Phase I – Dose evaluation To investigate feasibility of induction therapy with low dose Ara-C (20 mg/m2 sc injection d1-d14) and clofarabine at three different dose levels for the first induction cycle (Clofarabine 10, 15 or 20 mg/m2 1h iv infusion d1-d5). Phase II – Safety To assess safety (in terms of AEs/ARs, SAEs/SARs and Adverse reactions CTC grade 4 (AR4)) of induction therapy with low dose AraC in combination with Clofarabine (at the dose level resulting from the dose evaluation phase of the trial).