A Methylcellulose Microculture Assay for the In Vitro Assessment of Drug Toxicity on Granulocyte/macrophage Progenitors (CFU-GM)

Novel platform for the preparation of synthetic orally active peptidomimetics with hemoregulating activity. II. Hemosuppressor activity of 2,5-diketopiperazine-based cyclopeptides

The novel chemical platform formed by the branched piperazine-2,5-dione peptide derivatives (2,5-diketopiperazines) for creating non-invasive biologically active peptidomimetics has been developed. A successful application of this approach to orally available hemostimulatory peptidomimetics was demonstrated for all-L cyclopeptide from the Glu-Trp-peptide family. In the 1980s, we have separated and characterized a number of dipeptides from the thymus homogenate. The most active peptide Glu-Trp has been studied and developed into the immunostimulating drug Thymogen. The inversion of the amino acid optical form endows the dipeptides with suppressor properties: D-Glu-D-Trp-OH and D-Glu-(D-Trp)-OH, inhibit proliferation of hemopoietic progenitors in the intact bone marrow. Based on the peptide D-Glu-(D-Trp)-OH, the new immunosuppressive drug Thymodepressin has been prepared. In this work, we applied the platform mentioned above to the design and synthesis of orally active hemosuppressive Thymodepressin® analogs. The novel data for the hemosuppressor activity of the dipeptide D-Glu(D-Trp-OH)-OH and its cyclopeptide analogs are discussed. A new example is presented of a rare phenomenon when enantiomeric molecules demonstrate reciprocal (i.e., opposite) biological activities.

Gemcitabine Based Peptide Conjugate with Improved Metabolic Properties and Dual Mode of Efficacy

Gemcitabine is a clinically established anticancer agent potent in various solid tumors but limited by its rapid metabolic inactivation and off-target toxicity. We have previously generated a metabolically superior to gemcitabine molecule (GSG) by conjugating gemcitabine to a gonadotropin releasing hormone receptor (GnRH-R) ligand peptide and showed that GSG was efficacious in a castration resistant prostate cancer (CRPC) animal model. The current article provides an in-depth metabolic and mechanistic study of GSG, coupled with toxicity assays that strengthen the potential role of GSG in the clinic. LC-MS/MS based approaches were employed to delineate the metabolism of GSG, its mechanistic cellular uptake, and release of gemcitabine and to quantitate the intracellular levels of gemcitabine and its metabolites (active dFdCTP and inactive dFdU) resulting from GSG. The GnRH-R agonistic potential of GSG was investigated by quantifying the testosterone levels in animals dosed daily with GSG, while an in vitro colony forming assay together with in vivo whole blood measurements were performed to elucidate the hematotoxicity profile of GSG. Stability showed that the major metabolite of GSG is a more stable nonapeptide that could prolong gemcitabine's bioavailability. GSG acted as a prodrug and offered a metabolic advantage compared to gemcitabine by generating higher and steadier levels of dFdCTP/dFdU ratio, while intracellular release of gemcitabine from GSG in DU145 CRPC cells depended on nucleoside transporters. Daily administrations in mice showed that GSG is a potent GnRH-R agonist that can also cause testosterone ablation without any observed hematotoxicity. In summary, GSG could offer a powerful and unique pharmacological approach to prostate cancer treatment: a single nontoxic molecule that can be used to reach the tumor site selectively with superior to gemcitabine metabolism, biodistribution, and safety while also agonistically ablating testosterone levels.

Alternative methods in toxicology: CFU assays application, limitation and future prospective

Blood is a fluid connective tissue which plays a vital role for normal body function. It consist different type of blood cells which is continuously reproduce inside the bone marrow from hematopoietic system. Xenobiotics could be specifically toxic to the hematopoietic system and they can cause hematological disorders by disturbing the normal functions. In vitro hematopoietic colony-forming cell assays play a crucial role to evaluate potential toxic effects of new xenobiotics and also helpful in bridging the gap between preclinical toxicology studies in animal models and clinical investigations. Use of these assays in conjunction with, high-throughput screening reduces the cost and time associated with these assays. This article provides a critical view over in vitro hematopoietic colony-forming cell assays in assessment of hematotoxicity.

Loss of histone deacetylase 4 causes segregation defects during mitosis of p53-deficient human tumor cells

We investigated the role of histone deacetylase 4 (HDAC4) using RNA interference (RNAi) and knockout cells to specifically address its role in cell cycle progression in tumor and normal cells. Ablation of HDAC4 led to growth inhibition in human tumor cells but not to detectable effects in normal human dermal fibroblasts (NHDF) or myelopoietic progenitors. HDAC4-/+ or HDAC4-/- murine embryonic fibroblasts showed no detectable growth defects. On the other hand, HDAC4 RNAi in HeLa cells produced mitotic arrest followed by caspase-dependent apoptosis. Mitotically arrested cells showed chromosome segregation defects. Even though the growth of both p53-wild-type and p53-null tumor cells were affected by HDAC4 ablation, segregation defects were observed only in p53-null cells. HDAC4 associates with the PP2A-B56 regulatory subunit, which is known to be involved in chromosome segregation, and RNAi of either the structural subunit A or the regulatory subunit B56 of PP2A also caused chromosome segregation defects. We conclude that HDAC4 is required for cell cycle progression of tumor cells by multiple mechanisms, one of which seems to be specific to p53-deficient cells through chromosome segregation defects. On the contrary, HDAC4 is not required for the progression of NHDF. We therefore suggest that systemic selective interference with the expression or function of HDAC4 is expected to have a significant therapeutic window, in particular, for p53-deficient tumors.

Validation and Development of a Predictive Paradigm for Hemotoxicology Using a Multifunctional Bioluminescence Colony-Forming Proliferation Assay

The lympho-hematopoietic colony-forming assay has been redesigned into a rapid, nonsubjective and standardized proliferation assay that can measure the effects of compounds on multiple stem and progenitor cell populations from different species simultaneously using a sensitive, high-throughput bioluminescence readout. Eleven reference compounds from the Registry of Cytotoxicity (RC) and eight other compounds, including anticancer drugs, were studied over an 8- to 9-log dose range for their effects on seven cell populations from both human and mouse bone marrow simultaneously. The cell populations studied included a primitive (HPP-SP) and mature (CFC-GEMM) stem cell, three hematopoietic (BFU-E, GM-CFC, Mk-CFC) and two lymphopoietic (T-CFC, B-CFC) populations. The results reveal a five-point prediction paradigm for lympho-hematotoxicity. Depending on how and which populations are affected, the resulting effects in the periphery can be predicted. Validation against the RC Prediction Model produces a high degree of correlation between the in vitro IC(50) values and known in vivo LD(50) values, thereby allowing preclinical dosing to be predicted. If primary human hematopoietic target tissue is used, inhibitory concentration (IC(50)/IC(75)/IC(90)) values of anticancer and other drugs can be converted into predicted clinical doses which, when compared to published chemotherapeutic dosing regimen, are very similar. When performed during early drug screening, the prediction value of the assay should help reduce time and cost, but above all, provide increase efficacy and safety for the patient.