Loss of mitochondrial pyruvate carrier 1 supports proline-dependent proliferation and collagen biosynthesis in ovarian cancer.

The pyruvate transporter MPC1 (mitochondrial pyruvate carrier 1) acts as a tumour-suppressor, loss of which correlates with a pro-tumorigenic phenotype and poor survival in several tumour types. In high-grade serous ovarian cancers (HGSOC), patients display copy number loss of MPC1 in around 78% of cases and reduced MPC1 mRNA expression. To explore the metabolic effect of reduced expression, we demonstrate that depleting MPC1 in HGSOC cell lines drives expression of key proline biosynthetic genes; PYCR1, PYCR2 and PYCR3, and biosynthesis of proline. We show that altered proline metabolism underpins cancer cell proliferation, reactive oxygen species (ROS) production, and type I and type VI collagen formation in ovarian cancer cells. Furthermore, exploring The Cancer Genome Atlas, we discovered the PYCR3 isozyme to be highly expressed in a third of HGSOC patients, which was associated with more aggressive disease and diagnosis at a younger age. Taken together, our study highlights that targeting proline metabolism is a potential therapeutic avenue for the treatment of HGSOC.

Small-molecule signal-transduction inhibitors: targeted therapeutic agents for single-gene disorders.

Mutations affecting over 2000 of the 20 000 or so genes in the human genome have been linked so far to specific inherited diseases, most of which are rare and have been poorly understood. Many of the genes involved encode components of intracellular signalling pathways that regulate processes such as the growth, proliferation, differentiation and survival or programmed death of cells during development and the maintenance of tissues and organs. Mutations that change the function of genes encoding signalling proteins thereby cause disorders ranging from birth defects to cancer. For Mendelian disorders, the essentially causal relationship between mutation and disease may present direct opportunities to therapeutically manipulate intracellular signalling. Here, we review recent examples of the use of small-molecule drugs to target components of signalling networks in single-gene disorders. We also consider the limitations of these "molecularly targeted" approaches and the difficulties in their clinical development as therapies for rare genetic diseases.

Correction: Loss of tuberous sclerosis complex 2 sensitizes tumors to nelfinavir-bortezomib therapy to intensify endoplasmic reticulum stress-induced cell death.

This article was originally published under standard licence, but has now been made available under a CC BY 4.0 license. The PDF and HTML versions of the paper have been modified accordingly.

Energy Stress-Mediated Cytotoxicity in Tuberous Sclerosis Complex 2-Deficient Cells with Nelfinavir and Mefloquine Treatment.

To find new anti-cancer drug therapies, we wanted to exploit homeostatic vulnerabilities within Tuberous Sclerosis Complex 2 (TSC2)-deficient cells with mechanistic target of rapamycin complex 1 (mTORC1) hyperactivity. We show that nelfinavir and mefloquine synergize to selectively evoke a cytotoxic response in TSC2-deficient cell lines with mTORC1 hyperactivity. We optimize the concentrations of nelfinavir and mefloquine to a clinically viable range that kill cells that lack TSC2, while wild-type cells tolerate treatment. This new clinically viable drug combination causes a significant level of cell death in TSC2-deficient tumor spheroids. Furthermore, no cell recovery was apparent after drug withdrawal, revealing potent cytotoxicity. Transcriptional profiling by RNA sequencing of drug treated TSC2-deficient cells compared to wild-type cells suggested the cytotoxic mechanism of action, involving initial ER stress and an imbalance in energy homeostatic pathways. Further characterization revealed that supplementation with methyl pyruvate alleviated energy stress and reduced the cytotoxic effect, implicating energy deprivation as the trigger of cell death. This work underpins a critical vulnerability with cancer cells with aberrant signaling through the TSC2-mTORC1 pathway that lack flexibility in homeostatic pathways, which could be exploited with combined nelfinavir and mefloquine treatment.

Loss of tuberous sclerosis complex 2 sensitizes tumors to nelfinavir-bortezomib therapy to intensify endoplasmic reticulum stress-induced cell death.

Cancer cells lose homeostatic flexibility because of mutations and dysregulated signaling pathways involved in maintaining homeostasis. Tuberous Sclerosis Complex 1 (TSC1) and TSC2 play a fundamental role in cell homeostasis, where signal transduction through TSC1/TSC2 is often compromised in cancer, leading to aberrant activation of mechanistic target of rapamycin complex 1 (mTORC1). mTORC1 hyperactivation increases the basal level of endoplasmic reticulum (ER) stress via an accumulation of unfolded protein, due to heightened de novo protein translation and repression of autophagy. We exploit this intrinsic vulnerability of tumor cells lacking TSC2, by treating with nelvinavir to further enhance ER stress while inhibiting the proteasome with bortezomib to prevent effective protein removal. We show that TSC2-deficient cells are highly dependent on the proteosomal degradation pathway for survival. Combined treatment with nelfinavir and bortezomib at clinically relevant drug concentrations show synergy in selectively killing TSC2-deficient cells with limited toxicity in control cells. This drug combination inhibited tumor formation in xenograft mouse models and patient-derived cell models of TSC and caused tumor spheroid death in 3D culture. Importantly, 3D culture assays differentiated between the cytostatic effects of the mTORC1 inhibitor, rapamycin, and the cytotoxic effects of the nelfinavir/bortezomib combination. Through RNA sequencing, we determined that nelfinavir and bortezomib tip the balance of ER protein homeostasis of the already ER-stressed TSC2-deficient cells in favor of cell death. These findings have clinical relevance in stratified medicine to treat tumors that have compromised signaling through TSC and are inflexible in their capacity to restore ER homeostasis.

The use of everolimus in the treatment of neurocognitive problems in tuberous sclerosis (TRON): study protocol for a randomised controlled trial.

BACKGROUND: Tuberous sclerosis complex (TSC) is a genetic disorder affecting about 1 in 6000 people and is characterised by the development of tumours in many organs, including the skin and kidneys, and by a range of neurological and neuropsychiatric manifestations. TSC-associated neuropsychiatric disorders (TAND) occur in the majority of those with TSC, and they have a significant impact on patients and their families, given the everyday impact of TAND on education, employment, family and social life. The potential benefits of better treatment for TAND therefore include reduction in health care demands and wider benefits for patients and their carers. METHODS/DESIGN: We have planned a single-centre, two-arm, individually randomised, phase II, double-blind, placebo-controlled trial of everolimus versus placebo in the treatment of neurocognitive problems in patients with tuberous sclerosis. Everolimus is a licensed medicine in this patient group, but for a different target of effect. The present trial is a proof-of-principle study developed to provide effect size estimates which may be used to inform the design of subsequent trials. Forty-eight patients aged 16-60 years with tuberous sclerosis who have an IQ >60 and a significant deficit (at least -2 SD) in one or more primary outcome measures will be randomly allocated in a ratio of 2:1 to receive everolimus or placebo, respectively. Participants will be assessed for eligibility and then be started on study medication 4 weeks later. They will then be randomised and receive placebo or everolimus for 24 weeks. Neurocognitive and safety assessments will be carried out at baseline and weeks 4, 12, 24 and 36. DISCUSSION: This study is designed to determine the effect sizes of treatment with everolimus or placebo for 6 months on specific neurocognitive functions-recall memory (verbal and non-verbal) and executive function-in people affected by TSC who have significant deficits in these functions. These data will provide new evidence to determine whether larger-scale trials are indicated and to explore suitable outcome measures and analytical methods for neurocognitive trial design. TRIAL REGISTRATION: ISRCTN09739757 . Registered on 28 Dec 2011.

Endoplasmic reticulum stress and cell death in mTORC1-overactive cells is induced by nelfinavir and enhanced by chloroquine.

Inappropriate activation of mammalian/mechanistic target of rapamycin complex 1 (mTORC1) is common in cancer and has many cellular consequences including elevated endoplasmic reticulum (ER) stress. Cells employ autophagy as a critical compensatory survival mechanism during ER stress. This study utilised drug-induced ER stress through nelfinavir in order to examine ER stress tolerance in cell lines with hyper-active mTORC1 signalling. Our initial findings in wild type cells showed nelfinavir inhibited mTORC1 signalling and upregulated autophagy, as determined by decreased rpS6 and S6K1 phosphorylation, and SQTSM1 protein expression, respectively. Contrastingly, cells with hyper-active mTORC1 displayed basally elevated levels of ER stress which was greatly exaggerated following nelfinavir treatment, seen through increased CHOP mRNA and XBP1 splicing. To further enhance the effects of nelfinavir, we introduced chloroquine as an autophagy inhibitor. Combination of nelfinavir and chloroquine significantly increased ER stress and caused selective cell death in multiple cell line models with hyper-active mTORC1, whilst control cells with normalised mTORC1 signalling tolerated treatment. By comparing chloroquine to other autophagy inhibitors, we uncovered that selective toxicity invoked by chloroquine was independent of autophagy inhibition yet entrapment of chloroquine to acidified lysosomal/endosomal compartments was necessary for cytotoxicity. Our research demonstrates that combination of nelfinavir and chloroquine has therapeutic potential for treatment of mTORC1-driven tumours.

Sirolimus therapy for angiomyolipoma in tuberous sclerosis and sporadic lymphangioleiomyomatosis: a phase 2 trial.

PURPOSE: Renal angiomyolipomas are a frequent manifestation of tuberous sclerosis and sporadic lymphangioleiomyomatosis (LAM). These disorders are associated with mutations of TSC1 or TSC2 that lead to overactivation of mTOR complex 1 (mTORC1), suggesting an opportunity for targeted therapy by using mTORC1 inhibitors. This study investigated the efficacy and safety of the mTORC1 inhibitor sirolimus for treatment of renal angiomyolipomas in patients with these disorders. EXPERIMENTAL DESIGN: In this multicenter phase 2 nonrandomized open label trial, 16 patients with tuberous sclerosis or sporadic LAM and renal angiomyolipoma(s) were treated with oral sirolimus for up to 2 years. Steady-state blood levels were 3 to 10 ng/mL. The primary outcome was change in size of renal angiomyolipomas measured by MRI and assessed by Response Evaluation Criteria in Solid Tumors (RECIST) criteria. Secondary outcomes included safety, neurocognitive function, and pulmonary function. RESULTS: The response rate, by RECIST criteria, was 50%. Summated angiomyolipoma diameters were reduced in all 16 patients and by 30% or more in eight (all from the per protocol group of 10). Forty-one of 48 angiomyolipomas were smaller at the last measurement than at baseline. Most shrinkage occurred during the first year of treatment. There was little change in pulmonary function. Recall memory improved in seven of eight patients with tuberous sclerosis. Adverse events were consistent with the known toxicities of sirolimus. CONCLUSIONS: This study showed sustained regression of renal angiomyolipomas in patients with tuberous sclerosis or sporadic LAM receiving 2 years of sirolimus treatment. Possible effects on pulmonary function and neurocognition require further investigation.