Abstract
Photodynamic therapy (PDT) is an experimental approach to the treatment of neoplasms in which photosensitisers (PSs) accumulated in malignant tissues are photoactivated with appropriate wavelengths of light. The target specificity of PSs may be improved by linking them with carrier macromolecules such as monoclonal antibodies (MAbs). OC125 is a murine MAb that recognises the antigen CA 125, which is expressed on 80% of non-mucinous ovarian tumours. A chlorin derivative conjugated to OC125 was shown to be selectively phototoxic to ovarian cancer and other CA 125-positive cells in vitro and ex vivo. We now report in vivo studies using an ascitic Balb/c nude mouse ovarian cancer model. Ascites was induced by intraperitoneal injection of cells from the human ovarian cancer cell line NIH:OVCAR3. Six weeks after injection, when the animals had developed ascites, biodistribution studies were carried out by injecting the immunoconjugate (IC) or free PS intraperitoneally and sacrificing the animals at 3, 6, 12, 24, 48, 72 and 168 h later. The PS was quantitated by extraction and fluorescence spectroscopy. For both the IC and free PS, peak tumour concentrations were reached at 24 h; however, the absolute concentrations for the IC were always higher (2- to 3-fold) than the free PS. Tumour to non-tumour ratios at 24 h for the IC were 6.8 for blood, 6.5 for liver, 7.2 for kidney, 5.7 for skin and 3.5 for intestine. Evaluation of viable tumour cells in ascites following in vivo PDT with a single light exposure demonstrated a dose-dependent relationship with fluence and IC concentration. However, there was significant treatment-related toxicity at all fluences. With multiple low-dose treatments, the percentage of viable tumour cells was also significantly reduced and there were no treatment-related deaths. These data suggest that, while photoimmunotherapy remains promising as a new treatment modality for ovarian cancers, careful quantitative dosimetry of both IC and light may need to be combined with multiple treatments (as with radiation therapy and chemotherapy) to control malignant disease yet maintain acceptable toxicity in vivo.
Highlights
S_nminary Photodynamic therapy (PDT) is an experimental approach to the treatment of neoplasms in which photosensitisers (PSs) accumulated in malignant tissues are photoactivated with appropriate wavelengths of light
Ascites was induced by intraperitoneal injection of cells from the human ovarian cancer cell line NIH:OVCAR3
PDT is an experimental approach to the treatment of neoplasms which may alleviate some of the problems associated with the lack of specificity of conventional therapies and may be appropriate in the treatment of ovanran cancer because of the generally localised nature of the disease
Summary
NIH:OVCAR3 cells were a generous gift from Centocor (Malvern, PA, USA). This cell line was derived from the ascites of a patient with ovarian cancer (Hamilton et al, 1983). Cells were grown in RPMI-1640 medium supplemented with heat-inactivated fetal bovine serum and kept in an incubator at 37C in an atmosphere of 5% carbon dioxide. Cells were trypsinised (trypsin-EDTA, Gibco, Grand Island, NY, USA), centrifuged at 1,000 r.p.m. for 10 min (model 6000B, Sorvall Centrifuges, Dupont, Wilmington, DE, USA) and resuspended in 1 ml of phosphate-buffered saline (PBS) (Gibco) for intraperitoneal injection
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