Vion Pharmaceuticals Inc said that licensee Boehringer Ingelheim of Germany put further clinical studies of Viox's anti-cancer agent Promycin on hold because a Phase III trial was not meeting pre-determined criteria in an interin evaluation.

In the trial, Promycin was combined with radiotherapy versus radiotherapy alone in patients with head and neck cancer.

Boehringer maintains full managerial and financial responsibility for Promycin's development.

Under an amended agreement, Vion had accepted reduced milestone and royalty payments on all future sales.

A follow-up of all enrolled patients is planned. Final results will be reported when the study has passed the pre-determined number of events needed for full analysis.

Vion is disappointed with the interim evaluation results and Boehringer is making ``an extensive effort'' to further analyse and understand the data, Vion President and CEO Alan Kessman said in a statement.

Vion is focusing on clinical development of TAPET, a platform technology for drug delivery in cancer, and Triapine, a potent DNA synthesis and repair inhibitor that has demonstrated substantial activity in animal tumour models, Kessman said.

It is also in late preclinical development with a Sulfonyl Hydrazine Prodrug (SHP), an alkylating agent with broad antitumor activity in animal models, he said.

The company believes that TAPET, Triapine and SHPs ``are the product technologies that will form the foundation for our future success,'' Kessman said.