In the single agent Phase I dose-escalation phase patients will be enrolled and assigned to a dose level cohort. The starting dose will be 750 mg/m2, which equals to 1/10 of the human equivalent dose of the LD10 of DTP348 in mice.

A "3+3" dose-escalation design will be used. The study will investigate sequential cohorts consisting of 3-6 patients to be enrolled and treated at the applicable dose level. Planned dose levels for subsequent cohorts are 1000, 1250 mg/m2 and steps of 250 mg/m2 thereafter. There will be no intra-patient dose escalation. The treatment cycle in the dose-escalation part of the study will consist of 7 weeks (reflecting the typical duration of the course of radiotherapy). Patients will receive a continuous oral dose of DTP348 for 7 days per week. Food intake is not allowed one hour before and after the intake of the study drug. After the cycle of treatment, the patient will be followed until disease progression.

Blood samples for pharmacokinetic properties (PK) will be obtained on day 1 during the first 8 hours after oral administration and then daily on day 2, 3, 4 and 5, before the administration of the daily dosage. A patient will stay on treatment until disease progression, unacceptable toxicity, or discontinuation for any other reason. The dose limiting toxicity (DLT) observation period for each dose level will be day 1 until the end of week 7. Patients who do not complete the DLT observation period for other reasons than a DLT will be replaced.

Toxicity that can be expected from DTP348 is related to the nitro-imidazole compound and includes nausea, vomiting flushing, dizziness, skin rash, and neurotoxicity. Related to the sulfamide component in the study drug, the side-effects may include nausea and vomiting. In the experimental mice study, no toxicity was observed using a dose of 10 mg/kg i.v. 3 and up to 400 mg/kg per os, which corresponds to the Human Equivalent Dose (HED) of 1.2 g/m2 of nimorazole. Once the Maximum Tolerated Dose (MTD) of DTP348 has been established, 3 additional patients will be included in that dose-level. These patients will receive crushed tablets and undergo blood sampling for PK to investigate whether the administration of crushed tablets affects uptake and plasma levels of the study drug. This group of patients is added because of the frequent occurrence of swallowing problems in the HNSCC patient population and the use of tube feeding with the need of crushing tablets.

Once the MTD of DTP348 as single agent has been determined, the study will continue to the combination phase: In the DTP348 in combination with radiotherapy dose-escalation phase, again a 3+3 dose-escalation design will be used. The starting dose of DT348 will be the MTD minus two dose levels. DTP348 will be given continuously 7 days a week, starting 2 weeks before and during the whole course of radiation until and including the last day. The rationale to start the study drug 2 weeks before the start of radiotherapy is to have a similar design as in the phase II trial which will be performed following this study. The drug will be given orally 1-2 hours before the daily delivery of radiotherapy. Food intake is not allowed one hour before and after the intake of the study drug. The dose limiting toxicity (DLT) observation period for each dose level will be from day 1 of combined therapy until 4 weeks after the end of therapy. Patients who do not complete the DLT observation period for other reasons than a DLT will be replaced.

The radiation treatment in the DTP348 in combination with radiotherapy dose-escalation phase will be either conventional standard fractionated radiotherapy to a total dose of 70 Gy in 35 fractions over 7 weeks with a concomitant boost technique, 5 fractions a week or accelerated radiotherapy delivering a total dose to 68-70 Gy in a shortened overall treatment time (5.5 - 6 weeks). The 95% isodose of the prescribed dose should encompass at least 99% of the planning target and homogeneity will be according to ICRU guidelines. There is no restriction of the treatment techniques that may be used: multiple static conformal or intensity modulated beams, intensity modulated arc treatments, or robotic, non-isocentric treatments. Dummy run on virtual patients will need to be performed before inclusion. Subsequently, patients are allowed to be included in the trial.