Advanced Microbiology
Topic one: Use of bacteria in cancer therapy
1.1 Cancer – general information
1.1.1 Cancer burden in Belgium
• 2020: 77827 new diagnoses of cancer (♂: 54,2%)
o Highest incidence ♂: prostate cancer
o Highest incidence ♀: breast cancer
• Prostate, beast , lung and colorectal cancer
o 45% of the new diagnoses
• Highest mortality
o ♂: lung cancer
o ♀: breast cancer
1.1.2 Cancer definitions
Cancer: a malignant neoplasm in which cells are;
• Aggressive: cells grow and divide without respect to normal limits
• Invasive: cells invade and destroy adjacent tissues
• And/or metastatic: cells spread to other body locations
Tumor: a solid neoplasm
• Benign tumor: self-limiting growth, no invasion in tissues nor metastasis
• Malignant tumor: with characteristics of cancer (~80% of cancers)
Neoplasm: abnormal proliferation of genetically altered cells (benign or malignant)
1.1.3 Tumor types
Carcinoma:
• Malignant tumors: cells of ecto- or endodermal origin
o Ectodermal: the outer layer of the skin
o Endodermal: innermost of the three primary germ layers
• Most common cancers: breast, prostate, lung, colon and skin
Sarcoma:
• Malignant tumors: cells of mesodermal origin
o Connective, supportive or soft tissues
• Tumors related to bone, cartilage, fat, muscle and blood vessels
• Very rare → 1% of the cancers
1.1.4 Treatment modalities of tumors
• Conventional treatments
o Surgery
o Radiotherapy
o Chemotherapy
o Immunotherapy (most recent)
• Limitations of these treatments
o Surgery
▪ Inadequate removal of total tumor
▪ Existence of micro-extensions/-metastases
o Radio- and chemotherapy
▪ Tumor targeting
▪ Severe side effects
▪ Resistance of tumor cells to damaging agents
o Immunotherapy
▪ Still in its infancy
▪ Personalized medicine
1
,1.1.5 Tumor growth
• Tumor cell proliferation requires blood vessels to provide nutrients
o Neo-angiogenesis
• Tumor growth vs. vessel proliferation often impaired
o Aberrant blood vessel structure
▪ Irregular, blind ends, arteriovenous shunts
o Irregular blood flow
▪ Disturbed delivery of oxygen and nutrients
▪ Hypoxia and cell death → setting free cell debris (DNA and proteins)
Figure 1 Irregular tumor vasculature. Left - Normal tissue. Right - Tumor tissue, due to fast angiogenesis many mistakes are made .
Endothelial cells not fixed very well to each other causing leaks, holes and obstruction
1.1.6 Hypoxia in tumors
Figure 2. Hypoxia in tumor cells, blue is hypoxic and red is oxygenated
• Tumor has different regions
• Blood vessels go inside the clumb of tumor cells
o Some parts are closer to a blood vessel → better oxygenation
o Other parts suffer from anoxic/hypoxic conditions
• Anoxic/necrotic regions spread throughout tumor mass
1.1.6.1 Hypoxia: cause of intrinsic resistance
◆ Radiation resistance
• Hypoxic cells need stronger radio therapy than oxygenated cells
• Hypoxic cells are 3 times more resistant than aerobic cells
2
,◆ Drug resistance
• Hypoxic cells are not reached by drugs
o No blood vessels → drug cannot get there
• Chemotherapeutics often targeted at well-proliferating cells
o Less effective in hypoxic, non-proliferating cells
• Solution: hypoxia-induced prodrugs
• Ex. Tirapazamine (TPZ)
o Selective cytotoxicity in hypoxic mammalian cells
Figure 3 Tirapazamine. Hypoxia induced prodrug
1.1.6.2 Hypoxia: cause of molecular resistance
• Hypoxia-mediated induction of genetic and metabolic changes un tumor cells
o Hypoxia tolerance regulated by several pathways
o Hypoxia-inducible factor (HIF-1) pathway
• More malignant phenotype
o Induction of metastasis
o Increase of neo-angiogenesis
o Selection of cells with diminished apoptotic potential
• Accompanied by molecular therapy resistance
1.1.7 Alternative treatment modalities
• Gene therapy: introduction of therapeutic genes in tumor cells
• Protein therapy: delivery of therapeutic proteins to tumor cells
• Cancer immunotherapy: modulation of immune response to treat cancer
• Cancer vaccines: treatment or prevention of cancer by providing tumor antigens
• More effective drugs delivered by alternative mechanisms
1.2 Bacteria and cancer: cause or cure?
1.2.1 Helicobacter pylori as causative agent
• Acute H. pylori can evolve to chronic H. pylori infection
• May cause MALT lymphoma or gastric cancer
Figure 4 Evolution of Helicobacter pylori infection
3
, 1.2.2 Other bacteria associated with cancer
Streptococcus bovis
Colorectal cancer Bacteroides fragilis
Fusobacterium nucleatum
Gallbladder cancer Salmonella Typhi
Lung cancer Chlamydophilia pneumoniae
Esophageal cancer Streptococcus anginosus
Capnocytophaga gingivalis
Oral squamous cell carcinoma Prevotella spp.
Streptococcus mitis
Leukemia, lung cancer Mycoplasma
1.3 Bacterial approaches in cancer treatment
1.3.1 Experiences from the past
• 1831: cancer cure in patients suffering from Clostridium perfringens infection (gas gangrene)
o 1947: first injection of Clostridium spores to treat cancer
• Early 19th century: tumor regression/cancer cure upon Streptococcus pyogenes infection (erysipelas)
o “Coley’s toxin”: inactivated streptococci and Serratia marcescens
o Basis of cancer immunotherapy
• Late 19th century: lower frequency of cancer in tuberculosis patients
o 1921: isolation of attenuated Mycobacterium bovis strains
o 1970: BCG (Bacillus Calmette-Guerin) vaccine for bladder cancer
1.3.2 Bacterial DNA
• Unmethylated CpG sequences are 20x more in bacteria (and viruses) than mammalian DNA
• CpG motifs = PAMPs (pathogen associated molecular patterns)
• Endocytosed CpG motifs are recognized by toll-like-receptor 9 in plasmacytoid dendritic- and B-cells
• TLR9 activation → immunostimulation
o Bypass tumor-induced suppression of immune response
o Shift from T cell tolerance to strong cytotoxic T cell response against tumor antigens
Figure 5. Bacterial CpG motifs
4
Topic one: Use of bacteria in cancer therapy
1.1 Cancer – general information
1.1.1 Cancer burden in Belgium
• 2020: 77827 new diagnoses of cancer (♂: 54,2%)
o Highest incidence ♂: prostate cancer
o Highest incidence ♀: breast cancer
• Prostate, beast , lung and colorectal cancer
o 45% of the new diagnoses
• Highest mortality
o ♂: lung cancer
o ♀: breast cancer
1.1.2 Cancer definitions
Cancer: a malignant neoplasm in which cells are;
• Aggressive: cells grow and divide without respect to normal limits
• Invasive: cells invade and destroy adjacent tissues
• And/or metastatic: cells spread to other body locations
Tumor: a solid neoplasm
• Benign tumor: self-limiting growth, no invasion in tissues nor metastasis
• Malignant tumor: with characteristics of cancer (~80% of cancers)
Neoplasm: abnormal proliferation of genetically altered cells (benign or malignant)
1.1.3 Tumor types
Carcinoma:
• Malignant tumors: cells of ecto- or endodermal origin
o Ectodermal: the outer layer of the skin
o Endodermal: innermost of the three primary germ layers
• Most common cancers: breast, prostate, lung, colon and skin
Sarcoma:
• Malignant tumors: cells of mesodermal origin
o Connective, supportive or soft tissues
• Tumors related to bone, cartilage, fat, muscle and blood vessels
• Very rare → 1% of the cancers
1.1.4 Treatment modalities of tumors
• Conventional treatments
o Surgery
o Radiotherapy
o Chemotherapy
o Immunotherapy (most recent)
• Limitations of these treatments
o Surgery
▪ Inadequate removal of total tumor
▪ Existence of micro-extensions/-metastases
o Radio- and chemotherapy
▪ Tumor targeting
▪ Severe side effects
▪ Resistance of tumor cells to damaging agents
o Immunotherapy
▪ Still in its infancy
▪ Personalized medicine
1
,1.1.5 Tumor growth
• Tumor cell proliferation requires blood vessels to provide nutrients
o Neo-angiogenesis
• Tumor growth vs. vessel proliferation often impaired
o Aberrant blood vessel structure
▪ Irregular, blind ends, arteriovenous shunts
o Irregular blood flow
▪ Disturbed delivery of oxygen and nutrients
▪ Hypoxia and cell death → setting free cell debris (DNA and proteins)
Figure 1 Irregular tumor vasculature. Left - Normal tissue. Right - Tumor tissue, due to fast angiogenesis many mistakes are made .
Endothelial cells not fixed very well to each other causing leaks, holes and obstruction
1.1.6 Hypoxia in tumors
Figure 2. Hypoxia in tumor cells, blue is hypoxic and red is oxygenated
• Tumor has different regions
• Blood vessels go inside the clumb of tumor cells
o Some parts are closer to a blood vessel → better oxygenation
o Other parts suffer from anoxic/hypoxic conditions
• Anoxic/necrotic regions spread throughout tumor mass
1.1.6.1 Hypoxia: cause of intrinsic resistance
◆ Radiation resistance
• Hypoxic cells need stronger radio therapy than oxygenated cells
• Hypoxic cells are 3 times more resistant than aerobic cells
2
,◆ Drug resistance
• Hypoxic cells are not reached by drugs
o No blood vessels → drug cannot get there
• Chemotherapeutics often targeted at well-proliferating cells
o Less effective in hypoxic, non-proliferating cells
• Solution: hypoxia-induced prodrugs
• Ex. Tirapazamine (TPZ)
o Selective cytotoxicity in hypoxic mammalian cells
Figure 3 Tirapazamine. Hypoxia induced prodrug
1.1.6.2 Hypoxia: cause of molecular resistance
• Hypoxia-mediated induction of genetic and metabolic changes un tumor cells
o Hypoxia tolerance regulated by several pathways
o Hypoxia-inducible factor (HIF-1) pathway
• More malignant phenotype
o Induction of metastasis
o Increase of neo-angiogenesis
o Selection of cells with diminished apoptotic potential
• Accompanied by molecular therapy resistance
1.1.7 Alternative treatment modalities
• Gene therapy: introduction of therapeutic genes in tumor cells
• Protein therapy: delivery of therapeutic proteins to tumor cells
• Cancer immunotherapy: modulation of immune response to treat cancer
• Cancer vaccines: treatment or prevention of cancer by providing tumor antigens
• More effective drugs delivered by alternative mechanisms
1.2 Bacteria and cancer: cause or cure?
1.2.1 Helicobacter pylori as causative agent
• Acute H. pylori can evolve to chronic H. pylori infection
• May cause MALT lymphoma or gastric cancer
Figure 4 Evolution of Helicobacter pylori infection
3
, 1.2.2 Other bacteria associated with cancer
Streptococcus bovis
Colorectal cancer Bacteroides fragilis
Fusobacterium nucleatum
Gallbladder cancer Salmonella Typhi
Lung cancer Chlamydophilia pneumoniae
Esophageal cancer Streptococcus anginosus
Capnocytophaga gingivalis
Oral squamous cell carcinoma Prevotella spp.
Streptococcus mitis
Leukemia, lung cancer Mycoplasma
1.3 Bacterial approaches in cancer treatment
1.3.1 Experiences from the past
• 1831: cancer cure in patients suffering from Clostridium perfringens infection (gas gangrene)
o 1947: first injection of Clostridium spores to treat cancer
• Early 19th century: tumor regression/cancer cure upon Streptococcus pyogenes infection (erysipelas)
o “Coley’s toxin”: inactivated streptococci and Serratia marcescens
o Basis of cancer immunotherapy
• Late 19th century: lower frequency of cancer in tuberculosis patients
o 1921: isolation of attenuated Mycobacterium bovis strains
o 1970: BCG (Bacillus Calmette-Guerin) vaccine for bladder cancer
1.3.2 Bacterial DNA
• Unmethylated CpG sequences are 20x more in bacteria (and viruses) than mammalian DNA
• CpG motifs = PAMPs (pathogen associated molecular patterns)
• Endocytosed CpG motifs are recognized by toll-like-receptor 9 in plasmacytoid dendritic- and B-cells
• TLR9 activation → immunostimulation
o Bypass tumor-induced suppression of immune response
o Shift from T cell tolerance to strong cytotoxic T cell response against tumor antigens
Figure 5. Bacterial CpG motifs
4
