Hi Gavanji , What is the kind of this anticancer study? I mean what is the model you are using? You want to induce tumor model of liver, kidney, heart or what?
What sort of substitute are you looking for? If you just want something to kill cancer cells, you have literally thousands of options. If you want something else that interferes with DNA, you still have more options than can be reasonably listed.
If you want something that also interferes with DNA, is also given to patients in the clinic, and should be applicable to a certain model system (say, brain cancer), then one might narrow it down - in that case, I'd recommend temozolomide or carmustine, for instance.
But as Abdallah indicates, your question is just way too broad to be meaningfully answered.
for example in acute myeloblastic leukemia instead of doxorobicin you can use daunorubicin and if resistant the or relapse the to start with mitoxantrone