The overall objectives of my project were to decipher the interaction between the transcriptional and metabolic regulation of extracellular matrix (ECM) remodeling and how this novel metabolic activation can be targeted to inhibit breast cancer-derived metastases growth in the lung. First, the role of pyruvate, a nutrient particularly available in the lung, in ECM metabolism was investigated. The results obtained suggest that metabolic regulation by pyruvate is an important and transcriptionally independent determinant of collagen hydroxylation (the ECM modification process). In addition, inhibition of pyruvate metabolism by genetically blocking its transporter (MCT2) is sufficient to impair metastatic growth in the lung. Next, I tested whether pharmacological inhibition of pyruvate uptake (by blocking MCT2) could be potentially used in the clinics. Although both genetic and pharmacological MCT2 inhibition showed an effect on metastatic growth in vivo, this effect was less pronounced when using the MCT2 inhibitor α-cyano-4-hydroxycinnamate (4-CIN). Thus, I aimed to increase the efficacy of this compound by using a nanotechnology-based targeted drug-delivery system. However, although different approaches were tested, I found that using nanoparticles as a delivery system did not increase the efficacy of MCT2 inhibition. Additionally, I investigated whether pyruvate availability in the lung metastatic niche supports alternative pathways important for metastasis formation such as mTOR activation. These results show that blocking pyruvate uptake impaired mTORC1 signaling in metastases (see publication Rinaldi et al 2021). Taken together, the results of the first part of this project suggest that pyruvate availability is an important modulator of growth signaling during metastasis formation in the lung.
On the other hand, I continued investigating the nutrient availability of the lung environment in order to find new potential dependences of the metastasized cancer cells to colonize this niche. In this sense, I focused on cellular processes that can be regulated by metabolism, such as protein modification. Post-translational modifications are chemical modifications of the proteins that can dynamically change their functions. Protein acetylation, a type of post-translational modification, is crucial for many important cellular processes, which can in turn contribute to metastasis formation. I have discovered that metastatic breast cancer cells increase protein acetylation in order to acquire the capacity to metastasize and grow in the lung. During this process, metabolized nutrients are directly used by the tumor cells in the acetylation reaction to add chemicals called acetyl groups to the proteins. Hence, metabolic processes have an important role and physiological consequences that come along with protein acetylation. Specifically, I found that an important fatty acid, palmitic acid, is highly abundant in the lung environment and metastasized cancer cells arriving at this niche use them to sustain acetyl-CoA production through their oxidation in the mitochondria via carnitine palmitoyltransferase 1A (CPT1A). Importantly, I have observed that deletion of CPT1A abrogates metastases growth in breast cancer mouse models. Taken together, these results identify palmitate as a crucial nutrient in the lung metastatic niche and establish CPT1A as a novel potential target to prevent lung metastases formation.
In conclusion, this project has demonstrated that there are specific nutrients in the lung metastatic niche that sustain key processes to support the growth of metastasized cancer cells in the new environment. Furthermore, we have established two druggable components of metabolic regulatory pathways (MCT2 and CPT1A) that can be targeted to impair metastatic growth in the lung.
During the exploitation of this project, I have published relevant publications in the field of metastasis and cancer metabolism: two first author and one 2nd author review/method article (Altea-Manzano et al 2020 EMBO Reports; Altea-Manzano et al 2020 Methods in Molecular Biology; Fernandez-Garcia et al 2020 Trends in Biochemical Sciences) and one co-author research article (Rinaldi et al 2021 Molecular Cell). In addition, the main results of this proposal will be published shortly. I have delivered scientific knowledge to diverse audiences by engaging in various dissemination and teaching assignments. I was two times selected to orally present my research in a short talk at international meetings (2020 BCAR conference, Brussels, and 2021 Keystone Symposium Tumor Metabolism, online).
