Integrated bioinformatics and statistical approaches to explore molecular biomarkers for breast cancer diagnosis, prognosis and therapies

Integrated bioinformatics and statistical approaches are now playing the vital role in identifying potential molecular biomarkers more accurately in presence of huge number of alternatives for disease diagnosis, prognosis and therapies by reducing time and cost compared to the wet-lab based experimental procedures. Breast cancer (BC) is one of the leading causes of cancer related deaths for women worldwide. Several dry-lab and wet-lab based studies have identified different sets of molecular biomarkers for BC. But they did not compare their results to each other so much either computationally or experimentally. In this study, an attempt was made to propose a set of molecular biomarkers that might be more effective for BC diagnosis, prognosis and therapies, by using the integrated bioinformatics and statistical approaches. At first, we identified 190 differentially expressed genes (DEGs) between BC and control samples by using the statistical LIMMA approach. Then we identified 13 DEGs (AKR1C1, IRF9, OAS1, OAS3, SLCO2A1, NT5E, NQO1, ANGPT1, FN1, ATF6B, HPGD, BCL11A, and TP53INP1) as the key genes (KGs) by protein-protein interaction (PPI) network analysis. Then we investigated the pathogenetic processes of DEGs highlighting KGs by GO terms and KEGG pathway enrichment analysis. Moreover, we disclosed the transcriptional and post-transcriptional regulatory factors of KGs by their interaction network analysis with the transcription factors (TFs) and micro-RNAs. Both supervised and unsupervised learning's including multivariate survival analysis results confirmed the strong prognostic power of the proposed KGs. Finally, we suggested KGs-guided computationally more effective seven candidate drugs (NVP-BHG712, Nilotinib, GSK2126458, YM201636, TG-02, CX-5461, AP-24534) compared to other published drugs by cross-validation with the state-of-the-art alternatives top-ranked independent receptor proteins. Thus, our findings might be played a vital role in breast cancer diagnosis, prognosis and therapies.

Role of PI3K-AKT-mTOR Pathway as a Pro-Survival Signaling and Resistance-Mediating Mechanism to Therapy of Prostate Cancer

Androgen deprivation therapy (ADT) and androgen receptor (AR)-targeted therapy are the gold standard options for treating prostate cancer (PCa). These are initially effective, as localized and the early stage of metastatic disease are androgen- and castration-sensitive. The tumor strongly relies on systemic/circulating androgens for activating AR signaling to stimulate growth and progression. However, after a certain point, the tumor will eventually develop a resistant stage, where ADT and AR antagonists are no longer effective. Mechanistically, it seems that the tumor becomes more aggressive through adaptive responses, relies more on alternative activated pathways, and is less dependent on AR signaling. This includes hyperactivation of PI3K-AKT-mTOR pathway, which is a central signal that regulates cell pro-survival/anti-apoptotic pathways, thus, compensating the blockade of AR signaling. The PI3K-AKT-mTOR pathway is well-documented for its crosstalk between genomic and non-genomic AR signaling, as well as other signaling cascades. Such a reciprocal feedback loop makes it more complicated to target individual factor/signaling for treating PCa. Here, we highlight the role of PI3K-AKT-mTOR signaling as a resistance mechanism for PCa therapy and illustrate the transition of prostate tumor from AR signaling-dependent to PI3K-AKT-mTOR pathway-dependent. Moreover, therapeutic strategies with inhibitors targeting the PI3K-AKT-mTOR signal used in clinic and ongoing clinical trials are discussed.

A phase I study of a dual PI3-kinase/mTOR inhibitor BEZ235 in adult patients with relapsed or refractory acute leukemia

Background

Combined inhibition of phosphatidylinositol 3-kinase (PI3K) and the mammalian target of rapamycin (mTOR) complexes may be an efficient treatment for acute leukemia. The primary objective of this phase I single center open label study was to determine the maximum tolerated dose (MTD) and recommended phase II dose (RP2D) of the dual pan-class I PI3K and mTOR inhibitor BEZ235 in patients with advanced leukemia.

Methods

Herein patients > 18 years of age who had relapsed or showed refractory leukemia were treated with BEZ235 (orally at 300–400 mg BID (cohort − 1/1)) to assess safety, tolerability, preliminary efficacy and pharmacokinetic (PK). Adverse events data and serious adverse events were analyzed and haematological and clinical biochemistry toxicities were assessed from laboratory test parameters. Response was assessed for the first time at the end of cycle 1 (day 29) and after every subsequent cycle. Pharmacokinetic and pharmacodynamic analyses of BEZ235 were also included (BEZ235 plasma levels, phosphorylation of AKT, S6 and 4EBP1). On statistics this trial is a multiple ascending dose study in which a following variant of the 3 + 3 rule (“Rolling Six”), a minimum of 6 and a maximum of 12 patients was recruited for the dose escalation and another 5 were planned for the expansion phase.

Results

Twenty-four patients with ALL (n = 11) or AML (n = 12) or CML-BP (n = 1) were enrolled. All patients had failed one (n = 5) or more lines of therapy (n = 5) and 14 patients were in refractory / refractory relapse. No formal MTD was defined, stomatitis and gastrointestinal toxicity at 400 mg BID dose was considered incompatible with prolonged treatment. The RP2D of BEZ235 was defined as 300 mg BID. Four of 24 patients showed clinical benefit. Twenty-two of 24 patients discontinued because of progression, (median time to progression 27 days (4d-112d). There was no association between PK parameters and efficacy or tolerability.

Conclusions

Combined inhibition of PI3K and mTOR inhibits a clinically meaningful driver pathway in a small subset of patients with ALL, with no benefit in patients with AML.

Trial registration

ClinicalTrials.gov, identifier NCT01756118. retrospectively registered 19th December 2012, https://clinicaltrials.gov/ct2/show/NCT01756118.

Prognostic significance of VHL, HIF1A, HIF2A, VEGFA and p53 expression in patients with clear‑cell renal cell carcinoma treated with sunitinib as first‑line treatment

Clear cell renal cell carcinoma (ccRCC) is the most common subtype of renal cell cancer, characterized by the highest mortality rate among other RCC subtypes due to the occurrence of metastasis and drug resistance following surgery. The Von Hippel-Lindau tumor suppressor (VHL)-hypoxia-inducible factor 1 subunit α (HIF1A)/hypoxia-inducible factor 2α (HIF2A)-vascular endothelial growth factor A (VEGFA) protein axis is involved in the development and progression of ccRCC, whereas sunitinib, a tyrosine kinase inhibitor, blocks the binding of VEGFA to its receptor. The aim of the present study was to examine the possible association of the gene expression of VHL, HIF1A, HIF2A, VEGFA and tumor protein P53 (P53) in cancer tissue with the outcome of ccRCC patients who were treated with sunitinib as first-line therapy following nephrec-tomy. A total of 36 ccRCC patients were enrolled, 11 of whom were administered sunitinib post-operatively. Tumor and control samples were collected, and mRNA and protein levels were assessed by reverse transcription-quantitative polymerase chain reaction and western blot analysis, respectively. High mRNA and protein expression levels of HIF2A and VEGFA were found to be associated with shorter overall survival (OS) and progression-free survival (PFS) rates, as well as with unfavorable risk factors of cancer recurrence and mortality. Resistance to sunitinib was also observed; the OS and PFS rates were shorter (median OS and PFS: 12 and 6 months, respectively, vs. undetermined). Sunitinib resistance was associated with high HIF2A and VEGFA protein levels (b=0.57 and b=0.69 for OS and PFS, respectively; P<0.001). Taken together, the findings of this study suggest that the protein levels of HIF2A and VEGFA in tumor tissue may serve as independent prognostic factors in ccRCC. ccRCC patients with increased intratumoral HIF2A and VEGFA protein levels, and unaltered VHL protein levels, are not likely to benefit from sunitinib treatment following nephrectomy; however, this hypothesis requires verification by large-scale replication studies.

Investigational luteinizing hormone releasing hormone (LHRH) agonists and other hormonal agents in early stage clinical trials for prostate cancer

INTRODUCTION

The treatment and management of prostate cancer continues to evolve; newer classes of agents and combination therapies are being developed and some are being investigated in early phase clinical trials.

AREAS COVERED

We discuss investigational hormonal agents for the treatment of prostate cancer and focus primarily on luteinizing hormone releasing hormone (LHRH) agonists in early stage trials. We look at agents that target the hormonal axis, including anti-androgens, gonadotropins, estrogenic agents and progestogenic agents and other non-hormonal agents often used in combination with LHRH agonists. We review these candidates in the specific clinical niche in which they might find utility.

EXPERT OPINION

Of all candidate compounds being evaluated in clinical trials, very few will receive FDA approval. Few, if any of the investigational agents discussed here will be used routinely in clinical practice for treating prostate cancer. Recognizing the reasons for the failure of agents to advance to later stage trials is important. Furthermore, a thorough understanding of the mechanisms underlying prostate cancer pathogenesis, including various points in the HGPA and parallel pathways, will help identify potentially actionable targets.

A phase I study of single-agent BEZ235 special delivery system sachet in Japanese patients with advanced solid tumors

Purpose

BEZ235 is a dual kinase inhibitor of phosphatidylinositol 3-kinase (PI3K) and mammalian target of rapamycin, which are key components of the PI3K pathway. This was an open-label, multicenter, dose-escalation, phase I study of single-agent BEZ235 in Japanese oncology patients to determine the maximum tolerated dose (MTD) of BEZ235 based on dose-limiting toxicities (DLTs).

Methods

Dose escalation was guided by a standard 3 + 3 method and was based on DLTs observed in Cycle 1 and other safety, pharmacokinetic, and pharmacodynamic information. A total of 35 adult Japanese patients with advanced solid tumors received BEZ235 according to once daily (qd; n = 27) or twice daily (bid; n = 8) dosing schedules.

Results

Two DLTs, namely, allergic reaction and thrombocytopenia, were observed at 1200 and 1400 mg qd, respectively, while liver dysfunction was reported as a DLT at 400 mg bid. The most common adverse events suspected to be related to BEZ235 in both dosing schedules were diarrhea, nausea, decreased appetite, stomatitis, and thrombocytopenia.

Conclusions

Although the MTD was not established, the maximum clinically tolerable dose was determined to be 1200 mg because two out of six patients required dose reduction in Cycle 2. The recommended dose was determined to be 1000 mg qd, which was comparable with the results of the first-in-human BEZ235 study in Western patients with advanced solid tumors (NCT00620594). Additionally, the tolerability of BEZ235 400 mg bid in Japanese oncology patients was confirmed in this study.

ClinicalTrials.gov identifier

NCT01195376.

Electronic supplementary material

The online version of this article (10.1007/s00280-018-3725-2) contains supplementary material, which is available to authorized users.

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.

Phase II Study of BEZ235 versus Everolimus in Patients with Mammalian Target of Rapamycin Inhibitor-Naïve Advanced Pancreatic Neuroendocrine Tumors

Lessons Learned.

Treatment with BEZ235 has not been shown to demonstrate increased efficacy compared with everolimus and may be associated with a poorer tolerability profile.

The hypothesis of dual targeting of the phosphatidylinositol 3‐kinase and mammalian target of rapamycin pathways in patients with advanced pancreatic neuroendocrine tumors may warrant further study using other agents.

Background.

This phase II study investigated whether targeting the phosphatidylinositol 3‐kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway via PI3K, mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2) inhibition using BEZ235 may be more effective than mTORC1 inhibition with everolimus in patients with advanced pancreatic neuroendocrine tumors (pNET) who are naïve to mTOR inhibitor therapy.

Methods.

Patients with advanced pNET were randomized (1:1) to oral BEZ235 400 mg twice daily or oral everolimus 10 mg once daily on a continuous dosing schedule. The primary endpoint was progression‐free survival (PFS). Secondary endpoints included safety, overall response rate (ORR), overall survival (OS), and time to treatment failure.

Results.

Enrollment in this study was terminated early (62 enrolled of the 140 planned). The median PFS was 8.2 months (95% confidence interval [CI]: 5.3 to not evaluable [NE]) with BEZ235 versus 10.8 months (95% CI: 8.1–NE) with everolimus (hazard ratio 1.53; 95% CI: 0.72–3.25). The most commonly reported all‐grade adverse events (>50% of patients regardless of study treatment relationship) with BEZ235 were diarrhea (90.3%), stomatitis (74.2%), and nausea (54.8%).

Conclusion.

BEZ235 treatment in mTOR inhibitor‐naïve patients with advanced pNET did not demonstrate increased efficacy compared with everolimus and may be associated with a poorer tolerability profile.

Systemic Treatment Strategies for Patients with Hereditary Breast Cancer Syndromes

Hereditary breast cancer syndromes are associated with an increased risk of breast cancer and constitute a unique patient population, making up approximately 5%-10% of breast cancer cases in the United States. By virtue of the germline mutations that define these syndromes, invasive breast cancers in these patients have unique mechanisms that can be rationally targeted for therapeutic opportunities distinct from standard of care treatments in nongermline mutation associated breast cancers. This review intends to describe existing data on several of the most common hereditary breast cancer syndromes, including BRCA-related breast cancer syndrome, Li-Fraumeni syndrome, Cowden syndrome, Peutz-Jeghers syndrome, and hereditary diffuse gastric cancer syndrome, specifically focusing on rational therapeutics utilized in these distinct patient subgroups and completed or ongoing clinical trials evaluating their efficacy. By exploiting the distinct biologic features associated with these syndromes, tailored treatment strategies have the potential for improved efficacy and lower toxicity. Knowledge of the emergence of these targeted cancer therapies is critical for appropriate management in these patients, extending beyond treatment to highlight the need for appropriate genetic screening to allow for early recognition of these patients and therefore appropriate treatment.

IMPLICATIONS FOR PRACTICE

Molecular testing allows for identification of germline mutations that place individuals at high risk for breast cancer and that are associated with distinct histopathology and molecular characteristics that define the invasive breast cancer cases that these patients develop. These unique characteristics may ultimately provide rational targets for systemic treatments with improvements in both morbidity and efficacy. Identification of patients with these germline mutations is important for not only appropriate screening and prophylaxis, but knowledge of therapies specifically targeting several of the most common hereditary breast cancer syndromes is essential to ensure appropriate treatment of invasive breast cancers in these patients.

Phase Ib dose-finding study of abiraterone acetate plus buparlisib (BKM120) or dactolisib (BEZ235) in patients with castration-resistant prostate cancer

BACKGROUND

The phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt) signalling axis and androgen receptor (AR) pathways exhibit reciprocal feedback regulation in phosphatase and tensin homologue (PTEN)-deficient metastatic castration-resistant prostate cancer (CRPC) in preclinical models. This phase Ib study evaluated the pan-PI3K inhibitor buparlisib (BKM120) and the dual pan-PI3K/ mammalian target of rapamycin (mTOR) inhibitor dactolisib (BEZ235) in combination with abiraterone acetate (AA) in patients with CRPC.

MATERIALS AND METHODS

Patients with CRPC who had progressed on AA therapy received escalating doses of either buparlisib or dactolisib, along with fixed doses of AA (1000 mg once daily (qd)) and prednisone (5 mg twice daily (bid)). The primary objective was to define the maximum tolerated dose (MTD) and/or the recommended dose for expansion (RDE) of either buparlisib or dactolisib in combination with AA. Secondary objectives included safety, antitumour activity (Prostate Cancer Working Group 2 (PCWG2) criteria; 30% of prostate-specific antigen (PSA) decline at ≥week 12) and pharmacokinetic (PK) profile.

RESULTS

In buparlisib + AA arm, 25 patients received buparlisib + AA (median age, 67 years; Eastern Cooperative Oncology Group performance status (ECOG PS) of 0/1/2 for 7/17/1 patients, respectively). At 100 mg qd; two patients experienced dose-limiting toxicities (DLTs) (grade 3 hyperglycaemia; grade 2 asthenia), and this was the maximum buparlisib dose explored. Buparlisib + AA showed a 26% lower median area under the curve from time zero to 24°h (AUC_0-24) and 48% lower median maximum serum concentration (Cmax) versus the single-agent buparlisib assessed in first-in-human study. No objective response and few PSA decreases were reported. In dactolisib + AA arm, 18 patients (median age, 71 years; ECOG PS of 0/1 for 6/12 patients, respectively) received dactolisib + AA at the first dose level (200 mg bid). Five patients had 9 DLTs (grades 2&3 stomatitis; grade 3 hyperglycaemia; grades 2& 3 diarrhoea; grades 1& 2 pyrexia, grade 2 vomiting, and grade 2 chills).

CONCLUSIONS

Based on the assessment of available pharmacokinetics, safety, and efficacy data, no further study is planned for either buparlisib or dactolisib in combination with AA in CRPC.

A Phase Ib Study of BEZ235, a Dual Inhibitor of Phosphatidylinositol 3-Kinase (PI3K) and Mammalian Target of Rapamycin (mTOR), in Patients With Advanced Renal Cell Carcinoma

Lessons Learned

Our results highlight additional toxicities of dual PI3K/mTOR inhibition in the clinical setting that were unforeseen from preclinical models.

Because of toxicity and lack of efficacy, BEZ235 should not be further developed in the current formulation for patients with renal cell carcinoma.

Background.

Allosteric inhibitors of the mammalian target of rapamycin complex 1 (mTORC1) are approved for advanced renal cell carcinoma (RCC). Preclinical models have suggested that dual inhibition of phosphatidylinositol 3-kinase (PI3K) and mTOR kinase may establish superior anticancer effect. We aimed to establish safety for BEZ235, a potent inhibitor of both PI3K and mTOR, in advanced RCC.

Methods.

Patients with advanced RCC who had previously failed standard therapy received escalating doses of BEZ235 in sachet formulation twice daily until progression or unacceptable toxicity. Primary endpoints were to identify the maximally tolerated dose (MTD) and to determine the recommended dose for the phase II study.

Results.

The study was terminated early because of high incidence of dose-limiting toxicities (DLTs) across all dose levels tested. Ten patients were treated with BEZ235—six with clear cell and four with non-clear cell subtypes. Five of these patients suffered DLTs: 2 of 2 patients in the original 400 mg b.i.d. cohort, 1 of 6 in the 200 mg b.i.d. cohort, and 2 of 2 in the 300 mg b.i.d. cohort. DLTs included fatigue, rash, nausea and vomiting, diarrhea, mucositis, anorexia, and dysgeusia. Five patients were evaluable for response: Two had stable disease as best response, and three had progressive disease.

Conclusion.

BEZ235 twice daily resulted in significant toxicity without objective responses; further development of this compound will not be pursued in this disease.

ERRα-Regulated Lactate Metabolism Contributes to Resistance to Targeted Therapies in Breast Cancer

Imaging studies in animals and in humans have indicated that the oxygenation and nutritional status of solid tumors is dynamic. Furthermore, the extremely low level of glucose within tumors, while reflecting its rapid uptake and metabolism, also suggests that cancer cells must rely on other energy sources in some circumstances. Here, we find that some breast cancer cells can switch to utilizing lactate as a primary source of energy, allowing them to survive glucose deprivation for extended periods, and that this activity confers resistance to PI3K/mTOR inhibitors. The nuclear receptor, estrogen-related receptor alpha (ERRα), was shown to regulate the expression of genes required for lactate utilization, and isotopomer analysis revealed that genetic or pharmacological inhibition of ERRα activity compromised lactate oxidation. Importantly, ERRα antagonists increased the in vitro and in vivo efficacy of PI3K/mTOR inhibitors, highlighting the potential clinical utility of this drug combination.

Management of poor-risk metastatic renal cell carcinoma: current approaches, the role of temsirolimus and future directions

Targeted therapies have substantially improved outcomes in metastatic renal cell carcinoma (mRCC). As expected, poor-risk patients have the worst outcomes. Temsirolimus is currently the only agent licensed for treatment of poor-risk mRCC patients. It is associated with meaningful improvements in survival and quality of life, highlighting the importance of correctly stratifying risk in mRCC patients so they receive optimal treatment. Currently, data for other targeted therapies in poor-risk patients are relatively sparse. Optimizing outcomes in these patients is the subject of ongoing research, including studies of biomarkers and studies to elucidate the role of nephrectomy and neoadjuvant targeted therapy in poor-risk mRCC patients. The impacts of novel combinations including temsirolimus have also been explored to further improve outcomes.

Phase I Study of Apitolisib (GDC-0980), Dual Phosphatidylinositol-3-Kinase and Mammalian Target of Rapamycin Kinase Inhibitor, in Patients with Advanced Solid Tumors

PURPOSE

This first-in-human phase I trial assessed the safety, tolerability, and preliminary antitumor activity of apitolisib (GDC-0980), a dual inhibitor of class I PI3K, and mTOR kinases.

EXPERIMENTAL DESIGN

Once-daily oral apitolisib was administered to patients with solid tumors for days 1 to 21 or 1 to 28 of 28-day cycles. Pharmacokinetic and pharmacodynamic parameters were assessed.

RESULTS

Overall, 120 patients were treated at doses between 2 and 70 mg. The commonest ≥G3 toxicities related to apitolisib at the recommended phase 2 dose (RP2D) at 40 mg once daily included hyperglycemia (18%), rash (14%), liver dysfunction (12%), diarrhea (10%), pneumonitis (8%), mucosal inflammation (6%), and fatigue (4%). Dose-limiting toxicities (1 patient each) were G4 fasting hyperglycemia at 40 mg (21/28 schedule) and G3 maculopapular rash and G3 fasting hyperglycemia at 70 mg (21/28 schedule). The pharmacokinetic profile was dose-proportional. Phosphorylated serine-473 AKT levels were suppressed by ≥90% in platelet-rich plasma within 4 hours at the MTD (50 mg). Pharmacodynamic decreases in fluorodeoxyglucose positron emission tomography uptake of >25% occurred in 66% (21/32) of patients dosed at 40 mg once daily. Evidence of single-agent activity included 10 RECIST partial responses (PR; confirmed for peritoneal mesothelioma, PIK3CA mutant head-and-neck cancer, and three pleural mesotheliomas).

CONCLUSIONS

Apitolisib exhibited dose-proportional pharmacokinetics with target modulation at doses ≥16 mg. The RP2D was 40 mg once-daily 28/28 schedule; severe on-target toxicities were apparent at ≥40 mg, particularly pneumonitis. Apitolisib was reasonably tolerated at 30 mg, the selected dose for pleural mesothelioma patients given limited respiratory reserve. Modest but durable antitumor activity was demonstrated. Clin Cancer Res; 22(12); 2874-84. ©2016 AACR.

New agents and new targets for renal cell carcinoma

The vascular endothelial growth factor (VEGF) pathway blockers and mammalian target of rapamycin (mTOR) inhibitors have dramatically improved the treatment options and outcome for patients with advanced renal cell carcinoma (RCC). However, because the vast majority of patients will still succumb to their disease, novel treatment approaches are still necessary. Efforts to identify novel therapeutic target treatments are focused on better understanding unique aspects of tumor cell biology guided the Cancer Genome Atlas analyses and the interaction of the tumor with its microenvironment. Areas of promising investigation include a) the identification of mechanisms of acquired resistance to VEGF pathway inhibition and developing agents targeting these in combination with VEGF receptor (VEGFR) pathway blockade; b) the identification of novel therapeutic targets, particularly for patients with VEGF pathway blocker refractory disease; and c) the development of novel immunotherapies, particularly those involving checkpoint inhibitors used alone or in combination with other immunotherapies of VEGF pathway blockers. Specific targets or agents of interest include angiopoietins (trebaninib), c-Met (cabozantinib), activin receptor-like kinase-1 (ALK-1; dalantercept), interleukin (IL)-8, and HDM2 for acquired resistance to VEGF pathway inhibition; hypoxia inducible factor-2 alpha (HIF-2 alpha), TORC1/2, and the Hippo pathway for novel targets, and PD1 and PDL1 antibodies given either alone or in combination with other checkpoint inhibitors, other immunotherapies, or VEGF pathway blockers for novel immunotherapies. In addition, the application of genetic, immunologic, or other biomarkers developed in the context of this research has the potential to select patients with specific tumor types for therapy targeted to specific vulnerabilities within the tumor or tumor microenvironment. Together, these developments should enable the transition to a new era of rational and more effective therapy for patients with advanced RCC.

Tankyrase Inhibition Blocks Wnt/β-Catenin Pathway and Reverts Resistance to PI3K and AKT Inhibitors in the Treatment of Colorectal Cancer

PURPOSE

Oncogenic mutations in the KRAS/PI3K/AKT pathway are one of the most frequent alterations in cancer. Although PI3K or AKT inhibitors show promising results in clinical trials, drug resistance frequently emerges. We previously revealed Wnt/β-catenin signaling hyperactivation as responsible for such resistance in colorectal cancer. Here we investigate Wnt-mediated resistance in patients treated with PI3K or AKT inhibitors in clinical trials and evaluate the efficacy of a new Wnt/tankyrase inhibitor, NVP-TNKS656, to overcome such resistance.

EXPERIMENTAL DESIGN

Colorectal cancer patient-derived sphere cultures and mouse tumor xenografts were treated with NVP-TNKS656, in combination with PI3K or AKT inhibitors.We analyzed progression-free survival of patients treated with different PI3K/AKT/mTOR inhibitors in correlation with Wnt/β-catenin pathway activation, oncogenic mutations, clinicopathological traits, and gene expression patterns in 40 colorectal cancer baseline tumors.

RESULTS

Combination with NVP-TNKS656 promoted apoptosis in PI3K or AKT inhibitor-resistant cells with high nuclear β-catenin content. High FOXO3A activity conferred sensitivity to NVP-TNKS656 treatment. Thirteen of 40 patients presented high nuclear β-catenin content and progressed earlier upon PI3K/AKT/mTOR inhibition. Nuclear β-catenin levels predicted drug response, whereas clinicopathologic traits, gene expression profiles, or frequent mutations (KRAS, TP53, or PIK3CA) did not.

CONCLUSIONS

High nuclear β-catenin content independently predicts resistance to PI3K and AKT inhibitors. Combined treatment with a Wnt/tankyrase inhibitor reduces nuclear β-catenin, reverts such resistance, and represses tumor growth. FOXO3A content and activity predicts response to Wnt/β-catenin inhibition and together with β-catenin may be predictive biomarkers of drug response providing a rationale to stratify colorectal cancer patients to be treated with PI3K/AKT/mTOR and Wnt/β-catenin inhibitors.

Targeting the PI3K/Akt/mTOR pathway in malignancy: rationale and clinical outlook

The phosphatidylinositol 3-kinase (PI3K) pathway, including major downstream effectors Akt and mammalian target of rapamycin (mTOR), plays a critical role in malignant transformation and subsequent processes of growth, proliferation, and metastases. Not surprisingly, the PI3K/Akt/mTOR pathway has emerged as an attractive drug target and numerous agents directed against various elements of the pathway are currently in clinical development. While early clinical trials with the first generations of these agents have shown limited single-agent efficacy, efforts are now focused on the development of more specific inhibitors, patient selection strategies, and combinational approaches. In this review, we discuss the PI3K/Akt/mTOR pathway in cancer, the rationale for its emergence as a therapeutic target, and progress thus far in the clinical development of inhibitors targeting its various elements.

A phase 1 study of the sachet formulation of the oral dual PI3K/mTOR inhibitor BEZ235 given twice daily (BID) in patients with advanced solid tumors

Introduction The PI3 kinase (PI3K) pathway is a commonly dysregulated pathway in cancers and is an attractive target for antitumor therapy. BEZ235 is a potent, highly specific and selective dual PI3K/mTOR inhibitor. Methods Patients were enrolled in a 3 + 3 dose escalation design to determine the maximum tolerated dose (MTD), toxicities, and pharmacokinetics (PK) of BEZ235 when administered twice-daily as an oral sachet. For intrapatient PK comparison, patients were to receive a lead in of the total daily dose in a QD schedule for the first 8 days of the initial 28 day cycle. Patients continued treatment until unacceptable toxicity or disease progression occurred. Results Thirty-three patients received BEZ235. Initial dose levels of 200 and 400 mg BID had no DLTs. At the 600 mg BID dose level with 1200 mg QD lead in dose two DLTs of grade 3 mucositis occurred early in the first treatment cycle, the lead-in QD dosing was eliminated. Fatigue and mucositis limited dosing at 600 mg BID in subsequent patients. The 400 mg BID dose level was re-explored, with DLTs of grade 3 hyperglycemia, dehydration, fatigue, and grade 3 thrombocytopenia. Twelve patients were enrolled at an intermediate dose of 300 mg BID; a grade 3 mucositis DLT was reported in 1 patient, and this dose was declared the MTD. Preliminary PK data demonstrate a consistent increase in PK parameters (Cmax and AUC) with dose level compared to QD dosing. Fifteen patients experienced stable disease as their best response, including 10 (colorectal [4 patients], endometrial [3 patients], carcinoid NOS, pancreas, and melanoma) who had disease control for ≥16 weeks. Conclusions The recommended dose of BEZ235 administered BID as an oral sachet formulation is 300 mg BID. Toxicities seen have been reported for other dual PI3K/mTOR inhibitors.

Differential regulatory functions of three classes of phosphatidylinositol and phosphoinositide 3-kinases in autophagy

Autophagy is an evolutionarily conserved and exquisitely regulated self-eating cellular process with important biological functions. Phosphatidylinositol 3-kinases (PtdIns3Ks) and phosphoinositide 3-kinases (PI3Ks) are involved in the autophagic process. Here we aim to recapitulate how 3 classes of these lipid kinases differentially regulate autophagy. Generally, activation of the class I PI3K suppresses autophagy, via the well-established PI3K-AKT-MTOR (mechanistic target of rapamycin) complex 1 (MTORC1) pathway. In contrast, the class III PtdIns3K catalytic subunit PIK3C3/Vps34 forms a protein complex with BECN1 and PIK3R4 and produces phosphatidylinositol 3-phosphate (PtdIns3P), which is required for the initiation and progression of autophagy. The class II enzyme emerged only recently as an alternative source of PtdIns3P and autophagic initiator. However, the orthodox paradigm is challenged by findings that the PIK3CB catalytic subunit of class I PI3K acts as a positive regulator of autophagy, and PIK3C3 was thought to be an amino acid sensor for MTOR, which curbs autophagy. At present, a number of PtdIns3K and PI3K inhibitors, including specific PIK3C3 inhibitors, have been developed for suppression of autophagy and for clinical applications in autophagy-related human diseases.

Targeting the PI3K/AKT/mTOR pathway in squamous cell carcinoma of the head and neck

Despite recent advances in novel therapies, the prognosis for patients with squamous cell carcinoma of the head and neck (SCCHN) remains poor. Progress in understanding the biology of cancer has led to the development of personalized therapy targeted at blocking defective signaling pathways of cancer cells. These drugs aim to act selectively to reduce the adverse effects associated with systemic therapy. Cetuximab (Erbitux®), an anti-epidermal growth factor receptor gene (EGFR)-targeted agent, is the only approved targeted therapy for patients with SCCHN. However, resistance to EGFR therapy remains a major obstacle to achieving a positive clinical outcome with cetuximab. Other therapies that offer better clinical outcomes in patients with advanced SCCHN are urgently needed. The phosphoinositide 3-kinase (PI3K)/AKT/mammalian target of rapamycin pathway, which is downstream of EGFR, has also been implicated in SCCHN development and progression, and therefore, targeting this pathway offers another rational treatment approach. This review discusses the potential role of PI3K pathway inhibitors in the treatment of patients with advanced SCCHN, both alone and in combination with other therapies.

PI3K/AKT/mTOR pathway inhibitors: the ideal combination partners for breast cancer therapies?

Activation of the phosphatidylinositol 3-kinase (PI3K)/AKT/mTOR pathway is common in breast cancer. PI3K pathway activation has been associated with tumor growth and progression, and thus is a promising target for breast cancer therapy. Agents targeting the PI3K pathway can restore sensitivity to standard breast cancer therapies, including endocrine, HER2-targeted agents and chemotherapy, by suppressing PI3K pathway activation, which is central to the development of therapeutic resistance. The combination of endocrine therapy and PI3K pathway (mTOR) inhibition has proven clinical benefit, and novel combination strategies involving PI3K pathway inhibitors and other investigational targeted therapies are now being explored clinically in patients with breast cancer.

First-in-human study of CH5132799, an oral class I PI3K inhibitor, studying toxicity, pharmacokinetics, and pharmacodynamics, in patients with metastatic cancer

PURPOSE

This phase I dose-escalation study investigated the maximum-tolerated dose (MTD), dose-limiting toxicities (DLT), safety, pharmacokinetics (PK), pharmacodynamics (PD), and preliminary clinical activity of CH5132799.

EXPERIMENTAL DESIGN

Patients with metastatic solid tumors were eligible for the study. CH5132799 was administered orally once daily or twice daily in 28-day cycles.

RESULTS

Thirty-eight patients with solid tumors received CH5132799 at 2 to 96 mg once daily or 48 to 72 mg twice daily. The MTD was 48 mg on the twice-daily schedule but was not reached on the once daily schedule. DLTs were grade 3 elevated liver function tests (LFT), grade 3 fatigue, grade 3 encephalopathy, grade 3 diarrhea, and grade 3 diarrhea with grade 3 stomatitis; all DLTs were reversible. Most drug-related adverse events were grade 1/2. Diarrhea (34%) and nausea (32%) were the most common events. Mean Cmax and AUC0-24 in steady state at MTD were 175 ng/mL and 1,550 ng·h/mL, respectively, consistent with efficacious exposure based on preclinical modeling. Reduction in SUVmax with [(18)F] fluorodeoxyglucose positron emission tomography (FDG-PET) was observed in 5 of 7 patients at MTD. A patient with PIK3CA-mutated clear cell carcinoma of the ovary achieved a partial response by GCIG CA125 criteria and further, a heavily pretreated patient with triple-negative breast cancer had marked improvement in her cutaneous skin lesions lasting six cycles.

CONCLUSION

CH5132799 is well tolerated at the MTD dose of 48 mg twice daily. At this dose, the drug had a favorable PK and PD profile and preliminary evidence of clinical activity.

Growth factor and signaling pathways and their relevance to prostate cancer therapeutics

Treatments that target the androgen axis represent an effective strategy for patients with advanced prostate cancer, but the disease remains incurable and new therapeutic approaches are necessary. Significant advances have recently occurred in our understanding of the growth factor and signaling pathways that are active in prostate cancer. In conjunction with this, many new targeted therapies with sound preclinical rationale have entered clinical development and are being tested in men with castration-resistant prostate cancer. Some of the most relevant pathways currently being exploited for therapeutic gain are HGF/c-Met signaling, the PI3K/AKT/mTOR pathway, Hedgehog signaling, the endothelin axis, Src kinase signaling, the IGF pathway, and angiogenesis. Here, we summarize the biological basis for the use of selected targeted agents and the results from available clinical trials of these drugs in men with prostate cancer.

Targeting the genetic alterations of the PI3K-AKT-mTOR pathway: its potential use in the treatment of bladder cancers

Urothelial carcinoma of the bladder is the most frequent tumor of the urinary tract and represents the fifth cause of death by cancer worldwide. The current first line chemotherapy is a combination of cisplatin and gemcitabine with median survival not exceeding 15months. Vinflunine is the only drug approved by EMEA as second-line treatment and few progresses have been made for the past 20years to increase the survival of metastatic patients, especially those who are not eligible for cisplatin-based regimen. The recent studies characterizing the genetic background of urothelial cancers of the bladder, revealed chromosomal alterations that are not seen at the same level in other types of cancers. This is especially the case for mutations of genes involved in the PI3K/AKT/mTOR signaling pathway that occupies a major place in the etiology of these tumors. Here, we describe the mutations leading to constitutive activation of the PI3K/AKT/mTOR pathway and discuss the potential use of the different classes of PI3K/AKT/mTOR inhibitors in the treatment of urothelial bladder cancers. Despite the recent pivotal study evidencing specific mutations of TSC1 in bladder cancer patients responding to everolimus and the encouraging results obtained with other derivatives than rapalogs, few clinical trials are ongoing in bladder cancers. Because of the genetic complexity of these tumors, the cross-talks of the PI3K/AKT/mTOR pathway with other pathways, and the small number of eligible patients, it will be of utmost importance to carefully choose the drugs or drug combinations to be further tested in the clinic.

mTORC1 inhibition is required for sensitivity to PI3K p110α inhibitors in PIK3CA-mutant breast cancer

Activating mutations of the PIK3CA gene occur frequently in breast cancer, and inhibitors that are specific for phosphatidylinositol 3-kinase (PI3K) p110α, such as BYL719, are being investigated in clinical trials. In a search for correlates of sensitivity to p110α inhibition among PIK3CA-mutant breast cancer cell lines, we observed that sensitivity to BYL719 (as assessed by cell proliferation) was associated with full inhibition of signaling through the TORC1 pathway. Conversely, cancer cells that were resistant to BYL719 had persistently active mTORC1 signaling, although Akt phosphorylation was inhibited. Similarly, in patients, pS6 (residues 240/4) expression (a marker of mTORC1 signaling) was associated with tumor response to BYL719, and mTORC1 was found to be reactivated in tumors from patients whose disease progressed after treatment. In PIK3CA-mutant cancer cell lines with persistent mTORC1 signaling despite PI3K p110α blockade (that is, resistance), the addition of the allosteric mTORC1 inhibitor RAD001 to the cells along with BYL719 resulted in reversal of resistance in vitro and in vivo. Finally, we found that growth factors such as insulin-like growth factor 1 and neuregulin 1 can activate mammalian target of rapamycin (mTOR) and mediate resistance to BYL719. Our findings suggest that simultaneous administration of mTORC1 inhibitors may enhance the clinical activity of p110α-targeted drugs and delay the appearance of resistance.

Differentiating mTOR inhibitors in renal cell carcinoma

PI3K/Akt/mTOR signalling is dysregulated in many cancers, including renal cell carcinoma (RCC), and activation of this pathway has been suggested to correlate with aggressive behavior and poor prognosis in RCC tumors. mTOR inhibition plays a principal role in the targeted treatment of many cancer types, including RCC. Although mTOR inhibitors share the same mechanism of action, differences in metabolism, formulation and dosing schedule underpin distinct PK/PD profiles such that they may be differentiated for use in a variety of treatment niches. Approved mTOR inhibitors temsirolimus and everolimus serve as important therapeutic options within the current RCC treatment paradigm, although their recommended applications differ in setting and patient population characteristics. Clinical practice guidelines recommend temsirolimus for use in treatment-naive patients with poor-prognosis metastatic RCC of any histology (predominant clear cell or non-clear cell histology). Everolimus provides a standard-of-care therapy for patients with metastatic RCC whose disease has progressed after previous vascular endothelial growth factor receptor-tyrosine kinase inhibitor therapy. As therapeutic failure impacts the vast majority of patients with RCC, sequencing strategies of available agents or simultaneous targeting of multiple members of the PI3K/Akt/mTOR pathway may provide additional clinical benefit. Various classes of agents targeting the PI3K/Akt/mTOR pathway are currently being investigated, including mTORC1/mTORC2 kinase domain inhibitors, mTOR/PI3K dual inhibitors, PI3K-selective inhibitors, and programmed cell death 6 modulators. Clinical trials of mTOR inhibitors in a variety of tumor types are ongoing, and the role of mTOR inhibitors continues to evolve across the RCC treatment landscape.

Evaluation and clinical analyses of downstream targets of the Akt inhibitor GDC-0068

PURPOSE

The oncogenic PI3K/Akt/mTOR pathway is an attractive therapeutic target in cancer. However, it is unknown whether the pathway blockade required for tumor growth inhibition is clinically achievable. Therefore, we conducted pharmacodynamic studies with GDC-0068, an ATP competitive, selective Akt1/2/3 inhibitor, in preclinical models and in patients treated with this compound.

EXPERIMENTAL DESIGN

We used a reverse phase protein array (RPPA) platform to identify a biomarker set indicative of Akt inhibition in cell lines and human-tumor xenografts, and correlated the degree of pathway inhibition with antitumor activity. Akt pathway activity was measured using this biomarker set in pre- and post-dose tumor biopsies from patients treated with GDC-0068 in the dose escalation clinical trial.

RESULTS

The set of biomarkers of Akt inhibition is composed of 10 phosphoproteins, including Akt and PRAS40, and is modulated in a dose-dependent fashion, both in vitro and in vivo. In human-tumor xenografts, this dose dependency significantly correlated with tumor growth inhibition. Tumor biopsies from patients treated with GDC-0068 at clinically achievable doses attained a degree of biomarker inhibition that correlated with tumor growth inhibition in preclinical models. In these clinical samples, compensatory feedback activation of ERK and HER3 was observed, consistent with preclinical observations.

CONCLUSION

This study identified a set of biomarkers of Akt inhibition that can be used in the clinical setting to assess target engagement. Here, it was used to show that robust Akt inhibition in tumors from patients treated with GDC-0068 is achievable, supporting the clinical development of this compound in defined patient populations.

Triple-negative breast cancer: molecular characterization and targeted therapies

SUMMARY Triple-negative breast cancer is an aggressive subtype of breast cancer that does not have targeted therapies available. Recent research has focused on extensive molecular characterization in order to identify therapeutic targets. The Cancer Genome Atlas Network recently published one of the most extensive molecular reviews to date and identified modules of related mutations, some of which have been targeted in clinical trials. Due to tumor heterogeneity, it is unlikely that a single therapy will be effective. Identification of molecular targets and tailored treatments based on the molecular alterations in individual cancers hold the best promise for improving the outcomes of this aggressive breast cancer.

Targeting the PI3K/Akt/mTOR pathway in castration-resistant prostate cancer

The phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway is a key signaling pathway that has been linked to both tumorigenesis and resistance to therapy in prostate cancer and other solid tumors. Given the significance of the PI3K/Akt/mTOR pathway in integrating cell survival signals and the high prevalence of activating PI3K/Akt/mTOR pathway alterations in prostate cancer, inhibitors of this pathway have great potential for clinical benefit. Here, we review the role of the PI3K/Akt/mTOR pathway in prostate cancer and discuss the potential use of pathway inhibitors as single agents or in combination in the evolving treatment landscape of castration-resistant prostate cancer.

Targeting the PI3K/AKT/mTOR and Raf/MEK/ERK pathways in the treatment of breast cancer

Alterations of signal transduction pathways leading to uncontrolled cellular proliferation, survival, invasion, and metastases are hallmarks of the carcinogenic process. The phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) and the Raf/mitogen-activated and extracellular signal-regulated kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling pathways are critical for normal human physiology, and also commonly dysregulated in several human cancers, including breast cancer (BC). In vitro and in vivo data suggest that the PI3K/AKT/mTOR and Raf/MEK/ERK cascades are interconnected with multiple points of convergence, cross-talk, and feedback loops. Raf/MEK/ERK and PI3K/AKT/mTOR pathway mutations may co-exist. Inhibition of one pathway can still result in the maintenance of signaling via the other (reciprocal) pathway. The existence of such "escape" mechanisms implies that dual targeting of these pathways may lead to superior efficacy and better clinical outcome in selected patients. Several clinical trials targeting one or both pathways are already underway in BC patients. The toxicity profile of this novel approach of dual pathway inhibition needs to be closely monitored, given the important physiological role of PI3K/AKT/mTOR and Raf/MEK/ERK signaling. In this article, we present a review of the current relevant pre-clinical and clinical data and discuss the rationale for dual inhibition of these pathways in the treatment of BC patients.

Targeting PI3K and mTORC2 in metastatic renal cell carcinoma: new strategies for overcoming resistance to VEGFR and mTORC1 inhibitors

With the advent of molecularly targeted agents, treatment of metastatic renal cell carcinoma (mRCC) has improved significantly. Agents targeting the vascular endothelial growth factor receptor (VEGFR) and the mammalian target of rapamycin complex 1 (mTORC1) are more effective and less toxic than previous standards of care involving cytotoxic and cytokine therapies. Unfortunately, many patients relapse following treatment with VEGFR and mTORC1 inhibitors as a result of acquired resistance mechanisms, which are thought to lead to the reestablishment of tumor vasculature. Specifically, the loss of negative feedback loops caused by inhibition of mTORC1 leads to upregulation of downstream effectors of the phosphoinositide 3-kinase (PI3K)/AKT/mTOR pathway and subsequent activation of hypoxia-inducible factor, an activator of angiogenesis. De novo resistance involving activated PI3K signaling has also been observed. These observations have led to the development of novel agents targeting PI3K, mTORC1/2 and PI3K/mTORC1/2, which have demonstrated antitumor activity in preclinical models of RCC. Several agents--BKM120, BEZ235 and GDC-0980--are being investigated in clinical trials in patients with metastatic/advanced RCC, and similar agents are being tested in patients with solid tumors. The future success of mRCC treatment will likely involve a combination of agents targeting the multiple pathways involved in angiogenesis, including VEGFR, PI3K and mTORC1/2.

Trastuzumab as first-line therapy in HER2-positive metastatic breast cancer patients

Trastuzumab is a humanized monoclonal antibody against the extracellular domain of hEGF receptor-2 (HER2). Trastuzumab in combination with chemotherapy has proven efficacy in treating both early and metastatic HER2-positive breast cancer. In the metastatic setting, the addition of trastuzumab to chemotherapy is associated with a statistically significant longer time to disease progression, higher rate of objective response and improvement in overall survival. Trastuzumab efficacy is not influenced by hormone receptor status, but differences in median overall survival exist between HER2-positive and HER2-negative states. Reassessment of the benefit of re-exposing patients with metastatic breast cancer to trastuzumab following relapse in the adjuvant setting is necessary. Ongoing research into new HER2-targeted therapies and trials involving combination anti-HER2 drug therapy without chemotherapy show promise. This review is focused on the available results obtained with the use of trastuzumab in the subset of HER2-positive breast cancer patients with metastatic disease.

Management of metabolic effects associated with anticancer agents targeting the PI3K-Akt-mTOR pathway

Agents inhibiting the phosphoinositide 3-kinase-Akt-mammalian target of rapamycin (PAM) pathway are currently in various stages of clinical development in oncology, ranging from some in early-phase evaluations to others that have already received regulatory approval for treatment in advanced cancers. The administration of PAM pathway inhibitors has been associated with metabolic toxicities of hyperlipidemia and hyperglycemia. The PAM Task Force of the National Cancer Institute Investigational Drug Steering Committee convened an interdisciplinary expert panel to review the pathophysiology of hyperlipidemia and hyperglycemia induced by PAM pathway inhibitors, summarize the incidence of these metabolic toxicities induced by such agents in the current literature, advise on clinical trial screening and monitoring criteria, and provide management guidance and therapeutic goals on occurrence of these toxicities. The overarching aim of this consensus report is to raise awareness of these metabolic adverse events to enable their early recognition, regular monitoring, and timely intervention in clinical trials. Hyperglycemia and hyperlipidemia are generally not acutely toxic and most often reversible with therapeutic intervention. Dose modifications or discontinuation of PAM pathway inhibitors should only be considered in situations of severe events or if progressive metabolic derangement persists after therapeutic interventions have been attempted for a sufficient duration. Specialty consultation should be sought to aid clinical trial planning and the management of these metabolic adverse events.

Current clinical development of PI3K pathway inhibitors in glioblastoma

Glioblastoma (GBM) is the most common and lethal primary malignant tumor of the central nervous system, and effective therapeutic options are lacking. The phosphatidylinositol 3-kinase (PI3K) pathway is frequently dysregulated in many human cancers, including GBM. Agents inhibiting PI3K and its effectors have demonstrated preliminary activity in various tumor types and have the potential to change the clinical treatment landscape of patients with solid tumors. In this review, we describe the activation of the PI3K pathway in GBM, explore why inhibition of this pathway may be a compelling therapeutic target for this disease, and provide an update of the data on PI3K inhibitors in clinical trials and from earlier investigation.

PI3K and mTOR signaling pathways in cancer: new data on targeted therapies

The mammalian target of rapamycin (mTOR) and the phosphoinositide 3-kinase (PI3K) signaling pathways are commonly deregulated in cancers and promote cellular growth, proliferation, and survival. mTOR is part of two complexes, mTORC1 and mTORC2, with different biochemical structures and substrates specificity. PI3K/AKT activation may result from genetic hits affecting different components of the pathway, whereas the mechanisms leading to constitutive mTORC1 activation remain globally unknown. The connections between the PI3K and mTOR kinases are multiple and complex, including common substrates, negative feedback loops, or direct activation mechanisms. First-generation allosteric mTOR inhibitors (eg, rapamycin) are mainly active on mTORC1 and mostly display cytostatic anti-tumor activity. Recently, second-generation catalytic mTOR inhibitors targeting both mTOR complexes 1 and 2 have been developed. Some of them also inhibit class IA PI3K. Here, we highlight recent data generated with these new inhibitors against cancer cells and their potential as anti-cancer drugs.

Molecular prescreening to select patient population in early clinical trials

The efficacy of targeted therapies in patient populations selected for treatment on the basis of the molecular features of their tumours is shifting the current focus of treatment to biomarker-driven clinical trials. Phase I trials provide an arena for early hypothesis testing, examining not only safety and toxicity, but also target engagement, biologically effective dosages, and the appropriate patient population. In this Perspectives article, we describe this new trend in early drug development, establishing the different approaches for building a pre-screening programme in an academic institution that is involved in early drug development. Our experience establishing the phase I programme at Vall d'Hebrón serves as an example of how these approaches can be integrated in ongoing trials, and we believe these considerations will help others to implement similar programmes in their institutions.

Multi-level targeting of the phosphatidylinositol-3-kinase pathway in non-small cell lung cancer cells

Introduction

We assessed expression of p85 and p110α PI3K subunits in non-small cell lung cancer (NSCLC) specimens and the association with mTOR expression, and studied effects of targeting the PI3K/AKT/mTOR pathway in NSCLC cell lines.

Methods

Using Automated Quantitative Analysis we quantified expression of PI3K subunits in two cohorts of 190 and 168 NSCLC specimens and correlated it with mTOR expression. We studied effects of two PI3K inhibitors, LY294002 and NVP-BKM120, alone and in combination with rapamycin in 6 NSCLC cell lines. We assessed activity of a dual PI3K/mTOR inhibitor, NVP-BEZ235 alone and with an EGFR inhibitor.

Results

p85 and p110α tend to be co-expressed (p<0.001); p85 expression was higher in adenocarcinomas than squamous cell carcinomas. High p85 expression was associated with advanced stage and poor survival. p110α expression correlated with mTOR (ρ = 0.276). In six NSCLC cell lines, addition of rapamycin to LY294002 or NVP-BKM120 was synergistic. Even very low rapamycin concentrations (1 nM) resulted in sensitization to PI3K inhibitors. NVP-BEZ235 was highly active in NSCLC cell lines with IC₅₀s in the nanomolar range and resultant down-regulation of pAKT and pP70S6K. Adding Erlotinib to NVP-BEZ235 resulted in synergistic growth inhibition.

Conclusions

The association between PI3K expression, advanced stage and survival in NSCLC suggests that it might be a valuable drug target. Concurrent inhibition of PI3K and mTOR is synergistic in vitro, and a dual PI3K/mTOR inhibitor was highly active. Adding EGFR inhibition resulted in further growth inhibition. Targeting the PI3K/AKT/mTOR pathway at multiple levels should be tested in clinical trials for NSCLC.

Phosphatidylinositol 3-kinase and antiestrogen resistance in breast cancer

Although antiestrogen therapies targeting estrogen receptor (ER) α signaling prevent disease recurrence in the majority of patients with hormone-dependent breast cancer, a significant fraction of patients exhibit de novo or acquired resistance. Currently, the only accepted mechanism linked with endocrine resistance is amplification or overexpression of the ERBB2 (human epidermal growth factor receptor 2 [HER2]) proto-oncogene. Experimental and clinical evidence suggests that hyperactivation of the phosphatidylinositol 3-kinase (PI3K) pathway, the most frequently mutated pathway in breast cancer, promotes antiestrogen resistance. PI3K is a major signaling hub downstream of HER2 and other receptor tyrosine kinases. PI3K activates several molecules involved in cell-cycle progression and survival, and in ER-positive breast cancer cells, it promotes estrogen-dependent and -independent ER transcriptional activity. Preclinical tumor models of antiestrogen-resistant breast cancer often remain sensitive to estrogens and PI3K inhibition, suggesting that simultaneous targeting of the PI3K and ER pathways may be most effective. Herein, we review alterations in the PI3K pathway associated with resistance to endocrine therapy, the state of clinical development of PI3K inhibitors, and strategies for the clinical investigation of such drugs in hormone receptor-positive breast cancer.

A mechanism for synergy with combined mTOR and PI3 kinase inhibitors

Dysregulation of the mammalian target of rapamycin (mTOR) signaling has been found in many human cancers, particularly those with loss of the tumor suppressor PTEN. However, mTORC1 inhibitors such as temsirolimus have only modest activity when used alone and may induce acquired resistance by activating upstream mTORC2 and Akt. Other tumors that do not depend upon PI3K/Akt/mTOR signaling for survival are primarily resistant. This study tested the hypothesis that the limited clinical efficacy of temsirolimus is due to a compensatory increase in survival signaling pathways downstream of Akt as well as an incomplete block of 4E-BP1-controlled proliferative processes downstream of mTOR. We explored the addition of a PI3K inhibitor to temsirolimus and identified the mechanism of combinatorial synergy. Proliferation assays revealed that BEZ235 (dual PI3K/mTOR inhibitor) or ZSTK474 (pan PI3K inhibitor) combined with temsirolimus synergistically inhibited cell growth compared to cells treated with any of the agents alone. Co-treatment resulted in G0/G1 cell cycle arrest and up-regulation of p27. Cell death occurred through massive autophagy and subsequent apoptosis. While molecular profiling revealed that, in most cases, sensitivity to temsirolimus alone was most marked in cells with high basal phospho-Akt resulting from PTEN inactivation, combining a PI3K inhibitor with temsirolimus prevented compensatory Akt phosphorylation and synergistically enhanced cell death regardless of PTEN status. Another molecular correlate of synergy was the finding that temsirolimus treatment alone blocks downstream S6 kinase signaling, but not 4E-BP1. Adding BEZ235 completely abrogated 4E-BP1 phosphorylation. We conclude that the addition of a PI3K inhibitor overcomes cellular resistance to mTORC1 inhibitors regardless of PTEN status, and thus substantially expands the molecular phenotype of tumors likely to respond.

Emerging therapeutic approaches in the management of metastatic castration-resistant prostate cancer

Although treatment options for men with castration-resistant prostate cancer (CRPC) have improved with the recent and anticipated approvals of novel immunotherapeutic, hormonal, chemotherapeutic and bone-targeted agents, clinical benefit with these systemic therapies is transient and survival times remain unacceptably short. Thus, we devote the second section of this two-part review to discussing emerging therapeutic paradigms and research strategies that are entering phase II and III clinical testing for men with metastatic CRPC. We will discuss a range of emerging hormonal, immunomodulatory, antiangiogenic, epigenetic and cell survival pathway inhibitors in current clinical trials, with an emphasis on how these therapies may complement our existing treatment options.

Synergistic action of a RAF inhibitor and a dual PI3K/mTOR inhibitor in thyroid cancer

PURPOSE

In thyroid cancer clinical trials, agents targeting VEGF receptors (VEGFR) and RET, among other kinases, have led to partial responses but few complete or durable responses. The RAF-MEK-ERK and PI3K-AKT-mTOR signaling pathways are frequently activated in differentiated and medullary thyroid cancer (DTC and MTC) and may provide therapeutic targets for these diseases. We tested a novel drug combination targeting RAF, phosphoinositide 3-kinase (PI3K), and mTOR, plus VEGFR2 and RET, in thyroid cancer preclinical models with defined genetic backgrounds.

EXPERIMENTAL DESIGN

RAF265, an ATP-competitive pan-RAF inhibitor active against VEGFR2, and BEZ-235, a PI3K inhibitor also active against Torc1 and Torc2, were tested alone and in combination in a panel of thyroid cancer lines. We tested RAF265 and BEZ-235 for kinase inhibition, growth inhibition and cell-cycle alterations, and inhibition of signaling targets and tumor growth in xenograft models.

RESULTS

Both drugs potently inhibited their kinase targets in the extracellular signal-regulated kinase (ERK) and PI3K pathways. In addition, RAF265 had significant RET inhibitory activity (IC₅₀ = 25-50 nmol/L for RET(C634W)). The combination strongly inhibited proliferation of DTC and MTC cell lines with mutations in RAS, BRAF, PTEN, and RET. Synergy was shown for B-CPAP (BRAF(V600E)) and TT cells (RET(C634W)). The combination of both drugs significantly inhibited growth of CAL62 (KRAS(G12R/G12R)) and TT xenografts, thoroughly inhibiting ERK and PI3K pathway signaling.

CONCLUSIONS

Combined blockade of ERK and PI3K signaling potently inhibits growth in preclinical models representing the key genotypes seen in refractory thyroid cancer. These targets and therapies are promising for further development in both differentiated and medullary thyroid cancers.

Comparison of the effects of the PI3K/mTOR inhibitors NVP-BEZ235 and GSK2126458 on tamoxifen-resistant breast cancer cells

BACKGROUND

Treatment with anti-estrogens or aromatase inhibitors is commonly used for patients with estrogen receptor-positive (ER+) breast cancers; however resistant disease develops almost inevitably, requiring a choice of secondary therapy. One possibility is to use inhibitors of the PI3K/mTOR pathway and several candidate drugs are in development. We examined the in vitro effects of two inhibitors of the PI3K/mTOR pathway on resistant MCF-7 cells.

METHODS

We cultured MCF-7 cells for prolonged periods either in the presence of the anti-estrogen tamoxifen (3 sub-lines) or in estrogen free medium (2 sub-lines) to mimic the effects of clinical treatment. We then analyzed the effects of two dual PI3K/mTOR phosphoinositide-3-kinase inhibitors, NVP-BEZ235 and GSK2126458, on the growth and signaling pathways of these MCF-7 sub-lines. The functional status of the PI3K, mTOR and ERK pathways was analyzed by measuring phosphorylation of AKT, p70S6K, rpS6 and ERK.

RESULTS

The derived sub-lines showed increased resistance to tamoxifen but none exhibited concomitantly increased sensitivity to the PI3K inhibitors. NVP-BEZ235 and GSK2126458 acted mainly by induction of cell cycle arrest, particularly in G1-phase, rather than by induction of apoptosis. The lines varied considerably in their utilization of the AKT, p70S6K and ERK pathways. NVP-BEZ235 and GSK2126458 inhibited AKT signaling but NVP-BEZ235 showed greater effects than GSK2126458 on p70S6K and rpS6 signaling with effects resembling those of rapamycin.

CONCLUSION

Increased resistance to tamoxifen in these MCF-7 sub-lines is not associated with hypersensitivity to PI3K inhibitors. While both drugs inhibited AKT signaling, NVP-BEZ235 resembled rapamycin in inhibiting the mTOR pathway.