Epidermal growth factor receptor (EGFR) targeted photoimmunotherapy (PIT) for the treatment of EGFR expressing bladder cancer.

Abstract

291 Background: There are limited treatment options for patients with non-muscle invasive bladder cancer (NMIBC) who fail intravesical bacillus Calmette-Guerin (BCG). The use of light as a means of therapy for bladder cancer (BC) has a long history but has been hampered by a lack of tumor specificity and toxicity. Monoclonal antibody (mAb)-conjugates represent an emerging therapeutic approach for malignancies that improves upon tumor specificity. The use of a mAb-photo-absorber (PA) conjugate is a more selective method of delivering light therapy and has been termed “photoimmunotherapy” (PIT). In this report, PIT is used to target the epidermal growth factor receptor (EGFR). EGFR is a good tumor-specific target as it is enriched in the basal molecular subtype of BC. In the present study, anti-EGFR antibody panitumumab (pan) was labeled with the PA, IRDye 700Dx (IR700), to create a pan IR700 mAb-PA conjugate which is activated by near-infrared radiation (NIR). Methods: BC tissue microarray (TMA) and BC cell lines were analyzed for expression of EGFR. Mechanism of PIT induced cell death was studied using proliferation assays, transmission electron microscopy (TEM), and production of reactive oxygen species. Finally, the in vivo effect was studied in xenografts. Results: EGFR staining of TMAs showed that while most BCs have expression of EGFR to some degree, squamous cell carcinomas (SCC) have the highest expression of EGFR. Pan IR700 activated by NIR light rapidly killed UMUC-5 cells, a bladder SCC line. Pan alone, pan IR700 without NIR, or NIR alone had no effect on cells. TEM demonstrated that cell death is due to necrosis. Singlet oxygen species contributed towards cell death. NIR-PIT with pan IR700 reduced growth compared to only pan IR700 treated UMUC-5 xenograft tumors. Conclusions: PIT is a new targeted treatment for BC. Our data demonstrate that pan IR700-induced PIT selectively kills EGFR-expressing bladder cancer cells in vitro and in vivo and hence warrants further studies in orthotopic models and in patients. We suspect that EGFR-directed therapy with PIT is a viable strategy for the basal molecular subtype of BC and will be testing this hypothesis in the future.