A Pilot Study of Chemoradiotherapy Plus Temsirolimus (Torisel) for Advanced Head and Neck Cancer

Approximately 30,000 new cases of local-regionally advanced head and neck carcinoma (HNC) and head and neck squamous cell carcinoma (HNSCC) are diagnosed each year for which surgery is either insufficient, non-curative or not feasible. For these patients, radiation therapy is the mainstay of treatment often with the use of concurrent chemotherapy and/or concurrent cetuximab therapy. Radiation therapy is also commonly employed in the post-operative setting for patients with high risk features predisposing to recurrent disease. Although progress has been made, the prominent pattern of failure among these aggressively treated patients remains loco-regional failure.

The epidermal growth factor receptor (EGFR), a member of the ErbB family of receptor tyrosine kinases, is abnormally activated in nearly all epithelial cancers, including HNC. Nearly all HNC expressing high levels of EGFR have been associated with poor outcomes. Radiation therapy can lead to increased expression of EGFR in cancer cells, and blockade of EGFR signaling has been shown to sensitize cells to ionizing radiation. The use of monoclonal antibodies directed against EGFR has a rich pre-clinical record. However, it was not until the publication of the Bonner trial that combined radiotherapy plus anti-EGFR therapy was shown to be successful in the clinic to treat HNSCC. This study showed that the addition of single agent cetuximab 250 mg/m2 given weekly with concurrent radiation therapy improved median overall survival from 29 to 49 months. Furthermore, progression-free survival was improved from 12 to 17.1 months. In addition, patients were able to tolerate the regimen with no difference in rates of mucositis. Other toxicities were also similar to radiotherapy alone, with the exceptions of a small risk of infusion reactions, and the common - but non-dose limiting - occurrence of an acneiform rash.

Temsirolimus is a specific inhibitor of the mammalian target of rapamycin (mTOR), an enzyme that regulates cell growth and proliferation. Temsirolimus prevents progression from the G1 phase to the S phase of the cell cycle through inhibition of mTOR, which is a novel mechanism of action for an anticancer drug. This is also important for concurrent treatment with radiation, since S-phase represents the most radiation resistant phase of the cell cycle.

Temsirolimus is a structural analog of sirolimus (rapamycin) that has been formulated for IV or oral administration for the treatment of various malignancies. Sirolimus was shown to have potent immunosuppressive as well as antifungal and antitumor properties. Its mechanism of action results in part from binding to an intracellular cytoplasmic protein, FK506 (tacrolimus) binding protein (FKBP)-12. The complex of sirolimus bound to FKBP-12 blocks the activity of mTOR.

Cetuximab is an important agent in the treatment of HNSCC; however its success may be limited by downstream signaling molecules which may up-regulate and cause the malignant phenotype to persist. MET proto-oncogene amplification has been hypothesized to lead to EGFR-independent activation of the PI3K-Akt-mTOR pathway through activation of HER3-dependent signaling. We hypothesize that attacking HNC at two key points in the cellular proliferation and survival system will maximize HNC cell killing and irradicate subpopulations of cells which may be able to bypass the EGFR inhibition with independent activation of the PI3K-Akt-mTOR pathway. The concomitant use of cetuximab and temsirolimus permits active inhibition of both EGF, and the VEGF pathway related with angiogenesis, with synergistic responses as seen in experimental models.