Mcl-1 Antisense Therapy Chemosensitizes Human Melanoma in a SCID Mouse Xenotransplantation Model

Abstract

It is well established that high expression of the antiapoptotic Bcl-2 family proteins Bcl-2 and Bcl-xL can significantly contribute to chemoresistance in a number of human malignancies. Much less is known about the role the more recently described Bcl-2 family member Mcl-1 might play in tumor biology and resistance to chemotherapy. Using an antisense strategy, we here address this issue in melanoma, a paradigm of a treatment-resistant malignancy. After in vitro proof of principle supporting an antisense mechanism of action with specific reduction of Mcl-1 protein as a consequence of nuclear uptake of the Mcl-1 antisense oligonucleotides employed, antisense and universal control oligonucleotides were administered systemically in combination with dacarbazine in a human melanoma SCID mouse xenotransplantation model. Dacarbazine, available now for more than three decades, still remains the most active single agent for treatment of advanced melanoma. Mcl-1 antisense oligonucleotides specifically reduced target protein expression as well as the apoptotic threshold of melanoma xenotransplants. Combined Mcl-1 antisense oligonucleotide plus dacarbazine treatment resulted in enhanced tumor cell apoptosis and led to a significantly reduced mean tumor weight (mean 0.16 g, 95% confidence interval 0.08-0.26) compared to the tumor weight in universal control oligonucleotide plus dacarbazine treated animals (mean 0.35 g, 95% confidence interval 0.2-0.44) or saline plus dacarbazine treated animals (mean 0.39 g, 95% confidence interval 0.25-0.53). We thus show that Mcl-1 is an important factor contributing to the chemoresistance of human melanoma in vivo. Antisense therapy against the Mcl-1 gene product, possibly in combination with antisense strategies targeting other antiapoptotic Bcl-2 family members, appears to be a rational and promising approach to help overcome treatment resistance of malignant melanoma.

Down-Regulation of Mcl-1 by Small Interfering RNA Sensitizes Resistant Melanoma Cells to Fas-Mediated Apoptosis

“…In addition to our study, Mcl-1 has recently been shown to be involved both in the chemosensitization or radiosensitization of melanoma tumors (74)(75)(76), and in resistance of other solid tumors to TRAIL-induced apoptosis (77). In melanoma, resistance to TRAIL has been rather attributed to other antiapoptotic proteins, such as c-Flip and XIAP (31,49,78).…”

Down-Regulation of Mcl-1 by Small Interference RNA Induces Apoptosis and Sensitizes HL-60 Leukemia Cells to Etoposide

“…ELISA cell death assay showed that the chemotherapeutic agent etoposide, alone, caused remarkable apoptosis in leukemia cells. Of note, we found that the inhibition of Mcl-1 using siRNA also resulted in significant apoptosis in the absence of etoposide, which is in contrast to the finding of others on solid tumors (Thallinger et al, 2003, Thallinger et al, 2004. However, this observation is similar to that found on other studies on hematological malignancies (Hussain et al, 2007;Quinn et al, 2011), illustrating the important biological role of Mcl-1 in leukemic cells.…”

Beclin 1 restrains tumorigenesis through Mcl-1 destabilization in an autophagy-independent reciprocal manner

“…Conversely, Mcl-1 has been associated with melanoma progression 28 and shown to be critical for survival of melanoma cells undergoing ER stress 29 or anoikis 30 . Mcl-1 has also been implicated in mediating resistance of melanoma cells to radiation 31 and several chemotherapeutic agents [32][33][34] .…”

“…Melanoma is an example of tumours in which Mcl-1 plays crucial tumourpromoting roles by promoting survival on anoikis 30 and endoplasmic reticulum stress 29 and mediating resistance to radiation 31 and several anticancer agents such as Fas 32 , dacarbazine 33 contribution of these pathways to the observed upregulation of Mcl-1 in different types of tumours is not clear. In T-cell acute lymphoblastic leukaemia, follicular lymphoma, small cell lung carcinomas, ductal and colon adenocarcinoma, high Mcl-1 levels have mainly been attributed to decreased proteasomal degradation and increased stability of Mcl-1 protein 7,35 .…”