Hideo Masui

APOPTOSIS INDUCED BY AN ANTI-EPIDERMAL GROWTH FACTOR RECEPTOR MONOCLONAL ANTIBODY IN A HUMAN COLORECTAL CARCINOMA CELL LINE AND ITS DELAY BY INSULIN

Both EGF and insulin, or IGF, stimulate the growth of many cell types by activating receptors that contain tyrosine kinase activities. A monoclonal antibody (mAb 225) against the EGF receptor produced in this laboratory has been shown to competitively inhibit EGF binding and block activation of receptor tyrosine kinase. Here we report that a human colorectal carcinoma cell line, DiFi, which expresses high levels of EGF receptors on plasma membranes, can be induced to undergo G1 cell cycle arrest and programmed cell death (apoptosis) when cultured with mAb 225 at concentrations that saturate EGF receptors. Addition of IGF-1 or high concentrations of insulin can delay apoptosis induced by mAb 225, while the G1 arrest cannot be reversed by either IGF-1 or insulin. Insulin/IGF-1 cannot activate EGF receptor tyrosine kinase that has been inhibited by mAb 225. Moreover, an mAb against the IGF-1 receptor, which has little direct effect on DiFi cell growth, can block the capacity of insulin/IGF-1 to delay apoptosis induced by mAb 225, suggesting that the insulin/IGF-1-mediated delay of apoptosis is acting through the IGF-1 receptor. In contrast, insulin/IGF-1 cannot delay the apoptosis caused by the DNA damaging agent, cisplatin. The results indicate that EGF receptor activation is required both for cell cycle progression and for prevention of apoptosis in DiFi cells, and that a signal transduction pathway shared by receptors for insulin/IGF-1 and EGF may be involved in regulating apoptosis triggered by blockade of the EGF receptor.

Materials Indistinguishable from Iodotyrosines in Normal Human Serum and Human Serum Albumin

Materials indistinguishable from authentic mono- and diiodotyrosines were identified in extracts of normal human serum as well as in extracts of purified human serum albumin. These materials were not found in association with the other serum proteins. Identification of MIT and DIT was made by a technique using rechromatography to constant specific activity, as well as by the Barker wet ash distillation method, which established the compounds in question as being iodinated ones. By two different extraction and chromatographic methods we estimated the amounts of both MIT and DIT present in normal human serum or albumin; the estimates were in good agreement. These compounds together constituted between 19% and 25% of the extractable serum iodine.

Monoclonal Antibodies Directed towards Growth-Related Receptors on Human Tumors

The potential therapeutic uses of monoclonal antibodies in the treatment of cancer have attracted considerable interest. Attention has been focused upon two approaches: 1) Serotherapy, which relies upon the host immunological effector mechanisms to eliminate antibody-coated tumor cells, and 2) antibody-toxin conjugates which selectively target covalently bound drugs or toxins to malignant tissue. We have explored a third general approach to cancer therapy, which utilizes monoclonal antibodies that act as pharmacological agents to directly block biological functions essential for cell proliferation. Cell proliferation and differentiation can be regulated by extracellular signals such as hormones and growth factors. The biochemical mechanisms by which hormonal agents influence such complex biological responses are being actively investigated in a number of laboratories.