Gastrointestinal (GI) cancers represent the leading cause of cancer-related mortality worldwide. Antibody drug conjugates (ADCs) are a rapidly growing new class of anti-cancer agents which may improve GI cancer patient survival. ADCs combine tumour-antigen specific antibodies with cytotoxic drugs to deliver tumour cell specific chemotherapy. Currently, only two ADCs [brentuximab vedotin and trastuzumab emtansine (T-DM1)] have been Food and Drug Administration approved for the treatment of lymphoma and metastatic breast cancer, respectively. Clinical research evaluating ADCs in GI cancers has shown limited success. In this review, we will retrace the relevant clinical trials investigating ADCs in GI cancers, especially ADCs targeting human epidermal growth receptor 2, mesothelin, guanylyl cyclase C, carcinogenic antigen-related cell adhesion molecule 5 (also known as CEACAM5) and other GI malignancy specific targets. We will review potential hurdles for their success and provide new perspective for future treatment.

In 2018, the Nobel Prize in medicine was awarded to James P. Allison and Tasuku Honjo for their work on the description of immune checkpoint inhibitors which contributed to the development of new anti-cancer immunotherapies. However, although these new therapeutic strategies, which are designed to limit immune escape of cancer cells, have been used or tested successfully in many different cancers, a large proportion of patients have been described to resist and not respond to these new treatments. The new incoming challenge is now therefore to overcome these resistance and new recent data presented epigenetic modifications as promising targets to restore anti-tumor immunity. Indeed, both DNA methylation and post-translational histone modifications have been described to regulate immune checkpoint inhibitor expression, tumor-associated antigen presentation or cancer cell editing by the immune system and therefore establishing epigenetic drugs as a potential complement to immunotherapies to improve their efficiency.

Aberrant activation of the epidermal growth factor receptor (EGFR) is a driving force for cancer growth in a subgroup of non-small cell lung cancer patients. These patients can be identified by the presence of activating EGFR mutations. Currently three generations of EGFR-tyrosine kinase inhibitors (TKIs) have been approved by the Food and Drug Administration and European Medicine Agency. This paper reviews the structure of EGFR and the downstream signaling pathways of EGFR and describes the mechanisms of intrinsic and acquired resistance against EGFR-TKIs. These mechanisms include secondary or tertiary mutations in EGFR, the activation of bypassing signaling pathways or a histological transformation to small cell lung cancer. Moreover, drug efflux transporters will affect the cellular accumulation of EGFR-TKIs and penetration of the first generation of EGFR-TKI into the brain. Lysosomal sequestration of some EGFR-TKIs may also prevent the drugs to reach their target. In conclusion, resistance to EGFR-TKIs is multifactorial, including primary and acquired mutations in the EGFR gene, activation of bypassing pathways and limited uptake of drugs in the cells or target tissues. More pharmacological studies are needed in order to develop new specific compounds targeted to overcome new resistance mechanisms in order to enable a personalized treatment approach.

Aim: The purpose of the present study was to perform a comprehensive analysis of WT1 gene expression in high-risk pediatric acute lymphoblastic leukemia (ALL).

Methods: We performed a meta-analysis of WT1 gene expression for normal hematopoietic cells vs. primary leukemia cells from 801 pediatric ALL samples deposited in the Oncomine database combined with an in-depth gene expression analysis using our in-house database of gene expression profiles of primary leukemia cells from 1416 pediatric ALL cases. We also examined the expression of WT1 in primary leukemic cells from 299 T-lineage ALL patients in the Oncomine database and 189 T-lineage ALL patients in the archived datasets GSE13159, GSE13351, and GSE13159.

Results: Our data provide unprecedented evidence that primary leukemia cells from patients with MLL gene rearrangements (MLL-R) express highest levels of WT1 expression within the high-risk subsets of pediatric B-lineage ALL. Notably, MLL-R⁺ patients exhibited > 6-fold higher expression levels of the WT1 gene compared to the other B-lineage ALL subtypes combined (P < 0.0001). Our findings in 97 MLL-R⁺ infant B-lineage ALL cases uniquely demonstrated that WT1 is expressed at 1.5-4.2-fold higher levels in MLL-R⁺ infant leukemia cells than in normal hematopoietic cells and revealed that WT1 expression level was substantially higher in steroid-resistant infant leukemia cells when compared to non-leukemic healthy bone marrow cells. Furthermore, our study demonstrates for the first time that the WT1-regulated EWSR1, TP53, U2AF2, and WTAP genes (i.e., WT1 interactome) were differentially upregulated in MLL-R⁺ leukemia cells illustrating that the MLL-regulatory pathway is aberrantly upregulated in MLL-R⁺ pediatric B-lineage ALL. These novel insights provide a compelling rationale for targeting WT1 in second line treatment of MLL-R⁺ pediatric B-lineage ALL, including MLL-R⁺ infant ALL. Furthermore, our study is the first to demonstrate that leukemia cells from 370 Ph-like patients had significantly higher WT1 expression when compared to normal hematopoietic cells. Finally, our findings demonstrate for the first time that chemotherapy-resistant primarily leukemic cells from relapsed B-lineage ALL patients exhibit higher expression levels of WT1 than primary leukemia cells from newly diagnosed B-lineage ALL patients (P = 0.001).

Conclusion: Our findings indicate that the WT1 gene product may serve as a target for immunotherapy in high risk/poor prognosis subsets of newly diagnosed as well as relapsed pediatric B-lineage ALL. Our findings also significantly expand the current knowledge of WT1 expression in T-lineage ALL and provide new evidence that WT1 gene and its interactome are expressed in T-lineage ALL cells at significantly higher levels than in normal hematopoietic cells. This previously unknown differential expression profile uniquely indicates that the protein product of WT1 would be an attractive molecular target for treatment of T-lineage ALL as well.