Mechanisms of Cell Sensitization to α Radioimmunotherapy by Doxorubicin or Paclitaxel in Multiple Myeloma Cell Lines

Abstract

Purpose:The purpose of this study was to analyze different mechanisms (cell cycle synchronization, DNA damage, and apoptosis) that might underlie potential synergy between chemotherapy (paclitaxel or doxorubicin) and radioimmunotherapy with a radionuclides. Experimental Design:Three multiple myeloma cell lines (LP1, RMI 8226, and U266) were treated with 213 Bi-radiolabeled B-B4, a monoclonal antibody that recognizes syndecan-1 (CD138) 24 hours after paclitaxel (1nmol/L) or doxorubicin (10 nmol/L) treatment. Cell survival was assessed using a clonogenic survival assay. Cell cycle modifications were assessed by propidium iodide staining and DNA strand breaks by the comet assay. Level of apoptosis was determined by Apo 2.7 staining. Results: Radiation enhancement ratio showed that paclitaxel and doxorubicin were synergistic with a radioimmunotherapy. After a 24-hour incubation, paclitaxel and doxorubicin arrested all cell lines in the G 2 -M phase of the cell cycle. Doxorubicin combined with a radioimmunotherapy increased tail DNA in the RPMI 8226 cell line but not the LP1or U266 cell lines compared with doxorubicin alone or a radioimmunotherapy alone. Neither doxorubicin nor paclitaxel combined with a radioimmunotherapy increased the level of apoptosis induced by either drug alone or a radioimmunotherapy alone. Conclusion: Both cell cycle arrest in the G 2 -M phase and an increase in DNA double-strand breaks could lead to radiosensitization of cells by doxorubicin or paclitaxel, but apoptosis would not be involved in radiosensitization mechanisms.a-Emitting radioisotopes might be more effective for metabolic radiotherapy than other radionuclides because of their high linear energy transfer and short pathways and because they can target radiation to individual cancer cells (1) and micrometastases (2). Early results with a radioimmunotherapy have been encouraging (1). Like other radionuclides, they could be combined with chemotherapeutic drugs as this strategy has a strong biological rationale (3). However, up to now, most studies have considered combining drugs with Xrays or g-rays, and radiosensitizing of cells by paclitaxel to grays or X-rays (4, 5) has been attributed to three mechanisms: interactions with the cell cycle, apoptosis, and tumor hypoxia (6), those of doxorubicin to induction of DNA damage (7,8) and tumor hypoxia (9). Paclitaxel does not induce DNA damage but promotes microtubule polymerization (10). Our preliminary investigations on three myeloma cell lines (LP1, RPMI 8226, and U266) have shown that doxorubicin or paclitaxel combined with a radioimmunotherapy is more effective than drug alone or a radioimmunotherapy alone. In accordance with results obtained with other forms of radiation (6), the effect was stronger when a radioimmunotherapy was given 24 hours after doxorubicin or paclitaxel. Experiments are in progress to formally show synergism between a radioimmunotherapy and these drugs (11).We have investigated several mechanisms that might give rise to synergy between paclitaxel o...

Chemoradionuclide Therapy with186Re-Labeled Liposomal Doxorubicin: Toxicity, Dosimetry, and Therapeutic Response

“…[52][53][54] Studies have shown that doxorubicin causes DNA unwinding and DNA double-strand breaks, which lead to radiosensitization of the tumor cells. [55][56][57] Another possible reason for better therapeutic efficacy with 186 ReDoxil could be due to the increased blood circulation time, which allowed for better accumulation and distribution of the agent in the tumor. 35 Although 186 Re-PEG-liposomes were less effective in the treatment of large solid tumors in this study, they could be potentially used for the treatment of small tumors, as an inverse correlation between tumor size and accumulation of radioactivity has been shown in preclinical 47,48 and clinical studies.…”

Nutlin-3 radiosensitizes hypoxic prostate cancer cells independent of p53

“…Colonies were stained and counted under a microscope, with 50 cells as the minimum number to define a surviving colony. The best-fit survival curve was generated according to a linear-quadratic survival model and the mean inactivation dose (area under survival curve) was calculated as described previously (28). The sensitizing enhancement ratio (SER) was defined as SER = mean inactivation dose control irradiation / mean inactivation dose Nutlin-3 + irradiation.…”

“…For cell cycle analysis, cells were stained with propidium iodide and counted with a FACScan (Becton Dickinson) as described previously (28).…”

Enhancing Therapeutic Radiation Responses in Multiple Myeloma

“…In MM cell lines, Supiot et al demonstrated superior tumor cell killing by anti-CD138 (syndecan-1) B-B4 MAb labeled with bismuth-213 as compared to iodine-131-labeled antibody suggesting that alpha-RIT might be more suitable for treating www.intechopen.com single cell tumors such as MM (Supiot et al, 2002). Besides B-B4, the MAb MA5, which recognizes mucin-1 expressed by both normal and malignant plasma cells, has been coupled to bismuth-213 to target myeloma cells (Couturier et al, 1999;Supiot et al, 2005). In ASCT conditioning regimens, RIT is a good alternative to TBI as it results in less radiotoxicity for normal organ systems and delivers more radiation to tumors as reflected in improved cure rates (Gustavsson et al, 2003).…”