Patent ID: 8883718

Claim:
A cyclic peptide which comprises: (i) a CDK4 peptide region; and (ii) a cell-penetrating region; wherein the CDK4 peptide region comprises the amino acid sequence P 1 R 1 x 1 y 1 R 2 P 2 V (SEQ ID NO: 1), in which P 1 and P 2 are each proline, R 1 and R 2 are each arginine and each of x 1 and y 1 are either a linker or proline, wherein if x 1 is a linker then y 1 is proline or if x 1 is proline then y 1 is a linker, or wherein x 1 and y 1 when taken together form a linker, and wherein V may be present or absent; wherein each amino acid is the L stereoisomer or wherein the valine residue of the amino acid sequence P 1 R 1 x 1 y 1 R 2 P 2 V (SEQ ID NO: 1) of the CDK4 peptide region is the D stereoisomer and all other amino acids in the cyclic peptide are the L stereoisomer; and wherein the cell-penetrating region is capable of enhancing the uptake of the cyclic peptide or a part thereof into cancer cells and comprises an amphiphilic amino acid sequence; and wherein the cyclic peptide or a part thereof is cytotoxic to and/or inhibiting to the growth of a cancer cell.