Pathobiology of myelodysplastic syndromes

Effect of GM-CSF, 1, 25-Dihydroxycholecalciferol (Vit.D) and All-Trans-Retinoic Acid (ATRA) on the Proliferation and Differentiation of MDS-Bone Marrow (BM)-Cells In Vitro

Myelodysplastic syndromes (MDS) are a heterogenous group of stem cell disorders characterized by an impaired differentiation of the pluripotent stem cell resulting in dysplastic changes of all three hemopoietic lineages. We studied the effect of vitamin D (Vit.D) or all-trans retinoic acid (ATRA; 10(-6) and 10(-8)M) in combination with GM-CSF on the proliferation and differentiation of mononuclear bone marrow-cells (MNC) of 48 MDS-patients as compared to 9 normal bone marrow (BM)-controls in a special colony assay: 30,000 MNC were cultured in agar plugs for 7 days (d) and the resulting colonies immunophenotyped in situ by a panel of monoclonal antibodies. In 14 of 48 cultured MDS-BM-samples hemopoietic clones could be grown which expressed myelomonocytic antigens (CD14 (21%*), CD15 (35%*)) as well as blast antigens (CD20 (9%*), CD34 (10%*), Glycophorin A (Glyco A, 18%*)) whereas all normal BM-colonies were negative for blast markers. Vit.D or ATRA in combination with GM-CSF could not induce an (immunologically measurable) increased differentiation (5 higher percentage of differentiated clones) as compared to GM-CSF alone. We conclude that Vit.D and ATRA have no sufficient differentiation effect on MDS-cells. Our colony assay in combination with immunophenotyping enables an in vitro measurement of differentiation and proliferation in MDS. We suggest the use of this technique to measure effects of therapy in the course of the disease.

Innate chaos: I. The origin and genesis of complex morphologies and homeotic regulation

The genesis of complex morphologies is an inherent property of all dynamically expanding natural systems. In the inorganic and prebiotic world, chaotic movement of quantitable particles results in formation of ordered streamlined structures or micelles close to phase boundaries. In the course of chemical and colloid crystallization or development of living organisms, complex morphologies emerge, due to unusual chaotic attraction, diffusion limited aggregation (DLA) and multifractal organization suggesting that common mechanisms direct the morphogenesis in a wide range of natural systems. The development of a multicellular organism from a single fertilized oocyte requires intensive clonal proliferation sequential determinations and the organization of terminally differentiated cells in morphologically stable homeostatic functional units. Comparative data on insect and vertebrate embryogenesis revealed that the spatial organization of the developing body is orchestrated by several mechanisms: maternal effect genes or cell position specify the initial polarities and the main axes, while metameric segmentation, intrasegment identity and cell fate are determined by the programmed expression of morphogenetic determinants. They include evolutionarily conserved DNA binding proteins containing homeobox or pair-box sequences, endogenous ligands, activating specific nuclear hormone receptors, and humoral growth factors acting via specific membrane receptors and more ubiquitous transducing pathways. Morphogenetic regulators form intratissual gradients and demark fields required for the correct realization of the developmental programme. It has been recognized that the cell's freedom is limited to stringent developmental choices that in the end results in the formation of coherent cell colonies, many of them displaying chaotic behaviour. The linkage between embryonic regulation and adult tissue differentiation is not completely elucidated, however, data are emerging to show that several morphogenetic regulators may function throughout life in different human tissues. Genetically transmissible deletions or acquired impairments likely contribute to malignant tissue growth. Diffusible morphogenetic regulators may reverse the malignant phenotype in some cases and induce clinical remission. Further work is needed, however, to identify the dominant components of physiological regulatory networks and to understand what hierarchical organization and chaotic behaviour represent in order to elaborate new combined therapeutic protocols.

Roles for the heliodynamic hormones, all trans retinoic acid and 1 alpha, 25-dihydroxyvitamin D3, in control of the hematopoietic cell cycle

It is now well established that the production of primary hematopoietic cells is controlled at different levels of the biological organization. Bone marrow (BM) stromal cells, the extracellular matrix (ECM), polypeptide hematopoietic growth factors (HGF) as well as endogenous cell-division cycle (CDC) related factors play a dominant role in this control. Recent information suggest that the 2 lipophilic hormones, transRA and 1 alpha,25D3, depending on and/or perhaps mediating solar energy, play a role in the maintenance of BM homeostasis. Here we show that both transRA and 1 alpha,25D3: a) modulate the growth and/or stimulate the adipocytic differentiation of fibroblastic stromal cells (F-CFU); b) inhibit the synthesis and extracellular processing but stimulate the solubilization of matrix collagen; c) modulate the clonal growth of myeloid progenitor cells (GM-CFU) in synergy with HGFs; and d) inhibit the production of lactic acid in standard, normal long-term BM cultures (LTBMC). Comparative analysis of normal, preleukemic and leukemic BM cells in LTBMC indicated a positive correlation between the induction of terminal differentiation and reduced lactate production elicited by transRA or 1 alpha,25D3. These results raise a hypothesis according to which the terminal differentiation induced by the helicodynamic hormones is dependent on the mitochondrial aerobic ATP-generating system whose impairment may be a critical step during the process of leukemic transformation.

Retinoic acid in mono- or combined differentiation therapy of myelodysplasia and acute promyelocytic leukemia

Myelodysplastic preleukemic syndromes (MDPS) and acute promyelocytic leukemia (APL) share a surprising in vivo sensitivity to the hormonally acting 13 cis or all trans retinoic acids (transRA). Here we show that transRA as a monotherapeutic agent induced a stable remission in APL at the third relapse. In MDPS, treatment with prednisone and 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25D3) 13 cis RA induced a long-lasting hematological remission. Initially both patients had an impaired BM microenvironment which regenerated on retinoid therapy as judged by reappearance of the Hematon fraction in the BM aspirates. Our preclinical experiments using long-term liquid BM cultures (LTBMC) indicated that several individual patterns of growth and differentiation responses can be induced by combinations of transRA, 1 alpha,25D3 and hemopoietic growth factors (HGFs). The biological responses may vary from complete clonal extinction to a significant growth stimulation of the leukemic blast cell populations. These results further support the importance of preclinical studies in selecting "good" responders for, and excluding "poor" responders from protocols using differentiation therapy.