Endocrine neoplasms – searching for new forms of targeted therapy

Alicja Hubalewska-Dydejczyk, Agata Jabrocka-Hybel, Aleksandra Gilis-Januszewska

Jagiellonian University, Medical College, Department of Endocrinology

24th of June, 2008, Krakow, Poland

COST BM0607 Working Group Meeting

99mTc-Octreotate99mTc-Octreotate90Y-DOTA TATE

VI 2005 X 2006

CgA – 47,1U/lCgA – 206,8U/l

Currently known targeted therapy in endocrinology

As a standard therapy:

131I therapy of differentiated carcinoma of thyroid gland

131I MIBG therapy as complementary and palliative therapy of malignant pheochromocytomas and NETs

Somatostatin analogues radiolabelled (90Y/177Lu-DOTATOC/DOTATATE) – in nonoperative or disseminated NETs

Currently known targeted therapy in endocrinology

In clinical trials:

Medullary carcinoma:

131I-MIBG (positive response in 35-40% cases)

90Y/177Lu-DOTATOC/DOTATATE

radiolabelled gastrin e.g. 131I (in experimental studies)

preliminary reports with 90Y-minigastrin

malignant pheochromocytoma, GEP-NET

radiolabelled VIP

radiolabelled ligands for glukagon like peptides’ (GLP-1) receptors – in malignant insulinoma treatment as well as in malignant pheochromocytomas and in brain npls

“Sensitizers” as possible improvement of targeted therapy

Retinoid acid (retinoids): up to one-third of metastasized or recurrent thyroid carcinomas may dedifferentiate over time, dediferentation is characterized by a loss of growth-regulating mechanisms mediated by TSH and/or a decline in iodine avidity. Various groups of “redifferentiating” agents such as retinoid acids were investigated in vivo studies

131 I-MIBG with topotecan as topoisomerase I inhibitor in malignant pheochromocytoma treatment

an inhibitor of DNA methylation or histone deacetylaseincreases the expression of natrium iodide symporter in tumor cells and also inhibits tumor growth – this inhibitor was found in in vitro studies

New possibilities of targeted therapy

Tyrosin kinase inhibitors RAF kinase inhibitors (serine/threonine protein kinases)

Inhibitors of RAS farnesylation (correct functioning of Ras proteins requires post-translational modification)

Chaperone inhibitors Histon deacetylase inhibitors (inhibition of

proliferation and induction of differentiation and apoptosis of tumor cells)

Proteosoms inhibitors (inhibition of NF-κB, inflammatory cytokine expression, induction apoptosis)

Adrenocortical carcinoma

Proposed targeted therapy:Inhibitor of the IGF-I receptor (currently known agents: NVP-

AEW541-A and NVP-ADW742)

Explanation: Inactivating mutations at the 17p13 locus including the TP53

tumour suppressor gene and alterations of the 11p15 locus leading to IGF-II overexpression are frequently observed in adrenocortical carcinoma. In vitro experiments suggest that overexpressed IGF-II acting via the IGFI receptor is relevant for adrenal cancer cell proliferation. Thus, the IGF-II IGF-I receptor pathway is a promising target for future therapies in ACC.

Potential combined therapy:mitotan plus radiolabelled inhibitor of IGF-I receptor

IGF-II IGF-I receptor pathway as a therapeutic target in cancer

The insulin-like growth factor (IGF) system consists of the ligands, cell surface receptors, and the IGF binding proteins (IGFBPs). The insulin-like growth factor receptor (IGF-IR) is a tyrosine kinase cell-surface receptor that binds either IGF-I or IGF-II.

Paula D. Ryan, Paul E. Goss: ”The Emerging Role of the Insulin-Like Growth Factor Pathway as a Therapeutic Target in Cancer” The Oncologist, January, 2008

IGF-II IGF-I receptor pathway as a therapeutic target in cancer

Binding of the ligands IGF-I and IGF-II to IGF-IR activates its intrinsic tyrosine kinase activity resulting in signaling through cellular pathways that stimulates proliferation and inhibits apoptosis. Therapeutic approaches that target the IGF-I R are being tested clinically and include antibodies directed at the extracellular portion of the receptor and small molecule tyrosine kinase inhibitors with specificity for IGF-IR.

Paula D. Ryan, Paul E. Goss: ”The Emerging Role of the Insulin-Like Growth Factor Pathway as a Therapeutic Target in Cancer” The Oncologist, January, 2008

Adrenocortical carcinoma

Proposed targeted therapy:Inhibitor of the IGF-I receptor (currently known agents: NVP-

AEW541-A and NVP-ADW742)

Explanation: Inactivating mutations at the 17p13 locus including the TP53

tumour suppressor gene and alterations of the 11p15 locus leading to IGF-II overexpression are frequently observed in adrenocortical carcinoma. In vitro experiments suggest that overexpressed IGF-II acting via the IGF-I receptor is relevant for adrenal cancer cell proliferation. Thus, the IGF-II IGF-I receptor pathway is a promising target for future therapies in ACC.

Potential combined therapy:mitotan plus radiolabelled inhibitor of IGF-I receptor

Vascular targeted therapies in ACC

Proposed targeted therapy- antiangiogenic agents:

antibodies against VEGF (bevacizumab) or inhibitors of the VEGFR kinases

Explanation:

VEGF is the predominant signal for both endothelial cells proliferation and migration into sites of neovascularization, and blockade of this signal has been a major goal of research in this field (by VEGFR2)

Potential combined therapy:

mitotan plus radilabelled bevacizumab

- would such therapy be more effective than mitotane treatment only?

- would possible side-effects make this therapy useless?

Vascular targeted therapies in ACC

Proposed targeted therapy:• Inhibitors of matrix metalloproteinases• Inhibitors of other angiogenic molecules such as angipoietin• Monoclonal antibodies against tumour endothelial markers

Explanation:Expression of matrix metalloproteinase type 2 was discovered

in malignant adrenocortical tumours (75%)Additionally, serial analysis of gene expression of tumour

endothelium led to the identification of anonymous genes known as tumour endothelial markers (TEMs), of which TEM1 (endosialin), TEM5, and TEM8 have been shown to be specific for tumour vasculature. These proteins, all of which are cell surface antigens, provide potential targets for the development of agents that influence them directly

Other possible targets in ACC

Proposed targeted therapy:Inhibitors directed against enzymes specific for steroidogenesis or

antibodies against such enzymes/steroid hormones precursors; for example HSD3ß2 (hydroxy-steroid dehydrogenase) enzyme

Explanation:characteristic steroidogenesis enzyme in adrenal carcinoma is

HSD3ß2, responsible for conversion of pregnenolon to progesterone, it is expressed especially in granulosa and reticular stratum and it is very specific for adrenocortical carcinoma (high expression of this enzyme in hormonally active tumours).

Potential combined therpy:inhibitor of HSD3ß2 only (?) plus radiolabelled inhibitor of 11beta

hydroxylase (metyrapone)

Steridogenesis as a potential target in ACC

3ßHSD

3ß –

hydroxysteroid

dehydrogenase

11- ß

hydroxylase

metyrapon

ß

Other possible targets in ACC

Proposed targeted therapy:Inhibitors directed against enzymes specific for steroidogenesis or

antibodies against such enzymes/steroid hormones precursors; for example HSD3ß2 (hydroxy-steroid dehydrogenase) enzyme

Explanation:characteristic steroidogenesis enzyme in adrenal carcinoma is

HSD3ß2, responsible for conversion of pregnenolon to progesterone, it is expressed especially in granulosa and reticular stratum and it is very specific for adrenocortical carcinoma (high expression of this enzyme in hormonally active tumours).

Potential combined therpy:inhibitor of HSD3ß2 only (?) plus radiolabelled inhibitor of 11beta

hydroxylase (metyrapone)

Mutations in papillary thyroid cancer

RET (5-30%)

RAS (10%)

BRAF (40%)

RET and RAS are tyrosine kinases

Genetic factors in medullary thyroid carcinoma

MEN2A – 16%

MEN2B – 3%

Simply familial medullary thyroid carcinoma – 5%

Familial MTC is caused by germinal RET proto-oncogene mutation.

i.e. approximately 98% of all MEN2B patients carry a missense mutation in codon 918 of RET proto-oncogene.

Known tyrosine kinase inhibitors

Axitinib - renal cell carcinoma (RCC), pancreatic cancerBosutinibCediranib – non-small cell lung cancer, colorectal cancer tumors of

central nervous system in childrenDasatinib – chronic myelogenous leukemia (CML), Philadelphia

chromosome-positive acute lymphoblastic leukemia, metastatic melanoma

Erlotinib – lung cancer, pancreatic cancerGefitinib – metastatic non-small cell lung cancer (NSCLC)Imatinib - CML, gastrointestinal stromal tumors (GISTs) and a number

of other malignanciesLapatinib - solid tumors (breast and lung cancer) Lestaurinib - acute myelogenous leukemia (AML) and myeloproliferative

disordersNilotinib – CMLSemaxanib – advanced colorectal cancerSunitinib – RCC, GISTVandetanib - NSCLC

Chemical structures of small molecule kinase inhibitors

Inhibitors of the kinase activity of RET

Proposed targeted therapy:The RET kinase inhibitor NVP-AST487

Explanation:It inhibits the growth of human thyroid cancer cell lines with

activating mutations of RET but not the lines without RET mutations (for example with BRAF mutations).

Can RET kinase inhibitor be a ligand?

The structure and functions of RET

The tyrosine kinase RET is a single-pass transmembrane receptor that has a split intracellular domain with tyrosine kinase activity. The major autophosphorylation sites are shown as black points, arrows indicate potential targets (thyrosine kinase inhibitors).

„Molecular Therapeutic Targets in Medullary Thyroid Carcinoma” Nat Clin Pract Endocrinol Metab. 2007; 4(1):22-32. 2007

RET as a therapeutic target– RET activation

RET activation in cis RET activation in trans

the ligand binds to membrane-bound glycosylphosphatidylinositol-anchored GDNF-family coreceptors (GFR ) that are distributed within lipid rafts. Activation of RET leads to dimerization of RET, which consequently signals to the nucleus.

the ligand binds to the soluble form of its coreceptor (sGFR ) and the ligand-sGFR complex brings together two inactive RET monomers.

J. W. B. de Groot et al. Endocrine Reviews 27 (5): 535-560

Signaling network mediated by RET

J. W. B. de Groot et al. Endocrine Reviews 27 (5): 535-560

RET as a therapeutic target - strategies to inhibit RET

Ligand binding and formation of ligand-GFR complex (antagonists, antibodies) - 1

Receptor dimerization (inhibitors) - 2

Autophosphorylation (tyrosine kinase inhibitors) - 3

Recruitment of adaptor proteins (phosphatases, inhibitors of protein-protein interaction) - 4

Intercellular signaling (various inhibitors) - 5

Internalization and nuclear translocation (antibodies, inhibitors) - 6

Biosynthesis (gene therapy, mRNA) - 7

Tyrosine kinases receptor (Trk B)and medullary carcinoma

Proposed targeted therapy:

Activator of tyrosine kinases receptor (Trk B) –is it possible to find?

Explanation:

In medullary carcinoma, reduction in receptor TrkB expression isfound in the later stages of tumor progression. In a cell culture model, TrkB expression led to reduced VEGF concentrations and reduced tumorigenicity, suggesting that TrkB may inhibit medullary thyroid carcinoma angiogenesis and tumor growth.

Possible combined therapy:

TrkB activator with radiolabelled agents against VEGF pathway. The positive effect is uncertain.

Inhibitors of BRAF kinase

Proposed targeted therapy:

Using BAY 43-9006 – BRAF kinase inhibitor

Explanation:

gene BRAF mutation is the most frequent mutation in PTC (44%)

BRAF kinase inhibitor blocks the growth of thyroid cancer cells(more aggressive and less differentiated papillary tumours) that have RET/PTC or BRAF mutations

Hurthle cell carcinoma

Potential therapy:radiolabelled somatostatin analogues in disseminated Hurthle

cell carcinomas

Explanation:Hurthle cell carcinomas express the somatostatin receptor

type 2

Inhibition of HSP

Potential targeted therapy:Family of the ansamycin antibiotics acting through the heat

shock protein pathway

Explanation:Many oncogenic protein kinase depend on the molecular

chaperone HSP 90 – HSP90 inhibition

Malignant pheochromocytoma

Potential targeted therapy: inhibitors or/and monoclonal antibodies against pituitary

adenylate cyclase-activating peptide receptor

Explanation:Expression of PACAP – peptide structurally similar to

vasoactive intestinal peptide (VIP) acting by G protein-coupled receptor – found in neuroblastomas, non-functioning pituitary adenomas, somatotroph pituitary adenomas (PAC1) and in pheochromocytoma and paraganglioma (PAC2)

Malignant pheochromocytoma– other possibilities

• SSR 2,3,5 radiolabelled somatosatin analoques therapy combained with D 2 receptors agonist could be promising

• Inhibition of VEGF pathway – related to very high neoangiogenesis

GEP-NET – using kinase inhibitors

Potential targeted therapy:

Erlotinib (also gefitinib) as a small-molecule HER-1/EGFR tyrosine kinase inhibitor, acting on the intracellular domain of the receptor, preventing receptor activation and inhibiting downstream signal transduction and cell proliferation

Explanation:

HER-1/EGFR has a role in carcinogenesis in many types of cancer. This coexpression has been shown to stimulate tumor cell proliferation, and elevated HER-1/EGFR levels are linked to poor disease outcomes and lower sensitivity to chemotherapy. Blocking HER-1/EGFR should therefore help to stabilize tumor growth and improve prognosis via the inhibition of multiple HER-1/EGFR downstream signaling pathways. HER-1/EGFR expression has been found in the pulmonary NET.

Potential combined therapy:

Combination of radiolabelled erlotinib plus standard chemotherapy

GEP-NET – other possibilities Matrix metalloproteinase inhibitor marimastat or talomastat

Combined therapy: radiolabelled marimastat plus gemcitabine

Cetuximab – anti-HER-1/EGFR monoclonal antibody. This agent blocks the extracellular domain of HER-1/EGFR to prevent receptor activation.

Combined therapy: Cetuximab with radiolabelled somatostatin analogues in GEP NET therapy.

Labelled trastuzumab (monoclonal antibody against HER2-receptor)in HER-2 positive NET (intestinal, not gastric)

Gastrin releasing peptide (GRP) – brain-gut peptides including bombezin. Four different types of receptors are currently known. BB3 receptor is expressed in bronchial carcinoids. Neuromedin receptor is presented in ileal carcinoids, GRP receptors in gastrinomas.

Newly introduced NET therapy with SOM230 could be also used as the radiolabelled agent therapy.

Role of dopamine receptors

Potential targeted (combined) therapy: Using D2 receptor agonists and radiolabelled somatostatin

receptor analogues or combination of D2 receptor agonist with antiangiogenetic factors seem to be promising targeted therapy.

Explanation: Dopamine receptors are found in all types of neuroendocrine

tumors. Dopamine receptors – mostly D2 could mediate the inhibitory effect of dopaminergic drugs in these tumors, since cabergoline has been found to induce normalization of ACTH and consequently cortisol secretion.

The previous finding of dopamine receptors in GEP-NETcell lines and the recent finding of D2 receptors in GEP-NETsuggests a role for these receptors, and possibly a role of dopaminergic drugs in this category of neuroendocrine tumors.

Thank you