Akt inhibitors in clinical development for the treatment of cancer

IMPORTANCE OF THE FIELD

The evolution of targeted therapies is dependent upon identification of cellular moieties that can be pharmacologically modulated. As one such example, the serine-threonine kinase Akt was identified nearly two decades ago. Since then, its role in mediating multiple signaling cascades (ultimately leading to cell growth and proliferation) has since been identified. More recently, several agents have been developed that antagonize Akt--these agents are in various stages of clinical testing.

AREAS COVERED IN THIS REVIEW

Herein, we outline development of several promising Akt inhibitors, including perifosine, MK-2206, RX-0201, PBI-05204, GSK2141795 and others.

WHAT THE READER WILL GAIN

The reader will gain insight into the current pipeline of Akt inhibitors, and the degree to which these agents have been examined both clinically and preclinically.

TAKE HOME MESSAGE

With an emerging pipeline of agents targeting Akt, it will be critical to decipher which amongst them holds the greatest promise. Herein, we explore this drug pipeline and provide strategies for determining the future clinical application of these agents.

Combination treatment of prostate cancer cell lines with bioactive soy isoflavones and perifosine causes increased growth arrest and/or apoptosis

PURPOSE

To determine whether targeting the androgen receptor (AR) and Akt pathways using a combination of genistein combined polysaccharide (GCP) and perifosine is more effective at inducing growth arrest/apoptosis in prostate cancer cells compared with treatment with GCP or perifosine as single agents.

EXPERIMENTAL DESIGN

The effect of GCP and perifosine treatment was assessed in five prostate cancer cell lines: LNCaP (androgen sensitive), LNCaP-R273H, C4-2, Cds1, and PC3 (androgen insensitive). A clonogenic assay assessed the long-term effects on cell growth and survival. Flow cytometry and Western blot analysis of poly(ADP)ribose polymerase cleavage were used to assess short-term effects. Preliminary studies to investigate mechanism of action included Western blot for P-Akt, Akt, P-p70S6K, p70S6K, p53, and p21; prostate-specific antigen analysis; and the use of myristoylated Akt and AR-specific small interfering RNA.

RESULTS

Combination treatment with GCP and perifosine caused a decrease in clonogenic potential in all cell lines. In short-term assays, growth arrest was observed in the majority of cell lines, as well as increased inhibition of Akt activity and induction of p21 expression. Increased apoptosis was only observed in LNCaP. Knockdown of AR caused a further increase in apoptosis.

CONCLUSION

Combination treatment with GCP and perifosine targets the Akt pathway in the majority of the prostate cancer cell lines and causes increased inhibition of cell growth and clonogenicity. In LNCaP, combination treatment targets both the Akt and AR pathways and causes increased apoptosis. These data warrant clinical validation in prostate cancer patients.

Inhibition of Akt pathways in the treatment of prostate cancer

Akt is a serine/threonine kinase mediating multiple intracellular pathways involved in prostate cancer (CaP) biology. Increased understanding of the molecular mechanisms of Akt activation and signaling have led to the development of an increasing number of Akt inhibitors. These biologic agents demonstrate activity against a wide range of cancers in preclinical studies. Clinical studies of Akt inhibition in CaP are in progress, including agents such as celecoxib, perifosine and genistein. How best to integrate Akt inhibitors with standard CaP therapy or select patients most likely to benefit is the subject of ongoing research.

Rationale and clinical application of alkylphospholipid analogues in combination with radiotherapy

Concurrent treatment with radiotherapy and chemotherapy has emerged as an effective strategy to improve clinical outcome of cancer. In addition to combining radiation with classical anticancer agents, several new biological response modifiers are under investigation in pre-clinical and clinical studies. Synthetic alkylphospholipids are anticancer agents that in contrast to most anticancer drugs, do not target DNA, but insert in the plasma membrane and subsequently induce a broad range of biological effects, ultimately leading to cell death. Alkylphospholipids kill tumor cells directly by induction of both apoptotic and non-apoptotic cell death, and indirectly by interference with critical signal transduction pathways involved in phospholipid metabolism and survival. Due to their distinct mode of action, these drugs are considered as attractive candidates to combine with radiotherapy. In this review, we will discuss several alkylphospholipids that reached clinical application. These include first-generation alkyl-lysophospholipids edelfosine and ilmofosine, second-generation alkylphosphocholine-prototype miltefosine and more recently developed analogues perifosine and erucylphosphocholine. We focus on mechanisms of action and the rationale to combine these agents with radiotherapy. The preclinical results on molecular targeting underlying this approach will be reviewed, concluded with first clinical data on combined treatment of radiotherapy with perifosine.