Dual HER 1-2 targeting of hormone-refractory prostate cancer by ZD1839 and trastuzumab

From Therapy Resistance to Targeted Therapies in Prostate Cancer

Prostate cancer (PCa) is the second most common malignancy among men worldwide. Although early-stage disease is curable, advanced stage PCa is mostly incurable and eventually becomes resistant to standard therapeutic options. Different genetic and epigenetic alterations are associated with the development of therapy resistant PCa, with specific players being particularly involved in this process. Therefore, identification and targeting of these molecules with selective inhibitors might result in anti-tumoral effects. Herein, we describe the mechanisms underlying therapy resistance in PCa, focusing on the most relevant molecules, aiming to enlighten the current state of targeted therapies in PCa. We suggest that selective drug targeting, either alone or in combination with standard treatment options, might improve therapeutic sensitivity of resistant PCa. Moreover, an individualized analysis of tumor biology in each PCa patient might improve treatment selection and therapeutic response, enabling better disease management.

Vasoactive intestinal peptide (VIP) induces transactivation of EGFR and HER2 in human breast cancer cells

We analyzed the cross-talk between receptors for vasoactive intestinal peptide (VIP) and the human epidermal growth factor family of tyrosine kinase receptors (HER) in oestrogen-dependent (T47D) and oestrogen-independent (MDA-MB-468) human breast cancer cells. VIP treatment slowly increased the expression levels of EGFR but it rapidly augmented phosphorylation of EGFR and HER2 in both cell lines. This pattern of HERs transactivation was blocked by the specific VIP antagonist JV-1-53, supporting the direct involvement of VIP receptors in formation of P-EGFR and P-HER2. VIP-induced transactivation was also abolished by H89 (protein kinase A inhibitor), PP2 (Src inhibitor) or TAPI-1 (inhibitor of matrix metalloproteases), following a differential pattern. These results shed a new light on the specific signalling pathways involved in EGFR/HER2 transactivation by VPAC receptors and suggest the potential usefulness of VIP receptor antagonists together with current antibodies against EGFR/HER2 and/or tyrosine kinase inhibitors for breast cancer therapy.

Gene amplification and mutation analysis of epidermal growth factor receptor in hormone refractory prostate cancer

BACKGROUND

Amplification and mutation of the epidermal growth factor receptor (EGFR) and Her-2 genes were analyzed in both hormone sensitive and hormone refractory prostate cancer (HRPC).

METHODS

Gene amplifications of EGFR and Her-2 were analyzed by fluorescence in situ hybridization (FISH) with direct sequencing. Studies were performed on a total of 10 patients; tissues were sampled at the time of initial diagnosis and after the conversion to HRPC (a total of 20 tissue samples). Direct sequencing was performed on exons 18-24 of EGFR and exons 19 and 20 of Her-2. Amplification and mutation were compared with clinicopathologic features.

RESULTS

Gene amplification of EGFR was observed in 6 (30%) out of 20 samples. A total of six EGFR mutations in exons 18 and 19 were detected in three pairs of tissues (three patients). One patient, with hormone refractory status, had a novel deletion mutation in EGFR exon 19. EGFR mutations were associated with the acinar type of prostate cancer but were not associated with the ductal type. No significant correlation was found between mutation change and hormone sensitive or refractory status. However, the time to convert to HRPC was significantly shorter in the patients with a mutation in the EGFR gene (P = 0.017). There were no Her-2 gene amplifications or mutations found in any of the samples.

CONCLUSIONS

EGFR gene mutation and amplification occurred frequently in advanced prostate cancer cases. EGFR mutations do not appear to play a significant role in the hormone refractory pathway but are associated with prognosis.

Biology of Interactions: Antiepidermal Growth Factor Receptor Agents

Epidermal growth factor receptor (EGFR) signaling inhibition represents a highly promising arena for the application of molecularly targeted cancer therapies. Evolving from several decades of systematic research in cancer cell biology, a series of EGFR inhibitors from both the monoclonal antibody (mAb) and tyrosine kinase inhibitor (TKI) class have been developed and promoted into clinical application. Several EGFR inhibitors have recently gained US Food and Drug Administration approval for cancer therapy in the United States (and many other countries), including the mAbs cetuximab and panitumumab, and the small molecule TKIs gefitinib, erlotinib, and lapatinib. The rapidly expanding preclinical and clinical data contributing to these US Food and Drug Administration drug registrations validates a central role of the EGFR as an important molecular target in epithelial malignancies. In this review, we focus primarily on the biology of EGFR interactions. Through improved understanding of EGFR biology in human cancers, there is anticipation that more tumor-selective therapy approaches with diminished collateral normal tissue toxicity can be advanced. Many questions remain to be answered, particularly with regard to how best combine EGFR inhibitors with conventional cancer therapies, and how to select those patients (tumors) most likely to benefit from EGFR inhibition strategies.

Theoretical basis, experimental design, and computerized simulation of synergism and antagonism in drug combination studies

The median-effect equation derived from the mass-action law principle at equilibrium-steady state via mathematical induction and deduction for different reaction sequences and mechanisms and different types of inhibition has been shown to be the unified theory for the Michaelis-Menten equation, Hill equation, Henderson-Hasselbalch equation, and Scatchard equation. It is shown that dose and effect are interchangeable via defined parameters. This general equation for the single drug effect has been extended to the multiple drug effect equation for n drugs. These equations provide the theoretical basis for the combination index (CI)-isobologram equation that allows quantitative determination of drug interactions, where CI < 1, = 1, and > 1 indicate synergism, additive effect, and antagonism, respectively. Based on these algorithms, computer software has been developed to allow automated simulation of synergism and antagonism at all dose or effect levels. It displays the dose-effect curve, median-effect plot, combination index plot, isobologram, dose-reduction index plot, and polygonogram for in vitro or in vivo studies. This theoretical development, experimental design, and computerized data analysis have facilitated dose-effect analysis for single drug evaluation or carcinogen and radiation risk assessment, as well as for drug or other entity combinations in a vast field of disciplines of biomedical sciences. In this review, selected examples of applications are given, and step-by-step examples of experimental designs and real data analysis are also illustrated. The merging of the mass-action law principle with mathematical induction-deduction has been proven to be a unique and effective scientific method for general theory development. The median-effect principle and its mass-action law based computer software are gaining increased applications in biomedical sciences, from how to effectively evaluate a single compound or entity to how to beneficially use multiple drugs or modalities in combination therapies.

Enhancement of radiosensitivity by dual inhibition of the HER family with ZD1839 ("Iressa") and trastuzumab ("Herceptin")

PURPOSE

The aims of this study were twofold: (1) to examine the effects of dual inhibition of 2 members of the HER family, the epidermoid growth factor receptor (EGFR) and HER2/neu, by gefitinib (ZD1839) and trastuzumab on radiosensitivity; and (2) to explore the molecular mechanism of radiosensitization especially focusing on the survival signal transduction pathways by using A431 human vulvar squamous carcinoma cells expressing EGFR and HER2/neu.

METHODS AND MATERIALS

The effects of inhibitors on the radiation-induced activation of EGFR and/or HER2/neu, and the intracellular proteins that are involved in their downstream signaling, were quantified by the Western blot. Radiosensitizing effects by the blockage of EGFR and/or HER2/neu were determined by a clonogenic assay.

RESULTS

Radiation-induced activation of the EGFR and HER2/neu was inhibited with ZD1839 and/or trastuzumab. ZD1839 also inhibited the radiation-induced phosphorylation of HER2/neu. Radiation in combination with the HER family inhibitors inhibited the activation of Akt and MEK1/2, the downstream survival signaling of the HER family. ZD1839 enhanced radiosensitivity with a dose-modifying factor (DMF) (SF3) of 1.45 and trastuzumab did so with a DMF (SF3) of 1.11. Simultaneous blockade of EGFR and HER2/neu induced a synergistic radiosensitizing effect with a DMF (SF3) of 2.29.

CONCLUSIONS

The present data suggest that a dual EGFR and HER2/neu targeting may have potential for radiosensitization in tumors in which both of these pathways are active.

Human chorionic gonadotropin modulates prostate cancer cell survival after irradiation or HMG CoA reductase inhibitor treatment

The impact of human chorionic gonadotropin (hCG) on prostate carcinoma viability was investigated. Treatment of LNCaP and PC-3 cells with hCG modestly reduced cell viability within 96 h. Treatment of cells with hCG followed by exposure to ionizing radiation enhanced radiosensitivity. Exposure of LNCaP cells to hCG promoted activation of epidermal growth factor receptor (ERBB1) via a Galpha(i)-, mitogen-activated protein kinase kinase (MEK)1/2-, and metalloprotease-dependent paracrine mechanism, effects that were further enhanced after radiation exposure, and that were causal in prolonged intense activation of poly(ADP-ribose) polymerase (PARP). Inhibition of ERBB1, MEK1, or PARP1 function suppressed the radiosensitizing properties of hCG. Radiosensitization was also, in part, dependent upon c-Jun NH2-terminal kinase 1/2 signaling. PARP1-dependent radiosensitization was suppressed by a pan-caspase inhibitor and by knockdown of apoptosis-inducing factor expression. Inhibition of phosphatidylinositol 3-kinase, expression of dominant-negative AKT, or treatment with the HMG CoA reductase inhibitor lovastatin suppressed AKT phosphorylation and enhanced the cytotoxic effects of hCG. The enhancing effect of lovastatin was reproduced by incubation with a geranylgeranyl transferase inhibitor and blocked by coexposure to geranylgeranyl pyrophosphate. Treatment with hCG and lovastatin decreased expression of BCL-(XL) and XIAP, and increased expression of IkappaB. The cytotoxic effects of hCG were enhanced by expression of dominant-negative IkappaB, and they were abolished by coexpression of activated AKT. Expression of activated AKT maintained BCL-(XL) levels in cells expressing dominant-negative IkappaB. The promotion of hCG lethality by lovastatin was abolished by overexpression of BCL-(XL), and was dependent upon activation of caspase-9. Thus, hCG, in combination with radiation and lovastatin, may represent a novel approach to kill prostate cancer cells.

New Targets in the Management of Prostate Cancer

Our understanding of growth factors and growth-factor receptors, signal transduction pathways, cellular survival pathways, angiogenesis, and their potential roles in prostate-cancer tumorigenesis remains a work in progress. Novel agents targeting these key mechanisms are showing promise in clinical trials. Many more agents, including those not discussed in this article, such as radio-pharmaceuticals, bisphosphonates, nutriceuticals, immunotherapy, and newer generation chemotherapy, are also showing promise as emerging treatments for prostate cancer. It is important to recognize when designing clinical trials of novel agents that traditional endpoints of disease response may not be applicable in measuring success of biologic compounds. Especially in a disease where tumor marker levels are critical for both patient and physician, additional biomarkers are necessary to better assess response. Halting drug development due to lack of response in serum PSA may lead to an unnecessary demise of an active agent.As expected, the combination of biologic agent with cytotoxic chemotherapy has a higher traditional response rate compared with biologic agent alone. The challenge of combination trials is to determine if the combination of agents will produce a higher traditional response rate compared with chemotherapy alone. For several of the agents discussed, the clinical benefit derived from a combination of biologic agent and cytotoxic chemotherapy may not justify additional drug toxicity. Efficient trial design, appropriate selection of correlative markers,and close toxicity monitoring will help improve our ability to identify promising novel agents.

Gefitinib-trastuzumab combination on hormone-refractory prostate cancer xenograft

New drugs and new combinations of drugs have recently shown promising clinical activity in hormone refractory prostate cancer. We studied the association of gefitinib with trastuzumab on the androgen-refractory prostate cancer cell line DU145 expressing both epidermal growth factor receptor (EGFR) and HER-2. Drug combinations with radiotherapy (RT) were considered along with the analysis of factors linked to cell proliferation and apoptosis. The antitumour effects of gefitinib were more pronounced than those observed with trastuzumab. In mice receiving the gefitinib-trastuzumab combination, reduction in tumour volume was inferior to that predicted by the observed impact of the agents alone. The presence of trastuzumab markedly attenuated the relative increase on p27 expression and the Bax:Bcl2 ratio induced by gefitinib. The combination gefitinib-RT had similar antitumour effects as those predicted by the impact of the individual treatments, whereas the effect of the trastuzumab-RT combination was inferior to that predicted by the individual effects. The present data should be borne in mind when designing new clinical schedules for treatment of hormone-refractory prostate cancer including the use of HER inhibitors.

Prostate cancer relapse after therapy with curative intention: a diagnostic and therapeutic dilemma

Prostate cancer is the most common malignant disease and second in causes of cancer death among men in Western Europe and North America. Despite improved surgical and irradiation techniques tumor relapse after curatively intended therapy is not uncommon. Due to the difficulty in discriminating local and systemic progression, it is often difficult to decide what this means for the patient and what kind of second-line treatment has to be given. Modern imaging techniques (MRI with endorectal coil, Choline-PET-CT, ProstaScint-Scan) are used for diagnosis of prostate cancer relapse. Nevertheless, early detection of local tumor relapse and likewise the detection of disseminated tumor cells often fails. To differentiate between local and systemic progression, prognostic factors of the primary tumor (grading, surgical margins, infiltration of the seminal vesicles, lymph node metastases) and PSA kinetics are used. The time from initial treatment to biochemical relapse and PSA doubling time are of highest prognostic relevance. Local progression allows second-line local treatment with potentially curative results (local irradiation after radical prostatectomy, salvage-surgery / cryotherapy / HIFU after irradiation), while in the case of systemic progress a palliative systemic therapy (hormonal treatment, chemotherapy, bisphosphonates) is indicated. Before deciding on the most appropriate therapy, prognostic factors and the patient's individual situation (co-morbidity, life expectancy, individual wishes) should be taken into account.