Antagonists of growth-hormone-releasing hormone: an emerging new therapy for cancer

This article reviews the potential clinical uses of antagonists of growth-hormone-releasing hormone (GHRH) for tumor therapy. GHRH antagonists suppress the growth of various human cancer lines xenografted into nude mice; such tumors include breast, ovarian, endometrial and prostate cancers, lung cancers (small-cell lung carcinomas and non-small-cell lung carcinomas), renal, pancreatic, gastric and colorectal carcinomas, brain tumors (malignant gliomas), osteogenic sarcomas and non-Hodgkin's lymphomas. The antitumor effects of GHRH antagonists are exerted in part indirectly through the inhibition of the secretion of GH from the pituitary and the resulting reduction in the levels of hepatic insulin-like growth factor I (IGF-I). The main effects of the GHRH antagonists are, however, exerted directly on tumors. GHRH ligand is present in various human cancers and might function as an autocrine and/or paracrine growth factor. Pituitary-type GHRH receptors and their splice variants are also found in many human cancers. The inhibitory effects of GHRH antagonists seem to be due to the blockade of action of tumoral GHRH. Antagonists of GHRH can also suppress cancer growth by blocking production of IGF-I and/or IGF-II by the tumor. Further development of GHRH antagonists that are still-more potent should lead to potential therapeutic agents for various cancers.     

Special AT-rich sequence-binding protein 1 promotes cell growth and metastasis in colorectal cancer

AIM: To evaluate the expression of special AT-rich sequence-binding protein 1 (SATB1 ) gene in colorectal cancer and its role in colorectal cancer cell proliferation and invasion.METHODS: Immunohistochemistry was used to detect the protein expression of SATB1 in 30 colorectal cancer (CRC) tissue samples and pair-matched adjacent nontumor samples. Cell growth was investigated after enhancing expression of SATB1. Wound-healing assay and Transwell assay were used to investigate the impact of SATB1 on migratory and invasive abilities of SW480 cells in vitro . Nude mice that received subcutaneous implantation or lateral tail vein were used to study the effects of SATB1 on tumor growth or metastasis in vivo . RESULTS: SATB1 was over-expressed in CRC tissues and CRC cell lines. SATB1 promotes cell proliferation and cell cycle progression in CRC SW480 cells. SATB1 over-expression could promote cell growth in vivo . In addition, SATB1 could significantly raise the ability of cell migration and invasion in vitro and promote the ability of tumor metastasis in vivo . SATB1 could up-regulate matrix metalloproteases 2, 9, cyclin D1 and vimentin, meanwhile SATB1 could down-regulate E-cadherin in CRC. CONCLUSION: SATB1 acts as a potential growth and metastasis promoter in CRC. SATB1 may be useful as a therapeutic target for CRC.     

Antagonists of GHRH decrease production of GH and IGF-I in MXT mouse mammary cancers and inhibit tumor growth

The involvement of IGF-I in mammary carcinogenesis is well established, but the role of GH, as an autocrine growth factor for breast cancers is poorly understood. The goal of our study was to investigate whether antagonists of GHRH can interfere with the effects of GH and IGF-I in MXT mouse mammary cancers. GHRH antagonists JV-1-36 and JV-1-38 inhibited growth of estrogen-independent MXT mouse mammary cancers in vivo, producing about 50% reduction in tumor volume (P < 0.05). This growth inhibition was associated with a decrease in cell proliferation and an increase in apoptosis in MXT cancers. RIA and RT- PCR analyses showed that the concentrations of GH and IGF-I and the levels of mRNA for GH and IGF-I in MXT tumors were reduced by the therapy with GHRH antagonists. Messenger RNA for GH receptors was also decreased. In vitro, the proliferation of MXT cancer cells was strongly stimulated by GH and less effectively by IGF-I, indicating that both GH and IGF-I may act as growth factors for this mammary carcinoma. GHRH antagonist JV-1-38 inhibited the autonomous growth of MXT cells and the proliferation induced by IGF-I or GH and diminished (3)H-thymidine-incorporation stimulated by IGF-I and GH. These findings and a sustained increase in cyclin B2 concentrations in the cells shown by immunoblotting indicate that JV-1-38 causes a block at the end of the G(2) phase of cell cycle. Our results demonstrate that GHRH antagonists decrease the local production of both GH and IGF-I in MXT mouse mammary cancers, the resulting growth inhibition being the consequence of reduced cell proliferation and increased apoptosis.     

抗结核药物组合药效筛选研究进展

结核病至今仍是一个深受全球关注的健康问题。由于抗结核治疗需要组合用药,临床迫切需要开发有效的药物组合方案以提高治疗效果及缩短疗程。最佳药物组合方案的确定首先要经体外筛选,再通过体内实验进行验证。笔者就近年来抗结核药物组合及体内外筛选方法进行综述,以期为结核病的临床治疗提供快速有效的药物组合方案。     

基于GFP观察鼠伤寒沙门氏菌HilD介导ssrAB表达的初探

目的 以绿色荧光蛋白(GFP)标记的鼠伤寒沙门氏菌(Salmonella typhimurium,S.Typhi)为研究对象,秀丽隐杆线虫为模式生物,初步探究体内环境下HilD对ssrAB表达的调控作用。方法 通过基因工程技术分别构建携带gfp基因的亲本株S.Typhi(ssrAB-gfp+pcDNA3.1)、hilD基因缺失株S.Typhi(ΔhilD+ssrAB-gfp+pcDNA3.1)和hilD基因回补株S.Typhi(ΔhilD+ssrAB-gfp+pcDNA3.1-hilD) 标记菌。利用荧光显微技术,观察3株标记菌在饲喂感染秀丽隐杆线虫体内外的GFP表达状况及其定殖分布,并通过ImegJ软件进行荧光强度的比较。 结果 成功构建的3株标记菌在秀丽隐杆线虫体内外均呈现绿色荧光,荧光强度为S.Typhi(ssrAB-gfp+pcDNA3.1)高于S.Typhi(ΔhilD+ssrAB-gfp+pcDNA3.1-hilD)和S.Typhi(ΔhilD+ssr AB-gfp+pcDNA3.1),S.Typhi(ΔhilD+ssrAB-gfp+pcDNA3.1-hilD)高于S.Typhi(ΔhilD+ssrAB-gfp+pcDNA3.1);3株标记菌在线虫体内主要定殖分布于口咽部和肠道中,荧光强度为口咽部较肠道高。结论 GFP在鼠伤寒沙门氏菌中得到稳定表达,感染秀丽隐杆线虫后同样获得GFP的稳定表达,且在线虫的口咽部和肠道具有良好的定殖分布,首次初步证明体内环境下HilD介导ssrAB表达,但并非为单一的调控作用。     

硫异维甲类化合物A2对结核分枝杆菌抗菌效果的观察

目的 评价硫异维甲类化合物(SHetA2)在体内外对结核分枝杆菌(MTB)的抗菌效果。方法 (1)采用试管法,将SHetA2(2.5μg/ml、5.0μg/ml、10.0μg/ml、20.0μg/ml)分别加入苏通培养基内后,加入等量MTB标准菌株H37RV菌液[1mg/ml,每支接种0.1ml,含10 ⁶菌落形成单位(CFU)细菌],于37℃培养2周,测定SHetA2的最小抑菌浓度(MIC)。(2)将76只无特定病原体(SPF)级昆明小鼠采用雾化吸入感染装置构建肺结核感染模型,最终纳入60只建模成功的小鼠。采用数字表法随机将小鼠分为对照组、异烟肼组、SHetA2组,每组20只,分别采用生理盐水、异烟肼、SHetA2进行治疗。治疗45d后,观察各组小鼠体征及体质量变化、肺组织细菌载荷量计数及组织病理学变化。 结果 (1)体外实验结果显示,SHetA2对MTB标准菌株H37RV的MIC为10μg/ml。(2)体内抗结核实验显示,治疗45d后,对照组小鼠体质量为(27.21±2.85)g,明显低于异烟肼组[(37.98±3.09)g]和SHetA2组[(38.28±3.43)g],差异有统计学意义(F=4.05,P=0.023);异烟肼组与SHetA2组比较,小鼠体质量差异无统计学意义(q=0.10,P=0.998);对照组小鼠肺组织重度病变的构成比(80.0%,16/20)明显高于异烟肼组(15.0%,3/20)和SHetA2组(10.0%,2/20),差异有统计学意义(χ ²=32.18,P<0.01);对照组小鼠肺脏感染细菌数量[经对数转换(lg10CFU/ml)]为7.01±1.23,明显高于异烟肼组(2.59±0.87)和SHetA2组(2.25±0.94),差异有统计学意义(F=6.71,P=0.002);而异烟肼组与SHetA2组比较,差异无统计学意义(q=0.33,P=0.970)。 结论 SHetA2在体内外均对MTB有抗菌作用,或可成为新的抗结核化学药物的候选。     

Novel inhibitors of the trypanosome alternative oxidase inhibit Trypanosoma brucei brucei growth and respiration

African trypanosomiasis is a deadly disease for which few chemotherapeutic options are available. The causative agents, Trypanosoma brucei rhodesiense and T. b. gambiense, utilize a non-cytochrome, alternative oxidase (AOX) for their cellular respiration. The absence of this enzyme in mammalian cells makes it a logical target for therapeutic agents. We designed three novel compounds, ACB41, ACD15, and ACD16, and investigated their effects on trypanosome alternative oxidase (TAO) enzymatic activity, parasite respiration, and parasite growth in vitro. All three compounds contain a 2-hydroxybenzoic acid moiety, analogous to that present in SHAM, and a prenyl side chain similar to that found in ubiquinol. ACD15 and ACD16 are further differentiated by the presence of a solubility-enhancing carbohydrate moiety. Kinetic studies with purified TAO show that all three compounds competitively inhibit TAO, and two compounds, ACB41 and ACD15, have inhibition constants five- and three-fold more potent than SHAM, respectively. All three compounds inhibited the respiration and growth of continuously cultured T. b. brucei bloodstream cells in a dose-dependent manner. None of the compounds interfered with respiration of rat liver mitochondria, nor did they inhibit the growth of a continuously cultured mammalian cell line. Collectively, the results suggest we have identified a new class of compounds that are inhibitors of TAO, have trypanocidal properties in vitro, and warrant further investigation in vivo.     

Decline in CD28 T cells in centenarians and in long-term T cell cultures: A possible cause for both in vivo and in vitro immunosenescence

The dramatic decline in immune function with age, especially in T cell proliferative activity, has been documented extensively in experimental animal models and in clinical studies of the elderly. A similar proliferative decline is also seen in long-term T lymphocyte cultures used to study in vitro cellular senescence. We have compared the peripheral blood T lymphocytes of centenarians and younger controls for the cell surface expression of CD28, a costimulatory molecule that is required for optimal activation and proliferation following engagement of the T cell receptor. Our analysis shows a significant decrease (p < 0.001) in the percentage of T cells expressing CD28 in the elderly cohort, with values ranging from 44% to 90%, as compared to the mean control value of 91%. The decline in the percentage of CD28⁺ T cells correlates with a reduction in the CD4/CD8 ratio (r² = 0.695, p < 0.0001). Concommitantly, experiments using an in vitro T cell culture system showed a progressive loss of CD28 expression with culture “age”. The concordance of proliferative decline and loss of CD28 in the centenarians and in the in vitro cultures suggest that a Hayflick phenomenon may operate in vivo leading to immunosenescence.     

Antagonists of growth hormone-releasing hormone and somatostatin analog RC-160 inhibit the growth of the OV-1063 human epithelial ovarian cancer cell line xenografted into nude mice

The effects of antagonists of GHRH and the somatostatin analog RC-160 on the growth of OV-1063 human epithelial ovarian cancer cells xenografted into nude mice were investigated. Treatment with 20 microg/day of the GHRH antagonist JV-1-36 or MZ-5-156 and 60 microg/day of the somatostatin analog RC-160 for 25 days decreased tumor volume by 70.9% (P < 0.01), 58.3% (P < 0.05), and 60.6% (P < 0.01), respectively, vs. the control value. The levels of GH in serum were decreased in all of the treated groups, but only RC-160 significantly reduced serum insulin-like growth factor I (IGF-I). The levels of messenger ribonucleic acid (mRNA) for IGF-I and -II and for their receptors in OV-1063 tumors were investigated by multiplex RT-PCR. No expression of mRNA for IGF-I was detected, but treatment with JV-1-136 caused a 51.8% decrease (P < 0.05) in the level of mRNA for IGF-II in tumors. Exposure of OV-1063 cells cultured in vitro to GHRH, IGF-I, or IGF-II significantly (P < 0.05) stimulated cell growth, but 10(-5) mol/L JV-1-36 nearly completely inhibited (P < 0.001) OV-1063 cell proliferation. OV-1063 tumors expressed mRNA for GHRH receptors and showed the presence of binding sites for GHRH. Our results indicate that antagonistic analogs of GHRH and the somatostatin analog RC-160 inhibit the growth of epithelial ovarian cancers. The effects of RC-160 seem to be exerted more on the pituitary GH-hepatic IGF-I axis, whereas GHRH antagonists appear to reduce IGF-II production and interfere with the autocrine regulatory pathway. The antitumorigenic action of GHRH antagonists appears to be mediated by GHRH receptors found in OV-1063 tumors.     

Activity of azithromycin or erythromycin in combination with antimalarial drugs against multidrug-resistant Plasmodium falciparum in vitro

Azithromycin, an azalide analog of erythromycin was assayed for its in vitro activity against multidrug-resistant Plasmodium falciparum K1 strain by measuring the ³H-hypoxanthine incorporation. Azithromycin caused inhibitory effects on the parasite growth with IC₅₀ and IC₉₀ values of 8.4 ± 1.2 μM and 26.0 ± 0.9 μM, respectively. Erythromycin inhibited growth of P. falciparum with IC₅₀ and IC₉₀ values of 58.2 ± 7.7 μM and 104.0 ± 10.8 μM, respectively. The activity of antimalarial drugs in combination with azithromycin or erythromycin against P. falciparum K1 were compared. Combinations of chloroquine with azithromycin or erythromycin showed synergistic effects against parasite growth in vitro. Combinations of quinine–azithromycin and quinine–erythromycin showed potentiation. Additive effects were observed in mefloquine–azithromycin and mefloquine–erythromycin combinations. Similar results were also produced by pyronaridine in combination with azithromycin or erythromycin. However, artesunate–azithromycin and artesunate–erythromycin combinations had antagonistic effects. The in vitro data suggest that azithromycin and erythromycin will have clinical utility in combination with chloroquine and quinine. The worldwide spread of chloroquine-resistant P. falciparum might inhibit the ability to treat malaria patients with chloroquine–azithromycin and chloroquine–erythromycin in areas of drug-resistant. The best drug combinations against multidrug-resistant P. falciparum are quinine–azithromycin and quinine–erythromycin.     

Inhibition of growth and reduction in tumorigenicity of UCI-107 ovarian cancer by antagonists of growth hormone-releasing hormone and vasoactive intestinal peptide

PURPOSE: To evaluate the tumor inhibitory activities of antagonists of growth hormone-releasing hormone (GH-RH) and vasoactive intestinal peptide (VIP) in UCI-107 human ovarian cancer model, and to investigate the role of the insulin-like growth factor (IGF) system in the response. METHODS: In the present study we investigated the effects of GH-RH antagonist JV-1-36 and VIP antagonist JV-1-52, on the growth and tumorigenicity of UCI-107 ovarian cell carcinoma xenografted into nude mice. Studies on the effects of hGH-RH(1-29)NH2, IGF-I, IGF-II, JV-1-36, and JV-1-52 on the proliferation of UCI-107 cells cultured in vitro were also performed. RESULTS: After 22 days of therapy with JV-1-36 or JV-1-52 at the dose of 20 microg/day, the final volume of UCI-107 tumors was significantly (P<0.05) decreased by 50.5% and 56%, respectively, compared to controls. The concentration of IGF-II in tumors was reduced by 66% in the JV-1-36-treated group and by 62% in the group given JV-1-52 (both P < 0.05). Exposure in vitro to 1 microM concentrations of JV-1-36 or JV-1-52 for 24 h decreased the tumorigenicity of UCI-107 cells in nude mice. All ten mice injected with cells treated with medium alone developed tumors within 23 days after cell inoculation, while only eight of ten and four of ten mice injected with cells exposed to JV-1-36 or JV-1-52, respectively, had tumors. In vitro exposure of UCI-107 cells to 5-35 ng/ml IGF-II produced a significant suppression in the rate of cell proliferation (P < 0.01). CONCLUSION: Our results suggest that GH-RH and VIP antagonists inhibit the growth of UCI-107 ovarian cell carcinoma by mechanisms that appear to involve direct effects on the cancer cells.     

Secretion of insulin-like growth factor-I (IGF-I) and IGF-binding proteins from bovine mammary tissue in vitro.

In vitro, insulin-like growth factor-I (IGF-I) promotes both growth and development of bovine mammary tissue. In vivo, the effects of IGF-I may encompass endocrine, paracrine or autocrine mediation. We addressed the possibility of paracrine/autocrine effects of IGF-I in the mammary gland by examining the in-vitro secretion of IGF-I and IGF-binding proteins (IGFBPs) from bovine mammary tissue. Bovine mammary explants from pregnant non-lactating and lactating non-pregnant animals were found to synthesize and secrete IGF-I and IGFBPs. Mammary acini cultures, representative of mammary secretory epithelia, secreted both IGF-I and IGFBP, but synthesized only IGFBP. Concentrations of IGF-I in conditioned media from explants were 1.54 and 0.72 fmol/micrograms DNA for pregnant and lactating animals respectively. Concentrations of IGFBPs in conditioned media from explants were similar for both physiological states at 2529 pmol 125I-labelled IGF-I bound/micrograms DNA. Ligand/Western blotting procedures identified four IGFBPs of 29, 33, 37 and 44 kDa for acini cultures and five IGFBPs of 28, 31, 36, 44 and 46 kDa for explant cultures. Similar affinities for IGF-I and IGF-II were shown by IGFBP, using 125I-labelled recombinant human IGF-I as the competing ligand (median effective dose (ED50) of 0.085 pmol). When 125I-labelled bovine IGF-II was used as the ligand, only bovine IGF-II (ED50 of 0.25 pmol) inhibited binding. The addition of prolactin, insulin and cortisol, with or without GH, did not affect secretion of either IGF-I or IGFBP. This report describes the ability of normal mammary tissue to synthesize and secrete IGF-I and IGFBPs.     

Myeloid lineage of high proliferative potential human smooth muscle outgrowth cells circulating in blood and vasculogenic smooth muscle-like cells in vivo

Emerging experimental data supports a circulating precursor origin for some smooth muscle cells that participate in vasculogenesis but uncertainty exists on the precise phenotype and lineage of these vascular precursors. We determined the lineage of human smooth muscle outgrowth cells (SOC) derived from circulating blood mononuclear cells and smooth muscle-like cells present in regions of vasculogenesis in diseased arteries. Immunophenotypic characterization of SOC was performed using FACS and immunofluorescence (IF). An SOC hierarchy was determined based on in vitro clonogenic and proliferative potential. Lineage of smooth muscle-like cells in vasculogenic regions in vivo was also determined by dual IF for myeloid and smooth muscle specific markers combined with FISH for the X and Y chromosome in diseased vessel of human subjects who had undergone gender mismatched cardiac transplantation. We show here that primary high proliferative potential smooth muscle outgrowth cells (HPP-SOC) expanded in culture from human peripheral blood mononuclear cells (PBMC) and recipient-derived chimeric smooth muscle cells participating in vasculogenesis in vivo share a myeloid phenotype (CD68 and CD14 positivity). Moreover, HPP-SOC in vitro are distinct in being negative for several myeloid markers such as CD11b, CD13 and CD33, and CD45 surface antigens and chimeric SMC in vivo show no evidence of cell fusion propensity. This study provides evidence of a possible myeloid subpopulation origin for smooth muscle outgrowth cells in blood and vasculogenic smooth muscle-like cells in the intima and adventitial microvasculature of diseased arteries. These data have significant implications for understanding the role myeloid cells play in smooth muscle cell biology and vascular remodelling.     

The effects of insulin-like growth factor-I (IGF-I), IGF-II and des(1-3)IGF-I, a potent IGF analogue, on growth hormone and IGF-binding protein secretion from cultured rat anterior pituitary cells.

The effects of insulin-like growth factor-I (IGF-I), IGF-II and des(1-3)IGF-I, a potent IGF-I analogue, on the secretion of GH and IGF-binding protein (IGFBP) from cultured rat anterior pituitary cells were measured. IGF-I and des(1-3)IGF-I stimulated GH secretion at low concentrations (maximally effective at 1 and 0.1 micrograms/l respectively) and inhibited GH secretion at higher concentrations. The half-maximal inhibitory concentrations (IC50) were approximately 20 micrograms/l and 1 microgram/l for IGF-I and des(1-3)IGF-I respectively. Thus des(1-3)IGF-I was more potent than IGF-I in these effects on GH secretion. We postulate that the increased potency of des(1-3)IGF-I in affecting GH secretion is due to decreased binding of this peptide by pituitary IGFBP compared with IGF-I. In contrast with IGF-I and des(1-3)IGF-I, IGF-II did not stimulate GH secretion at low concentrations, but did inhibit GH secretion from pituitary cells with an IC50 of approximately 20 micrograms/l. Several IGFBPs ranging in molecular mass from 22,000 to 52,000 were detected in medium conditioned by cultured anterior pituitary cells. When measured by Western-ligand blotting and competitive ligand-binding techniques, these IGFBPs exhibited decreased binding of des(1-3)IGF-I compared with IGF-I and IGF-II. The production of IGFBP by anterior pituitary cells was stimulated by the addition of IGFs to the culture medium.     

Autotaxin and lysophosphatidic acid signalling in lung pathophysiology

Autotaxin (ATX or ENPP2) is a secreted glycoprotein widely present in biological fluids. ATX primarily functions as a plasma lysophospholipase D and is largely responsible for the bulk of lysophosphatidic acid (LPA) production in the plasma and at inflamed and/or malignant sites. LPA is a phospholipid mediator produced in various conditions both in cells and in biological fluids, and it evokes growth-factor-like responses, including cell growth, survival, differentiation and motility, in almost all cell types. The large variety of LPA effector functions is attributed to at least six G-protein coupled LPA receptors (LPARs) with overlapping specificities and widespread distribution. Increased ATX/LPA/LPAR levels have been detected in a large variety of cancers and transformed cell lines, as well as in non-malignant inflamed tissues, suggesting a possible involvement of ATX in chronic inflammatory disorders and cancer. In this review, we focus exclusively on the role of the ATX/LPA axis in pulmonary pathophysiology, analysing the effects of ATX/LPA on pulmonary cells and leukocytes in vitro and in the context of pulmonary pathophysiological situations in vivo and in human diseases.     

Storage of catecholamines in the heart Effect of amine oxidase inhibitors

Storage and release of catecholamines in the isolated heart and the heart in vivo were investigated.

The addition of DOPA to the perfusion fluid of a heart-lung preparation markedly increased the catecholamine concentration of the isolated heart. In vivo, the combination of iproniazid and DOPA had the same effect. Iproniazid alone failed to influence myocardial amine concentration.

Nicotine raised the catecholamine concentration in heart muscle; electrically induced tachycardia failed to lower the catecholamine content of the heart in vivo; reserpine caused a marked reduction.

The reasons for the absence of a pharmacologic effect of the stored catecholamines are discussed.     

Age differences in the binding of calcium in collagen fibres in vitro

Incorporation of ⁴⁵Ca into collagen fibres from tail tendon of rats of different ages was studied in vitro. Fibres from young rats take up more ⁴⁵Ca from the solution under all conditions studied, i.e. in different concentrations of Ca and ⁴⁵Ca, different pH (7·3 and 8·9) and in saturated CaCl₂ solution. ⁴⁵Ca, once incorporated into the fibres can be more easily extracted using inactive Ringer solution from the old than from the young fibres. Previous decalcification of young and old collagen fibres by chelatone or sodium oxalate reversed the affinity of fibres to ⁴⁵Ca in vitro: old decalcified fibres take up more ⁴⁵Ca from the solution than the young ones. Increase of the amount of cross-links in collagen fibres by formaldehyde treatment was without effect on the ontogenetic differences in ⁴⁵Ca incorporation in vitro.     

Insulin-like growth factor regulates peak bone mineral density in mice by both growth hormone-dependent and -independent mechanisms

To evaluate the relative contribution of the GH/IGF axis to the development of peak bone mineral density (BMD), we measured skeletal changes in IGF-I knockout (KO), IGF-II KO, and GH-deficient lit/lit mice and their corresponding control mice at d 23 (prepubertal), 31 (pubertal), and 56 (postpubertal) in the entire femur by dual energy x-ray absorptiometry and in the mid-diaphysis by peripheral quantitative computed tomography. Lack of growth factors resulted in different degrees of failure of skeletal growth depending on the growth period and the growth factor involved. At d 23, femoral length, size, and BMD were reduced by 25-40%, 15-17%, and 8-10%, respectively, in mice deficient in IGF-I, IGF-II, and GH compared with the control mice. During puberty, BMD increased by 40% in control mice and by 15% in IGF-II KO and GH-deficient mice, whereas it did not increase in the IGF-I KO mice. Disruption of IGF-I, but not IGF-II, completely prevented the periosteal expansion that occurs during puberty, whereas it was reduced by 50% in GH-deficient mice. At d 56, femoral length, size, and BMD were reduced by 40-55%, 11-18%, and 25-32%, respectively, in mice deficient in IGF-I, IGF-II, and GH compared with the control mice. Our data demonstrate that: 1) mice deficient in IGF-I exhibit a greater impairment in bone accretion than mice deficient in IGF-II or GH; 2) GH/IGF-I, but not IGF-II, is critical for puberty-induced bone growth; and 3) IGF-I effects on bone accretion during prepuberty are mediated predominantly via mechanisms independent of GH, whereas during puberty they are mediated via both GH-dependent and GH-independent mechanisms.