Different approaches to develop radio- and chemotherapy for treatment of human cancer

Abstract

Despite huge advancements in our knowledge and understanding of the molecular mechanisms of carcinogenesis, the prognoses of many malignant diseases have not improved dramatically. Improvements in the therapeutic efficacy of several anti-cancer therapies including radiotherapy and chemotherapy would be required to achieve effective treatment. In the present thesis we attempt to improve radiotherapy by proposing new molecular targets for overcoming radio-resistance and identify novel potent drugs effective against human malignancies.

Ion beams can be used to achieve therapeutic effects on tumors which are resistant to conventional radiation/photons. However the treatment planning system currently used in ion therapy centers are still based on data from conventional radiation to describe parameters for ion therapy. In paper I, we used two mathematical models to compare the cellular response to photons and ions. We found that the parameters determined for photons, using the RCR model could be used to predict the response to ion beams. The data also indicated that cells having efficient DNA repair capability are more sensitive to ion beams. In paper II, we compared photons and ion beams by analysis of the global phosphoproteome of a photon resistant cell line and identify signaling pathways responsible for photon resistance. We identified GSK3β to be important for cell proliferation and to have a protective effect on photon-induced tumor cell death. We also confirm the role of p38MAPK in photon resistance.

Cells propagated on plastic surfaces in monolayer culture do not represent accurate models of in vivo tumor tissue. The 3-D microenvironment of tumor tissue, including the presence of hypoxic regions, is better mimicked using the multicellular tumor spheroid model. Spheroids can be used for drug screening projects aimed to identify compounds effective on solid tumors. In paper III, we describe a novel small molecule capable of inducing apoptosis in 3D tumor spheroids and xenograft tumors. The compound triggered rapid increases of intracellular calcium levels. The drug was effective in inducing cell death of all cells of colon cancer spheroids, including cells in the hypoxic nutrient deficient cores. Interestingly, and in contrast to cells in peripheral cell layers, apoptosis did not appear to be induced in the hypoxic core regions. The results showed that novel drugs can be identified which have significantly stronger cytotoxic effects on multicellular spheroids as compared to conventional cancer therapeutics.

In paper IV, we report a novel inhibitor of the ubiquitin-proteasome system (UPS) that is cytotoxic to a number of cancer cell lines and patient tumor cells. This compound HRF-3, induces accumulation of polyubiquitinated proteins in the absence of a proteasomal blocking. Our results indicate that HRF-3 inhibits the UPS at a pre-proteasomal step and generates ROS similar to proteasomal inhibitors. Our data supports the notion that the UPS can be inhibited at several steps resulting in tumor cytotoxicity.

In paper V, we identified the 19S DUB inhibitor b-AP15 analogue VLX1570 which has similar biochemical activity as the hit compound. VLX1570 has strong anti-tumor activity in multiple myeloma cells and is capable of overcoming bortezomib resistance. The findings suggest that VLX1570 is a promising candidate for the clinical drug development against multiple myeloma.