Caspase-3, a novel therapeutic approach to the treatment of multiple myeloma.
Published: 2004
Language: eng
Number of pages: 130
Description: The karyotypically silent t(4;14)(p16;q2.3) translocation occurs in approximately 15% of all multiple myeloma (MM) cases, and results in the ectopic expression of fibroblast growth factor receptor 3 (FGFR3). In previous work we overexpressed FGFR3 or the constitutively active FGFR3-TD mutant in an interleukin-6 (IL-6)-dependent murine myeloma cell line, B9. High expression levels of FGFR3 conferred IL-6 independence, increased phosphorylation of STAT3 and upregulated the anti-apoptotic factor bcl-xL. Since bcl-xL can confer chemo-resistance in cancer cells, we hypothesized that FGFR3 overexpression may be sufficient to confer drug resistance to malignant plasma cells. To examine this issue, we tested FGFR3 expressing B9 cells for chemotherapy sensitivity. Melphalan or Doxorubicin both resulted in cell death comparable to controls at low concentrations of drug. In contrast no cell death was observed following exposure of FGFR3 engineered cell lines to Dexamethasone. Believing that this observed Dexamethasone resistance was due to the upregulation of bcl-xL, a bcl-x L antisense oligonucleotide was employed. Upon treatment with this oligonucleotide, FGFR3 expressing B9 cells were rendered sensitive to Dexamethasone. Activated caspase-3 cleaves proteins essential for cell survival, including bcl-x L. To explore the potential of caspase-3 as a cytotoxic molecule in the treatment of MM, the murine myeloma cell line, B9BM1, was transduced with an RU486-inducible caspase-3 retrovirus (B9BM-C3). After induction with RU486, apoptotic cell death of B9BM-C3 cells began by 4 hours and was complete by 48 hours post-induction, while non-transduced cells remained viable. Annexin V staining demonstrated 40%, 78% and 97% apoptotic cell death at 18, 24 and 30 hours post-induction. In co-culture experiments, induced B9BM-C3 cells generated a significant bystander effect. By MTT assay, a mix of 20:80 (B9BM-C3:parental cells) resulted in the death of 80% of the unmodified parental controls. B9BM-C3 cells formed tumors after subcutaneous injection in mice. Early treatment of these mice with RU486 eradicated tumor. Inducing caspase-3 expression in myeloma cells rapidly results in cell death and provides collateral cell damage via a putative bystander effect. These results indicate that therapeutic attempts to induce caspase-3 in myeloma cells may prove useful in the treatment of MM.
Notes: Adviser:  A. Keith Stewart.

Thesis (Ph.D.)--University of Toronto, 2004.

Electronic version licensed for access by U. of T. users.

Source: Dissertation Abstracts International, Volume: 65-05, Section: B, page: 2354.