Regulatory peptide receptors in human hepatocellular carcinomas

Abstract

Background: Overexpression of regulatory peptide receptors in selected human tumours is of diagnostic and therapeutic relevance.

Aims: To evaluate the expression of somatostatin, vasoactive intestinal peptide (VIP), substance P, cholecystokinin (CCK) A and B, and neurotensin receptors in hepatocellular carcinoma (HCC).

Methods: In vitro receptor autoradiography for the various peptide receptors using selective iodinated radioligands on tissue sections in 59 cases of HCC.

Results: 41% of HCC expressed somatostatin receptors; 47% expressed VIP receptors. VIP receptors were always identified in non-neoplastic liver tissue. Substance P receptors were only identified in 5% of HCC but in the majority of their peritumorous and intratumorous vessels. CCK-A and -B and neurotensin receptors were not detected in HCC. The somatostatin receptors showed high affinity for somatostatin and octreotide. The VIP receptors had high affinity for VIP, pituitary adenylate cyclase activating peptide (PACAP) 27, and a VIP1 selective analogue, suggesting the presence of VIP1/PACAP II type receptors. PACAP I receptors were identified in two cases. Substance P receptors were all of the NK1 subtype. The density of somatostatin receptors in HCC was low compared with the density found in liver metastases of neuroendocrine tumours. The VIP receptor density was always lower in HCC than in adjacent liver tissue.

Conclusions: Somatostatin, VIP, and substance P may have a receptor mediated role in HCC. Substance P receptors may be involved in regulation of tumour associated blood flow; somatostatin receptors and VIP receptors may mediate tumour growth. Diagnostic and therapeutic evaluation of somatostatin and VIP analogues may be of interest in receptor positive HCC.

Figures

Figure 1

Somatostatin receptors in hepatocellular carcinoma. (A,D) Haematoxylin and eosin stained sections. D is an area of A at higher magnification. (B,E) Autoradiograms showing total binding of 125I-labelled [Tyr3]-octreotide. Homogenous labelling of tumour (Tu) tissue can be seen clearly. (C,F) Autoradiograms showing non-specific binding of 125I-labelled [Tyr3]-octreotide (in the presence of 10−6 M unlabelled octreotide). Bars = 1 mm.

Figure 2

Vasoactive intestinal peptide (VIP) receptors in liver (A-D), hepatic adenoma (E-H), and hepatocellular carcinoma (HCC) (I-M). (A,E,I) haematoxylin and eosin stained sections. (B,F,K) Autoradiograms showing total binding of 125I-VIP. (C,G,L) Autoradiograms showing a discrete residual non-specific binding of 125I-VIP in the presence of 20 nM unlabelled VIP. (D,H,M) Autoradiograms showing the same residual non-specific binding of 125I-VIP in the presence of 20 nM pituitary adenylate cyclase activating peptide (PACAP) 27. All three tissues expressed VIP receptors. Bars = 1 mm.

Figure 3

Vasoactive intestinal peptide (VIP) and somatostatin receptors in a surgically resected sample of hepatocellular carcinoma (HCC) containing tumour and liver tissue. (A) Haematoxylin and eosin stained section showing HCC (T) and adjacent liver (L). (B) Autoradiogram showing total binding of 125I-VIP in the section shown in A. (C) Autoradiogram showing non-specific binding of 125I-VIP. (D) Autoradiogram showing total binding of 125I-[Tyr3]-octreotide (corresponding to a section different but consecutive to that in A). (E) Autoradiogram showing non-specific binding of 125I-[Tyr3]-octreotide. VIP receptors were identified in liver tissue but not in HCC (B); somatostatin receptors were identified in HCC but not in liver (D). Liver had high non-specific binding for 125I-[Tyr3]-octreotide (seen in E). Bar = 1 mm.

Figure 4

Substance P receptors in hepatocellular carcinoma (HCC) (A-C) and a hepatic adenoma (D-F). (A,D) Haematoxylin and eosin stained sections. In A, the tumour (T) is surrounded by stroma containing peritumorous vessels (PTV). In D, the adenoma contains arteries (arrowheads) and veins (arrows). (B,E) Autoradiograms showing total binding of 125I- BHSP (Bolton-Hunter substance P). (C,F) Autoradiograms showing non-specific binding of 125I- BHSP (in the presence of 10−6 M substance P). Peritumorous vessels are strongly labelled in B. Intratumorous arteries are strongly labelled in E, whereas veins are not. In both cases, the tumours are substance P receptor negative. Bars = 1 mm.

Figure 5

Displacement curve of 125I-labelled [Tyr3]-octreotide in tissue sections from hepatocellular carcinoma. Tissue sections were incubated with 65 pM 125I-labelled [Tyr3]-octreotide and increasing concentrations of unlabelled octreotide, somatostatin (SS) 28, or 1000 nM somatostatin 28(1-12). Each point represents the optical density of binding in a large, homogeneously labelled area of tumour tissue (n=4). Non-specific binding was subtracted from all values.

Figure 6

Displacement curves of specific 125I-vasoactive intestinal peptide (VIP) binding to tissue sections from (A) liver and (B) hepatocellular carcinoma. Tissue sections were incubated with 30 pM 125I-VIP and increasing concentrations of unlabelled VIP, pituitary adenylate cyclase activating peptide (PACAP) 27, [K15, R16, L17] VIP(1-7)/GRF(8-27), or 1000 nM of octreotide. Each point represents the optical density of binding in a large, homogeneously labelled area of liver or tumour tissue in one section. Non-specific binding was subtracted from all values.

Figure 7

Displacement curves of specific 125I-N-acetyl-pituitary adenylate cyclase activating peptide (PACAP) 27 binding to tissue sections from (A) liver and (B) hepatocellular carcinoma. Tissue sections were incubated with 30 pM 125I-N-acetyl-PACAP-27 and increasing concentrations of unlabelled PACAP-27, vasoactive intestinal peptide (VIP), or 1000 nM of somatostatin. Each point represents the optical density of binding in a large, homogeneously labelled area of liver or tumour tissue in one section. Non-specific binding was subtracted from all values.