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Cervical cancer is a second leading cancer death in women world-wide, with most cases in less developed countries. Notch signaling is highly conserved with its involvement in many cancers. In the present study, we established stable cervical cell lines with Notch activation and inactivation and found that Notch activation played a suppressive role in cervical cancer cells. Meanwhile, the transient overexpression of the active intracellular domain of all four Notch receptors (ICN1, 2, 3, and 4) also induced the suppression of cervical cancer Hela cell growth. ICN1 also induced cell cycle arrest at phase G1. Notch1 signaling activation affected the expression of serial genes, especially the genes associated with cAMP signaling, with an increase of genes like THBS1, VCL, p63, c-Myc and SCG2, a decrease of genes like NR4A2, PCK2 and BCL-2. Particularly, The nuclear receptor NR4A2 was observed to induce cell proliferation via MTT assay and reduce cell apoptosis via FACS assay. Furthermore, NR4A2's activation could reverse ICN1-induced suppression of cell growth while erasing ICN1-induced increase of tumor suppressor p63. These findings support that Notch signaling mediates cervical cancer cell growth suppression with the involvement of nuclear receptor NR4A2. Notably, Notch/NR4A2/p63 signaling cascade possibly is a new signling pathway undisclosed.

Background: Human pancreatic carcinoids, a type of neuroendocrine tumors, are asymptomatic and difficult to diagnose, with the effects of traditional anti-cancer therapies being limited. The histone deacetylase (HDAC) inhibitor valproic acid (VPA) was evaluated for its effects alone and in combination with receptor-targeting peptide-drug conjugate via increasing drug internalization., Materials and Methods: The in vitro and in vivo assays were used to evaluate the effects of VPA and somatostatin receptor-targeting camptothecin-somatostatin conjugate (CPT-SST)., Results: VPA induced proliferation suppression, cell apoptosis and cell cycle arrest. VPA acts as a HDAC inhibitor to induce a decrease of HDAC4 and an increase of acetylated histone 4 (AcH4). Meanwhile, most importantly, besides activating Notch signaling, VPA was observed to stimulate the expression of somatostatin receptor type 2 (SSTR2) that has been applied for receptor-targeting therapies. This characteristic was used for a combination therapy of VPA and CPT-SST. The combination displayed much more potent anti-tumor effects on carcinoid tumor growth by increasing SSTR2 density and drug internalization in target tumor cells., Conclusion: The combination of VPA and a SSTR2-targeting agent provides us a promising approach in treatment of carcinoid tumors.

Hepatocellular carcinoma (HCC) is a type of malignant cancer. Notch signaling is aberrantly expressed in HCC tissues with more evidence showing that this signaling plays a critical role in HCCs. In the present study, we investigate the effects of the anti-convulsant drug valproic acid (VPA) in HCC cells and its involvement in modulating Notch signaling. We found that VPA, acting as a histone deacetylase (HDAC) inhibitor, induced a decrease in HDAC4 and an increase in acetylated histone 4 (AcH4) and suppressed HCC cell growth. VPA also induced down-regulation of Notch signaling via suppressing the expression of Notch1 and its target gene HES1, with an increase of tumor suppressor p21 and p63. Furthermore, Notch1 activation via overexpressing Notch1 active form ICN1 induced HCC cell proliferation and anti-apoptosis, indicating Notch signaling played an oncogenic role in HCC cells. Meanwhile, VPA could reverse Notch1-induced increase of cell proliferation. Interestingly, VPA was also observed to stimulate the expression of G protein-coupled somatostatin receptor type 2 (SSTR2) that has been used in receptor-targeting therapies. This discovery supports a combination therapy of VPA with the SSTR2-targeting agents. Our in vitro assay did show that the combination of VPA and the peptide-drug conjugate camptothecin-somatostatin (CPT-SST) displayed more potent anti-proliferative effects on HCC cells than did each alone. VPA may be a potential drug candidate in the development of anti-HCC drugs via targeting Notch signaling, especially in combination with receptor-targeting cytotoxic agents.

Multiple Gαi protein-coupled somatostatin receptors (SSTRs) are expressed in human kidney and liver tissues. Also, aberrant cAMP signaling has been shown to play a critical role in cysto-genesis and enlargement of the human kidney and liver. Thus, somatostatin (SST) analogs become potential and promising alternatives in treating human polycystic kidney disease (PKD) and polycystic liver disease (PLD) via interacting with Gαi protein-coupled SSTRs and further blocking cAMP production. Lanreotide is a synthetic, long-acting SST analog with high binding affinity to SSTR2, and has been clinically approved for the treatment of acromegaly due to excessive growth hormone. Recently, this SST analog has been applied in the treatment of PKD and PLD, and has shown an effective reduction of liver and kidney volume compared to placebo. This review will discuss the discovery of this peptide and its clinical applications in the treatment of PKD/PLD patients.

The role of Notch signaling in cervical cancer is seemingly controversial. To confirm the function of Notch signaling in this type of cancer, we established a stable Notch1-activated cervical cancer HeLa cell line. We found that Notch1 activation resulted in apoptosis, cell cycle arrest, and tumor suppression. At the molecular level, we found that a variety of genes associated with cyclic AMP, G protein-coupled receptor, and cancer signaling pathways contributed to Notch1-mediated tumor suppression. We observed that the expression of somatostatin (SST) was dramatically induced by Notch1 signaling activation, which was accompanied by enhanced expression of the cognate SST receptor subtype 1 (SSTR1) and SSTR2. Certain genes, such as tumor protein 63 (TP63, p63), were upregulated, whereas others, such as B-cell lymphoma 2 (BCL-2), Myc, Akt, and STAT3, were downregulated. Subsequently, knockdown of Notch1-induced SST reversed Notch1-induced decrease of BCL-2 and increase of p63, indicating that Notch1-induced tumor suppression may be partly through upregulating SST signaling. Our findings support a possible crosstalk between Notch signaling and SST signaling. Moreover, Notch-induced SSTR activation could enhance SSTR-targeted cancer chemotherapy. Valproic acid (VPA), a histone deacetylase inhibitor, suppressed cell growth and upregulated the expression of Notch1 and SSTR2. A combination therapy with VPA and the SSTR2-targeting cytotoxic conjugate CPT-SST strongly led to greater suppression, as compared to each alone. Our findings thus provide us with a promising clinical opportunity for enhanced cancer therapy using combinations of Notch1-activating agents and SSTR2-targeting agents.

In our previous study, we found that several tumor cell lines displayed high receptor-specific binding affinity, one of which, the human pancreatic carcinoid BON cell line, demonstrates high affinity binding of the bombesin (BN) and somatostatin (SST) receptor-specific ligands. In the present study, BON cells, as a representative model, were further applied to evaluate various peptide analogs and cytotoxic receptor-targeted peptide conjugates. We observed quick ligand-receptor internalization in BON cells as well as high binding affinity. Furthermore, BON cells have high expression of multidrug resistance-associated genes (MDR1) and show camptothecin (CPT) resistance. Various receptor-specific cytotoxic conjugates were synthesized and evaluated in the BON cell model via in vitro and in vivo studies. We found that all the tested conjugates displayed potent antitumor ability in xenografts. Especially, the CPT conjugates, CPT-SST, and CPT-BN, are most likely to increase sensitivity to CPT-resistant BON cells. Our findings suggest that appropriately defined tumor cell lines may provide physiologically relevant cell-based evaluations of novel peptide analogs and receptor-targeted chemotherapeutics.

Many tumors highly express specific populations of G-protein-coupled receptors (GPCRs) that could be utilized for receptor-targeted therapy. We confirmed significant quantities of mRNAs specific for certain somatostatin (SST), vasoactive intestinal peptide (VIP), and bombesin (BN) receptors in various commercially available tumor cell lines. Very few of the tumor cell lines examined displayed the high receptor-binding affinity despite exhibiting the expression of appropriate mRNAs and proteins of the cognate receptors. However, binding assays establish that some tumor cell lines, such as pancreatic cancer CFPAC-1, prostate cancer DU-145, and pancreatic carcinoid BON, demonstrate high BN receptor binding. BON cells also demonstrate high somatostatin receptor (SSTR) affinity binding. We also found that tumor cell lines, such as BON and host cells expressing SST receptor subtypes 1 or 2 (CHO-R1 or CHO-R2), underwent a decrease in cell surface receptor density in multiple passages. BON and CHO-R2 cells also rapidly internalize a significant proportion of cell surface ligand-receptor complexes. The tumor cells CFPAC-1, DU-145, and BON with high receptor binding could be useful for peptide drug studies. BON cells were further applied to test SST/BN analogs and cytotoxic conjugates. Furthermore, the in vivo antitumor assay showed that the cytotoxic conjugate CPT-SST targeting all SSTR subtypes displayed a potent tumor-suppressive ability to BON tumors expressing multiple SSTR subtypes.

The major problems of traditional chemotherapy are non-selectivity and non-specificity, resulting in severe toxic side effects. Peptides are a new-generation of drug-delivery vector to increase efficacy of this therapy and avoid the resulting damage. The cytotoxic somatostatin (SST) conjugate JF-10-81 was developed by coupling camptothecin (CPT) to the N-terminus of a SST analog (JF-07-69) using an activated carbamate linker. This conjugate selectively targets somatostatin receptor subtype 2 (SSTR2) and also retains high binding affinity and rapid internalization as well as anti-proliferative activity towards various tumor cells. JF-10-81 was tested for its inhibitory activity against the growth of human tumors which included neuroblastoma (IMR32), pancreatic cancer (CFPAC-1), leukemia (MOLT-4), pancreatic carcinoid (BON) and prostate cancer (PC-3). Both SSTR2 mRNAs and proteins were detected in all these tumor cell lines. The conjugate displayed potent in vivo inhibitory activity, although some of the potency measured in in vitro experiments was lost. JF-10-81 was found to significantly inhibit growth of these SSTR-positive tumors, resulting in 87% tumor reduction in neuroblastoma IMR32 and 97% in leukemia MOLT-4 bearing animals, even inducing regression of CFPAC-1 tumors. SSTR-overexpressing BON tumors were unfortunately relatively CPT-insensitive in vitro, however, JF-10-81 again exhibited in vivo potency presumably by specifically increasing CPT concentrations inside the tumor cells so that the inhibition rate for JF-10-81 was 85%. Also, JF-10-81 was used to treat highly invasive PC-3 tumors where s.c. injections inhibited both tumor growth (almost 60% reduction) and tumor metastasis (over 70%). This conjugate demonstrated its broad and excellent anti-tumor activity by targeting SSTR2-specific tumor tissues, supporting that short peptides and their analogs may be applied as ideal drug-delivery carriers to improve the traditional chemotherapy.

Camptothecin (CPT) was conjugated to the N-terminal of a somatostatin analog (SSA) directly via a carbamate group and a basic N-terminal linking motif, D-Lys-D-Tyr-Lys-D-Tyr-D-Lys. This new CPT-SSA conjugate termed JF-10-81 was evaluated as a receptor-specific delivery system for its anti-invasive and anti-angiogenic activities. It was found that, in addition to blocking migration and invasion of highly invasive prostate cancer PC-3 cells, this conjugate also inhibited in vitro capillary-like tube formation of endothelial cells and in vivo angiogenesis in C57B1/6N female mice. JF-10-81 was found to block PC-3 cell attachment to various extracellular matrix components, mainly to vitronectin, the ligand of cell surface receptors integrin alphaVbeta3 and alphaVbeta5. Additionally, JF-10-81 reduced expression of integrins alphaVbeta3 and alphaVbeta5 on PC-3 cell surfaces, without effects on beta1 or any alphabeta1 heterodimers. This conjugate also inactivated phosphorylation of protein kinase B (PKB/Akt), down-regulated the expression of latent matrix metalloproteinase (MMP) -2 and MMP-9, but had little effect on MMP-3/-10. Meanwhile, membrane type-1 matrix metalloproteinase (MT1-MMP) and the tissue inhibitor of matrix metalloproteinase-2 (TIMP-2) were not detectable in PC-3 cells. alphaVbeta3/alphaVbeta5 and MMP-2/-9 are known to be highly expressed in many tumor cells and play an important role in tumor progression. Our results support that this conjugate could possibly inhibit prostate cancer PC-3 cell invasion through a signaling pathway involving PI3K/Akt, alphaVbeta3/alphaVbeta5 and MMP-2/-9, and this SSA could be used as an efficient vector to deliver CPT or other cytotoxic agents to target sites for cancer therapy.

Most human tumors overexpress or ectopically express peptide hormone/neurotransmitter receptors, which are being increasingly studied as a means to selectively deliver cytotoxic agents. Although a number of peptide ligand-constructs demonstrate tumor cytotoxicity, the role of specific tumoral receptor interaction in its mediation is unclear. To address this question, we synthesized camptothecin (CPT) bombesin (Bn) analogs, in which CPT was coupled via a novel carbamate linker, L2 [N-(N-methyl-amino-ethyl)-glycine carbamate], that were chemically similar but differed markedly in their potency/affinity for human Bn receptors. We then examined their ability to interact with Bn receptors and cause in vitro and in vivo tumor cytotoxicity. CPT-L2-[D-Tyr(6),beta-Ala(11),D-Phe(13),Nle(14)] Bn (6-14) (BA3) bound with high affinity and had high potency for all three human Bn receptor subtypes, whereas CPT-L2-[D-Tyr(6),beta-Ala(11), D-Phe(13),Nle(14)] Bn (6-14) [D-Phe-CPT-L2-BA3] had >1400-fold lower affinity/potency. (125)I-CPT-L2-BA3 but not (125)I-D-Phe-CPT-L2-BA3 was internalized by Bn receptor subtype-containing cells. CPT-L2-BA3 displayed significantly more cytotoxicity than D-Phe-CPT-L2-BA3 toward NCI-H1299 lung cancer cells in both 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide and clonogenic assays and more potently inhibited H1299 xenograft growth in nude mice. CPT-L2-BA3 was also metabolically more stable than its parent peptide and inhibited growth of a number of other tumor cell lines in vitro and in vivo. These results demonstrate that specific tumoral receptor interaction is important in mediating the ability of peptide ligand-cytotoxic constructs to cause cytotoxicity. Because many tumors overexpress Bn receptors, these results also demonstrate that CPT-L2-BA3 will be a useful agent for delivering receptor-mediated cytotoxicity to many different human tumors.