Targeted Alpha Therapy Symposium

The response of human papillomavirus associated head and neck squamous cell carcinoma cell lines on standard therapy and treatment with an experimental alpha-particle emitter immunoconjugate targeting EGFR (Bi-213-Cetuximab)

Not scheduled

15m

Fairmont Château Laurier Hotel

Preclinical

Speaker

Mr Michael Siegl (Department of Otolaryngology Head and Neck Surgery, Technical University of Munich, Munich, Germany)

Description

Introduction ------------ Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide. Despite considerable improvements in surgery, radio- and chemotherapy over the last decades, the five-year overall survival has not changed significantly. Radio resistance is a frequent issue that impedes success in therapy. Tumor hypoxia often is causing this resistance, hence targeted therapy with oxygenation-independent alpha-emitters could be a effective strategy for therapy of HNSCC. Another emerging factor for treatment response is infection with human papillomavirus (HPV). HPV associated HNSCC is known to have a better prognosis and therefore is described as distinct entity within HNSCC. Still there are contrary experimental studies on response to therapy and the underlying molecular mechanisms. Objectives ---------- Characterizing the relevance of HPV status of HNSCC cell lines for response to standard and experimental therapy with alpha-particle emitter immunoconjugate targeting EGFR ($^{213}$Bi-Cetuximab). Materials & Methods ------------------- We analyzed proliferation, colony forming capability, cell cycle and DNA double strand brakes (yH2AX) in six HNSCC cell lines (3 HPV pos./3 HPV neg.) after treatment with chemotherapeutics, alpha-particle emitter $^{213}$Bi-Cetuximab (9.25-111 kBq/mL) and irradiation by X-Rays (0.5-14 Gy). We also performed Western blot analysis and determined the impact of knockdown of DNA repair factors (RAD51, LIG4 or XRCC1) on proliferation. Results ------- HPV-positivity was significantly associated with a more pronounced antiproliferative response to treatment with various chemotherapeutics, $^{213}$Bi-Cetuximab as well as X-Ray irradiation with single or fractionated doses. Colony forming capability of the cells after treatment was also significantly correlated with HPV status. After treatment with $^{213}$Bi-Cetuximab cells accumulated in the G2-Phase. After X-Ray therapy this effect could be seen in the HPV-positive cell lines only. Treatment with $^{213}$Bi-Cetuximab (37 kBq/mL) resulted in a delayed, stronger and more persistent peak level of the DNA double strand break marker yH2AX compared to X-Ray therapy (2 Gy). HPV-positive cell lines showed slightly stronger yH2AX intensity changes with both treatments. Cleavage of PARP and phosphorylation of Erk1/2 after irradiation correlated with HPV-positivity. Rad51 protein level was HPV-independently upregulated, most notably with $^{213}$Bi-Cetuximab treatment. Knockdown of RAD51 had an antiproliferative effect on the cells - especially in HPV-positive cells – whereas knockdown of LIG4 or XRCC1 did not affect proliferation. Irradiation-induced antiproliferative effects could be enhanced by knockdown of these DNA-repair factors, noticing the strongest effect with knockdown of RAD51. Conclusion ---------- HPV associated HNSCC showed a better response to all forms of therapy tested. Our results are suggesting a more pronounced G2-arrest to be responsible for this observation. Compared to X-Rays, the experimental therapy with the alpha-particle emitter $^{213}$Bi-Cetuximab is a remarkably more effective approach to attenuate the proliferation potential of HNSCC. Since this superior response is also true for more radioresistant HPV-negative cell lines, targeted $^{213}$Bi-Cetuximab treatment of HNSCC is a promising option and should be further developed.