Investigational drug MLN0128, a novel TORC1/2 inhibitor, demonstrates potent oral antitumor activity in human breast cancer xenograft models

Exploring the role of PI3K/AKT/mTOR inhibitors in hormone-related cancers: A focus on breast and prostate cancer

Breast cancer (BC) and prostate cancer (PC) are at the top of the list when it comes to the most common types of cancers worldwide. The phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling pathway is important, in that it strongly influences the development and progression of these tumors. Previous studies have emphasized the key role of inhibitors of the PIK3/AKT/mTOR signaling pathway in the treatment of BC and PC, and it remains to be a crucial method of treatment. In this review, the inhibitors of these signaling pathways are compared, as well as their effectiveness in therapy and potential as therapeutic agents. The use of these inhibitors as polytherapy is evaluated, especially with the use of hormonal therapy, which has shown promising results.

Protein interaction network analysis of mTOR signaling reveals modular organization

The mammalian target of rapamycin (mTOR) is a serine-threonine kinase that acts as a central mediator of translation and plays important roles in cell growth, synaptic plasticity, cancer, and a wide range of developmental disorders. The signaling cascade linking lipid kinases (phosphoinositide 3-kinases), protein kinases (AKT), and translation initiation complexes (EIFs) to mTOR has been extensively modeled, but does not fully describe mTOR system behavior. Here, we use quantitative multiplex coimmunoprecipitation to monitor a protein interaction network (PIN) composed of 300+ binary interactions among mTOR-related proteins. Using a simple model system of serum-deprived or fresh-media-fed mouse 3T3 fibroblasts, we observed extensive PIN remodeling involving 27+ individual protein interactions after 1 h, despite phosphorylation changes observed after only 5 min. Using small molecule inhibitors of phosphoinositide 3-kinase, AKT, mTOR, MEK and ERK, we define subsets of the PIN, termed "modules", that respond differently to each inhibitor. Using primary fibroblasts from individuals with overgrowth disorders caused by pathogenic PIK3CA or MTOR variants, we find that hyperactivation of mTOR pathway components is reflected in a hyperactive PIN. Our data define a "modular" organization of the mTOR PIN in which coordinated groups of interactions respond to the activation or inhibition of distinct nodes, and demonstrate that kinase inhibitors affect the modular network architecture in a complex manner, inconsistent with simple linear models of signal transduction.

Multifaceted role of mTOR (mammalian target of rapamycin) signaling pathway in human health and disease

The mammalian target of rapamycin (mTOR) is a protein kinase that controls cellular metabolism, catabolism, immune responses, autophagy, survival, proliferation, and migration, to maintain cellular homeostasis. The mTOR signaling cascade consists of two distinct multi-subunit complexes named mTOR complex 1/2 (mTORC1/2). mTOR catalyzes the phosphorylation of several critical proteins like AKT, protein kinase C, insulin growth factor receptor (IGF-1R), 4E binding protein 1 (4E-BP1), ribosomal protein S6 kinase (S6K), transcription factor EB (TFEB), sterol-responsive element-binding proteins (SREBPs), Lipin-1, and Unc-51-like autophagy-activating kinases. mTOR signaling plays a central role in regulating translation, lipid synthesis, nucleotide synthesis, biogenesis of lysosomes, nutrient sensing, and growth factor signaling. The emerging pieces of evidence have revealed that the constitutive activation of the mTOR pathway due to mutations/amplification/deletion in either mTOR and its complexes (mTORC1 and mTORC2) or upstream targets is responsible for aging, neurological diseases, and human malignancies. Here, we provide the detailed structure of mTOR, its complexes, and the comprehensive role of upstream regulators, as well as downstream effectors of mTOR signaling cascades in the metabolism, biogenesis of biomolecules, immune responses, and autophagy. Additionally, we summarize the potential of long noncoding RNAs (lncRNAs) as an important modulator of mTOR signaling. Importantly, we have highlighted the potential of mTOR signaling in aging, neurological disorders, human cancers, cancer stem cells, and drug resistance. Here, we discuss the developments for the therapeutic targeting of mTOR signaling with improved anticancer efficacy for the benefit of cancer patients in clinics.

Protein interaction network analysis of mTOR signaling reveals modular organization

The mammalian target of rapamycin (mTOR) is a serine-threonine kinase that acts as a central mediator of translation, and plays important roles in cell growth, synaptic plasticity, cancer, and a wide range of developmental disorders. The signaling cascade linking lipid kinases (PI3Ks), protein kinases (AKT) and translation initiation complexes (EIFs) to mTOR has been extensively modeled, but does not fully describe mTOR system behavior. Here, we use quantitative multiplex co-immunoprecipitation to monitor a protein interaction network (PIN) composed of 300+ binary interactions among mTOR-related proteins. Using a simple model system of serum deprived or fresh-media-fed mouse 3T3 fibroblasts, we observed extensive PIN remodeling involving 27+ individual protein interactions after one hour, despite phosphorylation changes observed after only five minutes. Using small molecule inhibitors of PI3K, AKT, mTOR, MEK and ERK, we define subsets of the PIN, termed 'modules', that respond differently to each inhibitor. Using primary fibroblasts from individuals with overgrowth disorders caused by pathogenic PIK3CA or MTOR variants, we find that hyperactivation of mTOR pathway components is reflected in a hyperactive PIN. Our data define a "modular" organization of the mTOR PIN in which coordinated groups of interactions respond to activation or inhibition of distinct nodes, and demonstrate that kinase inhibitors affect the modular network architecture in a complex manner, inconsistent with simple linear models of signal transduction.

Targeting NFE2L2/KEAP1 Mutations in Advanced NSCLC With the TORC1/2 Inhibitor TAK-228

INTRODUCTION

Increased insight into the mutational landscape of squamous cell lung cancers (LUSCs) in the past decade has not translated into effective targeted therapies for patients with this disease. NRF2, encoded by NFE2L2, and its upstream regulator, KEAP1, control key aspects of redox balance and are frequently mutated in NSCLCs.

METHODS

Here, we describe the specific potent activity of TAK-228, a TORC1/2 inhibitor, in NSCLC models harboring NRF2-activating alterations and results of a phase 2 clinical trial of TAK-228 in patients with advanced NSCLC harboring NRF2-activating alterations including three cohorts (NFE2L2-mutated LUSC, KEAP1-mutated LUSC, KRAS/NFE2L2- or KEAP1-mutated NSCLC).

RESULTS

TAK-228 was most efficacious in a LUSC cohort with NFE2L2 alterations; the overall response rate was 25% and median progression-free survival was 8.9 months. Additional data suggest that concurrent inhibition of glutaminase with the glutaminase inhibitor CB-839 might overcome metabolic resistance to therapy in these patients.

CONCLUSIONS

TAK-228 has single-agent activity in patients with NRF2-activated LUSC. This study reframes oncogenic alterations as biologically relevant based on their downstream effects on metabolism. This trial represents, to the best of our knowledge, the first successful attempt at metabolically targeting NSCLC and identifies a promising targeted therapy for patients with LUSC, who are bereft of genotype-directed therapies.

Waldenström Macroglobulinemia: Mechanisms of Disease Progression and Current Therapies

Waldenström macroglobulinemia is an indolent, B-cell lymphoma without a known cure. The bone marrow microenvironment and cytokines both play key roles in Waldenström macroglobulinemia (WM) tumor progression. Only one FDA-approved drug exists for the treatment of WM, Ibrutinib, but treatment plans involve a variety of drugs and inhibitors. This review explores avenues of tumor progression and targeted drug therapy that have been investigated in WM and related B-cell lymphomas.

Ribosomopathies and cancer: pharmacological implications

INTRODUCTION

The ribosome is a ribonucleoprotein organelle responsible for protein synthesis, and its biogenesis is a highly coordinated process that involves many macromolecular components. Any acquired or inherited impairment in ribosome biogenesis or ribosomopathies is associated with the development of different cancers and rare genetic diseases. Interference with multiple steps of protein synthesis has been shown to promote tumor cell death.

AREAS COVERED

We discuss the current insights about impaired ribosome biogenesis and their secondary consequences on protein synthesis, transcriptional and translational responses, proteotoxic stress, and other metabolic pathways associated with cancer and rare diseases. Studies investigating the modulation of different therapeutic chemical entities targeting cancer in in vitro and in vivo models have also been detailed.

EXPERT OPINION

Despite the association between inherited mutations affecting ribosome biogenesis and cancer biology, the development of therapeutics targeting the essential cellular machinery has only started to emerge. New chemical entities should be designed to modulate different checkpoints (translating oncoproteins, dysregulation of specific ribosome-assembly machinery, ribosomal stress, and rewiring ribosomal functions). Although safe and effective therapies are lacking, consideration should also be given to using existing drugs alone or in combination for long-term safety, with known risks for feasibility in clinical trials and synergistic effects.

Targeting mTOR in the Context of Diet and Whole-body Metabolism

The mechanistic target of the rapamycin (mTOR) signaling pathway is the central regulator of cell growth and proliferation by integrating growth factor and nutrient availability. Under healthy physiological conditions, this process is tightly coordinated and essential to maintain whole-body homeostasis. Not surprisingly, dysregulated mTOR signaling underpins several diseases with increasing incidence worldwide, including obesity, diabetes, and cancer. Consequently, there is significant clinical interest in developing therapeutic strategies that effectively target this pathway. The transition of mTOR inhibitors from the bench to bedside, however, has largely been marked with challenges and shortcomings, such as the development of therapy resistance and adverse side effects in patients. In this review, we discuss the current status of first-, second-, and third-generation mTOR inhibitors as a cancer therapy in both preclinical and clinical settings, with a particular emphasis on the mechanisms of drug resistance. We focus especially on the emerging role of diet as an important environmental determinant of therapy response, and posit a conceptual framework that links nutrient availability and whole-body metabolic states such as obesity with many of the previously defined processes that drive resistance to mTOR-targeted therapies. Given the role of mTOR as a central integrator of cell metabolism and function, we propose that modulating nutrient inputs through dietary interventions may influence the signaling dynamics of this pathway and compensatory nodes. In doing so, new opportunities for exploiting diet/drug synergies are highlighted that may unlock the therapeutic potential of mTOR inhibitors as a cancer treatment.

Autophagy and cancer: Can tetrandrine be a potent anticancer drug in the near future?

Autophagy is an essential catabolic process in mammalian cells to maintain cellular integrity and viability by degrading the old and damaged cell organelles and other contents with the help of lysosomes. Deregulation in autophagy can be one of the major contributors leading to the continuous cell proliferation and development of tumors. Tetrandrine, a bisbenzylisoquinoline alkaloid known to have potent bioactivities such as anticancer, antimicrobial, anti-inflammatory, antidiabetic, antioxidant, immunosuppressive, cardiovascular, and calcium channel blocking effects. The present review evaluated the effectiveness of tetrandrine in targeting key proteins in the autophagy pathway to induce anticancer effect based on the available literature. An attempt is also made to understand the influence of tetrandrine in regulating autophagy by mTOR dependant and mTOR-independent pathways. In addition, the review also highlights the limitations involved and future perspectives in developing tetrandrine as a chemotherapeutic drug to treat cancer.

Identification of New Vulnerabilities in Conjunctival Melanoma Using Image-Based High Content Drug Screening

Recent evidence suggests that numerous similarities exist between the genomic landscapes of both conjunctival and cutaneous melanoma. Since alterations of several components of the MAP kinases, PI3K/mTOR, and cell cycle pathways have been reported in conjunctival melanoma, we decided to assess the sensitivity of conjunctival melanoma to targeted inhibition mostly of kinase inhibitors. A high content drug screening assay based on automated fluorescence microscopy was performed in three conjunctival melanoma cell lines with different genomic backgrounds with 489 kinase inhibitors and 53 other inhibitors. IC50 and apoptosis induction were respectively assessed for 53 and 48 compounds. The genomic background influenced the response to MAK and PI3K/mTOR inhibition, more specifically cell lines with BRAF V600E mutations were more sensitive to BRAF/MEK inhibition, while CRMM2 bearing the NRASQ61L mutation was more sensitive to PI3k/mTOR inhibition. All cell lines demonstrated sensitivity to cell cycle inhibition, being more pronounced in CRMM2, especially with polo-like inhibitors. Our data also revealed new vulnerabilities to Hsp90 and Src inhibition. This study demonstrates that the genomic background partially influences the response to targeted therapy and uncovers a large panel of potential vulnerabilities in conjunctival melanoma that may expand available options for the management of this tumor.

Sapanisertib plus Fulvestrant in Postmenopausal Women with Estrogen Receptor-Positive/HER2-Negative Advanced Breast Cancer after Progression on Aromatase Inhibitor

PURPOSE

This phase II study investigated daily or weekly sapanisertib (a selective dual inhibitor of mTOR complexes 1 and 2) in combination with fulvestrant.

PATIENTS AND METHODS

Postmenopausal women with estrogen receptor-positive (ER+)/HER2-negative (HER2-) advanced or metastatic breast cancer following progression during/after aromatase inhibitor treatment were randomized to receive fulvestrant 500 mg (28-day treatment cycles), fulvestrant plus sapanisertib 4 mg daily, or fulvestrant plus sapanisertib 30 mg weekly, until progressive disease, unacceptable toxicity, consent withdrawal, or study completion.

RESULTS

Among 141 enrolled patients, baseline characteristics were balanced among treatment arms, including prior cyclin-dependent kinase-4/6 (CDK4/6) inhibitor treatment in 33% to 35% of patients. Median progression-free survival (PFS; primary endpoint) was 3.5 months in the single-agent fulvestrant arm, compared with 7.2 months for fulvestrant plus sapanisertib daily [HR, 0.77; 95% confidence interval (CI), 0.47-1.26] and 5.6 months for fulvestrant plus sapanisertib weekly (HR, 0.88; 95% CI, 0.53-1.45). The greatest PFS benefits were seen in patients who had previously received CDK4/6 inhibitors. The most common adverse events were nausea, vomiting, and hyperglycemia, all occurring more frequently in the combination therapy arms. Treatment discontinuation due to adverse events occurred more frequently in the two combination therapy arms than with single-agent fulvestrant (32% and 36% vs. 4%, respectively).

CONCLUSIONS

Fulvestrant plus sapanisertib daily/weekly resulted in numerically longer PFS in patients with ER+/HER2- advanced or metastatic breast cancer, compared with single-agent fulvestrant. The combination was associated with increased toxicity. Further development of sapanisertib using these dosing schedules in this setting is not supported by these data.

mTOR inhibition by TAK-228 is effective against growth, survival and angiogenesis in preclinical retinoblastoma models

We and others have shown that aberrant activation of the mammalian target of rapamycin (mTOR) signalling is essential for retinoblastoma progression and has potential therapeutic value. TAK‐228 is a potent inhibitor of mTOR1 and 2 with preclinical activity in a variety of cancers. In this study, we report that TAK‐228 is a dual inhibitor of retinoblastoma and angiogenesis. TAK‐228 inhibits growth and induces apoptosis in a panel of retinoblastoma cell lines, with IC50 at ~0.2 μM. Under the same experimental conditions, TAK‐228 was less effective in inhibiting growth and survival in normal retinal and fibroblast cells than retinoblastoma cells. In addition, TAK‐228 inhibited retinal endothelial cell capillary network formation, migration, growth and survival. We further demonstrate that TAK‐228 inhibits retinoblastoma and retinal angiogenesis through inhibiting mTOR signalling. Rescue studies confirm that mTOR is the target of TAK‐228 in both retinoblastoma and retinal endothelial cells. Finally, we confirm the inhibitory effects of TAK‐228 on tumor and angiogenesis in retinoblastoma xenograft mouse model. Our findings provide a preclinical rationale to explore TAK‐228 as a strategy to treat retinoblastoma and highlight the therapeutic value of targeting mTOR in retinoblastoma.

Preclinical evaluation of the dual mTORC1/2 inhibitor sapanisertib in combination with cisplatin in nasopharyngeal carcinoma

A wide range of investigational drugs are being investigated in clinical trials for the treatment of nasopharyngeal carcinoma (NPC), including PI3K-mTOR inhibitor. The purpose of this study was to evaluate the effective combination of TORC1/2 inhibitor sapanisertib and chemotherapy drug cisplatin in preclinical models of NPC. In our work, sapanisertib at nanomolar concentrations decreases viability and proliferation in NPC cells regardless of varying genetic backgrounds. Sapanisertib acts synergistically with cisplatin via induces more G0/G1 arrest and apoptosis. At the same concentration, sapanisertib neither decreases viability nor proliferation in normal nasal epithelial cells. Sapanisertib also decreases NPC cell migration. It decreases phosphorylation of Akt, mTOR, p70S6K and 4EBP1 in NPC cells. The in vitro findings on the inhibitory effects of sapanisertib on NPC growth and mTOR signaling were also evident in the NPC xenograft mouse model. In addition, combination of sapanisertib with cisplatin resulted in better efficacy than monotherapy to inhibit NPC growth in mice without causing significant toxicity. These data clearly demonstrate efficacy and insignificant toxicity of sapanisertib alone and its combination with cisplatin in NPC preclinical models. Our findings will accelerate clinical trials evaluating combination of sapanisertib and chemotherapy for NPC treatment.

A Phase 1 Study of Sapanisertib (TAK-228) in East Asian Patients with Advanced Nonhematological Malignancies

BACKGROUND

Sapanisertib is an oral, highly selective inhibitor of mammalian target of rapamycin complexes 1 and 2.

OBJECTIVE

The aim of this study was to assess the safety, tolerability, pharmacokinetics, preliminary efficacy, and to establish the recommended phase 2 dose (RP2D) of sapanisertib.

PATIENTS AND METHODS

In this dose-escalation and expansion study, East Asian patients with nonhematologic malignancies received increasing sapanisertib doses once-daily (QD; starting at 2 mg) or once-weekly (QW; starting at 20 mg) in 28-day cycles.

RESULTS

Among 28 patients (QD dosing, n = 22; QW dosing, n = 6), three dose-limiting toxicities were reported (stomatitis [n = 2], gastrointestinal inflammation, gingivitis, and acute myocardial infarction [all n = 1]), all in the 4 mg QD cohort. The RP2D of sapanisertib was 3 mg QD. The most common adverse events were stomatitis (64%), nausea (50%), and decreased appetite (50%) in the QD arm, and nausea (100%), blood alkaline phosphatase increased (67%), and hyperglycemia (67%) in the QW arm. The T_max of sapanisertib was ~ 0.5-2.6 h and the T_1/2 was ~ 5.9-7.6 h. Three patients achieved stable disease for ≥ 6 months (1 each in 3 mg QD, 4 mg QD and 20 mg QW cohorts, respectively); the clinical benefit rate was 45% and 67% in the QD and QW arms, respectively.

CONCLUSIONS

The RP2D of sapanisertib in East Asian patients (3 mg QD) was lower than in Western patients (4 mg QD), but the pharmacokinetics and safety profiles were similar. Sapanisertib was well tolerated and showed moderate anti-tumor effects in heavily pretreated patients with nonhematologic malignancies.

NCT NUMBER

NCT03370302; Registered December 7, 2017.

Multiple strategies for the treatment of invasive breast carcinoma: A comprehensive prospective

In this review, we emphasize on evolving therapeutic strategies and advances in the treatment of breast cancer (BC). This includes small-molecule inhibitors under preclinical and clinical investigation, phytoconstituents with antiproliferative potential, targeted therapies as antibodies and antibody-drug conjugates (ADCs), vaccines as immunotherapeutic agents and peptides as a novel approach inhibiting the interaction of oncogenic proteins. We provide an update of molecules under different phases of clinical investigation which aid in the identification of loopholes or shortcomings that can be overcomed with future breast cancer research.

Targeting the PI3K/AKT/mTOR Pathway in Hormone-Positive Breast Cancer

Approximately 70% of invasive breast cancers have some degree of dependence on the estrogen hormone for cell proliferation and growth. These tumors have estrogen and/or progesterone receptors (ER/PR+), generally referred to as hormone receptor positive (HR+) tumors, as indicated by the presence of positive staining and varying intensity levels of estrogen and/or progesterone receptors on immunohistochemistry. Therapies that inhibit ER signaling pathways, such as aromatase inhibitors (letrozole, anastrozole, exemestane), selective ER modulators (tamoxifen), and ER down-regulators (fulvestrant), are the mainstays of treatment for hormone-receptor-positive breast cancers. However, de novo or acquired resistance to ER targeted therapies is present in many tumors, leading to disease progression. The PI3K/AKT/mTOR pathway is implicated in sustaining endocrine resistance and has become the target of many new drugs for ER+ breast cancer. This article reviews the function of the phosphoinositide 3-kinase (PI3K)/AKT/mTOR pathway and the various classes of PI3K pathway inhibitors that have been developed to disrupt this pathway signaling for the treatment of hormone-receptor-positive breast cancer.

Sapanisertib Plus Exemestane or Fulvestrant in Women with Hormone Receptor-Positive/HER2-Negative Advanced or Metastatic Breast Cancer

PURPOSE

This open-label, multicenter, phase IB/II study evaluated sapanisertib, a dual inhibitor of mTOR kinase complexes 1/2, plus exemestane or fulvestrant in postmenopausal women with hormone receptor-positive (HR⁺)/HER2-negative (HER2^-) advanced/metastatic breast cancer.

PATIENTS AND METHODS

Eligible patients had previously progressed on everolimus with exemestane/fulvestrant and received ≤3 (phase IB) or ≤1 (phase II) prior chemotherapy regimens. Patients received sapanisertib 3 to 5 mg every day (phase IB), or 4 mg every day (phase II) with exemestane 25 mg every day or fulvestrant 500 mg monthly in 28-day cycles. Phase II enrolled parallel cohorts based on prior response to everolimus. The primary objective of phase II was to evaluate antitumor activity by clinical benefit rate at 16 weeks (CBR-16).

RESULTS

Overall, 118 patients enrolled in phase IB (n = 24) and II (n = 94). Five patients in phase IB experienced dose-limiting toxicities, at sapanisertib doses of 5 mg every day (n = 4) and 4 mg every day (n = 1); sapanisertib 4 mg every day was the MTD in combination with exemestane or fulvestrant. In phase II, in everolimus-sensitive versus everolimus-resistant cohorts, CBR-16 was 45% versus 23%, and overall response rate was 8% versus 2%, respectively. The most common adverse events were nausea (52%), fatigue (47%), diarrhea (37%), and hyperglycemia (33%); rash occurred in 17% of patients. Molecular analysis suggested positive association between AKT1 mutation status and best treatment response (complete + partial response; P = 0.0262).

CONCLUSIONS

Sapanisertib plus exemestane or fulvestrant was well tolerated and exhibited clinical benefit in postmenopausal women with pretreated everolimus-sensitive or everolimus-resistant breast cancer.

A patent review of mTOR inhibitors for cancer therapy (2011-2020)

INTRODUCTION

The mammalian target of rapamycin (mTOR) kinase is a central component in the PI3K/Akt/mTOR pathway and plays a crucial role in tumor biology, making it one appealing therapeutic target. In the past decade, the mTORi (mTOR inhibitor) development field has made great progress, with more agents entering key trials and the proposal of third-generation mTORi concept. Yet to achieve significant clinical success, combined efforts from multiple disciplines are ever needed.

AREAS COVERED

This review focuses on the progress of mTORi development with anticancer potential from the perspective of the patent literature proposed between 2011 and 2020.

EXPERT OPINION

The highly complex regulatory mechanism network of mTOR proposes huge challenges to the development of clinically efficient mTORis. While in-depth biological research and fundamental medchemistry research are of importance to provide guidelines for improving mTORis, new technologies to pre-diagnose applicable populations is another key to provide precise personal cancer treatment. New mTOR agents are ever needed to tackle the common problems of side effects and drug resistance.

The Novel Oral mTORC1/2 Inhibitor TAK-228 Reverses Trastuzumab Resistance in HER2-Positive Breast Cancer Models

Simple Summary

Hyperactivation of the PI3K/AKT/mTOR cell signalling pathway is an important and well-described mechanism of trastuzumab resistance in HER2-positive breast cancer. In cell-line models of acquired trastuzumab resistance generated in our laboratory, we demonstrate this type of activation, which is independent of HER2-mediated regulation. We investigate whether the use of specific mTOR inhibitors, a PI3K/AKT/mTOR pathway effector, could lead to decreased activity of the pathway, influencing trastuzumab resistance. We demonstrate that TAK-228, a mTORC1 and mTORC2 inhibitor, can reverse resistance and increasing response to trastuzumab in models of primary and acquired resistance.

Abstract

The use of anti-HER2 therapies has significantly improved clinical outcome in patients with HER2-positive breast cancer, yet a substantial proportion of patients acquire resistance after a period of treatment. The PI3K/AKT/mTOR pathway is a good target for drug development, due to its involvement in HER2-mediated signalling and in the emergence of resistance to anti-HER2 therapies, such as trastuzumab. This study evaluates the activity of three different PI3K/AKT/mTOR inhibitors, i.e., BEZ235, everolimus and TAK-228 in vitro, in a panel of HER2-positive breast cancer cell lines with primary and acquired resistance to trastuzumab. We assess the antiproliferative effect and PI3K/AKT/mTOR inhibitory capability of BEZ235, everolimus and TAK-228 alone, and in combination with trastuzumab. Dual blockade with trastuzumab and TAK-228 was superior in reversing the acquired resistance in all the cell lines. Subsequently, we analyse the effects of TAK-228 in combination with trastuzumab on the cell cycle and found a significant increase in G0/G1 arrest in most cell lines. Likewise, the combination of both drugs induced a significant increase in apoptosis. Collectively, these experiments support the combination of trastuzumab with PI3K/AKT/mTOR inhibitors as a potential strategy for inhibiting the proliferation of HER2-positive breast cancer cell lines that show resistance to trastuzumab.

Differential alternative RNA splicing and transcription events between tumors from African American and White patients in The Cancer Genome Atlas

Individuals of African ancestry suffer disproportionally from higher incidence, aggressiveness, and mortality for particular cancers. This disparity likely results from an interplay among differences in multiple determinants of health, including differences in tumor biology. We used The Cancer Genome Atlas (TCGA) SpliceSeq and TCGA aggregate expression datasets and identified differential alternative RNA splicing and transcription events (ARS/T) in cancers between self-identified African American (AA) and White (W) patients. We found that retained intron events were enriched among race-related ARS/T. In addition, on average, 12% of the most highly ranked race-related ARS/T overlapped between any two analyzed cancers. Moreover, the genes undergoing race-related ARS/T functioned in cancer-promoting pathways, and a number of race-related ARS/T were associated with patient survival. We built a web-application, CanSplice, to mine genomic datasets by self-identified race. The race-related targets have the potential to aid in the development of new biomarkers and therapeutics to mitigate cancer disparity.

Recent developments in anticancer kinase inhibitors based on the pyrazolo[3,4-d]pyrimidine scaffold

Pyrazolo[3,4-d]pyrimidines have become of significant interest for the medicinal chemistry community as a privileged scaffold for the development of kinase inhibitors to treat a range of diseases, including cancer. This fused nitrogen-containing heterocycle is an isostere of the adenine ring of ATP, allowing the molecules to mimic hinge region binding interactions in kinase active sites. Similarities in kinase ATP sites can be exploited to direct the activity and selectivity of pyrazolo[3,4-d]pyrimidines to multiple oncogenic targets through focussed chemical modification. As a result, pharma and academic efforts have succeeded in progressing several pyrazolo[3,4-d]pyrimidines to clinical trials, including the BTK inhibitor ibrutinib, which has been approved for the treatment of several B-cell cancers. In this review, we examine the pyrazolo[3,4-d]pyrimidines currently in clinical trials for oncology patients, as well as those published in the literature during the last 5 years for different anticancer indications.

Phase 1 study of mTORC1/2 inhibitor sapanisertib (TAK-228) in advanced solid tumours, with an expansion phase in renal, endometrial or bladder cancer

Background

This Phase 1 dose-escalation/expansion study assessed safety/tolerability of sapanisertib, an oral, highly selective inhibitor of mTORC1/mTORC2, in advanced solid tumours.

Methods

Eligible patients received increasing sapanisertib doses once daily (QD; 31 patients), once weekly (QW; 30 patients), QD for 3 days on/4 days off QW (QD × 3dQW; 33 patients) or QD for 5 days on/2 days off QW (QD × 5dQW; 22 patients). In expansion cohorts, 82 patients with renal cell carcinoma (RCC), endometrial or bladder cancer received sapanisertib 5 mg QD (39 patients), 40 mg QW (26 patients) or 30 mg QW (17 patients).

Results

Maximum tolerated doses of sapanisertib were 6 mg QD, 40 mg QW, 9 mg QD × 3dQW and 7 mg QD × 5dQW. Frequent dose-limiting toxicities (DLTs) included hyperglycaemia, maculo-papular rash (QD), asthenia and stomatitis (QD × 3dQW/QD × 5dQW); expansion phase doses of 5 mg QD and 30 mg QW were selected based on tolerability beyond the DLT evaluation period. One patient with RCC achieved complete response; nine experienced partial responses (RCC: seven patients; carcinoid tumour/endometrial cancer: one patient each). Sapanisertib pharmacokinetics were time-linear and supported multiple dosing. Pharmacodynamic findings demonstrated treatment-related reductions in TORC1/2 biomarkers.

Conclusions

Sapanisertib demonstrated a manageable safety profile, with preliminary antitumour activity observed in RCC and endometrial cancer.

Clinical trial registration

ClinicalTrials.gov, NCT01058707.

Preclinical and Dose-Finding Phase I Trial Results of Combined Treatment with a TORC1/2 Inhibitor (TAK-228) and Aurora A Kinase Inhibitor (Alisertib) in Solid Tumors

PURPOSE

The purpose of this study was to evaluate the rational combination of TORC1/2 inhibitor TAK-228 and Aurora A kinase inhibitor alisertib in preclinical models of triple-negative breast cancer (TNBC) and to conduct a phase I dose escalation trial in patients with advanced solid tumors.

EXPERIMENTAL DESIGN

TNBC cell lines and patient-derived xenograft (PDX) models were treated with alisertib, TAK-228, or the combination and evaluated for changes in proliferation, cell cycle, mTOR pathway modulation, and terminal cellular fate, including apoptosis and senescence. A phase I clinical trial was conducted in patients with advanced solid tumors treated with escalating doses of alisertib and TAK-228 using a 3+3 design to determine the maximum tolerated dose (MTD).

RESULTS

The combination of TAK-228 and alisertib resulted in decreased proliferation and cell-cycle arrest in TNBC cell lines. Treatment of TNBC PDX models resulted in significant tumor growth inhibition and increased apoptosis with the combination. In the phase I dose escalation study, 18 patients with refractory solid tumors were enrolled. The MTD was alisertib 30 mg b.i.d. days 1 to 7 of a 21-day cycle and TAK-228 2 mg daily, continuous dosing. The most common treatment-related adverse events were neutropenia, fatigue, nausea, rash, mucositis, and alopecia.

CONCLUSIONS

The addition of TAK-228 to alisertib potentiates the antitumor activity of alisertib in vivo, resulting in increased cell death and apoptosis. The combination is tolerable in patients with advanced solid tumors and should be evaluated further in expansion cohorts with additional pharmacodynamic assessment.

Phase 1 Study to Evaluate the Effect of the Investigational Anticancer Agent Sapanisertib on the QTc Interval in Patients With Advanced Solid Tumors

The aim of this phase 1 study was to determine the effects of sapanisertib on the heart rate–corrected QT (QTc) interval in patients with advanced solid tumors. Adult patients with advanced solid tumors were enrolled to receive a single sapanisertib 40‐mg dose. Blood samples for pharmacokinetic analysis were collected and electrocardiogram readings were recorded at baseline and up to 48 hours after dosing. Patients could continue to receive sapanisertib 30 mg once weekly in 28‐day cycles for up to 12 months. The primary objective was to characterize the effect of a single dose of sapanisertib (40 mg) on the QT interval. Secondary objectives were to evaluate safety, tolerability, and pharmacokinetics. Following a single sapanisertib 40‐mg dose in 44 patients, the maximum least squares mean (upper bound of 1‐sided 95% confidence interval) changes from time‐matched baseline were 7.1 milliseconds (11.4 milliseconds) for individual rate‐corrected QT interval at 24 hours after dosing, and 1.8 milliseconds (5.6 milliseconds) for Fridericia‐corrected QTc at 1 hour post‐dose. There was no sapanisertib plasma concentration‐dependent increase in the change from time‐matched baseline individual rate‐corrected QTc interval or Fridericia‐corrected QTc. The most common adverse events following sapanisertib 30 mg once‐weekly dosing were nausea (80%), fatigue (61%), vomiting (57%), and decreased appetite (45%). A single sapanisertib 40 mg dose did not produce clinically relevant effects on QTc interval in patients with advanced solid tumors. The safety profile of sapanisertib 30 mg once weekly was favorable, and no new safety signals were observed (NCT02197572, clinicaltrials.gov).

Signal Transduction Pathways in Breast Cancer: The Important Role of PI3K/Akt/mTOR

Breast cancer is the cancer with the highest prevalence in women and is the number-one cause of cancer mortality worldwide. Cell transduction is a fundamental process in the development and progression of cancer. Modifications in various cell signalling pathways promote tumour cell proliferation, progression, and survival. The PI3K/Akt/mTOR pathway is an example of that, and it is involved in growth, proliferation, survival, motility, metabolism, and immune response regulation. Activation of this pathway is one of the main causes of cancer cell resistance to antitumour therapies. This makes PI3K/Akt/mTOR signalling a crucial object of study for understanding the development and progression of this disease. Thus, this pathway may have a role as a potential therapeutic target, as well as prognostic and diagnostic value, in patients with breast cancer. Despite the existence of selective PI3K/Akt/mTOR pathway inhibitors and current clinical trials, the cellular mechanisms are not yet known. The present review aims to understand the current state of this important disease and the paths that must be forged.

Recent nanotechnological interventions targeting PI3K/Akt/mTOR pathway: A focus on breast cancer

Breast cancer is the major cause of deaths in women worldwide. Detection and treatment of breast cancer at earlier stages of the disease has shown encouraging results. Modern genomic technologies facilitated several therapeutic options however the diagnosis of the disease at an advanced stage claim more deaths. Therefore more research directed towards genomics and proteomics into this area may lead to novel biomarkers thereby enhancing the survival rates in breast cancer patients. Phosphoinositide-3-kinase/Akt/mammalian target of rapamycin (PI3K/Akt/mTOR) signaling pathway was shown to be hyperactivated in most of the breast carcinomas resulting in excessive growth, proliferation, and tumor development. Development of nanotechnology has provided many interesting avenues to target the PI3K/Akt/mTOR pathway both at the pre-clinical and clinical stages. Therefore, the current review summarizes the underlying mechanism and the importance of targeting PI3K/Akt/mTOR pathway, novel biomarkers and use of nanotechnological interventions in breast cancer.

Targeting mTOR for cancer therapy

Mechanistic target of rapamycin (mTOR) is a protein kinase regulating cell growth, survival, metabolism, and immunity. mTOR is usually assembled into several complexes such as mTOR complex 1/2 (mTORC1/2). In cooperation with raptor, rictor, LST8, and mSin1, key components in mTORC1 or mTORC2, mTOR catalyzes the phosphorylation of multiple targets such as ribosomal protein S6 kinase β-1 (S6K1), eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1), Akt, protein kinase C (PKC), and type-I insulin-like growth factor receptor (IGF-IR), thereby regulating protein synthesis, nutrients metabolism, growth factor signaling, cell growth, and migration. Activation of mTOR promotes tumor growth and metastasis. Many mTOR inhibitors have been developed to treat cancer. While some of the mTOR inhibitors have been approved to treat human cancer, more mTOR inhibitors are being evaluated in clinical trials. Here, we update recent advances in exploring mTOR signaling and the development of mTOR inhibitors for cancer therapy. In addition, we discuss the mechanisms underlying the resistance to mTOR inhibitors in cancer cells.

An In silico Approach to Identify High Affinity Small Molecule Targeting m-TOR Inhibitors for the Clinical Treatment of Breast Cancer

Breast cancer is the most frequent malignancy among women. It is a heterogeneous disease with different subtypes defined by its hormone receptor. A hormone receptor is mainly concerned with the progression of the PI3K/AKT/mTOR pathway which is often dysregulated in breast cancer. This is a major signaling pathway that controls the activities such as cell growth, cell division, and cell proliferation. The present study aims to suppress mTOR protein by its various inhibitors and to select one with the highest binding affinity to the receptor protein. Out of 40 inhibitors of mTOR against breast cancer, SF1126 was identified to have the best docking score of -8.705, using Schrodinger Suite which was further subjected for high throughput screening to obtain best similar compound using Lipinski’s filters. The compound obtained after virtual screening, ID: ZINC85569445 is seen to have the highest affinity with the target protein mTOR. The same result based on the binding free energy analysis using MM-GBSA showed that the compound ZINC85569445 to have the the highest binding free energy. The next study of interaction between the ligand and receptor protein with the pharmacophore mapping showed the best conjugates, and the ZINC85569445 can be further studied for future benefits of treatment of breast cancer.

Synergistic anti-cancer activity of CDK4/6 inhibitor palbociclib and dual mTOR kinase inhibitor MLN0128 in pRb-expressing ER-negative breast cancer

PURPOSE

Palbociclib is an approved cyclin-dependent kinase (CDK) 4/6 inhibitor for treatment of patients with ER-positive and HER2-negative breast cancers. While Retinoblastoma protein (pRb), a major substrate of CDK4/6, is a potential target in triple negative breast cancer (TNBC), the usefulness of CDK4/6 inhibitors in this cancer has not been established. This preclinical study investigated the combination effects of palbociclib and the dual mammalian target of rapamycin (mTOR) kinase inhibitor MLN0128 in estrogen receptor (ER)-negative breast cancer in vitro and in vivo.

METHODS

The combined effects of two drugs on three TNBC cell lines (MB231, MB468, and CAL148) and an ER-negative and HER2-positive cell line (MB453) were investigated by MTT assay and colony formation analysis. Cell cycle measurements were examined as well as changes in expression of molecules related to G1/S transition and the mTOR pathway. Importantly, a pRb-expressing TNBC patient-derived xenograft (PDX) model was used to assess the effects of the combination in vivo.

RESULTS

A combination of palbociclib and MLN0128 synergistically inhibited the proliferation of pRb-expressing cell lines and induced G1 cell cycle arrest. Western blot analysis revealed that CDK4/6-pRb and mTOR pathways were inhibited by these treatments. In pRb-expressing TNBC PDX, the combination treatment drastically suppressed tumor growth compared to either the control or single drug treatments. In addition, the combination treatment significantly reduced the number of Ki67-positive cells.

CONCLUSIONS

We revealed that palbociclib and MLN0128 had synergistic anti-cancer activity in both pRb + ER-negative cell lines and a TNBC PDX model. Our results indicate that such combination therapy is worthy of further investigation in a clinical setting.

Activating Mutations in Pik3ca Contribute to Anal Carcinogenesis in the Presence or Absence of HPV-16 Oncogenes

PURPOSE

Over 95% of human anal cancers are etiologically associated with high-risk HPVs, with HPV type 16 (HPV16) the genotype most commonly found. Activating mutations in the catalytic subunit of Phosphatidylinositol (3,4,5)-trisphosphate kinase (PI3K), encoded by the Pik3ca gene, are detected in approximately 20% of human anal cancers.Experimental Design: We asked if common activating mutations in Pik3ca contribute to anal carcinogenesis using an established mouse model for anal carcinogenesis in which mice are topically treated with the chemical carcinogen 7,12-Dimethylbenz(a)anthracene (DMBA). Mice expressing in their anal epithelium one of two activating mutations in Pik3ca genes, Pik3ca^H1047R or Pik3ca^E545K , were monitored for anal carcinogenesis in the presence or absence of transgenes expressing the HPV16 E6 and E7 oncogenes.

RESULTS

Both mutant forms of Pik3ca increased susceptibility to anal carcinogenesis in the absence of HPV16 oncogenes, and cooperated with HPV16 oncogenes to induce the highest level and earliest onset of anal cancers. The combination of HPV16 oncogenes and Pik3ca mutations led to anal cancers even in the absence of treatment with DMBA. We further observed that the investigational mTOR1/2 dual inhibitor, TAK-228, significantly reduced the size of anal cancer-derived tumor spheroids in vitro and reduced the growth rates of anal cancer-derived tumor grafts in vivo.

CONCLUSIONS

These data demonstrate that activating mutations in Pik3ca drive anal carcinogenesis together with HPV16 oncogenes, and that the PI3K/mTOR pathway is a relevant target for therapeutic intervention.

mTORC1/2 inhibition re-sensitizes platinum-resistant ovarian cancer by disrupting selective translation of DNA damage and survival mRNAs

Platinum resistance is a major cause of treatment failure and mortality in epithelial ovarian cancer. mTORC1/2 inhibitors, which impair mRNA translation, can re-sensitize resistant ovarian cancer cells to platinum chemotherapy but the mechanism remains poorly described. Using platinum-resistant OVCAR-3 cells treated with the selective mTORC1/2 inhibitor INK128/MLN128, we conducted genome-wide transcription and translation studies and analyzed the effect on cell proliferation, AKT-mTOR signaling and cell survival, to determine whether carboplatin resistance involves selective mRNA translational reprogramming, and whether it is sensitive to mTORC1/2 inhibition. Gene ontology and Ingenuity Pathway Analysis (IPA) were used to categorize gene expression changes into experimentally authenticated biochemical and molecular networks. We show that carboplatin resistance involves increased mTORC1/2 signaling, resulting in selective translation of mRNAs involved in DNA damage and repair responses (DDR), cell cycle and anti-apoptosis (survival) pathways. Re-sensitization of ovarian cancer cell killing by carboplatin required only modest mTORC1/2 inhibition, with downregulation of protein synthesis by only 20-30%. Genome-wide transcriptomic and translatomic analyses in OVCAR-3 cells revealed that the modest downregulation of global protein synthesis by dual mTORC1/2 inhibition is associated with greater selective inhibition of DDR, cell cycle and survival mRNA translation, which was confirmed in platinum-resistant SKOV-3 cells. These data suggest a clinical path to re-sensitize platinum resistant ovarian cancer to platinum chemotherapy through partial inhibition of mTORC1/2, resulting in selective translation inhibition of DDR and anti-apoptosis protective mRNAs.

mTOR inhibitor INK128 attenuates dextran sodium sulfate-induced colitis by promotion of MDSCs on Treg cell expansion

Accumulating evidence has shown that mammalian target of rapamycin (mTOR) pathway and myeloid-derived suppressor cells (MDSCs) are involved in pathogenesis of inflammatory bowel diseases (IBDs). INK128 is a novel mTOR kinase inhibitor in clinical development. However, the exact roles of MDSCs and INK128 in IBD are unclear. Here, we showed that the INK128 treatment enhanced the resistance of mice to dextran sodium sulfate (DSS)-induced colitis and inhibited the differentiation of MDSCs into macrophages. Moreover, interferon (IFN)-α level was elevated in INK128-treated colitis mice. When stimulated with IFN-α in vitro, MDSCs showed a superior immunosuppression activity. Of note, the regulatory T cells (Tregs) increased but Th1 cells decreased in INK128-treated colitis mice. These results indicate that mTOR inhibitor INK128 attenuates DSS-induced colitis via Treg expansion promoted by MDSCs. Our work provides a new evidence that INK128 is potential to be a therapeutic drug on DSS-induced colitis via regulating MDSCs as well as maintaining Treg expansion.

The next generation of PI3K-Akt-mTOR pathway inhibitors in breast cancer cohorts

The PI3K/Akt/mTOR pathway plays a role in various oncogenic processes in breast cancer and key pathway aberrations have been identified which drive the different molecular subtypes. Early drugs developed targeting this pathway produced some clinical success but were hampered by pharmacokinetics, tolerability and efficacy problems. This created a need for new PI3K pathway-inhibiting drugs, which would produce more robust results allowing incorporation into treatment regimens for breast cancer patients. In this review, the most promising candidates from the new generation of PI3K-pathway inhibitors is explored, presenting evidence from preclinical and early clinical research, as well as ongoing trials utilising these drugs in breast cancer cohorts. The problems hindering the development of drugs targeting the PI3K pathway are examined, which have created problems for their use as monotherapies. PI3K pathway inhibitor combinations therefore remains a dynamic research area, and their role in combination with immunotherapies and epigenetic therapies is also inspected.

A Population of Heterogeneous Breast Cancer Patient-Derived Xenografts Demonstrate Broad Activity of PARP Inhibitor in BRCA1/2 Wild-Type Tumors

Background: Breast cancer patients who do not respond to neoadjuvant therapy have a poor prognosis. There is a pressing need for novel targets and models for preclinical testing. Here we report characterization of breast cancer patient-derived xenografts (PDX) largely generated from residual tumors following neoadjuvant chemotherapy.Experimental Design: PDXs were derived from surgical samples of primary or locally recurrent tumors. Normal and tumor DNA sequencing, RNASeq, and reverse phase protein arrays (RPPA) were performed. Phenotypic profiling was performed by determining efficacy of a panel of standard and investigational agents.Results: Twenty-six PDXs were developed from 25 patients. Twenty-two were generated from residual disease following neoadjuvant chemotherapy, and 24 were from triple-negative breast cancer (TNBC). These PDXs harbored a heterogeneous set of genomic alterations and represented all TNBC molecular subtypes. On RPPA, PDXs varied in extent of PI3K and MAPK activation. PDXs also varied in their sensitivity to chemotherapeutic agents. PI3K, mTOR, and MEK inhibitors repressed growth but did not cause tumor regression. The PARP inhibitor talazoparib caused dramatic regression in five of 12 PDXs. Notably, four of five talazoparib-sensitive models did not harbor germline BRCA1/2 mutations, but several had somatic alterations in homologous repair pathways, including ATM deletion and BRCA2 alterations.Conclusions: PDXs capture the molecular and phenotypic heterogeneity of TNBC. Here we show that PARP inhibition can have activity beyond germline BRCA1/2 altered tumors, causing regression in a variety of molecular subtypes. These models represent an opportunity for the discovery of rational combinations with targeted therapies and predictive biomarkers. Clin Cancer Res; 23(21); 6468-77. ©2017 AACR.

The TORC1/2 inhibitor TAK228 sensitizes atypical teratoid rhabdoid tumors to cisplatin-induced cytotoxicity

Background

Atypical teratoid/rhabdoid tumors (AT/RTs) are deadly pediatric brain tumors driven by LIN28. Mammalian target of rapamycin (mTOR) is activated in many deadly, drug-resistant cancers and governs important cellular functions such as metabolism and survival. LIN28 regulates mTOR in normal cells. We therefore hypothesized that mTOR is activated downstream of LIN28 in AT/RT, and the brain-penetrating mTOR complex 1 and 2 (mTORC1/2) kinase inhibitor TAK228 would reduce AT/RT tumorigenicity.

Methods

Activation of mTOR in AT/RT was determined by measuring pS6 and pAKT (Ser473) by immunohistochemistry on tissue microarray of 18 primary AT/RT tumors. In vitro growth assays (BrdU and MTS), death assays (CC3, c-PARP by western blot), and survival curves of AT/RT orthotopic xenograft models were used to measure the efficacy of TAK228 alone and in combination with cisplatin.

Results

Lentiviral short hairpin RNA-mediated knockdown of LIN28A led to decreased mTOR activation. Primary human AT/RT had high levels of pS6 and pAKT (Ser473) in 21% and 87% of tumors by immunohistochemistry. TAK228 slowed cell growth, induced apoptosis in vitro, and nearly doubled median survival of orthotopic xenograft models of AT/RT. TAK228 combined with cisplatin synergistically slowed cell growth and enhanced cisplatin-induced apoptosis. Suppression of AKT sensitized cells to cisplatin-induced apoptosis and forced activation of AKT protected cells. Combined treatment with TAK228 and cisplatin significantly extended survival of orthotopic xenograft models of AT/RT compared with each drug alone.

Conclusions

TAK228 has efficacy in AT/RT as a single agent and synergizes with conventional chemotherapies by sensitizing tumors to cisplatin-induced apoptosis. These results suggest TAK228 may be an effective new treatment for AT/RT.

CD44 positive and sorafenib insensitive hepatocellular carcinomas respond to the ATP-competitive mTOR inhibitor INK128

The mTOR pathway is activated in about 50% of patients with hepatocellular carcinoma (HCC). In an effort to identify new pathways and compounds to treat advanced HCC, we considered the ATP-competitive mTOR inhibitor INK128. ATP-competitive mTOR inhibitors attenuate both mTORC1 and mTORC2. INK128 was evaluated in sorafenib sensitive and insensitive HCC cell lines, CD44_low and CD44_high HCC and those cell lines with acquired sorafenib resistance. CD44 was significantly increased in Huh7 cells made resistant to sorafenib. Forced expression of CD44 enhanced cellular proliferation and migration, and rendered the cells more sensitive to the anti-proliferative effects of INK128. INK128 suppressed CD44 expression in HCC cells while allosteric mTOR inhibitors did not. CD44 inhibition correlated with 4EBP1 phosphorylation status. INK128 showed better anti-proliferative and anti-migration effects on the mesenchymal-like HCC cells, CD44_high HCC cells compared to the allosteric mTOR inhibitor everolimus. Moreover, a combination of INK128 and sorafenib showed improved anti-proliferative effects in CD44_high HCC cells. INK128 was efficacious at reducing tumor growth in CD44_high SK-Hep1 xenografts in mice when given as monotherapy or in combination with sorafenib. Since the clinical response to sorafenib is highly variable, our findings suggest that ATP-competitive mTOR inhibitors may be effective in treating advanced, CD44-expressing HCC patients who are insensitive to sorafenib.

Phase I study of the investigational oral mTORC1/2 inhibitor sapanisertib (TAK-228): tolerability and food effects of a milled formulation in patients with advanced solid tumours

Background

Sapanisertib (TAK-228) is an investigational, orally available, potent and highly selective mTORC1/2 inhibitor demonstrating promise in numerous malignancies. This phase I study (NCT02412722) evaluated the safety, tolerability, pharmacokinetics and antitumour activity of single-agent TAK-228 (milled capsules), administered daily (QD) or weekly (QW) and in combination with paclitaxel in patients with advanced solid tumours. Pharmacokinetic comparisons of milled versus unmilled TAK-228 and the impact of food were also investigated.

Methods

Patients were enrolled to receive: TAK-228 QD, TAK-228 3 days/week plus paclitaxel 80 mg/m² days 1, 8, 15 (TAK-228+P) or TAK-228 QW (all 28-day cycles); starting TAK‑228 doses were 4, 6 and 20 mg, respectively.

Results

Sixty-one adults were enrolled. Maximum tolerated doses for milled TAK-228 were 3 mg (TAK-228 QD), 6 mg (TAK-228+P) and 30 mg (TAK-228 QW). Most patients reported ≥1 adverse event (AE); there were no meaningful differences in drug-related AEs across regimens or doses. Three on-study deaths occurred, all considered unrelated to study drugs. TAK-228 pharmacokinetics did not differ between unmilled/milled capsules or with/without paclitaxel. However, TAK-228 C_max decreased by ~40% in fed versus fasted patients. Objective response rates were 12% (TAK-228 QD), 18% (TAK-228+P) and 0% (TAK-228 QW). One patient receiving TAK-228+P had a complete response; three patients receiving TAK-228+P and two patients receiving TAK-228 QD had partial responses.

Conclusions

Milled TAK-228 was well tolerated with signs of antitumour activity; administration did not reduce overall exposure (area under the plasma concentration–time curve) but reduced C_max, which is expected when dosed in the fed state. These promising findings warrant further investigation.

Trial registration number

NCT02412722.

MLN0128, a novel mTOR kinase inhibitor, disrupts survival signaling and triggers apoptosis in AML and AML stem/ progenitor cells

mTOR activation leads to enhanced survival signaling in acute myeloid leukemia (AML) cells. The active-site mTOR inhibitors (asTORi) represent a promising new approach to targeting mTOR in AKT/mTOR signaling. MLN0128 is an orally-administered, second-generation asTORi, currently in clinical development. We examined the anti-leukemic effects and the mechanisms of action of MLN0128 in AML cell lines and primary samples, with a particular focus on its effect in AML stem/progenitor cells. MLN0128 inhibited cell proliferation and induced apoptosis in AML by attenuating the activity of mTOR complex 1 and 2. Using time-of-flight mass cytometry, we demonstrated that MLN0128 selectively targeted and functionally inhibited AML stem/progenitor cells with high AKT/mTOR signaling activity. Using the reverse-phase protein array technique, we measured expression and phosphorylation changes in response to MLN0128 in 151 proteins from 24 primary AML samples and identified several pro-survival pathways that antagonize MLN0128-induced cellular stress. A combined blockade of AKT/mTOR signaling and these pro-survival pathways facilitated AML cell killing. Our findings provide a rationale for the clinical use of MLN0128 to target AML and AML stem/progenitor cells, and support the use of combinatorial multi-targeted approaches in AML therapy.

mTOR complex-2 stimulates acetyl-CoA and de novo lipogenesis through ATP citrate lyase in HER2/PIK3CA-hyperactive breast cancer

The mechanistic target of rapamycin (mTOR) is a major regulator of cell growth and is frequently dysregulated in cancer. While mTOR complex-1 (mTORC1) is a validated cancer target, the role of mTOR complex-2 (mTORC2) remains less defined. Here, we reveal mTORC2 as a critical regulator of breast cancer metabolism. We showed that hyperphosphorylation in ATP citrate lyase (ACL) occurs frequently in human breast tumors and correlates well with HER2+ and/or PIK3CA-mutant (HER2+/PIK3CAmut) status in breast tumor cell lines. In HER2+/PIK3CAmut cells, mTORC2 controls Ser-455 phosphorylation of ACL thereby promoting acetyl-CoA production, de novo lipogenesis and mitochondrial physiology, all of which were inhibited by an mTORC1/mTORC2 kinase inhibitor (mTOR-KI) or cellular depletion of mTORC2 or ACL. mTOR-KI but not rapamycin blocked the IGF-1-induced ACL phosphorylation and glucose to lipid conversion. Depletion of mTORC2 but not mTORC1 specifically inhibited the ACL-dependent acetyl-CoA production. In the HER2+/PIK3CAmut MDA361, MDA453, BT-474 and T47D cells, depletion of mTORC2 or ACL led to growth inhibition and mitochondrial hyperpolarization, which were partially rescued by an alternate source of acetyl-CoA. These same changes were not apparent in mTORC2- or ACL-depleted HER2-/PIK3CAwt MDA231 and HCC1806 cells, highlighting a differential dependence of mTORC2-ACL for survival in these two cell types. Moreover, ACL Ser-455 mutants S455E (phosphomimetic) and S455A (non-phosphorylatable) each increased or decreased, respectively, the acetyl-CoA production, mitochondrial homeostasis and survival in ACL-depleted MDA453 cells. These studies define a new and rapamycin-resistant mechanism of mTORC2-ACL in lipogenesis and acetyl-CoA biology and provide a rationale for targeting of mTORC1 and mTORC2 in HER2+/PIK3CAmut breast cancer.

PI3K/AKT/mTOR: role in breast cancer progression, drug resistance, and treatment

Anti-cancer cancer-targeted therapies are designed to exploit a particular vulnerability in the tumor, which in most cases results from its dependence on an oncogene and/or loss of a tumor suppressor. Mutations in the phosphoinositide 3-kinase (PI3K)/AKT/mTOR pathway are freqcuently found in breast cancers and associated with cellular transformation, tumorigenesis, cancer progression, and drug resistance. Several drugs targeting PI3K/ATK/mTOR are currently in clinical trials, mainly in combination with endocrine therapy and anti-HER2 therapy. These drugs are the focus of this review.

Dual mTOR Kinase Inhibitor MLN0128 Sensitizes HR+/HER2+ Breast Cancer Patient-Derived Xenografts to Trastuzumab or Fulvestrant

Purpose: Therapeutic strategies against hormonal receptor-positive (HR⁺)/HER2⁺ breast cancers with poor response to trastuzumab need to be optimized.Experimental Design: Two HR⁺/HER2⁺ patient-derived xenograft (PDX) models named as COH-SC1 and COH-SC31 were established to explore targeted therapies for HER2⁺ breast cancers. RNA sequencing and RPPA (reverse phase protein array) analyses were conducted to decipher molecular features of the two PDXs and define the therapeutic strategy of interest, validated by in vivo drug efficacy examination and in vitro cell proliferation analysis.Results: Estrogen acted as a growth driver of trastuzumab-resistant COH-SC31 tumors but an accelerator in the trastuzumab-sensitive COH-SC1 model. In vivo trastuzumab efficacy examination further confirmed the consistent responses between PDXs and the corresponding tumors. Integrative omics analysis revealed that mammalian target of rapamycin (mTOR) and ERα signaling predominantly regulate tumor growth of the two HR⁺/HER2⁺ PDXs. Combination of the dual mTOR complex inhibitor MLN0128 and anti-HER2 trastuzumab strongly suppressed tumor growth of COH-SC1 PDX accompanied by increasing ER-positive cell population in vivo Instead, MLN0128 in combination with antiestrogen fulvestrant significantly halted the growth of HR⁺/HER2⁺ cancer cells in vitro and trastuzumab-resistant COH-SC31 as well as trastuzumab-sensitive COH-SC1 tumors in vivoConclusions: Compared with the standard trastuzumab treatment, this study demonstrates alternative therapeutic strategies against HR⁺/HER2⁺ tumors through establishment of two PDXs coupled with integrative omics analyses and in vivo drug efficacy examination. This work presents a prototype of future "co-clinical" trials to tailor personalized medicine in clinical practice. Clin Cancer Res; 24(2); 395-406. ©2017 AACR.

TAK-228 (formerly MLN0128), an investigational dual TORC1/2 inhibitor plus paclitaxel, with/without trastuzumab, in patients with advanced solid malignancies

PURPOSE

This phase I trial evaluated the safety, pharmacokinetic profile, and antitumor activity of investigational oral TORC1/2 inhibitor TAK-228 plus paclitaxel, with/without trastuzumab, in patients with advanced solid malignancies.

METHODS

Sixty-seven patients received TAK-228 6-40 mg via three dosing schedules; once daily for 3 days (QDx3d QW) or 5 days per week (QDx5d QW), and once weekly (QW) plus paclitaxel 80 mg/m² (dose-escalation phase, n = 47) and with/without trastuzumab 2 mg/kg (expansion phase, n = 20). Doses were escalated using a modified 3 + 3 design, based upon dose-limiting toxicities in cycle 1.

RESULTS

TAK-228 pharmacokinetics exhibited dose-dependent increase in exposure when dosed with paclitaxel and no apparent differences when administered with or 24 h after paclitaxel. Dose-limiting toxicities were dehydration, diarrhea, stomatitis, fatigue, rash, thrombocytopenia, neutropenia, leukopenia, and nausea. The maximum tolerated dose of TAK-228 was determined as 10-mg QDx3d QW; the expansion phase proceeded with 8-mg QDx3d QW. Overall, the most common grade ≥3 drug-related toxicities were neutropenia (21%), diarrhea (12%), and hyperglycemia (12%). Of 54 response-evaluable patients, eight achieved partial response and six had stable disease lasting ≥6 months.

CONCLUSION

TAK-228 demonstrated a safety profile consistent with other TORC inhibitors and promising preliminary antitumor activity in a range of tumor types; no meaningful difference was noted in the pharmacokinetics of TAK-228 when administered with or 24 h after paclitaxel. These findings support further investigation of TAK-228 in combination with other agents including paclitaxel, with/without trastuzumab, in patients with advanced solid tumors. CLINICALTRIALS.

GOV IDENTIFIER

NCT01351350.

The dual mTOR kinase inhibitor TAK228 inhibits tumorigenicity and enhances radiosensitization in diffuse intrinsic pontine glioma

Diffuse intrinsic pontine glioma (DIPG) is an invasive and treatment-refractory pediatric brain tumor. Primary DIPG tumors harbor a number of mutations including alterations in PTEN, AKT, and PI3K and exhibit activation of mammalian Target of Rapamycin Complex 1 and 2 (mTORC1/2). mTORC1/2 regulate protein translation, cell growth, survival, invasion, and metabolism. Pharmacological inhibition of mTORC1 is minimally effective in DIPG. However, the activity of dual TORC kinase inhibitors has not been examined in this tumor type. Nanomolar levels of the mTORC1/2 inhibitor TAK228 reduced expression of p-AKT^S473 and p-S6^S240/244 and suppressed the growth of DIPG lines JHH-DIPG1, SF7761, and SU-DIPG-XIII. TAK228 induced apoptosis in DIPG cells and cooperated with radiation to further block proliferation and enhance apoptosis. TAK228 monotherapy inhibited the tumorigenicity of a murine orthotopic model of DIPG, more than doubling median survival (p = 0.0017) versus vehicle. We conclude that dual mTOR inhibition is a promising potential candidate for DIPG treatment.

The emerging role of PI3K/AKT-mediated epigenetic regulation in cancer

The PI3-kinase/AKT pathway integrates signals from external cellular stimuli to regulate essential cellular functions, and is frequently aberrantly activated in human cancers. Recent research demonstrates that tight regulation of the epigenome is critical in preserving and restricting transcriptional activation, which can impact cellular growth and proliferation. In this review we examine mechanisms by which the PI3K/AKT pathway regulates the epigenome to promote oncogenesis, and highlight how connections between PI3K/AKT and the epigenome may impact the future therapeutic treatment of cancers featuring a hyperactivated PI3K/AKT pathway.

mTORC1/2 inhibition preserves ovarian function and fertility during genotoxic chemotherapy

The ovary contains oocytes within immature (primordial) follicles that are fixed in number at birth. Activation of follicles within this fixed pool causes an irreversible decline in reproductive capacity, known as the ovarian reserve, until menopause. Premenopausal women undergoing commonly used genotoxic (DNA-damaging) chemotherapy experience an accelerated loss of the ovarian reserve, leading to subfertility and infertility. Therefore, there is considerable interest but little effective progress in preserving ovarian function during chemotherapy. Here we show that blocking the kinase mammalian/mechanistic target of rapamycin (mTOR) with clinically available small-molecule inhibitors preserves ovarian function and fertility during chemotherapy. Using a clinically relevant mouse model of chemotherapy-induced gonadotoxicity by cyclophosphamide, and inhibition of mTOR complex 1 (mTORC1) with the clinically approved drug everolimus (RAD001) or inhibition of mTORC1/2 with the experimental drug INK128, we show that mTOR inhibition preserves the ovarian reserve, primordial follicle counts, serum anti-Mullerian hormone levels (a rigorous measure of the ovarian reserve), and fertility. Chemotherapy-treated animals had significantly fewer offspring compared with all other treatment groups, whereas cotreatment with mTOR inhibitors preserved normal fertility. Inhibition of mTORC1 or mTORC1/2 within ovaries was achieved during chemotherapy cotreatment, concomitant with preservation of primordial follicle counts. Importantly, our findings indicate that as little as a two- to fourfold reduction in mTOR activity preserves ovarian function and normal birth numbers. As everolimus is approved for tamoxifen-resistant or relapsing estrogen receptor-positive breast cancer, these findings represent a potentially effective and readily accessible pharmacologic approach to fertility preservation during conventional chemotherapy.

Dual mTOR inhibitor MLN0128 suppresses Merkel cell carcinoma (MCC) xenograft tumor growth

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine skin cancer. Pathologic activation of PI3K/mTOR pathway and elevated expression of c-Myc are frequently detected in MCC. Yet, there is no targeted therapy presently available for this lethal disease. Recently, MLN0128, a second-generation dual TORC1/2 inhibitor is shown to have therapeutic efficacy in preclinical studies. MLN0128 is currently in clinical trials as a potential therapy for advanced cancers. Here we characterize the therapeutic efficacy of MLN0128 in the preclinical setting of MCC and delineate downstream targets of mTORC1/2 in MCC cellular systems. MLN0128 significantly attenuates xenograft MCC tumor growth independent of Merkel cell polyomavirus. Moreover, MLN0128 markedly diminishes MCC cell proliferation and induces apoptosis. Further investigations indicate that senescence does not contribute to MLN0128-mediated repression of xenograft MCC tumor growth. Finally, we also observe robust antitumor effects of MLN0128 when administered as a dual therapy with JQ1, a bromodomain protein BRD4 inhibitor. These results suggest dual blockade of PI3K/mTOR pathway and c-Myc axis is effective in the control of MCC tumor growth. Our results demonstrate that MLN0128 is potent as monotherapy or as a member of combination therapy with JQ1 for advanced MCC.

Determination of MLN0128, an investigational antineoplastic agent, in human plasma by LC-MS/MS

MLN0128, an mTOR kinase inhibitor, is currently undergoing clinical investigation for treatment of a variety of cancers. To support this work, an LC-MS/MS method has been developed for the determination of MLN0128 in human plasma. A structural analog STK040263 was used as the internal standard. Both MLN0128 and the IS were first extracted from plasma using methyl tert-butyl ether; then separated on a Waters XTerra® MS C₁₈ column using a mobile phase consisting of methanol-acetonitrile-10.0 mm ammonium formate (34:6:60, v/v/v) at a flow rate of 0.300 mL min^-1 . Quantitation of MLN0128 was done by positive electrospray ionization tandem mass spectrometry in multiple-reaction-monitoring mode. This method has a total run time of <4 min with the retention times of 1.95 and 2.94 min for the IS and MLN0128, respectively. The method has been validated per the US Food and Drug Administration guidance for bioanalytical method validation. It has a calibration range of 0.100-50.0 ng mL^-1 in human plasma with a correlation coefficient > 0.999. The overall assay accuracy and precision were ≤ ± 4 and ≤8%, respectively. The IS normalized recovery of MLN0128 was 98-100%. The stability studies showed that MLN0128 was stable under all tested conditions. The method developed may be useful for clinical studies of MLN0128.