Head and Neck Cancer: RPK-739 Immunotherapy
Background
Head and neck cancer is the term given to a variety of malignant tumours that develop in the mouth, throat, nasal cavity, larynx or salivary glands. In the United States, head and neck cancers account for 3.2% of all new cancers and 2.2% of all cancer deaths. With 40,000 new cases emerging annually in the United States, and a worldwide incidence of more than 500,000, analysts estimate that the head and neck segment of the oncology market will command $US1.8 billion by 2015.
Current Treatment
There is an urgent need for new treatments, as this form of cancer is poorly treated with chemotherapy. Surgery and radiation therapy are the standard of care, but any product offering an alternative to these treatments will substantially improve quality of life and disease management.
RPK-739 Immunotherapy
Replikun's cancer immunotherapy is a Kunjin replicon expressing granulocyte macrophage-colony stimulating factor (GM-CSF) delivered as a VLP (RPK-739). GM-CSF is a natural protein involved in co-ordinating an immune response to cancer and other diseases. The discovery of its activity led to the conclusion that GM-CSF could be a useful protein for attracting immune cells to the site of the tumour, and this indeed was proved to be the case in both animal testing and early patient studies.
Replikun identified an opportunity to provide a more effective way of delivering GM-CSF by application of its Kunjin Replicon technology. The goal is to “deliver” an RNA form of GM-CSF directly into tumour cells. In this way, the tumour cells are directed to produce and secrete GM-CSF into the local tumour environment (see figure below).
The Kunjin replicon selected for this application incorporates the Ala30Pro mutation in Kunjin non-structural protein 2A. As discussed in "Kunjin replicon properties", this mutation disables the Kunjin replicon’s ability to attenuate IFN-α/b induction resulting in the production of significantly greater levels of IFN-α/b. IFN-α/b mediates a range of direct anti-cancer activities and likely synergizes with GM-CSF to enhance induction of anti-cancer CD8+ T cells which are thought to be responsible for tumour destruction.
Figure: Anti-cancer activity of the RPK-739 product. A: Virus-like-particles (VLPs) are injected into tumours and taken up by tumour cells. VLPs are broken down in the cancer cell cytoplasm, releasing the Kunjin Replicon vector encoding GMCSF. The Kunjin Replicon is amplified within the cells, and begins directing the synthesis of GM-CSF, which is secreted to the local tumour environment. B: secreted GM-CSF triggers the migration of dendritic cells to the tumour site. C: Kunjin Replicon vectors provide additional immune stimulation, working with GM-CSF to help the immune system target tumour cells. D: dendritic cells present tumour antigens to T-cells in the lymph nodes, leading to the priming of specific cytotoxic T cells directed against cells carrying tumour antigen (CD8+ Effector T-Cells) E: CD8+ Effector T-Cells target the tumour mass for rapid killing.
Preclinical Studies Back to Top
Expression Studies
In expression studies, RPK-739 replicon transfected BHK-21 and B16 melanoma cells produced approximately 10-100 ng/ml of murine GM-CSF over 3 days per 2.5 x 104 infected cells.
Production of GM-CSF by the Kunjin Replicon
RPK-739 RNA was transfected into BHK (BHK + RPK-739) and B16 cells (B16 + RPK-739) by electroporation. Cells were incubated for 3 days. Cellular supernatants were assayed for the presence and biological activity of murine GM-CSF.
Murine Tumour Models Back to Top
When used to treat established B16 melanoma or CT26 colon carcinoma tumours (with an area of 10-20 mm2), RPK-739 VLPs demonstrated substantial anti-cancer activity compared to control KUN VLPs encoding β-galactosidase (KUN rep Beta-gal) or vehicle alone (see Figure below). Treatment regressed 40-50% of tumours.
Anti-Tumour B16 and CT26 activity of RPK-739 VLPs
Preliminary data also shows that RPK-739 VLP therapy in AE17 mesothelioma cells, TUBO mammary adenocarcinoma, MC38 colon carcinoma, and 4T1 mammary adenocarcinoma gives significant protection.
Synergy with cancer vaccines Back to Top
Using the B16-OVA tumour model we have also been able to show synergy between RPK-739 therapy and a cancer vaccine. Ovalbumin (OVA) represents the model cancer neo-antigen and the cancer vaccine was KUN-mpt VLPs, which is the Kunjin replicon encoding a OVA epitope. The combined therapy was able to cure 100% of established 10-20 mm2 B16-OVA tumours (see figure below, RPK-739 + Vaccine), with the tumours slowly shrinking from day 4 post treatment initiation, and no longer visible by day 25-30. Synergy might be expected as anti-cancer CD8+ T cells are central to the anti-cancer activity induced by this vaccine and by GM-CSF therapy.
Synergy between Intra-Tumoural Gene Therapy and a Cancer Vaccine
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