Stimulation Of Cellular Proliferation Research Articles

Keynote address: Modulation of normal tissue toxicity by combined modality therapy: Considerations for improving the therapeutic gain

The aim of combined modality treatment schedules is to achieve increased killing in the tumor cell populations without an equivalent increase in normal tissue damage. There is, however, some increased risk of normal tissue toxicity that must be taken into account when assessing the therapeutic potential. An understanding of the mechanisms involved in combined modality therapy, for example, increased radiosensitivity, inhibition or stimulation of cellular proliferation, or independent additive toxicities, should improve the chances of achieving a therapeutic gain. A review of the literature of normal tissue effects after combined treatment with drugs and radiation has lead to the following general conclusions: a) The sequence and timing of the two agents have a marked influence on the extent of normal tissue damage, with the most damage occurring when simultaneous drug and irradiation are given within a few days of each other; b) Separation of the two modalities can lead to an improved therapeutic gain since tumor effects are less strongly dependent on the interval between drug and X rays; and c) Chemotherapy can markedly alter the time of expression of radiation damage, particularly in slowly dividing normal tissues, where more rapid expression of injury occurs after combined modality therapy. The above concepts and some possible ways for improving the therapeutic gain in future trials are discussed in this review.

Head activator acts as an autocrine growth factor for NH15-CA2 cells in the G2/mitosis transition.

The neuropeptide head activator (HA) acts as an autocrine growth factor for the neural cell line NH15-CA2. Cell proliferation is increased in the presence of HA and inhibited by HA peptide-specific antisera. Stimulation of cellular proliferation is visible 2 h after HA application as an increase in cells in mitosis. HA has no direct effect on stimulating DNA synthesis. HA thus functions as a control signal in the G2/mitosis transition and not in the G1/S transition. Receptors for HA are present on small round cells in clusters of foci and not on cells with differentiated morphology, suggesting cell-cycle-dependent HA receptor expression.

Transforming growth factor beta modulates proliferation of osteoblastic cells: relation to its effect on receptor levels for epidermal growth factor.

The effect of transforming growth factor beta (TGF-beta) on cellular proliferation of osteoblastic MC3T3-E1 cells was studied with particular emphasis on its effect on modulation of epidermal growth factor (EGF) receptors. In other cells, TGF-beta has been reported to augment EGF receptors. Exposure of MC3T3-E1 cells to TGF-beta initially increased cell surface EGF receptor levels and decreased the rate of DNA synthesis. The initial elevation of EGF receptor levels was due to increased receptor number per cell, not to changes in binding affinity. On the contrary, prolonged exposure (longer than 40 h) resulted in a decrease in EGF receptor and an increase in the rate of DNA synthesis. Thus, the effects of TGF-beta on these cells appears to be biphasic, reflecting complex mechanisms of action; the early effects of TGF-beta may be consistent with cellular differentiation to the osteoblastic phenotype with decreased cellular proliferation, whereas chronic exposure of these cells to TGF-beta stimulated cellular proliferation and inhibited osteoblastic phenotype expression. It is not likely that stimulation of cellular proliferation was through elevation of EGF receptor levels, because TGF-beta did not enhance the stimulatory effect of EGF on cellular proliferation. Thus, we conclude that TGF-beta possesses a stimulatory effect on the cellular proliferation of osteoblastic MC3T3-E1 cells independent of its modulative effect on EGF receptor level.

38] Measurement of growth factor-induced changes in intracellular pH

Publisher Summary This chapter focuses on measurement of growth factor-induced changes in intracellular p H . In cultured Chinese hamster fibroblasts, it has been demonstrated that a variant lacking Na + /H + exchange activity is unable to emerge from quiescence upon addition of growth factors in a medium at neutral p H which does not contain bicarbonate buffer. However, this variant shows a mitogenic response to growth factors similar to the wild-type cells when p Hi is elevated by other means such as relatively alkaline extracellular pH or the presence of a bicarbonate buffer, suggesting that p Hi elevation by growth factors may serve a permissive role rather than a causal role in the stimulation of cellular proliferation in hamster fibroblasts. Determination of growth factor-induced elevation of p Hi depends on the availability of methods to reliably determine the cytoplasmic pH in cells which grow in monolayer culture. Two major techniques are currently available to measure p Hi of cells grown in monolayers, the weak acid distribution methods and the intracellularly trapped fluorescent pH indicator method.

Stimulation of cellular proliferation and differentiation in the intact and regenerating planarian Dugesia(G) tigrina by the neuropeptide substance P

The neuropeptide substance P (SP) is shown to be a potent mitogen for intact and regenerating planarians. At nanomolar concentrations, SP markedly enhances cellular proliferation causing an increase in the mitotic index and in the number of blastema cells. Moreover, albeit to a lower extent, SP enhances cellular differentiation as shown by the increases in eye and pharynx length in regenerating organisms. On the basis of these observations, we hypothesize that SP may be one of the postulated growth factors necessary for the stimulation of proliferation, and to a lesser extent differentiation of cells in intact and regenerating planarians.

The effect of pulsating electromagnetic fields on condylar growth in guinea pigs

The purpose of this study was to determine if a simple, noninvasive method could be developed for the application of pulsed electromagnetic fields that would lend itself to future clinical applications. Specifically, the modulation and control of condylar cellular metabolism and the stimulation of cellular proliferation were attempted in order to increase the amount of mandibular condylar growth. A pulsed electromagnetic field with a frequency of 100 hertz was applied for 8 hours per day to the mandibular condylar area of rapidly growing, male, Hartley guinea pigs. Ten guinea pigs were exposed for 10 days and a second group of 10 guinea pigs was exposed for 30 days. In addition, 5 guinea pigs were used as controls for each experimental period. During the experimental period the guinea pigs were placed in specially constructed, plastic animal holders with their heads positioned in an area of uniform magnetic field. After 10 days of pulsed electromagnetic field exposure, there were increases in vascularity, secretion of cartilagenous intercellular matrix, and woven-bone formation in the guinea pig condyle. After 30 days, there were continued but attenuated vascular and calcification responses with an increase noted in marrow hemopoietic elements. An increase in the number of osteoclasts was also noted after 10 days. This effect was transient and was not present at the end of the 30-day experimental period. The application of the pulsed electromagnetic field did not result in a significant increase in the overall anteroposterior or vertical size of the guinea pig mandible compared to controls. The results of this study suggest that it is possible to affect condylar cartilagenous and bony metabolism through the application of a noninvasive, pulsed electromagnetic field.

Second neoplasms following radiotherapy or chemotherapy for cancer

While radiotherapy and antineoplastic chemotherapy often control malignancies they may, paradoxically, cause new cancers to develop as long-term complications. Although almost any type of neoplasm can occur, radiation-induced malignancies are most likely to affect the myelopoietic tissues and the thyroid gland. The former tissues are also most frequently involved by chemotherapy. The combination of intensive radiotherapy and intensive chemotherapy is particularly leukemogenic. Acute myeloid leukemia has occurred with increased frequency following treatment of Hodgkin's disease, non-Hodgkin's lymphoma, multiple myeloma, ovarian cancer, polycythemia vera, carcinoma of the thyroid gland, and carcinoma of the breast. Radiation-induced malignancies usually occur in the field of irradiation. For example, radiotherapy for carcinoma of the cervix may be followed by the development of carcinomas of the endometrium, vagina, urinary bladder, colon , rectum, and anus, as well as mesotheliomas of the peritoneum and osteosarcomas of the pelvis. Tumors developing in an irradiated field include a substantial number of soft tissue sarcomas or osteosarcomas. There is a 20-fold increase of second cancers following treatment of childhood malignancies, mostly sarcomas of bone and soft tissues, but including leukemia, and carcinomas of the thyroid gland, skin, and breast. The latent period between radiotherapy and the appearance of a second cancer ranges from 2 years to several decades, often being 10-15 years. With chemotherapy the mean latent period is shorter, approximately 4 years. The mechanism of oncogenesis by radiotherapy or chemotherapy is poorly understood and probably involves a complex interplay of somatic mutation, co-oncogenic effects, depression of host immunity, stimulation of cellular proliferation, and genetic susceptibility. The danger of developing second malignancies following radiotherapy or chemotherapy emphasizes the need for lifelong follow-up of patients given these forms of treatment; particularly in those with a long life expectancy as are those treated for childhood neoplasms.

Effect of nutritional changes on chromatin template activity and non-histone chromosomal protein synthesis in WI-38 and 3T6 cells

Quiescent confluent monolayers of WI-38 human diploid fibroblasts and of 3T6 mouse fibroblasts were stimulated to proliferate by nutritional changes. WI-38 cells had a stringent requirement for serum factor(s) but 3T6 did not require serum in order to proliferate again. In both cell lines there was an early increase in the synthesis of non-histone chromosomal proteins shortly after stimulation of cellular proliferation and this increase was linearly correlated to the number of cells entering the S phase several hours later. Only WI-38 diploid fibroblasts, however, showed an early increase in chromatin template activity 1 h after stimulation of cellular proliferation, while chromatin template activity in 3T6 cells remained unchanged. It is suggested that the activation of gene function represents a critical step for the passage of WI-38 cells in the G0 resting phase to the G1 phase of the cell cycle. It is also suggested that 3T6 cells are unable to enter or stay in a G0 phase but can be arrested predominantly in the G1 phase by nutritional deficit, probably amino acid starvation.

Template activity of chromatin during stimulation of cellular proliferation in human diploid fibroblasts.

1. Contact-inhibited confluent monolayers of WI-38 human diploid fibroblasts can be stimulated to divide by replacing the medium with fresh medium containing 30% foetal calf serum. 2. Of the cells 40-75% are stimulated to divide with a peak DNA synthesis between 15 and 21h and a peak mitotic index between 28 and 30h after stimulation. 3. In the first 12h before the initiation of DNA synthesis there is a biphasic increase in the incorporation of [(3)H]uridine into RNA of whole cells. 4. This is paralleled by a similar biphasic stimulation of chromatin template activity measured in vitro in a system in which purified cell chromatin is incubated with an exogenous RNA polymerase isolated from Escherichia coli. 5. The changes in chromatin template activity are believed to represent activation of the genome, with more sites available for RNA synthesis, and to account almost entirely for the changes in RNA synthesis occurring in the whole cell.

Induction of 19S Antibody Synthesis without Stimulation of Cellular Proliferation

ANTIGEN evokes a heterogeneous immunoglobulin response in which each molecular species is probably synthesized by a different cell population1,2. Although recent reports3–8 have suggested that antigen stimulates both proliferation and antibody synthesis in the same lymphoid cell, these two functions may not necessarily be associated in all the types of cells which respond to antigen. This possibility was examined in cells making 19S antibody—one of the four antibody classes known in the mouse9.