ROR1 targeting with the antibody-drug conjugate VLS-101 is effective in Richter syndrome patient-derived xenograft mouse models

Novel humanized monoclonal antibodies against ROR1 for cancer therapy

BACKGROUND

Overexpression of receptor tyrosine kinase-like orphan receptor 1 (ROR1) contributes to cancer cell proliferation, survival and migration, playing crucial roles in tumor development. ROR1 has been proposed as a potential therapeutic target for cancer treatment. This study aimed to develop novel humanized ROR1 monoclonal antibodies and investigate their anti-tumor effects.

METHODS

ROR1 expression in tumor tissues and cell lines was analyzed by immunohistochemistry and flow cytometry. Antibodies from mouse hybridomas were humanized by the complementarity-determining region (CDR) grafting technique. Surface plasmon resonance spectroscopy, ELISA assay and flow cytometry were employed to characterize humanized antibodies. In vitro cellular assay and in vivo mouse experiment were conducted to comprehensively evaluate anti-tumor activity of these antibodies.

RESULTS

ROR1 exhibited dramatically higher expression in lung adenocarcinoma, liver cancer and breast cancer, and targeting ROR1 by short-hairpin RNAs significantly inhibited proliferation and migration of cancer cells. Two humanized ROR1 monoclonal antibodies were successfully developed, named h1B8 and h6D4, with high specificity and affinity to ROR1 protein. Moreover, these two antibodies effectively suppressed tumor growth in the lung cancer xenograft mouse model, c-Myc/Alb-cre liver cancer transgenic mouse model and MMTV-PyMT breast cancer mouse model.

CONCLUSIONS

Two humanized monoclonal antibodies targeting ROR1, h1B8 and h6D4, were successfully developed and exhibited remarkable anti-tumor activity in vivo.

Unlocking the potential: advancements and future horizons in ROR1-targeted cancer therapies

While receptor tyrosine kinase-like orphan receptor 1 (ROR1) is typically expressed at low levels or absent in normal tissues, its expression is notably elevated in various malignant tumors and conditions, including chronic lymphocytic leukemia (CLL), breast cancer, ovarian cancer, melanoma, and lung adenocarcinoma. This distinctive feature positions ROR1 as an attractive target for tumor-specific treatments. Currently, several targeted drugs directed at ROR1 are undergoing clinical development, including monoclonal antibodies, antibody-drug conjugates (ADCs), and chimeric antigen receptor T-cell therapy (CAR-T). Additionally, there are four small molecule inhibitors designed to bind to ROR1, presenting promising avenues for the development of PROTAC degraders targeting ROR1. This review offers updated insights into ROR1's structural and functional characteristics, embryonic development implications, cell survival signaling pathways, and evolutionary targeting strategies, all of which have the potential to advance the treatment of malignant tumors.

Receptor tyrosine kinase-like orphan receptor serves as a potential target in cancer immunotherapy

Receptor tyrosine kinase-like orphan receptor (ROR), consisting of ROR1 and ROR2, is a conserved family of receptor tyrosine kinase superfamily that plays crucial roles during embryonic development with limited expression in adult normal tissues. However, it is overexpressed in a range of hematological malignancies and solid tumors and functions in cellular processes including cell survival, polarity, and migration, serving as a potential target in cancer immunotherapy. This review summarizes the expression and structure of ROR in developmental morphogenesis and its function in cancers associated with Wnt5a signaling and highlights the cancer immunotherapy strategies targeting ROR.

Mouse models of chronic lymphocytic leukemia and Richter transformation: what we have learnt and what we are missing

Although the chronic lymphocytic leukemia (CLL) treatment landscape has changed dramatically, unmet clinical needs are emerging, as CLL in many patients does not respond, becomes resistant to treatment, relapses during treatment, or transforms into Richter. In the majority of cases, transformation evolves the original leukemia clone into a diffuse large B-cell lymphoma (DLBCL). Richter transformation (RT) represents a dreadful clinical challenge with limited therapeutic opportunities and scarce preclinical tools. CLL cells are well known to highly depend on survival signals provided by the tumor microenvironment (TME). These signals enhance the frequency of immunosuppressive cells with protumor function, including regulatory CD4+ T cells and tumor-associated macrophages. T cells, on the other hand, exhibit features of exhaustion and profound functional defects. Overall immune dysfunction and immunosuppression are common features of patients with CLL. The interaction between malignant cells and TME cells can occur during different phases of CLL development and transformation. A better understanding of in vivo CLL and RT biology and the availability of adequate mouse models that faithfully recapitulate the progression of CLL and RT within their microenvironments are "conditio sine qua non" to develop successful therapeutic strategies. In this review, we describe the xenograft and genetic-engineered mouse models of CLL and RT, how they helped to elucidate the pathophysiology of the disease progression and transformation, and how they have been and might be instrumental in developing innovative therapeutic approaches to finally eradicate these malignancies.

Mouse models of CLL: In vivo modeling of disease initiation, progression, and transformation

Chronic lymphocytic leukemia (CLL) is a highly complex disease characterized by the proliferation of CD5+ B cells in lymphoid tissues. Current modern treatments have brought significant clinical benefits to CLL patients. However, there are still unmet needs. Patients relapse on Bruton's tyrosine kinase inhibitors and BCL2 inhibitors and often develop more aggressive diseases including Richter transformation (RT), an incurable complication of up to ∼10% patients. This evidence underscores the need for improved immunotherapies, combination treatment strategies, and predictive biomarkers. A mouse model that can recapitulate human CLL disease and certain components of the tumor immune microenvironment represents a promising preclinical tool for such purposes. In this review, we provide an overview of CRISPR-engineered and xenograft mouse models utilizing either cell lines, or primary CLL cells suitable for studies of key events driving the disease onset, progression and transformation of CLL. We also review how CRISPR/Cas9 established mouse models carrying loss-of-function lesions allow one to study key mutations driving disease progression. Finally, we discuss how next generation humanized mice might improve to generation of faithful xenograft mouse models of human CLL.

Recent insights into the therapeutic strategies targeting the pseudokinase PTK7 in cancer

The generation of drugs counteracting deregulated protein kinases has been a major focus in cancer therapy development. Breakthroughs in this effort have produced many therapeutic agents to the benefit of patients, mostly through the development of chemical or antibody-based drugs targeting active kinases. These strategies are challenged when considering catalytically inactive protein kinases (or pseudokinases), which represent 10% of the human kinome with many of relevance in cancer. Among the so-called pseudotyrosine kinases, the PTK7 receptor tyrosine kinase (RTK) stands as a bona fide target overexpressed in several solid tumors and hematological malignancies and linked to metastasis, poor prognosis, and resistance to treatment. Despite the lack of catalytic activity, PTK7 has signaling capacities through heterodimerization with active RTKs and offers pharmacological targeting opportunities through its inactive kinase domain. Moreover, PTK7-targeting strategies based on antibody-drug conjugates, aptamers, and CAR-T cell-based therapies have demonstrated encouraging results in preclinical and clinical settings. We review the most recent data assigning to PTK7 a prominent role in cancer progression as well as current preclinical and clinical targeting strategies against RTK family pseudokinases including PTK7.

Dihydroartemisinin inhibits tumor progress via blocking ROR1-induced STAT3-activation in non-small cell lung cancer

In non-small cell lung cancer (NSCLC), identifying a component with certain molecular targets can aid research on cancer treatment. Dihydroartemisinin (DHA) is a semisynthetic derivative of artemisinin which induced the anti-cancer effects via the STAT3 signaling pathway, but the underlying molecular mechanism is still elusive. In this study, we first proved that DHA prohibits the growth of tumors both in vitro and in vivo. Data from transcriptomics showed that DHA reduced the expression level of the genes involved in cell cycle-promoting and anti-apoptosis, and most importantly, DHA restricted the expression level of receptor tyrosine kinase-like orphan receptor 1 (ROR1) which has been reported to have abnormal expression on tumor cells and had close interaction with STAT3 signaling. Then, we performed comprehensive experiments and found that DHA remarkably decreased the expression of ROR1 at both mRNA and protein levels and it also diminished the phosphorylation level of STAT3 in NSCLC cell lines. In addition, our data showed that exogenously introduced ROR1 could significantly enhance the phosphorylation of STAT3 while blocking ROR1 had the opposite effects indicating that ROR1 plays a critical role in promoting the activity of STAT3 signaling. Finally, we found that ROR1 overexpression could partially reverse the decreased activity of STAT3 induced by DHA which indicates that DHA-induced anti-growth signaling is conferred, at least in part, through blocking ROR1-mediated STAT3 activation. In summary, our study indicates that in NSCLC, ROR1 could be one of the critical molecular targets mediating DHA-induced STAT3 retardation.

Decreased apoptotic priming and loss of BCL-2 dependence are functional hallmarks of Richter's syndrome

Richter's syndrome (RS) is the transformation of chronic lymphocytic leukemia (CLL) into a high-grade B-cell malignancy. Molecular and functional studies have pointed out that CLL cells are close to the apoptotic threshold and dependent on BCL-2 for survival. However, it remains undefined how evasion from apoptosis evolves during disease transformation. Here, we employed functional and static approaches to compare the regulation of mitochondrial apoptosis in CLL and RS. BH3 profiling of 17 CLL and 9 RS samples demonstrated that RS cells had reduced apoptotic priming and lower BCL-2 dependence than CLL cells. While a subset of RS was dependent on alternative anti-apoptotic proteins and was sensitive to specific BH3 mimetics, other RS cases harbored no specific anti-apoptotic addiction. Transcriptomics of paired CLL/RS samples revealed downregulation of pro-apoptotic sensitizers during disease transformation. Albeit expressed, effector and activator members were less likely to colocalize with mitochondria in RS compared to CLL. Electron microscopy highlighted reduced cristae width in RS mitochondria, a condition further promoting apoptosis resistance. Collectively, our data suggest that RS cells evolve multiple mechanisms that lower the apoptotic priming and shift the anti-apoptotic dependencies away from BCL-2, making direct targeting of mitochondrial apoptosis more challenging after disease transformation.

A molecular circuit linking the BCR to the NAD biosynthetic enzyme NAMPT is an actionable target in Richter syndrome

ABSTRACT

This works defines, to the best of our knowledge, for the first time a molecular circuit connecting nicotinamide mononucleoside phosphoribosyl transferase (NAMPT) activity to the B-cell receptor (BCR) pathway. Using 4 distinct xenograft models derived from patients with Richter syndrome (RS-PDX), we show that BCR cross-linking results in transcriptional activation of the nicotinamide adenine dinucleotide (NAD) biosynthetic enzyme NAMPT, with increased protein expression, in turn, positively affecting global cellular NAD levels and sirtuins activity. NAMPT blockade, by using the novel OT-82 inhibitor in combination with either BTK or PI3K inhibitors (BTKi or PI3Ki), induces rapid and potent apoptotic responses in all 4 models, independently of their mutational profile and the expression of the other NAD biosynthetic enzymes, including nicotinate phosphoribosyltransferase. The connecting link in the circuit is represented by AKT that is both tyrosine- and serine-phosphorylated by PI3K and deacetylated by sirtuin 1 and 2 to obtain full kinase activation. Acetylation (ie, inhibition) of AKT after OT-82 administration was shown by 2-dimensional gel electrophoresis and immunoprecipitation. Consistently, pharmacological inhibition or silencing of sirtuin 1 and 2 impairs AKT activation and induces apoptosis of RS cells in combination with PI3Ki or BTKi. Lastly, treatment of RS-PDX mice with the combination of PI3Ki and OT-82 results in significant inhibition of tumor growth, with evidence of in vivo activation of apoptosis. Collectively, these data highlight a novel application for NAMPT inhibitors in combination with BTKi or PI3Ki in aggressive lymphomas.

The molecular map of CLL and Richter's syndrome

Clonal expansion of B-cells, from the early stages of monoclonal B-cell lymphocytosis through to chronic lymphocytic leukemia (CLL), and then in some cases to Richter's syndrome (RS) provides a comprehensive model of cancer evolution, notable for the marked morphological transformation and distinct clinical phenotypes. High-throughput sequencing of large cohorts of patients and single-cell studies have generated a molecular map of CLL and more recently, of RS, yielding fundamental insights into these diseases and of clonal evolution. A selection of CLL driver genes have been functionally interrogated to yield novel insights into the biology of CLL. Such findings have the potential to impact patient care through risk stratification, treatment selection and drug discovery. However, this molecular map remains incomplete, with extant questions concerning the origin of the B-cell clone, the role of the TME, inter- and intra-compartmental heterogeneity and of therapeutic resistance mechanisms. Through the application of multi-modal single-cell technologies across tissues, disease states and clinical contexts, these questions can now be addressed with the answers holding great promise of generating translatable knowledge to improve patient care.

Are we closer to a standard of care for Richter's syndrome? Novel treatments on the horizon

INTRODUCTION

The therapeutic landscape for chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) has significantly evolved over the past decade with dramatically improved outcomes with the introduction of targeted therapies. This unfortunately has not been the case for Richter transformation (RT), the histologic transformation to a more aggressive lymphoma, most typically diffuse large B-cell lymphoma (DLBCL). As such, RT continues to be one of the most challenging complications of CLL/SLL. Historically, RT has a poor response to treatment, with a minority reaching complete remission (CR) and overall survival (OS) being less than a year.

AREAS COVERED

The focus of this review is to discuss the effectiveness of commonly used regimens, and review existing data for emerging regimens being examined in ongoing clinical trials to improve prognosis and outcomes in patients with RT. Despite extensive efforts to optimize therapies for RT, there is still no generalized consensus on either first-line treatment regimens or regimens in the relapsed/refractory setting. RT continues to carry a high mortality rate without durable response to current therapeutic agents.

EXPERT OPINION

Ongoing and future research may identify novel treatment approaches that will eventually improve outcomes for patients with RT. The optimal care for RT patients is a clinical trial, when feasible.

How receptor tyrosine kinase-like orphan receptor 1 meets its partners in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is the most common leukemia in western societies, recognized by clinical and molecular heterogeneity. Despite the success of targeted therapies, acquired resistance remains a challenge for relapsed and refractory CLL, as a consequence of mutations in the target or the upregulation of other survival pathways leading to the progression of the disease. Research on proteins that can trigger such pathways may define novel therapies for a successful outcome in CLL such as the receptor tyrosine kinase-like orphan receptor 1 (ROR1). ROR1 is a signaling receptor for Wnt5a, with an important role during embryogenesis. The aberrant expression on CLL cells and several types of tumors, is involved in cell proliferation, survival, migration as well as drug resistance. Antibody-based immunotherapies and small-molecule compounds emerged to target ROR1 in preclinical and clinical studies. Efforts have been made to identify new prognostic markers having predictive value to refine and increase the detection and management of CLL. ROR1 can be considered as an attractive target for CLL diagnosis, prognosis, and treatment. It can be clinically effective alone and/or in combination with current approved agents. In this review, we summarize the scientific achievements in targeting ROR1 for CLL diagnosis, prognosis, and treatment.

Chronic lymphocytic leukemia patient-derived xenografts recapitulate clonal evolution to Richter transformation

Chronic lymphocytic leukemia (CLL) is a B-cell neoplasm with a heterogeneous clinical behavior. In 5-10% of patients the disease transforms into a diffuse large-B cell lymphoma known as Richter transformation (RT), which is associated with dismal prognosis. Here, we aimed to establish patient-derived xenograft (PDX) models to study the molecular features and evolution of CLL and RT. We generated two PDXs by injecting CLL (PDX12) and RT (PDX19) cells into immunocompromised NSG mice. Both PDXs were morphologically and phenotypically similar to RT. Whole-genome sequencing analysis at different time points of the PDX evolution revealed a genomic landscape similar to RT tumors from both patients and uncovered an unprecedented RT subclonal heterogeneity and clonal evolution during PDX generation. In PDX12, the transformed cells expanded from a very small subclone already present at the CLL stage. Transcriptomic analysis of PDXs showed a high oxidative phosphorylation (OXPHOS) and low B-cell receptor (BCR) signaling similar to the RT in the patients. IACS-010759, an OXPHOS inhibitor, reduced proliferation, and circumvented resistance to venetoclax. In summary, we have generated new RT-PDX models, one of them from CLL cells that mimicked the evolution of CLL to RT uncovering intrinsic features of RT cells of therapeutical value.

A phase 1b study of zilovertamab in combination with paclitaxel for locally advanced/unresectable or metastatic Her2-negative breast cancer

BACKGROUND

Zilovertamab is a humanized monoclonal antibody targeting ROR1, an onco-embryonic antigen expressed by malignant cells of a variety of solid tumors, including breast cancer. A prior phase 1 study showed that zilovertamab was well tolerated and effective in inhibiting ROR1-signaling, which leads to activation of ERK1/2, NF-κB, and NRF2 target genes. This phase 1b study evaluated the safety and tolerability of zilovertamab with paclitaxel in patients with advanced breast cancer.

PATIENTS AND METHODS

Eligible patients had locally advanced, unresectable, or metastatic HER2- breast cancer with Eastern Cooperative Group performance status of 0-2 and without prior taxane therapy in the advanced setting. Study treatment included 600 mg of zilovertamab administered intravenously (IV) on Days 1 and 15 of Cycle 1 and then Day 1 of each 28-day cycle along with paclitaxel weekly at 80 mg/m2 IV.

RESULTS

Study patients had received a median of 4 prior therapies (endocrine therapy + chemotherapy) for locally advanced, unresectable, or metastatic disease. No patient discontinued therapy due to toxicity ascribed to zilovertamab. Adverse events were consistent with the known safety profile of paclitaxel. Of 16 patients, 6 (38%) had a partial response, and 6/16 (38%) patients had stable disease as best tumor response.

CONCLUSION

The combination of zilovertamab and paclitaxel was safe and well tolerated in heavily pre-treated advanced breast cancer patients. Further evaluation of ROR1 targeting in breast cancer patients with zilovertamab is warranted.

TRIAL REGISTRATION

NCT02776917. Registered on ClinicalTrials.gov on 05/17/2016.

Exploration of macrocyclic peptide binders to the extracellular CRD domain of human receptor tyrosine kinase-like orphan receptor 1 (ROR1)

Elevated levels of receptor tyrosine kinase-like orphan receptor 1 (RORl) expression are observed in multiple hematological and solid tumors, but not in most of the healthy adult tissues, identifying ROR1 as an attractive target for tumor-specific therapy. Herein we will describe the discovery of macrocyclic peptides as binders of the extracellular Cysteine-Rich Domain (CRD) of human ROR1 via mRNA in vitro selection technology using the PDPS platform, followed by exploration of sidechain SAR of parent macrocycle peptides, fluorescently labeled analogs, and a Peptide Drug Conjugate (PDC). The parent macrocyclic peptides represented by Compound 1 and Compound 14 displayed nanomolar cell-based binding to ROR1 and relatively good internalization in 786-O and MDA-MB-231 tumor cell lines. However, these peptides were not observed to induce apoptosis in Mia PaCa-2 cells, a model pancreatic tumor cell line with a relatively low level of cell surface expression of ROR1.

SOHO State of the Art Updates and Next Questions | Treatment of Richter's Transformation

Richter's transformation (RT) is a rare condition, represented by the development of an aggressive lymphoma arising from underlying chronic lymphocytic leukemia/small lymphocytic lymphoma. The management of RT remains challenging, necessitating combined therapeutic strategies to achieve favorable outcomes. Traditional treatment options for RT have involved intensive chemotherapy regimens, often with limited success due to the high-risk nature of the disease. However, recent advances in the understanding of RT pathogenesis have led to the emergence of novel targeted therapies that show promising results. Noncovalent Bruton tyrosine kinase inhibitors, T-cell-engaging bispecific antibodies, chimeric antigen receptor T-cells, and conjugated monoclonal antibodies may hold promise for improved outcomes in RT, especially when combined in a multitargeted fashion. Further prospective randomized trials and collaborative efforts are warranted to optimize treatment algorithm and ultimately improve patient outcomes in this dismal condition. This review provides a comprehensive overview of the current treatment options for RT.

Accelerated Chronic Lymphocytic Leukemia and Richter Transformation in the Era of Novel Agents

BACKGROUND

Tremendous developments in the field of chronic lymphocytic leukemia (CLL) in recent years have led to a revolutionary change in the treatment approach, which today is based on targeted treatments with a good response and optimal prognosis. Nevertheless, CLL can present or progress to "accelerated CLL" (A-CLL) or to "Richter transformation" (RT) and these two entities have a more aggressive course and are still characterized by challenges in the fields of diagnosis and therapy. In the current review, we summarized the latest knowledge in terms of diagnostic approaches to A-CLL, available treatments and clinical trials, for both A-CLL and RT which still pose an unmet need and require additional basic and clinical investigations.

SUMMARY

A-CLL is a rare and underdiagnosed entity that probably stands in the "gray zone" between CLL and RT, generally holding an intermediate prognosis. Its diagnosis is mainly based on histological findings including expanded proliferation centers, increased mitotic activity, and/or high Ki-67 index. Due to its rarity, its treatment approach has still not been defined, but it seems that novel agents, especially Bruton tyrosine kinase inhibitors (BTKi), are effective. As for RT, the standard therapy still consists of chemo-immunotherapy followed by stem-cell transplantation for fit responders with a dismal prognosis. New approaches are recently adopted including B-cell inhibition via novel agents (BTKi, venetoclax), T-cell engagers (checkpoint inhibitors, bispecific antibodies [BiTe] or the chimeric antigen receptor [CAR] technology), antibody-drug conjugates, or drug combinations. Although both CAR-T and BiTe seem promising, especially when combined with BTKi, evidence is still insufficient, and patients should generally be recruited in clinical trials.

KEY MESSAGES

The field of CLL has been a subject of major advances in recent years, but A-CLL and RT remain topics of "unmet need" and require further studies to identify the best diagnostic approach and a more effective treatment.

Crosstalk between Wnt/β-catenin signaling pathway and DNA damage response in cancer: a new direction for overcoming therapy resistance

Wnt signaling plays an important role in regulating the biological behavior of cancers, and many drugs targeting this signaling have been developed. Recently, a series of research have revealed that Wnt signaling could regulate DNA damage response (DDR) which is crucial for maintaining the genomic integrity in cells and closely related to cancer genome instability. Many drugs have been developed to target DNA damage response in cancers. Notably, different components of the Wnt and DDR pathways are involved in crosstalk, forming a complex regulatory network and providing new opportunities for cancer therapy. Here, we provide a brief overview of Wnt signaling and DDR in the field of cancer research and review the interactions between these two pathways. Finally, we also discuss the possibility of therapeutic agents targeting Wnt and DDR as potential cancer treatment strategies.

Antibody-Drug Conjugates for Breast Cancer Treatment: Emerging Agents, Targets and Future Directions

To achieve the scheme of "magic bullets" in antitumor therapy, antibody-drug conjugates (ADCs) were developed. ADCs consist of antibodies targeting tumor-specific antigens, chemical linkers, and cytotoxic payloads that powerfully kill cancer cells. With the approval of ado-trastuzumab emtansine (T-DM1) and fam-trastuzumab deruxtecan (T-DXd), the therapeutic potentials of ADCs in breast cancer have come into the spotlight. Nearly 30 ADCs for breast cancer are under exploration to move targeted therapy forward. In this review, we summarize the presenting and emerging agents and targets of ADCs. The ADC structure and development history are also concluded. Moreover, the challenges faced and prospected future directions in this field are reviewed, which give insights into novel treatments with ADCs for breast cancer.

Richter syndrome: novel insights into the biology of transformation

Although the genetic landscape of chronic lymphocytic leukemia (CLL) has been broadly profiled by large-scale sequencing studies performed over the past decade, the molecular basis of the transformation of CLL into aggressive lymphoma, or Richter syndrome (RS), has remained incompletely characterized. Recent advances in computational methods of clonal deconvolution, as well as extensive sample collection efforts in this rapidly progressive malignancy, have now enabled comprehensive analysis of paired CLL and RS samples and have led to multiple new studies investigating the genetic, transcriptomic, and epigenetic origins of RS. In parallel, new genetically engineered and xenograft mouse models have provided the opportunity for gleaning fresh biological and mechanistic insights into RS development and stepwise evolution from antecedent CLL. Altogether, these studies have defined RS driver lesions and CLL risk lesions and identified pathways dysregulated in transformation. Moreover, unique molecular subtypes of RS have been revealed, including a disease marked by profound genomic instability with chromothripsis/chromoplexy and whole genome duplication. Novel profiling approaches, including single-cell DNA and transcriptome sequencing of RS biopsy specimens and cell-free DNA profiling of patient plasma, demonstrate promise for the timely identification of RS clones and may translate to noninvasive identification and early diagnosis of RS. This review summarizes the recent scientific advances in RS and supports the integrated study of human genomics with mouse modeling to provide an advanced understanding of the biological underpinnings of transformation. These recent studies have major implications for much-needed novel therapeutic strategies for this still largely incurable malignancy.

Association of baseline ROR1 and ROR2 gene expression with clinical outcomes in the I-SPY2 neoadjuvant breast cancer trial

PURPOSE

ROR1 and ROR2 are Type 1 tyrosine kinase-like orphan receptors for Wnt5a that are associated with breast cancer progression. Experimental agents targeting ROR1 and ROR2 are in clinical trials. This study evaluated whether expression levels of ROR1 or ROR2 correlated with one another or with clinical outcomes.

METHODS

We interrogated the clinical significance of high-level gene expression of ROR1 and/or ROR2 in the annotated transcriptome dataset from 989 patients with high-risk early breast cancer enrolled in one of nine completed/graduated/experimental and control arms in the neoadjuvant I-SPY2 clinical trial (NCT01042379).

RESULTS

High ROR1 or high ROR2 was associated with breast cancer subtypes. High ROR1 was more prevalent among hormone receptor-negative and human epidermal growth factor receptor 2-negative (HR-HER2-) tumors and high ROR2 was less prevalent in this subtype. Although not associated with pathologic complete response, high ROR1 or high ROR2 each was associated with event-free survival (EFS) in distinct subtypes. High ROR1 associated with a worse EFS in HR + HER2- patients with high post-treatment residual cancer burden (RCB-II/III) (HR 1.41, 95% CI = 1.11-1.80) but not in patients with minimal post-treatment disease (RCB-0/I) (HR 1.85, 95% CI = 0.74-4.61). High ROR2 associated with an increased risk of relapse in patients with HER2 + disease and RCB-0/I (HR 3.46, 95% CI = 1.33-9.020) but not RCB-II/III (HR 1.07, 95% CI = 0.69-1.64).

CONCLUSION

High ROR1 or high ROR2 distinctly identified subsets of breast cancer patients with adverse outcomes. Further studies are warranted to determine if high ROR1 or high ROR2 may identify high-risk populations for studies of targeted therapies.

The Role of ROR1 in Chemoresistance and EMT in Endometrial Cancer Cells

Background and Objectives: Receptor tyrosine kinase-like orphan receptor type 1 (ROR1) plays a critical role in embryogenesis and is overexpressed in many malignant cells. These characteristics allow ROR1 to be a potential new target for cancer treatment. The aim of this study was to investigate the role of ROR1 through in vitro experiments in endometrial cancer cell lines. Materials and Methods: ROR1 expression was identified in endometrial cancer cell lines using Western blot and RT-qPCR. The effects of ROR1 on cell proliferation, invasion, migration, and epithelial-mesenchymal transition (EMT) markers were analyzed in two endometrial cancer cell lines (HEC-1 and SNU-539) using either ROR1 silencing or overexpression. Additionally, chemoresistance was examined by identifying MDR1 expression and IC50 level of paclitaxel. Results: The ROR1 protein and mRNA were highly expressed in SNU-539 and HEC-1 cells. High ROR1 expression resulted in a significant increase in cell proliferation, migration, and invasion. It also resulted in a change of EMT markers expression, a decrease in E-cadherin expression, and an increase in Snail expression. Moreover, cells with ROR1 overexpression had a higher IC50 of paclitaxel and significantly increased MDR1 expression. Conclusions: These in vitro experiments showed that ROR1 is responsible for EMT and chemoresistance in endometrial cancer cell lines. Targeting ROR1 can inhibit cancer metastasis and may be a potential treatment method for patients with endometrial cancer who exhibit chemoresistance.

Wnt Signaling in Brain Tumors: A Challenging Therapeutic Target

The involvement of Wnt signaling in normal tissue homeostasis and disease has been widely demonstrated over the last 20 years. In particular, dysregulation of Wnt pathway components has been suggested as a relevant hallmark of several neoplastic malignancies, playing a role in cancer onset, progression, and response to treatments. In this review, we summarize the current knowledge on the instructions provided by Wnt signaling during organogenesis and, particularly, brain development. Moreover, we recapitulate the most relevant mechanisms through which aberrant Wnt pathway activation may impact on brain tumorigenesis and brain tumor aggressiveness, with a particular focus on the mutual interdependency existing between Wnt signaling components and the brain tumor microenvironment. Finally, the latest anti-cancer therapeutic approaches employing the specific targeting of Wnt signaling are extensively reviewed and discussed. In conclusion, here we provide evidence that Wnt signaling, due to its pleiotropic involvement in several brain tumor features, may represent a relevant target in this context, although additional efforts will be needed to: (i) demonstrate the real clinical impact of Wnt inhibition in these tumors; (ii) overcome some still unsolved concerns about the potential systemic effects of such approaches; (iii) achieve efficient brain penetration.

Patient-derived xenograft models in cancer therapy: technologies and applications

Patient-derived xenograft (PDX) models, in which tumor tissues from patients are implanted into immunocompromised or humanized mice, have shown superiority in recapitulating the characteristics of cancer, such as the spatial structure of cancer and the intratumor heterogeneity of cancer. Moreover, PDX models retain the genomic features of patients across different stages, subtypes, and diversified treatment backgrounds. Optimized PDX engraftment procedures and modern technologies such as multi-omics and deep learning have enabled a more comprehensive depiction of the PDX molecular landscape and boosted the utilization of PDX models. These irreplaceable advantages make PDX models an ideal choice in cancer treatment studies, such as preclinical trials of novel drugs, validating novel drug combinations, screening drug-sensitive patients, and exploring drug resistance mechanisms. In this review, we gave an overview of the history of PDX models and the process of PDX model establishment. Subsequently, the review presents the strengths and weaknesses of PDX models and highlights the integration of novel technologies in PDX model research. Finally, we delineated the broad application of PDX models in chemotherapy, targeted therapy, immunotherapy, and other novel therapies.

In Vivo Modeling of CLL Transformation to Richter Syndrome Reveals Convergent Evolutionary Paths and Therapeutic Vulnerabilities

Transformation to aggressive disease histologies generates formidable clinical challenges across cancers, but biological insights remain few. We modeled the genetic heterogeneity of chronic lymphocytic leukemia (CLL) through multiplexed in vivo CRISPR-Cas9 B-cell editing of recurrent CLL loss-of-function drivers in mice and recapitulated the process of transformation from indolent CLL into large cell lymphoma [i.e., Richter syndrome (RS)]. Evolutionary trajectories of 64 mice carrying diverse combinatorial gene assortments revealed coselection of mutations in Trp53, Mga, and Chd2 and the dual impact of clonal Mga/Chd2 mutations on E2F/MYC and interferon signaling dysregulation. Comparative human and murine RS analyses demonstrated tonic PI3K signaling as a key feature of transformed disease, with constitutive activation of the AKT and S6 kinases, downmodulation of the PTEN phosphatase, and convergent activation of MYC/PI3K transcriptional programs underlying enhanced sensitivity to MYC/mTOR/PI3K inhibition. This robust experimental system presents a unique framework to study lymphoid biology and therapy.

SIGNIFICANCE

Mouse models reflective of the genetic complexity and heterogeneity of human tumors remain few, including those able to recapitulate transformation to aggressive disease histologies. Herein, we model CLL transformation into RS through multiplexed in vivo gene editing, providing key insight into the pathophysiology and therapeutic vulnerabilities of transformed disease. This article is highlighted in the In This Issue feature, p. 101.

Immunological Aspects of Richter Syndrome: From Immune Dysfunction to Immunotherapy

Richter Syndrome (RS) is defined as the development of an aggressive lymphoma in patients with a previous or simultaneous diagnosis of chronic lymphocytic leukemia (CLL). Two pathological variants of RS are recognized: diffuse large B-cell lymphoma (DLBCL)-type and Hodgkin lymphoma (HL)-type RS. Different molecular mechanisms may explain the pathogenesis of DLBCL-type RS, including genetic lesions, modifications of immune regulators, and B cell receptor (BCR) pathway hyperactivation. Limited data are available for HL-type RS, and its development has been reported to be similar to de novo HL. In this review, we focus on the immune-related pathogenesis and immune system dysfunction of RS, which are linked to BCR over-reactivity, altered function of the immune system due to the underlying CLL, and specific features of the RS tumor microenvironment. The standard of care of this disease consists in chemoimmunotherapy, eventually followed by stem cell transplantation, but limited possibilities are offered to chemo-resistant patients, who represent the majority of RS cases. In order to address this unmet clinical need, several immunotherapeutic approaches have been developed, namely T cell engagement obtained with bispecific antibodies, PD-1/PD-L1 immune checkpoint blockade by the use of monoclonal antibodies, selective drug delivery with antibody-drug conjugates, and targeting malignant cells with anti-CD19 chimeric antigen receptor-T cells.

Molecular characterization of Richter syndrome identifies de novo diffuse large B-cell lymphomas with poor prognosis

Richter syndrome (RS) is the transformation of chronic lymphocytic leukemia (CLL) into aggressive lymphoma, most commonly diffuse large B-cell lymphoma (DLBCL). We characterize 58 primary human RS samples by genome-wide DNA methylation and whole-transcriptome profiling. Our comprehensive approach determines RS DNA methylation profile and unravels a CLL epigenetic imprint, allowing CLL-RS clonal relationship assessment without the need of the initial CLL tumor DNA. DNA methylation- and transcriptomic-based classifiers were developed, and testing on landmark DLBCL datasets identifies a poor-prognosis, activated B-cell-like DLBCL subset in 111/1772 samples. The classification robustly identifies phenotypes very similar to RS with a specific genomic profile, accounting for 4.3-8.3% of de novo DLBCLs. In this work, RS multi-omics characterization determines oncogenic mechanisms, establishes a surrogate marker for CLL-RS clonal relationship, and provides a clinically relevant classifier for a subset of primary "RS-type DLBCL" with unfavorable prognosis.

Emerging Therapies for the Management of Richter Transformation

Richter transformation (RT) refers to the development of an aggressive lymphoma in patients with underlying chronic lymphocytic leukemia/small lymphocytic lymphoma. Aside from a small subgroup of patients with clonally unrelated and previously untreated chronic lymphocytic leukemia, the disease responds poorly to standard therapies and prognosis is dismal. Recent developments in the understanding of the biology of RT and the advent of several targeted agents may result in improved outcomes for these patients. The purpose of this review is to analyze recent data on the pathogenesis and treatment of RT. We reviewed studies addressing the pathophysiology of RT and analyzed the data for frontline chemoimmunotherapy and emerging targeted therapies likely to play a significant role in the future management of RT. Several biologic and clinical factors may help identify those who are unlikely to respond to conventional chemoimmunotherapy; where possible, these patients should be managed with a novel approach. Emerging therapies for the management of RT include chimeric antigen receptor T-cell therapy, noncovalent Bruton tyrosine kinase inhibitors, and T-cell-engaging bispecific antibodies. The use of less toxic and more effective targeted therapies may result in improved outcomes. Larger, prospective clinical trials are required to confirm efficacy and safety of novel agents for the management of RT, particularly when used in combination with other targeted therapies and in addition to chemoimmunotherapy regimens.

Meta-Analysis of Survival Effects of Receptor Tyrosine Kinase-like Orphan Receptor 1 (ROR1)

Background and Objectives: Identification and targeting of membrane proteins in tumor cells is one of the key steps in the development of cancer drugs. The receptor tyrosine kinase-like orphan receptor (ROR) type 1 is a type-I transmembrane protein expressed in various cancer tissues, which is in contrast to its limited expression in normal tissues. These characteristics make ROR1 a candidate target for cancer treatment. This study aimed to identify the prognostic value of ROR1 expression in cancers. Materials and Methods: We conducted a comprehensive systematic search of electronic databases (PubMed) from their inception to September 2021. The included studies assessed the effect of ROR1 on overall survival (OS) and progression-free survival (PFS). Hazard ratios (HR) from collected data were pooled in a meta-analysis using Revman version 5.4 with generic inverse-variance and random effects modeling. Results: A total of fourteen studies were included in the final analysis. ROR1 was associated with worse OS (HR 1.95, 95% confidence interval (CI) 1.50−2.54; p < 0.001) with heterogeneity. The association between poor OS and ROR1 expression was high in endometrial cancer, followed by ovarian cancer, and diffuse large B cell lymphoma. In addition, ROR1 was associated with poor PFS (HR 1.84, 95% CI 1.60−2.10; p < 0.001), but heterogeneity was not statistically significant. In subgroup analysis, high ROR1 expression showed a significantly higher rate of advanced stage or lymph node metastasis. Conclusions: This meta-analysis provides evidence that ROR1 expression is associated with adverse outcome in cancer survival. This result highlights ROR1 as a target for developmental therapeutics in cancers.

Macrophage- and BCR-derived but not TLR-derived signals support the growth of CLL and Richter syndrome murine models in vivo

A large amount of circumstantial evidence has accumulated suggesting that Toll-like receptor (TLR) signals are involved in driving chronic lymphocytic leukemia (CLL) cell proliferation, but direct in vivo evidence for this is still lacking. We have now further addressed this possibility by pharmacologically inhibiting or genetically inactivating the TLR pathway in murine CLL and human Richter syndrome (RS) patient-derived xenograft (PDX) cells. Surprisingly, we show that pharmacologic inhibition of TLR signaling by treatment with an IRAK1/4 inhibitor delays the growth of the transplanted malignant cells in recipient mice, but genetic inactivation of the same pathway by CRISPR/Cas9-mediated disruption of IRAK4 or its proximal adaptor MyD88 has no effect. We further show that treatment with the IRAK1/4 inhibitor results in depletion of macrophages and demonstrate that these cells can support the survival and enhance the proliferation of both murine Eμ-TCL1 leukemia and human RS cells. We also show that genetic disruption of the B-cell receptor (BCR) by CRISPR/Cas9 editing of the immunoglobulin M constant region gene inhibits the growth of human RS-PDX cells in vivo, consistent with our previous finding with murine Eμ-TCL1 leukemia cells. Finally, we show that genetic disruption of IRAK4 does not result in negative selection of human CLL cell lines xenografted in immunodeficient mice. The obtained data suggest that TLR signals are unlikely to represent a major driver of CLL/RS cell proliferation and provide further evidence that signals from macrophages and the BCR promote the growth and survival of CLL and RS cells in vivo.

Learning from TCR Signaling and Immunological Synapse Assembly to Build New Chimeric Antigen Receptors (CARs)

Chimeric antigen receptor (CAR) T cell immunotherapy is a revolutionary pillar in cancer treatment. Clinical experience has shown remarkable successes in the treatment of certain hematological malignancies but only limited efficacy against B cell chronic lymphocytic leukemia (CLL) and other cancer types, especially solid tumors. A wide range of engineering strategies have been employed to overcome the limitations of CAR T cell therapy. However, it has become increasingly clear that CARs have unique, unexpected features; hence, a deep understanding of how CARs signal and trigger the formation of a non-conventional immunological synapse (IS), the signaling platform required for T cell activation and execution of effector functions, would lead a shift from empirical testing to the rational design of new CAR constructs. Here, we review current knowledge of CARs, focusing on their structure, signaling and role in CAR T cell IS assembly. We, moreover, discuss the molecular features accounting for poor responses in CLL patients treated with anti-CD19 CAR T cells and propose CLL as a paradigm for diseases connected to IS dysfunctions that could significantly benefit from the development of novel CARs to generate a productive anti-tumor response.

A ROR1 Small Molecule Inhibitor (KAN0441571C) Induced Significant Apoptosis of Mantle Cell Lymphoma (MCL) Cells

The receptor tyrosine kinase orphan receptor 1 (ROR1) is absent in most normal adult tissues but overexpressed in various malignancies and is of importance for tumor cell survival, proliferation, and metastasis. In this study, we evaluated the apoptotic effects of a novel small molecule inhibitor of ROR1 (KAN0441571C) as well as venetoclax (BCL-2 inhibitor), bendamustine, idelalisib (PI3Kδ inhibitor), everolimus (mTOR inhibitor), and ibrutinib (BTK inhibitor) alone or in combination in human MCL primary cells and cell lines. ROR1 expression was evaluated by flow cytometry and Western blot (WB). Cytotoxicity was analyzed by MTT and apoptosis by Annexin V/PI staining as well as signaling and apoptotic proteins (WB). ROR1 was expressed both in patient-derived MCL cells and human MCL cell lines. KAN0441571C alone induced significant time- and dose-dependent apoptosis of MCL cells. Apoptosis was accompanied by decreased expression of MCL-1 and BCL-2 and cleavage of PARP and caspase 3. ROR1 was dephosphorylated as well as ROR1-associated signaling pathway molecules, including the non-canonical WNT signaling pathway (PI3Kδ/AKT/mTOR). The combination of KAN0441571C and ibrutinib, venetoclax, idelalisib, everolimus, or bendamustine had a synergistic apoptotic effect and significantly prevented phosphorylation of ROR1-associated signaling molecules as compared to KAN0441571C alone. Our results suggest that targeting ROR1 by a small molecule inhibitor, KAN0441571C, should be further evaluated particularly in combination with other targeting drugs as a new therapeutic approach for MCL.

ROR1: an orphan becomes apparent

Since its initial identification in 1992 as a possible class 1 cell-surface receptor without a known parent ligand, receptor tyrosine kinase-like orphan receptor 1 (ROR1) has stimulated research, which has made apparent its significance in embryonic development and cancer. Chronic lymphocytic leukemia (CLL) was the first malignancy found to have distinctive expression of ROR1, which can help distinguish leukemia cells from most noncancer cells. Aside from its potential utility as a diagnostic marker or target for therapy, ROR1 also factors in the pathophysiology of CLL. This review is a report of the studies that have elucidated the expression, biology, and evolving strategies for targeting ROR1 that hold promise for improving the therapy of patients with CLL or other ROR1-expressing malignancies.

Richter Syndrome: From Molecular Pathogenesis to Druggable Targets

Richter syndrome (RS) represents the occurrence of an aggressive lymphoma, most commonly diffuse large B-cell lymphoma (DLBCL), in patients with chronic lymphocytic leukemia (CLL). Most cases of RS originate from the direct transformation of CLL, whereas 20% are de novo DLBCL arising as secondary malignancies. Multiple molecular mechanisms contribute to RS pathogenesis. B-cell receptor (BCR) overreactivity to multiple autoantigens is due to frequent stereotyped BCR configuration. Genetic lesions of TP53, CDKN2A, NOTCH1 and c-MYC deregulate DNA damage response, tumor suppression, apoptosis, cell cycle and proliferation. Hyperactivation of Akt and NOTCH1 signaling also plays a role. Altered expression of PD-1/PD-L1 and of other immune checkpoints leads to RS resistance to cytotoxicity exerted by T-cells. The molecular features of RS provide vulnerabilities for therapy. Targeting BCR signaling with noncovalent BTK inhibitors shows encouraging results, as does the combination of BCL2 inhibitors with chemoimmunotherapy. The association of immune checkpoint inhibitors with BCL2 inhibitors and anti-CD20 monoclonal antibodies is explored in early phase clinical trials with promising results. The development of patient-derived xenograft mice models reveals new molecular targets for RS, exemplified by ROR1. Although RS still represents an unmet medical need, understanding its biology is opening new avenues for precision medicine therapy.

WNT signaling and cancer stemness

Cancer stemness, defined as the self-renewal and tumor-initiation potential of cancer stem cells (CSCs), is a cancer biology property featuring activation of CSC signaling networks. Canonical WNT signaling through Frizzled and LRP5/6 receptors is transmitted to the β-catenin-TCF/LEF-dependent transcription machinery to up-regulate MYC, CCND1, LGR5, SNAI1, IFNG, CCL28, CD274 (PD-L1) and other target genes. Canonical WNT signaling causes expansion of rapidly cycling CSCs and modulates both immune surveillance and immune tolerance. In contrast, noncanonical WNT signaling through Frizzled or the ROR1/2 receptors is transmitted to phospholipase C, Rac1 and RhoA to control transcriptional outputs mediated by NFAT, AP-1 and YAP-TEAD, respectively. Noncanonical WNT signaling supports maintenance of slowly cycling, quiescent or dormant CSCs and promotes epithelial-mesenchymal transition via crosstalk with TGFβ (transforming growth factor-β) signaling cascades, while the TGFβ signaling network induces immune evasion. The WNT signaling network orchestrates the functions of cancer-associated fibroblasts, endothelial cells and immune cells in the tumor microenvironment and fine-tunes stemness in human cancers, such as breast, colorectal, gastric and lung cancers. Here, WNT-related cancer stemness features, including proliferation/dormancy plasticity, epithelial-mesenchymal plasticity and immune-landscape plasticity, will be discussed. Porcupine inhibitors, β-catenin protein-protein interaction inhibitors, β-catenin proteolysis targeting chimeras, ROR1 inhibitors and ROR1-targeted biologics are investigational drugs targeting WNT signaling cascades. Mechanisms of cancer plasticity regulated by the WNT signaling network are promising targets for therapeutic intervention; however, further understanding of context-dependent reprogramming trajectories might be necessary to optimize the clinical benefits of WNT-targeted monotherapy and applied combination therapy for patients with cancer.

Developing ROR1 Targeting CAR-T Cells against Solid Tumors in Preclinical Studies

Chimeric antigen receptor (CAR)-modified T-cells (CAR-T) have demonstrated promising clinical benefits against B-cell malignancies. Yet, its application for solid tumors is still facing challenges. Unlike haematological cancers, solid tumors often lack good targets, which are ideally expressed on the tumor cells, but not by the normal healthy cells. Fortunately, receptor tyrosine kinase-like orphan receptor 1 (ROR1) is among a few good cancer targets that is aberrantly expressed on various tumors but has a low expression on normal tissue, suggesting it as a good candidate for CAR-T therapy. Here, we constructed two ROR1 CARs with the same antigen recognition domain that was derived from Zilovertamab but differing in hinge regions. Both CARs target ROR1⁺ cancer cells specifically, but CAR with a shorter IgG4 hinge exhibits a higher surface expression and better in vitro functionality. We further tested the ROR1 CAR-T in three human solid tumor xenografted mouse models. Our ROR1 CAR-T cells controlled the solid tumor growth without causing any severe toxicity. Our results demonstrated that ROR1 CAR-T derived from Zilovertamab is efficacious and safe to suppress ROR1⁺ solid tumors in vitro and in vivo, providing a promising therapeutic option for future clinical application.

The landscape of chimeric antigen receptor T cell therapy in breast cancer: Perspectives and outlook

Chimeric antigen receptor-T (CAR-T) cell therapy is a revolutionary adoptive cell therapy, which could modify and redirect T cells to specific tumor cells. Since CAR-T cell therapy was first approved for B cell-derived malignancies in 2017, it has yielded unprecedented progress in hematological tumors and has dramatically reshaped the landscape of cancer therapy in recent years. Currently, cumulative evidence has demonstrated that CAR-T cell therapy could be a viable therapeutic strategy for solid cancers. However, owing to the immunosuppressive tumor microenvironment (TME) and heterogenous tumor antigens, the application of CAR-T cell therapy against solid cancers requires circumventing more challenging obstacles. Breast cancer is characterized by a high degree of invasiveness, malignancy, and poor prognosis. The review highlights the underlying targets of CAR-T cell therapy in breast cancer, summarizes the challenges associated with CAR-T cell therapy, and proposes the strategies to overcome these challenges, which provides a novel approach to breast cancer treatment.

Emerging drug targets for triple-negative breast cancer: A guided tour of the preclinical landscape

INTRODUCTION

Triple-negative breast cancer (TNBC) is the most fatal molecular subtype of breast cancer because of its aggressiveness and resistance to chemotherapy. FDA-approved therapies for TNBC are limited to poly(ADP-ribose) polymerase inhibitors, immune checkpoint inhibitors, and trophoblast cell surface antigen 2-targeted antibody-drug conjugate. Therefore, developing a novel effective targeted therapy for TNBC is an urgent unmet need.

AREAS COVERED

In this narrative review, we discuss emerging targets for TNBC treatment discovered in early translational studies. We focus on cancer cell membrane molecules, hyperactive intracellular signaling pathways, and the tumor microenvironment (TME) based on their druggability, therapeutic potency, specificity to TNBC, and application in immunotherapy.

EXPERT OPINION

The significant challenges in the identification and validation of TNBC-associated targets are 1) application of appropriate genetic, molecular, and immunological approaches for modulating the target, 2) establishment of a proper mouse model that accurately represents the human immune TME, 3) TNBC molecular heterogeneity, and 4) failure translation of preclinical findings to clinical practice. To overcome those difficulties, future research needs to apply novel technology, such as single-cell RNA sequencing, thermostable group II intron reverse transcriptase sequencing, and humanized mouse models. Further, combination treatment targeting multiple pathways in both the TNBC tumor and its TME is essential for effective disease control.

Biology and Treatment of Richter Transformation

Richter transformation (RT), defined as the development of an aggressive lymphoma on a background of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), represents a clinical unmet need because of its dismal prognosis. An increasing body of knowledge in the field of RT is arising from the recent development of preclinical models depicting the biology underlying this aggressive disease. Consistently, new therapeutic strategies based on a genetic rationale are exploring actionable pathogenic pathways to improve the outcome of patients in this setting. In this review, we summarize the current understandings on RT biology and the available treatment options.

Novel Approaches for the Treatment of Patients with Richter's Syndrome

OPINION STATEMENT

In the last 10-15 years, the way to treat cancers has dramatically changed towards precision medicine approaches. These treatment options are mainly based on selective targeting against signaling pathways critical for or detrimentally activated in cancer cells in cancer cells, as well as exploiting molecules that are specifically expressed on neoplastic cells, also known as tumor-associated antigens. These considerations hold true also in the hematological field where a plethora of novel targeted agents have reached patients' bedside, significantly improving clinical responses. Chronic lymphocytic leukemia (CLL) is an example of how targeted therapies, such as BTK, PI3K, or Bcl-2 inhibitors as well as anti-CD20 antibodies, have improved patients' management, even when adopted as frontline treatment. However, these advancements do not apply to Richter's syndrome (RS), the transformation of CLL into a very aggressive and fatal lymphoma, occurring in 2-10% of patients. RS is usually a fast-growing lymphoma of the diffuse large B cell or the Hodgkin's variant, with a dismal prognosis. Despite advancements in depicting and understanding the genetic background of RS and its pathogenesis, no significant clinical results have been registered. In the last couple of years, several studies have started to investigate the impact of novel drugs or drug combinations and some of them have opened for clinical trials, currently in phase I or II, whose results will be soon available. This review will present an overview of current and most recent therapeutic options in RS, discussing also how results coming from xenograft models may help in designing and identifying novel treatment opportunities to overcome the lack of effective therapies.

Immunotherapeutic Strategies in Chronic Lymphocytic Leukemia: Advances and Challenges

Immune-based therapeutic strategies have drastically changed the landscape of hematological disorders, as they have introduced the concept of boosting immune responses against tumor cells. Anti-CD20 monoclonal antibodies have been the first form of immunotherapy successfully applied in the treatment of CLL, in the context of chemoimmunotherapy regimens. Since then, several immunotherapeutic approaches have been studied in CLL settings, with the aim of exploiting or eliciting anti-tumor immune responses against leukemia cells. Unfortunately, despite initial promising data, results from pilot clinical studies have not shown optimal results in terms of disease control - especially when immunotherapy was used individually - largely due to CLL-related immune dysfunctions hampering the achievement of effective anti-tumor responses. The growing understanding of the complex interactions between immune cells and the tumor cells has paved the way for the development of new combined approaches that rely on the synergism between novel agents and immunotherapy. In this review, we provide an overview of the most successful and promising immunotherapeutic modalities in CLL, including both antibody-based therapy (i.e. monoclonal antibodies, bispecific antibodies, bi- or tri- specific killer engagers) and adoptive cellular therapy (i.e. CAR T cells and NK cells). We also provide examples of successful new combination strategies and some insights on future perspectives.

Targeted Drug Delivery and Theranostic Strategies in Malignant Lymphomas

Malignant lymphomas represent the most common type of hematologic malignancies. The first clinically approved TDD modalities in lymphoma patients were anti-CD20 radioimmunoconjugates (RIT) 131I-tositumomab and 90Y-ibritumomab-tiuxetan. The later clinical success of the first approved antibody-drug conjugate (ADC) for the treatment of lymphomas, anti-CD30 brentuximab vedotin, paved the path for the preclinical development and clinical testing of several other ADCs, including polatuzumab vedotin and loncastuximab tesirine. Other modalities of TDD are based on new formulations of "old" cytostatic agents and their passive trapping in the lymphoma tissue by means of the enhanced permeability and retention (EPR) effect. Currently, the diagnostic and restaging procedures in aggressive lymphomas are based on nuclear imaging, namely PET. A theranostic approach that combines diagnostic or restaging lymphoma imaging with targeted treatment represents an appealing innovative strategy in personalized medicine. The future of theranostics will require not only the capability to provide suitable disease-specific molecular probes but also expertise on big data processing and evaluation. Here, we review the concept of targeted drug delivery in malignant lymphomas from RIT and ADC to a wide array of passively and actively targeted nano-sized investigational agents. We also discuss the future of molecular imaging with special focus on monoclonal antibody-based and monoclonal antibody-derived theranostic strategies.

Antibody-drug conjugates: Resurgent anticancer agents with multi-targeted therapeutic potential

Antibody-drug conjugates (ADCs) constitute a relatively new group of anticancer agents, whose first appearance took place about two decades ago, but a renewed interest occurred in recent years, following the success of anti-cancer immunotherapy with monoclonal antibodies. Indeed, an ADC combines the selectivity of a monoclonal antibody with the cell killing properties of a chemotherapeutic agent (payload), joined together through an appropriate linker. The antibody moiety targets a specific cell surface antigen expressed by tumor cells and/or cells of the tumor microenvironment and acts as a carrier that delivers the cytotoxic payload within the tumor mass. Despite advantages in terms of selectivity and potency, the development of ADCs is not devoid of challenges, due to: i) low tumor selectivity when the target antigens are not exclusively expressed by cancer cells; ii) premature release of the cytotoxic drug into the bloodstream as a consequence of linker instability; iii) development of tumor resistance mechanisms to the payload. All these factors may result in lack of efficacy and/or in no safety improvement compared to unconjugated cytotoxic agents. Nevertheless, the development of antibodies engineered to remain inert until activated in the tumor (e.g., antibodies activated proteolytically after internalization or by the acidic conditions of the tumor microenvironment) together with the discovery of innovative targets and cytotoxic or immunomodulatory payloads, have allowed the design of next-generation ADCs that are expected to possess improved therapeutic properties. This review provides an overview of approved ADCs, with related advantages and limitations, and of novel targets exploited by ADCs that are presently under clinical investigation.

Zilovertamab Vedotin Targeting of ROR1 as Therapy for Lymphoid Cancers

BACKGROUND: Receptor tyrosine kinase-like orphan receptor 1 (ROR1) is an oncofetal protein present on many cancers. Zilovertamab vedotin (ZV) is an antibody–drug conjugate comprising a monoclonal antibody recognizing extracellular ROR1, a cleavable linker, and the anti-microtubule cytotoxin monomethyl auristatin E. METHODS: In this phase 1, first-in-human, dose-escalation study, we accrued patients with previously treated lymphoid cancers to receive ZV every 3 weeks until the occurrence of cancer progression or unacceptable toxicity had occurred. RESULTS: We enrolled 32 patients with tumor histologies of mantle cell lymphoma (MCL) (n=15), chronic lymphocytic leukemia (n=7), diffuse large B-cell lymphoma (DLBCL) (n=5), follicular lymphoma (n=3), Richter transformation lymphoma (n=1), or marginal zone lymphoma (n=1). Patients had received a median of four previous drug and/or cellular therapies. Starting dose levels were 0.5 (n=1), 1.0 (n=3), 1.5 (n=3), 2.25 (n=11), and 2.5 (n=14) mg per kg of body weight (mg/kg). Pharmacokinetic and pharmacodynamic data documented systemic ZV exposure and exposure-dependent ZV targeting of ROR1 on circulating tumor cells. As expected with an monomethyl auristatin E-containing antibody–drug conjugate, adverse events (AEs) included acute neutropenia and cumulative neuropathy resulting in a recommended ZV dosing regimen of 2.5 mg/kg every 3 weeks. No clinically concerning AEs occurred to suggest ROR1-mediated toxicities or nonspecific ZV binding to normal tissues. ZV induced objective tumor responses in 7 of 15 patients with MCL (47%; 4 partial and 3 complete) and in 3 of 5 patients with DLBCL (60%; 1 partial and 2 complete); objective tumor responses were not observed among patients with other tumor types. CONCLUSIONS: In heavily pretreated patients, ZV demonstrated no unexpected toxicities and showed evidence of antitumor activity, providing clinical proof of concept for selective targeting of ROR1 as a potential new approach to cancer therapy. (ClinicalTrials.gov number, NCT03833180.)

A FZD7-specific Antibody-Drug Conjugate Induces Ovarian Tumor Regression in Preclinical Models

Although WNT signaling is frequently dysregulated in solid tumors, drugging this pathway has been challenging due to off-tumor effects. Current clinical pan-WNT inhibitors are nonspecific and lead to adverse effects, highlighting the urgent need for more specific WNT pathway-targeting strategies. We identified elevated expression of the WNT receptor Frizzled class receptor 7 (FZD7) in multiple solid cancers in The Cancer Genome Atlas, particularly in the mesenchymal and proliferative subtypes of ovarian serous cystadenocarcinoma, which correlate with poorer median patient survival. Moreover, we observed increased FZD7 protein expression in ovarian tumors compared with normal ovarian tissue, indicating that FZD7 may be a tumor-specific antigen. We therefore developed a novel antibody-drug conjugate, septuximab vedotin (F7-ADC), which is composed of a chimeric human-mouse antibody to human FZD7 conjugated to the microtubule-inhibiting drug monomethyl auristatin E (MMAE). F7-ADC selectively binds human FZD7, potently kills ovarian cancer cells in vitro, and induces regression of ovarian tumor xenografts in murine models. To evaluate F7-ADC toxicity in vivo, we generated mice harboring a modified Fzd7 gene where the resulting Fzd7 protein is reactive with the human-targeting F7-ADC. F7-ADC treatment of these mice did not induce acute toxicities, indicating a potentially favorable safety profile in patients. Overall, our data suggest that the antibody-drug conjugate approach may be a powerful strategy to combat FZD7-expressing ovarian cancers in the clinic.

Understanding CLL biology through mouse models of human genetics

Rapid advances in large-scale next-generation sequencing studies of human samples have progressively defined the highly heterogeneous genetic landscape of chronic lymphocytic leukemia (CLL). At the same time, the numerous challenges posed by the difficulties in rapid manipulation of primary B cells and the paucity of CLL cell lines have limited the ability to interrogate the function of the discovered putative disease "drivers," defined in human sequencing studies through statistical inference. Mouse models represent a powerful tool to study mechanisms of normal and malignant B-cell biology and for preclinical testing of novel therapeutics. Advances in genetic engineering technologies, including the introduction of conditional knockin/knockout strategies, have opened new opportunities to model genetic lesions in a B-cell-restricted context. These new studies build on the experience of generating the MDR mice, the first example of a genetically faithful CLL model, which recapitulates the most common genomic aberration of human CLL: del(13q). In this review, we describe the application of mouse models to the studies of CLL pathogenesis and disease transformation from an indolent to a high-grade malignancy (ie, Richter syndrome [RS]) and treatment, with a focus on newly developed genetically inspired mouse lines modeling recurrent CLL genetic events. We discuss how these novel mouse models, analyzed using new genomic technologies, allow the dissection of mechanisms of disease evolution and response to therapy with greater depth than previously possible and provide important insight into human CLL and RS pathogenesis and therapeutic vulnerabilities. These models thereby provide valuable platforms for functional genomic analyses and treatment studies.

Perspectives on the development of antibody-drug conjugates targeting ROR1 for hematological and solid cancers

Antibody–drug conjugates (ADCs) are targeted therapeutics generated by conjugation of cytotoxic small molecules to monoclonal antibodies (mAbs) via chemical linkers. Due to their selective delivery of toxic payloads to antigen-positive cancer cells, ADCs demonstrate wider therapeutic indexes compared with conventional chemotherapy. After decades of intensive research and development, significant advances have been made in the field, leading to a total of 10 U.S. food and drug administration (FDA)-approved ADCs to treat cancer patients. Currently, ~80 ADCs targeting different antigens are under clinical evaluation for treatment of either hematological or solid malignancies. Notably, three ADCs targeting the same oncofetal protein, receptor tyrosine kinase like orphan receptor 1 (ROR1), have attracted considerable attention when they were acquired or licensed successively in the fourth quarter of 2020 by three major pharmaceutical companies. Apparently, ROR1 has emerged as an attractive target for cancer therapy. Since all the components of ADCs, including the antibody, linker and payload, as well as the conjugation method, play critical roles in ADC’s efficacy and performance, their choice and combination will determine how far they can be advanced. This review summarizes the design and development of current anti-ROR1 ADCs and highlights an emerging trend to target ROR1 for cancer therapy.

Richter Transformation in Chronic Lymphocytic Leukemia: Update in the Era of Novel Agents

Richter transformation (RT) is a poorly understood complication of chronic lymphocytic leukemia (CLL) with a dismal prognosis. It is associated with a switch in histopathology and biology, generally with a transformation of the original CLL clone to diffuse large B-cell lymphoma (DLBCL) or less frequently to Hodgkin's variant of Richter transformation (HVRT). It occurs in 2-10% of CLL patients, with an incidence rate of 0.5-1% per year, and may develop in treatment-naïve patients, although it is more common following therapy. In recent years, there has been a deeper understanding of the molecular pathogenesis of RT that involves the inactivation of the TP53 tumor suppressor gene in 50-60% of cases and the activation of aberrations of NOTCH1 and MYC pathways in about 30% of cases. Compared to the preceding CLL, 80% of cases with DLBCL-RT and 30% of HVRT harbor the same IGHV-D-J rearrangements, indicating a clonal evolution of the disease, while the remaining cases represent de novo lymphomas that are clonally unrelated. Despite advances in understanding the molecular variations and the pathogenesis of the disease, there is still no significant improvement in patient outcomes. However, if no clinical trials were designed for patients with RT in the past, now there many studies for these patients that incorporate new drugs and novel combinations that are being explored. In this review, we summarize the new information accumulated on RT with special emphasis on results involving the novel therapy tested for this entity, which represents an unmet clinical need.

The antibody drug conjugate VLS-101 targeting ROR1 is effective in CAR T-resistant mantle cell lymphoma

Mantle cell lymphoma (MCL) is a rare, aggressive and incurable subtype of non-Hodgkin’s B-cell lymphoma. The principal barrier is frequent clinical relapse to multiple lines of therapies, including new FDA-approved biologics and cell therapy. Brexucabtagene autoleucel, the first and only FDA approved chimeric antigen receptor (CAR) T product in MCL, demonstrated unprecedented efficacy in overcoming resistance to Bruton’s tyrosine kinase inhibitors. However, relapses have inevitably occurred and once relapsed these patients display a very poor clinical outcome. Currently, there is no optional therapy specifically designed for these patients. The development of tailored and more efficacious therapies is therefore critical and represents a new medical need. We found that while the receptor tyrosine kinase-like orphan receptor 1 (ROR1) is expressed across most of the MCL cells, it is significantly elevated in CAR T-relapsed MCL tumors. To see whether this aberrant ROR1 expression contributed to CAR T resistance, we targeted ROR1 using VLS-101, a monomethyl auristatin E conjugated anti-ROR1 antibody. VLS-101 showed potent anti-MCL activity in vitro in ROR1-expressing MCL cell lines and ex vivo in primary patient samples. Importantly, VLS-101 safely induced tumor regression in PDX models resistant to CAR T-cell therapy, ibrutinib and/or venetoclax. These data advocate for targeting ROR1 as a viable approach in the treatment of ROR1-positive MCL tumors, especially those with failure to prior therapies. These data also provide strong evidence for future enrollment of post-CD19 CAR T-cell relapsed MCL patients in a first in-human phase 1b VLS-101 trial. The upcoming testing in a clinical setting will provide important insights on this new therapeutic development aiming to overcome the CAR T resistance via targeting ROR1, which is a rising unmet clinical need in MCL.