Derivatisation of buforin IIb, a cationic henicosapeptide, to afford its complexation to platinum(ii) resulting in a novel platinum(ii)-buforin IIb conjugate with anti-cancer activity

Herein we report the synthesis of buforin IIb, its novel malonate derivative malBuf and its Pt(ii) complex cis-[Pt(NH3)2(malBuf-2H)]. We decided to harness the cell targeting, cell-penetrating and anti-proliferative effects of buforin IIb to help target a cytotoxic dose of a Pt DNA binding species, {Pt(NH3)2} to cancer cells whilst also delivering a peptide with potent anti-cancer properties. Preliminary in vitro data shows cis-[Pt(NH3)2(malBuf-2H)] to be more cytotoxic against the cisplatin resistant ovarian cancer cell line (A2780cisR) relative to buforin IIb, cisplatin and cis-[Pt(NH3)2(malonate)].

Platinum(iv) oxaliplatin–peptide conjugates targeting memHsp70+ phenotype in colorectal cancer cells

Novel Pt(iv) tumour penetrating peptide (TPP) conjugates are reported.

Polymeric prodrug combination to exploit the therapeutic potential of antimicrobial peptides against cancer cells

The first targeted anticancer polymeric prodrug candidates of antimicrobial peptides, intended for combination therapy with another polymeric prodrug of an approved antineoplastic agent (doxorubicin) are reported.

Click-modified cyclodextrins as nonviral vectors for neuronal siRNA delivery

RNA interference (RNAi) holds great promise as a strategy to further our understanding of gene function in the central nervous system (CNS) and as a therapeutic approach for neurological and neurodegenerative diseases. However, the potential for its use is hampered by the lack of siRNA delivery vectors which are both safe and highly efficient. Cyclodextrins have been shown to be efficient and low toxicity gene delivery vectors in various cell types in vitro. However, to date, they have not been exploited for delivery of oligonucleotides to neurons. To this end, a modified β-cyclodextrin (CD) vector was synthesized, which complexed siRNA to form cationic nanoparticles of less than 200 nm in size. Furthermore, it conferred stability in serum to the siRNA cargo. The in vitro performance of the CD in both immortalized hypothalamic neurons and primary hippocampal neurons was evaluated. The CD facilitated high levels of intracellular delivery of labeled siRNA, while maintaining at least 80% cell viability. Significant gene knockdown was achieved, with a reduction in luciferase expression of up to 68% and a reduction in endogenous glyceraldehyde phosphate dehydrogenase (GAPDH) expression of up to 40%. To our knowledge, this is the first time that a modified CD has been used as a safe and efficacious vector for siRNA delivery into neuronal cells.

Proteasome inhibition can induce an autophagy-dependent apical activation of caspase-8

Antiapoptotic Bcl-2 family proteins are often highly expressed in chemotherapy-resistant cancers and impair mitochondrial outer membrane permeabilisation (MOMP), an important requirement for caspase activation via the intrinsic apoptosis pathway. Interestingly, although Bcl-2 overexpression in HeLa cervical cancer cells abrogated caspase processing in response to intrinsic apoptosis induction by staurosporine, tunicamycin or etoposide, residual caspase processing was observed following proteasome inhibition by bortezomib ([(1R)-3-methyl-1-({(2S)-3-phenyl-2-[(pyrazin-2-ylcarbonyl)amino]propanoyl}amino)butyl]boronic acid), epoxomicin (N-acetyl-N-methyl-lisoleucyl-L-isoleucyl-N-[(1S)-3-methyl-1-[[(2R)-2-methyloxiranyl]carbonyl]butyl]-L-threoninamide) or MG-132 (N-(benzyloxycarbonyl)leucinylleucinylleucinal). Similar responses were found in Bcl-2-overexpressing H460 NSCLC cells and Bax/Bak-deficient mouse embyronic fibroblasts. Mild caspase processing resulted in low DEVDase activities, which were MOMP independent and persisted for long periods without evoking immediate cell death. Surprisingly, depletion of caspase-3 and experiments in caspase-7-depleted MCF-7-Bcl-2 cells indicated that the DEVDase activity did not originate from effector caspases. Instead, Fas-associated death domain (FADD)-dependent caspase-8 activation was the major contributor to the slow, incomplete substrate cleavage. Caspase-8 activation was independent of death ligands, but required the induction of autophagy and the presence of Atg5. Depletion of XIAP or addition of XIAP-antagonising peptides resulted in a switch towards efficient apoptosis execution, suggesting that the requirement for MOMP was bypassed by activating the caspase-8/caspase-3 axis. Combination treatments of proteasome inhibitors and XIAP antagonists therefore represent a promising strategy to eliminate highly resistant cancer cells, which overexpress antiapoptotic Bcl-2 family members.

Elucidating the role of Staphylococcus epidermidis serine-aspartate repeat protein G in platelet activation

BACKGROUND

Staphylococcus epidermidis is a commensal of the human skin that has been implicated in infective endocarditis and infections involving implanted medical devices. S. epidermidis induces platelet aggregation by an unknown mechanism. The fibrinogen-binding protein serine-aspartate repeat protein G (SdrG) is present in 67-91% of clinical strains.

OBJECTIVES

To determine whether SdrG plays a role in platelet activation, and if so to investigate the role of fibrinogen in this mechanism.

METHODS

SdrG was expressed in a surrogate host, Lactococcus lactis, in order to investigate its role in the absence of other staphylococcal components. Platelet adhesion and platelet aggregation assays were employed.

RESULTS

L. lactis expressing SdrG stimulated platelet aggregation (lag time: 2.9 +/- 0.5 min), whereas the L. lactis control did not. L. lactis SdrG-induced aggregation was inhibited by alpha(IIb)beta3 antagonists and aspirin. Aggregation was dependent on both fibrinogen and IgG, and the platelet IgG receptor FcgammaRIIa. Preincubation of the bacteria with Bbeta-chain fibrinopeptide inhibited aggregation (delaying the lag time six-fold), suggesting that fibrinogen acts as a bridging molecule. Platelets adhered to L. lactis SdrG in the absence of fibrinogen. Adhesion was inhibited by alpha(IIb)beta3 antagonists, suggesting that this direct interaction involves alpha(IIb)beta3. Investigation using purified fragments of SdrG revealed a direct interaction with the B-domains. Adhesion to the A-domain involved both a fibrinogen and an IgG bridge.

CONCLUSION

SdrG alone is sufficient to support platelet adhesion and aggregation through both direct and indirect mechanisms.

A novel functional role for the highly conserved alpha-subunit KVGFFKR motif distinct from integrin alphaIIbbeta3 activation processes

BACKGROUND

The highly conserved integrin alpha-subunit membrane-proximal motif KVGFFKR plays a decisive role in modulating the activation of integrin alphaIIbbeta3. Previously, we have shown that a platelet permeable palmityl (pal)-peptide with this seven amino acid sequence can directly activate alphaIIbbeta3 leading to platelet aggregation.

OBJECTIVES

To investigate further the role of the KVGFFKR motif in integrin alphaIIbbeta3 function.

METHODS

We used two sequence-specific complementary model systems, palmityl pal-peptides in platelets, and mutant alphaIIbbeta3-expressing Chinese Hamster Ovary (CHO) cell lines.

RESULTS

In platelets we show that the two phenylalanine amino acids in pal-KVGFFKR (pal-FF) peptide are critical for stimulating platelet aggregation. Pal-FF peptide treatment of platelets also gives rise to a tyrosine phosphorylation signal despite the presence of inhibitors of fibrinogen binding. In CHO cells, a double alanine substitution, alphaIIb(F992A, F993A)beta3, induces constitutive integrin activation but prevents actin stress fiber formation upon adhesion to fibrinogen, suggesting that alphaIIbbeta3-mediated cytoskeletal reorganization is also dependent on F992 and F993. This further highlights a critical role for the two phenylalanine residues in both of these alphaIIbbeta3-mediated processes.

CONCLUSION

In addition to regulating integrin alphaIIbbeta3 activation state, the KVGFFKR motif also influences cytoskeletal reorganization. This activity is critically determined by F992 and F993 within the seven amino acid sequence.

A peptide corresponding to the neuropilin-1-binding site on VEGF(165) induces apoptosis of neuropilin-1-expressing breast tumour cells

There is increasing evidence that vascular endothelial growth factor (VEGF) has autocrine as well as paracrine functions in tumour biology. Vascular endothelial growth factor-mediated cell survival signalling occurs via the classical tyrosine kinase receptors Flt-1, KDR/Flk-1 and the more novel neuropilin (NP) receptors, NP-1 and NP-2. A 24-mer peptide, which binds to neuropilin-1, induced apoptosis of murine and human breast carcinoma cells, whereas a peptide directed against KDR had no effect. Both anti-NP1 and anti-KDR peptides induced endothelial cell apoptosis. Confocal microscopy using 5-(6)-carboxyfluorescein-labelled peptides showed that anti-NP1 bound to both tumour and endothelial cells, whereas anti-KDR bound endothelial cells only. This study demonstrates that NP-1 plays an essential role in autocrine antiapoptotic signalling by VEGF in tumour cells and that NP1-blockade induces tumour cell and endothelial cell apoptosis. Specific peptides can therefore be used to target both autocrine (tumour cells) and paracrine (endothelial cells) signalling by VEGF.

A novel family of hydroxamate-based acylating inhibitors of cyclooxygenase

Aspirin irreversibly inhibits cyclooxygenase (COX) by acetylating a serine residue in the active site. We synthesized a series of novel acylating agents based on our previously reported acetylating compound, O-acetylsalicylhydroxamic acid. One of these, triacetylsalicylhydroxamic acid (TriAcSHA) was more effective than aspirin and O-acetylsalicylhydroxamic acid in inactivating both COX-1 and COX-2. Preincubation of COX-1 with inhibitor for 5 min yielded IC(50) values of 18 microM for TriAcSHA and 60 microM for acetylsalicylic acid. Inhibition was time-dependent, with complete inhibition within 10 min at a concentration of 50 microM. As with aspirin, mutation of the serine 530 of COX-1 to alanine abolished the activity of the TriAcSHA. Mutation of the alanine 119 to a glutamine markedly reduced the sensitivity to TriAcSHA, suggesting that this residue was necessary for the interaction with the enzyme. TriAcSHA was also more effective than aspirin as an inhibitor of platelet aggregation induced by arachidonic acid. The diacetylated phenylhydroxamates N-methyl-O,O-diacetylsalicylhydroxamic acid, N,O-diacetylbenzohydroxamic acid, and 2-methyl-O,N-diacetylbenzohydroxamic acid showed reduced or absent activity against COX-1. In addition, we synthesized a series of triacylsalicylhydroxamic acids with progressively longer acyl groups (three to six carbons). All of the compounds inhibited COX-1 and demonstrated progressively greater COX-1 selectivity with increasing number of carbons. Hence, salicylhydroxamic acid provides a versatile backbone for the generation of a family of acylating inhibitors of cyclooxygenase.

O-acetylsalicylhydroxamic acid, a novel acetylating inhibitor of prostaglandin H2 synthase: structural and functional characterization of enzyme-inhibitor interactions

Aspirin is unique among clinically used nonsteroidal antiinflammatory drugs in that it irreversibly inactivates prostaglandin (PG) H2 synthase (PGHS) via acetylation of an active-site serine residue. We report the synthesis and characterization of a novel acetylating agent, O-acetylsalicylhydroxamic acid (AcSHA), which inhibits PGE2 synthesis in vivo and blocks the cyclooxygenase activity of PGHS in vitro. AcSHA requires the presence of the active-site residue Ser-529 to be active against human PGHS-1; the S529A mutant is resistant to inactivation by the inhibitor. Analysis of PGHS inactivation by AcSHA, coupled with the X-ray crystal structure of the complex of ovine PGHS-1 with AcSHA, confirms that the inhibitor elicits its effects via acetylation of Ser-529 in the cyclooxygenase active site. The crystal structure reveals an intact inhibitor molecule bound in the enzyme's cyclooxygenase active-site channel, hydrogen bonding with Arg-119 of the enzyme. The structure-activity profile of AcSHA can be rationalized in terms of the crystal structure of the enzyme-ligand complex. AcSHA may prove useful as a lead compound to facilitate the development of new acetylating inhibitors.