Targeting AKT with the proapoptotic peptide, TAT‐CTMP: A novel strategy for the treatment of human pancreatic adenocarcinoma

Abstract

Pancreatic adenocarcinoma carries an ominous prognosis and has little effective treatment. Several studies have demonstrated that the potently anti-apoptotic phosphatidyl inositol 3’-kinase (PI3K) - protein kinase B/AKT pathway is active in pancreas cancer. A recent study identified an endogenous AKT antagonist, carboxyl terminal modular protein (CTMP). CTMP inhibits the phosphorylation of AKT, preventing full activation of the kinase. We screened several cell permeable peptides from the N-terminal domain of CTMP (termed TAT-CTMP1 - 4) in vitro and found one that caused significant apoptosis in pancreatic adenocarcinoma cell lines. An inactive variant of this peptide was synthesized and used as a negative control. In all cell lines tested, TAT-CTMP4 induced a dose-dependent increase in apoptosis as detected by %-TUNEL positive cells and %-active caspase-3 (% active caspase-3 ranged from 31.2 to 61.9 at the highest dose tested (10µM)). A screening of various cell and tissue types revealed that the pro-apoptotic activity was highest in pancreatic adenocarcinoma. TAT-CTMP induced similar levels of active caspase-3 as several other known inducers of apoptosis: gemcitabine, radiation therapy, wortmannin, and recombinant tumor necrosis factor (TNF)-α. No apoptosis was observed in donor human peripheral blood mononuclear cells (PBMC, P<0.01). We further showed that TAT-CTMP4 could augment either gemcitabine chemotherapy or radiation therapy, standard therapies for pancreas cancer. Pancreatic adenocarcinoma xenografts, treated with a single dose of TAT-CTMP4 demonstrated a marked increase in caspase-3 positive tumor cells when compared to untreated controls. Additionally, pancreatic adenocarcinoma allografts treated with intratumoral TAT-CTMP and systemic gemcitabine displayed a significantly smaller tumor burden while undergoing treatment than mice in control groups (P<0.001). These data indicate that inhibiting AKT with CTMP may be of therapeutic benefit in the treatment of pancreatic adenocarcinoma and, when combined with established therapies, may result in an increase in tumor cell death.

Carboxyl-Terminal Modulator Protein Positively Regulates Akt Phosphorylation and Acts as an Oncogenic Driver in Breast Cancer

“…polypeptides derived from CTMP N-terminal domain in pancreatic cancer cells (36). The antiproliferation and apoptotic effects of CTMP have also been shown in different in vitro cell models (22,37,38).…”

Carboxyl‐Terminal Modulator Protein Ameliorates Pathological Cardiac Hypertrophy by Suppressing the Protein Kinase B Signaling Pathway

“…Although dysregulation of AKT signaling is implicated in a broad range of diseases, including cancer, brain disorders, and diabetes mellitus, the CTMP‐AKT axis has been reported to possess different functions in certain contexts because of different pathological processes. Inhibiting AKT signaling with CTMP may have an ameliorative effect in the treatment of liver cancer,12 lung cancer,13, 41 and pancreatic adenocarcinoma 8. In contrast, CTMP had the opposite effect on neuroprotection after brain injury9, 14, 17, 42 and insulin resistance,15 via restraining AKT signaling.…”

“…Carboxyl‐terminal modulator protein (CTMP), also known as thioesterase superfamily member 4, contains 2 functional domains, including a C‐terminal thioesterase domain and a conserved mitochondrial‐related N‐terminal domain 8, 9. CTMP is ubiquitously expressed in various tissues, including the heart 10.…”

“…On cell death stimulation, CTMP is released to the cytosol and makes cells sensitive to apoptosis 11. Meanwhile, accumulating evidence suggests that CTMP plays vital roles in numerous pathological processes, such as tumor,8, 12, 13 neuroprotection,14 and metabolism 15. Initially, CTMP has been determined to exert a complex influence in multiple cancers by regulating cell survival, proliferation, and angiogenesis 12, 13, 16.…”

Challenges of drug resistance in the management of pancreatic cancer

“…Inhibition of Akt using a cell-permeable derivative of the proapoptotic peptide and Akt antagonist C-terminal modulator protein (CTMP; termed TAT-CTMP) in combination with gemcitabine or radiation therapy augments the effects of gemcitabine and radiotherapy in vitro and in vivo [34]. NF-κB plays an important role in cancer progression and increased expression promotes cellular resistance to anticancer therapy.…”