Photoimmunotherapy of HER2-expressing Breast Cancer Cells.

BACKGROUND/AIM: Breast cancer (BC) is the most common malignant disease worldwide. Localized stages of BC can be successfully treated by surgery. However, local recurrence occurs in about 4-10% of patients, requiring systemic treatments that impair the patients' quality of life and shortens life expectancy. Therefore, new therapeutic options are needed, which can be used intraoperatively and contribute to the complete removal of residual tumor cells in the surgical area. In the present study, we describe a cysteine-modified variant of the anti-HER2 antibody trastuzumab, that was coupled to the silicon phthalocyanine photosensitizer dye WB692-CB1 for the photoimmunotherapy (PIT) of BC. MATERIALS AND METHODS: The cysteine modified trastuzumab variant was cloned and expressed in Expi293F cells. After purification via immobilized affinity chromatography, the antibody was coupled to the dye. Cell binding of the antibody and the antibody dye conjugate was measured by flow cytometry. After incubation of BC cells with the conjugate and activation of the dye by irradiation with red light, cell viability was determined. RESULTS: The antibody and the conjugate showed specific binding to HER2-expressing BC cells. Treatment of the HER2high BC cell line SK-BR-3 with the conjugate followed by irradiation with a red light dose of 32 J/cm2 led to complete cell killing within 24 h. CONCLUSION: Our novel antibody dye conjugate represents a promising candidate for intraoperative treatment of localized BC, aiming to eliminate residual tumor cells in the surgical area and potentially reduce local recurrence, thereby improving recovery prospects for BC patients.

Photoimmunotherapy of Prostate Cancer With Antibody and Fab Fragments Targeting the Prostate Specific Membrane Antigen.

BACKGROUND/AIM: The standard treatment for localized prostate cancer involves surgical removal of the prostate with curative intent. However, when tumor cells persist in the operation site, there is high risk of local recurrence and tumor spread, leading to stressful follow-up treatments, impaired quality of life, and reduced overall survival. This study examined photoimmunotherapy (PIT) as a new treatment option for prostate cancer cells. MATERIALS AND METHODS: We generated conjugates consisting of either a humanized antibody or Fab fragments thereof targeting the prostate specific membrane antigen (PSMA), along with our silicon phthalocyanine photosensitizer dye WB692-CB1. PSMA-expressing prostate cancer cells were incubated with the antibody dye or Fab dye conjugates and cell binding was measured using flow cytometry. Cells were irradiated with varying doses of red light for dye activation, and cytotoxicity was determined by erythrosin B staining and subsequent analysis using a Neubauer counting chamber. RESULTS: Specific cytotoxicity was induced with the antibody dye conjugate in the prostate cancer cells in a light dose-dependent manner. Treatment of the cells with the Fab dye conjugate resulted in lower cytotoxicity, which could be attributed to a reduced binding affinity and a reduced dye uptake of the Fab fragment. CONCLUSION: Our new antibody dye and Fab dye conjugates offer potential for future intraoperative PIT in patients with localized prostate cancer, with the aim to ensure complete removal of tumor cells from the surgical area, to avoid local recurrence, and to improve clinical outcome.

Antibody-dye Conjugates Targeting EGFR and HER2 for the Photoimmunotherapy of Bladder Cancer.

BACKGROUND/AIM: Although there are curative treatment options for non-muscle-invasive bladder cancer, the recurrence of this tumor is high. Therefore, novel targeted therapies are needed for the complete removal of bladder cancer cells in stages of localized disease, in order to avoid local recurrence, to spare bladder cancer patients from stressful and expensive treatment procedures and to increase their quality of life and life expectancy. This study tested a new approach for the photoimmunotherapy (PIT) of bladder cancer. MATERIALS AND METHODS: We generated a cysteine modified recombinant version of the antibody cetuximab targeting the epidermal growth factor receptor (EGFR) on the surface of bladder cancer cells. Then, we coupled the novel photoactivatable phthalocyanine dye WB692-CB1 via a maleimide linker to the free cysteines of the antibody. PIT was performed by incubating bladder cancer cells with the antibody dye conjugate followed by irradiation with visible red light. RESULTS: The conjugate was able to induce specific cytotoxicity in EGFR-positive bladder cancer cells in a light dose-dependent manner. Enhanced cytotoxicity in RT112 bladder cancer cells was evoked by addition of a second antibody dye conjugate targeting HER2 or by repeated cycles of PIT. CONCLUSION: Our new antibody dye conjugate targeting EGFR-expressing bladder cancer cells is a promising candidate for the future PIT of bladder cancer patients.