Clostridium novyi Scientific classification Kingdom: Bacteria Phylum: Firmicutes Class: Clostridia Order: Clostridiales Family: Clostridiaceae Genus: Clostridium Species: C. novyi Binomial name Clostridium novyi
Clostridium novyi (oedematiens) a Gram-positive, endospore- forming, obligate anaerobic bacteria of the class clostridia. It is ubiquitous, being found in the soil and faeces. It is pathogenic, causing a wide variety of diseases in man and animals. It comes in three types, labelled A, B, and a non-pathogenic type C distinguished by the range of toxins they produce. Some authors include Clostridium haemolyticum as Clostridium novyi type D. C novyi is closely related to Clostridium botulinum types C and D as Yoshimasa Sasaki et al. have demonstrated by 16S rDNA sequence analysis. The PAGE analysis reported in ref 1 seems to indicate that the differences between these closely related types is a matter of gene expression rather than major genetic differences.[original research?] For example type C can be induced to produce the lethal alpha-toxin.
Growth in culture proceeds through 3 stages: Initial growth wherein no toxin is produced; vigorous growth wherein toxin is produced; and spore formation wherein endospores are formed and toxin production decreases. It is suggested that type C may be type B that forms spores more readily so does not go through the toxin-production stage.
It is also fastidious and difficult to culture, requiring the presence of thiols.
- The toxins are designated by Greek letters. The toxins normally produced by the various types are shown in table 1
Table 1 C novyi type Toxins A alpha, gamma, delta, epsilon B alpha, beta, zeta C gamma
The alpha-toxin of Clostridium botulinum types C and D, is similar to the C novyi beta-toxin. The A and B toxins of Clostridium difficile show homology with the alpha-toxin of C novyi as does the lethal toxin of clostridium sordellii.
The alpha-toxin is characterised as lethal and necrotizing.
The type A alpha-toxin is oedematising. It acts by causing morphological changes to all cell types especially endothelial cells by inhibition of signal transduction pathways, resulting in the breakdown of cytoskeletal structures. The cells of the microvascular system become spherical and the attachments to neighbouring cells are reduced to thin strings. This results in leakage from the capillaries, leading to oedema. The threshold concentration for this action to occur is 5 ng/ml (5 parts per billion) with 50% of cells rounded at 50 ng/ml.
- The duodenum is particularly sensitive to the toxin. Injection into dogs resulted in extreme oedema of the submucosal tissues of the duodenum while leaving the stomach uninjured. Injection into the eye resulted in lesions similar to flame haemorrhages found in diabetic retinopathy.
- The toxin is a large 250-kDa protein the active part of which is the NH2-terminal 551 amino acid fragment. Alpha-toxins are glycosyltransferases, modifying and thereby inactivating different members of the Rho and Ras subfamily of small GTP-binding proteins. C novyi type A alpha-toxin is unique in using UDP-N-acetylglucosamine rather than UDP-glucose as a substrate.
The beta-toxin is characterised as haemolytic, necrotizing lecithinase.
The gamma-toxin is characterised as haemolytic, lecithinase.
The delta-toxin is characterised as oxygen labile haemolysin.
The epsilon-toxin is characterised as lecithino-vitelin and thought to be responsible for the pearly layer found in cultures.
The zeta-toxin is characterised as haemolysin.
The type and severity of the disease caused depends on penetration of the tissues. The epithelium of the alimentary tract, in general, provides an effective barrier to penetration. However, spores may escape from the gut and lodge in any part of the body and result in spontaneous infection should local anaerobic conditions occur.
Wound infection by C novyi and many other clostridium species cause gas gangrene Spontaneous infection is mostly associated with predisposing factors of hematologic or colorectal malignancies and with diabetes mellitus, although Gram-negative organisms, including Escherichia coli, may lead to a gas gangrene-like syndrome in diabetic patients. This presents with cellulitis and crepitus, and may be mistaken for gas gangrene. Spontaneous, nontraumatic, or intrinsic infections from a bowel source have been increasingly reported recently.
C novyi has been implicated in mortality among injecting illegal drug users. A review of the literature reveals that the organism Clostridium novyi type A is capable of inducing most of the symptoms of type 2 diabetes and its complications. There is also anecdotal evidence that claim that antibiotic treatment for this organism produces remission of these symptoms.
Testing is problematical with figures presented by McLauchlin and Brazier [cited above] suggesting a false negative rate of about 40% under ideal conditions. Only positive results may be regarded as reliable. In the absence of a positive test, C. novyi type A may be inferred from characterisation by clinical observation, table 2.
Table 2 Observation Comment Oedema Especially if extreme with rapid onset. In view of the sensitivity of the duodenum to the alpha-toxin, oedematous duodenum is always suspect. Anaerobic Infection occurs at an anaerobic site such as the gut or salivary gland. It may also occur at a site temporarily made anaerobic by occlusion and maintained in this state by oedema. Gram positive If penicillin causes remission of oedema then a Gram positive organism is the causative agent.
Chronic infection leading to leaky capillaries may also cause retinal haemorrhages and oedema in the lower extremities leading to necrosis and gangrene. Leaky nephrons may compromise the ability of kidneys to concentrate urine leading to frequent urination and dehydration.
Gas gangrene: Infectious necrotic hepatitis (Black disease)
Clostridium novyi-NT - Potential Therapeutic Uses in Cancers
In general, solid tumors are characterized by a hypoxic area in the tumor cores. This is due to irregular and insufficient tumor vasculature growth and heavy metabolic demands of the surrounding tumor cells.
Much of a tumor core is necrotic, however some tumor cells survive there – often in a quiescent state. Therefore, these cells are often quite resistant to standard treatments such as radiotherapy (which relies heavily on DNA damage from radiation induction of oxygen-based free radical species), and chemotherapy (which (1) can have difficulty accessing the poorly perfused tumor core, and (2) often has weak effect on quiescent cells.). As a result, cells in the hypoxic tumor core often survive treatment and become a source for subsequent cancer recurrence and spread.
Clostridium novyi-NT is a genetically modified form of Clostridium novyi that lacks a major toxin. Because Clostridium novyi is a strict anaerobe; it grows selectively in hypoxic tumor cores; elsewhere, it forms inactive spores. Clostridium novyi-NT activates and very effectively infects and lyses tumor cells in hypoxic tumor cores.
Early work on use of strict anaerobes in tumors goes back several decades. Strongly lytic, infective bacteria tended to be the most effective (however, most earlier research was abandoned due to the risk of toxicity from release of toxin).
One major limitation on the use of Clostridium novyi-NT or other strict anaerobes in cancer treatment – is that it tends to affect only the hypoxic tumor core – , leaving the active cancer cells in the well-perfused tumor rim alive and intact.
It is not surprising, then, that this has led to attempts to combine Clostridium novyi-NT with traditional chemotherapy and/or with radiotherapy (both of which tend to be preferentially effective within the well-perfused tumor rim).
A variety of other clever approaches are under continuing investigation, these include :
- "RAIT" (radioactive immunotherapy) – Radioactive monoclonal antibodies against common antigens on the tumor cells (for example, CEA) – or perhaps against epitopes on the Clostridium novyi-NT itself) can be used to more specifically localize and deliver radiation near the tumor cells and less to surrounding tissue. (In a sense, this could be viewed as a sort of molecular brachytherapy).
- Prodrug converting enzymes can be produced by further genetic modification of the Clostridium novyi-NT. Chemotheraputic prodrugs can be given systemically and then will be more specifically activated near the tumor site.
- Other chemotherapy delivery technologies using liposomes or minicells can be used to more specifically deliver chemotheraputic agents to the site of the remaining tumor rim. (Again, it may be useful to use bispecific antibodies to epitopes on the Clostridium novyi-NT itself – instead of just using bispecific antibodies to variably expressed tumor antigens (like CEA). (Minicells are a very promising technology in themselves that uses bispecific antibodies to dramatically increase the delivery specificity of chemotheraputic drugs by several orders of magnitude – potentially allowing effective chemotheraputic dosages that are hundreds of times current tolerated systemic levels. (Nevertheless, minicells are limited by perfusion access to tumor cores – so combination with Clostridium novyi-NT may provide an excellent complement).
- Various genetic modifications to Clostridium novyi-NT seek to further stimulate local inflammation and immune response – to boost the immunogenicity of the tumor rim. Many of these approaches secrete immunomodulators/cytokines; others try to use siRNA or other approaches to further shut down tumor cells.
- The hypoxic core can be made temporarily wider by use of drugs like dolastatin, or by temporarily reducing oxygenation. This then allows Clostridium novyi-NT to lyse more of the tumor.
- Most approaches have used single administrations of Clostridium novyi-NT, but it may be useful to give repeated injections to promote immune response in the area of the active bacteria (the former tumor core and adjacent rim) to create a "bystander effect" on the nearby tumor cells (e.g., boosting the immune response not only to the Clostridium novyi-NT but also to the tumor cells). It may also help slow relapses by colonizing metastases early (although only after they became large enough to have a significantly sized hypoxic core).
In summary, Clostridium novyi-NT is a promising new component to treatment of solid tumors - effectively targeting the hypoxic tumor cores that were a source of ongoing treatment resistance and recurrence. It is likely that additional modalities will be needed to treat the well-perfused tumor rims.
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