TSP expression alone resulted in moderate tumor inhibition.Values represent means SEM for tumors of each clone and time point.Moreover, no alterations in cellular morphologyand grow th rates on plastic tissue culture dishes were detected. Similar results were obtainedwith A clones stably expressing both TSP and TSP.For comparison of TSP ef fectswith the prev iously described ef fects of the endogenous angiogenesis inhibitor TSP, mice were also injectedwith three TSP transfected clones andwith three clones of A cells that were transfectedwith both TSP and TSP.A and vectortransfected control cells formed rapidly grow ing squamous cell carcinomas, reaching a volume of, mmwithin weeks. None of the three clones cotransfectedwith both TSP and TSP formed anyvisible tumors over an obser vation period of up to weeks. The blot was also probed with a bactin cDNA probe to control for loading.In control transfected tumors, TSP was detected in the basal epidermal layer of adjacent normal skin but not in tumor cells. Focally, high VEGF mRNA expression was obser ved adjacent to necrotic areas in all samples studied.Strong VEGF mRNA expression was maintained both in control tumors, whereas little VEGF expression was detected in adjacent normal tissue. TSP inhibits tumor angiogenesis.In particular, TSP expression resulted in the complete absence of blood vessels larger than, mm, which represented of all blood vessels in control tumors. However, the biological role of TSP for tumor grow th and angiogenesis has remained unknown.We studied the ef fects of induced TSP gene expression in an established orthotopic nude mouse model of cutaneous squamous cell carcinoma, by using the human squamous cell carcinoma cell line A stably transfectedwith a TSP expression vector orwith vector alone.The A cell line was chosen because of the complete absence of TSP expression in these cells and because we prev iously found a Apremilast marked antitumor and antiangiogen ic ef fect of TSP in this model. Our results demonstrate for the first time that tumor cell expression of TSP potently inhibited the orthotopic grow th of human squamous cell carcinomas, as comparedwith control tumors transfectedwith vector alone.The antitumoral ef fect of TSP was stronger than the ef fect of TSP, which led to only tumor inhibition in the identical experimental model.Importantly, combined expression of TSP and TSP in A cells completely prevented tumor grow th during an obser vation period of weeks, suggesting potential additive or synergistic ef fects of these two related proteins.Moreover, injection of control A cells resulted in a marked inhibition of tumor grow th, as comparedwith injection of control A cells alone, demonstrating that TSP can act to slow adjacent cell grow th. Similar dif ferences were obser ved when tumors of the same size were evaluated.It remains to be established Silodosin whether the inhibitoryef fects of TSP on tumor angiogenesis apply to the majority of human malignancies or only to select types of cancer.Whereas no sign ificant correlation between TSP mRNA expression and angiogenesis was obser ved in invasive breast carcinomas, preliminaryev idence suggests downregulation of TSP expression in human squamous cell carcinomas of the sk in, as comparedwith normal human sk in, and a correlation between TSP gene expression and decreased vascularity was reported in nonsmall cell lung cancers.