1. Epigenetic alterations are common in lung cancers and affect genes like CDKN2A. Methylation of these genes can predict lymph node recurrence in stage I cancers. 2. The p53 tumor suppressor gene is frequently mutated in lung cancers, especially SCLC and squamous cell NSCLC, due to smoking-related DNA damage. Mutations in p53 downstream effectors also contribute to lung cancer pathogenesis. 3. Deregulation of cell cycle, apoptosis, and growth factor signaling pathways involved in lung cancer development and progression include alterations in p16/INK4A, LKB1/AMPK/mTOR, immune checkpoint proteins, telomerase, BCL2, death receptors,

1. MOLECULAR BASIS OF LUNG
CANCER (PART 2)
PRESENTED BY DAVID TABAGARI

2. EPIGENETICS/EPIGENOME
• Epigenetic alternation is almost universal in cancers, especially
in lung cancer.
• Methylation status of CDKN2A, CHD13, RASSF1A, and APC are
predictive of lymph node recurrence in stage I cancers.
• Despite discovery of this mechanism, the inhibitors of this

3. P53 PATHWAY
• P53 found of chr.17 is crucial for cellular integrity in the face of radiation, carcinogens,
chemotherapy and etc.
• It is the most frequently mutated gene in malignancies, and affects 90% od SCLC and
>50% of NSCLC; in NSCLC the mutation occurs in SQCC in 81% and 50% in
adenocarcinoma.
• Most P53 mutations are G to T transversions associated with smoking. This missense
mutation results in a mutant p53 which inhibits normally functioning wild type 53.
• In addition to p53, its downstream pathways and regulatory proteins might be mutated,
for instance ATM(which is associated with bad prognosis in adenocarcinoma) and also
MDM2(ubiquitin ligase inhibiting p53).
• A trial of p53 vaccine in SCLC increased tumor specific immune response and improved
outcome in these patients.

4. • When p53 is
functional, it is
activated by
phosphorylation in
response to cellular
stress (e.g., DNA
damage). Once
activated, p53
strongly induces the
expression of other
tumor suppressor
genes that control
cell cycle
checkpoints (e.g.,
p21WAF1/CIP1),
apoptosis (BAX),
DNA repair
(GADD45), and
angiogenesis
(thrombospondin).
P53 activation has
also been found to
alter miRNA

5. P16/INK4A • P16 is a cyclin dependent
kinase(CDK) inhibitor active
in G1 phase. Loss of p16 will
result in RB
hyperphosphorylation and its
inhibition leading to
abnormal proliferation.
Almost 40% of primary
NSCLC lose p16 with point
mutation or
hypermethilation(early
preneoplastic event in
SQCC).
• P14 and p16 are encoded on
the same gene, alternative
splicing differentiated p14
from p16; p14 stabilizes p53
pathway and loss of p16 will
also result in p53
dysfunction due to loss of
p14.

6. LKB1, AMPK, AND MTOR PATHWAY
• LKB1 is a serine/threonine kinas which serves a master regulator in
several key intracellular pathways. LKB1 phosphorylates AMPK and
activates it, in turn tuberous sclerosis complex suppressor is
activated, which inhibits mTOR pathway.
• LKB1 is mutated in 20-30% of adenocarcinoma of the lung.
• Metformin is an activator of AMPK and has been found to inhibit
proliferation in vitro. Retrospective analysis also concluded a
decreased incidence of cancer with patients taking metformin.
Although metformin appears to require functional LKB1 in order to
effect AMPK activation, other compounds have been identified that
circumvent this requirement.

7. IMMUNE CHECKPOINT INHIBITORS
• CTLA-4 is expressed on T cells and inhibit
T cell signaling.
• PDL1(programmed death receptor ligand)
is expressed on chancer cells and activate
PD1( programmed death receptor) and
inhibit immune function.
• Inhibitors of these factors are currently in
clinical trials in both SCLC and NSCLC.
• Ipalimumab inhibits CTLA-4 and is
currently used in melanoma. Randomized
phase II trial in SCLC demonstrated
promising results with ipalimumab
combined with chemotherapy.
• Nivolumab is a PD1 inhibitor, decreasing
its interaction with PDL1 and 2. A large
phase I trial of nivolumab included 129
NSCLC patients and reported a 17.1%
response rate, 1-year survival of 42%, and
2-year survival of 24%.

8. TELOMERASE
• Telomerase is an enzyme expressed normaly in fetal tissue and
abnormally by tumor cells; its main action is addition of nucleotides at
the ends of the chromosomes.
• Human telomerase reverse transcriptase(hTERT) catalytic subunit is the
major determinant for telomerase activity.
• Approximately 100% of SCLCs and 80% to 85% of NSCLCs have been
demonstrated to express high levels of telomerase activity. Elevated
telomerase activity in stage I NSCLC is associated with poor prognosis.

9. BCL2
• BCL2 is an antiapoptotic protein abnormally overexpressed in
75-90% of SCLC and some NSCLC( 25% of SQCC and 10%
adenocarcinoma).
• BCL-2 is localized to the outer membrane of mitochondria and
stabilizes it.
• BCL2 is considered a good prognostic factor in NSCLC.
• Cytotoxicity of many chemotherapeutic agents is induced
through the Bcl-2 apoptotic pathway; overexpression of Bcl-2
is associated with increased resistance to these agents.

10. EXTRINSIC DEATH RECEPTOR PATHWAY
• Best characterized death receptor is Fas(CD95). FasL is expressed
excessively on lung cancer cells and by so doing they inhibit T cells
responsible of killing them.
• Fas is decreased on the tumor cells as well as expression of caspase 8 and
and 10. Homozygous deletion or methylation of the CASP8 gene has been
observed in SCLC cell lines, with 79% demonstrating loss of expression,
suggesting that therapies that utilize the TNF/TRAIL receptor pathway of
apoptotic activation may not achieve success in SCLC.
• Of note, TRAIL induced apoptosis is independent of p53 gene status.
Conversely, because NSCLC has high rates of p53 inactivation (but
predominantly intact caspase 8 pathways) and high levels of TRAIL receptor
expression, this mode of therapy may prove beneficial.

12. INHIBITORS OF APOPTOSIS
• Inhibitor of apoptosis (IAP) promote tumor survival; their main action is
inhibition of caspase 3 and 7. IAP also modulates apoptosis by modulation
of nuclear factor κ B (NF-κB).
• One well none IAP is survivin, which is expressed in tumor cells and is nearly
nonexistent in normal tissue, it is associated with poor prognosis in NSCLC.
• The suppression of survivin has been shown to sensitize lung cancer cells to
radiation, suggesting that it can be a potential target for intervention.
• During the activation of apoptosis, another class of proteins called Smac
proteins are released from the mitochondria and neutralize IAPs, by
competing with caspases for the binding of IAPs.