Combined treatment of the experimental human papilloma virus-16-positive cervical and head and neck cancers with cisplatin and radioimmunotherapy targeting viral E6 oncoprotein

Abstract

Background: Human papilloma virus (HPV) is implicated in >99% of cervical cancers and ∼40% of head and neck squamous cell carcinoma (HNSCC). We previously targeted E6 oncogene with (188)Rhenium-labelled monoclonal antibody (mAb) C1P5 to HPV16 E6 in cervical cancer and HNSCC. Intranuclear E6 can be accessed by mAbs in non-viable cells with leaky membranes. As radioimmunotherapy (RIT) efficacy depends on the availability of target protein-we hypothesised that pretreatment with cisplatin will kill some tumour cells and increase E6 availability for RIT.

Methods: Mice with subcutaneous HPV16+ cervical (CasKi) and HNSCC (2A3) tumours were pretreated with 0-7.5 mg kg(-1) per day cisplatin for 3 days followed by (188)Re-C1P5 and biodistribution was performed 24 h later. For RIT, the animals were treated with: 5 mg kg(-1) per day cisplatin for 3 days; or 5 mg kg(-1) per day cisplatin for 3 days followed 200 or 400μCi (188)Re-C1P5 mAb; or 200 or 400μCi (188)Re-C1P5 mAb; or left untreated, and observed for tumour growth for 24 days.

Results: Pretreatment with cisplatin increased the uptake of (188)Re-C1P5 in the tumours 2.5 to 3.5-fold and caused significant retardation in tumour growth for CasKi and 2A3 tumours in both RIT alone and cisplatin, and RIT groups in comparison with the untreated control and cisplatin alone groups (P<0.05). The combined treatment was more effective than either modality alone (P<0.05).

Conclusion: Our study demonstrates that preceding RIT targeting E6 oncogene with chemotherapy is effective in suppressing tumour growth in mouse models of HPV16+ cancers.

Figure 1

Lactate dehydrogenase assay of CasKi and 2A3 cells treated in vitro with various concentrations of cisplatin.

Figure 2

Tumour uptake of E6-binding mAb ¹⁸⁸Re-C1P5 in nude mice-bearing CasKi and 2A3 tumours post treatment with cisplatin. Mice were treated with various doses of cisplatin for 3 days, ¹⁸⁸Re-C1P5 mAb was administered 24 h after the last dose of cisplatin, and the tumour uptake was assessed 24 h post ¹⁸⁸Re-C1P5 administration: (A) CasKi; (B) 2A3; (C, D) TUNEL staining of the untreated and cisplatin-treated tumours. Apoptotic cells stained brown. Original magnification × 400: (C) CasKi tumours—untreated (left panel) and treated with 5 mg kg⁻¹ cisplatin (right panel); (D) 2A3 tumours—untreated (left panel) and treated with 5 mg kg⁻¹ cisplatin (right panel).

Figure 3

Therapy with cisplatin and RIT with E6-binding mAb ¹⁸⁸Re-C1P5 of nude mice-bearing 2A3 (A) and CasKi (B) tumours. Tn—tumour volume on the day of measurement; T₀—tumour volume on day 0. The mice with 2A3 HNSCC tumours were treated IP with: 400 μCi ¹⁸⁸Re-C1P5 mAb on day 0; or 5 mg kg⁻¹ per day cisplatin on days 0, 1, 2 followed by 400 μCi ¹⁸⁸Re-C1P5 mAb on day 3; or 5 mg kg⁻¹ cisplatin alone on days 0, 1, 2; or left untreated. The mice with CasKi cervical tumours were treated IP with: 200 μCi ¹⁸⁸Re-C1P5 mAb on day 0; or 5 mg kg⁻¹ per day cisplatin on days 0, 1, 2 followed by 200 μCi ¹⁸⁸Re-C1P5 mAb on day 3; or 5 mg kg⁻¹ cisplatin alone on days 0. 1, 2; or left untreated.

Figure 4

¹⁸F-FDG microPET/CT images of 2A3 tumour-bearing on day 15 post treatment: left panel—untreated mouse, middle panel—the mouse treated with cisplatin alone, right panel—the mouse treated with cisplatin and RIT. Green arrows are pointing to the tumours.

Figure 5

Immunohistochemical evaluation of E6 and E7 oncogenes expression in RIT-treated CasKi and 2A3 cells. (A) E6 in CasKi cells, (B) E7 in CasKi cells; (C) E6 in 2A3 cells; (D) E7 in 2A3 cells. Left panels show untreated cells and right panels RIT-treated cells. Cells positive for E6 and E7 oncogenes stained brown. Original magnification × 400.