Belzutifan for von Hippel-Lindau Disease: Pancreatic Lesion Population of the Phase 2 LITESPARK-004 Study.

PURPOSE: Primary analysis of the ongoing, single-arm, phase 2 LITESPARK-004 study (NCT03401788) showed clinically meaningful antitumor activity in von Hippel-Lindau (VHL) disease-associated renal cell carcinoma (RCC) and other neoplasms with belzutifan treatment. We describe results of belzutifan treatment for VHL disease-associated pancreatic lesions [pancreatic neuroendocrine tumors (pNET) and serous cystadenomas]. PATIENTS AND METHODS: Adults with VHL diagnosis based on germline VHL alteration, ≥1 measurable RCC tumor, no renal tumor >3 cm or other VHL neoplasm requiring immediate surgery, Eastern Cooperative Oncology Group performance status of 0 or 1, and no prior systemic anticancer treatment received belzutifan 120 mg once daily. End points included objective response rate (ORR), duration of response (DOR), progression-free survival (PFS), and linear growth rate (LGR) in all pancreatic lesions and pNETs per RECIST version 1.1 by independent review committee, and safety. RESULTS: All 61 enrolled patients (100%) had ≥1 pancreatic lesion and 22 (36%) had ≥1 pNET measurable at baseline. Median follow-up was 37.8 months (range, 36.1-46.1). ORR was 84% [51/61; 17 complete responses (CR)] in pancreatic lesions and 91% (20/22; 7 CRs) in pNETs. Median DOR and median PFS were not reached in pancreatic lesions or pNETs. After starting treatment, median LGR for pNETs was -4.2 mm per year (range, -7.9 to -0.8). Eleven patients (18%) had ≥1 grade 3 treatment-related adverse event (AE). No grade 4 or 5 treatment-related AEs occurred. CONCLUSIONS: Belzutifan continued to show robust activity and manageable safety in VHL disease-associated pNETs.

MITF regulates IDH1 and NNT and drives a transcriptional program protecting cutaneous melanoma from reactive oxygen species.

Microphthalmia-associated transcription factor (MITF) plays pivotal roles in melanocyte development, function, and melanoma pathogenesis. MITF amplification occurs in melanoma and has been associated with resistance to targeted therapies. Here, we show that MITF regulates a global antioxidant program that increases survival of melanoma cell lines by protecting the cells from reactive oxygen species (ROS)-induced damage. In addition, this redox program is correlated with MITF expression in human melanoma cell lines and patient-derived melanoma samples. Using a zebrafish melanoma model, we show that MITF decreases ROS-mediated DNA damage in vivo . Some of the MITF target genes involved, such as IDH1 and NNT , are regulated through direct MITF binding to canonical enhancer box (E-BOX) sequences proximal to their promoters. Utilizing functional experiments, we demonstrate the role of MITF and its target genes in reducing cytosolic and mitochondrial ROS. Collectively, our data identify MITF as a significant driver of the cellular antioxidant state. One Sentence Summary: MITF promote melanoma survival via increasing ROS tolerance.

Diseases of Hereditary Renal Cell Cancers.

Germline mutations in tumor suppressor genes and oncogenes lead to hereditary renal cell carcinoma (HRCC) diseases, characterized by a high risk of RCC and extrarenal manifestations. Patients of young age, those with a family history of RCC, and/or those with a personal and family history of HRCC-related extrarenal manifestations should be referred for germline testing. Identification of a germline mutation will allow for testing of family members at risk, as well as personalized surveillance programs to detect the early onset of HRCC-related lesions. The latter allows for more targeted and therefore more effective therapy and better preservation of renal parenchyma.

Understanding the Impact of Belzutifan on Treatment Strategies for Patients with VHL.

Belzutifan was recently approved for the management of Von Hippel-Lindau disease (VHL). Given the morbidity of recurrent treatment, systemic therapy to reduce or eliminate the need for surgery has been long-awaited. Herein, we sought to gain insight about future utilization by surveying VHL kidney cancer experts in the United States. A survey developed by members of the VHL Alliance (VHLA) Clinical Advisory Council was distributed to kidney cancer providers at VHLA and National Comprehensive Cancer Network (NCCN) centers. Surveys were administered on a secure web-based platform. A total of 60 respondents from 29 institutions participated. Urologists (50%) and medical oncologists (43%) represented the majority of participants. The majority (98%) of respondents anticipated that belzutifan's approval would significantly change the current treatment landscape. Most reported that therapy should be continuous (76%). There was a difference in willingness to prescribe belzutifan by specialty (38% of urologists vs 91% of medical oncologists (P = 0.02)). In individuals with renal tumors <3 cm, 36% would still recommend surveillance, while 36% would initiate belzutifan to prevent growth. In those with multifocal renal lesions and growth of a solitary tumor on belzutifan, 50% would proceed with only treatment of that site. In conclusion, VHL kidney cancer specialists anticipate a paradigm shift with the approval of belzutifan. Provider roles may change with movement away from surgical management. Opinions on treatment indications, such as when to initiate therapy and how to best salvage, vary widely and therefore collaborative efforts among experts may assist in the development of new clinical guidelines.

Telaglenastat Plus Cabozantinib or Everolimus for Advanced or Metastatic Renal Cell Carcinoma: An Open-Label Phase I Trial.

PURPOSE: Dual inhibition of glucose and glutamine metabolism results in synergistic anticancer effects in solid tumor models. Telaglenastat, an investigational, small-molecule, glutaminase inhibitor, exhibits modest single-agent activity in renal cell carcinoma (RCC) patients. This phase Ib trial evaluated telaglenastat plus cabozantinib or everolimus, agents known to impair glucose metabolism in patients with metastatic RCC (mRCC). PATIENTS AND METHODS: mRCC patients received escalating doses of telaglenastat [400-800 mg per os (p.o.) twice daily] in a 3 + 3 design, plus either everolimus (10 mg daily p.o.; TelaE) or cabozantinib (60 mg daily p.o.; TelaC). Tumor response (RECISTv1.1) was assessed every 8 weeks. Endpoints included safety (primary) and antitumor activity. RESULTS: Twenty-seven patients received TelaE, 13 received TelaC, with median 2 and 3 prior therapies, respectively. Treatment-related adverse events were mostly grades 1 to 2, most common including decreased appetite, anemia, elevated transaminases, and diarrhea with TelaE, and diarrhea, decreased appetite, elevated transaminases, and fatigue with TelaC. One dose-limiting toxicity occurred per cohort: grade 3 pruritic rash with TelaE and thrombocytopenia with TelaC. No maximum tolerated dose (MTD) was reached for either combination, leading to a recommended phase II dose of 800-mg telaglenastat twice daily with standard doses of E or C. TelaE disease control rate (DCR; response rate + stable disease) was 95.2% [20/21, including 1 partial response (PR)] among 21 patients with clear cell histology and 66.7% (2/3) for papillary. TelaC DCR was 100% (12/12) for both histologies [5/10 PRs as best response (3 confirmed) in clear cell]. CONCLUSIONS: TelaE and TelaC showed encouraging clinical activity and tolerability in heavily pretreated mRCC patients.

Seventh BHD international symposium: recent scientific and clinical advancement.

The 7th Birt-Hogg-Dubé (BHD) International Symposium convened virtually in October 2021. The meeting attracted more than 200 participants internationally and highlighted recent findings in a variety of areas, including genetic insight and molecular understanding of BHD syndrome, structure and function of the tumor suppressor Folliculin (FLCN), therapeutic and clinical advances as well as patients' experiences living with this malady.

The fission yeast FLCN/FNIP complex augments TORC1 repression or activation in response to amino acid (AA) availability.

The target of Rapamycin complex1 (TORC1) senses and integrates several environmental signals, including amino acid (AA) availability, to regulate cell growth. Folliculin (FLCN) is a tumor suppressor (TS) protein in renal cell carcinoma, which paradoxically activates TORC1 in response to AA supplementation. Few tractable systems for modeling FLCN as a TS are available. Here, we characterize the FLCN-containing complex in Schizosaccharomyces pombe (called BFC) and show that BFC augments TORC1 repression and activation in response to AA starvation and supplementation, respectively. BFC co-immunoprecipitates V-ATPase, a TORC1 modulator, and regulates its activity in an AA-dependent manner. BFC genetic and proteomic networks identify the conserved peptide transmembrane transporter Ptr2 and the phosphoribosylformylglycinamidine synthase Ade3 as new AA-dependent regulators of TORC1. Overall, these data ascribe an additional repressive function to Folliculin in TORC1 regulation and reveal S. pombe as an excellent system for modeling the AA-dependent, FLCN-mediated repression of TORC1 in eukaryotes.

Belzutifan for Renal Cell Carcinoma in von Hippel-Lindau Disease.

BACKGROUND: Patients with von Hippel-Lindau (VHL) disease have a high incidence of renal cell carcinoma owing to VHL gene inactivation and constitutive activation of the transcription factor hypoxia-inducible factor 2α (HIF-2α). METHODS: In this phase 2, open-label, single-group trial, we investigated the efficacy and safety of the HIF-2α inhibitor belzutifan (MK-6482, previously called PT2977), administered orally at a dose of 120 mg daily, in patients with renal cell carcinoma associated with VHL disease. The primary end point was objective response (complete or partial response) as measured according to the Response Evaluation Criteria in Solid Tumors, version 1.1, by an independent central radiology review committee. We also assessed responses to belzutifan in patients with non-renal cell carcinoma neoplasms and the safety of belzutifan. RESULTS: After a median follow-up of 21.8 months (range, 20.2 to 30.1), the percentage of patients with renal cell carcinoma who had an objective response was 49% (95% confidence interval, 36 to 62). Responses were also observed in patients with pancreatic lesions (47 of 61 patients [77%]) and central nervous system hemangioblastomas (15 of 50 patients [30%]). Among the 16 eyes that could be evaluated in 12 patients with retinal hemangioblastomas at baseline, all (100%) were graded as showing improvement. The most common adverse events were anemia (in 90% of the patients) and fatigue (in 66%). Seven patients discontinued treatment: four patients voluntarily discontinued, one discontinued owing to a treatment-related adverse event (grade 1 dizziness), one discontinued because of disease progression as assessed by the investigator, and one patient died (of acute toxic effects of fentanyl). CONCLUSIONS: Belzutifan was associated with predominantly grade 1 and 2 adverse events and showed activity in patients with renal cell carcinomas and non-renal cell carcinoma neoplasms associated with VHL disease. (Funded by Merck Sharp and Dohme and others; MK-6482-004 ClinicalTrials.gov number, NCT03401788.).

Genetic risk assessment for hereditary renal cell carcinoma: Clinical consensus statement.

BACKGROUND: Although renal cell carcinoma (RCC) is believed to have a strong hereditary component, there is a paucity of published guidelines for genetic risk assessment. A panel of experts was convened to gauge current opinions. METHODS: A North American multidisciplinary panel with expertise in hereditary RCC, including urologists, medical oncologists, clinical geneticists, genetic counselors, and patient advocates, was convened. Before the summit, a modified Delphi methodology was used to generate, review, and curate a set of consensus questions regarding RCC genetic risk assessment. Uniform consensus was defined as ≥85% agreement on particular questions. RESULTS: Thirty-three panelists, including urologists (n = 13), medical oncologists (n = 12), genetic counselors and clinical geneticists (n = 6), and patient advocates (n = 2), reviewed 53 curated consensus questions. Uniform consensus was achieved on 30 statements in specific areas that addressed for whom, what, when, and how genetic testing should be performed. Topics of consensus included the family history criteria, which should trigger further assessment, the need for risk assessment in those with bilateral or multifocal disease and/or specific histology, the utility of multigene panel testing, and acceptance of clinician-based counseling and testing by those who have experience with hereditary RCC. CONCLUSIONS: In the first ever consensus panel on RCC genetic risk assessment, 30 consensus statements were reached. Areas that require further research and discussion were also identified, with a second future meeting planned. This consensus statement may provide further guidance for clinicians when considering RCC genetic risk assessment. LAY SUMMARY: The contribution of germline genetics to the development of renal cell carcinoma (RCC) has long been recognized. However, there is a paucity of guidelines to define how and when genetic risk assessment should be performed for patients with known or suspected hereditary RCC. Without guidelines, clinicians struggle to define who requires further evaluation, when risk assessment or testing should be done, which genes should be considered, and how counseling and/or testing should be performed. To this end, a multidisciplinary panel of national experts was convened to gauge current opinion on genetic risk assessment in RCC and to enumerate a set of recommendations to guide clinicians when evaluating individuals with suspected hereditary kidney cancer.

NNT mediates redox-dependent pigmentation via a UVB- and MITF-independent mechanism.

Ultraviolet (UV) light and incompletely understood genetic and epigenetic variations determine skin color. Here we describe an UV- and microphthalmia-associated transcription factor (MITF)-independent mechanism of skin pigmentation. Targeting the mitochondrial redox-regulating enzyme nicotinamide nucleotide transhydrogenase (NNT) resulted in cellular redox changes that affect tyrosinase degradation. These changes regulate melanosome maturation and, consequently, eumelanin levels and pigmentation. Topical application of small-molecule inhibitors yielded skin darkening in human skin, and mice with decreased NNT function displayed increased pigmentation. Additionally, genetic modification of NNT in zebrafish alters melanocytic pigmentation. Analysis of four diverse human cohorts revealed significant associations of skin color, tanning, and sun protection use with various single-nucleotide polymorphisms within NNT. NNT levels were independent of UVB irradiation and redox modulation. Individuals with postinflammatory hyperpigmentation or lentigines displayed decreased skin NNT levels, suggesting an NNT-driven, redox-dependent pigmentation mechanism that can be targeted with NNT-modifying topical drugs for medical and cosmetic purposes.

Differential substrate use in EGF- and oncogenic KRAS-stimulated human mammary epithelial cells.

Many metabolic phenotypes in cancer cells are also characteristic of proliferating nontransformed mammalian cells, and attempts to distinguish between phenotypes resulting from oncogenic perturbation from those associated with increased proliferation are limited. Here, we examined the extent to which metabolic changes corresponding to oncogenic KRAS expression differed from those corresponding to epidermal growth factor (EGF)-driven proliferation in human mammary epithelial cells (HMECs). Removal of EGF from culture medium reduced growth rates and glucose/glutamine consumption in control HMECs despite limited changes in respiration and fatty acid synthesis, while the relative contribution of branched-chain amino acids to the TCA cycle and lipogenesis increased in the near-quiescent conditions. Most metabolic phenotypes measured in HMECs expressing mutant KRAS were similar to those observed in EGF-stimulated control HMECs that were growing at comparable rates. However, glucose and glutamine consumption as well as lactate and glutamate production were lower in KRAS-expressing cells cultured in media without added EGF, and these changes correlated with reduced sensitivity to GLUT1 inhibitor and phenformin treatment. Our results demonstrate the strong dependence of metabolic behavior on growth rate and provide a model to distinguish the metabolic influences of oncogenic mutations and nononcogenic growth.

Evaluation, diagnosis and surveillance of renal masses in the setting of VHL disease.

This brief report focuses on the evaluation and diagnosis of clinically localized renal masses in children and adults with Von Hippel-Lindau (VHL) disease. Counseling considerations pertinent to the urologists, medical oncologists, and multidisciplinary teams involved in the care of these patients are addressed. As practice patterns regarding the evaluation and management of VHL tumors can vary considerably, this report aims to provide guidance on some of the controversies associated with the diagnostic evaluation and initial management of localized renal masses in VHL patients.

Nitrogen Trapping as a Therapeutic Strategy in Tumors with Mitochondrial Dysfunction.

Under conditions of inherent or induced mitochondrial dysfunction, cancer cells manifest overlapping metabolic phenotypes, suggesting that they may be targeted via a common approach. Here, we use multiple oxidative phosphorylation (OXPHOS)-competent and incompetent cancer cell pairs to demonstrate that treatment with α-ketoglutarate (aKG) esters elicits rapid death of OXPHOS-deficient cancer cells by elevating intracellular aKG concentrations, thereby sequestering nitrogen from aspartate through glutamic-oxaloacetic transaminase 1 (GOT1). Exhaustion of aspartate in these cells resulted in immediate depletion of adenylates, which plays a central role in mediating mTOR inactivation and inhibition of glycolysis. aKG esters also conferred cytotoxicity in a variety of cancer types if their cell respiration was obstructed by hypoxia or by chemical inhibition of the electron transport chain (ETC), both of which are known to increase aspartate and GOT1 dependencies. Furthermore, preclinical mouse studies suggested that cell-permeable aKG displays a good biosafety profile, eliminates aspartate only in OXPHOS-incompetent tumors, and prevents their growth and metastasis. This study reveals a novel cytotoxic mechanism for the metabolite aKG and identifies cell-permeable aKG, either by itself or in combination with ETC inhibitors, as a potential anticancer approach. SIGNIFICANCE: These findings demonstrate that OXPHOS deficiency caused by either hypoxia or mutations, which can significantly increase cancer virulence, renders tumors sensitive to aKG esters by targeting their dependence upon GOT1 for aspartate synthesis. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/17/3492/F1.large.jpg.

Early onset renal cell carcinoma in an adolescent girl with germline FLCN exon 5 deletion.

Birt-Hogg-Dube (BHD) disease is an autosomal dominant cancer syndrome characterized by benign skin tumors, renal cancer and spontaneous pneumothorax and is caused by mutations in the Folliculin (FLCN) gene. Benign skin tumors and pneumothorax occur in the majority of patients affected by BHD syndrome, but only 30-45% of them develop renal cell carcinoma (RCC) with a median age of diagnosis at 48. The earliest onset of RCC in a BHD patient has been reported at age 20. Here we report a case of a 14 year-old patient with germline FLCN mutation leading to an early-onset bulky RCC that could not be classified strictly according to existing histological types. Germline genetic testing revealed a deletion at FLCN exon 5. The father of the patient was identified as the asymptomatic carrier. We report the youngest patient with BHD-related RCC. This early onset presentation supports genetic testing of at-risk patients and initiation of imaging surveillance for RCC in early adolescence. In addition, future studies are necessary to understand the determinants of reduced penetrance in BHD disease.

Negative regulation of EGFR signalling by the human folliculin tumour suppressor protein.

Germline mutations in the Folliculin (FLCN) tumour suppressor gene result in fibrofolliculomas, lung cysts and renal cancers, but the precise mechanisms of tumour suppression by FLCN remain elusive. Here we identify Rab7A, a small GTPase important for endocytic trafficking, as a novel FLCN interacting protein and demonstrate that FLCN acts as a Rab7A GTPase-activating protein. FLCN-/- cells display slower trafficking of epidermal growth factor receptors (EGFR) from early to late endosomes and enhanced activation of EGFR signalling upon ligand stimulation. Reintroduction of wild-type FLCN, but not tumour-associated FLCN mutants, suppresses EGFR signalling in a Rab7A-dependent manner. EGFR signalling is elevated in FLCN-/- tumours and the EGFR inhibitor afatinib suppresses the growth of human FLCN-/- cells as tumour xenografts. The functional interaction between FLCN and Rab7A appears conserved across species. Our work highlights a mechanism explaining, at least in part, the tumour suppressor function of FLCN.

Glutaminase and poly(ADP-ribose) polymerase inhibitors suppress pyrimidine synthesis and VHL-deficient renal cancers.

Many cancer-associated mutations that deregulate cellular metabolic responses to hypoxia also reprogram carbon metabolism to promote utilization of glutamine. In renal cell carcinoma (RCC), cells deficient in the von Hippel-Lindau (VHL) tumor suppressor gene use glutamine to generate citrate and lipids through reductive carboxylation (RC) of α-ketoglutarate (αKG). Glutamine can also generate aspartate, the carbon source for pyrimidine biosynthesis, and glutathione for redox balance. Here we have shown that VHL-/- RCC cells rely on RC-derived aspartate to maintain de novo pyrimidine biosynthesis. Glutaminase 1 (GLS1) inhibitors depleted pyrimidines and increased ROS in VHL-/- cells but not in VHL+/+ cells, which utilized glucose oxidation for glutamate and aspartate production. GLS1 inhibitor-induced nucleoside depletion and ROS enhancement led to DNA replication stress and activation of an intra-S phase checkpoint, and suppressed the growth of VHL-/- RCC cells. These effects were rescued by administration of glutamate, αKG, or nucleobases with N-acetylcysteine. Further, we observed that the poly(ADP-ribose) polymerase (PARP) inhibitor olaparib synergizes with GLS1 inhibitors to suppress the growth of VHL-/- cells in vitro and in vivo. This work describes a mechanism that explains the sensitivity of RCC tumor growth to GLS1 inhibitors and supports the development of therapeutic strategies for targeting VHL-deficient RCC.

Assessment of Overall Survival, Quality of Life, and Safety Benefits Associated With New Cancer Medicines.

IMPORTANCE: There is a dearth of evidence examining the impact of newly licensed cancer medicines on therapy. This information could otherwise support clinical practice, and promote value-based decision-making in the cancer drug market. OBJECTIVE: To evaluate the comparative therapeutic value of all new cancer medicines approved by the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) between 2003 and 2013. DESIGN, SETTING, AND PARTICIPANTS: We used a narrative synthesis approach to systematically synthesize and analyze English, French, and Australian health technology assessments (HTAs) of all new cancer medicines licensed in the United States and Europe between 2003 and 2013. INTERVENTIONS: Sixty-two new molecular entities with a primary oncology indication. MAIN OUTCOMES AND MEASURES: Overall survival (OS), quality of life (QoL), and safety. RESULTS: Of the 62 new active cancer molecules approved by the FDA and EMA between 2003 and 2013, 53 were appraised by English, French, or Australian HTA agencies through May 2015. Of these 53 drugs, 23 (43%) increased OS by 3 months or longer, 6 (11%) by less than 3 months, and 8 (15%) by an unknown magnitude; there was no evidence to suggest that the remaining 16 (30%) increased OS over best alternative treatments. Where overall survival gains could be quantified, all new cancer drugs were associated with a mean (SE) total increase in OS of 3.43 (0.63) months over the treatments that were available in 2003. Drug-related improvements in OS were, however, widely distributed across therapeutic targets-ranging between 0 (thyroid, ascites) and 8.48 months (breast cancers)-and were sometimes based on modeled data, indirect or nonactive comparisons, or nonvalidated evidence. Although 22 (42%) of 53 new medicines were associated with an increase in QoL, 24 (45%) were also associated with reduced patient safety. Of the 53 new cancer drugs, 42 (79%) were associated with at least some improvement in OS, QoL, or safety. CONCLUSIONS AND RELEVANCE: Although innovation in the oncology drug market has contributed to improvements in therapy, the magnitude and dimension of clinical benefits vary widely, and there may be reasons to doubt that claims of efficacy reflect real-world effectiveness exactly. These findings raise important questions for clinical decision-making and value-based policy.

Loss of vhl in the zebrafish pronephros recapitulates early stages of human clear cell renal cell carcinoma.

Patients with von Hippel-Lindau (VHL) disease harbor a germline mutation in the VHL gene leading to the development of several tumor types including clear cell renal cell carcinoma (ccRCC). In addition, the VHL gene is inactivated in over 90% of sporadic ccRCC cases. 'Clear cell' tumors contain large, proliferating cells with 'clear cytoplasm', and a reduced number of cilia. VHL inactivation leads to the stabilization of hypoxia inducible factors 1a and 2a [HIF1a and HIF2a (HIF2a is also known as EPAS1)] with consequent up-regulation of specific target genes involved in cell proliferation, angiogenesis and erythropoiesis. A zebrafish model with a homozygous inactivation in the VHL gene (vhl(-/-)) recapitulates several aspects of the human disease, including development of highly vascular lesions in the brain and the retina and erythrocytosis. Here, we characterize for the first time the epithelial abnormalities present in the kidney of the vhl(-/-) zebrafish larvae as a first step in building a model of ccRCC in zebrafish. Our data show that the vhl(-/-) zebrafish kidney is characterized by an increased tubule diameter, disorganized cilia, the dramatic formation of cytoplasmic lipid vesicles, glycogen accumulation, aberrant cell proliferation and abnormal apoptosis. This phenotype of the vhl(-/-) pronephros is reminiscent of clear cell histology, indicating that the vhl(-/-) mutant zebrafish might serve as a model of early stage RCC. Treatment of vhl(-/-) zebrafish embryos with a small-molecule HIF2a inhibitor rescued the pronephric abnormalities, underscoring the value of the zebrafish model in drug discovery for treatment of VHL disease and ccRCC.

Metabolic requirements for cancer cell proliferation.

BACKGROUND: The study of cancer metabolism has been largely dedicated to exploring the hypothesis that oncogenic transformation rewires cellular metabolism to sustain elevated rates of growth and division. Intense examination of tumors and cancer cell lines has confirmed that many cancer-associated metabolic phenotypes allow robust growth and survival; however, little attention has been given to explicitly identifying the biochemical requirements for cell proliferation in a rigorous manner in the context of cancer metabolism. RESULTS: Using a well-studied hybridoma line as a model, we comprehensively and quantitatively enumerate the metabolic requirements for generating new biomass in mammalian cells; this indicated a large biosynthetic requirement for ATP, NADPH, NAD(+), acetyl-CoA, and amino acids. Extension of this approach to serine/glycine and glutamine metabolic pathways suggested lower limits on serine and glycine catabolism to supply one-carbon unit synthesis and significant availability of glutamine-derived carbon for biosynthesis resulting from nitrogen demands alone, respectively. We integrated our biomass composition results into a flux balance analysis model, placing upper bounds on mitochondrial NADH oxidation to simulate metformin treatment; these simulations reproduced several empirically observed metabolic phenotypes, including increased reductive isocitrate dehydrogenase flux. CONCLUSIONS: Our analysis clarifies the differential needs for central carbon metabolism precursors, glutamine-derived nitrogen, and cofactors such as ATP, NADPH, and NAD(+), while also providing justification for various extracellular nutrient uptake behaviors observed in tumors. Collectively, these results demonstrate how stoichiometric considerations alone can successfully predict empirically observed phenotypes and provide insight into biochemical dynamics that underlie responses to metabolic perturbations.