Disclosed are isolated cytotoxic peptides having similar sequences as the basic region (BR) of Hexamethylene Bisacetamide Inducible Protein 1 (HEXIM1). Preferred embodiments include QLGKKKHRRRPSKKKRHW (SEQ ID No: 3). QLGRRRHRRRPSRRRRHW (SEQ ID No: 4) and QLGKKILAARPSKKKRHW (SEQ ID No: 5). Also encompassed are isolated nucleic acid molecules encoding for the claimed peptides, vectors comprising the isolated nucleic acids, compositions comprising peptides conjugated to cell-targeting or penetrating peptides or antibodies, nucleic acid molecules or vectors expressing conjugates thereof； methods of treating or preventing diseases or conditions, including cancers and obesity as well as a method of eliminating undifferentiated stem cells.
