This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Chemotherapy: General Principles, Subject name: Pharmacology
[{'content': 'Methotrexate resistance is due to: \nSelect and explain. \nA. Depletion of folate, B. Overproduction of DHFRase, C. Overproduction of thymidylate kinase, D. Decreased DHFRase', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. (B) Overproduction of DHFRase(Ref: Goodman and Gilman, 11th/e p1336)Mechanisms of methotrexate resistanceImpaired transport of methotrexate into cellsProduction of altered forms of DHFR that have decreased affinity for the inhibitorIncreased concentrations of intracellular DHFR through gene amplification or altered gene regulationDecreased ability to synthesize methotrexate polyglutamatesIncreased expression of a drug efflux transporter, of the MRP (multidrug resistance protein) class.', 'role': 'assistant'}]