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Many tumour cells show dependence on exogenous serine and dietary serine and glycine starvation can inhibit the growth of these cancers and extend survival in mice. However, numerous mechanisms promote resistance to this therapeutic approach, including enhanced expression of the de novo serine synthesis pathway (SSP) enzymes or activation of oncogenes that drive enhanced serine synthesis. Here we show that inhibition of PHGDH, the first step in the SSP, cooperates with serine and glycine depletion to inhibit one-carbon metabolism and cancer growth. In vitro, inhibition of PHGDH combined with serine starvation leads to a defect in global protein synthesis, which blocks the activation of an ATF-4 response and more broadly impacts the protective stress response to amino acid depletion. In vivo, the combination of diet and inhibitor shows therapeutic efficacy against tumours that are resistant to diet or drug alone, with evidence of reduced one-carbon availability. However, the defect in ATF4-response seen in vitro following complete depletion of available serine is not seen in mice, where dietary serine and glycine depletion and treatment with the PHGDH inhibitor lower but do not eliminate serine. Our results indicate that inhibition of PHGDH will augment the therapeutic efficacy of a serine depleted diet. Dietary serine and glycine starvation has emerged as a potential therapy for cancer. Here, the authors show that inhibition of PHGDH, which mediates the first step in the serine synthesis pathway, improves the therapeutic efficacy of serine depletion diet in mouse xenograft models.

The enzyme serine hydroxymethyltransferse (SHMT) converts serine into glycine and a tetrahydrofolate-bound one-carbon unit. Folate one-carbon units support purine and thymidine synthesis, and thus cell growth. Mammals have both cytosolic SHMT1 and mitochondrial SHMT2, with the mitochondrial isozyme strongly up-regulated in cancer. Here we show genetically that dual SHMT1/2 knockout blocks HCT-116 colon cancer tumor xenograft formation. Building from a pyrazolopyran scaffold that inhibits plant SHMT, we identify small-molecule dual inhibitors of human SHMT1/2 (biochemical IC50 ∼ 10 nM). Metabolomics and isotope tracer studies demonstrate effective cellular target engagement. A cancer cell-line screen revealed that B-cell lines are particularly sensitive to SHMT inhibition. The one-carbon donor formate generally rescues cells from SHMT inhibition, but paradoxically increases the inhibitor’s cytotoxicity in diffuse large B-cell lymphoma (DLBCL). We show that this effect is rooted in defective glycine uptake in DLBCL cell lines, rendering them uniquely dependent upon SHMT enzymatic activity to meet glycine demand. Thus, defective glycine import is a targetable metabolic deficiency of DLBCL.

Multiple p38 MAP kinase inhibitors have been developed for the treatment of inflammatory diseases such as rheumatoid arthritis, but their effectiveness has been limited due to toxicity and tachyphylaxis, leading to a lack of clinical benefit. Efforts have been made to circumvent this limitation by targeting individual substrates downstream of p38, including MK2 and MK5. This approach has failed to yield clinical benefit despite preclinical evidence of a therapeutic effect. We hypothesized that there is redundancy in the MAPK activating kinase family that would necessitate blocking multiple kinases to sufficiently impact inflammatory processes. We used heterobifunctional protein degraders that either specifically degraded MK2 selectively or degraded MK2/3/5 simultaneously to test the hypothesis, in addition to genetic approaches to enable knockdown. In human PBMCs, elimination of MK2/3/5 with heterobifunctional degraders resulted in full reduction of TLR4 or TLR7/8 induced TNFα, whereas MK2-specific degradation only attenuated TNFα biosynthesis. In contrast, both specific MK2 degradation and broad MK2/3/5 degradation inhibited TGF-β-induced collagen production in human fibroblasts. This observation was consistent with genetic deletions of MK2, MK3 and MK5 (singly and in combination) whereby single deletion of MK2, MK3 or MK5 attenuated lipopolysaccharide (LPS) induced TNFα production and had no effect on R848-induced TNFα production. Double deletion of MK2 and MK3 or MK2 and MK5 or MK2/3/5 triple deletion had a significantly greater effect on TNFα production regardless of stimulus. The combined data suggest cooperativity between MK2 and either MK3 or MK5 for efficient, cell context-dependent modulation of inflammatory responses.

Toll-like receptor–driven and interleukin-1 (IL-1) receptor–driven inflammation mediated by IL-1 receptor–associated kinase 4 (IRAK4) is involved in the pathophysiology of hidradenitis suppurativa (HS) and atopic dermatitis (AD). KT-474 (SAR444656), an IRAK4 degrader, was studied in a randomized, double-blind, placebo-controlled phase 1 trial where the primary objective was safety and tolerability. Secondary objectives included pharmacokinetics, pharmacodynamics and clinical activity in patients with moderate to severe HS and in patients with moderate to severe AD. KT-474 was administered as a single dose and then daily for 14 d in 105 healthy volunteers (HVs), followed by dosing for 28 d in an open-label cohort of 21 patients. Degradation of IRAK4 was observed in HV blood, with mean reductions after a single dose of ≥93% at 600–1,600 mg and after 14 daily doses of ≥95% at 50–200 mg. In patients, similar IRAK4 degradation was achieved in blood, and IRAK4 was normalized in skin lesions where it was overexpressed relative to HVs. Reduction of disease-relevant inflammatory biomarkers was demonstrated in the blood and skin of patients with HS and patients with AD and was associated with improvement in skin lesions and symptoms. There were no drug-related infections. These results, from what, to our knowledge, is the first published clinical trial using a heterobifunctional degrader, provide initial proof of concept for KT-474 in HS and AD to be further confirmed in larger trials. ClinicalTrials.gov identifier: NCT04772885 . The heterobifunctional degrader KT-474 shows target engagement and is safe to use in healthy volunteers and in patients with hidradenitis suppurativa and patients with atopic dermatitis, and it exhibits preliminary efficacy in the improvement of skin lesions and symptoms in patients.

The complement pathway is an important part of the immune system, and uncontrolled activation is implicated in many diseases. The human complement component 5 protein (C5) is a validated drug target within the complement pathway, as an anti-C5 antibody (Soliris) is an approved therapy for paroxysmal nocturnal hemoglobinuria. Here, we report the identification, optimization and mechanism of action for the first small-molecule inhibitor of C5 complement protein. An inhibitor of the complement pathway of the innate immune system targets the human complement component 5 protein (C5) by binding to an interfacial pocket to prevent its proteolytic cleavage by the last enzyme of the complement pathway, C5 convertase.

A hallmark of metastasis is the adaptation of tumor cells to new environments. Although it is well established that the metabolic milieu of the brain is severely deprived of nutrients, particularly the amino acids serine and its catabolite glycine, how brain metastases rewire their metabolism to survive in the nutrient-limited environment of the brain is poorly understood. Here we demonstrate that cell-intrinsic de novo serine synthesis is a major determinant of brain metastasis. Whole proteome comparison of triple-negative breast cancer (TNBC) cells that differ in their capacity to colonize the brain reveals that 3-phosphoglycerate dehydrogenase (PHGDH), which catalyzes the rate-limiting step of glucose-derived serine synthesis, is the most significantly upregulated protein in cells that efficiently metastasize to the brain. Genetic silencing or pharmacological inhibition of PHGDH attenuated brain metastasis and improved overall survival in mice, whereas expression of catalytically active PHGDH in a non-brain trophic cell line promoted brain metastasis. Collectively, these findings indicate that nutrient availability determines serine synthesis pathway dependence in brain metastasis, and suggest that PHGDH inhibitors may be useful in the treatment of patients with cancers that have spread to the brain. Our study highlights how limited serine and glycine availability within the brain microenvironment potentiates tumor cell sensitivity to serine synthesis inhibition. This finding underscores the importance of studying cancer metabolism in physiologically-relevant contexts, and provides a rationale for using PHGDH inhibitors to treat brain metastasis.