Synthesis and activity of 6-substituted purine linker amino acid immunostimulants

Synthesis of some new pyrazolo[3,4-d]pyrimidine derivatives of expected anticancer and radioprotective activity

On the account of the reported anticancer activity of pyrazolo[3,4-d]pyrimidines, a new series of pyrazolo[3,4-d]pyrimidine derivatives were synthesized and tested for in-vitro anticancer activity against Ehrlich Ascites Carcinoma (EAC) cell line. Moreover, one of the target products was evaluated for in-vivo radioprotective activity. The reaction of o-aminoester 1 with benzylamine in presence of triethylorthoformate yielded the corresponding 5-benzylpyrazolopyrimidine derivative 2. The N-amino derivative 3 was used to synthesize new derivatives of pyrazolopyrimidines 4-7. The corresponding 1,3,4-oxadiazolopyrazolopyrimidine derivatives 12 and 14 were obtained via reaction of compound 9 with reagent 10 and/or triethylorthoformate. Thiophosgenation of compound 1 furnished the corresponding 5-isothiocyanate derivative 15, which was reacted with o-phenylenediamine, thiosemicarbazide and anthranilic acid to give benzimidazolopyrazolopyrimidine, 17, pyrazolotriazolopyrimidine, 19 and pyrazolopyrimidobenzoxazine, 20 respectively. The structures of the synthesized compounds were confirmed by microanalyses, IR, NMR, and mass spectral data. Compounds 2 and 9 showed intermediate anticancer activity compared to doxorubicin as positive control with IC50 values of 90 and 100 microg/ml, respectively. On the other hand, compound 5 showed significant radioprotective effect.

Enhancement of Th1 type cytokine production and primary T cell activation by PBI-1393

In previous reports, we have shown that PBI-1393 (formerly BCH-1393), N,N-Dimethylaminopurine pentoxycarbonyl D-arginine, stimulates cytotoxic T-lymphocyte (CTL) responses both in vitro and in vivo in normal immune status and immunosuppressed mice. Additionally, PBI-1393 was tested for anticancer activity in syngeneic mouse experimental tumor models and it displayed significant inhibition of tumor outgrowths when given in combination with sub-therapeutic doses of cytotoxic drugs (cyclophosphamide, 5-fluorouracil, doxorubicin and cis-platinum). However, the mechanism of action of PBI-1393 was still unknown. Here, we report that PBI-1393 enhances IL-2 and IFN-gamma production in human activated T cells by 51% and 46% respectively. PBI-1393 increases also IL-2 and IFN-gamma mRNA expression as shown by RT-PCR. The physiological relevance of IL-2 and IFN-gamma gene modulation by PBI-1393 is illustrated by the advantageous increase of T cell proliferation (39+/-0.3% above control) and human CTL response against prostate (PC-3) cancer cells (42+/-0.03%). The enhancement of human T cell proliferation and CTL activation by PBI-1393 demonstrates that this compound potentiates the immune response and in this regard, it could be used as an alternative approach to IL-2 and/or IFN-gamma therapy against cancer.

Immunostimulant oxidized β-glucan conjugates

beta-Glucans are polysaccharides that act as nonspecific immune system stimulants. However, many beta-Glucans are sparingly soluble in water. This work describes an oxidative procedure, which solubilizes the beta-Glucan from Saccharomyces cerevisiae and maintains its immunostimulatory properties. Furthermore, the carboxylates at the site of oxidation allow for the conjugation of small molecule immunostimulants. Both the parent oxidized beta-glucan and its conjugates with O-beta-alanyl-5-[6-(N,N'-dimethylamino)purin-9-yl]pentanol stimulate cytotoxic T-lymphocytes (CTLs), B cells and macrophages. In addition, they both stimulate natural killer (NK) cells, a property which the small molecule purine does not possess.

Synergistic anti-tumor activity of a novel immunomodulator, BCH-1393, in combination with cyclophosphamide

N,N-dimethylaminopurine pentoxycarbonyl D-arginine (BCH-1393) is a novel low molecular weight synthetic immunomodulator that has been shown to significantly stimulate cytotoxic T-lymphocyte responses both in vitro and in vivo (Zacharie B, Gagnon L, Attardo G, Connolly TP, St-Denis Y, Penney CL. Synthesis and activity of 6-substituted purine linker amine immunostimulants. J. Med. Chem. 1997;40:2883-94). Prompted by this evidence, we extended evaluation of BCH-1393 for anticancer activity in syngeneic mouse experimental tumor models. Consistent with previous findings, in vitro assessment of BCH-1393 activity demonstrated a significant increase in the CTL responses in the range of 10(-9)-10(-5) M. Treatment of mice with four consecutive daily intraperitoneal injections at 25 and 50 mg/kg resulted in a significant increase of the relative percentage of blood CD4+, CD8+, NK and monocyte subsets without any evidence of toxicity. In vivo anti-tumor activity of BCH-1393 was evaluated, either alone or in combination with subtherapeutic doses of cyclophosphamide (Cy), against weakly immunogenic mouse breast carcinoma DA-3 and strongly immunogenic colon adenocarcinoma MC38. Daily intraperitoneal injection of BCH-1393 at 50 mg/kg alone was well tolerated but produced a relatively weak anti-tumor effect in both tumor models. However, a significant inhibition of tumor outgrowth and suppression of established tumor growth was observed when BCH-1393 was administered in combination with subtherapeutic doses of Cy. Combination treatment of 50 mg/kg BCH-1393 with 100 mg/kg Cy (given as single intravenous bolus injection) starting 2 days prior to DA-3 tumor cell inoculation prevented tumor outgrowth in 70-80% of treated mice. In the remaining 20-30% of mice that had developed tumors, a nearly complete (90%) tumor growth inhibition was observed at days 22-24 post tumor implant. In the MC38 tumor model, combination treatment of established tumors with BCH-1393 and Cy (CTX) at 50 mg/kg resulted in a significant delay in tumor growth compared to CTX treatment alone. The observed concomitant anti-tumor activity of BCH-1393 with cyclophosphamide warrants further investigation of this immunomodulator as an adjunctive treatment of cancer.

Synthesis of enantiomerically pure, sn-1 modified sn-2-deoxy-2-amido-glycero-3-phospholipids

The synthesis of two types of enantiomerically pure sn-2-deoxy-2-amido-glycero-phospholipids differing in the connection of the alkyl chain at the sn-1-position is described. Both types of lipids were prepared from L-serine-methylester as the chiral starting material.

Synthesis and cytokine modulation properties of pyrrolo[2, 3-d]-4-pyrimidone nucleosides

A series of pyrrolo[2,3-d]pyrimidone nucleosides were synthesized and evaluated for their ability to enhance Type 2 cytokines and to suppress Type 1 cytokines in human T cells activated in vitro. Compounds 16b, 16c, 16d, 18c, and 19b induced substantial enhancement of IL-4 (a Type 2 cytokine) levels while three compounds (16b, 16c, and 16f) showed significant suppression of IFNgamma (a Type 1 cytokine) levels. The results revealed a strict structural requirement for the nucleoside-mediated enhancement of IL-4. Modifications of the ribofuranose moiety of the nucleosides either abolished or dramatically reduced the activity. Both the 5'-hydroxy and 5-carboxamidine are crucial for the activity. Of the few nucleoside analogues that demonstrated enhancement on Type 2 cytokine production, 7-(beta-D-ribofuranosyl)pyrrolo[2, 3-d]-4-pyrimidone-5-carboxamidine (16c) showed a dramatic enhancement (>200%) of IL-4 levels and a significant enhancement (36%) of IL-5 levels. Moreover, this compound showed substantial suppression of the Type 1 cytokines, IFNgamma (42%), IL-2 (54%), and TNFalpha (55%). Similarly, compound 16b showed a substantial enhancement of IL-4 (46%) and suppression of IL-2 (35%), IFNgamma (30%), and TNFalpha (26%). To our knowledge, these are the first nucleoside analogues that induce a Type 2 cytokine bias in T cells. The cytokine modulation property of 16c and 16b merits the therapeutic evaluation of these compounds in treating diseases in which immunopathology is associated with polarized Type 1 cytokine responses.

Synthesis and activity of dipeptides, linked to targeting ligands, as specific NK cell enhancers

Water soluble analogues of the lipophilic immunostimulant, octadecyl D-alanyl-L-glutamine, BCH-527, were synthesized and evaluated for the ability to stimulate natural killer (NK) cells. One of these compounds in which the octadecyl chain of BCH-527 was replaced with a shorter chain alcohol, 6-(D-alanyl-L-glutaminylamino)hexan-1-ol, 9, displayed an in vitro stimulation of NK cells comparable to that of interleukin 2 (IL 2). However, when the hydroxyl of 9 was linked to L-fucose to yield 1-beta-[6-(D-alanyl-L-glutaminylamino)hex-1-yl]-L- fucopyranose (BCH-2537, 1), the observed stimulation of NK cells was greater than that observed with IL 2. Further evaluation of these compounds revealed that the improved in vitro activity of BCH-2537 was more pronounced in vivo. That is, while both compounds significantly increased splenic NK cells, only BCH-2537 significantly increased the activity of these cells in vivo. In terms of a structure-activity relationship, NK cell activity was sensitive to minor structural modifications. It was influenced by conservative substitutions within the dipeptide, the length of the hydrocarbon chain, and the functionality at the end of the chain. No other compound enhanced NK cell activity to the extent exhibited by BCH-2537, although a few were equipotent to 9.