Stem Cell Induction and Mobilization

A unique property of the CBLB600 series of Protectans is that injection of these compounds results in increased numbers of hematopoietic stem cells (HSC) in both the bone marrow and peripheral blood. This activity may contribute to the radioprotective effects of CBLB600 Series compounds. Moreover, given the ability of HSC to self-renew and differentiate into all of the different types of blood and immune cells and potentially other cell types as well, these findings present innovative options for treatment of a broad spectrum of human diseases, some of which currently lack effective treatment.

The differentiated cells that constitute our organs, including the hematopoietic (HP) system, originate from a pluripotent population of stem cells. While most differentiation occurs during embryonic development, a small number of “adult stem cells” persist in various tissues of the body throughout adulthood serving to replace cells that are lost due to injury, disease or normal attrition. The best studied population of adult stem cells is the HSCs that reside in the bone marrow, with a small fraction circulating in the peripheral blood. HSCs undergo cell division resulting in self-renewal of the HSC population as well as progeny HSCs that can differentiate into all of the different types of blood cells. In addition, there is evidence suggesting that bone marrow HSCs may undergo “transdifferentiation” to form other, non-blood cell types, including skeletal and cardiac muscle cells, brain cells, liver cells, skin cells, lung cells, kidney cells, intestinal cells, and pancreatic cells. The great potential for medicinal use of stem cells lies in the theoretical possibility that, given the right conditions, stem cells can be manipulated to generate any desired cell type. This would allow damaged organs or tissues to be replaced with an exact genetic match arising from stems cells from the individual patient, eliminating the need for donors and immunosuppression and the risk of transplant rejection.

Transplantation of bone marrow-derived HSC has been used clinically since 1959 in the form of total bone marrow transplantation to treat hematopoietic cancers (leukemias and lymphomas) and to aid immune system recovery from high-dose chemotherapy of non-hematopoietic cancers. Other indications for HSC use include diseases that involve genetic or acquired bone marrow failure, such as aplastic anemia, thalassemia, sickle cell anemia, and autoimmune diseases. In addition to these traditional uses, stem cells are also being investigated as potential treatments for diseases such as diabetes, heart disease, Parkinson’s disease, etc. where the primary defect is not necessarily in a blood cell compartment.

An important advance in the clinical use of HSCs came from the finding that the small number of HSCs circulating in the peripheral blood can be increased by injecting the donor with the purified cytokine, granulocyte-colony stimulating factor (G-CSF). Recombinant forms of G-CSF (Neupogen® and Neulasta®) are among the lead products of Amgen, bringing in revenues of approximately $4.5 billion through their use in treatment of a broad range of clinical conditions requiring restoration of the immune system. Mobilization of HSCs to the circulation via G-CSF treatment allows them to be collected for transplantation in a much less invasive procedure from the peripheral blood rather than the bone marrow. As described below, CBLB600 Series Protectans represent a new, and perhaps improved, class of drugs for this application.

CBLI’s lead compound for stem cell applications is Protectan CBLB612, a pharmacologically improved synthetic derivative of mycoplasma lipopeptide. Like native mycoplasma lipopeptide, CBLB612 and other CBLB600 Series Protectans bind and activate the mammalian TLR2/TLR6 heterodimeric cell surface receptor, resulting in activation of NF-kappaB and inhibition of stress-induced apoptosis in normal cells. This activity contributes to protection of the HP system and increased survival of mice following exposure to lethal doses of radiation. In examining the radioprotective effect of CBLB600 Series compounds, CBLI found that circulating G-CSF levels were increased following administration of the compounds. Given the known stimulatory effect of G-CSF on HSCs, these data suggest that 1) upregulation of G-CSF might play a role in the radioprotective efficacy of CBLB600 Series Protectans, and 2) CBLB600 Series compounds might be useful in other medical applications through induction of HSC. Indeed, CBLI found that a single administration of CBLB612 (in the absence of radiation) resulted in powerful induction of HSCs in both mice and non-human primates (Macaca mulatta). Increased numbers of HSC were found in both the bone marrow and the peripheral blood. Circulating HSCs induced by CBLB612 in mice were fully functional in that transferred peripheral blood was capable of rescuing lethally irradiated mice from bone marrow deficiency.

These data demonstrate that CBLB600 Series Protectans may be useful drugs for medical applications that require harvesting of HSCs. These Protectans are as efficient as G-CSF in inducing bone marrow HSCs and mobilizing them to enter the circulation, yet only require a single injection and are more cost effective. Moreover, there is opportunity for use of CBLB600 Series Protectans in combination with G-CSF or as a substitute in G-CSF-insensitive patients.

CBLI is currently engaged in additional preclinical studies focused on specific aspects of the activity of CBLB612 on stem cells. These studies include investigation of the effect of the compound on 1) recovery from the myelosuppression (reduced bone marrow activity) that accompanies chemotherapy, 2) restoration of the vasculature in injured tissues/healing wounds, and 3) collection of HSCs from peripheral blood by stem cell apharesis, the procedure currently used to generate an enriched pool of stem cells that can be stored and used in place of bone marrow.