Roscovitine strongly enhances the effect of olaparib on radiosensitivity for HPV neg. but not for HPV pos. HNSCC cell lines

Abstract

At present, advanced stage human Papillomavirus (HPV) negative and positive head and neck squamous cell carcinoma (HNSCC) are treated by intense multimodal therapy that includes radiochemotherapy, which are associated with relevant side effects. Patients with HPV positive tumors possess a far better prognosis than those with HPV negative cancers. Therefore, new therapeutic strategies are needed to improve the outcome especially of the latter one as well as quality of life for all HNSCC patients. Here we tested whether roscovitine, an inhibitor of cyclin-dependent kinases (CDKs), which hereby also blocks homologous recombination (HR), can be used to enhance the radiation sensitivity of HNSCC cell lines.In all five HPV negative and HPV positive cell lines tested, roscovitine caused inhibition of CDK1 and 2. Surprisingly, all HPV positive cell lines were found to be defective in HR. In contrast, HPV negative strains demonstrated efficient HR, which was completely suppressed by roscovitine. In line with this, for HPV negative but not for HPV positive cell lines, treatment with roscovitine resulted in a pronounced enhancement of the radiation-induced G2 arrest as well as a significant increase in radiosensitivity. Due to a defect in HR, all HPV positive cell lines were efficiently radiosensitized by the PARP-1 inhibitor olaparib. In contrast, in HPV negative cell lines a significant radiosensitization by olaparib was only achieved when combined with roscovitine.

HPV‐negative and HPV‐positive HNSCC cell lines show similar numerical but different structural chromosomal aberrations

“…It was previously shown that HPV‐positive cell lines are characterized by an increased radiosensitivity and chemosensitivity, which is considered to result from a defective cell cycle control as well as impaired DSB repair . The latter was recently shown to result from a defect in HR, which is one of the two main DSB repair pathways relevant for mammalian cells …”

“…22,23,25 The latter was recently shown to result from a defect in HR, which is one of the two main DSB repair pathways relevant for mammalian cells. [29][30][31] In respect to this pathway, there are two important key players, Fanconi anemia group D2 protein, FANCD2, and the ataxia telangiectasia and Rad3-related protein, ATR, which are both located on chromosome 3. In fact, when expression of these two proteins were determined for 89 HNSCC tumor samples including 36 from HPV-positive tumors via immunohistochemistry, for HPV-positive tumors the expression of ATR was about eight times lower (P < .001) and for FANCD2, about twofold lower when compared to HPV-negative tumors, which may cause the defect in HR.…”

“…The higher sensitivity of HPV‐positive cell lines cannot be attributed to a depressed p53/p21 activation as recently shown by us but rather to a defect in cell cycle regulation and repair of DNA double‐strand breaks (DSBs) . Recent data indicate that the defect in DSB repair might result from impaired homologous recombination (HR) . However, whether these defects are associated with respective variations in genomic instability still needs to be exploited.…”

“…22,23 Recent data indicate that the defect in DSB repair might result from impaired homologous recombination (HR). [29][30][31] However, whether these defects are associated with respective variations in genomic instability still needs to be exploited.…”

Dual PI3K/mTOR Inhibitor NVP-BEZ235 Enhances Radiosensitivity of Head and Neck Squamous Cell Carcinoma (HNSCC) Cell Lines Due to Suppressed Double-Strand Break (DSB) Repair by Non-Homologous End Joining

“…and five HPV pos. HNSCC cell lines, with the second group showing an enhanced cellular radiosensitivity [24], which is attributed to an impaired DSB repair [25,26]. BEZ235 strongly increases the cellular radiosensitivity of all HNSCC cell lines, independently from HPV status.…”