Photodynamic therapy of human breast cancer xenografts lacking caspase-3
Cecilia M Whitacre1, Taroh H Satoh, Liang yan Xue
1Department of Medicine, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.
Abstract:
The human breast cancer cell line MCF-7 is deficient in procaspase-3 and in caspase-3-dependent steps in apoptosis due to deletion of the CASP-3 gene. We previously found that the cells transfected with empty vector (MCF-7v cells) were considerably less sensitive to photodynamic treatment in vitro with the phthalocyanine photosensitizer Pc 4 than were the cells stably transfected with human procaspase-3 cDNA (MCF-7c3 cells); however, overall cell killing, as determined by a clonogenic assay, was not affected by the presence of procaspase-3. The present study was undertaken to determine whether photodynamic therapy (PDT) in vivo was dependent on the ability of the cells to carry out the late steps in apoptosis that are catalyzed by this caspase. Xenografts of MCF-7 cells and the isogenic-derived MCF-7v and MCF-7c3 cells were generated in female athymic nude mice implanted with an estrogen pellet. MCF-7c3 xenografts, but not those of the other two lines, continued to express procaspase-3, as revealed by Western blots of proteins from the cells and the xenografts. When the xenografts reached 50-120 mm(3), some were treated with PDT (1mg/kg Pc 4 i.v. followed 48 h later by 150 J/cm(2) light at 672 nm and 150 mW/cm(2)), while others served as controls (no treatment, light alone, or Pc 4 alone). All Pc 4-PDT-treated tumors and none of the controls exhibited either complete or strong partial responses, and complete responses were durable for the entire observation period of 16 days. The responses were not dependent upon the presence of procaspase-3 in the xenografts. The results indicate that the rapid response of Pc 4-PDT-treated tumors in vivo is not due to their ability to carry out the major caspase-3-mediated late steps in apoptosis.
Insights
Photodynamic therapy (PDT) using Pc 4 effectively treated breast cancer xenografts in mice. Tumor response to PDT was independent of the caspase-3 protein, a key factor in apoptosis.
Area of Science:
- Oncology
- Biochemistry
- Photobiology
Background:
- The human breast cancer cell line MCF-7 lacks functional caspase-3, a key enzyme in apoptosis.
- Previous in vitro studies showed MCF-7 cells with restored caspase-3 (MCF-7c3) were more sensitive to Pc 4 photodynamic treatment (PDT), but overall cell killing was unaffected.
- The role of caspase-3 in the in vivo efficacy of PDT remains unclear.
Purpose of the Study:
- To investigate whether photodynamic therapy (PDT) efficacy in vivo is dependent on the late apoptotic steps mediated by caspase-3.
- To compare the response of MCF-7 breast cancer xenografts with varying caspase-3 expression levels to Pc 4-PDT.
Main Methods:
- Generated xenografts in mice using MCF-7 cells and isogenic variants MCF-7v (vector control) and MCF-7c3 (caspase-3 expressing).
- Confirmed procaspase-3 expression in xenografts via Western blot.
- Administered Pc 4 intravenously followed by light irradiation (672 nm) to treat tumors, with control groups receiving no treatment, light alone, or Pc 4 alone.
Main Results:
- Pc 4-PDT treatment resulted in complete or strong partial responses in all treated xenografts, regardless of caspase-3 expression.
- Complete responses were durable for the 16-day observation period.
- Tumor responses to Pc 4-PDT were not dependent on the presence of procaspase-3.
Conclusions:
- The rapid and effective response of Pc 4-PDT-treated breast cancer xenografts in vivo is not mediated by caspase-3-dependent apoptosis.
- These findings suggest alternative mechanisms contribute to PDT efficacy in this model.
- Targeting caspase-3 is not essential for achieving therapeutic responses with Pc 4-PDT in vivo.
