use of bacteria in cancer therapy Flashcards
A cancer
can be metastatic, invasive, malignant and agressive
it is a general term that refers to a group of disease characterized by growth and spread of abnormal growth
a tumour
can be benign or malignant. Abnormal growth of tissue
It is defined by a solid mass, a neoplasm that does not invade or does surrounding tissues
malignant tumors
a neoplasm
are cells that starts to grow abnormally. Can be benign or malignant but they start to proliferate
it is every abnormal proliferation of genetically altered cells benign or malignant
carcinoma
affect skin, colon or lung. They are abnormally of ectodermal and endodermal tie-ssues
sarcoma
abnormalities of mesodermal tissues such as blood vessels, bone, fat.
helicobacter as causative agent
chronic infection can cause MALT lymphoma y increase acid production. Can also cause Gastric cancer by increasing acid productions though dysplasia and ulcer formation
Bacteria can promote carcinogenesis
Bacterial DNA
bacteria are richer in CpG unmethylated sequence, whay more than mammalian. These are detected as PAMPS by TLR on B cell and dendritic cells.
This TLR9 activation leads to a strong cytotoxic T CELL response and help to bypass the tumor induced suppression of the immune system
In B cells, it lease to the production go IL6, 12 and chemokine, as well as IgM production.
in DC, the expression of MHC is enhanced, which increase IL1,6? 12, 18 and TNF production, as well as increase APC function, which activate T helper cells.
CD4 cells than can activate CTL cell, produce interferon gamma and B cell leads the adaptive immunity with IgG production.
These bacteria DNA is used to boost the tumor antigen recognition by the immune system.
drawbacks include the fact that it is hard to purify CpG rich bacterial DNA for human application because of LPS contamination (toxins causing fever), bacterial DNA tend to be degraded by human nucleases and it is hard to engineer them to directly target the tumors.
The solutions at the moments are the production of nuclease resistance synthetic CpG oligodeoxynucleotides (ODN) to counteract LPS contamination. Improved uptake by self assembled nonmaterial CpG ODN complexes
bacterial toxins
A) toxins to target receptor directly
A) toxins to target receptor directly
Clostridium perfringens can produce an enterotoxins which is release in small intestins and bind to epithelial cells. It usually cause food poisoning. It works by directed binding to cell via a tight junction proteins, which causes conformational changes and pore like structure creating change in the membrane permeability.
As anti tumoral agents, it would be use to change the cell permeability, causing osmotic imbalance in tumor cells and therefore cytolysis.
They recurrently working on recombinant CPE that could be combine to therapeutic proteins or drug loaded nanoparticles.
However, the tumor specificity is not clear yet. This is because CPE receptor are over expressed in a lot of different cancer ok ok but also a low level in healthy cells which could lead to a systemic toxicity.
It limits its use but For example could be used in brain metastases cause CPE receptor is absent in normal brain tissue
bacterial toxins
b) immunotoxins: ligand bound toxins
basically it is an adaptations of the toxins. they use for example the diphtheria toxins or the pseudomonas toxins which are both AB toxins and both bind to a lot of receptors in many cell type! For tumor treatment these AB toxins can be exploited by removing the receptor binding domain and replace it by a ligand that could directly target the tumor receptor. By this you gain specificity and keep the cytotoxins effect.
bacterial toxins
c) superantigens
super antigens are not produced by APC.
They are functional molecules which do not require further processing and that can directly bind to MHC class 2 molecular of APC. The MHC super AG complex can then directly interact with TCR and it boost it so much it can give sepsis!! It can activate up to 20% of T cells, release loads of cytokines and disturb the normal immune response.
loads of bacterial toxins can act as super AG, it gives an advantage as it allow to evade the immune system and prolong survival by causing a local inflammation and therefore they get plenty of blood and nutrient.
For tumeurs targeted superantigens (TTS), the idea would be to induce a strong and local cytotoxic T cell attach that would kill the tumor cells and produce inflammation. This can be done by using recombinant super antigens. The super antigens would be mutated by linking it to a Fab or a monoclonal antibody that is directly targeted against a tumor antigens.
Exemple:naptumomab estafenatox: the modified enterotoxins is fused to FAB which recognized the 5T4 antigens . 5T4 is expressed in a lot of cancer but not on normal tissues; so the FAB bind to it, then the toxins aka Super AG allow binding to MHC2 (increase safety profile), which activate the T lymphocyte and allow direct killing.
bacterial toxins:
d) anti-tumor antibiotics
super important chemotherapeutics. They have a lot of MOA such as DNA intercalation, inhibition of RNA transcription, preventing the protein synthesis, etc
exemples:
Azurin is secreted by pseudomonas aeruginosa. It has a Cu-containing electron transfer protein and allow it to preferentially penetrate cancer cells. It leads to a complex formation with p 53 (tumor suppressor protein), leading to increase p53 concentration which causes cell shrinkage and death through apoptosis and growth arrest. +++ inhibit the tumor angiogenesis. BUUUT the question of tumor specificity is not entirely answered.
limitation of bacterial products
the MOA is not always well understood. There is still work done to diminish toxicity and enhance the specificity.
the numbers will increase thanks to the development in combinatorial bio synthesis and the advancement in meta genomic.
live bacteria in cancer therapy
3 approaches can be taken
either bacteria is a vector for protein transfer to the tumor site
or
the bacteria is an immune adjuvant to evoke the immune repose indirectly
or
the bacteria is used as a DNA/protein vaccine to target the cancer
live bacteria as a protein transfer system - Clostridium
a) can be used to target tumor colonization with obligate anaerobic bacteria. You use the tumor hypoxia to bring and produce your proteins to attack the tumor cells
b) same by using facultative anaerobic bacteria. These are auxotrophic strains that would benefit of the tumor micro environnement.
example: Clostridium (anaerobic obligate bacteria: endospore formation))
in the 1900 it was used for cancer treatment as it was shown that colonisation was restricted to the tumors, released bacterials proteins and destroyed large tumors parts. However, the outer rime of the viables cells seemed to persist and the oncolysis ofter led to tumor lysis syndrome . So basically it was killing the tumor from inside but not the outside.
in A99(, an attenuated stain was used (deletion of a lethal gene) that seem to spread extensively throughout the tumor. It had great oncolytic properties as it produced enzyme that attacked the tumor cells and causing enlargement of necrotic regions. It was also causing a strong immune response. It was a good balance but the outer viable rime problem was not solved. The solution for this was COBALT: combination bacteriolytic therapy which combined the use of C. novyi NT treatment and radio/chemotherapy. So C. novae NT and Doxil (liposome encapsulated doxorubicin) was given and let to a great survival rate.
other non pathogenic recombinant clostridium can be used such as proteolytic clostridia or recombinantly ended with therapeutic gene clostridium. This is called CDEPT: clostridium directed enzyme prodrug therapy. the enzyme of the bacteria convert the produce, leading to the production of targeted cytotoxic, immune modulation or anti vascular proteins at the site of action wanted. The use of c novae in combination actually allow to reduce conventional therapy level .
live bacteria as protein transfer system - Salmonella
- Salmonella Typhimurium Prine mutant (need external purine sources - auxotrophs): You gain tumors specificity based on the excessive presence of purine the in necrotic area of the tumor regions. In this case, recombinant strain are often used - Tumour amplified protein expression therapy (TAPET)
- Salmonella typhimurium A1-R (leu-arg auxotroph): need tumor tissue to survive.
