Effects of Betulinic Acid Alone and in Combination with Irradiation in Human Melanoma Cells

Abstract

Recently, betulinic acid was identified as a highly selective inhibitor of human melanoma growth and was reported to induce apoptosis in these cells. We have investigated the growth-inhibitory properties of this compound alone and in combination with ionizing radiation in a panel of established human melanoma cell lines as well as in normal human melanocytes. Betulinic acid strongly and consistently suppressed the growth and colony-forming ability of all human melanoma cell lines investigated. In combination with ionizing radiation the effect of betulinic acid on growth inhibition was additive in colony-forming assays. Betulinic acid also induced apoptosis in human melanoma cells as demonstrated by Annexin V binding and by the emergence of cells with apoptotic morphology. The growth-inhibitory action of betulinic acid was more pronounced in human melanoma cell lines than in normal human melanocytes. Notably, despite the induction of apoptosis, analysis of the expression of Bcl-2 family members in betulinic-acid-treated cells revealed that expression of the anti-apoptotic protein Mcl-1 was induced. Furthermore, the antiproliferative action of betulinic acid seemed to be independent of the p53 status. The properties of betulinic acid make it an interesting candidate, not only as a single agent but also in combination with radiotherapy. We conclude that the strictly additive mode of growth inhibition in combination with irradiation suggests that the two treatment modalities may function by inducing different cell death pathways or by affecting different target cell populations.

Betulinic acid inhibits autophagic flux and induces apoptosis in human multiple myeloma cells in vitro

“…Acta Pharmacologica Sinica npg tion and apoptosis analyses [25] . Peripheral blood lymphocytes and human skin fibroblasts were also identified as being highly resistant to BA treatment [26] .…”

A novel chenodeoxycholic derivative HS-1200 enhances radiation-induced apoptosis in MCF-7 cells

“…Not only did the combination treatment of betulinic acid and irradiation also induce the apoptotic effect in human melanoma cells (20), but proteasome inhibitors and the human immunodeficiency virus protease inhibitor, saquinavir, have been demonstrated to modulate the apoptotic response through the inhibition of NF-κB activation (21)(22)(23). Several publications have provided evidence that signaling cascades originating at the epidermal growth factor receptor (EGFR) activate anti-apoptotic signaling pathways and increase the radiation resistance of tumor cells (24)(25)(26).…”

“…TRAIL (11)(12)(13), synthetic phospholipids such as alkyllysophospholipids (14)(15)(16), the PKC inhibitor, PKC412 (17), other drugs such as Cox-2 inhibitors, betulinic acid, and proteasome inhibitors have all been suggested as radiosensitizers (18)(19)(20)(21).…”

Targeted inhibition of tumor proliferation, survival, and metastasis by pentacyclic triterpenoids: Potential role in prevention and therapy of cancer

“…In a cell-free system, BetA has been demonstrated to directly cause mitochondrial outer membrane permeabilization and cytochrome-c release in a Bcl-2 or Bcl-xL-dependent manner, yet independently of caspases [52][53][54]. BetA has also been reported to induce apoptosis in a p53-independent fashion, including chemotherapy-refractory cases [44,45,[54][55][56][57][58] indicating that this tritepene can also overcome chemoresistance, which is frequently encountered during cancer therapy suggesting tremendous potential for development as a therapeutic agent. Recent evidence indicates that the anticancer activity of BetA can be markedly increased when it is used in combination with conventional chemotherapy, ionizing radiation or cytokine TRAIL [57,59,60].…”

“…BetA has also been reported to induce apoptosis in a p53-independent fashion, including chemotherapy-refractory cases [44,45,[54][55][56][57][58] indicating that this tritepene can also overcome chemoresistance, which is frequently encountered during cancer therapy suggesting tremendous potential for development as a therapeutic agent. Recent evidence indicates that the anticancer activity of BetA can be markedly increased when it is used in combination with conventional chemotherapy, ionizing radiation or cytokine TRAIL [57,59,60]. Furthermore BetA analogs have displayed significant anti-inflammatory activities in various animal models [61].…”