Oncolytic Viruses

“Onco” = cancer “Lytic” = killing

An innovative cancer therapy that seeks to harness the natural properties of viruses to aid in the fight against cancer. These non-human viruses replicate in cancer cells and leave normal cells largely unaffected.

Clinical data indicates that oncolytic viruses have a very high therapeutic index, in some instances 100000:1. This therapeutic index is significantly higher than the index commonly seen in chemotherapy - 6:1- and may result in greater efficacy with fewer side effects.

Scientific American

October 2003

Early human trials using viruses in anti-cancer treatments initially yielded excitement as tumor regression was often seen without toxicity; however, tumor regression was followed by tumor progression during the late stages of these trials.

As a result of these early clinical trials, the idea of using viral vectors diminished in the hopes that a better understanding of cancer biology would allow for the development of more effective approaches.

Recently there has been a renewed interest and optimism in virotherapy with the convergence of ideas from molecular oncology and virology, and the development of recombinant virus technologies.

A Historical Perspective on Therapeutic Viruses

Vesicular Stomatitis Virus

VSV is not a human pathogen and thus the host lacks neutralizing antibody against the virus. VSV generally causes mild, non-fatal disease in cattle and swine.

The inability of VSV to cause mortality in animals or humans is a result of its sensitivity to the host antiviral response - a response that appears defective in cancer cells.

VSV is an attractive candidate as a viral delivery system for a variety of reasons: 1. VSV is easily manipulated by recombinant techniques.2. VSV can be grown to very high titers (1010 pfu/ml)3. VSV is non-pathogenic in humans.

Nucleocapsid (N)

Phosphoprotein (P)

Matrix (M)

Glycoprotein (G) Large (L) Polymerase

45 -100 nm

Nucleocapsid (N)

Matrix (M)

Phosphoprotein (P)

100 - 430 nm

Large Polymerase (L)

Glycoprotein (G)

Morphology and Genomic Organizationof Vesicular Stomatitis Virus

VSV Oncolytic Activity Targets Many Different Tumor Types

Breast tumour-derived cells and tissue

Ovarian carcinoma

Prostate cancer

Melanoma

Colon carcinoma

Lung tumour-derived cells and tissues

Why is VSV Oncolytic?

Normal Cell IFN

Anti-Viral Response

Transformed Cell IFN

Anti-Anti-Viral Viral ResponseResponseX

Although it has been known for some time that VSV selectively Although it has been known for some time that VSV selectively infects and kills transformed cells, the mechanism has remained infects and kills transformed cells, the mechanism has remained unknown.unknown.

The IFN response system is disrupted in transformed cells, thus permitting selective VSV oncolytic activity, while sparing normal non-transformed cells.

Eradication of CT26 Lung Metastases Following Intravenous or Intranasal VSV Inoculation

8 hours 11 hours 27 hours 72 hours

VSV GFP time course in CT26 lung metastasis model

0 12 2412 72

5x108 VSV GFP + 5x108 VSV RFP 12hrVSV in Action: Imaging Oncolysis

Conclusions

VSV is an excellent candidate oncolytic virus with a broad range of anti tumor effects

Attenuated VSV strains with mutations in the viral matrix protein fail to block the development of innate immunity and provide a better therapeutic virus

Curing cancer in mice is easy …….. the challenge is to determine the efficacy of several different oncolytic viruses in a variety of human tumors

Oncolytic Viruses in Clinical Trials

Name Strain Alterations Mechanism Disease Phase

1. Onyx-015 Ad2/5 ∆E1B-55kD p53 deficient Head/Neck Cancer II-III Ovarian, Liver I-II

Pancreatic Cancer I

2. CV706 Ad5 ∆E3 Deletion Oncolysis of PSA Prostate Cancer I-II E1A-PSA promoter expressing cells

3. G207 HSV-1 ∆ 145.5 deletion Removal of viral Malignant glioma I-II counter-attack

4. V/GM-CSF VV GM-CSF Insertion Immune Melanoma I-II Recruitment

5. Reo Reovirus Naturally Ras/PKR Advanced solid I-II Attenuated Defects Tumors

6. VSV AV1 Naturally IFN Advanced solid I Attenuated Defects Tumors