Autocrine function for insulin-like growth factor I in human small cell lung cancer cell lines and fresh tumor cells.
We showed previously that insulin-like growth factor I (IGF-I) is detectable in small cell lung cancer (SCLC) tumor biopsies and cell lines and that recombinant human IGF-I stimulates DNA synthesis in SCLC cells. Here we report further studies on the role of IGF-I in 2 SCLC cell lines: HC12, classic; and ICR-SC17, variant. Immunoreactive IGF-I was detected in medium conditioned by HC12 but not ICR-SC17. Both HC12 and ICR-SC17 bound IGF-I with 100-fold greater affinity than insulin. Scatchard analysis revealed two classes of IGF-I binding site of high (Kd 0.1 nM, n = 2,300) and lower (Kd 3 nM, n = 28,000) affinity. In both cell lines [3H]thymidine incorporation was enhanced by recombinant human IGF-I, 100-1000 ng/ml. ICR-SC17 also showed growth enhancement as measured by increase in cell numbers. There was no response in HC12, probably due to endogenous IGF-I production. 125I-IGF-I binding and basal and IGF-I-stimulated mitogenesis were inhibited by monoclonal antibodies to IGF-I (SM1.20B, SM1.25) or the type I IGF receptor alpha IR3 but not an isotypic control monoclonal antibody. Antiproliferative effects were manifest in [3H]thymidine incorporation assays in serum-free conditions and growth of serum-supplemented liquid cultures. We also tested fresh or newly cultured tumor cells obtained by fine needle aspiration of metastases in three previously untreated and four relapsed patients with SCLC. IGF-I binding sites were demonstrable on fresh SCLC cells, and specific binding was inhibited by SM1.20B. All seven samples showed stimulation of [3H]thymidine incorporation in the presence of recombinant human IGF-I, 100-500 ng/ml. As in cultured cells, basal and IGF-I-stimulated DNA synthesis was inhibited by monoclonal antibodies SM1.20B, SM1.25, and alpha IR3 but not the isotypic control. These results confirm the findings of previous studies and suggest that IGF-I can function as an autocrine growth factor in SCLC in vitro and possibly also in vivo.
Macaulay
V M
VM
Section of Medicine Research Laboratories, Institute of Cancer Research, Belmont, Surrey, United Kingdom.
Everard
M J
MJ
Teale
J D
JD
Trott
P A
PA
Van Wyk
J J
JJ
Smith
I E
IE
Millar
J L
JL
D000911:Antibodies, Monoclonal; D018288:Carcinoma, Small Cell / Q000473:pathology*; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D004261:DNA Replication / Q000187:drug effects; D005455:Fluorescent Antibody Technique; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000494:pharmacology* / Q000502:physiology; D007700:Kinetics; D008175:Lung Neoplasms / Q000473:pathology*; D011863:Radioimmunoassay; D011869:Radioligand Assay; D011956:Receptors, Cell Surface / Q000378:metabolism; D017451:Receptors, Somatomedin; D011994:Recombinant Proteins / Q000494:pharmacology; D013002:Somatomedins / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000166:cytology* / Q000187:drug effects
D000911:Antibodies, Monoclonal; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D011994:Recombinant Proteins; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I