ICNCT-16, June 2014, Helsinki Who benefits most of BNCT? – A review on literature data on the prognostic value of protein expression of amino acid transporter

ICNCT-16, June 2014, Helsinki

Who benefits most of BNCT? –

A review on literature data on the prognostic value of protein expression of amino acid

transporter 4F2hc/LAT1

C. L. Schütz1; D. Ngoga1; A. Detta1; S. Green2; G. Cruickshank1

1University of Birmingham, School of Cancer Sciences, Queen Elizabeth Hospital, Department of Neurosurgery

2University of Birmingham, Queen Elizabeth Hospital, Department of Medical Physics

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Who profits most of BNCT? – The role of 4F2hc/LAT1

ICNCT-16, Helsinki, June 2014 / Christian Schütz

Location, dimension and stage of lesions: Historically in BNCT mostly glioma, H&N tumours and melanoma - Application of a neutron beam is comparably easy

Outcome of BNCT is unsystematic within many cohorts, the effectiveness of the applied protocols varies: While certain patients, even so-called lost cases, show complete response, other do not respond at all

Do we know the reason for the very different outcome?

Could we select patients accordingly before therapy?

Patient selection for clinical trials

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Targeting and boron compounds

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Oxygenationnitromidazoles

Transporters

carbohydratesamino acids

vitamins

Metabolism enzyme substratescarbohydrates

amino acids

Proliferation (DNA)nucleosides

intercalation/binding

Receptors/Integrinshormonesvitamins

growth factors…

AngiogenesiscRGD-peptides

Targeting

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no selectivity / specificity

lipophilic / crossing BBB

very high boron loading

enhanced permeability and retention effect (epr-effect)

protocols are well-established

ability for coupling chemistry

conjugates with carbohydrates

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BHHB

HB

BH

BH

BH

BH

BH

HC

HB

B

BH

SH

2Na+

Na mercapto-undecahydro-closo-dodecaborate (BSH)

Clinically relevant boron compounds

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4-dihydroxyboryl-L-phenylalanine (BPA)

no selectivity/specificity, but increased AA need ( LAT1)

low loading high blood levels of compound needed

low toxicity, resistance in tumor cells, low background

coupling to fructose / mannitol to increase solubility

uptake mostly regulated via amino acid transporter 4F2hc/LAT1

B

OH

HO NH2

O

OH

Clinically relevant boron compounds

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Why is BPA-BNCT effective in tumour therapy?

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Amino acid transport is facilitated by a number of transport proteins, several of those being heterodimers – like 4F2hc/LAT1, an obligate exchanger, whose main role is to regulate amino acid transport in growing cells and across some endothelial / epithelial barriers

Amino acid transporters

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4F2hc/LAT1 - structure

heavy chain (also called CD98)

light chain

The monomers alone do not function as transporter!

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Mechanism and specificity of LAT1

• LAT1 shows high affinity for bulky, neutral amino acids like phenylalanine

• It interacts in a complex system of neutral AA transporters

Unidirectional amino acid transport in combination with the LAT exchanger

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Substrates of LAT1

• To act as substrate for LAT1, an amino acid must have a free -NH2 and –COOH group with a certain bonding angle and charge, without the C=O participating in hydrogen bonding (Uchino et al., 2002)

>>>

• Substrate recognition increases with hydrophobicity

• α-L-amino acids are preferred by both LAT1&2, though not obligatory

• Size and branching of side chain is directly related to substrate affinity, most probably due to hydrophobic interaction with binding site

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Substrates of LAT1: Phe derivatives

• Phenylalanine

• L-p-hydroxiphenylalanine / L-tyrosine• 2-[18F]fluoro-L-tyrosine (FTyr)• L-[3-18F]‑α‑methyltyrosine (L-[18F]FAMT)

• L-3,4-dihydroxiphenylalanine / L-DOPA• 3-O-methyl-6-[18F]fluoro-L-DOPA (18F-OMFD)

• L-Thyroxine

• p-[10B]borono-phenylalanine

• Gabapentin• 2-amino-bicyclo[2.2.1]-2-carboxylic acid (BCH)

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The role and potential of 4F2hc/LAT in tumour therapy

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A suitable neutron source providing the right beam or field

A non toxic, highly selective boron compound

The biological effectiveness of the applied boron compound in combination with neutron irradiation must be proven and detailed knowledge about the pharmacokinetics and uptake behaviour must be given

Online dose monitoring and monitoring of blood or extracellular boron levels during treatment

Selection of the right patients

What do we need for clinical success?

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Protein expression of LAT1 in esophageal carc.

• Normal esophageal mucosa, esophageal carcinoma (all paraff. human tissue), Kobayashi et al., Journal of Surgical Oncology 2005;90:233–238

LAT1 expression according to histopathological grade. LAT1 ratio in G1 (well differentiated), G2 (moderately differentiated), and G3 (poorly differentiated) tumors

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Confirmed protein expression of LAT1 in H&N

• Normal esophageal mucosa, esophageal carcinoma (all paraff. human tissue), Kobayashi et al., Journal of Surgical Oncology 2005;90:233–238

LAT1 expression according to depth of invasion

LAT1 expression according to stage

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Prognostic value of LAT1:Non small cell lung ca

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LAT1 prognostic in pancreatic ductal adenocarcinoma (PDAC)

In this study: no correlation to Ki-67

Prognostic value of LAT1 alone – Pancreatic Ca

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Prognostic value of 4F2hc/LAT1 together

...in transitional cell carcinoma

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Prognostic value of 4F2hc/LAT1 – Adenoid cystic Ca.

Overall survival Progression free survival

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(part 3)

4F2hc/LAT1 together have more prognostic significance than LAT1 alone!

Prognostic value of 4F2hc/LAT1:Tripple negative breast Ca.

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• LAT1 is a prognostic factor for a considerable number of tumours (including glioma, NSCLC, SCLC, SCC and neuro-endocrine tumours of the lung, esophageal cancer, prostate cancer, pancreatic ductal adenocarcinoma, hepatocellular carcinoma, triple negative breast cancer, and transitional cell carcinoma), but not for all that have been tested!

• Statistical correlation of outcome and progression with the whole transporter (4F2hc/LAT1) is usually higher than with LAT1 alone

• The correlation to ki-67, VEGF and CD31/34 is random and was never proved through double staining, only statistical evidence

• Most samples were obtained from patients before/without radiotherapy or chemotherapy and usually before surgery

LAT1 vs 4F2hc(CD98): prognostic value of LAT1

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The potential of BPA-BNCT – if offered to the right patient

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• Uptake of BPA is mostly regulated by 4F2hc/LAT1, an obligate exchanger regulating the transport of large neutral amino acids

• 4F2hc/LAT1 protein expression can be used for the prognosis of the disease for several kinds of tumours (including glioma, NSCLC, SCLC, SCC and neuro-endocrine tumours of the lung, esophageal cancer, prostate cancer, pancreatic ductal adenocarcinoma, hepatocellular carcinoma, triple negative breast cancer, and transitional cell carcinoma).

• BPA-BNCT has a demonstrated potential for therapeutic efficacy and benefit even for progressed diseases, possibly because of 4F2hc/LAT1 expression

• 4F2hc/LAT1 expression levels offer an opportunity for stratified BNCT and a means of trgeting patients for whom conventional therapy is inneffective.

The potential of BPA-BNCT

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> BPA-uptake?

The more aggressive the tumour

> Efficacy of BNCT?

Implications of high LAT1 expression

> LAT1 expression

Selection of patients?

Could we conclude…?

Thank you for your attention

Further questions? [email protected] // [email protected]

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ICNCT-16, June 2014, Helsinki Who benefits most of BNCT? – A review on literature data on the prognostic value of protein expression of amino acid transporter