Available online xxx Keywords:Can cer Me tab o lism Mi to chon dria Het ero gene ity Metas ta sis A B S T R A C T Al tered me tab o lism in can cer cells is piv otal for tu mor growth, most no tably by pro vid ing en ergy, re duc ing equiv a lents and build ing blocks while sev eral metabo lites ex ert a sig nal ing func tion pro mot ing tu mor growth and pro gres sion. A can cer tis sue can not be sim ply re duced to a bulk of pro lif er at ing cells. Tu mors are in deed com plex and dy namic struc tures where sin gle cells can het ero ge neously per form var i ous bi o log i cal ac tiv i ties with dif fer ent meta bolic re quire ments. Be cause tu mors are com posed of dif fer ent types of cells with meta bolic ac tiv i ties af fected by dif fer ent spa tial and tem po ral con texts, it is im por tant to ad dress me tab o lism tak ing into ac count cel lu lar and bi o log i cal het ero gene ity. In this re view, we de scribe this het ero gene ity also in meta bolic fluxes, thus show ing the rel a tive con tri bu tion of dif fer ent meta bolic ac tiv i ties to tu mor pro gres sion ac cord ing to the cel lu lar con text. This ar ti cle is part of a Spe cial Is sue en ti tled Res pi ra tory com plex I, edited by Giuseppe Gas parre, Ro drigue Rossig nol and Pierre Son veaux. Abbreviations: ACL, ATP cit rate lyase; AMPK, adeno sine monophos phate ki nase; ARG1, L argi nine me tab o liz ing en zyme arginase 1; BCAA, branched chain amino acid; Bcl2, B cell lym phoma 2; CAF, can cer as so ci ated fi brob last; CIC, can cer ini ti at ing cell; COX2, cy tochrome ox i dase; CSC, can cer stem cell; CREB, cyclic adeno sine monophos phate re sponse el e ment bind ing pro tein; DEC1, dif fer en tially ex pressed in chon dro cytes 1; EMT, ep ithe lial to mes enchy mal tran si tion; FAK, fo cal ad he sion ki nase; FAS, fatty acid syn thase; FBP, fruc tose 1,6 bis pho s phate; FDG PET, [ F] flu o rodeoxyglu cose positron emis sion to mog ra phy; GAPDH, glyc er alde hyde 3 phos phate de hy dro ge nase; HIF 1, hy poxia ac ti vated fac tor 1; HK2, hex ok i nase 2; HMGB1, high mo bil ity group box 1; HU VEC, hu man um bil i cal vein en dothe lial cell; IFN γ, in ter feron gamma; LDH, lac tate de hy dro ge nase; MEF, murine em bry onic fi brob last; MET, mes enchy mal to ep ithe lial tran si tion; MRI, mag netic res o nance imag ing; mTORC1, mam malian tar get of ra pamycin com plex 1; NSCLC, non small cell lung can cer; OX PHOS, ox ida tive phos pho ry la tion; PDAC, pan cre atic duc tal ade no car ci noma; PHD, pro lyl hy drox y lase; pHe, ex tra cel lu lar pH; pHi, in tra cel lu lar pH; PK, pyru vate ki nase; PPP, pen tose phos phate path way; REDD1, reg u lated in de vel op ment and DNA dam age re sponse 1; RhoA, Ras ho molog gene fam ily, mem ber A; ROS, re ac tive oxy gen species; SASP, senes cence as so ci ated se cre tory phe no type; SCO2, syn the sis of cy tochrome ox i dase 2; SGK 1, serum and glu co cor ti coid reg u lated ki nase 1 Sirt1, sir tuin 1; TAM, tu mor as so ci ated macrophage; TIGAR, TP53 in duced gly col y ...

The rediscovery and reinterpretation of the Warburg effect in the year 2000 occulted for almost a decade the key functions exerted by mitochondria in cancer cells. Until recent times, the scientific community indeed focused on constitutive glycolysis as a hallmark of cancer cells, which it is not, largely ignoring the contribution of mitochondria to the malignancy of oxidative and glycolytic cancer cells, being Warburgian or merely adapted to hypoxia. In this review, we highlight that mitochondria are not only powerhouses in some cancer cells, but also dynamic regulators of life, death, proliferation, motion and stemness in other types of cancer cells. Similar to the cells that host them, mitochondria are capable to adapt to tumoral conditions, and probably to evolve to 'oncogenic mitochondria' capable of transferring malignant capacities to recipient cells. In the wider quest of metabolic modulators of cancer, treatments have already been identified targeting mitochondria in cancer cells, but the field is still in infancy.

◥Ovarian cancer is an aggressive disease that affects about 300,000 patients worldwide, with a yearly death count of about 185,000. Following surgery, treatment involves adjuvant or neoadjuvant administration of taxane with platinum compounds cisplatin or carboplatin, which alkylate DNA through the same chemical intermediates. However, although platinum-based therapy can cure patients in a number of cases, a majority of them discontinues treatment owing to side effects and to the emergence of resistance. In this study, we focused on resistance to cisplatin and investigated whether metabolic changes could be involved. As models, we used matched pairs of cisplatin-sensitive (SKOV-3 and COV-362) and cisplatin-resistant (SKOV-3-R and COV-362-R) human ovarian carcinoma cells that were selected in vitro following exposure to increasing doses of the chemotherapy. Metabolic comparison revealed that resistant cells undergo a shift toward a more oxidative metabolism. The shift goes along with a reorganization of the mitochondrial network, with a generally increased mitochondrial compartment. More functional mitochondria in cisplatin-resistant compared with cisplatin-sensitive cells were associated to enzymatic changes affecting either the electron transport chain (SKOV-3/SKOV-3-R model) or mitochondrial coupling (COV-362/COV-362-R model). Our findings further indicate that the preservation of functional mitochondria in these cells could be due to an increased mitochondrial turnover rate, suggesting mitophagy inhibition as a potential strategy to tackle cisplatin-resistant human ovarian cancer progression.Implications: Besides classical mechanisms related to drug efflux and target modification, we report that preserving functional mitochondria is a strategy used by human ovarian cancer cells to resist to cisplatin chemotherapy.

Cancers develop metabolic strategies to cope with their microenvironment often characterized by hypoxia, limited nutrient bioavailability and exposure to anticancer treatments. Among these strategies, the metabolic symbiosis based on the exchange of lactate between hypoxic/glycolytic cancer cells that convert glucose to lactate and oxidative cancer cells that preferentially use lactate as an oxidative fuel optimizes the bioavailability of glucose to hypoxic cancer cells. This metabolic cooperation has been described in various human cancers and can provide resistance to anti-angiogenic therapies. It depends on the expression and activity of monocarboxylate transporters (MCTs) at the cell membrane. MCT4 is the main facilitator of lactate export by glycolytic cancer cells, and MCT1 is adapted for lactate uptake by oxidative cancer cells. While MCT1 inhibitor AZD3965 is currently tested in phase I clinical trials and other inhibitors of lactate metabolism have been developed for anticancer therapy, predicting and monitoring a response to the inhibition of lactate uptake is still an unmet clinical need. Here, we report the synthesis, evaluation and in vivo validation of (±)-[18F]-3-fluoro-2-hydroxypropionate ([18F]-FLac) as a tracer of lactate for positron emission tomography. [18F]-FLac offers the possibility to monitor MCT1-dependent lactate uptake and inhibition in tumors in vivo.

The clinical management of head and neck squamous cell carcinoma (HNSCC) commonly involves chemoradiotherapy, but recurrences often occur that are associated with radioresistance. Using human SQD9 laryngeal squamous cell carcinoma cancer cells as a model, we aimed to identify metabolic changes associated with acquired radioresistance. In a top-down approach, matched radiosensitive and radioresistant SQD9 cells were generated and metabolically compared, focusing on glycolysis, oxidative phosphorylation (OXPHOS) and ROS production. The cell cycle, clonogenicity, tumor growth in mice and DNA damage-repair were assessed. Mitochondrial DNA (mtDNA) was sequenced. In a bottom-up approach, matched glycolytic and oxidative SQD9 cells were generated using FACS-sorting, and tested for their radiosensitivity/radioresistance. We found that acquired radioresistance is associated with a shift from a glycolytic to a more oxidative metabolism in SQD9 cells. The opposite was also true, as the most oxidative fraction isolated from SQD9 wild-type cells was also more radioresistant than the most glycolytic fraction. However, neither reduced hexokinase expression nor OXPHOS were directly responsible for the radioresistant phenotype. Radiosensitive and radioresistant cells had similar proliferation rates and were equally efficient for ATP production. They were equally sensitive to redox stress and had similar DNA damage repair, but radioresistant cells had an increased number of mitochondria and a higher mtDNA content. Thus, an oxidative switch is associated with but is not responsible for acquired radioresistance in human SQD9 cells. In radioresistant cells, more abundant and fitter mitochondria could help to preserve mitochondrial functions upon irradiation.

Glioblastoma represents the highest grade of brain tumors. Despite maximal resection surgery associated with radiotherapy and concomitant followed by adjuvant chemotherapy with temozolomide (TMZ), patients have a very poor prognosis due to the rapid recurrence and the acquisition of resistance to TMZ. Here, initially considering that TMZ is a prodrug whose activation is pH-dependent, we explored the contribution of glioblastoma cell metabolism to TMZ resistance. Using isogenic TMZ-sensitive and TMZ-resistant human glioblastoma cells, we report that the expression of O6-methylguanine DNA methyltransferase (MGMT), which is known to repair TMZ-induced DNA methylation, does not primarily account for TMZ resistance. Rather, fitter mitochondria in TMZ-resistant glioblastoma cells are a direct cause of chemoresistance that can be targeted by inhibiting oxidative phosphorylation and/or autophagy/mitophagy. Unexpectedly, we found that PARP inhibitor olaparib, but not talazoparib, is also a mitochondrial Complex I inhibitor. Hence, we propose that the anticancer activities of olaparib in glioblastoma and other cancer types combine DNA repair inhibition and impairment of cancer cell respiration.

<p>Figure S3 shows that inhibiting cell respiration or glycolysis does not selectively kill cisplatin-resistant human ovarian cancer cells.</p>

<p>Figure S4 shows that inhibiting autophagy better preserves mtDNA in SKOV-3-R versus SKOV-3 cells.</p>