Abstract P6-09-09: A second-generation proteasome inhibitor (SGPI) inhibits proliferation of triple negative breast cancer cells to a greater extent than doxorubicin while decreasing IL-6/NF-kB pathway inflammatory activity Free

Background: Proteasome inhibitors limit tumor growth by lowering the capacity of cancer cells to degrade pro-apoptotic signals. Given the success of proteasome inhibitors as a treatment for multiple myeloma, this class of drugs has been investigated as a possible treatment for other malignancies with poor prognoses, such as metastatic triple negative breast cancer (TNBC). Doxorubicin (DOX), is the current standard of treatment for TNBC but it has a very toxic side effect profile. Furthermore, it has been shown that the pro-inflammatory markers IL-6/NF-kB plays a critical role in angiogenesis, anti-apoptosis, metastasis and hematogenous spread of tumor cells, and is elevated at baseline in TNBC and increases further with DOX treatment. Recent studies with SGPI on myeloma patients have reported that only 2-5% patients exhibited side effects as compared to the 25% heart failure seen with DOX, a more tolerable side-effect profile. However, in a recent clinical trial, Bortezomib (BOR), a first-generation proteasome inhibitor, showed limited activity in metastatic breast cancer when used as single agent. SGPI differs from BOR in its structure and its activity on the proteasome complex. Therefore, we studied the effect of SGPI on proliferation and inflammation in the triple negative breast cancer cell line MDA-MB-231.

Method: MDA-MB-231 cells were treated with known D50 concentrations of DOX, SGPI, and BOR alone and in combination for 24 hours. Cells were then incubated in complete medium for another 24 hours. The viability of each group was analyzed by quantitating cell proliferation (MTT assay). The inflammatory markers IL-6 and NF-kB were measured by ELISA and lentiviral signal assay.

Results: DOX (2 uM) decreased TNBC proliferation by 40% while SGPI (10nM) and the combined regimen decreased it by over 70%. BOR (5 nM) was less efficacious than DOX or SGPI.

Although the combination showed no appreciable synergism, the large proliferation difference between the treatments suggests that SGPI has a greater anti-tumor activity than DOX at a D50 concentration. The DOX/BOR combination also showed no synergism. SGPI halved baseline IL-6 levels and reduced DOX-stimulated levels 6-fold. Similar results were seen with NF-kB. BOR also lowered inflammation but to a lesser extent.

Conclusion: SGPI is more efficacious than either DOX or BOR in inhibiting TNBC proliferation in vitro, perhaps as a result of a reduced IL-6/NF-kB pathway pro-inflammatory response, which represents a potential improvement in the toxicity profile of existing chemotherapy. These preliminary results indicate that SGPI might reduce angiogenesis and metastasis.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P6-09-09.