GST-P1 or not to be?

TS to be? Heinz-Josef Lenz, MD

Associate Professor of Medicine Co-Director, Colorectal Center

Co-Director, GI Oncology Program

USC/Norris Comprehensive Cancer Center

USC Keck School of Medicine

Peripheral Neurotoxicity

• Mechanism not well understood– Dorsal root ganglia neuronopathy– Axonopathy

• Agents implicated: cisplatin, oxaliplatin, taxanes, 5-FU (rare)

• Various mechanisms proposed: Sodium, Calcium Channels, DNA repair, Homocystein pathway, Cox-2

Oxaliplatin-related peripheral neuropathy

• It has 2 components: – acute neurotoxicity: axonopthay – chronic neurotoxicity: dorsal root ganglia

Mechanism of action of oxaliplatin on Na+ channels (Axonopathy)

+

ATP ATP

EXTRA

Membrane

INTRACa2+

oxalate

TTXHg2+

Dach-Pt

Na+

oxaliplatin

Inward Na+current inhibition by oxaliplatin in

patch clamp technique

Inward Na+currentAction

potential

Sodium channels

• Sodium channels regulate excitability of nerve and muscle cells (Ca dependent)

• At least seven different Na+ channels expressed in sensory neurons

• Oxaliplatin increases nerve refractory time through its effect in Na+ channels

Neurotoxicity as reason for treatment discontinuation

Gamelin et al, Clin Cancer Res 2004

0

5

10

15

20

25

30

35

85 100 130

oxaliplatin dosage (mg/m2)

% o

f d

rop

ou

ts f

or

ne

uro

tox

icit

y

CaMg

no CaMg

Folate-Homocysteine

• Elevated homocysteine neuronal damage– NMDA receptor stimulation Ca influx

reactive oxygen species (ROS) neural apoptosis

– Oxidative damage to endothelial cells

• High Thymidylate synthase low Homocysteine levels

DNA repair

• ↓ ERCC1, XRCC1, XPD function ↑ susceptibility of dorsal root ganglia to platinum-damage peripheral neuropathy

• Oxidative Stress leading to damage of dorsal root ganglia (MnSOD, GST)

Cycle to any Mucositis GSTP1-105 Ile/Ile 58 1 Ile/Val 53 1.30 (0.67-2.53) Val/Val 12 4.03 (1.75-9.30) <0.001 COX 2 G/G 83 1 G/C, C/C 40 1.70 (0.94-3.07) 0.061 TS-5’ G C SNP G/G 60 1 G/C 56 0.60 (0.32-1.15) C/C 7 2.14 (0.81-5.65) 0.020 Cycle to grade 2+ Neurotoxicity

XPD 312 Asp/Asp, Asp/Asn 99 1 Asn/Asn 24 0.43 (0.15-1.21) 0.084 TS-5’ G C SNP G/G, G/C 116 1 C/C 7 2.37 (0.83-6.77) 0.082

USC Data on 130 patients treated with CIFOX prospectively in second line

Lipid peroxidationDNA damage

Off Due to Neurotoxicity P-Value*

GSTP1 T/T (N=120) C/T (N=130) C/C (N=38)

11 (9%)13 (10%)9 (24%)

0.039

ERCC2 Other G/G

30 (12%)5 (13%)

0.779

XRCC1 Other C/C

16 (10%)17 (13%)

0.572

GSTM1 Absent Present

16 (11%)19 (12%)

0.742

*Chi-square P-value

Polymorphisms and Treatment Discontinuation Due to Neurotoxicity

Polymorphisms and Treatment Discontinuation Due to Neurotoxicity

GSTP1

< 600 mg/m2 < 800 mg/m2

Grade 2/3 Grade 2/3

C/C (N=38)20% 27%

C/T (N=130)

T/T (N=120) 11% 18%

Cumulative OxaCumulative Oxaliplatin-Dose platin-Dose and Early Neurotoxicityand Early Neurotoxicity

Cumulative OxaCumulative Oxaliplatin-Dose platin-Dose and Early Neurotoxicityand Early Neurotoxicity

Chi-Square P = 0.030*

*Fisher’s exact P-value = 0.036

P = 0.143

Future: Neurotoxicity

• To understand the mechanisms of the acute and chronic neurotoxicity

• To investigate the role of oxidative stress such as GST-P1 in neurotoxicity and how to prevent it (antioxidants?)

Is TS prognostic, predictive or both?

• Prognostic markers (survival, recurrence)– Not applicable for individual patients – Usually used high/low, presence/absence

• Predictive markers (response, survival, toxicity)– Used for an individual patient– Usually absolute number

Iqbal et al. Iqbal et al. Curr Gastroenterol RepCurr Gastroenterol Rep. 2003;5:399-405.. 2003;5:399-405.

Metabolism and mechanism of action of 5-Fluorouracil (5-FUra)

5-FUra H2FUra

-F--alaFdUrd

dThd phosphorylase

DPD

FdUMP

dUMP

thymidylate synthase

dTMP DNA

DNADNA

mRNAmRNA

ProteinProtein

Type of ChangeNature of Change

Tools Used to Study

Polymorphisms

Allelic deletions (LOH)

Qualitative

Static

PCR

DNA Sequencing

Gene expressionQuantitative

Dynamic

Quantitative RT- PCR

Microarrays

Protein expression Protein function

Quantitative Dynamic

Enzyme assays

IHC

Iqbal et al. Iqbal et al. Curr Gastroenterol RepCurr Gastroenterol Rep. 2003;5:399-405.. 2003;5:399-405.

Assessment of TS Expression

TS and Adjuvant Chemotherapy Evaluation by IHC

Author # of patients

Patient Characteristics

Outcome

Johnston, PG

294 Rectal cancer, Dukes B, CAdj Ctx

TS an independent prognosticator of DFS and OS; adj ctx for high TS equiv to low TS (with and w/o ctx)

Edler, D 862 30% rectal cancer, 70% colon cancer Dukes B & CAdj ctx

TS of no prognostic value; low TS better OS, high TS higher rate of recurrence, Pts with low TS and adj ctx had worst OS

Allegra, C

709 465 Patients220 Dukes B2245 Dukes C

TS prognostic of OS and DFS; high TS assoc with high recurrence

TS Protein Expression• 5 studies have evaluated TS in adjuvant

chemotherapy for CRC• 4/5 studies consistently show TS as an independent

prognosticator of DFS and OS• Conclusions

– Patients with high TS who received chemotherapy did as well as patients with low TS with or without chmotx.

– The advantage to receiving adjuvant ctx for patients with low TS was less than for patient with high TS

– Patients with low TS have a better outcome– The benefit of adjuvant chemotherapy demonstrated

in patients with high TS

Thymidylate Synthase Expression and Prognosis in

Colorectal Cancer: A Systematic Review and Meta-Analysis:

13 studies with 887 patients MCRC7 studies 2610 patients LCRC

Popat et al J Clin Onc February 2004, 529-536

Popat et al J Clin Onc February 2004, 529-536

TS IHC versus RT-PCR

The value of TS expression in predicting poor OS seems strongest in studies using RTPCR and not IHC.

Popat et al J Clin Onc February 2004, 529-536

TS Repeat Polymorphisms in 221 patients with Dukes C

Patients with the 3R/3R polymorphism (n = 58, 26%) showed no significant long-term survival benefit from chemotherapy (RR = 0.62, 95% CI: 0.30-1.25, P = 0.18)

Patients with the 2R/2R or 2R/3R genotype (n = 163, 74%) showed significant gains in survival from this treatment (RR = 0.52, 95% CI: 0.52-0.82, P = 0.005).

High TS

Low TS

5-FU

NO 5-FU

It all makes sense again?

• High TS associated with poor outcome• High TS does not benefit from 5-FU adjuvant

chemotherapy • Consistent with data from meta analysis and

data from TS polymorphisms and gene expression data.

• Controversial data due to difference in technologies, cut off levels, patients populations

Overall Survival by TS Intensity (Stage II)S

UR

VIV

AL

(Pro

ba

bil

ity

Ra

te)

Years since surgery

P=0.47

High TS

Low TS

SU

RV

IVA

L (

Pro

ba

bil

ity

Ra

te)

YEARS SINCE SURGERY

Overall Survival by Treatment within high TS Staining Tumours (Stage IIIC)

5-FU

No 5-FUP=0.12

The is a partial list of some common external causes of free radicals:

• Toxins – carbon tetrachloride – paraquat – benzo(a)pyrene – aniline dyes – Toluene

• Drugs – Adriamycin,bleomycin,nitrofurantoin – chlorpromazine

• Air pollution: Primary sources – carbon monoxide, nitric oxide – passive tobacco smoke

• Ingested substances – alcohol – smoked and barbecued food – peroxidized fats in meat and cheese – deep-fried foods – trans fats in processed foods