Negative feedback represents the principal mechanism for regulating growth in biological systems. Over the past 20 years, our understanding of the role played by inhibitory factors governing this process has advanced considerably. This is particularly well illustrated in the field of experimental hematology with the recognition of hemopoietic progenitor cell proliferation inhibitors, an expanding group of unrelated peptides that act to limit proliferation in hemopoietic precursor cells. The characterization and subsequent production of these molecules by chemical synthesis or recombinant DNA technology has enabled investigators to explore their role in normal hemopoiesis and define a potential role in clinical medicine. A number of inhibitory factors, including macrophage inflammatory protein-1 alpha (MIP-1 alpha) and the tetrapeptide AcSDKP appear to share a relative specificity to hemopoietic progenitor cell subsets. Others, such as interferon and tumor necrosis factor, have a more complex action and their hemopoietic effects are likely to be indirect and nonspecific. In addition to the role of inhibitors in normal steady state, it has become increasingly evident that loss of sensitivity to the normal feedback inhibitory signals may be of central importance in carcinogenesis and tumor promotion. This presumably represents a developmental strategy that allows the neoplastic cell to maintain a growth advantage over its normal cell counterpart. The underlying mechanisms that terminate in inhibitor-resistance are yet to be elucidated, but in some instances they may be associated with aberrant tumor suppressor gene function.

Amino Acid Sequence↗

PubMed1996

Extraction of a horizontally impacted mandibular canine through a genioplasty approach: report of a case.

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Adolescent↗

PubMed1996

BB-10010/MIP-1 alpha in vivo maintains haemopoietic recovery following repeated cycles of sublethal irradiation.

Macrophage inflammatory protein-1 alpha (MIP-1 alpha) is an inhibitor of stem cell proliferation affording protection against damage from agents that express their cytotoxicity specifically in the DNA synthesis phase of the cell cycle. Its ability also to modify the self-renewal capacity of the regenerating cells is now shown to improve and maintain haemopoietic recovery following therapy (sublethal irradiation) whose cytotoxic damage is not limited solely to the DNA-S phase of this cycle. Such non-cell cycle-active cytotoxic agents are used clinically in repeated treatment regimens, which are often limited or terminated because of accumulating haemopoietic damage. BB-10010, a non-aggregating variant of MIP-1 alpha, was administered as a continuous dose (1600 micrograms kg-1 24 h-1) via a subcutaneously implanted pump over a period of 7 days. A dose of 4.5 Gy total-body gamma-rays was given 3-4 h after implantation. Day 8 and 12 spleen colony-forming units (CFU-S) were assayed on days 1, 7 and 14 after irradiation. This cycle of treatment was repeated four times (total 56 days), and on day 14 of the last two cycles the marrow-repopulating ability (MRA) was also measured. In the control bone marrow (no BB-10010) CFU-S fell to < 1% of normal within 1 day of irradiation and recovered to 40% at 14 days. Repeated treatments increased the level of damage, and after four cycles CFU-S recovered to only 10% of normal. BB-10010 afforded little benefit in the first treatment cycle, but by the end of the fourth cycle CFU-S still recovered to 35% of normal. MRA was reduced to 7% of normal by the irradiation protocol-about half that maintained by BB-10010 protection. We conclude that BB-10010 (MIP-1 alpha) reduces the degree of accumulated haemopoietic stem cell damage following repeated non-cell cycle-specific cytotoxic insults-a principle which should be valuable in repeated clinical cytotoxic therapy regimens.

Animals↗