Cell growth and p53 expression in primary acquired melanosis and conjunctival melanoma

State of the Art of Pharmacological Activators of p53 in Ocular Malignancies

The pivotal role of p53 in the regulation of a vast array of cellular functions has been the subject of extensive research. The biological activity of p53 is not strictly limited to cell cycle arrest but also includes the regulation of homeostasis, DNA repair, apoptosis, and senescence. Thus, mutations in the p53 gene with loss of function represent one of the major mechanisms for cancer development. As expected, due to its key role, p53 is expressed throughout the human body including the eye. Specifically, altered p53 signaling pathways have been implicated in the development of conjunctival and corneal tumors, retinoblastoma, uveal melanoma, and intraocular melanoma. As non-selective cancer chemotherapies as well as ionizing radiation can be associated with either poor efficacy or dose-limiting toxicities in the eye, reconstitution of the p53 signaling pathway currently represents an attractive target for cancer therapy. The present review discusses the role of p53 in the pathogenesis of these ocular tumors and outlines the various pharmacological activators of p53 that are currently under investigation for the treatment of ocular malignancies.

IGF-1R is a molecular determinant for response to p53 reactivation therapy in conjunctival melanoma

As the p53 tumor suppressor is rarely mutated in conjunctival melanoma (CM), we investigated its activation as a potential therapeutic strategy. Preventing p53/Mdm2 interaction by Nutlin-3, the prototypical Mdm2 antagonist, or via direct siRNA Mdm2 depletion, increased p53 and inhibited viability in CM cell lines. The sensitivity to Nutlin-3 p53 reactivation with concomitant Mdm2 stabilization was higher than that achieved by siRNA, indicative of effects on alternative Mdm2 targets, identified as the cancer-protective IGF-1R. Nutlin-3 treatment increased the association between IGF-1R and β-arrestin1, the adaptor protein that brings Mdm2 to the IGF-1R, initiating receptor degradation in a ligand-dependent manner. Controlled expression of β-arrestin1 augmented inhibitory Nutlin-3 effects on CM survival through enhanced IGF-1R degradation. Yet, the effect of IGF-1R downregulation on cell proliferation is balanced by β-arrestin1-induced p53 inhibition. As mitomycin (MMC) is a well-established adjuvant treatment for CM, and it triggers p53 activation through genotoxic stress, we evaluated how these alternative p53-targeting strategies alter the cancer-relevant bioactivities of CM. In 2D and 3D in vitro models, Nutlin-3 or MMC alone, or in combination, reduces the overall cell tumor growth ~30%, with double treatment inhibition rate only marginally higher than single-drug regimens. However, histopathological evaluation of the 3D models revealed that Nutlin-3 was the most effective, causing necrotic areas inside spheroids and complete loss of nuclear staining for the proliferative marker Ki67. These findings were further validated in vivo; zebrafish xenografts demonstrate that Nutlin-3 alone has higher efficacy in restraining CM tumor cell growth and preventing metastasis. Combined, these results reveal that β-arrestin1 directs Mdm2 toward different substrates, thus balancing IGF-1R pro-tumorigenic and p53-tumor suppressive signals. This study defines a potent dual-hit strategy: simultaneous control of a tumor-promoter (IGF-1R) and tumor-suppressor (p53), which ultimately mitigates recurrent and metastatic potential, thus opening up targeted therapy to CM.

MIB-1 and PC-10 immunostaining for the assessment of proliferative activity in primary acquired melanosis without and with atypia

AIMS

To compare the proliferative activity of intraepithelial melanocytes in primary acquired melanosis (PAM) without atypia and PAM with atypia by immunohistochemical staining for the Ki-67 antigen and the proliferating cell nuclear antigen (PCNA).

METHODS

Formalin fixed, paraffin embedded sections from 35 archival specimens of PAM without atypia (n = 19) and with atypia (n = 16) were studied by immunostaining with MIB-1 and PC-10 monoclonal antibodies that react with the Ki-67 antigen and PCNA respectively. The results were calculated as the mean number of positive cells per eyepiece grid. All specimens were evaluated by two masked observers, and the interobserver reproducibility was assessed.

RESULTS

The means of the positive cell count in PAM with atypia were significantly higher compared with PAM without atypia for both observers, in both the PC-10 and the MIB-1 stained sections. In a linear least square model that estimated the interobserver and between group variation, the difference of MIB-1 and PC-10 positive cell count between PAM without and with atypia remained highly significant. The difference between the observers was not significant.

CONCLUSIONS

Immunostaining with MIB-1 and PC-10 demonstrated that PAM with atypia has higher proliferative activity than PAM without atypia. This method was found to be reproducible between different observers.

Prognostic accuracy of the mean of the largest nucleoli, vascular patterns, and PC-10 in posterior uveal melanoma

OBJECTIVE

This study aimed to compare the prognostic value and the predictive accuracy of the PC-10 cell cycling marker with the largest tumor diameter, the mean of the largest nucleoli, and vascular patterns in posterior uveal melanoma.

DESIGN

The study design was a case-control study.

PARTICIPANTS

Eyes enucleated for posterior uveal melanoma from patients who either died of metastatic melanoma or survived without signs of metastatic disease 10 years or more after surgery were studied.

INTERVENTION

Three observers assessed the above prognostic indicators and standard histopathologic characteristics from microslides without access to survival data.

MAIN OUTCOME MEASURES

Univariate and multivariate Cox models for survival were constructed, and a multiparameter prognostic index was calculated for each patient, based on covariates obtained from the final Cox model. The prognostic accuracy was determined by receiver operating characteristic curve analysis.

RESULTS

The log PC-10 count, vascular networks, mean of the largest nucleoli, largest tumor diameter, age of patient, and prognostic index were independently associated with outcome. However, each of these indicators had no more than a poor-to-moderate predictive accuracy, and only the prognostic index was significantly better than the largest tumor diameter.

CONCLUSIONS

The PC-10 count retains a prognostic value in uveal melanoma when adjusting for the effect of the mean of the largest nucleoli and diverse vascular patterns. A prognostic index combining two or more indicators may improve the predictive precision.

Conjunctival melanoma

Conjunctival melanoma is an uncommon tumor that is likely to recur and carries an overall mortality rate of approximately 30%. The seemingly unpredictable and enigmatic character of this entity has initiated much debate over the past decades regarding the etiology, histogenesis, prognosis, and preferred management. This review outlines the historical perspective; incidence and demographics; etiologic factors; histogenesis; cytogenetic findings; clinical characteristics; histopathologic and ultrastructural features; differential diagnoses; classifications; management of primary, recurrent, and systemic disease; survival after conjunctival melanoma; and diverse factors of potential prognostic significance. Finally, a brief outlook on present and future research objectives is provided.

Tumour cell proliferation after failed ruthenium plaque radiotherapy for posterior uveal melanoma

Enucleation following ruthenium plaque radiotherapy for posterior uveal melanoma indicates failure of treatment. This study focused on the histopathological findings and remaining tumour cell growth fraction in 42 of 46 patients with failed ruthenium plaque treatment (of 266 patients treated) for melanoma of the choroid or ciliary body. The cause for enucleation was clinically detected tumour regrowth in 27 (64%) patients, treatment-related ocular side effects in 12 (29%) cases and the patient's personal preference in three (7%) cases. The median time elapsing from plaque radiotherapy to enucleation was not significantly different for patients with recurrent tumour growth (23 months) compared to those enucleated without clinical signs of regrowth (19 months). While all tumours showed some regressive features by histopathological examination, only five melanomas were completely necrotic and viable-appearing tumours cells were present in all of the remaining 37 (88%) irradiated tumours. Microwave processed PC-10 immunostainings increased the sensitivity to detect cycling cells compared to the sole use of mitotic cell counts. By the former technique, proliferating tumour cells were detected in 17 of 23 (74%) studied melanomas of eyes enucleated for tumour regrowth following brachytherapy. Also, the number of cycling melanoma cells was similar to that of non-irradiated controls managed solely by enucleation. In contrast, the proliferative compartments of irradiated, but non-recurrent, posterior uveal melanomas were significantly reduced compared to those of matched controls. Still, cycling tumour cells were present in four of 13 (31%) irradiated melanomas, clinically assumed to be successfully treated.