Antineoplastic effect of decoy oligonucleotide derived from MGMT enhancer.

Silencing of O(6)-methylguanine-DNA-methyltransferase (MGMT) in tumors, mainly through promoter methylation, correlates with a better therapeutic response and with increased survival. Therefore, it is conceivable to consider MGMT as a potential therapeutic target for the treatment of cancers. Our previous results demonstrated the pivotal role of NF-kappaB in MGMT expression, mediated mainly through p65/NF-kappaB homodimers. Here we show that the non-canonical NF-KappaB motif (MGMT-kappaB1) within MGMT enhancer is probably the major inducer of MGMT expression following NF-kappaB activation. Thus, in an attempt to attenuate the transcription activity of MGMT in tumors we designed locked nucleic acids (LNA) modified decoy oligonucleotides corresponding to the specific sequence of MGMT-kappaB1 (MGMT-kB1-LODN). Following confirmation of the ability of MGMT-kB1-LODN to interfere with the binding of p65/NF-kappaB to the NF-KappaB motif within MGMT enhancer, the efficacy of the decoy was studied in-vitro and in-vivo. The results of these experiments show that the decoy MGMT-kB1-LODN have a substantial antineoplastic effect when used either in combination with temozolomide or as monotherapy. Our results suggest that MGMT-kB1-LODN may provide a novel strategy for cancer therapy

<i>In-vivo</i> efficacy of long-term repetitive intralesional administration of the compound drug (kB1-MGMT-LODN and the carrier) in A375P human melanoma xenografts.

<p>Kaplan Meier survival curve of mice bearing A375P subcutaneous xenograft. IL treatment with either 25 ug of MGMT-kB1-LODN or with control ODN or with vehicle (5% glucose) was started once tumor volume approached 75 mm³ (on day 6 post inoculation) and treatment was repeated every 4 to 5 days for up to 55 days after tumor induction.</p

The activity induced by the NF-kappaB sites within the MGMT enhancer and their corresponding mutant sites as measured by luciferase fold induction.

<p>The HEK293T cell line was transiently transfected with a reporter gene construct either alone or with other plasmids as indicated on the graph. The CMVβ-galactosidase expression vector (CMVβgal) was included in each transfection to normalize the transfection efficiency. The observed enhancer activity is relative to the corresponding reporter plasmid transfected alone. An asterisk indicates a significant difference <i>(p<0.05)</i> compared with the control (reporter plasmid transfected alone).</p

Interference with NF-kappaB binding to the MGMT-NFkB1 site using LODN (locked modified ODN).

<p>The HEK293T cell line was transiently transfected with either the kB1-MGMT-luc or pNF-kB-Luc reporter gene construct together with NFkappaB/p65. LODN corresponding to the MGMT-kB1 site were added at the indicated concentrations. The CMVβ-galactosidase expression vector (CMVβgal) was included in each transfection to normalize the transfection efficiency. The observed enhancer activity is relative to the corresponding reporter plasmid transfected with NFkappaB/p65. All concentrations of MGMT-kB1 LODN significantly reduced the levels of luciferase expression <i>(p<0.05)</i> compared with cells transfected with control ODN. The control bars indicate the average inhibition of three different concentrations of ODN as indicated for MGMT-kB1 LODN. An asterisk indicates a significant difference of <i>p<0.05</i> and a double asterisk indicates <i>p<0.01</i>.</p

The cytotoxic efficacy of MGMT-kB1-LODN treatment given either in sequence with Temozolomide or as a monotherapy in three tumor cell lines.

<p>The effect of combination treatment with MGMT-kB1-decoy LMODNs and TMZ in three tumor cell lines (A) T98G, (B) U87MG and (C) A375P. The cells were transfected with the indicated concentrations of MGMT-kB1-LODN, and 3 hrs later were treated with the indicated doses of TMZ. The percentage of cell survival was evaluated 72 hrs later. (D) The effect of MGMT-kB1-LODN as a monotherapy. Each point represents the average viability percentage ± SEM. (A, B) An asterisk indicates a significant difference of <i>p<0.05</i> and double asterisk indicates <i>p<0.01</i>, between cells treated with MGMT-kB1-LODN and untreated cells. (D) The results are expressed as percentage of cell survival compared with cells treated with control ODN.</p

<i>In-vivo</i> efficacy of the compound drug (kB1-MGMT-LODN and the carrier) with or without temozolomide in A375P human melanoma xenografts.

<p>Athymic nude mice were inoculated subcutaneously with 5*10⁶ tumor cells (A375P) and randomized into treatment groups. (A) a single dose of IP treatment (indicated by red arrows) was administered as follows: 10% DMSO (control) or TMZ at a dose of 100 mg/kg or 200 mg/Kg or 300 mg/kg. (B) Treatment started on day 5 when the tumors grew to an approximate size of 75 mm³. Mice were injected IL (indicated by black arrows) with 25 ug of MGMT-kB1 LODN or with vehicle (5% glucose) on days 5 and 7. On day 6 IP treatments (red arrow) were given with either 100 mg/kg TMZ or with vehicle (10% DMSO). An asterisk indicates a significant difference <i>(p<0.05)</i> between the treated and control group (10% DMSO). Each point represents the average tumor size ± SEM.</p