Cyclobenzaprine hydrochloride (MK130 hydrochloride) , a centrally acting muscle relaxant with antidepressant activity, leads to a reduction in muscle spasms.

DNA synthesis assay : The rate of DNA synthesis is measured by the incorporation of radioactive thymidine into DNA. HL-60 and KG1a cells are suspended in 2 mL RPMI medium containing 10% fetal serum in 6-well (35 mm diameter) dishes and incubated with different concentrations of corresponding drugs for 48 hours (drugs are added simultaneously). At 48 hours, 0.5 μCi [3H] thymidine (6.7 Ci/mmol) is added to each well and incubated for an additional 24 hours. The cells are placed on GF/C glass fiber filters (2.4 cm diameter), washed with cold 0.9% NaCl, 5% cold trichloroacetic acid and ethanol. The filters containing the DNA are then dried, placed in EcoLite scintillation liquid (ICN) and the radioactivity measured using Beckman LS 6000IC scintillation counter. The IC50 is defined as the concentration of drug that inhibits 50% of the DNA synthesis of the leukemic cell lines from the dose–response curve.