Promotion of triplex formation by morpholino modification: thermodynamic and kinetic studies.

We examined the effect of morpholino (MOR) backbone modification of triplex-forming oligonucleotide (TFO) on the pyrimidine motif triplex formation at neutral pH, a condition where pyrimidine motif triplexes are unstable. The binding constant of the pyrimidine motif triplex formation at pH 6.8 with MOR-modified TFO was approximately 60 times larger than that observed with unmodified TFO. Kinetic data demonstrated that the observed increase in the binding constant at neutral pH by the MOR backbone modification resulted mainly from the considerable increase in the association rate constant. The present results certainly support the idea that the MOR backbone modification of TFO could be a key modification and may eventually lead to progress in therapeutic applications of the antigene strategy in vivo.