Evaluation of small molecule inhibitors of HER2, PI3K, mTOR and Bcl-2 for their radiomodulatory effects in human breast cancer cell lines

Hamunyela, Roswita Hambeleleni (2016-12)

Thesis (PhD)--Stellenbosch University, 2016.

Thesis

ENGLISH SUMMARY : Breast cancer remains the most commonly diagnosed cancer in women. It is responsible for 32% of all cancers and 15% of all cancer-related deaths in females. Patients with triple-negative breast cancers (TNBC) constitute about one-fifth of all breast cancer patients. TNBC is an aggressive and heterogeneous disease entity in comparison with other types of breast cancer and, therefore, tends to be resistant to existing treatment regimens, such as, targeted and hormone therapies. Although cancer treatment has evolved from being invasive and highly toxic to being more specific with reduced normal tissue toxicity, intrinsic tumor resistance still limits the benefit of therapy with radiation, drugs, and antibodies. To address this important clinical challenge, attempts have been made to better understand the molecular determinants of treatment resistance. This resistance can be attributed to the heterogeneity in the distribution of potential target antigens in a given tumor cell population, which leads to the inability to effectively target all cells with toxic levels of a particular therapeutic agent. There is evidence to suggest that proliferative pathways of triple-negative tumors are still poorly understood, which could be the reason for the observed treatment resistance. Targeted treatment modalities that are singly effective for triple-negative breast cancer are lacking, partly due to paucity of relevant targets as they are devoid of the human epidermal growth factor receptor 2 (HER2), progesterone receptor (PR), and oestrogen receptor (ER). Novel treatment approaches are, therefore, needed to overcome the challenges in the treatment of triple-negative breast cancers if treatment outcomes are to be improved. Concomitant targeting of cell signaling entities other than HER2, PR and ER may sensitize triple-negative tumors to radiotherapy. In this study, inhibition of HER2, phosphoinositide 3-kinase (PI3K), mammalian target of rapamycin (mTOR), and the pro-survival gene (Bcl-2) with small molecule inhibitors, TAK-165 (against HER2), NVP-BEZ235 (against PI3K and mTOR), and ABT-263 (against Bcl-2), singly or as cocktails, resulted in significant radio sensitization of human breast cell lines with features similar to those of triple negative cancers. This radio sensitization was seen at 2 and 6 Gy, indicating that a therapeutic benefit could be derived in conventional as well as stereotactic radiotherapy. A moderate to strong synergism was also demonstrated for NVPBEZ235/TAK-165 and NVP-BEZ235/ABT-263 cocktails. The strongest synergy was seen in the latter cocktail. In conclusion, inhibition of PI3K, mTOR and Bcl-2 could potentially be effective in the treatment of triple-negative breast cancer. The therapeutic benefit can be improved, if the target inhibition is followed by radiotherapy.

AFRIKAANSE OPSOMMING : Borskanker bly steeds die mees gediagnoseerde kanker en is die oorsaak van 32% van alle kankers en 15% van kankersterftes in vrouens. Pasiente met drievoudigenegatiewe-borskanker (TNBC) bedra een-vyfde van alle borskankerpasiente. Dit is ‘n aggressiewe en heterogene siekte in vergelyking met ander tipes borskanker, en blyk weerstandig te wees teen geteikende en hormoonterapiee. Alhoewel kankerbehandeling vanaf ‘n ingrypende en hoogs toksiese terapie verander het na ‘n behandelingstrategie wat hoogs spesifiek met ’n laer toksisiteit is, word die sukses van kombinasie terapie met bestraling, teenliggaampies en middels weens inherente tumorweerstand ondermyn. Om hierdie belangrike kliniese uitdaging te oorbrug, is strategiee dus nodig om die onderliggende molekulêre meganismes van behandelingsweerstand te verstaan, en dan uit te skakel. Hierdie weerstand is die gevolg van die heterogeniteit in die verspreiding van potensiele antigene in ‘n tumorselpopulasie, wat veroorsaak dat nie al die selle geteiken word met ‘n toksiese dosis van die terapeutiese middel nie. Daar is aanduidings dat gebrekkige begrip en benadering van die proliferasiebane van drievoudige tumore dalk die fundamentele rede vir die waargenome behandelingsweerstand kan wees. Verder is daar ‘n gebrek aan geteikende modaliteitsterapiee wat doeltreffend is vir die behandeling van drievoudige borskanker, as gevolg van die lae uitdrukking van relevante teikens soos menslike epidermale groeifaktorreseptor-2 (HER2), progesteroonreseptor (PR) en estrogeenreseptor (ER). Nuwe behandelingstrategiee is dus nodig om die uitdagings met die behandeling van drievoudige-negatiewe-borskanker te bekamp en om resultate in pasiente dus aansienlik te verbeter. ‘n Alternatiewe benadering sou kon wees om ander selseinoordragentiteite as HER2, PR en ER te teiken en die tumore daardeur moontlik meer kwesbaar vir bestraling te maak. In hierdie studie het inhibisie van HER2, fosforinositied-3-kinase (PI3K), soogdierteiken vir rapamisien (mTOR), en die oorlewensgeen (Bcl-2) met klein molekuulinhibitore, TAK-165 (teen HER2), NVP-BEZ235 (teen PI3K en mTOR), en ABT-263 (teen Bcl-2), afsonderlik of in kombinasie, bewys dat betekenisvolle stralingsensitiwiteit in alternatiewe mensborssellyne, anders as die TNBC maar met dieselfde eienskappe, verkry kon word. Die stralingsensitiwiteit is merkbaar met beide 2 en 6 Gy, wat aandui dat beide gewone en stereotaktiese stralingsterapie ‘n terapeutiese voordeel inhou. ‘n Matige tot sterk sinergisme is ook aangetoon vir NVP-BEZ235/TAK-165- en NVP-BEZ235/ABT-263-kombinasies. Die sterkste sinergie kom in die laasgenoemde mengsel voor. Opsommend: Chemoterapeutiese inhibisie van PI3K, mTOR en Bcl-2 kan potensieel effektief wees vir die behandeling van drievoudige-negatiewe-borskanker en die kliniese uitkoms kan verder verbeter word indien teikeninhibisie vóór bestraling kan plaasvind.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100016
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