Persistent Activation of the Akt Pathway in Head and Neck Squamous Cell Carcinoma

Abstract

Squamous carcinomas of the head and neck (HNSCC) represent the sixth most common cancer among men worldwide and a major cause of morbidity and mortality due to its relatively poor prognosis. As part of ongoing studies addressing the molecular events underlying tumor progression in HNSCC, we have explored the nature of the proliferative pathways in which dysregulation may promote aberrant cell growth in this tumor type. The serine/threonine protein kinase Akt is a downstream target of phosphatidylinositol 3-kinase and a key regulator of normal and cancerous growth and cell fate decisions. Therefore, in this study, we have examined the status of activation of Akt in different stages of squamous cell carcinoma development in mice and in clinical samples from HNSCC patients. By immunohistochemical analysis, using a recently developed phosphorylation state-specific antibody, we demonstrated that Akt activation correlates closely with the progression of mouse skin squamous cell carcinoma. We also observed that activation of Akt is a frequent event in human HNSCC because active Akt can be detected in these tumors with a pattern of expression and localization correlating with the progression of the lesions. In line with these observations, Akt was constitutively activated in a large fraction of HNSCCderived cell lines. We also provide evidence that the Akt signaling pathway may represent a biologically relevant target for a novel antineoplastic agent, UCN-01, which recently has been shown to be active in cellular and xenograft models for HNSCC at concentrations safely achievable in clinically relevant situations.

Potentiation of the anticancer effect of valproic acid, an antiepileptic agent with histone deacetylase inhibitory activity, by the kinase inhibitor Staurosporine or its clinically relevant analogue UCN-01

“…On the other hand, there was a profound and durable inhibition of ERK1/2 activation in UCN-01-treated cells. This is in direct contrast to previous studies that described activation of MEK/ ERK1/2 by UCN-01 in head/neck squamous cell carcinoma cell lines (Amornphimoltham et al, 2004;Kondapaka et al, 2004) or leukaemia cell lines (Dai et al, 2001(Dai et al, , 2002. The mechanism of this discrepancy is not clear and may relate to the intrinsic difference of cell lines and experimental conditions employed.…”

“…Staurosporine profoundly inhibited ERK1/2 activation and at the same time mediated phosphorylation of Akt in cultured thoracic cancer cells within the similar time interval. This effect of STP on Akt phosphorylation was surprising, given the fact that its closely related analogue UCN-01 suppressed Akt phosphorylation (Sato et al, 2002;Amornphimoltham et al, 2004;Kondapaka et al, 2004; and also our own observation). This was totally unexpected but very reproducible in many independent experiments with our cell lines and the molecular basis of this discrepancy was unclear.…”

“…Indeed, UCN-01 has been shown to downregulate Akt activation (but concomitantly stimulate ERK1/2) in head and neck squamous cell carcinoma (Amornphimoltham et al, 2004;Kondapaka et al, 2004). Continuous exposure of thoracic cancer cells to UCN-01 (250 -1000 nM) in 10% FCS RPMI culture medium (in contrast to low serum conditions as were previously described (Amornphimoltham et al, 2004;Kondapaka et al, 2004)) led to a profound but short-lived reduction of pAkt at 1 h after drug exposure followed by a strong activation of Akt at 24 h time point. On the other hand, there was a profound and durable inhibition of ERK1/2 activation in UCN-01-treated cells.…”

“…More recent studies have identified these compounds as kinase inhibitors with a broader range of molecular targets in vivo, including chk1/2 and PDK1, a kinase that act directly upstream of Akt and MAP/extracellular signal-regulated kinase (ERK) kinase (MEK) (Sato et al, 2002). Exposure of cultured cancer cells to UCN-01 (250 -1000 nM) resulted in complete abrogation of phosphorylation at Ser473 and Thr308 residues of Akt, both of which are essential for full activation of Akt kinase activity (Amornphimoltham et al, 2004;Kondapaka et al, 2004). Clinical trials of UCN-01 in patients with refractory neoplasms, as monotherapy or in combination with cytotoxic chemotherapeutics, have been reported (Sausville et al, 2001).…”

Chemokine receptor 7 activates phosphoinositide-3 kinase-mediated invasive and prosurvival pathways in head and neck cancer cells independent of EGFR

“…Once activated, Akt/PKB inhibits cell death pathways by directly phosphorylating and inactivating proapoptotic proteins, including Bad and procaspase 9 (Datta et al, 1999;Amornphimoltham et al, 2004;Wells and Lillien, 2004). Also, Akt/PKB has been implicated as a signaling intermediate upstream of survival genes, dependent on the transcription factor NF-kB, which induces cellular inhibitors of apoptosis (Beraud et al, 1999;Kane et al, 2001).…”