Sebastian Igelmann

Cancer cells that seed in the lung require lipids often produced by alveolar type II (AT2) cells. However, whether overt metastases depend on AT2 cell–derived lipids and whether AT2 cells can be targeted to reduce metastasis growth remains unknown. We discovered that breast cancer–derived lung metastases stimulate the proliferation of AT2 cells in their vicinity and reprogram them into lipid feeder cells in mice and patients using spatial analysis. Mechanistically, the metastasis secretome activates the transcription factor sterol regulatory element–binding transcription factor 1 (SREBP-1) in AT2 cells, enhancing the expression of key de novo lipid synthesis genes, including fatty acid synthase (FASN) and glycerol-3-phosphate acyltransferase 1 (GPAM). Deleting Fasn selectively in AT2 cells or targeting FASN and GPAM systemically significantly impairs lung metastasis growth in mice. In summary, we discovered that overt metastases reprogram AT2 cells and that targeting the lipid metabolism of AT2 cells impairs metastasis growth.Significance:Current therapies in oncology targeting the cancer or immune cell compartment of tumors show limited efficacy against breast cancer–derived metastases. We discovered that decreasing the lipid metabolism of lung resident AT2 cells is sufficient to impair lung metastasis growth in mice without apparent adverse effects.

Supplementary Figure 1 Surfactant lipids are enriched in the vicinity of lung metastases from patients with breast cancer; Supplementary Figure 2 AT2 cells and surfactant lipids co-localize in the vicinity of metastases from mice; Supplementary Figure 3 Metastases progression increases the enrichment of AT2 cells; Supplementary Figure 4 The metastasis secretome reprograms AT2 cell lipid metabolism by activating SREBP-1; Supplementary Figure 5 Gpam knockdown in cancer cells does not affect 3D spheroid growth in vitro; Supplementary Figure 6 GPAM and FASN inhibition in cancer cells does not affect metastasis formation in vitro and in vivo

Short hairpin RNAs (shRNAs) used to generate knockdown cell lines

Patients with colorectal cancer (CRC) frequently develop liver metastases^1-3. The prognosis of these patients is skewed by the histopathological heterogeneity of their liver metastases^4,5. Patients with 'replacement' metastases have a 5-year overall survival of less than 44.2%, compared with 73.4% in patients with 'encapsulated' (previously known as desmoplastic) metastases⁵; yet there are currently no approved therapies targeting replacement liver metastases. Here we show that treatment-naive patients with CRC with liver steatosis have an increased occurrence of replacement metastases compared with patients without steatosis. Mechanistically, we find that steatosis-promoted fatty acid oxidation increases formation of replacement metastases by increasing MYC stability through acetylation. In turn, MYC activates proline synthesis, fuelling collagen production, enabling growth of replacement metastases. Targeting MYC, P5CS or COL1A1 suppresses the occurrence and growth of replacement metastases in patient-derived organoids, mouse or patient-derived xenograft models. Spatial metabolite and protein analyses of liver metastases from patients with CRC further support this mechanism. In conclusion, we provide a mechanistic understanding of the emergence of liver metastases with poor prognosis in treatment-naive patients with CRC, identifying potential targets for therapeutic intervention.

Metabolic plasticity of cancer cells plays a major role in metastasis. Use of alternative carbon fuels (e.g., lactate) boosts metabolic plasticity, but the underlying mechanisms remain obscure. We show that lactate dehydrogenase B (LDHB) cooperates with the hydride ion transfer complex (HTC) comprised of pyruvate carboxylase (PC), malic enzyme (ME1) and malate dehydrogenase (MDH1) to form a metabolon that confers metabolic flexibility through lactate assimilation under physiological conditions. HTC/LDHB metabolon assembles in the aggressive breast cancer subtypes and reprograms nicotinamide adenine dinucleotide (NAD) metabolism to promote migration, invasion and escape from anoikis - thereby driving metastasis. Altogether, this work identifies a lactate-fueled metabolon that propels metastatic dissemination of breast cancer.

Cancer cells that seed in the lung require lipids often produced by alveolar type II (AT2) cells. However, whether overt metastases depend on AT2 cell–derived lipids and whether AT2 cells can be targeted to reduce metastasis growth remains unknown. We discovered that breast cancer–derived lung metastases stimulate the proliferation of AT2 cells in their vicinity and reprogram them into lipid feeder cells in mice and patients using spatial analysis. Mechanistically, the metastasis secretome activates the transcription factor sterol regulatory element–binding transcription factor 1 (SREBP-1) in AT2 cells, enhancing the expression of key de novo lipid synthesis genes, including fatty acid synthase (FASN) and glycerol-3-phosphate acyltransferase 1 (GPAM). Deleting Fasn selectively in AT2 cells or targeting FASN and GPAM systemically significantly impairs lung metastasis growth in mice. In summary, we discovered that overt metastases reprogram AT2 cells and that targeting the lipid metabolism of AT2 cells impairs metastasis growth. Significance: Current therapies in oncology targeting the cancer or immune cell compartment of tumors show limited efficacy against breast cancer–derived metastases. We discovered that decreasing the lipid metabolism of lung resident AT2 cells is sufficient to impair lung metastasis growth in mice without apparent adverse effects.

Lung metastases occur in up to 54% of patients with metastatic tumours^1,2. Contributing factors to this high frequency include the physical properties of the pulmonary system and a less oxidative environment that may favour the survival of cancer cells³. Moreover, secreted factors from primary tumours alter immune cells and the extracellular matrix of the lung, creating a permissive pre-metastatic environment primed for the arriving cancer cells^4,5. Nutrients are also primed during pre-metastatic niche formation⁶. Yet, whether and how nutrients available in organs in which tumours metastasize confer cancer cells with aggressive traits is mostly undefined. Here we found that pulmonary aspartate triggers a cellular signalling cascade in disseminated cancer cells, resulting in a translational programme that boosts aggressiveness of lung metastases. Specifically, we observe that patients and mice with breast cancer have high concentrations of aspartate in their lung interstitial fluid. This extracellular aspartate activates the ionotropic N-methyl-d-aspartate receptor in cancer cells, which promotes CREB-dependent expression of deoxyhypusine hydroxylase (DOHH). DOHH is essential for hypusination, a post-translational modification that is required for the activity of the non-classical translation initiation factor eIF5A. In turn, a translational programme with TGFβ signalling as a central hub promotes collagen synthesis in lung-disseminated breast cancer cells. We detected key proteins of this mechanism in lung metastases from patients with breast cancer. In summary, we found that aspartate, a classical biosynthesis metabolite, functions in the lung environment as an extracellular signalling molecule to promote aggressiveness of metastases.

Senescent cells, which accumulate with age, exhibit a pro-inflammatory senescence-associated secretory phenotype (SASP) that includes the secretion of cytokines, lipids, and extracellular vesicles (EVs). Here, we established an in vitro model of senescence induced by Raf-1 oncogene in RAW 264.7 murine macrophages (MΦ) and compared them to senescent MΦ found in mouse lung tumors or primary macrophages treated with hydrogen peroxide. The transcriptomic analysis of senescent MΦ revealed an important inflammatory signature regulated by NFkB. We observed an increased secretion of EVs in senescent MΦ, and these EVs presented an enrichment for ribosomal proteins, major vault protein, pro-inflammatory miRNAs, including miR-21a, miR-155, and miR-132, and several mRNAs. The secretion of senescent MΦ allowed senescent murine embryonic fibroblasts to restart cell proliferation. This antisenescence function of the macrophage secretome may explain their pro-tumorigenic activity and suggest that senolytic treatment to eliminate senescent MΦ could potentially prevent these deleterious effects.

Pancreatic cancer (pancreatic ductal adenocarcinoma: PDAC) is one of the most aggressive neoplastic diseases. Metformin use has been associated with reduced pancreatic cancer incidence and better survival in diabetics. Metformin has been shown to inhibit PDAC cells growth and survival, both in vitro and in vivo. However, clinical trials using metformin have failed to reduce pancreatic cancer progression in patients, raising important questions about molecular mechanisms that protect tumor cells from the antineoplastic activities of metformin. We confirmed that metformin acts through inhibition of mitochondrial complex I, decreasing the NAD⁺/NADH ratio, and that NAD⁺/NADH homeostasis determines metformin sensitivity in several cancer cell lines. Metabolites that can restore the NAD⁺/NADH ratio caused PDAC cells to be resistant to metformin. In addition, metformin treatment of PDAC cell lines induced a compensatory NAMPT expression, increasing the pool of cellular NAD⁺. The NAMPT inhibitor FK866 sensitized PDAC cells to the antiproliferative effects of metformin in vitro and decreased the cellular NAD⁺ pool. Intriguingly, FK866 combined with metformin increased survival in mice bearing KP4 cell line xenografts, but not in mice with PANC-1 cell line xenografts. Transcriptome analysis revealed that the drug combination reactivated genes in the p53 pathway and oxidative stress, providing new insights about the mechanisms leading to cancer cell death.