From the Microbial World

Some clinically important antibiotics
Antibiotic	Producer organism	Activity	Site or mode of action
Penicillin	Penicillium chrysogenum	Gram-positive bacteria	Wall synthesis
Cephalosporin	Cephalosporium acremonium	Broad spectrum	Wall synthesis
Griseofulvin	Penicillium griseofulvum	Dermatophytic fungi	Microtubules
Bacitracin	Bacillus subtilis	Gram-positive bacteria	Wall synthesis
Polymyxin B	Bacillus polymyxa	Gram-negative bacteria	Cell membrane
Amphotericin B	Streptomyces nodosus	Fungi	Cell membrane
Erythromycin	Streptomyces erythreus	Gram-positive bacteria	Protein synthesis
Neomycin	Streptomyces fradiae	Broad spectrum	Protein synthesis
Streptomycin	Streptomyces griseus	Gram-negative bacteria	Protein synthesis
Tetracycline	Streptomyces rimosus	Broad spectrum	Protein synthesis
Vancomycin	Streptomyces orientalis	Gram-positive bacteria	Protein synthesis
Gentamicin	Micromonospora purpurea	Broad spectrum	Protein synthesis
Rifamycin	Streptomyces mediterranei	Tuberculosis	Protein synthesis

Antibiotics are the new "old frontier " for target therapy for cancer treatment
and I am not talking of cell wall  agents,  but  agents that target miRNA.  Griseofulvin targets Microtubules but there is a different in nature of microtubules that makes it ineffective for human. It may need some tweaking. Anti ribosomal drugs (80s) may also be of interest.

Go ahead and look into these

1. Polymyxin
2. Rifamycin
3. Avenacin
4. Cinnamic Acid
5. Phtalic Acid 
6. Suramin  ie.
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NCI
" Suramin 

A polysulphonated naphthylurea with potential antineoplastic activity. Suramin blocks the binding of various growth factors, including insulin-like growth factor I (IGF-I), epidermal growth factor (EGF), platelet-derived growth factor (PDGF), and tumor growth factor-beta (TGF-beta), to their receptors, thereby inhibiting endothelial cell proliferation and migration. This agent also inhibits vascular endothelial growth factor (VEGF)- and basic fibroblast growth factor (bFGF)-induced angiogenesis; retroviral reverse transcriptase; uncoupling of G-proteins from receptors; topoisomerases; cellular folate transport; and steroidogenesis. Check for active clinical trials or closed clinical trials using this agent. (NCI Thesaurus)'"

More HYPOTHESIS FOR CANCER RESEARCH

Given what we know now, could intermittent use of Cipro and laxative (5 days every 6-8weeks) be the most effective prevention against Colorectal cancer?  The CRBCM is reviewing data to make this assumption. There is sufficient scientific data to suggest this is true and a larger clinical trial is warranted to assess this hypothesis.
Through the work of others, we now know that Ciprofloxacin has anti-topoisomerase activity.  That is comparable in its mechanism  to some powerful chemotherapy drug.   But compared to chemotherapy drugs, it has been used for longer periods safely.   It is not innocuous, nothing is, however, it has been used broadly and side effects denounced to date may all be reversible.  The major concern of such broad use of an antibiotic will be potential hematologic toxicity and bacterial resistance. This is to be balanced against prevention of a deadly disease (colorectal cancer).  Intermittent use could address some of these concerns.
Development of other safer mild anti-topoisomerase could result to avoid CIPRO use, and preserve it in our Antibiotic armamentarium.

It is now known that certain bacteria produce chemical molecules such as nitrates that affect the colonic epithelium.  And that the progression to Colon cancer is an evolutionary process, possibly this evolution to cancer cells is driven by chronic continuous irritation.  Cleaning intermittently the colon has been assumed to be good as it provides an interruption in these irritations.  It would make sense if the laxative follows the Cipro.

ADDING AN ANTI-PROSTAGLANDIN MAY HAVE ADDITIONAL EFFECT.

Given the fact that this may be controversial, it would make sense to have a broader discussion before implementing this idea. Tell me what you think!