The activation of de novo serine/glycine biosynthesis in a subset of tumors has been described as a major contributor to tumor pathogenesis, poor outcome, and treatment resistance. Amplifications and mutations of de novo serine/glycine biosynthesis enzymes can trigger pathway activation; however, a large group of cancers displays serine/glycine pathway overexpression induced by oncogenic drivers and unknown regulatory mechanisms. A better understanding of the regulatory network of de novo serine/glycine biosynthesis activation in cancer might be essential to unveil opportunities to target tumor heterogeneity and therapy resistance. In the current review, we describe how the activation of de novo serine/glycine biosynthesis in cancer is linked to treatment resistance and its implications in the clinic. To our knowledge, only a few studies have identified this pathway as metabolic reprogramming of cancer cells in response to radiation therapy. We propose an important contribution of de novo serine/glycine biosynthesis pathway activation to radioresistance by being involved in cancer cell viability and proliferation, maintenance of cancer stem cells (CSCs), and redox homeostasis under hypoxia and nutrient-deprived conditions. Current approaches for inhibition of the de novo serine/glycine biosynthesis pathway provide new opportunities for therapeutic intervention, which in combination with radiotherapy might be a promising strategy for tumor control and ultimately eradication. Further research is needed to gain molecular and mechanistic insight into the activation of this pathway in response to radiation therapy and to design sophisticated stratification methods to select patients that might benefit from serine/glycine metabolism-targeted therapies in combination with radiotherapy.

The RPSAP52 pseudogene is transcribed in the opposite direction to the oncofetal gene HMGA2 and is reexpressed in various human cancers. Here, we investigate the impact of RPSAP52 in ovarian cancer (OC) and explore the potential therapeutic application of GapmeR antisense oligonucleotides against RPSAP52 in preclinical models. RPSAP52 and HMGA2 expression were investigated in TCGA for OC and further explored in a panel of orthotopic PDXs and commercial cell lines by RT-qPCR. The Kaplan-Meier method was used to estimate survival associated with RPSAP52 expression in a dataset within the OC TCGA cohort. The effect of specific silencing of RPSAP52 on tumor growth in vitro and in vivo was evaluated by lentiviral-mediated depletion and antisense LNA GapmeRs against RPSAP52. The pseudogene RPSAP52 was overexpressed in epithelial OC in both patient samples and OC preclinical models coinciding with the overexpression of HMGA2. Elevated expression levels of RPSAP52 in the early stages of OC were associated with poorer clinical outcomes and could stratify patients in stages I and II. The specific depletion of RPSAP52 led to a reduction in OC tumor growth in vitro and in vivo. Furthermore, the treatment with antisense LNA GapmeRs against RPSAP52 showed significant antitumoral effect in OC cell lines and in a PDOX model (without evident toxicity). Our findings demonstrate that RPSAP52 displays pro-growth features in OC, underscoring the significance of pseudogenes in cancer pathophysiology. This pseudogene has potential utility as therapeutic target in OC and as valuable prognostic biomarker for the early stages of this disease.

Background : T-cell acute lymphoblastic leukemia (T-ALL) and peripheral T-cell lymphoma (PTCL) are aggressive hematological malignancies requiring novel therapeutic strategies. The majority of T-ALL and PTCL tumors display metabolic activation and addiction to endogenous serine/glycine synthesis (SSP), providing opportunities for targeted therapy with the clinically used antidepressant sertraline, inhibiting SSP enzymes SHMT1/2. However, sertraline monotherapy only induces cell cycle arrest and has limited efficacy to suppress disease progression in vivo . Methods : Drug synergy of sertraline combined with clinically used proteasome inhibitors carfilzomib and bortezomib was evaluated. Drug effects on cell cycle, proliferation and apoptosis were assessed in T-ALL, PTCL and healthy blood cells using flow cytometry assays. Proteomic, lipidomic and metabolic analyses on drug treated T-ALL cells were performed to elucidate the molecular mechanisms underlying drug synergy, followed by validation of changes of interest, metabolic rescues and shRNA-knockdown of SSP enzymes in T-ALL cells. In vivo therapeutic efficacy and immune remodelling were evaluated in an immunocompetent MYCN-overexpressing PTCL mouse model. Results : Sertraline acted synergistically with clinically used proteasome inhibitor carfilzomib to induce cell cycle arrest and apoptosis in T-ALL and PTCL cells with SSP activity, with minimal effects on SSP-inactive T-ALL cells or healthy blood cells. Adding carfilzomib also enhanced the therapeutic efficacy of sertraline in an aggressive MYCN PTCL model. Sertraline rewired cell metabolism towards increased cholesterol uptake and biosynthesis in SSP-active T-ALL cells, and this effect was not obtained by other means of SSP inhibition. In contrast to sertraline, carfilzomib promoted cholesterol efflux. Moreover, carfilzomib reduced total lipid levels, further restricting nutrients in sertraline-carfilzomib treated cells. Additionally, the drug combination impaired mitochondrial respiration and elevated reactive oxygen species (ROS) levels and DNA damage in SSP-active tumor cells, which was rescued by citrate supplementation. Interestingly, these metabolic changes were associated with microenvironmental changes in our mouse model, where the drug combination elevated natural killer T-cells, neutrophils and eosinophils. Conclusions : Our study identifies synergy of sertraline-carfilzomib combination treatment mediated through metabolic impairment and is associated with remodelling of the immune microenvironment. This invites for further clinical investigation of this drug combination as a therapeutic strategy for SSP-active T-cell malignancies.