Synthesis and Evaluation of a Monomethyl Auristatin E─Integrin αvβ6 Binding Peptide-Drug Conjugate for Tumor Targeted Drug Delivery

Many anticancer drugs exhibit high systemic off-target toxicities causing severe side effects. Peptide-drug conjugates (PDCs) that target tumor-specific receptors such as integrin αvβ6 are emerging as powerful tools to overcome these challenges. The development of an integrin αvβ6-selective PDC was achieved by combining the therapeutic efficacy of the cytotoxic drug monomethyl auristatin E with the selectivity of the αvβ6-binding peptide (αvβ6-BP) and with the ability of positron emission tomography (PET) imaging by copper-64. The [64Cu]PDC-1 was produced efficiently and in high purity. The PDC exhibited high human serum stability, integrin αvβ6-selective internalization, cell binding, and cytotoxicity. Integrin αvβ6-selective tumor accumulation of the [64Cu]PDC-1 was visualized with PET-imaging and corroborated by biodistribution, and [64Cu]PDC-1 showed promising in vivo pharmacokinetics. The [natCu]PDC-1 treatment resulted in prolonged survival of mice bearing αvβ6 (+) tumors (median survival: 77 days, vs αvβ6 (-) tumor group 49 days, and all other control groups 37 days).

Preclinical evaluation of 68Ga- and 177Lu-labeled integrin αvβ6-targeting radiotheranostic peptides

Rationale: The integrin α_vβ₆, an epithelial-specific cell surface receptor, is overexpressed on numerous malignancies, including the highly lethal pancreatic ductal adenocarcinomas (PDAC). Here, we developed and tested a novel α_vβ₆-targeting peptide, DOTA-5G (1) radiolabeled with gallium-68 for positron emission tomography/computed tomography (PET/CT) imaging, and lutetium-177 for treatment. With the goal to develop a radiotheranostic, further modifications were made for increased circulation time, renal recycling, and tumor uptake, yielding DOTA-ABM-5G (2). Methods: Peptides 1 and 2 were synthesized on solid phase and their affinity for αvβ6 assessed by ELISA. The peptides were radiolabeled with gallium-68 and lutetium-177. In vitro cell binding, internalization, and efflux of ⁶⁸Ga-1 and ¹⁷⁷Lu-2 were evaluated in α_vβ₆ (+) BxPC-3 human pancreatic cancer cells. PET/CT imaging of ⁶⁸Ga-1 and ⁶⁸Ga-2 was performed in female nu/nu mice bearing subcutaneous BxPC-3 tumors. Biodistribution was performed for ⁶⁸Ga-1 (1 and 2 h p.i.), ⁶⁸Ga-2 (2 and 4 h p.i.), and ¹⁷⁷Lu-1 and ¹⁷⁷Lu-2 (1, 24, 48, and 72 h p.i.). The ¹⁷⁷Lu-2 biodistribution data were extrapolated for human dosimetry data estimates using OLINDA/EXM 1.1. Therapeutic efficacy of ¹⁷⁷Lu-2 was evaluated in mice bearing BxPC-3 tumors. Results: Peptides 1 and 2 demonstrated high affinity for α_vβ₆ by ELISA. ⁶⁸Ga-1, ⁶⁸Ga-2, ¹⁷⁷Lu-1 and ¹⁷⁷Lu-2 were synthesized in high radiochemical purity (RCP). Rapid in vitro binding and internalization of ⁶⁸Ga-1 and ¹⁷⁷Lu-2 were observed in BxPC-3 cells. PET/CT imaging and biodistribution studies demonstrated uptake in BxPC-3 tumors. Introduction of the ABM in ¹⁷⁷Lu-2 resulted in a 5-fold increase in tumor uptake and retention over time. Based on the extended dosimetry data the dose-limiting organ for ¹⁷⁷Lu-2 are the kidneys. Treatment with ¹⁷⁷Lu-2 prolonged survival. Conclusion: ⁶⁸Ga-1 and ¹⁷⁷Lu-2 demonstrated high affinity for the integrin α_vβ₆ both in vitro and in vivo, were rapidly internalized into BxPC-3 cells, and were stable in mouse and human serum. Both radiotracers showed favorable pharmacokinetics in pre-clinical studies with predominantly renal excretion and good tumor-to-normal tissue ratios. Favorable human dosimetry data suggest the potential of ¹⁷⁷Lu-2 as a treatment for PDAC.

Repurposing an atherosclerosis targeting peptide for tumor imaging

Cancer and atherosclerosis are chronic diseases that share common characteristics at both early and advanced stages and can arise from multiple factors. Both diseases are characterized by uncontrolled cell proliferation, inflammation, angiogenesis and apoptosis. Herein we investigated the ability of a peptide (CTHRSSVVC), that was previously reported to bind atherosclerotic lesions to home in the tumor microenvironment. The CTHRSSVVC peptide was synthesized on solid phase and N-terminally labeled with a sulfo-Cy5 dye. The specific binding to macrophage was evaluated in vitro with flow cytometry and immunofluorescence and in vivo for tumor targeting in BALB/c mice bearing a 4T1 tumor using optical imaging. The sulfo-Cy5-CTHRSSVVC peptide was synthesized in greater than 99% purity. No selective binding of the sulfo-Cy5-CTHRSSVVC peptide to macrophages in vitro was observed, however in vivo the sulfo-Cy5-CTHRSSVVC peptide accumulated in the 4T1 tumor, with a tumor-to-normal tissue ratio of 7.21 ± 1.44 at 2 h post injection. Ex vivo analysis of tumor tissue by confocal microscopy suggested that the sulfo-Cy5-CTHRSSVVC peptide had accumulated in the stroma of the tumor specifically, in regions of spindle shaped cells. In conclusion, although the target for the sulfo-Cy5-CTHRSSVVC peptide remains to be identified, the Cy5-CTHRSSVVC peptide warrants further investigation as a tumor imaging agent.

Evaluation of Copper-64-Labeled αvβ6-Targeting Peptides: Addition of an Albumin Binding Moiety to Improve Pharmacokinetics

The incorporation of non-covalent albumin binding moieties (ABMs) into radiotracers results in increased circulation time, leading to a higher uptake in the target tissues such as the tumor, and, in some cases, reduced kidney retention. We previously developed [¹⁸F]AlF NOTA-K(ABM)-α_vβ₆-BP, where α_vβ₆-BP is a peptide with high affinity for the cell surface receptor integrin α_vβ₆ that is overexpressed in several cancers, and the ABM is an iodophenyl-based moiety. [¹⁸F]AlF NOTA-K(ABM)-α_vβ₆-BP demonstrated prolonged blood circulation compared to the non-ABM parent peptide, resulting in high, α_vβ₆-targeted uptake with continuously improving detection of α_vβ₆(+) tumors using PET/CT. To further extend the imaging window beyond that of fluorine-18 (t_1/2 = 110 min) and to investigate the pharmacokinetics at later time points, we radiolabeled the α_vβ₆-BP with copper-64 (t_1/2 = 12.7 h). Two peptides were synthesized without (1) and with (2) the ABM and radiolabeled with copper-64 to yield [⁶⁴Cu]1 and [⁶⁴Cu]2, respectively. The affinity of [^natCu]1 and [^natCu]2 for the integrin α_vβ₆ was assessed by enzyme-linked immunosorbent assay. [⁶⁴Cu]1 and [⁶⁴Cu]2 were evaluated in vitro (cell binding and internalization) using DX3puroβ6 (α_vβ₆(+)), DX3puro (α_vβ₆(-)), and pancreatic BxPC-3 (α_vβ₆(+)) cells, in an albumin binding assay, and for stability in both mouse and human serum. In vivo (PET/CT imaging) and biodistribution studies were done in mouse models bearing either the paired DX3puroβ6/DX3puro or BxPC-3 xenograft tumors. [⁶⁴Cu]1 and [⁶⁴Cu]2 were synthesized in ≥97% radiochemical purity. In vitro, [^natCu]1 and [^natCu]2 maintained low nanomolar affinity for integrin α_vβ₆ (IC₅₀ = 28 ± 3 and 19 ± 5 nM, respectively); [⁶⁴Cu]1 and [⁶⁴Cu]2 showed comparable binding to α_vβ₆(+) cells (DX3puroβ6: ≥70%, ≥42% internalized; BxPC-3: ≥19%, ≥12% internalized) and ≤3% to the α_vβ₆(-) DX3puro cells. Both radiotracers were ≥98% stable in human serum at 24 h, and [⁶⁴Cu]2 showed a 6-fold higher binding to human serum protein than [⁶⁴Cu]1. In vivo, selective uptake in the α_vβ₆(+) tumors was observed with tumor visualization up to 72 h for [⁶⁴Cu]2. A 3-5-fold higher α_vβ₆(+) tumor uptake of [⁶⁴Cu]2 vs [⁶⁴Cu]1 was observed throughout, at least 2.7-fold improved BxPC-3-to-kidney and BxPC-3-to-blood ratios, and 2-fold improved BxPC-3-to-stomach ratios were noted for [⁶⁴Cu]2 at 48 h. Incorporation of an iodophenyl-based ABM into the α_vβ₆-BP ([⁶⁴Cu]2) prolonged circulation time and resulted in improved pharmacokinetics, including increased uptake in α_vβ₆(+) tumors that enabled visualization of α_vβ₆(+) tumors up to 72 h by PET/CT imaging.

The Effects of an Albumin Binding Moiety on the Targeting and Pharmacokinetics of an Integrin αvβ6-Selective Peptide Labeled with Aluminum [18F]Fluoride

PURPOSE

The α_vβ₆-BP peptide selectively targets the integrin α_vβ₆, a cell surface receptor recognized as a prognostic indicator for several challenging malignancies. Given that the 4-[¹⁸F]fluorobenzoyl (FBA)-labeled peptide is a promising PET imaging agent, radiolabeling via aluminum [¹⁸F]fluoride chelation and introduction of an albumin binding moiety (ABM) have the potential to considerably simplify radiochemistry and improve the pharmacokinetics by increasing biological half-life.

PROCEDURES

The peptides NOTA-α_vβ₆-BP (1) and NOTA-K(ABM)-α_vβ₆-BP (2) were synthesized on solid phase, radiolabeled with aluminum [¹⁸F]fluoride, and evaluated in vitro (integrin ELISA, albumin binding, cell studies) and in vivo in mouse models bearing paired DX3puroβ6 [α_vβ₆(+)]/DX3puro [α_vβ₆(-)], and for [¹⁸F]AlF 2, BxPC-3 [α_vβ₆(+)] cell xenografts (PET imaging, biodistribution).

RESULTS

The peptides were radiolabeled in 23.0 ± 5.7 % and 22.1 ± 4.4 % decay-corrected radiochemical yield, respectively, for [¹⁸F]AlF 1 and [¹⁸F]AlF 2. Both demonstrated excellent affinity and selectivity for integrin α_vβ₆ by ELISA (IC₅₀(α_vβ₆) = 3-7 nM vs IC₅₀(α_vβ₃) > 10 μM) and in cell binding studies (51.0 ± 0.7 % and 47.2 ± 0.7 % of total radioactivity bound to DX3puroβ6 cells at 1 h, respectively, vs. ≤ 1.2 % to DX3puro for both compounds). The radiotracer [¹⁸F]AlF 1 bound to human serum at 16.3 ± 1.9 %, compared to 67.5 ± 1.0 % for the ABM-containing [¹⁸F]AlF 2. In vivo studies confirmed the effect of the ABM on blood circulation (≤ 0.1 % ID/g remaining in blood for [¹⁸F]AlF 1 as soon as 1 h p.i. vs. > 2 % ID/g for [¹⁸F]AlF 2 at 6 h p.i.) and higher α_vβ₆(+) tumor uptake (4 h: DX3puroβ6; [¹⁸F]AlF 1: 3.0 ± 0.7 % ID/g, [¹⁸F]AlF 2: 7.2 ± 0.7 % ID/g; BxPC-3; [¹⁸F]AlF 2: 10.2 ± 0.1 % ID/g).

CONCLUSION

Both compounds were prepared using standard chemistries; affinity and selectivity for integrin α_vβ₆ in vitro remained unaffected by the albumin binding moiety. In vivo, the albumin binding moiety resulted in prolonged circulation and higher α_vβ₆-targeted uptake.

Targeting PSMA with a Cu-64 Labeled Phosphoramidate Inhibitor for PET/CT Imaging of Variant PSMA-Expressing Xenografts in Mouse Models of Prostate Cancer

PURPOSE

Prostate-specific membrane antigen (PSMA) is highly up-regulated in prostate tumor cells, providing an ideal target for imaging applications of prostate cancer. CTT-1297 (IC50 = 27 nM) is an irreversible phosphoramidate inhibitor of PSMA that has been conjugated to the CB-TE1K1P chelator for incorporation of Cu-64. The resulting positron emission tomography (PET) agent, [(64)Cu]ABN-1, was evaluated for selective uptake both in vitro and in vivo in PSMA-positive cells of varying expression levels. The focus of this study was to assess the ability of [(64)Cu]ABN-1 to detect and distinguish varying levels of PSMA in a panel of prostate tumor-bearing mouse models.

PROCEDURES

CTT-1297 was conjugated to the CB-TE1K1P chelator using click chemistry and radiolabeled with Cu-64. Internalization and binding affinity of [(64)Cu]ABN-1 was evaluated in the following cell lines having varying levels of PSMA expression: LNCaP late-passage > LNCaP early passage ≈ C4-2B > CWR22rv1 and PSMA-negative PC-3 cells. PET/X-ray computed tomography imaging was performed in NCr nude mice with subcutaneous tumors of the variant PSMA-expressing cell lines.

RESULTS

[(64)Cu]ABN-1 demonstrated excellent uptake in PSMA-positive cells in vitro, with ∼80 % internalization at 4 h for each PSMA-positive cell line with uptake (fmol/mg) correlating to PSMA expression levels. The imaging data indicated significant tumor uptake in all models. The biodistribution for late-passage LNCaP (highest PSMA expression) demonstrated the highest specific uptake of [(64)Cu]ABN-1 with tumor-to-muscle and tumor-to-blood ratios of 30 ± 11 and 21 ± 7, respectively, at 24 h post-injection. [(64)Cu]ABN-1 cleared through all tissues except for PSMA-positive kidneys.

CONCLUSION

[(64)Cu]ABN-1 demonstrated selective uptake in PSMA-positive cells and tumors, which correlated to the level of PSMA expression. The data reported herein suggest that [(64)Cu]ABN-1 will selectively target and image variant PSMA expression and in the future will serve as a non-invasive method to follow the progression of prostate cancer in men.

Structure-Activity Relationship of (18)F-Labeled Phosphoramidate Peptidomimetic Prostate-Specific Membrane Antigen (PSMA)-Targeted Inhibitor Analogues for PET Imaging of Prostate Cancer

A series of phosphoramidate-based prostate specific membrane antigen (PSMA) inhibitors of increasing lipophilicity were synthesized (4, 5, and 6), and their fluorine-18 analogs were evaluated for use as positron emission tomography (PET) imaging agents for prostate cancer. To gain insight into their modes of binding, they were also cocrystallized with the extracellular domain of PSMA. All analogs exhibited irreversible binding to PSMA with IC50 values ranging from 0.4 to 1.3 nM. In vitro assays showed binding and rapid internalization (80-95%, 2 h) of the radiolabeled ligands in PSMA(+) cells. In vivo distribution demonstrated significant uptake in CWR22Rv1 (PSMA(+)) tumor, with tumor to blood ratios of 25.6:1, 63.6:1, and 69.6:1 for [(18)F]4, [(18)F]5, and [(18)F]6, respectively, at 2 h postinjection. Installation of aminohexanoic acid (AH) linkers in the phosphoramidate scaffold improved their PSMA binding and inhibition and was critical for achieving suitable in vivo imaging properties, positioning [(18)F]5 and [(18)F]6 as favorable candidates for future prostate cancer imaging clinical trials.

Caged [(18)F]FDG Glycosylamines for Imaging Acidic Tumor Microenvironments Using Positron Emission Tomography

Solid tumors are hypoxic with altered metabolism, resulting in secretion of acids into the extracellular matrix and lower relative pH, a feature associated with local invasion and metastasis. Therapeutic and diagnostic agents responsive to this microenvironment may improve tumor-specific delivery. Therefore, we pursued a general strategy whereby caged small-molecule drugs or imaging agents liberate their parent compounds in regions of low interstitial pH. In this manuscript, we present a new acid-labile prodrug method based on the glycosylamine linkage, and its application to a class of positron emission tomography (PET) imaging tracers, termed [(18)F]FDG amines. [(18)F]FDG amines operate via a proposed two-step mechanism, in which an acid-labile precursor decomposes to form the common radiotracer 2-deoxy-2-[(18)F]fluoro-d-glucose, which is subsequently accumulated by glucose avid cells. The rate of decomposition of [(18)F]FDG amines is tunable in a systematic fashion, tracking the pKa of the parent amine. In vivo, a 4-phenylbenzylamine [(18)F]FDG amine congener showed greater relative accumulation in tumors over benign tissue, which could be attenuated upon tumor alkalinization using previously validated models, including sodium bicarbonate treatment, or overexpression of carbonic anhydrase. This new class of PET tracer represents a viable approach for imaging acidic interstitial pH with potential for clinical translation.

A high-affinity [(18)F]-labeled phosphoramidate peptidomimetic PSMA-targeted inhibitor for PET imaging of prostate cancer

INTRODUCTION

In this study, a structurally modified phosphoramidate scaffold, with improved prostate-specific membrane antigen (PSMA) avidity, stability and in vivo characteristics, as a PET imaging agent for prostate cancer (PCa), was prepared and evaluated.

METHODS

p-Fluorobenzoyl-aminohexanoate and 2-(3-hydroxypropyl)glycine were introduced into the PSMA-targeting scaffold yielding phosphoramidate 5. X-ray crystallography was performed on the PSMA/5 complex. [(18)F]5 was synthesized, and cell uptake and internalization studies were conducted in PSMA(+) LNCaP and CWR22Rv1 cells and PSMA(-) PC-3 cells. In vivo PET imaging and biodistribution studies were performed at 1 and 4 h post injection in mice bearing CWR22Rv1 tumor, with or without blocking agent.

RESULTS

The crystallographic data showed interaction of the p-fluorobenzoyl group with an arene-binding cleft on the PSMA surface. In vitro studies revealed elevated uptake of [(18)F]5 in PSMA(+) cells (2.2% in CWR22Rv1 and 12.1% in LNCaP) compared to PSMA(-) cells (0.08%) at 4 h. In vivo tumor uptake of 2.33% ID/g and tumor-to-blood ratio of 265:1 was observed at 4 h.

CONCLUSIONS

We have successfully synthesized, radiolabeled and evaluated a new PSMA-targeted PET agent. The crystal structure of the PSMA/5 complex highlighted the interactions within the arene-binding cleft contributing to the overall complex stability. The high target uptake and rapid non-target clearance exhibited by [(18)F]5 in PSMA(+) xenografts substantiates its potential use for PET imaging of PCa.

ADVANCES IN KNOWLEDGE

The only FDA-approved imaging agent for PCa, Prostascint®, targets PSMA but suffers from inherent shortcomings. The data acquired in this manuscript confirmed that our new generation of [(18)F]-labeled PSMA inhibitor exhibited promising in vivo performance as a PET imaging agent for PCa and is well-positioned for subsequent clinical trials. Implications for Patient Care Our preliminary data demonstrate that this tracer possesses the required imaging characteristics to be sensitive and specific for PCa imaging in patients at all stages of the disease.

Development of inhibitor-directed enzyme prodrug therapy (IDEPT) for prostate cancer

Prostate cancer (PCa) is the second most common cause of cancer death among American men after lung cancer. Unfortunately, current therapies do not provide effective treatments for patients with advanced, metastatic, or hormone refractory disease. Therefore, we seek to generate therapeutic agents for a novel PCa treatment strategy by delivering a suicide enzyme (yCD_triple) to a cell membrane bound biomarker found on PCa cells (prostate-specific membrane antigen (PSMA)). This approach has resulted in a new PCa treatment strategy reported here as inhibitor-directed enzyme prodrug therapy (IDEPT). The therapeutic agents described were generated using a click chemistry reaction between the unnatural amino acid (p-azidophenylalanine (pAzF)) incorporated into yCD_triple and the dibenzylcyclooctyne moiety of our PSMA targeting agent (DBCO-PEG₄-AH₂-TG97). After characterization of the therapeutic agents, we demonstrate significant PCa cell killing of PSMA-positive cells. Importantly, we demonstrate that this click chemistry approach can be used to efficiently couple a therapeutic protein to a targeting agent and may be applicable to the ablation of other types of cancers and/or malignancies.

PSMA-targeted SPECT agents: mode of binding effect on in vitro performance

BACKGROUND

The enzyme-biomarker prostate-specific membrane antigen (PSMA) is an active target for imaging and therapeutic applications for prostate cancer. The internalization of PSMA has been shown to vary with inhibitors' mode of binding: irreversible, slowly reversible, and reversible.

METHODS

In the present study, PSMA-targeted clickable derivatives of an irreversible phosphoramidate inhibitor DBCO-PEG(4) -CTT-54 (IC(50) = 1.0 nM) and a slowly reversible phosphate inhibitor, DBCO-PEG(4) -CTT-54.2 (IC(50) = 6.6 nM) were clicked to (99m) Tc(CO)(3) -DPA-azide to assemble a PSMA-targeted SPECT agent. The selectivity, percent uptake, and internalization of these PSMA-targeted SPECT agents were evaluated in PSMA-positive and PSMA-negative cells.

RESULTS

In vitro studies demonstrated that PSMA-targeted SPECT agents exhibited selective cellular uptake in the PSMA-positive LNCaP cells compared to PSMA-negative PC3 cells. More importantly, it was found that (99m) Tc(CO)(3) -DPA-DBCO-PEG(4) -CTT-54 based on an irreversible PSMA inhibitor core, exhibited greater uptake and internalization than (99m) Tc(CO)(3) -DPA-DBCO-PEG(4) -CTT-54.2 constructed from a slowly reversible PSMA inhibitor core.

CONCLUSIONS

We have demonstrated that a PSMA-targeted SPECT agent can be assembled efficiently using copper-less click chemistry. In addition, we demonstrated that mode of binding has an effect on internalization and percent uptake of PSMA-targeted SPECT agents; with the irreversible targeting agent demonstrating superior uptake and internalization in PSMA+ cells. The approach demonstrated in this work now supports a modular approach for the assembly of PSMA-targeted imaging and therapeutic agents.

A phosphoramidate-based prostate-specific membrane antigen-targeted SPECT agent

BACKGROUND

Prostate-specific membrane antigen (PSMA) remains an active target for imaging and therapeutic applications for prostate cancer.

METHODS

In the present study, an irreversible phosphoramidate inhibitor, CTT-54 (IC50 = 14 nM), has been modified to deliver 99mTc-(CO)3-DTPA as a SPECT imaging payload to PSMA+ cells in vivo and in vitro. Percent uptake, competitive binding, and internalization will evaluate the imaging agent in vitro. Preliminary biodistribution and imaging will be utilized for in vivo evaluation.

RESULTS

In vitro studies demonstrate that the radiotracer 99mTc-(CO)3-DTPA-CTT-54 exhibits increasing cellular uptake in the PSMA+ LNCaP cells over time. More importantly, it was found that 99mTc-(CO)3-DTPA-CTT-54 is rapidly internalized into LNCaP cells, presumably through the PSMA enzyme-inhibitor complex. In a pilot biodistribution study, increasing accumulation of the radiotracer in LNCaP xenografts was observed from 2 to 4 hr and significant clearance from non-target tissues.

CONCLUSIONS

While DTPA may not represent the ideal chelate structure for 99mTc(CO)3, the data provides proof-of-concept support for the development of a next-generation phosphoramidate-based PSMA inhibitor-conjugates for use as SPECT imaging agents.

The hydrazide/hydrazone click reaction as a biomolecule labeling strategy for M(CO)3 (M = Re, (99m)Tc) radiopharmaceuticals

Facile reactivity of hydrazides and aldehydes was explored as potential coupling partners for incorporation into M(CO)(3) (M = Re, (99m)Tc) based radiopharmaceuticals. Both 'click, then chelate' and 'prelabel, then click' synthetic routes produced identical products in high yields and lacked metal-hydrazide/-hydrazone interactions, highlighting the potential of this click strategy.

Inactivation of indispensable bacterial proteins by early proteins of bacteriophages: implication in antibacterial drug discovery

Bacteriophages utilize host bacterial cellular machineries for their own reproduction and completion of life cycles. The early proteins that phage synthesize immediately after the entry of their genomes into bacterial cells participate in inhibiting host macromolecular biosynthesis, initiating phage-specific replication and synthesizing late proteins. Inhibition of synthesis of host macromolecules that eventually leads to cell death is generally performed by the physical and/or chemical modification of indispensable host proteins by early proteins. Interestingly, most modified bacterial proteins were shown to take part actively in phage-specific transcription and replication. Research on phages in last nine decades has demonstrated such lethal early proteins that interact with or chemically modify indispensable host proteins. Among the host proteins inhibited by lethal phage proteins, several are not inhibited by any chemical inhibitor available today. Under the context of widespread dissemination of antibiotic-resistant strains of pathogenic bacteria in recent years, the information of lethal phage proteins and cognate host proteins could be extremely invaluable as they may lead to the identification of novel antibacterial compounds. In this review, we summarize the current knowledge about some early phage proteins, their cognate host proteins and their mechanism of action and also describe how the above interacting proteins had been exploited in antibacterial drug discovery.

Primary electron-transfer dynamics in 2-phenylindole-9-cyanoanthracene system. A comparative study with 2-methylindole

Electrochemical measurements by cyclic voltammetry predict the possibility of occurrence of photoinduced electron-transfer (PET) reactions between the ground state of 2-phenylindole (2PI) (electron donor) and the excited singlet of 9-cyanoanthracene (9CNA) molecule acting as an electron acceptor. However, 2PI should be expected to behave as a relatively weaker electron donating agent than the structurally related donor 2-methylindole (2MI) as it possesses higher oxidation potential value. Both steady-state and time-resolved spectroscopic measurements in the polar acetonitrile (ACN) and ethanol (EtOH) solvents show that the fluorescence quenching phenomenon of 9CNA in presence of 2PI is primarily due to the involvement of dynamic process which in high probability should be PET. Nevertheless, in less polar tetrahydrofuran (THF) medium, the quenching of 9CNA results from the combined effect of dynamic and static modes. The transient absorption spectra, measured by using nanosecond laser flash photolysis, of 9CNA in presence of 2PI exhibit the signature of the bands of the anionic species of 9CNA, cation of the donor 2PI and the contact neutral radical. Observations of the transient absorption at the different delays infer that ion-recombination mechanism is responsible for production of the monomeric triplets of both 9CNA and 2PI. From the transient absorption decays in ACN medium, it has been demonstrated that the diffusional separation of ions from geminate ion-pair is facilitated in the case of 2MI-9CNA pair whereas for 2PI-9CNA system the energy wasting charge recombination dominates over the process of charge dissociation. From the above observations, the possibility of developing much potential photosynthetic model compounds with the donor 2MI, rather than with the other donor 2PI molecule has been hinted.

Non-radiative depletion of the excited electronic states of 9-cyanoanthracene in presence of tetrahydronaphthols

Both steady state and time resolved spectroscopic measurements reveal that the prime process involved in quenching mechanism of the lowest excited singlet (S1) and triplet (T1) states of the well known electron acceptor 9-Cyanoanthracene (9CNA) in presence of 5,6,7,8-tetrahydro-1-naphthol (TH1N) or 5,6,7,8-tetrahydro-2-naphthol (TH2N) is H-bonding interaction. It has been confirmed that the fluorescence of 9CNA is not at all affected in presence of 5,6,7,8-tetrahydro-2-methoxy naphthalene (TH2MN) both in non-polar n-heptane (NH) and highly polar acetonitrile (ACN) media. This indicates that the H-bonding interaction is crucial for the occurrence of the quenching phenomenon observed in the present investigations with TH1N (or TH2N) donors and 9CNA acceptor. In ACN solvent both contact ion-pair (CIP) and solvent-separated (or dissociated) ions are formed due to intermolecular H-bonding interactions in the excited electronic states (both singlet and triplet). In NH environment due to stronger H-bonding interactions, the large proton shift within excited charge transfer (CT) or ion-pair complex, 1 or 3(D+-H...A-), causes the formation of the neutral radical, 3(D+H-A)*, due to the complete detachment of the H-atom. It is hinted that both TH1N and TH2N due to their excellent H-bonding ability could be used as antioxidants.

Nature of non-radiative processes involved in the excited state of 9-cyanoanthracene in presence of 2-methylindole/2-methylindoline quenchers. A laser flash photolysis study to reveal the medium effects

By using steady state and time-resolved (laser flash photolysis and single photon counting) spectroscopic techniques the quenching of the lowest excited singlet (S1) state of 9-cyanoanthracene (9CNA) by the donors (quenchers) 2-methylindole (2MI) and 2-methylindoline (2MIN) in solvents of different polarity has been studied. Both the transient absorption, by laser flash photolysis technique, and photobleaching measurements were made at the ambient temperature both in non-polar n-heptane (NH) and highly polar acetonitrile (ACN) solvents. The photobleaching efficiency (alpha) was found to depend significantly on the polarity of surrounding solvents and also on the molecular structures of the quenchers. In NH the values of alpha are found to be larger than the corresponding values observed in ACN for both 2MI and 2MIN which possess highly reactive H atom bound to the heterocyclic N atom. Following the results obtained from the transient absorption spectra of the present donor-acceptor molecules in the different polarity solvents, a scheme describing the overall reaction mechanisms of the different photoreactions involved has been proposed. The probable causes for the changes observed in the mechanisms of the photoreactions involved in the cases of 2MI and 2MIN donors have been discussed in the light of their canonical structures.

Induction of apoptosis in a human erythroleukemic cell line K562 by tylophora alkaloids involves release of cytochrome c and activation of caspase 3

Tylophora alkaloids are plant products known for their antiasthamatic and antiproliferative activities. The underlying cellular changes resulting from inhibition of proliferation were investigated. Tylophora alkaloids induced apoptosis in K562 cells with characteristic apoptotic features like nuclear condensation, apoptotic body formation, flipping of membrane phosphatidylserine, activation of caspase 3 and release of mitochondrial cytochrome c. These studies suggest that the Tylophora alkaloids, in addition to their antiproliferative effects also induce apoptosis in erythroleukemic cells. These observations imply that Tylophora alkaloids could be useful molecules for their antiproliferative activity and for induction of apoptosis in tumor cells.

Synthesis and studies on spectroscopic as well as electron donating properties of the two alkoxy benzo[b]thiophenes

Synthesis, characterization, steady state and time resolved, using time correlated single photon counting as well as laser flash photolysis techniques, spectroscopic investigations were made for two alkoxy benzo[b]thiophene molecules: 5-methoxy benzo[b]thiophene (5MBT) and 5-methoxymethyl benzo[b]thiophene (5MMBT). In both non-polar n-heptane (NH) and polar acetonitrile (ACN) solvents and at ambient temperature the electronic absorption spectra of these thiophenes exhibit different band systems whose assignments were made from the measurements of the steady state excitation polarization spectra. Steady state fluorescence spectra of these molecules in the different polarity solvents show the presence of non-specific interactions. From the redox properties of the benzothiophenes, measured by cyclic voltammetry, their electron donating properties were observed in the presence of the well-known electron acceptor 9cyanoanthracene (9CNA). Further, detailed studies by laser flash photolysis techniques show that ion-recombination mechanism predominates after the initial excitation of the acceptor moiety using the third harmonic of Nd:YAG laser. This recombination together with the external heavy atom effect (the donor containing 'sulphur' atom) appears to be responsible for the formation of the triplet of the monomeric acceptor 9CNA. From the steady state experiments it is shown that both in non-polar NH and highly polar ACN the quenching in the fluorescence emission of 9CNA in the presence of the benzothiophene donors is brought about primarily by the external heavy atom effect and in ACN, although the presence of the photoinduced ET reaction is confirmed, this process seems, from the observed bimolecular dynamic quenching rate, kq to be significantly masked by the external heavy atom effect.

Immunomodulatory effect of Tylophora indica on Con A induced lymphoproliferation

Our preliminary studies with tylophora alkaloids had shown that they inhibit cellular immune responses like contact sensitivity to dinitro-flurobenzene and delayed hypersensitivity to sheep red blood cells, in vivo. Investigations were hence carried out to determine the cellular targets of tylophora alkaloids in in vitro systems. Con A induced proliferation of splenocytes was used as a model system to study the effect of the alkaloids on cellular immune responses. The alkaloid mixture was found to inhibit proliferation of splenocytes at higher concentrations and augment the same at lower concentrations. Both macrophages and T cells were found to be vulnerable to tylophora alkaloids. The alkaloid mixture suppressed IL-2 production in Con A stimulated splenocytes at the inhibitory or higher concentrations and enhanced production at the lower concentrations. IL-1 production by activated macrophages on the contrary was doubled in the presence of inhibitory concentrations of tylophora. These studies indicate that tylophora alkaloids have a concentration dependent biphasic effect on Con A induced mitogenesis. At lower concentrations they augment Con A induced lymphoproliferation by enhancing IL-2 production. Inhibition of proliferation at higher concentrations of the alkaloid is due to inhibition of IL-2 production and activation of macrophages, which have a cytostatic effect.

Inhibition of cellular immune responses by Tylophora indica in experimental models

Tylophora alkaloids have been shown to have antiasthmatic, antiinflammatory and antianaphylactic properties. Since all these disorders are a consequence of altered immunological status, the effect of these alkaloids on model immune reactions were studied. Crude extract of the leaves of Tylophora indica inhibited delayed hypersensitivity reaction to sheep red blood cells in rats when the alkaloid mixture was administered before and after immunization with these cells. The alkaloid mixture also inhibited contact sensitivity to dinitro-fluorobenzene in mice when given prior to or after contact sensitization. Lymphocytes taken from contact sensitized mice, when treated with tylophora alkaloid in vitro and transferred into naive syngeneic hosts, could suppress the transfer of delayed type hypersensitivity (DTH) response. However, the tylophora alkaloids could not suppress primary humoral (IgM) immune response to SRBC in mice at the same dose. These studies suggest that tylophora alkaloids suppress cellular immune responses when administered at any stage during the immune response.

Caucasian family with two independent mutations: 2594delC in BRCA1 and 5392delAG in BRCA2 gene

Germline mutations in two breast cancer susceptibility genes, BRCA1 and BRCA2, predispose individuals to early onset breast and ovarian cancer. The frequency of mutations in these genes in the general population is very low. Therefore, the prior probability of finding any family with mutations in both genes is even lower. This study reports the presence of two mutations, one in BRCA1 and a second in BRCA2, in a single family with variable expression. The BRCA1 mutation, 2594delC, was identified first in the proband. Analysis on a related family member with early onset bilateral breast cancer for the same mutation was negative. Further analysis on the same individual led to the identification of a second germline mutation, 5392delAG in BRCA2 gene in this family. Without the knowledge of the second mutation in this family, many asymptomatic individuals would have been given a negative test result and be falsely reassured. Further analysis reveals differential expression of the two mutations. The spectrum of cancers as well as the age of onset is variable between the mutations and the generations. Finally, the study exemplifies the fact that molecular analysis of a genetically heterogeneous disease can be very complex and requires a team effort of the patients and their family members, genetic counselors or referring physicians as well as the personnel from the testing laboratory.

Studies on unimolecular and bimolecular photoprocesses of a newly synthesized selenium compound, 7-chloro-2-phenyl-9H-[1]-benzopyrano[3,2-b]-selenophene-9-one (SeP)

Using steady state/time resolved spectroscopic and electrochemical techniques the spectroscopic and photophysical studies were made on a novel synthesized selenophene compound SeP in nonpolar methylcyclohexane (MCH), polar aprotic acetonitrile (ACN) and polar protic ethanol (EtOH) solvents at the ambient temperature as well as at 77 K. Both from the studies on unimolecular and bimolecular photoprocesses this selenophene compound was found to possess several electronic levels, 1Bb, 1La, 1Lb (all are of pi pi* nature and 1Lb is hidden within 1La band envelop like the characteristics of most of the acenes) and 1(nO pi*) state arising due to carbonyl oxygen atom. In polar ACN environment this nO pi* state disappears because it moves within the envelop of intense 1La band due to large destabilization. Large overlapping of different band systems within the 1La band of SeP was confirmed from the observed depolarization effect. The lack of phosphorescence of SeP both in MCH and EtOH rigid glassy matrix at 77 K has been inferred due to large vibronic interactions between closely lying triplets of the corresponding 1nO pi* and 1Lb states. From the bimolecular investigations, it reveals that SeP acts as a good electron donor in presence of the well known electron acceptor 9 cyanoanthracene (9CNA). Transient absorption spectra measured by laser flash photolysis technique demonstrate the formation of ion-pair when the acceptor is excited. From the analysis of the fluorescence quenching data it seemingly indicates that the major contribution in the diminution of the fluorescence intensity of the acceptor 9CNA in presence of SeP is not only due to the photoinduced electron transfer (ET) but also originates from static type (instantaneous) quenching processes along with external heavy atom effect. The possibility of occurrence of photoinduced ET reaction in Marcus inverted region is hinted.

Electron transfer compatible molecular design of benzothiophene-acetophenone bichromophores: a theoretical approach

Computational work has been done for a bichromophore (4MBA) comprising a donor 4-methoxy-benzo[b]thiophene (4MBT) and an acceptor molecule p-chloro-acetophenone (pclA) linked together by a HC=CH bond which shows large hyperpolarizability. The charge transfer in this bichromophoric system is computed by semiemperical theoretical calculation. Ground state and excited state dipole moment difference of the bichromophore 4MBA indicates a large electron transfer probability.

Genetic testing for breast cancer susceptibility: frequency of BRCA1 and BRCA2 mutations

Genetic testing for breast cancer susceptibility became a reality after two cancer predisposition genes, BRCA1 and BRCA2, were identified. Mutations in these two genes were predicted to account for 85% to 90% of hereditary breast and ovarian cancer syndromes. We present results of mutation analysis of the coding sequence of these two genes in 110 consecutive non-Jewish breast cancer patients with a positive family history of breast and/or ovarian cancer. The individuals were identified in various cancer risk evaluation centers in the country. Twenty-two (20%) mutations in the BRCA1 gene and 8 mutations (7%) in the BRCA2 gene were detected. We also analyzed 52 Ashkenazi Jewish breast cancer patients for mutations in the BRCA1 and BRCA2 genes. Eleven Jewish individuals (21%) carried either one of the two common mutations, 185delAG and 5382InsC, in the BRCA1 gene and 4 individuals (8%) had the 6174delT mutation in the BRCA2 gene. The frequency of mutations in BRCA genes in affected people in this ethnic group was not significantly different from the non-Jewish population. On further analysis, the data demonstrate that neither age of onset nor phenotype of the disease had any significant predictive value for the frequency of mutations in these genes. These data confirm the lower prevalence of mutations in either of the BRCA genes in clinical families when compared to high-risk families used for obtaining linkage data in a research setting.

High throughput fluorescence-based conformation-sensitive gel electrophoresis (F-CSGE) identifies six unique BRCA2 mutations and an overall low incidence of BRCA2 mutations in high-risk BRCA1-negative breast cancer families

Mutational analysis of cancer susceptibility genes has opened up a new era in clinical genetics. In this report we present the results of mutational analysis of the BRCA2 coding sequences in 105 high-risk individuals affected with breast cancer and/or ovarian cancer and previously found to be negative for mutations of the BRCA1 coding sequence in our laboratory. These individuals have a positive family history with three or more cases of breast cancer and/or ovarian cancer at any age from the same side of the family tree. In order to perform a high throughput and reliable mutational analysis of the BRCA genes, we have adapted the conformation-sensitive gel electrophoresis mutation-scanning assay to a fluorescent platform. The advantages are speed, reproducibility and enhanced resolving power of the scanning method. Four unique mutations, including one missense and three frameshift mutations, were identified in the pool of 60 non-Jewish patients (7%). Two cases of the 6174delT mutation were identified in the 45 Ashkenazi Jewish individuals studied (5%). In addition, two novel frameshift mutations, not characteristic of the Jewish subgroup, were identified. Thus there were four mutations in total in this ethnic subgroup (9%). The six mutations identified in this combined patient pool, excluding the 6174delT mutations, are novel and have not been previously reported in the Breast Cancer Information Core (BIC) database. The results indicate that BRCA2 mutations account for the disease in less than 10% of this patient population. In addition, there is no significant difference in frequency of BRCA2 mutations between the Ashkenazi Jewish and non-Jewish families in our clinical patient pool.

In vitro rejoining of double-strand breaks in cellular DNA by factors present in extracts of HeLa cells

We described previously a cell-free assay, that could be employed to study the rejoining of radiation-induced DNA double-strand breaks (dsb) in agarose embedded nuclei by activities present in an extract prepared from exponentially growing HeLa cells. Here, we extend the study and present an in vitro assay for rejoining of radiation-induced DNA dsb that employs 'naked' DNA prepared from agarose-embedded cells as a substrate and extract of HeLa cells as an enzyme source. There is no detectable residual protein on substrate DNA after extensive lysis with ionic detergents and treatment with proteases, as determined by SDS-PAGE and silver staining. We demonstrate that rejoining of dsb is absolutely dependent on cell extract and that, under optimal reaction conditions, it proceeds to an extent and with kinetics similar to those observed in intact cells. Dsb rejoining in this assay requires Mg 2+ and is inhibited by high concentrations of either K+ or Na+. This assay complements the nuclei assay for DNA dsb repair previously developed, and may be preferable to the latter in the purification of factors involved in DNA dsb repair, as it employs as substrate DNA deprived of proteins.

A cell-free assay using cytoplasmic cell extracts to study rejoining of radiation-induced DNA double-strand breaks in human cell nuclei

We describe a cell-free assay that can be employed to study rejoining of radiation-induced DNA double-strand breaks (dsbs) under in vitro conditions. The assay uses nuclei prepared from irradiated, agarose-embedded human A549 cells as substrate and cytoplasmic cell extracts prepared from exponentially growing HeLa cells as the source of enzymes. We demonstrate that rejoining of dsbs is absolutely dependent on cell extract and that, under optimal reaction conditions, it proceeds to an extent similar to that observed in intact cells, albeit with about six times longer half time. Dsb rejoining in this assay requires Mg2+ and is inhibited by high concentrations of either K+ or Na+. The assay should provide means for the biochemical characterization of the enzymology of eukaryotic cell DNA repair under conditions that retain chromatin structure. The assay can also be adapted to study repair of other types of damage induced in the DNA by ionizing or non-ionizing radiations, as well as by diverse chemical agents.

Prolactin increases mRNA encoding Na(+)-TC cotransport polypeptide and hepatic Na(+)-TC cotransport

We have shown that prolactin (Prl) increases the transhepatic transport of taurocholate (TC) in postpartum rats and following treatment of ovariectomized (Ovx) rats with ovine Prl (oPrl). The present studies were designed to determine if treatment of Ovx rats with oPrl (100, 300, or 600 micrograms/day, 7 days iv) 1) increases Na(+)-TC cotransport in basolateral plasma membrane vesicles (bLPM), 2) induces a corresponding increase in the steady-state levels of Na(+)-TC cotransport polypeptide (Ntcp mRNA), and 3) if the oPrl-mediated increase in Na(+)-TC cotransport activity is blocked by cycloheximide, an inhibitor of protein synthesis. oPrl (300 micrograms/day) induced a twofold increase in the maximal velocity for Na(+)-TC cotransport in both hepatocytes and bLPM vesicles with little change in the Michaelis constant. Infusion of oPrl at a dose of 100, 300, or 600 micrograms/day increased steady-state Ntcp mRNA four-, ten-, and twofold, respectively. Finally, cycloheximide blocked the oPrl-mediated increase in Na(+)-TC cotransport but did not affect basal activity. These data support the hypothesis that an increase in Ntcp mRNA followed by increased synthesis and incorporation of Ntcp in the plasma membrane is responsible for the oPrl-mediated increase in Na(+)-TC cotransport in the basolateral plasma membrane domain of the hepatocyte.

Prolactin increases Na+/taurocholate cotransport in isolated hepatocytes from postpartum rats and ovariectomized rats

The role of prolactin (PRL) in regulating the transport of the bile acid taurocholate (TC) was assessed using isolated rat hepatocytes. Na(+)-dependent TC cotransport was determined in hepatocytes from female nonpregnant, pregnant (19-20 days pregnant), postpartum (48 hr postpartum) and postpartum rats treated with bromocriptine to block PRL secretion. In separate experiments ovariectomized rats were infused i.v. with solvent alone (OVX) or with ovine PRL (100, 300 and 600 micrograms/day) for 7 days (OVX+oPRL). The least squares estimates of Km (microM) and Vmax (nmol/min/mg protein) for Na(+)-dependent TC uptake were, respectively: 15 and 1 in nonpregnant, 9 and 0.4 in pregnant, 9 and 1.1 in postpartum and 15 and 1 in bromocriptine-treated postpartum rats, and were 15 and 1 in OVX, 15 and 1 in OVX+oPRL (100 micrograms/day), 30 and 2 in OVX+oPRL (300 micrograms/day) and 18 and 2 in OVX+oPRL (600 micrograms/day) rats, respectively. Calculation of the 95% joint confidence limits for Km and Vmax showed that Na(+)-dependent TC uptake was significantly decreased in pregnant rats, and significantly increased in postpartum rats relative to nonpregnant controls. Bromocriptine-treated postpartum rats were not different from controls. Infusion of 300 and 600 micrograms/day oPRL significantly increased Na(+)-dependent TC transport relative to OVX rats. Na(+)-K(+)-ATPase activity did not differ among the groups. These data indicate that PRL is responsible for the increased Na(+)-dependent transport of TC in the maternal liver postpartum, and that administration of oPRL to ovariectomized rats increases this transport in a dose-dependent manner.

Inhibition of DNA polymerase activity by thymine hydrates

Ultraviolet irradiation of DNA results in various pyrimidine modifications. We have demonstrated formation of both cis-thymine hydrate and trans-thymine hydrate (6-hydroxy-5,6-dihydrothymine) in UV-irradiated poly(dA-dT):poly(dA-dT). Both are released from DNA as free bases by bacterial and human glycosylases. Thymine hydrates are stable in DNA and can be detected in control, unirradiated substrates. We examined the effects of thymine hydrates in UV-irradiated substrate poly(dA-dT):poly(dA-dT) on E. coli DNA polymerase I activity. Enzymic incorporation of labeled thymidine-5'-monophosphate significantly decreased with increasing UV dose. Reversal of DNA thymine hydrates to thymines by mild heating of the substrate prior to enzymic reaction resulted in partial recovery of nucleotide incorporation. Cyclobutane thymine dimers are formed between non-adjacent thymines in UV-irradiated poly(dA-dT):poly(dA-dT). These are responsible for the incomplete recovery of DNA polymerase activity following heating due to their heat stability. Analyses of the irradiated and hydrolyzed substrate also demonstrated formation of minor yields of photoproducts formed by covalent linkage of adjacent thymines and adenines by UV-irradiation. Therefore, the thymine hydrates formed in UV-irradiated DNA partially inhibit polymerase activity during DNA synthesis and thus could be potentially lethal if unrepaired.