About topotecana topoisomerase i inhibitor, natural source (plant) derivative, antineoplastic.mechanism of action of topotecanthis antineoplastic drug inhibits the action of enzyme topoisomerase 1(this enzyme produces reversible single strand breaks in dna during dna replication) by binding to it. this results topoisomeras1-dna complex and prevents the relegation of dna strand, resulting in double strand dna breakage and cell death. the drug has also radiation-sensitizing ability. indications for topotecan1. ovarian cancer 2. lung cancer 3. chronic myelomonocytic leukemia (cmml) 4. myelodysplastic syndrome (mds) 5. glioma 6. multiple myeloma 7. neuroblastoma 8. pancreatic cancer 9. rhabdomyosarcoma 10. ewing`s sarcoma