A 80-year-old male patient recently diagnosed with non-Hodgkin's lymphoma was staed on treatment with R- CHOP chemotherapy regimen. After few days, the patient comes to the clinic with complaints of tingling in his hands and feet. Neurological examination shows symmetric "stocking and glove" type distal neuropathy. If the patient's symptoms are believed to be due to chemotherapy regimen, the drug responsible for these symptoms causes cell cycle arrest during which of the following stages?