Novel peptides from the RAS-p21 and p53 proteins for the treatment of cancer.

We have employed a novel computer-based molecular modeling method to design peptides from the ras-p21 and p53 proteins that block proliferation of cancer cells. The rationale of our approach is to identify peptide domains from each protein that alter conformation in response to oncogenic amino acid substitutions in their polypeptide chain. We accomplish this by first generating and comparing low energy average structures for oncogenic and wild-type proteins using conformational energy calculations. Peptides are then synthesized corresponding to these domains. These domains are then linked to a trans-membrane-penetrating sequence (called penetratin) and tested against cancer and untransformed cell lines. Remarkably, we have found that two ras-p21 peptides, 35-47 and 96-110, called PNC-7 and PNC-2, respectively, can induce phenotypic reversion of ras-transformed TUC-3 pancreatic cancer cells and ras-transformed HT1080 human fibrosarcoma cells to their untransformed phenotypes. Moreover, both peptides were found to be cytotoxic to ras-transformed human MIA-PaCa-2 pancreatic carcinoma cells and human U-251 astrocytoma cells. Importantly, these peptides have no effect on the growth of their normal cellular counterparts. We have also synthesized peptides from the p53 protein corresponding to its hdm-2-binding domain sequences (residues 12-26), also linked to the penetratin sequence. Surprisingly, we have found that these peptides induce 100 percent tumor cell necrosis, not apoptosis, in 13 different human cancer cell lines but have no effect on normal pancreatic acinar cells, breast epithelial cells, and human stem cells. Moreover, these peptides are cytotoxic to TUC-3 pancreatic tumor cells in nude mice plus eradicate these tumor cells when administered at sites near these tumors. These novel peptides appear to hold much promise as new, non-toxic anti-cancer agents.