The invention relates to pharmaceutical compositions comprising a zinc2+ salt and a α-polyglutamic acid carrier, and, optionally, an NF-κB inhibitor as a tumor-sensitizing agent, and methods for using such compositions to treat tumors in patients. Methods include administering a liquid dosage form or a solid dosage form of a therapeutically effective amount of a Zn(II) salt and a α-polyglutamic acid carrier to a patient in need thereof. Methods of treating a broad spectrum of human tumors, including tumors with a drug-resistant phenotype, using the disclosed compositions are provided. Tumors that respond to the pharmaceutical compositions disclosed herein include neuroendocrine (neuroblastoma), gastric, uterine, and lung tumors.
