mTORC1 promotes TOP mRNA translation through site-specific phosphorylation of LARP1.

LARP1 is a key repressor of TOP mRNA translation. It binds the m7Gppp cap moiety and the adjacent 5'TOP motif of TOP mRNAs, thus impeding the assembly of the eIF4F complex on these transcripts. mTORC1 controls TOP mRNA translation via LARP1, but the details of the mechanism are unclear. Herein we elucidate the mechanism by which mTORC1 controls LARP1's translation repression activity. We demonstrate that mTORC1 phosphorylates LARP1 in vitro and in vivo, activities that are efficiently inhibited by rapamycin and torin1. We uncover 26 rapamycin-sensitive phospho-serine and -threonine residues on LARP1 that are distributed in 7 clusters. Our data show that phosphorylation of a cluster of residues located proximally to the m7Gppp cap-binding DM15 region is particularly sensitive to rapamycin and regulates both the RNA-binding and the translation inhibitory activities of LARP1. Our results unravel a new model of translation control in which the La module (LaMod) and DM15 region of LARP1, both of which can directly interact with TOP mRNA, are differentially regulated: the LaMod remains constitutively bound to PABP (irrespective of the activation status of mTORC1), while the C-terminal DM15 'pendular hook' engages the TOP mRNA 5'-end to repress translation, but only in conditions of mTORC1 inhibition.

Active-site mTOR inhibitors augment HSV1-dICP0 infection in cancer cells via dysregulated eIF4E/4E-BP axis.

Herpes Simplex Virus 1 (HSV1) is amongst the most clinically advanced oncolytic virus platforms. However, efficient and sustained viral replication within tumours is limiting. Rapamycin can stimulate HSV1 replication in cancer cells, but active-site dual mTORC1 and mTORC2 (mammalian target of rapamycin complex 1 and 2) inhibitors (asTORi) were shown to suppress the virus in normal cells. Surprisingly, using the infected cell protein 0 (ICP0)-deleted HSV1 (HSV1-dICP0), we found that asTORi markedly augment infection in cancer cells and a mouse mammary cancer xenograft. Mechanistically, asTORi repressed mRNA translation in normal cells, resulting in defective antiviral response but also inhibition of HSV1-dICP0 replication. asTORi also reduced antiviral response in cancer cells, however in contrast to normal cells, transformed cells and cells transduced to elevate the expression of eukaryotic initiation factor 4E (eIF4E) or to silence the repressors eIF4E binding proteins (4E-BPs), selectively maintained HSV1-dICP0 protein synthesis during asTORi treatment, ultimately supporting increased viral replication. Our data show that altered eIF4E/4E-BPs expression can act to promote HSV1-dICP0 infection under prolonged mTOR inhibition. Thus, pharmacoviral combination of asTORi and HSV1 can target cancer cells displaying dysregulated eIF4E/4E-BPs axis.

La-related Protein 1 (LARP1) Represses Terminal Oligopyrimidine (TOP) mRNA Translation Downstream of mTOR Complex 1 (mTORC1).

The mammalian target of rapamycin complex 1 (mTORC1) is a critical regulator of protein synthesis. The best studied targets of mTORC1 in translation are the eukaryotic initiation factor-binding protein 1 (4E-BP1) and ribosomal protein S6 kinase 1 (S6K1). In this study, we identify the La-related protein 1 (LARP1) as a key novel target of mTORC1 with a fundamental role in terminal oligopyrimidine (TOP) mRNA translation. Recent genome-wide studies indicate that TOP and TOP-like mRNAs compose a large portion of the mTORC1 translatome, but the mechanism by which mTORC1 controls TOP mRNA translation is incompletely understood. Here, we report that LARP1 functions as a key repressor of TOP mRNA translation downstream of mTORC1. Our data show the following: (i) LARP1 associates with mTORC1 via RAPTOR; (ii) LARP1 interacts with TOP mRNAs in an mTORC1-dependent manner; (iii) LARP1 binds the 5'TOP motif to repress TOP mRNA translation; and (iv) LARP1 competes with the eukaryotic initiation factor (eIF) 4G for TOP mRNA binding. Importantly, from a drug resistance standpoint, our data also show that reducing LARP1 protein levels by RNA interference attenuates the inhibitory effect of rapamycin, Torin1, and amino acid deprivation on TOP mRNA translation. Collectively, our findings demonstrate that LARP1 functions as an important repressor of TOP mRNA translation downstream of mTORC1.

Budget Impact Of Eltrombopag As First-Line Treatment For Severe Aplastic Anemia In The United States.

BACKGROUND: Severe aplastic anemia (SAA) is a rare autoimmune condition resulting in low blood cell counts across lineages. Immunosuppressive therapy (IST) has demonstrated low response, toxicity, and risk of transformation. In a Phase I/II trial, the addition of eltrombopag to first-line IST increased response rates relative to an IST-only historical cohort. METHODS: A model was developed to estimate the budget impact of treating SAA with eltrombopag-based therapy from a US private healthcare system perspective. A simulated cohort of newly diagnosed SAA patients based on the total US population received 6 months of IST ± eltrombopag and were followed for 1 year, with mutually exclusive patient cohorts entering in years 1, 2, and 3. The model assessed the budget impact of first-year treatment for each cohort without considering subsequent years. At 6 months, responders in either arm received maintenance therapy (low-dose cyclosporine), and non-responders received 6 months of second-line eltrombopag monotherapy. Costs considered included first-line, maintenance, and second-line therapy, administration, routine care, mortality, and adverse events (AEs). All cost data were reported in 2018 US dollars. RESULTS: The annual incidence of aplastic anemia was 0.000234%, with 83.8% of cases assumed to be SAA. Based on trial data, 94% of patients receiving eltrombopag and IST responded versus 66% of patients receiving IST, with a 0.3% reduction in the annual risk of mortality for the eltrombopag + IST group. Use of first-line eltrombopag in a model SAA population based on the total US population increased overall costs by $50 million over 3 years. First-line drug costs accounted for an increase of $69 million, while improved response produced $19 million in secondary therapy cost savings. Sensitivity analyses confirmed the robustness of the analysis. CONCLUSION: High response rates combined with reduced rescue medication use and mortality in patients treated with eltrombopag and IST mediated higher medication costs.

Matching-adjusted indirect treatment comparison of ribociclib and palbociclib in HR+, HER2- advanced breast cancer.

BACKGROUND: Ribociclib (RIBO) and palbociclib (PALBO), combined with letrozole (LET), have been evaluated as treatments for hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer in separate Phase III randomized controlled trials (RCTs), but not head-to-head. Population differences can lead to biased results by classical indirect treatment comparison (ITC). Matching-adjusted indirect comparison (MAIC) aims to correct these differences. We compared RIBO and PALBO in hormone receptor-positive/human epidermal growth factor receptor 2-negative advanced breast cancer using MAIC. METHODS: Patient-level data were available for RIBO (MONALEESA-2), while only published summary data were available for PALBO (PALOMA-2). Weights were assigned to MONALEESA-2 patient data such that mean baseline characteristics matched those reported for PALOMA-2; the resulting matched cohort was used in comparisons. Limited by the results reported in PALOMA-2, progression-free survival (PFS) was the primary comparison. Cox regression models were used to calculate adjusted hazard ratios (HRs) for PFS, before indirect treatment comparison (ITC) was performed with 95% confidence intervals. An exploratory analysis was performed similarly for overall survival using earlier PALBO data (PALOMA-1). Grade 3/4 adverse events were also compared. RESULTS: Racial characteristics, prior chemotherapy setting, and the extent of metastasis were the most imbalanced baseline characteristics. The unadjusted PFS HRs were 0.556 (0.429, 0.721) for RIBO+LET versus LET alone and 0.580 (0.460, 0.720) for PALBO+LET versus LET alone. MAIC adjustment resulted in an HR of 0.524 (0.406, 0.676) for RIBO+LET versus LET. PFS ITC using unadjusted trial data produced an HR of 0.959 (0.681, 1.350) for RIBO versus PALBO, or 0.904 (0.644, 1.268) with MAIC. Unadjusted overall survival HR of RIBO versus PALBO was 0.918 (0.492, 1.710); while exploratory MAIC was 0.839 (0.440, 1.598). ITC of grade 3/4 adverse events yielded a risk ratio of 0.806 (0.604, 1.076). CONCLUSION: MAIC was performed for RIBO and PALBO in the absence of a head-to-head trial: though not statistically significant, the results favored RIBO.

A decision framework for treating chronic immune thrombocytopenia with thrombopoietin receptor agonists.

Aim: Eltrombopag and romiplostim are comparable second-line therapies in chronic immune thrombocytopenia. Treatment decisions are made in different contexts. A framework was created to outline decision pathways for physicians and payers. Materials & methods: The costs of drugs, administration, routine care, bleeding, other adverse events and mortality were included in the year-long calculation of total costs from a US private payer perspective. Treatment parameters and outcome data were obtained from relevant clinical trials. Results: The total cost per year, per patient of eltrombopag was US$51,000 versus US$76,000 for romiplostim. Drug costs and costs associated with bleeding-related events were the main drivers of cost difference. Conclusion: This framework facilitates decision-making in the management of chronic immune thrombocytopenia with eltrombopag and romiplostim.