Epidemiologic data suggest that cancer survivors tend to develop a protuberant number of adverse late effects, including second primary malignancies (SPM), as a result of cytotoxic chemotherapy. Besides the genotoxic potential of these drugs that directly inflict mutational burden on genomic DNA, the precise mechanisms contributing to SPM development are poorly understood. Cancer is nowadays perceived as a complex process that goes beyond the concept of genetic disease and includes tumor cell interactions with complex stromal and immune cell microenvironments. The cancer immunoediting theory offers an explanation for the development of nascent neoplastic cells. Briefly, the theory suggests that newly emerging tumor cells are mostly eliminated by an effective tissue immunosurveillance, but certain tumor variants may occasionally escape innate and adaptive mechanisms of immunological destruction, entering an equilibrium phase, where immunologic tumor cell death “equals” new tumor cell birth. Subsequent microenvironmental pressures and accumulation of helpful mutations in certain variants may lead to escape from the equilibrium phase, and eventually cause an overt neoplasm. Cancer immunoediting functions as a dedicated sentinel under the auspice of a highly competent immune system. This perspective offers the fresh insight that chemotherapy-induced thymic involution, which is characterized by the extensive obliteration of the sensitive thymic epithelial cell (TEC) compartment, can cause long-term defects in thymopoiesis and in establishment of diverse T cell receptor repertoires and peripheral T cell pools of cancer survivors. Such delayed recovery of T cell adaptive immunity may result in prolonged hijacking of the cancer immunoediting mechanisms, and lead to development of persistent and mortal infections, inflammatory disorders, organ-specific autoimmunity lesions, and SPMs. Acknowledging that chemotherapy-induced thymic involution is a potential risk factor for the emergence of SPM demarcates new avenues for the rationalized development of pharmacologic interventions to promote thymic regeneration in patients receiving cytoreductive chemotherapies.
Midkine (MDK) is a pleiotropic heparin-binding growth factor, contributing to both normal tissue homeostasis and disease development. MDK expression is gradually increased during carcinogenesis, acting as a mediator for the acquisition of cancer hallmarks, such as invasion/metastasis, and immunosuppression. Tissue-wide gene expression analysis using publicly available databases reveal that MDK is significantly upregulated in most human carcinomas. In the thyroid, MDK has been associated with increased metastatic potential in the context of papillary thyroid cancer, which is an otherwise relatively non-aggressive thyroid tumor. We thus theorized that more aggressive types of thyroid cancers may be linked to increased MDK expression/function from an earlier onset. To gain such insights, we developed a digital pathology infrastructure to investigate MDK expression in a characterized mouse model of Anaplastic Thyroid Carcinoma (ATC), the most aggressive and lethal type of thyroid cancer with low but increased prevalence in the human population, and an intrinsic resistance to available therapeutic options. Mice with conditional ablation of tumor suppressors, Pten and p53, in thyrocytes [Pten, p53]thyr-/− develop thyroid carcinomas with mixed follicular and anaplastic components, and histological hallmarks of high aggressiveness, including giant cells, bone metaplasia, and muscular/tracheal invasion, which are all recapitulated in human disease. MDK was more highly expressed in anaplastic, when compared to follicular components of the same animal tumors. When the above hallmarks were topographically and microanatomically demarcated within the anaplastic component, it was found that MDK expression was higher near and around giant cell islets, as well as within the anaplastic lesions invading beyond the cartilaginous rings of tracheal mucosal epithelium. Based on recent evidence that MDK does not solely function in the extracellular space, but can also be endocytosed within tumor cells, whereby it exerts tumor-promoting functions, we further quantified the intra/extranuclear MDK fraction using intensity thresholding immunofluorescence. Of interest, MDK+ follicular lesions, were primarily characterized by nuclear MDK expression, whereas MDK was mostly found secreted in the extracellular space of anaplastic lesions, thus implying different modes of MDK trafficking, secretion, and possibly function in them. The take home message is to work towards establishing and developing gain- and loss-of-function experiments, to elucidate mechanistic underpinnings on the role of MDK in the development of aggressive ATC lesions. Citation Format: Dimitra P. Anastasiadou, Antonio Di Cristofano, George S. Karagiannis. An emerging paradigm of heterogeneous midkine expression in thyroid cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB273.
The Cxcl12/Cxcr4 signaling axis has been shown to promote metastasis in multiple mouse models of breast carcinoma, and has been linked to breast cancer cell seeding, homing, survival, and proliferation at future metastatic sites. The precise mechanism by which Cxcr4+ breast cancer cells escape the primary tumors (which also highly express Cxcl12), remains poorly understood. By using a novel multichannel immunofluorescence (mIF) based methodology for quantifying chemotactic gradients in fixed tissue, we here demonstrate that Cxcl12 gradients in mouse primary breast tumors are concentrically expressed around sites of cancer cell intravasation known as Tumor Microenvironment of Metastasis (TMEM) doorways. Via distance analysis algorithms, we additionally demonstrate that TMEM doorway-mediated Cxcl12 gradients associate with Cxcr4+ breast cancer cells migrating towards the underlying TMEM doorways. Consistent with this observation, pharmacological inhibition of the Cxcl12/Cxcr4 pathway significantly abrogates the translocation of Cxcr4+ cancer cells to TMEM doorways, suppressing TMEM doorway-mediated metastatic dissemination. However, targeted elimination of the Cxcr4 gene specifically from breast cancer cells, paradoxically results in a suboptimal response, thus suggesting the existence of a bypass or compensatory mechanism. Previously, it was shown that Cxcr4+ tumor-associated macrophages (TAMs) support the invasive and migratory properties of tumor cells that utilize TMEM doorways. We thus hypothesized that, absent Cxcr4 expression in tumor cells, accompanying Cxcr4+ TAMs may still “read” TMEM-generated Cxcl12 chemotactic gradients. Indeed, clodronate-mediated TAM depletion results in the significant suppression of Cxcr4+ cancer cell translocation to TMEM doorways and their subsequent dissemination to the peripheral circulation and future metastatic sites. Finally, we used a variety of stromal and immune cell lineage markers to identify the precise source of TMEM doorway-generated Cxcl12 gradients in mouse primary breast cancers. Despite the fact that blood vessels (irrespective of presence of TMEM doorways) were primarily lined by Pdgfrb+ stromal cells with basal Cxcl12 expression, TMEM-generated Cxcl12 gradients were specifically linked to a subset of Cxcl12+Iba1+ perivascular TAMs. Pharmacological inhibition of Pdgfrb depletes Pdgfrb+Cxcl12+ stromal cells, but does not significantly affect Cxcl12/Cxcr4- mediated translocation of Cxcr4+ tumor cells to TMEM doorways. Overall, our data support a new paradigm implicating the Cxcl12/Cxcr4 axis during the early stages of the metastatic cascade, and point to a new avenue for rationalized antimetastatic treatments for breast cancer. Citation Format: Dimitra P. Anastasiadou, Luis R. Sanchez, Camille L. Duran, Joseph Burt, Xiaoming Chen, Yu Lin, Robert Eddy, Allison S. Harney, David Entenberg, John S. Condeelis, Maja H. Oktay, George S. Karagiannis. An emerging paradigm of Cxcl12 & Cxcr4 involvement in breast cancer metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 60.
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