitors also rendered tumor cells sensitive for recognition by CD8 T cells in culture conditions of metabolic stress. Conclusions These data revealed a strong impact of metabolic stress on the presentation of tumor antigens by MHC class I and suggest that this type of tumor escape takes place at hypoxic areas even during times of active T cell immunity and IFNy release.

Homologous recombination repair deficiency (HRD) can be observed in virtually all cancer types. Although HRD sensitizes tumors to DNA-damaging chemotherapy and poly(ADP-ribose) polymerase (PARP) inhibitors, all patients ultimately develop resistance to these therapies. Therefore, it is necessary to identify therapeutic regimens with a more durable efficacy. HRD tumors have been suggested to be more immunogenic and, therefore, more susceptible to treatment with checkpoint inhibitors. In this review, we describe how HRD might mechanistically affect antitumor immunity and summarize the available translational evidence for an association between HRD and antitumor immunity across multiple tumor types. In addition, we give an overview of all available clinical data on the efficacy of checkpoint inhibitors in HRD tumors and describe the evidence for using treatment strategies that combine checkpoint inhibitors with PARP inhibitors.

Purpose: Androgen receptor pathway inhibitors (ARPI) are standard of care for treatment-naïve metastatic castration-resistant prostate cancer (mCRPC), but rapid resistance is common. Early identification of resistance will improve management strategies. We investigated whether changes in circulating tumor DNA (ctDNA) fraction during ARPI treatment are linked with mCRPC clinical outcomes. Experimental Design: Plasma cell-free DNA was collected from 81 patients with mCRPC at baseline and after 4 weeks of first-line ARPI treatment during two prospective multicenter observational studies (NCT02426333; NCT02471469). ctDNA fraction was calculated from somatic mutations in targeted sequencing and genome copy-number profiles. Samples were classified into detected versus undetected ctDNA. Outcome measurements were progression-free survival (PFS) and overall survival (OS). Nondurable treatment response was defined as PFS ≤6 months. Results: ctDNA was detected in 48/81 (59%) baseline and 29/81 (36%) 4-week samples. ctDNA fraction for samples with detected ctDNA was lower at 4 weeks versus baseline (median 5.0% versus 14.5%, P = 0.017). PFS and OS were shortest for patients with persistent ctDNA at 4 weeks (univariate HR, 4.79; 95% CI, 2.62–8.77 and univariate HR, 5.49; 95% CI, 2.76–10.91, respectively), independent of clinical prognostic factors. For patients exhibiting change from detected to undetected ctDNA by 4 weeks, there was no significant PFS difference versus patients with baseline undetected ctDNA. ctDNA change had a positive predictive value of 88% and negative predictive value of 92% for identifying nondurable responses. Conclusions: Early changes in ctDNA fraction are strongly linked to duration of first-line ARPI treatment benefit and survival in mCRPC and may inform early therapy switches or treatment intensification. See related commentary by Sartor, p. 2745