Haruo Takaku

High-level expression of Mycoplasma arginine deiminase in Escherichia coli and its efficient renaturation as an anti-tumor enzyme.

The arginine deiminase (AD) gene was cloned from Mycoplasma arginini and expressed in the cytosol of Escherichia coli as inclusion bodies with an expression level of at least 20% of the total bacterial proteins. The inclusion bodies were solubilized with 6 M guanidine hydrochloride (Gdn-HCl) under reducing conditions, in order to avoid incorrect disulfide-bond formation of the recombinant (r-) AD molecules, and renaturation was performed under various refolding conditions. The optimum renaturation conditions were found to be incubation for 90 h at pH 7.5 and 15 degrees C. The resulting completely refolded r-AD was purified to homogeneity by anion-exchange and arginine-affinity chromatography and its activity yield was 72.5%. The specific activity of the purified r-AD was comparable to and its amino acid composition was identical to those of Mycoplasma AD, and NH2-terminal sequence analysis revealed that its methionine residue corresponding to the translation initiation codon had been removed completely. Anti-tumor activity analyses showed that r-AD inhibited the growth of two mouse cell lines, hepatoma MH134 and fibrosarcoma Meth A, strongly in vitro at concentrations in excess of 10 ng ml-1. Moreover, when MH134-implanted mice were given single intravenous injections of r-AD at doses of 50 mg kg-1 and higher, their survival times were prolonged significantly. These results, taken together, indicate that the enzymatic properties and biological actions of r-AD were highly consistent with those of Mycoplasma AD.

Synthesis and Biological Evaluation of 8-Oxoadenine Derivatives as Toll-like Receptor 7 Agonists Introducing the Antedrug Concept

Systemic administration of a Toll-like receptor 7 (TLR7) agonist is effective to in suppressing Th2 derived inflammation, however systemic induction of various cytokines such as IL-6, IL-12, and type I interferon (IFN) is observed. This cytokine induction would be expected to cause flu-like symptoms. We have previously reported adenine compounds (3, 4) as interferon inducing agents acting as TLR7 agonists. To identify potent anti-inflammatory compounds without systemic side effects, a labile carboxylic ester as an antedrug functionality onto the N(9)-benzyl group of the adenine was introduced. We found that 9e was a potent TLR7 agonist (EC(50) 50 nM) and rapidly metabolized by human plasma (T(1/2) 2.6 min) to the pharmacologically much less active carboxylic acid 16. Intratracheal administration of 9e effectively inhibited allergen-induced airway inflammation without inducing cytokines systemically. Therefore, the TLR7 agonist with antedrug characteristics 9e (SM-324405) is a novel candidate for immunotherapy of allergic diseases.

Chemical modification by polyethylene glycol of the anti-tumor enzyme arginine deiminase from Mycoplasma arginini.

Ammo acid‐degrading enzymes are known to inhibit the growth of tumor cells in culture by depleting amino acids in the medium. Here we demonstrate that arginine deiminase (EC 3.5.3.6) from Mycoplasma arginini had stronger growth‐inhibitory activity against all 4 kinds of tumor cell lines tested than L‐asparaginase and arginase, which are well‐known anti‐tumor enzymes. Next, chemical modification of the arginine deiminase molecule with polyethylene glycol was shown to enhance its potency as an anti‐tumor enzyme. The percentage of modified amino groups per molecule was estimated to be 51% of the total amino groups, and the average molecular weight was estimated to be about 400,000 by gel‐filtration HPLC. The enzymic activity of the modified enzyme was 25.5 units/mg protein, which was equivalent to 57% of that of the native enzyme. The modified enzyme strongly inhibited growth of a mouse hepatoma cell line, MH134, at a concentration of more than 10 ng/ml, showing almost the same dose‐response curve as the native enzyme. When a bolus of 5 units of the modified enzyme was intravenously injected into male BDF1 mice, L‐arginine in the blood completely disappeared within 5 rain, and remained undetectable for more than 8 days. On the other hand, in the case of bolus injection of the same number of units of native enzyme, the plasma L‐arginine level recovered up to 66% of the control level at 8 days. These results suggest that this modified enzyme has a longer plasma clearance time and may be more effective as a new anti‐tumor agent than the native enzyme.

Synthesis and structure-activity relationships of 2-substituted-8-hydroxyadenine derivatives as orally available interferon inducers without emetic side effects.

Recently we reported the adenine derivatives (2-4) as new interferon (IFN) inducers. In the present study, we conducted a detailed structure and activity relationship study of 4 and its related derivatives on IFN inducing activity. From this study, we found that compound 4 exhibited the most potent IFN inducing activity in vitro with a minimum effective concentration of 0.01 microM, and 4 also showed strong IFN-inducing activity at doses of more than 0.3mg/kg by oral administration in mice. This potency was 10-fold stronger than that of Imiquimod. Moreover, 4 did not cause emesis in ferrets even at doses as high as 10mg/kg, whereas, 80% of animals were emetic when orally administered with the same dose of Imiquimod. These results indicate that compound 4 is superior to Imiquimod with respect to efficacy and safety.

KNI‐577, a Potent Small‐Sized HIV Protease Inhibitor Based on the Dipeptide Containing the Hydroxymethylcarbonyl Isostere as an Ideal Transition‐State Mimic

The development of an effective therapeutic agent for the treatment of AIDS continues to be a challenging problem. Since the discovery that the virally encoded HIV protease is vital for propagation, inhibition of this enzyme has become a major target for AIDS chemotherapy. Consequently, numerous efforts aimed at the development of potent and selective inhibitors have been undertaken[2]. Based on the substrate transition state, we designed and synthesized a novel class of HIV protease inhibitors containing allophenylnorstatine [Apns; (2S,3S)‐3‐amino‐2‐hydroxy‐4‐phenylbutyric acid] with a hydroxymethylcarbonyl (HMC) isostere. Among them, the tripeptide KNI‐272 was a highly selective and superpotent HIV protease inhibitor (Ki=5.5 pM)[3]. KNI‐272 exhibited potent in vitro and in vivo antiviral activities with low cytotoxicity[4]. The NMR, X‐ray crystallography, and molecular modeling studies showed that the HMC group in KNI‐272 interacted excellently with the aspartic acid carboxyl groups of the HIV protease active site[5].

Biological characterization of a novel class of toll‐like receptor 7 agonists designed to have reduced systemic activity

BACKGROUND AND PURPOSE Toll‐like receptor 7 (TLR7) agonists have potential in the treatment of allergic diseases. However, the therapeutic utility of current low molecular weight TLR7 agonists is limited by their systemic activity, resulting in unwanted side effects. We have developed a series of TLR7‐selective ‘antedrugs’, including SM‐324405 and AZ12441970, which contain an ester group rapidly cleaved in plasma to reduce systemic exposure.

Synthesis and structure–activity relationship of diarylamide urea derivatives as selective inhibitors of the proliferation of human coronary artery smooth muscle cells

A series of diarylamide urea derivatives were synthesized and evaluated for their inhibitory activities against human coronary artery smooth muscle cells (SMCs) and human coronary artery endothelial cells (ECs). Compound 2o was superior to the lead compound, Tranilast, in terms of its potency of the inhibitory activity and cell selectivity.

Synthesis and Structure-Activity Relationship of Diarylamide Derivatives as Selective Inhibitors of the Proliferation of Human Endothelial Cells

A series of diarylamide urea derivatives were synthesized and evaluated for their inhibitory activities against human coronary artery endothelial cells (ECs) and human coronary artery smooth muscle cells (SMCs). Compound was superior to Tranilast, in terms of both cell selectivity and the potency of its inhibitory activity toward the proliferation and angiogenesis of ECs.

Mechanism of Action of Inhibition of Allergic Immune Responses by a Novel Antedrug TLR7 Agonist

Triggering innate immune responses through TLRs is expected to be a novel therapeutic strategy for the treatment of allergic diseases. TLR agonists are able to modulate Th2 immune responses through undefined mechanisms. We investigated the mechanism of action of the suppression of Th2 immune responses with a novel antedrug TLR7 agonist. The antedrug is rapidly metabolized by plasma esterases to an acid with reduced activity to limit systemic responses. Topical administration of this compound inhibited features of the allergic airway inflammatory response in rat and murine allergic airways model. Type I IFN played a role in the suppression of Th2 cytokines produced from murine splenocytes. Inhibition of Th2 immune responses with the antedrug TLR7 agonist was shown to be via a type I IFN–dependent mechanism following short-term exposure to the compound, although there might be type I IFN–independent mechanisms following long-term exposure. We have demonstrated that local type I IFN signaling and plasmacytoid dendritic cells, but not Th1 immune responses, are required for in vivo efficacy against murine airway Th2-driven eosinophilia. Furthermore, migration of dendritic cell subsets into the lung was related to efficacy and is dependent on type I IFN signaling. Thus, the mechanism of action at the cytokine and cellular level involved in the suppression of Th2 allergic responses has been characterized, providing a potential new approach to the treatment of allergic disease.

Intratracheal and oral administration of SM-276001: A selective TLR7 agonist, leads to antitumor efficacy in primary and metastatic models of cancer

Topical TLR7 agonists such as imiquimod are highly effective for the treatment of dermatological malignancies; however, their efficacy in the treatment of nondermatological tumors has been less successful. We report that oral administration of the novel TLR7‐selective small molecule agonist; SM‐276001, leads to the induction of an inflammatory cytokine and chemokine milieu and to the activation of a diverse population of immune effector cells including T and B lymphocytes, NK and NKT cells. Oral administration of SM‐276001 leads to the induction of IFNα, TNFα and IL‐12p40 and a reduction in tumor burden in the Balb/c syngeneic Renca and CT26 models. Using the OV2944‐HM‐1 model of ovarian cancer which spontaneously metastasizes to the lungs following subcutaneous implantation, we evaluated the efficacy of intratracheal and oral administration of SM‐276001 in an adjuvant setting following surgical resection of the primary tumor. We show that both oral and intratracheal TLR7 therapy can reduce the frequency of pulmonary metastasis, and metastasis to the axillary lymph nodes. These results demonstrate that SM‐276001 is a potent selective TLR7 agonist that can induce antitumor immune responses when dosed either intratracheally or orally.