Nature Sub-Journal: EGFR/HER2 Dual Targeted PDC Combination for the Treatment of Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is the fourth most common cause of cancer-related death and is the most aggressive cancer, with a five-year survival of less than 5%.

Gemcitabine is a first-line treatment for PDAC but provides little therapeutic value, with a response rate of about 20% and a median survival of 6 months
.
Even if gemcitabine is used in combination with other drugs to improve the efficacy of PDAC, its effect is still very limited, usually only increasing the survival time
of patients for a few weeks to a few months.

Because PDAC's resistance to chemotherapy develops rapidly, and PDAC has a severe symptomatic effect
.
In addition, PD-1/PD-L1 immunotherapy, which is widely used in other cancers, has even shown poor results
for pancreatic cancer.
Therefore, additional treatment strategies
for pancreatic cancer are urgently needed.

Among them, the typical genetic mutations observed in PDAC include activation of the oncogene KRAS (%3E90%), inactivation or deletion of tumor suppressor genes, such as CDKN2A (95%), TP53 (50-75%), SMAD4 (~55%), PTEN (~60%), and DNA repair gene BRCA 2 (7-19%) mutations, which can lead to tumor progression or recurrence, however, unfortunately, few of these drivers are currently druggable , so it is difficult to design effective therapies
against PDAC.

To date, therapeutic research has selectively inhibited EGFR and its associated pathways with molecularly targeted drugs that may lead to breakthroughs
in the treatment of pancreatic cancer.
Currently available drugs for this target are tyrosine kinase inhibitors (erlotinib, gefitinib, etc.
) and monoclonal antibodies (cetuximab
).
Moreover, some progress
has been made in the treatment of pancreatic cancer with a combination of gemcitabine and EGFR targeted drugs.
With the combination of erlotinib and gemcitabine, the overall survival time for unoperated pancreatic cancer patients is 12.
5 months, and the 1-year survival rate is 51%.

Because of the intercorrelated effects between receptor members of the ErbB family, blocking two receptors at the same time may be more important
than blocking only a single receptor for effective treatment of cancer and limiting drug resistance.
The antitumor antibiotic, Lidamycin (LDM), because of its effective inhibition of tumor angiogenesis and promotion of apoptosis of tumor cells, makes it an ideal warhead
for targeted drugs such as antibody-conjugated drugs ADC.

Liang Li's team from the Chinese Academy of Medical Sciences and the Institute of Pharmaceutical Biotechnology at Peking Union Medical College has developed a bispecific antibody-drug conjugate (ADC)-like drug, which is a bi-targeted ligand-based lindamycin (DTLL)
based on a HER2/EGFR targeted conjugate.
(Patent No.
:CN109954130,CN109957591)

On September 20, the team published an article titled "An EGFR/HER2-targeted conjugate sensitizes gemcitabine-sensitive and resistant pancreatic cancer through different SMAD4-mediated" in Nature Communications Mechanisms", which explains the efficacy of DTLL in combination with gemcitabine in vitro and explains its possible mechanism
of action.

DTLL

DTLL (named Ridamycin based on the double-targeted ligand) has been shown to be a very potent bispecific oligopeptide-drug conjugate-like drug consisting
of two oligopeptides that are anti-EGFR and HER2 and an alkenediyne antibiotic ridamycin (LDM).
Not only does it inhibit the activity of EGFR and HER2, but it can also be combined with the cytotoxic effects of LDM, and previous studies have shown that DTLL is more effective in the treatment of ovarian cancer, PDAC and esophageal cancer than with discretionary LDM
alone.
In addition, in PDAC, DTLL may inhibit the progression of pancreatic tumors by EGFR/HER2-dependent blocking of AKT/mTOR signaling and PD-L1/PD1-mediated evasion
immune monitoring.
However, the use of DTLL in the combination therapy of gemcitabine has not been explored
.
To distinguish what induces the drivers of PDAC cell line sensitivity to gemcitabine therapy, and to ensure the accuracy of the combined clinical trial, the researchers conducted experiments
in different PDAC cell lines.

Drivers of gemcitabine resistance in PDAC cells

The researchers studied the drug response
of eight human pancreatic cancer cell lines (AsPC-1, MIA PaCa-2, BxPC-3, PANC-1, CFPAC-1, Panc0403, HuPT-3, and SU86.
86 cells) exposed to 72h gemcitabine.
(as shown in the following figure)

Among them, MIA PaCa-2 and HupT-3 cells are most sensitive to gemcitabine, while AsPC-1 and BxPC-3 cells respond significantly weaker to the drug
.
Since after ruling out interference from other factors, the researchers found that SMAD4 was highly expressed in MIA PaCa-2, HupT-3, and PANC-1 cells, and almost none detected in AsPC-1, BxPC-3, and CFPAC-1 cells, meaning that SMAD4 expression may be related
to the susceptibility of these cells to gemcitabine.
Subsequent protein analyses confirm this view
.

In addition, the researchers collected publicly available data on patients with TCGA pancreatic cancer (TCGA-PAAD project), which included clinical information on gemcitabine therapy and SMAD4 expression datasets, to determine whether SMAD4 expression in PDAC patients was clinically
related to gemcitabine response.
They found that in 35 patients with high expression of SMAD4, 17 (48.
57%) of the sample responded positively to the drug, while only 34.
38% of patients with low levels of Smad 4 (11 out of 32 samples) had a positive response
to gemcitabine.
Its odds ratio was 1.
98 (p = 0.
22), which indicates that high levels of expression of SMAD4 promote gemcitabine response clinically,

These results, whether in vitro experiments or clinically, SMAD4 is associated not only with the occurrence and development of PDAC, but also with the drug response to gemcitabine therapy
.

Based on the differences in the genetic status and protein expression of SMAD4 and drug sensitivity between AsPC-1 and MIA PaCa-2 cells, the researchers selected these two cell lines as models of SMAD4 deficiency/gemcitabine resistance and SMAD4 adequacy/gemcitabine-sensitive PDAC as models for combined drug use
.

The synergy of DTLL and gemcitabine

Choosing a reference for drug resistance and sensitivity to drugs, then it is necessary to further determine whether DTLL can make cells sensitive to other drugs, and the researchers also selected a variety of antitumor drugs widely used in pancreatic cancer treatment to detect DTLL with 5-fluorouracil (antimetabolite), oxaliplatin (DNA crosslinking), paclitaxel (antimicrotubule), irinotecan (topoisomerase I inhibitor), etoposide (topoisomerase II inhibitor) and lapatinib ( The combined effect of HER2 and EGFR tyrosine kinase dual inhibitors, the results show that combination therapy produces significant synergistic inhibition of tumor cell growth, especially for SMAD4-deficient/gemcitabine-resistant AsPC-1 cells or xenografted tumors
.
In the SMAD4-deficient/gemcitabine resistance model, combination therapy significantly inhibits the growth
of PDAC tumors mainly through the SMAD4-dependent signaling pathway.

Figure: DTLL enhances gemcitabine-induced proliferation inhibition and cell cycle arrest

In a PDAC model sensitive to gemcitabine, the researchers found that combination therapy enhances antitumor activity
by blocking the AKT/mTOR signaling pathway.
They also observed decreased expression of SMAD4 and AKT/mTOR signals (shown in the figure below), suggesting that DTLL blocking AKT/mTOR signaling or combination therapy in SMAD4-sufficient PDAC cells may not only block EGFR/HER2 signaling, but also reduce SMAD4
.

Different mechanisms of SMAD4 in different lineages

The researchers also found that depending on the SMAD4 lineage (mutant type - gemcitabine inhibition and wild type - gemcitabine sensitivity), DTLL was able to make gemcitabine-resistant cells or gemcitabine-sensitive cells sensitive
to gemcitabine efficacy (or even other chemotherapy drugs) through different mechanisms of action.
(as shown in the following figure)

If SMAD4 adequate/gemcitabine-sensitive PDAC cells are given, DTLL combination therapy may not only prevent tumor proliferation by blocking ATK/mTOR signaling and anti-apoptotic proteins (Bcl-2 and MCL1) mediated by impaired NF-κB function, but also restore the biological activity of SMAD4 as a tumor inhibitor to trigger downstream NF-κB regulatory signals
for apoptosis in SMAD4-deficient/gemcitabine-resistant tumors.

The inhibitory effect of DTLL alone or in combination with gemcitabine suggests that it plays a double-edged sword in PDAC tumor growth, with completely different drug response behaviors and molecular mechanisms
of action between the synergistic efficacy between gemcitabine-resistant and gemcitabine-sensitive PDAC.

summary

In summary, regardless of whether SMAD4 expression is adequate, the synergistic effect of DTLL combination therapy on PDAC may enhance the therapeutic effect
of gemcitabine on patients.
The researchers note that for future clinical translation directions, they may also need biomarkers to identify possible PDAC responders based on the tumor's inherent SMAD4 status and use them in a reasonable combination of
AKT or TGF-β inhibitors.

However, the researchers acknowledge that there is still a need to study the role of other signaling pathways in this process to deepen understanding
of this treatment regimen.

Reference source:

Yao, H.
, Song, W.
, Cao, R.
 et al.
 An EGFR/HER2-targeted conjugate sensitizes gemcitabine-sensitive and resistant pancreatic cancer through different SMAD4-mediated mechanisms.
 Nat Commun 13, 5506 (2022).
https://doi.
org/10.
1038/s41467-022-33037-x