PI3K/AKT/mTOR signaling pathway as a therapeutic target for ovarian cancer

BACKGROUND

Ovarian cancer is one of the major causes of death in women worldwide. Despite improvements in conventional treatment approaches, such as surgery and chemotherapy, a majority of patients with advanced ovarian cancer experience relapse and eventually succumb to the disease; the outcome of patients remains poor. Hence, new therapeutic strategies are urgently required. The phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) is activated in approximately 70 % of ovarian cancers, resulting in hyperactive signaling cascades that relate to cellular growth, proliferation, survival, metabolism, and angiogenesis. Consistent with this, a number of clinical studies are focusing on PI3K pathway as an attractive target in the treatment of ovarian cancer. In this review, we present an overview of PI3K pathway as well as its pathological aberrations reported in ovarian cancer. We also discuss inhibitors of PI3K pathway that are currently under clinical investigations and the challenges these inhibitors face in future clinical utility.

METHODS

PubMed was searched for articles of relevance to ovarian cancer and the PI3K pathway. In addition, the ClinicalTrials.gov was also scanned for data on novel therapeutic inhibitors targeting the PI3K pathway.

RESULTS

Genetic aberrations at different levels of PI3K pathway are frequently observed in ovarian cancer, resulting in hyperactivation of this pathway. The alterations of this pathway make the PI3K pathway an attractive therapeutic target in ovarian cancer. Currently, several inhibitors of PI3K pathway, such as PI3K/AKT inhibitors, rapamycin analogs for mTOR inhibition, and dual PI3K/mTOR inhibitors are in clinical testing in patients with ovarian cancer.

CONCLUSIONS

PI3K pathway inhibitors have shown great promise in the treatment of ovarian cancer. However, further researches on selection patients that respond to PI3K inhibitors and exploration of effective combinatorial therapies are required to improve the management of ovarian cancer.

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.

Melanoma: new insights and new therapies

Metastatic melanoma has historically been considered as one of the most therapeutically challenging malignancies. However, for the first time after decades of basic research and clinical investigation, new drugs have produced major clinical responses. The discovery of BRAF mutations in melanoma created the first opportunity to develop oncogene-directed therapy in this disease and led to the development of compounds that inhibit aberrant BRAF activity. A decade later, vemurafenib, an orally available and well-tolerated selective BRAF inhibitor, ushered in a new era of molecular treatments for advanced disease. Additional targets have been identified, and novel agents that impact on various signaling pathways or modulate the immune system hold the promise of a whole new therapeutic landscape for patients with metastatic melanoma. One of the major thrusts in melanoma therapy is now focused on understanding and targeting the network of signal transduction pathways and on attacking elements that underlie the tumor's propensity for growth and chemoresistance. In this article, we review the novel targeted anticancer approaches that are under consideration in melanoma treatment.

Targeting the mTOR kinase domain: the second generation of mTOR inhibitors

The mTOR signaling pathway is dysregulated in ∼50% of all human malignancies and is a major cancer drug target. Although rapamycin analogs (rapalogs) have shown clinical efficacy in a subset of cancers, they do not fully exploit the antitumor potential of mTOR targeting. Because the mTOR kinase domain is important for rapamycin-sensitive and -insensitive functions, mTOR catalytic inhibitors have been developed recently as the second generation of anti-mTOR agents. Importantly, they have shown marked improvement of antitumor activity in vivo and in vitro. This review will detail the potential therapeutic value and issues of these novel antineoplastic agents, with emphasis placed on those that have already entered clinical trials.

New drugs for aggressive B-cell and T-cell lymphomas

Over the past decade an unprecedented number of new drugs for lymphomas have been developed. Most of these new drugs target molecules or pathways that are important for the growth and proliferation of lymphomas. The introduction of the B-lymphoma specific monoclonal anti-CD20 antibody, rituximab, has improved the prognosis of patients with B-cell lymphomas more than any other drug in the past 50 years; today less than half of the patients with aggressive B-cell lymphomas die of their disease than in the pre-rituximab era. Many new drugs are now available for clinical testing in addition to new CD20 antibodies and antibodies directed against other surface molecules specifically or preferentially expressed on the lymphoma-cell surface. A prerequisite for the development of these drugs was the recognition of aberrant cell-signal transduction involved in lymphoma pathogenesis and progression. New therapeutic targets include receptor tyrosine and cyclin-dependent kinases, histone deacetylases, and molecules involved in the regulation of apoptosis. The definition of the role of these new drugs alone or in combination with established chemotherapy regimens in adequately designed prospective trials represents one of the major challenges in clinical lymphoma research.

Systemic therapy of non-resectable metastatic melanoma

In advanced metastatic melanoma (non-resectable stage III/IV), the prognosis still remains poor, with median survival times between six and twelve months. Systemic therapeutic approaches for metastatic melanoma include chemotherapy, immunotherapy, immunochemotherapy, small molecules and targeted therapy. In this review, we will focus on the various treatment modalities as well as new agents used for targeted therapy.

Small molecules and targeted therapies in distant metastatic disease

Chemotherapy, biological agents or combinations of both have had little impact on survival of patients with metastatic melanoma. Advances in understanding the genetic changes associated with the development of melanoma resulted in availability of promising new agents that inhibit specific proteins up-regulated in signal cell pathways or inhibit anti-apoptotic proteins. Sorafenib, a multikinase inhibitor of the RAF/RAS/MEK pathway, elesclomol (STA-4783) and oblimersen (G3139), an antisense oligonucleotide targeting anti-apoptotic BCl-2, are in phase III clinical studies in combination with chemotherapy. Agents targeting mutant B-Raf (RAF265 and PLX4032), MEK (PD0325901, AZD6244), heat-shock protein 90 (tanespimycin), mTOR (everolimus, deforolimus, temsirolimus) and VEGFR (axitinib) showed some promise in earlier stages of clinical development. Receptor tyrosine-kinase inhibitors (imatinib, dasatinib, sunitinib) may have a role in treatment of patients with melanoma harbouring c-Kit mutations. Although often studied as single agents with disappointing results, new targeted drugs should be more thoroughly evaluated in combination therapies. The future of rational use of new targeted agents also depends on successful application of analytical techniques enabling molecular profiling of patients and leading to selection of likely therapy responders.

Status of PI3K inhibition and biomarker development in cancer therapeutics

The phosphatidylinositol 3-kinase (PI3K) signalling pathway is integral to diverse cellular functions, including cellular proliferation, differentiation and survival. The 'phosphate and tensin homologue deleted from chromosome 10' (PTEN) tumor suppressor gene plays a critical role as a negative regulator of this pathway. An array of genetic mutations and amplifications has been described affecting key components of this pathway, with implications not only for tumorigenesis but also for resistance to some classic cytotoxics and targeted agents. Emerging preclinical research has significantly advanced our understanding of the PI3K pathway and its complex machinations and interactions. This knowledge has enabled the evolution of rationally designed drugs targeting elements of this pathway. It is important that the development of suitable biomarkers continues in parallel to optimize use of these agents. A new generation of PI3K inhibitors is now entering early clinical trials, with much anticipation that they will add to the growing armamentarium of targeted cancer therapeutics.

Phosphatidylinositol-3-kinase as a therapeutic target in melanoma

PURPOSE

Phosphatidylinositol-3 kinases (PI3K) are critical for malignant cellular processes including growth, proliferation, and survival, and are targets of drugs in clinical development. We assessed expression of PI3K in melanomas and nevi, and studied associations between PI3K pathway members and in vitro response to a PI3K inhibitor, LY294002.

EXPERIMENTAL DESIGN

Using Automated Quantitative Analysis, we quantified expression of p85 and p110alpha subunits in 540 nevi and 523 melanomas. We determined the IC(50) for LY294002 for 11 melanoma cell lines and, using reverse phase protein arrays, assessed the association between levels of PI3K pathway members and sensitivity to LY294002.

RESULTS

p85 and p110alpha tend to be coexpressed (P < 0.0001); expression was higher in melanomas than nevi (P < 0.0001) for both subunits, and higher in metastatic than primary melanomas for p85 (P < 0.0001). Although phospho-Akt (pAkt) levels decreased in all cell lines treated with LY294002, sensitivity was variable. We found no association by t tests between baseline p85, p110alpha, and pAkt levels and sensitivity to LY294002, whereas pS6 Ser(235) and Ser(240) were lower in the more resistant cell lines (P = 0.01 and P = 0.004, respectively).

CONCLUSIONS

Expression of p85 and p110alpha subunits is up-regulated in melanoma, indicating that PI3K is a good drug target. Pretreatment pS6 levels correlated with sensitivity to the PI3K inhibitor, LY294002, whereas PI3K and pAkt did not, suggesting that full activation of the PI3K pathway is needed for sensitivity to PI3K inhibition. pS6 should be evaluated as a predictor of response in melanoma patients treated with PI3K inhibitors, as these drugs enter clinical trials.

First-in-class, first-in-human phase I results of targeted agents: highlights of the 2008 American society of clinical oncology meeting

This review summarizes phase I trial results of 11 drugs presented at the American Society of Clinical Oncology meeting held in Chicago IL from May 30 to June 3rd 2008: BMS-663513, CT-322, CVX-045, GDC-0449, GRN163L, LY2181308, PF-00562271, RAV12, RTA 402, XL765, and the survivin vaccine.

PTEN hamartoma tumor syndromes

The PTEN hamartoma tumor syndromes (PHTS) are a collection of rare clinical syndromes characterized by germline mutations of the tumor suppressor PTEN. These syndromes are driven by cellular overgrowth, leading to benign hamartomas in virtually any organ. Cowden syndrome (CS), the prototypic PHTS syndrome, is associated with increased susceptibility to breast, thyroid, and endometrial cancer. PTEN is located on chromosome 10q22-23 and negatively regulates the prosurvival PI3K/Akt/mTOR pathway through its lipid phosphatase activity. Loss of PTEN activates this pathway and leads to increased cellular growth, migration, proliferation, and survival. Clinical management of patients with PHTS, particularly those with CS, should include early and frequent screening, surveillance, and preventive care for associated malignancies. Concomitant with improved understanding of the biology of PTEN and the PI3K/Akt/mTOR pathway, inhibitors of this pathway are being developed as anticancer agents. These medications could have applications for patients with PHTS, for whom no medical options currently exist.