Overexpression Of βIII-tubulin Research Articles

Abstract 5472: Class III beta-tubulin in castration resistant human prostate cancer

Abstract BACKGROUND: Class III β-tubulin (βIII-tubulin) is expressed in tissues of neuronal lineage but it is also expressed in several human malignancies including non small cell lung carcinoma, breast and ovarian cancer. Overexpression of βIII-tubulin in these tumors is associated with an unfavorable outcome and resistance to taxane-based therapies. βIII-tubulin deregulation however is still poorly documented in prostate cancer. Previously, we reported that βIII-tubulin expression is increased in prostate cancer (PCa) cells by androgen ablation. Here we sought to better characterize the contribution of βIII-tubulin to castration resistant PCa, the stage of the tumor most responsible for mortality from PCa. METHODS: βIII-tubulin expression was assayed by immunohistochemistry in prostate tumors obtained from patients with castration resistant PCa. Protein expression was scored as null (0), weak (1), moderate (2) and strong (3) and considered significant when the score was 2 or more in more than 10% of cancer cells. Consecutive sections were also immunostained for neuroendocrine biomarkers, neuron specific enolase (NSE) and chromogranin A (CgA). An androgen independent (AI) variant of LNCaP cells (AI-LNCaP) was assessed for the effects of docetaxel treatment on βIII-tubulin expression. Finally, DU145 cells stably overexpressing βIII-tubulin were tested for their sensitivity to docetaxel relative to control vector-transfected cells. RESULTS: 24/40 specimens of castration resistant tumors were found to express significant levels of βIII-tubulin. In 6 out of 22 cases analyzed, regions of the tumor positively co-stained for both βIII tubulin and NSE, however none of 8 evaluated cases showed co-staining for βIII-tubulin and CgA. AI-LNCaP cells treated with 5 to 10 nM docetaxel showed a time dependent increase in βIII-tubulin expression. DU145 cells stably overexpressing βIII-tubulin were found to be more resistant to docetaxel than the parental counterpart with a 2-fold increase in the IC50. CONCLUSION: Our data indicate that βIII-tubulin is expressed in the majority of castration resistant prostate tumors. Although βIII-tubulin immunostaining of prostate tumor cells sometimes coincides with staining for neuroendocrine markers, most βIII-tubulin positive tumor cells examined did not show coincidental staining so increased βIII-tubulin expression may occur independently of NE differentiation. Regardless, our in vitro studies support a role for βIII-tubulin in the emergence of doxetaxel resistance by androgen independent human PCa cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5472.

Paclitaxel-Related Peripheral Neuropathy Associated with Improved Outcome of Patients with Early Stage HER2+ Breast Cancer Who Did Not Receive Trastuzumab in the N9831 Clinical Trial.

Abstract Background: Microtubules are crucial for spindle formation during mitosis and for cellular proliferation. The antineoplastic effect of paclitaxel is mainly related to its ability to bind the beta subunit of tubulin, thus preventing tubulin chain depolarization and inducing apoptosis. Tubulins are expressed in human peripheral nerves and the binding of paclitaxel to tubulin may lead to neuropathy. Peripheral neuropathy is a common dose limiting toxicity of paclitaxel. We hypothesized that the occurrence of peripheral neuropathy may correlate with outcome (disease-free survival; DFS).Methods: This analysis sought to describe incidence of peripheral neuropathy following paclitaxel and its association to outcome (DFS) in patients who received paclitaxel (weekly x 12) in the adjuvant HER2+ intergroup trial N9831. Only eligible pts who initiated paclitaxel and did not have peripheral neuropathy at initiation of paclitaxel that were randomized to arms A (955 pts; chemotherapy alone) and C (889 pts; chemotherapy plus concurrent trastuzumab) of N9831 were included. Cox regression analysis stratified by ER/PR status and nodal status was used to compare DFS within arm between patients with and without peripheral neuropathy.Results: Out of 1844 eligible pts, 379 developed neuropathy (20.5%). For pts in arm A, those who developed neuropathy had better DFS than pts who did not (3 yr DFS: 86.2% vs 81.8%; HR 0.65; p=0.01), despite lower doses of paclitaxel in the pts with neuropathy. Grade of neuropathy did not appear to impact DFS. No statistical difference was noted for pts treated in the trastuzumab-containing arm (3 yr DFS: 92.8% vs 91.1% for pts with neuropathy vs not; HR 0.79; p=0.34). There were no differences in paclitaxel dose intensity between arms A and C.Conclusion: Patients with early stage HER2+ breast cancer who received adjuvant paclitaxel-containing chemotherapy in arm A and developed peripheral neuropathy had a better DFS than pts who did not develop neuropathy. This effect was possibly abrogated by the use of trastuzumab in Arm C. This side effect may represent effective bindings of paclitaxel to the target tubulin, lack of point mutations in tubulin at the paclitaxel binding site and/or lack of selective overexpression of β-III tubulin. This is a hypothesis generating study and additional analysis needs to be conducted from other large taxane-based trials.Partial support from Genentech and the Breast Cancer Research Foundation Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 2100.

Markers predicting clinical benefit in breast cancer from microtubule-targeting agents

Taxanes (e.g. paclitaxel, docetaxel) and epothilones (e.g. ixabepilone) are microtubule-targeting agents, which disrupt cellular processes and induce apoptosis. Although their mechanisms of action are similar, clinical data in breast cancer patients support at least partial non-cross resistance between the classes, and even between individual compounds. Several biomarkers might contribute to the identification of patient groups likely to derive benefit from one class of microtubule-targeting agent or even one agent. Overexpression of P-glycoprotein is associated with resistance to taxanes, but not ixabepilone, in vitro; its role in vivo remains unclear. Mutations in β-tubulin linked to resistance to taxanes but not epothilones are observed in vitro; somatic mutations of β-tubulin appear rare clinically. Overexpression of the βIII-tubulin isoform is associated with taxane resistance in cell lines; some clinical studies support a relationship between poor response to taxanes and overexpression of βIII-tubulin. βIII-tubulin overexpression seems not to affect sensitivity to ixabepilone [1]. Estrogen receptor negativity, low expression of microtubule-associated protein tau, and perhaps HER2 amplification may define a subset of patients with higher than average sensitivity to paclitaxel. Large scale pharmacogenomic analysis has identified molecular markers potentially capable of distinguishing patients with differential sensitivity to paclitaxel and ixabepilone. These markers require validation in clinical trials.

βIII-Tubulin Induces Paclitaxel Resistance in Association with Reduced Effects on Microtubule Dynamic Instability

The development of resistance to paclitaxel in tumors is one of the most significant obstacles to successful therapy. Overexpression of the betaIII-tubulin isotype has been associated with paclitaxel resistance in a number of cancer cell lines and in tumors, but the mechanism of resistance has remained unclear. Paclitaxel inhibits cancer cell proliferation by binding to the beta-subunit of tubulin in microtubules and suppressing microtubule dynamic instability, leading to mitotic arrest and cell death. We hypothesized that betaIII-tubulin overexpression induces resistance to paclitaxel either by constitutively enhancing microtubule dynamic instability in resistant cells or by rendering the microtubules less sensitive to the suppression of dynamics by paclitaxel. Using Chinese hamster ovary cells that inducibly overexpress either betaI- or betaIII-tubulin, we analyzed microtubule dynamic instability during interphase by microinjection of rhodamine-labeled tubulin and time-lapse fluorescence microscopy. In the absence of paclitaxel, there were no differences in any aspect of dynamic instability between the two beta-tubulin-overexpressing cell types. However, in the presence of 150 nm paclitaxel, dynamic instability was suppressed to a significantly lesser extent (suppressed only 12%) in cells overexpressing betaIII-tubulin than in cells overexpressing similar levels of betaI-tubulin (suppressed 47%). The results suggest that overexpression of betaIII-tubulin induces paclitaxel resistance by reducing the ability of paclitaxel to suppress microtubule dynamics. The results also suggest that endogenous regulators of microtubule dynamics may differentially interact with individual tubulin isotypes, supporting the idea that differential expression of tubulin isotypes has functional consequences in cells.