Hydroxyurea mechanism of action in cancer is by inhibiting the enzyme -

Ans. is 'a' i.e., Ribonucleoside diphosphate reductase Hydroxyureao It blocks the conversion of ribonucleotides to deoxyribonucleotides by inhibiting the enzyme ribonucleoside diphosphate reductase; thus inhibits the DNA synthesis; S phase specific,o Myelosuppression is the major toxicity. GI disturbances and cutaneous reactions (pigmentation) also occur,o It is used in CML, psoriasis, polycythemia vera and some solid tumors.o It is also used as radiosensitizer before radiotherapy and is a first line drug for sickle cell disease in adults.