A 50 years okl smoker and hypeensive was diagnose to have non-small cell lung carcinoma with brain metastases. He is on enalapril and hydrochlorothiazide for hypeension. On investigation, he had a serum Sodium 120 mg/dl|, Urinary Sodium ll0 mg/dl, Serum creatinine 0.8 mg/dL, Serum osmolarity 285 mOsm/L, Urinary osmolarity 35l mOsm/L, Urinary K+ 9 mg/dl, Blood sugar ll2 mgldL and BP of 150/90 mm Hg. Which of the following is the mnst probable cause for his hyponatremia?