Designing a drug that specifically targets and inhibits dihydrofolate reductase DHFR in cancer cells without affecting healthy cells can be achieved through a multi-step process. Here is a possible approach:1. Identify differences between cancerous and healthy cells: The first step is to identify specific differences in the structure, function, or expression of DHFR in cancer cells compared to healthy cells. These differences can be exploited to design a drug that selectively targets the cancer-associated form of the enzyme.2. High-throughput screening: Develop a high-throughput screening assay to identify potential drug candidates that selectively inhibit the cancer-associated DHFR. This can be done by testing a large library of small molecules for their ability to inhibit the enzyme in vitro, while not affecting the healthy cell-associated DHFR.3. Structure-based drug design: Utilize the crystal structures of both the cancer-associated and healthy cell-associated DHFR to guide the design of small molecules that selectively bind to and inhibit the cancer-associated enzyme. This can be done using computational methods, such as molecular docking and molecular dynamics simulations, to predict the binding affinity and specificity of potential drug candidates.4. Optimization of drug candidates: Once potential drug candidates have been identified, optimize their chemical structure to improve their potency, selectivity, and pharmacokinetic properties. This can be done through medicinal chemistry approaches, such as structure-activity relationship SAR studies and optimization of physicochemical properties.5. In vitro and in vivo testing: Test the optimized drug candidates in vitro using cell-based assays to confirm their selective inhibition of cancer-associated DHFR and their ability to inhibit cancer cell proliferation. Then, evaluate the drug candidates in vivo using animal models of cancer to assess their efficacy, safety, and pharmacokinetic properties.6. Clinical trials: If the drug candidates show promising results in preclinical studies, proceed to clinical trials to evaluate their safety and efficacy in human patients.By following this approach, it is possible to design a drug that selectively targets and inhibits DHFR in cancer cells, without affecting healthy cells. This would provide a more targeted and potentially less toxic treatment option for cancer patients.