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A p53-derived C-terminal peptide induced rapid apoptosis in breast cancer cell lines carrying endogenous p53 mutations or overexpressed wild-type (wt) p53 but was not toxic to nonmalignant human cell lines containing wt p53. Apoptosis occurred through a Fas/APO-1 signaling pathway involving increased extracellular levels of Fas/FasL in the absence of protein synthesis, as well as activation of a Fas/APO-1-specific protease, FLICE. The peptide activity was p53-dependent, and it had no effect in three tumor cell lines with null p53. Furthermore, the C-terminal peptide bound to p53 protein in cell extracts. Thus, p53-dependent, Fas/APO-1 mediated apoptosis can be induced in breast cancer cells with mutant p53 similar to the recently described Fas/APO-1 induced apoptosis by wt p53. However, mutant p53 without p53 peptide does not induce a Fas/ APO-1 activation or apoptosis. Docking of the computed low energy conformations for the C-terminal peptide with those for a recently defined proline-rich regulatory region from the N-terminal domain of p53 suggests a unique low energy complex between the two peptide domains. The selective and rapid induction of apoptosis in cancer cells carrying p53 abnormalities may lead to a novel therapeutic modality.

We have synthesized three peptides from the mdm-2 binding domain of human p53, residues 12-26 (PPLSQETFSDLWKLL), residues 12-20, and 17-26. To enable transport of the peptides across the cell membrane and at the same time to maximize the active mdm-2 binding ␣-helical conformation for these peptides, each was attached at its carboxyl terminus to the penetratin sequence, KKWKMRRNQF-WVKVQRG, that contains many positively charged residues that stabilize an ␣-helix when present on its carboxyl terminal end. All three peptides were cytotoxic to human cancer cells in culture, whereas a control, unrelated peptide attached to the same penetratin sequence had no effect on these cell lines. The same three cytotoxic peptides had no effect on the growth of normal cells, including human cord blood-derived stem cells. These peptides were as effective in causing cell death in p53-null cancer cells as in those having mutant or normal p53. Peptide-induced cell death is not accompanied by expression of apoptosis-associated proteins such as Bax and waf p21 . Based on these findings, we conclude that the antiproliferative effects of these p53-derived peptides are not completely dependent on p53 activity and may prove useful as general anticancer agents.

Abstractβ-Cell mass (BCM) influences the total amount of insulin secreted, varies by individual and by the degree of insulin resistance, and is affected by physiologic and pathologic conditions. The islets of Langerhans, however, appear to have a reserve capacity of insulin secretion and, overall, assessments of insulin and blood glucose levels remain poor measures of BCM, β-cell function and progression of diabetes. Thus, novel noninvasive determinations of BCM are needed to provide a quantitative endpoint for novel therapies of diabetes, islet regeneration and transplantation. Built on previous gene expression studies, we tested the hypothesis that the targeting of vesicular monoamine transporter 2 (VMAT2), which is expressed by β cells, with [ 11 C]dihydrotetrabenazine ([ 11 C]DTBZ), a radioligand specific for VMAT2, and the use of positron emission tomography (PET) can provide a measure of BCM. In this report, we demonstrate decreased radioligand uptake within the pancreas of Lewis rats with streptozotocininduced diabetes relative to their euglycemic historical controls. These studies suggest that quantitation of VMAT2 expression in β cells with the use of [ 11 C]DTBZ and PET represents a method for noninvasive longitudinal estimates of changes in BCM that may be useful in the study and treatment of diabetes.