4-5-dibromorhodamine-123 and Breast-Neoplasms

Photodynamic therapy (PDT), a cancer treatment already used early in this century, has distinctive advantages over conventional chemotherapy, namely its often observed preferential accumulation in cancer cells and its low intrinsic toxicity. Aggressive therapeutic modalities using high doses of chemotherapy and/or radiation therapy are now commonplace treatments for leukaemia, lymphoma and various non-haematologic malignancies. These intensive approaches have often been used in association with haematopoietic-progenitor-cell support and have induced major responses and remissions in patients with relapsed and refractory diseases, ultimately contributing to improve the disease-free survival of patients with high risk. This has encouraged Theratechnologies, a Montreal-based pharmaceutical company, to develop photodynamic ex vivo purging procedures, including the development of new photosensitizers and irradiation devices for the safe eradication of neoplastic cells from autologous grafts. Our first specific objective, therefore, was to design, synthesize, purify and test photoactive rhodamine derivatives. We have also selected a gas and phosphorus coating characteristic of an efficient scanning fluorescent source for extra-corporeal PDT using rhodamine derivatives. 4,5-Dibromorhodamine 123 (TH9402) was selected because of its photophysical properties, low toxicity and stability. TH9402 photodynamic-cell-therapy process conditions recognized as safe for normal human haematopoietic stem cells and progenitors demonstrated the efficacy of the purging procedure on various leukaemias (including chronic-myelogenous-leukaemia as well as non-Hodgkin-leukaemias and metastatic-breast-cancer cell lines.

Topics: Animals; Bone Marrow Purging; Bone Marrow Transplantation; Breast Neoplasms; Combined Modality Therapy; Humans; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Lymphoma, Non-Hodgkin; Photochemotherapy; Photosensitizing Agents; Rhodamines

High-dose chemotherapy combined with autologous transplantation using bone marrow or peripheral blood-derived stem cells (PBSC) is now widely used in the treatment of hematologic malignancies as well as some solid tumors like breast cancer (BC). However, some controversial results were recently obtained in the latter case. The presence of malignant cells in the autograft has been associated with the recurrence of the disease, and purging procedures are needed to eliminate this risk. The aim of this study was to evaluate the potential of the photosensitizer 4,5-dibromorhodamine methyl ester (TH9402), a dibrominated rhodamine derivative, to eradicate multiple myeloma (MM) and BC cell lines, while sparing more than 50% of normal pluripotential blood stem cells from healthy volunteers. The human BC MCF-7 and T-47D and MM RPMI 8226 and NCI-H929 cell lines were used to optimize the photodynamic purging process. Cell concentration and the cell suspension thickness as well as the dye and light doses were varied in order to eventually treat 1-2 L of apheresis. The light source consisted of two fluorescent scanning tubes emitting green light centered about 515 nm. The cellular uptake of TH9402 was measured during the incubation and washout periods and after photodynamic treatment (PDT) using spectrofluorometric analysis. The limiting dilution assay showed that an eradication rate of more than 5 logs is obtained when using a 40 min incubation with 5-10 microM dye followed by a 90 min washout period and a light dose of 5-10 J/cm2 (2.8 mW/cm2) in all cell lines. Agitating the 2 cm thick cell suspension containing 20 x 10(6) cells/mL during PDT was essential for maximal photoinactivation. Experiments on mobilized PBSC obtained from healthy volunteers showed that even more drastic purging conditions than those found optimal for maximal eradication of the malignant cell lines were compatible with a good recovery of hematopoietic progenitors cells. The absence of significant toxicity towards normal hematopoietic stem cells, combined with the 5 logs eradication of cancer cell lines induced by this procedure suggests that TH9402 offers an excellent potential as an ex vivo photodynamic purging agent for autologous transplantation in MM and BC treatment.

Topics: Breast Neoplasms; Hematopoietic Stem Cell Transplantation; Humans; Multiple Myeloma; Photochemotherapy; Rhodamines; Tumor Cells, Cultured