Gallium-68-Labeled KISS1-54 Peptide for Mapping KISS1 Receptor via PET: Initial Evaluation in Human Tumor Cell Lines and in Tumor-Bearing Mice

Kisspeptins (KPs, KISS1) and their receptor (KISS1R) play a pivotal role as metastasis suppressor for many cancers. Low or lost KP expression is associated with higher tumor grade, increased metastatic potential, and poor prognosis. Therefore, KP expression has prognostic relevance and correlates with invasiveness in cancers. Furthermore, KISS1R represents a very promising target for molecular imaging and therapy for KISS1R-expressing tumors. The goal of this study was to evaluate the developed KISS1-54 derivative, [68Ga]KISS1-54, as a PET-imaging probe for KISS1R-expressing tumors. The NODAGA-KISS1-54 peptide was labeled by Gallium-68, and the stability of the resulting [68Ga]KISS1-54 evaluated in injection solution and human serum, followed by an examination in different KISS1R-expressing tumor cell lines, including HepG2, HeLa, MDA-MB-231, MCF7, LNCap, SK-BR-3, and HCT116. Finally, [68Ga]KISS1-54 was tested in LNCap- and MDA-MB-231-bearing mice, using µ-PET, assessing its potential as an imaging probe for PET. [68Ga]KISS1-54 was obtained in a 77 ± 7% radiochemical yield and at a >99% purity. The [68Ga]KISS1-54 cell uptake amounted to 0.6-4.4% per 100,000 cells. Moreover, the accumulation of [68Ga]KISS1-54 was effectively inhibited by nonradioactive KISS1-54. In [68Ga]KISS1-54-PET, KISS1R-positive LNCap-tumors were clearly visualized as compared to MDA-MB-231-tumor implant with predominantly intracellular KISS1R expression. Our first results suggest that [68Ga]KISS1-54 is a promising candidate for a radiotracer for targeting KISS1R-expressing tumors via PET.

Expression of kisspeptin and KISS1 receptor in pituitary neuroendocrine tumours - an immunohistochemical study

INTRODUCTION

Pituitary neuroendocrine tumours (PitNETs), traditionally designated as pituitary adenomas, show elatively frequent invasive growth with exceptional metastatic potential, the causes of which are not entirely elucidated. Kisspeptins, which perform their activity through KISS1 receptor (KISS1R), are recognised as metastatic suppressors in many malignant tumours. This study aimed to investigate the immunohistochemical expression of kisspeptin and KISS1R in different types of PitNETs and to compare it with the expression in the normal anterior pituitary, using tissue microarray.

MATERIAL AND METHODS

The experimental group consisted of 101 patients with PitNETs, with 45 (37.3%) being of gonadotroph, 40 (33.9%) somatotroph, 4 (3.4%) corticotroph, 4 (3.4%) thyrotroph, 3 (2.5%) lactotroph, and 6 (5.1%) null-cell type. The control group consisted of anterior pituitary tissue accidentally removed during the surgery for PitNETs in 17 patients.

RESULTS

Kisspeptin expression was observed in both experimental and control groups, without statistically significant differences in the staining intensity. Negative kisspeptin staining was detected in 10 (9.9%), weak in 79 (78.2%), and moderate in 12 tumours (11.9%); none of the tumours had strong staining intensity. The weak staining intensity was predominant in all PitNET types except thyrotroph tumours. Significant statistical difference in terms of kisspeptin expression between types of PitNET and the control group was not observed. Immunohistochemical expression of KISS1R was not observed in the control group or in the experimental group.

CONCLUSIONS

We conclude that immunohistochemistry, as a method, cannot confirm the involvement of kisspeptin in tumourigenesis and aggressiveness of PitNETs, but potentially supports its antimetastatic role. The absence of KISS1R immunohistochemical expression in all anterior pituitaries and PitNETs in our cohort needs verification through the use of different procedures designed for the detection of the presence and localisation of proteins in the cell.

Melatonin-induced KiSS1 expression inhibits triple-negative breast cancer cell invasiveness

Breast cancer is one of the most common types of cancer in women, and its metastasis increases the risk of mortality. Melatonin, a hormone that regulates the circadian rhythm, has been revealed to inhibit breast cancer growth and metastasis. However, its involvement in highly metastatic triple-negative breast cancer cells is yet to be elucidated. The present study demonstrated that melatonin inhibited the metastatic abilities of triple-negative breast cancer cells and prolonged its inhibitory effect via the expression of kisspeptin (KiSS1), which is a suppressor of metastasis. Melatonin at concentrations ranging from 1 nM to 10 µM did not affect the proliferation of metastatic MDA-MB-231 and HCC-70 triple-negative breast cancer cells. However, melatonin repressed invasiveness in triple-negative breast cancer cells. Additionally, conditional medium from melatonin-treated MDA-MB-231 cells repressed the invasiveness of triple-negative breast cancer cells. Melatonin promoted the production of KiSS1, a metastasis suppressor encoded by the KiSS1 gene. In addition, melatonin increased KiSS1 expression via the expression and transcriptional activation of GATA binding protein 3. Silencing of KiSS1 weakened melatonin inhibition of breast cancer cell invasiveness. Therefore, the present study concluded that melatonin activates KiSS1 production in metastatic breast cancer cells, suggesting that melatonin activation of KiSS1 production may regulate the process of breast cancer metastasis.

Kisspeptins: a multifunctional peptide system with a role in reproduction, cancer and the cardiovascular system

The pairing of the kisspeptins (KP) with the KISS1 (GPR54) receptor has received growing attention since the description of the receptor as a molecular switch for puberty. The role of KP and its receptor, GPR54, in puberty is the most exciting finding made in the field of reproductive biology since the discovery of Gonadotropin Releasing Hormone (GnRH) in 1970s. A significant body of evidence across several species now suggests that KISS1 (GPR54) activation is a critical point in the commencement of puberty, although further investigation is required to characterize the interaction between KP and GnRH cascade. Given such pivotal roles of kisspeptins and GPR54 as gatekeepers of reproductive function, and the proven ability of sex steroids to physiologically regulate this system, it is plausible that environmental compounds with ability to interfere oestrogen and/or androgen signaling (agonists or antagonists) may target the hypothalamic kiss-1/GPR54 system, thereby inducing functional alterations of the hypothalamic-pituitary-gonadal axis. Synthetic agonists targeting KISS1 (GPR54) may represent novel therapeutic agents for the treatment of hypogonadotrophic hypogonadism in some affected individuals. The diverse multifunctional nature of the KP is beginning to unravel. The unexpected role of these peptides in puberty has raised a number of important questions that remain to be answered.