Importance of the tumour microenvironment in the treatment response of prostate tumours

• Main Author: Byrne, Niall Maurice
• Published: Ulster University 2014
• Subjects: 616.99
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.674729

Androgen deprivation therapy (ADT) such as bicalutamide (BCA) has become the mainstay of treatment for locally-advanced prostate cancer (PCa). Despite initial remissions, ADT resistance almost inevitably occurs with progression to metastatic castrate-resistant PCa. Hypoxia is a common hallmark of many solid tumours and is associated with treatment failure and malignant progression; androgen withdrawal has been shown to induce profound hypoxia in androgen-sensitive tissue. This prompted an investigation into the effect of ADT on tumour oxygenation and malignant progression in PCa. Androgen-dependent luciferase-expressing PCa xenografts (LNCaP-luc) were implanted in SCID mice. When tumours reached -150mm3 mice were treated daily with SCA (2 or 6mg/kg). A reduction in tumour oxygen was observed within 24hrs (Oxylite™ oxygenelectrode); this continued to a nadir of 0.1 % oxygen at day 3 or 7 respectively. Tumours remained profoundly hypoxic until day 14-21 when oxygen levels began to rise, concomitant to time-dependent remodelling of the tumour vasculature (dorsal skin fold model). By day 28, BCA-treated xenografts were more malignant and showed greater metastatic spread to the lungs. Gene expression changes during BCA treatment of LNCaP xenografts were investigated using qPCR arrays; significant differences were found in the expression many genes involved in angiogenesis, invasion and metastasis, apoptosis resistance and the PI3K1AktimTOR signalling pathway. Informed treatment regimens combining SCA with a unidirectional hypoxia activated prod rug (AQ4N and its novel analogue OCT1002; 50mg/kg, day 7) or an Akt inhibitor (30mg/kg t.i.w) resulted in a reduction in tumour growth and metastatic spread to the lungs. When the anti-angiogenic VEGF-inhibitor (B20.4.1.1; 5mg/kg, day 14) was combined with bicalutamide, this blocked the revascularisation associated with BCA alone. This study shows that BCA-induced hypoxia induces critical changes in the tumour microenvironment which cause modified gene expression and drives malignant progression. Targeted therapeutic regimens, informed by this knowledge, may improve treatment outcomes of androgen-dependent PCa.