i would be so grateful if this presentation adds to your knowlege and i welcome any comments. thanks in advance

1. Molecular target therapy in
metastatic colorectal cancer
PRESENTED BY : HEBAT-ALLAH MAHMOUD BAKRI
ASSISSTANT LECTURER IN CLINICAL ONCOLOGY DEP.
ASSUIT UNIVERSITY HOSPITAL

2.  Colorectal cancer (CRC) is the third most common cancer in men and the
second most common cancer in women, accounting for about 700,000 deaths
per year.
 The majority of 70–80 % sporadic,
while around 20–30 % hereditary , due to either :
1- susceptibility syndromes, such as Lynch Syndrome (LS) (3–4 %)
2- familial adenomatous polyposis (FAP) (∼1 %) ,
3- consequence of inflammatory bowel diseases of about 1–2 %

3.  CRC is not a homogenous disease, but can be
classified into different subtypes, which are characterized
by specific molecular and morphological alterations.
 A major feature of CRC is genetic instability that
can arise by at least two different mechanisms.
1- chromosomal instability 2- Mismatch repair

4. 1- chromosomal instability :
#The most common (around ∼84 % of sporadic CRC)
PATHOPHYSIOLOGY : 4 mechanisms :
1- gross changes in chromosome number and structure including deletions, gains,
translocations and other chromosomal rearrangements.
2- inactivating mutations or losses in the Adenomatous Polyposis Coli (APC) tumour
suppressor gene, which occur as an early event in the development of neoplasia of the
colorectum in this sequence

5. 3- CIN tumors usually arise as a consequence of a combination of oncogene
activation (e.g. KRAS, PIK3CA) and tumour suppressor gene inactivation (e.g. APC,
SMAD4 and TP53).
4-Hyperactivation of the WNT signaling pathway, usually arising from mutations of the
APC gene.

6. WNT PATHWAY :
 is a network of proteins that passes signals from receptors on the surface of the cell
to DNA expression in the nucleus.
 It controls cell-cell communication in the embryo and adult
 controls beta-catenin, which enters the nucleus, binds to DNA, and turns on the
expression of genes and proliferation .

10. 

11. 2- Microsatellite instability (MSI)
*
About ∼13–16 % of sporadic CRC are hypermutated or (dMMR) defective DNA
mismatch repair and associated with wild-type TP53 and a near-diploid pattern of
chromosomal instability

13. Clinical
application of
CMS GROUPS

16. MOLECULAR
PATHWAYS
AND
IMPLICATION
IN TRATMENT
OUTLINES
 1- MSI
 2- RAS ( ANTI EGFR )
 3- others (PI3K- HER2 NEU
– ALK AND ROS 1- BRAF-
MET GENE )
 4- VEGF

17. 1- Microsatellite Instability:
 Genes encoding for DNA damage repair (DDR) proteins are commonly mutated in
cancer.
 Dysregulation of this process permits an accumulation of somatic mutations and
contributes to genomic instability, now recognized as critical in cancer development and
metastasis
 As a pathway involved in both hereditary and sporadic forms of CRC, the mutator
phenotype with mismatch repair deficiency (dMMR) is of particular interest.

18. NORMALLY :
* Mismatch repair (MMR) maintains genomic stability by eliminating single-base
mismatches and insertion-deletion loops of short repeated nucleotide sequences
(microsatellites) occurring during DNA replication .
Through interaction of critical MMR proteins comprising MLH1, MSH2, MSH3,
MSH6 and PMS2 is required for proofreading and correction of these insertion-deletion
loops.
• ABNORMALLY :
Mutation of genes encoding for these MMR proteins or hypermethylation of the
MLH1 promoter causes gene silencing, with dMMR and subsequent microsatellite
instability (MSI).

20. MSI CRCs are more frequently:
- located in :the proximal bowel
- Differentiation: poor
- subtype : mucinous
- lymphocytic infiltration: dense, suggestive of a strong anti tumoural immune response .
- Patients with sporadic MSI CRC are older AS Loss of MLH1 expression increases with
age
- Tumors are characterized by frequent BRAF (V600E) mutation and absence of MLH1
and PMS2 proteins

21.  Lymphocytic infiltration as a characteristic
feature of MSI CRC has prompted further
investigation due to the increasing availability of
effective immunotherapies.
The reasons for this immunogenic phenotype are
unclear.
 However, it is postulated that this may occur due
to the creation of tumor-specific neoantigens
during accumulation of mutations.
 The critical role of the immune system in tumour
regulation is associated with lower rate of relapse
and improved prognosis

22. HOW it is discoverd ?
 Analysis of this patient subset identified high levels:
1- infiltration of activated CD8+ primary tumour tissue from cytotoxic T-cells
2 - activated Th1 cells with interferon-γ (IFNγ)
3- T-box expressed in T cells (TBET), a Th1 transcription factor.
4 - upregulated expression of the immune checkpoints cytotoxic T lymphocyte-associated
antigen 4 (CTLA4), (PD-1), (PD-L1), lymphocyte activation gene 3 (LAG3) and
indoleamine 2,3-dioxygenase (IDO) was noted in MSI tumours

23.  SOOOO Current immunotherapeutic strategies incorporate
antibodies to directly inhibit the CTLA4 and PD-1 pathways.
 Further studies of immune checkpoint inhibitors are ongoing in this
patient population

24. Prognostic and Predictive Implications for
MSI
 MSI status has been evaluated as a prognostic biomarker in CRC,
 Molecular subtyping strategies have highlighted a predictive value as lower disease-
specific mortality in patients with MSI CRC regardless of the initiating defect .

37. 2- RAS Mutation
 The discovery of KRAS mutation as a predictive biomarker providing clinical relevance
to the molecular and genetic heterogeneity of colorectal tumors and a proof of principle for
targeted therapy.
 Activating mutations in this pathway will result in transcription of the gene for
transforming growth factor-α (TGFα), a ligand of the EGFR. Which creates an autocrine
signaling loop that contributes to tumoural resistance to the anti-EGFR monoclonal
antibodies (mAbs), cetuximab and panitumumab

38.  In combination with
chemotherapy, these therapies are
the only approved biomarker-
driven therapies currently
licensed for treatment of CRC
and have extended survival up
to 41.3 months in patients with
tumours wild type (WT) for
KRAS and NRAS

50. But in 2nd line no side restriction

51. However despite improved survival for a subset of patients . Absence of this
mutation is not an accurate predictor of response, as only 40–50 % of patients with
KRAS/NRAS WT disease respond to the anti-EGFR monoclonal mAbs
as KRAS WT CRC, high expression of AREG and EREG messenger RNA
(mRNA) Binding of amphiregulin (AREG) and epiregulin (EREG) ligands to the EGFR
stimulate mitogenesis
( is predictive of improved response rate, progression-free survival and overall survival in
patients treated with cetuximab ) but these biomarkers are not validated for use in clinical
practice.

53. But many
resistance
mechanisms
developed !!!!
1ry & 2nd

55. Acquired mechanisms of resistance:
1-Activation of MAPK pathway: due to somatic mutation in CRC 50 %
and 40% d.t RAS mutation
2- PIK3CA and PTEN :
- normally PI3K signaling is negatively regulated by PTEN,
1- PIK3CA mutation. This gene encodes for the catalytic subunit of PI3K
and is present in 10–18 % CRC.
2 - loss of PTEN expression in 30 % CRC.

56. sooooo
Early phase clinical trials are investigating the combination of
MEK inhibition with AKT, PI3K and mTOR inhibition, but
results to date have been disappointing

57. primary resistance mechanisms:
1- Downstream activation of BRAF and MEK. Causes EGFR activation
via an alternate signalling pathway within the interlinked RAS-MAPK-PI3K or may be
mediated by type 1 insulin-like growth factor receptor (IGF-1R).
2-Reduced affinity of the EGFR ligand or mutations within the gene, resulting in a
conformational change to the binding site, impair the ability of the monoclonal antibody to
effectively bind to and inhibit activation of the EGFR
3- Based upon preclinical research demonstrating HER2 as a resistance pathway to EGFR
inhibitors,

59. 34 % response
rate and 44 %
stable disease
from trastuzumab
and lapatinib in
23 patients.

60. 3-BRAF Mutation :
 This occurs in 8–10 % of CRC, very rarely occurs in conjunction with RAS mutations,
but is strongly associated with sporadic MSI CRC and confers resistance to anti-EGFR
therapy
 Patients with these tumours have a poor prognosis in the metastatic setting with
aggressive tumour biology.

61.  SO Targeted BRAF blockade using single-agent TKI was attempted
BUT this approach was unsuccessful, with preclinical data suggesting therapeutic
failure was due to aberrant upstream signaling via MEK and activation of the PTEN-PI3K-
AKT pathway
AS demonstrated that BRAF-mutated cells acquired resistance to vemurafenib by
stimulation of EGFR, there by perpetuating cell proliferation
Soooo a triple combination of targeted agents concurrently inhibiting BRAF, MEK and
EGFR is currently under investigation for treatment of BRAF-mutant CRC

62.  Other approaches undergoing trials include:
* use of ERK inhibitors
* combinations of irinotecan, BRAF and EGFR inhibitors;
*BRAF, EGFR and PI3K inhibitors;
*BRAF, EGFR and WNT pathway inhibitors and FOLFOXIRI with bevacizumab.

64. Vemurafenib : is kinase inhibitor selective for mutated
BRAF protein.
 Vemurafenib monotherapy associated with limited activity in mCRC
 Phase I study suggested improved survival and response in combination with
irinotecan + cetuximab in refractory mCRC with BRAF V600E.

69. 4- MET Gene
 (MET) a receptor with tyrosine-kinase activity targeting hepatocyte growth factor (HGF).
 Activation of this pathway has been implicated in metastatic progression of CRC.
 EGFR and MET are co expressed in CRC and MET activation has been implicated in
resistance to the anti-EGFR mAb cetuximab .
 c-MET is overexpressed in 50–60 %, amplified in 10 % and mutated in 5 % CRC

70. 2 studies :
The French National AcSé programme.
The MET inhibitor crizotinib was trialed as a single agent for treatment of MET-amplified
CRC , 0/13 CRC patients with MET amplification derived clinical benefit from this agent
The MErCuRIC1 study :
Based upon preclinical work demonstrating synergistic activity in CRC between MEK and
MET inhibitors is investigating the combination of the MEK inhibitor PD-0325901 and
crizotinib in patients with KRAS mutant, or KRAS WT, MET-amplified CRC

71. 5- ALK/ROS1 Translocations
* In CRC, ALK or ROS1, gene rearrangements have not been extensively studied.
Several papers have detailed a unique subpopulation of between 0.8–2.5 % patients
with metastatic CRC (mCRC) with either ALK or ROS1 rearrangement of their
tumour .
Due to small patient numbers and inconsistent and expensive testing methods for
ROS1 translocations, developing a clinical trial of targeted therapy for this patient
subset poses considerable challenges.

73. 6- VEGF receptors :

76. An updated analysis:
improved OS with
FOLFOXIRI/bev vs
FOLFIRI/bev in the
overall population
(29.8 vs 25.8 months;
P = .03).

77. a molecular subgroup analysis of 357 patients with RAS and BRAF
mutations suggests that :
patients BRAF-mutated CRC—a group that tends to do much
worse than their wild-type and may benefit from the more aggressive
FOLFOXIRI/bevacizumab combination regimen vs FOLFIRI/bevacizumab (19.0 vs
10.7 months.

97. 1- Molecular biomarkers are imp. in metastatic setting (RAS, BRAF , MSI )
2- Cetuxi or panitumumab can be used in 1st line lt side met.CRC KRAS WT
. But no side restriction in 2nd or 3rd line
3- Bevacizumab can be used in both side with preference to Rt side acc to
PEAK AND FIRE 3 trial .

98. !!!!Dose of
beva
differs acc.
To regimen
used

100. 00

102. Different mechanisms of resistance
evolved d.t tumor heterogenicity and
intelligence
But can we fight it one day with
marvelous advancement in clinical researches
and molecular biology ????
Hoping sooooooooooooooo