Synthesis and Evaluation of Chirally Defined Side Chain Variants of 7-Chloro-4-Aminoquinoline To Overcome Drug Resistance in Malaria Chemotherapy.

A novel 4-aminoquinoline derivative [(S)-7-chloro-N-(4-methyl-1-(4-methylpiperazin-1-yl)pentan-2-yl)-quinolin-4-amine triphosphate] exhibiting curative activity against chloroquine-resistant malaria parasites has been identified for preclinical development as a blood schizonticidal agent. The lead molecule selected after detailed structure-activity relationship (SAR) studies has good solid-state properties and promising activity against in vitro and in vivo experimental malaria models. The in vitro absorption, distribution, metabolism, and excretion (ADME) parameters indicate a favorable drug-like profile.

Sixteen-years of clinically relevant dipeptidyl peptidase-IV (DPP-IV) inhibitors for treatment of type-2 diabetes: a perspective.

Inhibition of DPP-IV enzyme has taken centre stage as a validated drug target for type 2 diabetes therapy and as a result of research efforts done towards developing effective DPP-IV inhibitors, the first clinical candidate of this class came in focus in 1998. Thus, from 1998 to 2013, these 16-years have witnessed heightened research activities in the discovery and development of clinically relevant inhibitors of DPP-IV as antidiabetic agents. The effective DPP-IV inhibitors have played a key role in this endeavour and as result there are eight approved gliptins in the clinical usage while others are in different stages of clinical trials. A wide variety of DPP-IV inhibitors were synthesized and evaluated; and were classified into several categories based on their core structural features. In this article, classification of all the clinically relevant DPP-IV inhibitors based on selectivity, clinical efficacy and safety profiles is reviewed in terms of generations. This review also encompasses clinical phase wise discussion, developmental progress, chemistry and binding modes of all clinical DPP-IV inhibitors. In addition, major challenges facing the future design and development of safe clinical DPP-IV inhibitor are also briefly mentioned.

Thiazolidin-4-one and thiazinan-4-one derivatives analogous to rosiglitazone as potential antihyperglycemic and antidyslipidemic agents.

A number of thiazolidin-4-one and thiazinan-4-one derivatives were prepared by three component condensation in one pot reaction method. These compounds were evaluated for anti-hyperglycemic activity by in vitro and in vivo assay systems. The compounds with thiazolidin-4-one and thiazinan-4-one moieties exhibited significant anti-hyperglycemic activity. A few compounds (3a, 3b, 4a and 4b) have exhibited both anti-hyperglycemic and anti-dyslipidemic activities. Among them the thiazinan-4-one derivative 4a showed maximal (45%) improvement in oral glucose tolerance test in db/db mice at 30 mg/kg oral dose.

Design, synthesis of 4-aminoquinoline-derived thiazolidines and their antimalarial activity and heme polymerization inhibition studies.

The present study describes the synthesis of a series of new 4-aminoquinoline-derived thiazolidines and evaluation of their antimalarial activity against a NF-54 strain of Plasmodium falciparum in vitro and N-67 strain of Plasmodium yoelii in vivo. Among the series, two compounds, 2-(4-chloro-phenyl)-thiazolidine-4-carboxylic acid [2-(7-chloro-quinolin-4-ylamino)-ethyl]-amide hydrochloride (14) and 2-(2,6-dichloro-phenyl)-thiazolidine-4-carboxylic acid [2-(7-chloro-quinolin-4-ylamino)-ethyl]-amide hydrochloride (22) exhibited significant suppression of parasitaemia in the in vivo assay. All the analogues were found to form strong complex with haematin and inhibited the ß-haematin formation in vitro. These results suggest that these compounds act on heme polymerization target.

Design and synthesis of 3-[(7-chloro-1-oxidoquinolin-4-ylamino)alkyl]-1,3-thiazolidin-4-ones as antimalarial agents.

A new series of quinoline analogs have been synthesized and found active against P. falciparum in vitro and P. yoelli in vivo. Compounds 8, 10 and 11 exhibited superior in vitro activity compared to chloroquine. Selected compounds 8, 10 and 11 exhibited significant suppression of parasitaemia in vivo assay. These analogs form a complex with hematin and inhibit the ß-hematin formation, suggesting that this class of compounds act on a heme polymerization target. Further this study confirms that quinoline ring nitrogen is essential for both transportation of the molecule across the membrane as well as for tight binding to hematin.

CpG oligodeoxynucleotide 2006 and miltefosine, a potential combination for treatment of experimental visceral leishmaniasis.

In view of the severe immunosuppression in visceral leishmaniasis (VL), a rational approach to effectively combat the parasitic scourge would be to enhance the immune status of the host. Use of CpG oligodeoxynucleotide (CpG-ODN) against leishmaniasis has previously been reported, especially as an immunomodulator and adjuvant with various immunogens. In the present study, experiments were carried out with BALB/c mice and hamsters infected with Leishmania donovani. Immunostimulating class B bacterial CpG-ODN namely, ODN-2006, was administered at various doses by the intraperitoneal (i.p.) route. The dose of CpG-ODN-2006 (1 nM/single dose) showing the most antileishmanial activity was given as free and liposomal forms with different doses of miltefosine, namely, 5 and 10 mg/kg of body weight, for 5 days in mice and hamsters, respectively. Among the various groups, mice coadministered liposomal CpG-ODN and miltefosine (5 mg/kg) showed the best inhibitory effect (97% parasite inhibition) compared with free CpG-ODN plus miltefosine and miltefosine, free CpG-ODN, and liposomal CpG-ODN given separately. Similar responses were observed in the case of hamsters, where the combination of liposomal CpG-ODN with miltefosine (10 mg/kg) gave 96% parasite inhibition. Promising antileishmanial efficacy was observed in animals treated with liposomal CpG-ODN and miltefosine.

4-Aminoquinoline derived antimalarials: synthesis, antiplasmodial activity and heme polymerization inhibition studies.

A new series of 4-aminoquinoline derivatives have been synthesized and found to be active against both susceptible and resistant strains of Plasmodium falciparum in vitro. Compound 1-[3-(7-chloro-quinolin-4-ylamino)-propyl]-3-cyclopropyl-thiourea (7) exhibited superior in vitro activity against resistant strains of P. falciparum as compared to chloroquine (CQ). All the compounds showed resistance factor between 0.59 and 4.31 as against 5.05 for CQ. Spectroscopic studies suggested that this class of compounds act on heme polymerization target.

CpG oligodeoxynucleotide augments the antileishmanial activity of miltefosine against experimental visceral leishmaniasis.

OBJECTIVES: To evaluate the combination of CpG oligodeoxynucleotide (CpG ODN) and miltefosine for the treatment of experimental visceral leishmaniasis (VL). METHODS: The experiments were carried out using BALB/c mice and hamsters, infected with Leishmania donovani. CpG ODN was administered at various doses by the intraperitoneal (ip) route. The dose of CpG ODN (1 nM/single dose) showing best antileishmanial activity was given as free and liposomal forms with a subcurative dose of miltefosine, namely 2.5 and 5 mg/kg x 5 days in mice and hamsters, respectively. RESULTS: Among the various groups of mice, co-administered liposomal CpG ODN and miltefosine showed the best inhibitory effect (85% inhibition) compared with free CpG ODN and miltefosine, and miltefosine, free CpG ODN and liposomal CpG ODN separately. Production of Th1 cytokines, nitric oxide (NO), reactive oxygen species (ROS) and H(2)O(2) was enhanced. A remarkable increase in the phagocytosis index was also observed, indicating overall immunological support to antileishmanial activity of miltefosine by CpG ODN. Similar responses were observed in hamsters. CONCLUSIONS: Promising antileishmanial efficacy was observed in animals treated with liposomal CpG ODN and miltefosine, strongly supported by enhancement of Th1 cytokines as well as NO, ROS and H(2)O(2) levels. The correlation of experimental findings in both the models (mouse and hamster) strengthens the potential of CpG ODN as an immunomodulator in combination with miltefosine against VL.

Derivatives of human beta-casein fragments (54-59) exhibit highly potent immunosuppressant activity.

Human beta-casein fragment (54-59) having the amino acid sequence Val-Glu-Pro-Ile-Pro-Tyr, has shown potent immunostimulant activity. Several analogs of this hexapeptide have been synthesized with modification at the N-terminal region and two analogs, viz. peptide I and peptide II have shown significant immunosuppressant activity in-vivo mouse model. Effect on cell mediated immunity (CMI) and humoral immunity was studied in mouse/SRBC model. Both the peptides failed to stimulate immune response in vivo and showed inhibition of CMI and humoral response to sheep red blood cells (SRBC). Peptides showed inhibition in alloantigen induced lymphocyte proliferation, i.e., mixed lymphocyte reaction (MLR) in vitro. Treatment with peptides inhibited the production of interferon-gamma (IFN-gamma), and increased the production of interleukin-4 (IL-4) as well as improved the skin graft survival. Cyclosporine a known immunosuppressant showed similar effect on mouse model. Present study thus provides a lead for the development of safe and effective immunosuppressant.

Synthesis and antimalarial activity of novel side chain modified antimalarial agents derived from 4-aminoquinoline.

Malaria is one of the foremost public health problems in developing countries affecting nearly 40% of the global population. Apart from this, the past two decade's emergence of drug resistance has severely limited the choice of available antimalarial drugs. Furthermore, the general trend emerging from the SAR-studies is that chloroquine resistance does not involve any change to the target of this class of drugs but involves compound specific efflux mechanism. Based on this premise a number of groups have developed short chain analogues of 4-aminoquinoline, which are active against CQ-resistant strains of P. falciparum in in vitro studies. However, these derivatives undergo biotransformation (de-alklyation) significantly affecting lipid solubility of the drug. In view of this background information, we thought that it would be interesting to study the effect of additional lipophilicity and cationic charge at the lateral side chain of 4-aminoquinoline. This prompted us to explore the cationic amino acid conjugates namely, lysine and ornithine of 4-aminoquinoline with a view to achieve improved antimalarial activity and to the best of our knowledge such amino acid conjugates have not been hitherto reported in the literature in the case of 4-aminoquinolines. In the present study, a new series of side-chain modified 4-aminoquinolines have been synthesized and found active against both susceptible and multidrug resistant strains of P. falciparum in vitro and P. yoelli in vivo. The seminal finding of the present study is that a new series of compounds having significantly more activity against CQ resistant parasites has been identified.

Synthesis and antimalarial activity of side chain modified 4-aminoquinoline derivatives.

A new series of side-chain modified 4-aminoquinolines have been synthesized and found active against P. falciparum in vitro and P. yoelli in vivo. Compounds 6, 11, 12, and 19 exhibited superior in vitro activity compared to chloroquine. Selected compounds 6, 12, and 19 exhibited significant suppression in the in vivo assay. These analogs form a complex with hematin and inhibit the beta-hematin formation, suggesting that this class of compounds act on a heme polymerization target.

Design, synthesis and antimalarial activity of a new class of iron chelators.

Iron is crucial for many biochemical reactions involved in the growth and multiplication of the malaria parasite Plasmodium falciparum. There are many reports indicating that the iron chelators have antimalarial activity in vitro, in vivo and in human studies. However, these compounds suffer from a number of serious problems such as limited membrane permeability, short half-life and require long subcutaneous infusions. To circumvent these drawbacks we have designed a new class of iron chelators, wherein EDTA is tethered to 4-aminoquinoline. Here 4-aminoquinoline scaffold is used as a carrier to penetrate biological membrane and facilitate targetting the compounds to acidic food vacuole of the parasite. This study describes the synthesis of novel iron chelators and their in vitro antimalarial activity against P. falciparum strain of NF-54. The calculated LogP values of these compounds suggest the importance of lipophilicity for the antimalarial activity. The EDTA esters are more active than the corresponding acids. The biophysical studies suggest that these compounds may inhibit the parasite growth by iron chelation mechanism.

Immunomodulatory activity of analog of muramyl dipeptide and their use as adjunct to chemotherapy of Leishmania donovani in hamster.

In search of a potent immunomodulator to be used as an immunoprophylactic agent and as adjunct to chemotherapy against Leishmania infection, two analogs of muramyl dipeptide, viz. N.Ac-norMur-MeVal-D-isoGln (86/448) and N.AcMur-Acc-D-isoGln (89/729) were evaluated for desired activity. Effect of these peptides on cell mediated and humoral immunity was studied by immunizing the peptide treated mouse with sheep red blood cells (SRBC) and determining HA-titer, plaque forming cells assay and delayed type of hypersensitivity (DTH) response after 4-5 days. Both the peptides stimulated cell mediated immunity (CMI), humoral response as well as macrophage function in terms of super oxide anion (O2-) and nitric oxide (NO) generation. Mitogen induced lymphocyte proliferation and production of IL-2 and INF-gamma increased while that of IL-4 and IL-10 decreased by both the peptides showing a typical Th1 type response. After establishing the immunostimulatory activity, these peptides were evaluated for immunoprophylactic efficacy as well as for use as adjunct to chemotherapy with stibanate (SSG) against Leishmania donovani infection in golden hamster. These peptides were found quite effective in both the modes. In adjunct use the treatment may require lower dose of SSG and thereby reduce the chances of drug toxicity.

Tuftsin-bearing liposomes as antibiotic carriers in treatment of macrophage infections.

Tuftsin is a tetrapeptide (Thr-Lys-Pro-Arg) that specifically binds monocytes, macrophages, and polymorphonuclear leukocytes and potentiates their natural killer activity against tumors and pathogens. The antimicrobial activity of this peptide is significantly increased by attaching at the C-terminus a fatty acyl residue through the ethylenediamine spacer arm. This activity is further augmented by incorporating the modified tuftsin in the liposomes. The tuftsin-bearing liposomes not only enhance the host's resistance against a variety of infections but also serve as useful vehicles for the site-specific delivery of drugs in a variety of macrophage-based infections, such as tuberculosis and leishmaniasis.

Adjunct effect of immunostimulating hexapeptide analogous to human beta-casein fragment (54-59) to sodium stibogluconate against experimental visceral leishmaniasis.

Visceral leishmaniasis (VL) is a major public health problem in many tropical countries of the world. The available chemotherapeutics require parenteral administration and have other limitations like cost, toxicity, variable efficacy or restricted supplies. There is no effective treatment for immunosuppressed patients with leishmaniasis- HIV co-infection. Hence, new therapies, that are effective when treatment with the currently available drugs fails, must be developed. One of the major strategies for effective and safe treatment of leishmaniasis and other infectious diseases, in the last decade, involves the use of immunomodulators as adjunct to chemotherapy. In this context, we studied the immunomodulatory activity of a hexapeptide Val-Glu-Pro-Ile-Gly-Tyr (CDRI compound 89-215) corresponding to (54-59) fragment of human beta-casein in mice and its efficacy in adjunct chemotherapy with SSG using L. donovani/hamster model. The hexapeptide was found to enhance both humoral and CMI responses. In animal model the hexapeptide per se showed no antileishmanial activity. However, when given alongwith suiboptimal dose of SSG, it enhanced the efficacy of SSG from 24% to 80%. The activity was very close to the efficacy (85%) recorded for curative dose of SSG. Adjunct chemotherapy with immunomodulator in visceral leishmaniasis appears to be a fruitful preposition.

Synthesis and antimicrobial activity of erythromycin-A oxime analogs.

A series of erythromycin-A oxime ether as well as esters have been synthesized. Ether derivatives were synthesized through the epoxy ether intermediate of erythromycin-9-oxime, followed by opening of the epoxy linkage through various amines, whereas esters have been prepared through DCC mediated protocol. These derivatives have been evaluated for antibacterial activity and found to be as active as erythromycin-A.

Generating neutralizing antibodies, Th1 response and MHC non restricted immunogenicity of HIV-I env and gag peptides in liposomes and ISCOMs with in-built adjuvanticity.

For enhancing immunogenicity and develop vaccine strategies using peptide based constructs against HIV-1, a chimeric peptide containing V3 loop and transmembrane sequence of gp41 with two glycine motifs as spacer was constructed. The V3-gp41, gp41 peptide and p17 and p24 peptides separately or in a cocktail were entrapped with or without MA729 as an immunoadjuvant in liposomes or ISCOMs. The immunogenicity, antigen induced T-cell proliferation and cytokine profiles of various formulations were studied in four different inbred strains of mice of H-2d, H-2b, H-2k and H-2q haplotypes, keeping alum as a control adjuvant. Both liposomes and ISCOM preparations elicited high titer and long lasting antibody response (60 days and above). When compared to the alum formulation, the liposomes co-entrapped with MA729 produced high antibody levels, comparable with that induced by ISCOMs. Peptide in alum, liposomes and ISCOMs enhanced both antigen specific IgG2a and IgG2b isotypes and high T-cell stimulation index. Peptide formulations also induced antibodies with high affinity and in vitro neutralizated the formation of HIV-1 syncytia. T-cell supernatants contained high levels of IFN-gamma and IL-2. Thus formulation in these adjuvants induced a predominant Th1 like response with MA729 as a versatile novel delivery vehicle for stimulating the appropriate arm of the immune response that can selectively modulate MHC class I or MHC class II response. The above peptide can be of wide vaccination interest as a means to improve immune responses to several other HIV-1 antigens and may serve as candidates for vaccine development.

Reversal of T cell anergy in leprosy patients: in vitro presentation with Mycobacterium leprae antigens using murabutide and Trat peptide in liposomal delivery.

Mycobacterium leprae, the causative agent of leprosy resides and multiplies within the host monocytes and macrophages, thereby evading host immune system. Cell-mediated immune response (CMI) plays a vital role as evidenced from the high CMI in BT/TT (borderline and tuberculoid) patients and conversely low in BL/LL (borderline and lepromatous) patients. In the present study, an attempt was made to immunomodulate the anergized T cells of lepromatous leprosy patients by presenting the mycobacterial antigen in combination with T cell adjuvant, murabutide (active analog of muramyl' dipeptide, MDP-BE) and a Trat peptide (T cell epitope of Integral membrane protein (Trat) from Escherichia coli) in particulate form (liposomes) or soluble form (media). PBMNC of normal, BT/TT and BL/LL were stimulated in vitro with five mycobacterial antigens (Ag) in the following formulations, Ag, Ag+murabutide, Ag+murabutide+Trat peptide either in liposomes or in medium. All the five antigen(s) when delivered in liposomes containing murabutide and Trat peptide showed a very high lymphoproliferative response (p<0.001) in all the three groups. IFN-gamma and IL-2 were significantly (p<0.001) high in these culture supernatants compared to IL-10 and IL-4 confirming a shift from CD4+Th2 to Th1 response in leprosy patients with particulate mode of antigen presentation. Interestingly, PBMNC derived from lepromatous patients also showed consistent T cell proliferation with all the formulations. Further, the mechanism of liposomal processing of antigens was studied using different inhibitors that interfere at different stages of antigen presentation. Results indicate that this study may pave way for an immunotherapeutic approach for reverting the anergic T cells of lepromatous patients to proliferating T cells with the release of Th1 cytokines thereby restoring the CMI response in these patients.

Immunomodulator tuftsin augments antifilarial activity of diethylcarbamazine against experimental brugian filariasis.

In the present study, we evaluated the potential of an immunomodulator tuftsin in increasing the efficacy of liposomised diethylcarbamazine (DEC) against experimental filarial infection of Brugia malayi. The liposomised form of DEC, when used at sub-optimal dose of 25 mg/kg body weight, successfully eliminated filarial parasite from systemic circulation in animals inflicted with B. malayi infection. However, the formulation was effective upto 60 days post infection only, followed by recurrence of the infection. In contrast, the co-administration of liposomal formulation of DEC along with an immunomodulator tuftsin was found to be competent enough to suppress microfilarial stage of parasite till 90 days post treatment. Interestingly, tuftsin bearing DEC liposomes were found to be effective against adult parasite as well.

Use of tuftsin bearing nystatin liposomes against an isolate of Candida albicans showing less in vivo susceptibility to amphotericin B.

In the present study, we evaluated tuftsin bearing nystatin liposomes for their potential against an isolate of Candida albicans (C. albicans) showing less in vivo susceptibility to amphotericin B (Amp B). The liposomised-Amp B in higher doses was found to be effective in elimination of less susceptible strain of C. albicans (C. albicans JMCR) in Balb/c mice, but may not be recommended due to toxicity constraints. On the other hand, liposomal nystatin was shown to possess higher efficacy as compared to that of Amp B, and was pertinent in treatment of C. albicans JMCR strain. The data of present work reveals that the incorporation of nystatin in tuftsin-bearing-liposomes results in a significant increase in its efficacy against experimental murine candidiasis. Interestingly, the pre-treatment of animals with liposomised-tuftsin prior to challenge with C. albicans infection was more effective in elimination of the pathogen from host and shows an advantage in prophylactic perspectives.