Summary Under certain circumstances sequence-specific inhibition of gene expression may be achieved in intact cells using exogenous anti-sense oligodeoxynucleotides. The efficacy of this approach to investigating gene function is limited in part by the rapid serum nuclease mediated degradation of oligodeoxynucleotides in culture media. In order to determine the relative contributions of 3'-exonuclease, 5'-exonuclease and endonuclease activity in fetal calf serum to oligodeoxynucleotide destruction, we have tested chimeric N-ras anti-sense sequence molecules protected against exonuclease attack with terminal methylphosphonate diester linkages. An 18-mer with two methylphosphonate diester linkages at the 3'-terminus, a 20-mer with two methylphosphonate diester groups at both ends, and the 16-mer 3'-methylphosphonate monoester components of their respective piperidine hydrolysates were totally resistant to venom phosphodiesterase, whereas the 16-mer 3'-hydroxyl components of the hydrolysates were rapidly degraded. Both the chimeric oligodeoxynucleotides and 3'-methylphosphonate monoesters were considerably more stable than normal 3'-hydroxyl oligodeoxynucleotides at 37'C in McCoy's 5A medium containing 15% heat inactivated fetal calf serum. Typically 20-30% of the former (initial concentration 10-100 jM) remained intact at 20 h as compared to the latter which were 88-100% degraded in 4 h and undetectable at 20 h. We conclude that a 3'-phosphodiesterase activity is a predominant nuclease responsible for oligodeoxynucleotide degradation by fetal calf serum, and that for cell culture studies, significant protection of oligodeoxynucleotides may be achieved by incorporating 3'-terminal methylphosphonate diester or even monoester end groups.
Summary Forty-six previously untreated patients with advanced ovarian cancer were treated with combination chemotherapy comprising cisplatin 80mgm 2 i.v. and cyclophosphamide 1 gm-2 i.v. every 28 days for 5 cycles. Eighty-five percent of patients received more than 75% of the calculated doses, and of 43 evaluable patients, a complete response was achieved in 31 (72%), a partial response in 4 (9.3%) and 8 patients had static or progressive disease. The actuarial survival of the whole group is 60% at a median follow-up of 2 years. Twenty-four patients in complete clinical or pathological remission were then treated with whole abdominal radiotherapy 2,500cGy followed by a pelvic boost of 2,000cGy. The pelvic boost was omitted in 3 patients, and the overall radiotherapy treatment time extended in a further 4 patients on account of myelosuppression. The actuarial survival of the 24 patients receiving both treatments at a median of 30 months follow-up is 75%. In the 10 patients with negative second-look procedures completing both treatments there have been no tumour related deaths at a median follow-up of 33 months.
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