Rb-Raf-1 interaction disruptor RRD-251 induces apoptosis in metastatic melanoma cells and synergizes with dacarbazine.
Metastatic melanoma is an aggressive cancer with very low response rate against conventional chemotherapeutic agents such as dacarbazine (DTIC). Inhibitor of Rb-Raf-1 interaction RRD-251 was tested against the melanoma cell lines SK-MEL-28, SK-MEL-5, and SK-MEL-2. RRD-251 was found to be a potent inhibitor of melanoma cell proliferation, irrespective of V600E B-Raf mutation status of the cell lines. In a SK-MEL-28 xenograft experiment, RRD-251 exerted a significant suppression of tumor growth compared with vehicle (P = 0.003). Similar to in vitro effects, tumors from RRD-251-treated animals showed decreased Rb-Raf-1 interaction in vivo. Growth suppressive effects of RRD-251 were associated with induction of apoptosis as well as a G(1) arrest, with an accompanying decrease in S-phase cells. RRD-251 inhibited Rb phosphorylation and downregulated E2F1 protein levels in these cells. Real-time PCR analysis showed that RRD-251 caused downregulation of cell-cycle regulatory genes thymidylate synthase (TS) and cdc6 as well as the antiapoptotic gene Mcl-1. Combinatorial treatment of RRD-251 and DTIC resulted in a significantly higher apoptosis in DTIC resistant cell lines SK-MEL-28 and SK-MEL-5, as revealed by increased caspase-3 activity and PARP cleavage. Because aberrant Rb/E2F pathway is associated with melanoma progression and resistance to apoptosis, these results suggest that the Rb-Raf-1 inhibitor could be an effective agent for melanoma treatment, either alone or in combination with DTIC.
Drug Discovery Department, H Lee Moffitt Cancer Center and Research Institute, Tampa, Florida 33612, USA.
Sandeep
S
Singh
Rebecca
R
Davis
Vignesh
V
Alamanda
Roberta
R
Pireddu
Daniel
D
Pernazza
Said
S
Sebti
Nicholas
N
Lawrence
Srikumar
S
Chellappan
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D003606:Dacarbazine / Q000494:pharmacology* / Q000627:therapeutic use; D004357:Drug Synergism; D006801:Humans; D008545:Melanoma / Q000188:drug therapy / Q000473:pathology*; D051379:Mice; D009362:Neoplasm Metastasis; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D016160:Retinoblastoma Protein / Q000378:metabolism*; D013890:Thiourea / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D023041:Xenograft Model Antitumor Assays
D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; D018797:Cell Cycle Proteins; C556907:RRD 251; D016160:Retinoblastoma Protein; D003606:Dacarbazine; D019908:Proto-Oncogene Proteins c-raf; D013890:Thiourea