Andrzej Kutner

The rationale for deltanoids in therapy for myeloid leukemia: Role of KSR–MAPK–C/EBP pathway

The evidence for the promising potential for derivatives of Vitamin D (deltanoids) in the treatment of myeloid leukemias is increasing, but currently is not matched by the understanding of the precise mechanisms by which these anti-neoplastic effects are achieved. Unlike solid tumors in which growth retardation by deltanoids appears to result from inhibition of cell proliferation and the promotion of cell death by apoptosis, control of myeloid leukemia proliferation by deltanoids results from the induction of differentiation of the immature myelo-monocytic cells towards functional monocytic cells. We present here the accumulating evidence that a pathway that is initiated by deltanoid activation of Vitamin D receptor (VDR) and leads to monocytic differentiation of human myeloblastic HL60 cells, includes the MEK-ERK and JNK mitogen-activated protein kinases (MAPKs), their positive and negative regulators and a downstream effector C/EBPbeta. As in other cells, the abundance of VDR protein increases shortly after an exposure of HL60 cells to 1alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2) D(3)). Other early events include a parallel upregulation of kinase suppressor of Ras (KSR-1) and the activation of the ERK MAPK pathway and data suggest that KSR-1 acts to amplify the signal provided by low concentrations of 1alpha,25(OH)(2) D(3). Maintenance of monocytic differentiation may be enhanced by JNK, but diminished by p38, MAPK signaling. Downstream, one of the targets of these pathways is C/EBPbeta, which can directly interact with the promoter for CD14, a gene characteristically expressed in monocytes. Importantly, in freshly obtained acute myeloid leukemia (AML)-M2 cells exposed to PRI-2191, a novel deltanoid with a modified side chain, upregulation of C/EBPbeta paralleled the induction of monocytic differentiation. These data provide a basis for the hypothesis that deltanoid-induced upregulation of C/EBPbeta bypasses the block to granulocytic differentiation in myeloid leukemia cells by redirecting the cells to monocytic differentiation.

Cell differentiating and anti-proliferative activity of side-chain modified analogues of 1,25-dihydroxyvitamin D3

Besides its calcium mobilizing activity in vivo, 1,25-dihydroxyvitamin D3 has the ability to induce differentiation of human promyelocytic leukemia cells in vitro. We studied the cell differentiating activity of four novel analogues of 1,25-dihydroxyvitamin D3, using the HL60 cell line as a model. We also analyzed the influence of these compounds on the proliferation of HL60 cells, normal human keratinocytes, normal fibroblasts from human skin and human keratinocytes transfected with human papillomavirus type 16. Two of the four analogues, i.e. those with extended side-chain, were found to display similar cell differentiating and anti-proliferative activities as 1,25-dihydroxyvitamin D3. The other two analogues, with a shortened side-chain which included an additional hydroxyl, showed a substantially lower activity than that of 1,25-dihydroxyvitamin D3. We observed distinct differences in sensitivity to the anti-proliferative activity of either 1,25-dihydroxyvitamin D3 or its analogues between cells of different origin.

Biological activity in vitro of side-chain modified analogues of calcitriol.

The results of our studies on the biological activity of side-chain modified analogues of vitamin D are reviewed. These analogues appeared to be effective in induction of cell differentiation, inhibition of tumour cell proliferation in vitro and in increasing of antitumour effect of cytostatics. On the other hand, inhibition of cytostatic-induced apoptosis by these compounds was observed. The mechanism of the antiproliferative effect of calcitriol analogues in vitro is discussed. The induction of antigens CD14 and CD11b expression and phagocytic activity of HL-60 cells after exposure to these compounds is related to their effect on cell differentiation. The differentiation of the HL-60 leukaemia cells induced by side-chain modified analogues of calcitriol increases their sensitivity to the antiproliferative effect of cisplatin, doxorubicin and genistein, despite of that this pretreatment causes resistance of these cells to cytostatics-induced apoptosis. We observed a synergistic antiproliferative effect of the combined therapy using analogues of calcitriol with subsequent treatment with the above-mentioned cytostatics. This effect was measured as a significant decrease of the ID50 values for each cytostatic applied after pretreatment of the tumour cells with the calcitriol analogues. The results presented suggest that the improved therapeutic effect may be achieved also in vivo by the combined application of the analogues (without calcemic activity) of calcitriol with antitumour agents.

Side-chain modified vitamin D analogs induce rapid accumulation of VDR in the cell nuclei proportionately to their differentiation-inducing potential

1,25-Dihydroxyvitamin D(3) (1,25D) regulates gene transcription through a nuclear vitamin D receptor (VDR) which acts as a ligand-regulated transcription factor. Some structural vitamin D analogs (VDAs) are selective in their biological actions, because they retain cell-differentiating potential, while their calcemic activity is reduced. In this article we have shown that in untreated HL60 cells the expression level of VDR is low, in spite of constant presence of VDR mRNA. Furthermore we have shown that one of the most rapid effects of either 1,25D or VDAs is nuclear accumulation of VDR, which is proportional to the differentiation-inducing potential of given analog. We observed this effect not only in HL60 cells, but also in blast cells isolated from patients with acute myeloid leukemias. After longer incubation time of the cells with various VDAs, the expression levels of VDR have become unrelated to the final differentiation effect.

Synthesis and antiproliferative activity of side-chain unsaturated and homologated analogs of 1,25-dihydroxyvitamin D2 (24E)-(1S)-24-Dehydro-24a-homo-1,25-dihydroxyergocalciferol and congeners

A series of analogs of 1,25-dihydroxyergocalciferol (1-4) was synthesized and screened for their antiproliferative activity in vitro. The structure of new analogs was designed based on biological activity of the previously obtained side-chain modified analogs of vitamin D(2) and D(3). The analogs were obtained by the Julia olefination of C(22)-vitamin D sulfone 11 with side-chain aldehyde 15. The analogs were tested for their antiproliferative activity against the cells of human breast cancer lines T47D and MCF7 as well as human and mouse leukemia lines, HL-60 and WEHI-3, respectively. Analog 2 (PRI-1907) showed the strongest antiproliferative activity out of the present series of analogs of 1,25-dihydroxyvitamin D(2) with the mono homologated and double unsaturated side chain. The activity of 2 was 3-150 times stronger, depending on the cell line, than that of 1,25-dihydroxycholecalciferol (calcitriol), used as standard.

Toxicity and antineoplastic effect of (24R)-1,24-dihydroxyvitamin D3 (PRI-2191)

Many efforts have been made to obtain active and less toxic Vitamin D analogs for new clinical applications. The results of previous studies demonstrated the efficacy and safety of topical treatment of psoriasis with one of these analogs, 1,24-dihydroxyvitamin D(3), tacalcitol (1,24-(OH)(2)D(3)). In the present study, we evaluated the toxicity and antitumor effect of this analog. Lethal toxicity of 1,24-(OH)(2)D(3) after s.c. injection was significantly lower than that of calcitriol. No significant differences were observed in the toxicity of the analogs when administered p.o. Calcium levels in the serum of mice treated with calcitriol were significantly higher (111%) than those in mice treated with 1,24-(OH)(2)D(3) (89%) at 5 day after the first s.c. (10 microg/kg/day) administration in comparison to the control (healthy, untreated animals). Oral administration increased the calcium level by 78% for calcitriol and only to 47% over the control for 1,24-(OH)(2)D(3). Parallel administration of clodronate prevented the calcitriol- and 1,24-(OH)(2)D(3)-induced lethal toxicity and also prevented increase in calcium levels. Single therapy with calcitriol did not affect tumor growth in the 16/C mouse mammary cancer model. In contrary, 1,24-(OH)(2)D(3) alone reduced tumor volume to 41% of control. Cisplatin alone did not affect growth of 16/C tumor in these conditions. The growth of tumors in the presence of cisplatin was inhibited by 1,24-(OH)(2)D(3) but not by calcitriol. Interestingly, the inhibition of tumor growth in cisplatin-treated mice by 1,24-(OH)(2)D(3) was greater, than that observed in mice treated with this analog alone. In conclusion, 1,24-(OH)(2)D(3) revealed higher antitumor and lower calcemic activity and toxicity than calcitriol. Application of biphosphonates along with Vitamin D analogs is sufficient to overcome the calcemic and toxic side effects of the proposed treatment.

Vitamin D analogs combined with 5-fluorouracil in human HT-29 colon cancer treatment

In the present study, we evaluated the antitumor effect of two synthetic analogs of vitamin D, namely PRI-2191 [(24R)-1,24-dihydroxyvitamin D3] and PRI-2205 (5,6-trans calcipotriol), in combined human colon HT-29 cancer treatment with 5-fluorouracil (5-FU). Mice bearing HT-29 tumors transplanted subcutaneously or orthotopically were injected with vitamin D analogs and 5-FU in various schedules. A statistically significant inhibition of subcutaneous or orthotopic tumor growth was observed as a result of combined therapy. In HT-29 tumors and in cells from in vitro culture, we observed increased vitamin D receptor (VDR) expression after treatment with either PRI-2205 or 5-FU alone, or in combination. Moreover, PRI-2205 decreased the percentage of cells from intestinal tumors in G2/M and S stages and increased sub-G1. Increased VDR expression was also observed after combined treatment of mice with 5-FU and PRI-2191. Moreover, our docking studies showed that PRI-2205 has stronger affinity for VDR, DBP and CAR/RXR ligand binding domains than PRI-2191. PRI-2191 analog, used with 5-FU, increased the percentage of subcutaneous tumor cells in G0/G1 and decreased the percentage in G2/M, S and sub-G1 populations as compared to 5-FU alone. In in vitro studies, we observed increased expression of p21 and p-ERK1/2 diminution via use of both analogs as compared to use of 5-FU alone. Simultaneously, PRI-2191 antagonizes some pro-apoptotic activities of 5-FU in vitro. However, in spite of these disadvantageous effects in terms of apoptosis, the therapeutic effect expressed as tumor growth retardation by PRI-2191 is significant. Our results suggest that the mechanism of potentiation of 5-FU antitumor action by both analogs is realized via increased p21 expression and decreased p-ERK1/2 level which may lead to diminution of thymidylate synthase expression. Higher binding affinity for VDR, DBP, but also for CAR\RXR ligand binding domain of PRI-2205 may, in part, explain its very low toxicity with sustained anticancer activity.

Structure–function analysis of vitamin D2 analogs as potential inducers of leukemia differentiation and inhibitors of prostate cancer proliferation

We characterized a structure-function relationships of four analogs of vitamin D(2) with extended and branched side-chains. We tested their ability to induce differentiation of human acute myeloid leukemia (AML) cells both in vitro and ex vivo. Our experiments on five human cell lines revealed substantial differences among tested analogs. Analogs with side-chains extended by one (PRI-1906) or two carbon units (PRI-1907) displayed similar or elevated cell-differentiating activity in comparison to 1,25-dihydroxyvitamin D(3) (1,25D), whereas further extending side-chain resulted in substantially lower biological activity (PRI-1908 and PRI-1909). Similar pattern of cell-differentiating activities to that observed in human cell lines has also been shown in blast cells isolated from patients diagnosed with AML. The ability of the analogs to activate expression of CYP24A1 gene has been studied in HL60 cell line. The analog PRI-1906 activated expression of CYP24A1 similarly to 1,25D, while PRI-1907 weaker than 1,25D. In addition, the analogs PRI-1906 and PRI-1907 were able to moderately inhibit proliferation and significantly activate expression of CYP24A1 mRNA in prostate cancer cells PC-3. Finally, we examined the molecular actions triggered by these analogs and found that their biological activity was related to their ability to induce expression and nuclear translocation of VDR and C/EBPβ.

Physicochemical Characteristics of Sunitinib Malate and its Process-Related Impurities

In this article, details of crystal and molecular structures of sunitinib malate (SUM), an anticancer therapeutic, and its key synthetic intermediate are presented. Both these compounds were also characterized spectroscopically and thermally. SUM crystallizes in the monoclinic P2(1) space group with two molecules in the asymmetric part of the unit cell, whereas the intermediate crystallises in the triclinic P-1 space group with four independent molecules in the asymmetric unit. The three-dimensional structure of SUM consists of two different layers of molecules. The first one is built of the malic anions, whereas the other layer consists of more hydrophobic sunitinib molecules. This layer is formed by two types of molecules creating a herring bond-like pattern with pairs of neighboring cations forming the V-shape arrangement of molecules. The V-shaped pairs of molecules form ribbons by fitting into two neighboring V shapes. The characteristic V-shape assemble of the moieties is hold together with three C-H…F weak interactions. Besides, process-related impurities of SUM were identified and their structures confirmed by separate synthesis. These impurities were fully characterized by spectroscopic and crystallographic methods as well as by differential scanning calorimetry and thermogravimetric analysis. The H-, (13)C-, and (15)N-nuclear magnetic resonance signals were fully assigned structurally and the resulting structures were confirmed by Fourier-transformed infrared spectroscopy. It was the herein elaborated synthesis of impurity-free SUM that allowed for growing of its single crystals suitable for X-ray crystallographic studies. Comparison of the powder X-ray diffraction pattern for SUM with that derived from single-crystal X-ray crystallographic analysis indicated that SUM formed the polymorph I crystal phase, which is also encountered in its pharmaceutical formulation.

Double Point Modified Analogs of Vitamin D as Potent Activators of Vitamin D Receptor

Rational design, chemical synthesis, structural analysis, molecular modeling and biological evaluation are reviewed for all the double point modified vitamin D analogs that have been developed as potential therapeutics over the last several years. The idea of double modifications was based on the 3D structure of the ligand binding domain of the model of the vitamin D receptor. It was recently proved that structural modifications in the two remote parts of the vitamin D molecule might have additive biological effects resulting in an increased functional activity and lowered calcemic side effect. Recent in vivo experiments clearly demonstrated the potential use of these analogs in new therapeutic areas such as autoimmune and hyper-proliferative diseases, including cancer and the systemic treatment of psoriasis. Although some of these analogs are already approaching clinical trials, the molecular mechanism of action and their improved efficiency still remain to be fully understood. In this review the key steps of the convergent synthetic strategies that combine the modified A-ring and the CD-ring fragment carrying the altered side-chain are presented. The advantages of using the natural alicyclic and acyclic precursors are demonstrated as well as all the modern synthetic methodologies used for combining structural fragments. The results of molecular mechanics modeling are critically examined as well as the advantages and limitations of the use of the models of vitamin D proteins for the docking experiments and the design of new analogs. The potential use of advanced structural approaches, including high resolution X-ray crystallography, is discussed as to the prospect of providing a better understanding of the observed activity of modified analogs. Biological profiles in vitro and in vivo for groups of analogs are presented in a new tabular form to illustrate structure activity relationships.