Valproic acid enhances immune reprogramming in locally advanced rectal cancer: Insights from the VshoRTR3 trial

Rectal cancer, a common subtype of colorectal cancer, is rising worldwide due to lifestyle factors and aging population. Patients with locally advanced rectal cancer (LARC) are commonly treated with neoadjuvant chemoradiotherapy and surgery; however, recurrence rates remain high, ranging from 25% to 40%, depending on disease stage. Among the hallmarks of cancer, metabolic dysregulation and immune suppression play a critical role in tumor recurrence. Valproic acid (VPA), a histone deacetylase inhibitor, has shown potential in modulating these processes. The V-shoRT-R3 clinical trial (NCT01898104) have investigated the combination of VPA with short-course radiotherapy (SCRT) and capecitabine in LARC patients, aiming to enhance therapeutic efficacy by targeting some cancer hallmarks. To assess the biological effects of VPA within the V-shoRT-R3 trial, a multi-omic approach was employed. Peripheral blood samples were collected at baseline and after 10 days of VPA treatment, and analyzed by cytokine profiling (48-plex Bio-Plex assay) and metabolomics (1H-NMR and LC-MS). Gene expression was profiled (770-plex Nanostring panel) on matched biopsy and surgical specimens. Validation studies are ongoing using spatial transcriptomics and immunohistochemistry in an expanded patient's cohort. Preliminary data from 48 patients suggest that adding VPA to SCRT and capecitabine improves clinical outcomes. Specifically, the VPA-based regimen was associated with a significant increase in relapse-free survival compared to standard treatment. At a median follow up of 70,14 months (IQR 63-77) 3 pts in SCRT arm relapsed, with a RFS rate of 83% (cv scrt), 71% SCRT 66% CSCRT 40% V SCRT respectively. Cytokine analysis revealed a significant downregulation of IL1beta, LIF, CSF1, and CSF2, following VPA treatment, suggesting suppression of the myeloid compartment. Metabolomic analysis revealed altered amino acid and energy metabolism, with enrichment in immune-related pathways. Notably, VPA induces increased tryptophan and decreased kynurenine levels suggesting a reduction of indoleamine 2,3-dioxygenase (IDO) activity confirmed also by its reduced expression indicating a shift away from immunosuppressive metabolism. Moreover, gene expression analysis revealed activation of NK cell, IL10, and cytotoxicity signatures in VPA-treated patients, indicating marked immune modulation. VPA promotes immune activation and metabolic reprogramming, improving outcomes in LARC. Multi-omics analyses and ongoing validations will define VPA-driven mechanisms to inform for more personalized therapeutic strategies.