A 64-year-old woman had a blood pressure (BP) of 162/90 mmHg during a physical exam 6 months ago, with normal urinalysis (UA) and renal function. She was then treated with captopril. One month ago, she developed nocturia, fatigue, and BP of 190/110 mmHg. UA showed protein (+), renal function tests revealed blood urea nitrogen (BUN) 16 mmol/L, creatinine (Cr) 324 μmol/L, and serum potassium (K) 3.0 mmol/L. Renal ultrasound showed left kidney 11.8 cm × 5.2 cm and right kidney 9.0 cm × 3.8 cm. Based on these findings, the most likely diagnosis is: