Acridine-modified, clamp-forming antisense oligonucleotides synergize with cisplatin to inhibit c-Myc expression and B16-F0 tumor progression

Abstract

The c-myc protooncogene plays a key role in the abnormal growth regulation of melanoma cells. We have targeted three polypurine sequences within the mouse myc mRNA with acridine-modified, clamp-forming antisense oligonucleotides (AS ODNs) in an effort to inhibit growth of murine melanoma cells. These ODNs are unique in that they hybridize to the target mRNA by both Watson-Crick and Hoogsteen hydrogen bond interactions, forming a triple-stranded structure. At a concentration of 3 microM E1C, E2C and E3C inhibit B16-F0 proliferation by 76, 66 and 78%, respectively. Both immunofluorescent staining and western blot analysis corroborate a proportional reduction in c-Myc expression by all three ODNs. There were clear distinctions in the ability of these ODNs to inhibit tumor progression in C57BL/6 mice as a function of Myc expression. There was no synergy demonstrated between ODN E1C with cisplatin (DDP), which inhibited tumor growth by 77% alone and 82% in combination. Although E2C inhibited growth by 54%, its effect was decreased to 32% with DDP, when compared with controls. E3C, on the other hand, demonstrated a synergistic effect with DDP, inhibiting growth by 72% in combination, but only by 1% as a single agent. Immunofluorescence analysis of tumors for each group revealed a concomitant reduction in c-Myc expression in tumors from mice treated with the most active clamp ODN alone (E1C) or clamp ODN + DDP (E1C/E3C + DDP). Western blot analysis confirmed this decrease in target protein expression. Our results document the growth-inhibitory activity of two myc-targeting antisense clamp ODNs; E1C, which has activity as a single agent, and E3C, which has in vivo synergy with DDP pretreatment. These data confirm the antiproliferative effects of these novel ODNs and document an interesting synergy with the chemotherapeutic agent DDP.

Targeted Gene Correction with 5′ Acridine-Oligonucleotide Conjugates

“…As previously observed in other uses of intercalating agents (Brunet et al, 2005;Stewart et al, 2001Stewart et al, , 2002, we have found that psoralen activity was less important than the acridine one (Figs. 1B and 2).…”

“…Acridine and psoralen both comprise hydrophobic tricyclic ring and present similar mode of intercalation. Acridine might provide a more stable hybridization and a better intracellular delivery (Brunet et al, 2005;Stewart et al, 2002). Psoralen is actually mainly used in association with irradiation, as a photoactive DNA crosslinker or as a mutagen of triplex sites (Wang et al, 1995).…”

The future of antisense therapy: combination with anticancer treatments

“…When administered in combination with cisplatin, INX-6295 produces a complete tumor regression in approximately 30% of treated mice . The efficacy of cMyc downregulation to inhibit cell proliferation and to synergize with cisplatin in melanoma cells has been subsequently observed by other authors by using psoralen-and acridine-modified ASOs (Stewart et al, 2001(Stewart et al, , 2002. A dose-escalation phase I clinical study in combination with cisplatin has been completed on patients with solid tumors and lymphomas (Gelmon et al, 2001).…”

Small-molecule inhibitors of c-Myc transcriptional factor suppress proliferation and induce apoptosis of promyelocytic leukemia cell via cell cycle arrest

“…23 This chemotherapy-sensitivity characteristic of leukemia encourages researchers to find more specific and potent drugs. For instance, several agents have been found that reduce the expression of c-Myc oncoprotein, work in cell lines 24,25 and inhibit the dimerization of Myc/Max protein. [26][27][28] In the present study, we prepared recombinant c-Myc and Max encompassing the human-origin DNA binding (basic) and dimerization (HLHZip) domains, tested the inhibitory effect of 6480 small molecules on the formation of the c-Myc/Max/DNA complex, and selected 5 compounds as potent inhibitors.…”