Radiosensitisation of androgen-dependent and independent tumour cells as a therapeutic strategy in prostate cancer

Thesis (PhD)--Stellenbosch University, 2019.ENGLISH SUMMARY : Metastatic prostate cancer continues to be a leading cause of cancer-related death in men. Increased incidences and mortality have been reported globally, although treatment of locally confined prostate cancer has been shown to be successful. However, aggressive and incurable castration-resistant prostate cancer (CRPC) is a major clinical concern. The combination of radiotherapy and androgen deprivation therapy (ADT) is the current standard-of-care treatment strategy for prostate cancer (PCa). The androgendependent stage of tumour is successfully managed, until the cancer switches to androgen-independence when resistance to treatment severe. The mechanism underlying this switch is still not clear and poorly understood. However, the implicated survival pathways of PI3K/mTOR, EGFR and AR might help explain remissions of PCa after treatment. Thus, the rationale for this study was to target these pathways with respective inhibitors, namely, MDV3100 (for AR), AG-1478 (for EGFR), and NVPBEZ235 (for PI3K and mTOR). The “traditional” prostate cancer cell lines, (DU145 and LNCaP), which are derived from metastatic regions, and (1542N and BPH-1) from normal tissue and a primary benign tumour, respectively, served as biological models in this research. The following were investigated: (1) androgen sensitivity of cell lines, (2) the intrinsic cellular radiosensitivity, (3) the cytotoxicity of specific inhibitors of AR, EGFR, PI3K and mTOR, (4) interaction of the respective inhibitors, and (5) the radiomodulatory effects of inhibitors, either singly or in combination. The “classical” androgen-independent cell lines were found to switch into androgendependence when treated with high concentrations of 5α-DHT. Very strong synergistic interactions of inhibitors were demonstrated in all cell lines, except the LNCaP cell line in which inhibitors were antagonistic. Concomitant use of these inhibitors in intrinsically androgen-dependent prostate cancers might not be beneficial. The use of inhibitor cocktails with radiation at low doses (2 Gy) is highly desirable as the normal cells were protected, especially with the dual inhibitor of PI3K/mTOR (NVP-BEZ235). However, at higher doses (6 Gy) the potential benefit is great in tumour cell lines, but very limited in the normal cell line. Therefore, at fractional doses of relevance to conventional radiotherapy, use of cocktails containing the PI3K/mTOR inhibitor as an adjuvant may be beneficial in the management of androgen-dependent cancer. It is concluded that these findings might assist in the design of more effective treatment approaches for cancers that typically display resistance to radiotherapy and chemotherapy.AFRIKAANSE OPSOMMING : Metastatiese prostaatkanker (PCa) bly steeds een van die leidende oorsake van kankerverwante sterfte in mans. 'n Toename in die insidensie en mortaliteit is wêreldwyd gerapporteer, alhoewel behandeling van prostaatkanker wat lokaal beperk is, bewys is om suksesvol te wees. Daarenteen bly aggressiewe en ongeneeslike kastrasieweerstandige prostaatkanker (KWPK) 'n ernstige kliniese probleem. Die kombinasie van radioterapie en androgeenontnemingsterapie (AOT) is die huidige standaardbehandelingstrategie vir PCa. Die androgeenafhanklike stadium van die tumor word suksesvol beheer, totdat die kanker oorgaan na androgeenonafhanklikheid, wat ernstige weerstand teen behandeling beteken. Die onderliggende meganisme, wat hierdie omskakeling bewerkstellig, is steeds nog onduidelik en onverklaarbaar. Die paaie van PI3K/mTOR, EGFR en AR mag van waarde wees om remissies van PCa na behandeling te verklaar. Teen hierdie agtergrond is die doelwit van hierdie studie om hierdie paaie te teiken met die onderskeie inhibitore, naamlik; MDV3100 (vir AR), AG-1478 (vir EGFR) en NVPBEZ235 (vir PI3K/mTOR). Die tradisionele prostaatkankersellyne (DU145 en LNCaP), verkry vanaf metastatiese streke, asook (1542N en BPH-1), verkry vanaf normale weefsels en 'n primêre benigne tumor respektiewelik, het gedien as biologiese modelle in hierdie navorsing. Die volgende aspekte is ondersoek: (1) Androgeensensitiwiteit van sellyne; (2) Die intrinsieke radiosensitiwiteit van die selle; (3) Die sitotoksisiteit van spesifieke inhibitore van AR, EGFR, PI3K en mTOR; (4) Interaksie van die onderskeie inhibitore; (5) Die radiomodulerende uitwerking van inhibitore, afsonderlik of gekombineerd. Dit is gevind dat die “klassieke” androgeen- onafhanklike sellyne omgeskakel het na androgeenafhankheid wanneer dit behandel is met hoë konsentrasies van 5α- dihidrotestosteroon (5α-DHT). Merkwaardige sinergistiese interaksies tussen inhibitore is gedemonstreer in alle sellyne, behalwe die LNCaP–sellyn waar die inhibitore antagonisties was. Gekombineende gebruik van hierdie inhibitore in intrinsieke androgeenafhanklike prostaatkankers mag nie voordelig wees nie. Die gebruik van inhibitormengsels saam met bestraling teen n lae dosis (2Gy) is hoogs wenslik, omdat die normale selle beskerm is, veral met die dubbele inhibitor van PI3K/mTOR (NVP-BEZ235). Daarenteen is die potensiël voordeel van n hoë dosis (6Gy) groot in tumorsellyne, maar baie beperk teen die normale sellyne. Gevolglik, teen fraksionele dosisse van betekenis by konvensionele radioterapie, mag die aanwending van 'n kombinasie van die PI3K/mTOR – inhibitor as adjuvant voordelig wees by die behandeling van androgeenafhanklike kanker. Die gevogtrekking word gemaak dat hierdie bevindinge kan bydra tot die ontwerp van meer doeltreffende behandelingstrategieë teen kankers wat tipies weerstandig is teen radioterapie en chemoterapie.Doctora