On May 3, 2023, ImmunoGen announced that its FRα-targeting antibody-drug conjugates drug Elahere has successfully completed the phase III verification clinical trial of MIRASOL, becoming the first new drug to prolong the survival of patients with platinum-resistant ovarian cancer. Elahere is an antibody-drug conjugate (ADC) targeting folate receptor-α (FRα), mainly indicated for the treatment of adult patients with FRα-positive platinum-resistant epithelial ovarian cancer, fallopian tube cancer or primary peritoneal cancer, and these patients had previously received one to three systemic regimens.
In recent years, FRα targeting drug development continues to increase, and Elahere successfully demonstrated FRα's potential in ovarian cancer. In China, there were more than 60,000 new cases of ovarian cancer in 2020, and hundreds of thousands of cases of recurrence and maintenance treatment every year, but currently there is no specific therapy to meet the huge clinical demand. Previously, it was difficult to develop drugs targeting FRα. Small molecule conjugated drugs and monoclonal antibody drugs all encountered failures. Elahere was only conditionally approved based on small-scale phase III clinical data. This phase III clinical success means that FRα targets will overcome twists and turns and usher in new breakthroughs.
Introduction to FRα Targets
Folate receptor alpha (FRα), encoded by FOLR1, is a cell surface glycoprotein with a molecular weight of 38-40 kD. It was first discovered as a folate-binding protein and cloned as a tumor-associated antigen in 1991. FRα is a member of the high-affinity FRs family, which also includes FRβ, FRγ, and FRδ, encoded by FOLR2, FOLR3, and FOLR4, respectively.
FRα has a high affinity for reductive folic acid (such as 5-methyltetrahydrofolic acid and tetrahydrofolic acid) and folic acid, which is absorbed through endocytosis. FRα is essential in embryonic development, folic acid supplementation, and is an important strategy for the prevention of birth defects. In addition to delivering folate, FRα is involved in the regulation of tumor cell proliferation and metastasis.
F1 Clinical application of FRα-targeted drugs in cancer diagnosis and treatment
Source: Nature Reviews Clinical Oncology
FRα is a potential therapeutic target for tumor therapy. In addition to transporting folic acid, it is also involved in regulating the proliferation and metastasis of tumor cells. FRα is almost not expressed in normal tissues. However, FRα is widely and highly expressed in tumor tissues, especially in non-small cell lung cancer (14-74%), triple-negative breast cancer (35-68%), mesothelioma (72-100%), and epithelial ovarian cancer (76-89%). Therefore, FRα is an ideal target for the development of tumor targeting drugs. A variety of drugs targeting FRα through various mechanisms such as ADC, CAR-T, and double antibody are currently under development.
F2 FRa expression levels in different types of tumors
Mechanism of FRα in Tumor
There are four main mechanisms of frα-mediated folic acid internalization and cancer cell signaling regulation:
1. Folate binding to FRα can induce STAT3 activation through a JAK-dependent process mediated by GP130 co-receptors.
2. FRα can form a macromolecular complex with LYN tyrosine kinase to regulate the phosphorylation of PEAK1 to promote the activation of ERK and STAT3.
3. GPI-anchored FRα is internalized in caveolae vesicles, forming early endosomes, which undergo acidification and subsequent degradation and fuse with lysosomes to release FRα and folic acid. FRα is then translocated to the nucleus and functions directly as a transcription factor.
4. FRα acts as a folate transporter; Rapidly proliferating cells require adequate intake of folic acid for single-carbon metabolic reactions and DNA synthesis, repair, and methylation.
F3 Mechanism of FRα in tumor
Research on FRα Targeted Therapy
Potential FRα targeted therapies include folic acid derivatives, ADCs, small molecules, vaccines, CAR-T, nuclides, and monoclonal antibodies. The six mechanisms are briefly described below:
1. Folate drug-conjugates: chemotherapeutic agents, such as vintafolide, have been conjugated to folate for FRα-targeted therapy.
2. Vaccines targeting FRα: autologous dendritic cells engineered with FRα mRNA commence an anti-FRα immune response, mediated by T-cells.
3. Chimeric antigen receptor (CAR) T cells: CAR T cells recognizing FRα trigger tumor cell killing.
4. Monoclonal antibodies (direct effects): Specific recognition of FRα lead to inhibition of downstream signaling events that cause tumor cell death.
5. Monoclonal antibodies (immune effector cell engagement): antibodies link FRα-expressing tumor cells with immune effector cells that bear Fc receptors, potentiate effector cell activation and target-neutralizing functions by engendering antibody-dependent effector cell-mediated cytotoxicity (ADCC), phagocytosis (ADCP).
6. Killing cancer cells through complement-dependent cytotoxicity (CDC) activation.
F4 Research on FRα targeted therapy
FRα and Ovarian Cancer
Folate receptor alpha (FRα) is a potent anticancer drug target. It includes limited expression in non-malignant tissues, combined with overexpression in malignant tissues in some cancers, making FRα a potential target using multiple platforms such as antibodies, antibody-drug conjugates (ADCs), bispecific antibodies or chimeric antigen receptor (CAR) T cells.
F5 FRα as a therapeutic target in cancer patients
In the 2023 V1 version of the NCCN Guidelines for Ovarian Cancer, the ADC drug Mirvetuximab soravtansine-gynx is listed as a recommended drug for the recurrent platinum-resistant diseases. It is a tumor target for FRα expression.
For the treatment of gynecological malignant tumors, surgery, chemotherapy, radiotherapy mainly used in clinical comprehensive treatment measures, postoperative adjuvant chemotherapy, can effectively control the tumor subclinical micro tumor lesions, so as to improve the clinical cure rate of tumors. From traditional small molecule chemotherapy drugs to antibody drugs, and then to the newly developed antibody drug conjugate (ADC), the development of chemotherapy is more and more tending to stronger targeting, higher cytotoxicity, less adverse reactions and other therapeutic measures.
In late 2022, the FDA accelerated approval of Mirvetuximab soravtansine-gynx for Frα-positive, platinum-resistant ovarian, fallopian tube, or peritoneal epithelial carcinoma.
The drug was approved based on an evaluation of study 0417 (NCT04296890), a one-arm trial of 106 patients with FRα-positive, platinum-resistant ovarian epithelial, fallopian tube, or primary peritoneal cancer. Among 104 patients with platinum-resistant, measurable disease who received at least one dose, the confirmed ORR was 31.7% (95%CI: 22.9, 41.6) and the median DOR was 6.9 months (95%CI: 5.6, 9.7).
Table 1 NCT04296890 Research data
Future Research Prospects of FRα in Gynecological Tumors
FRα is a highly relevant and potentially available target for cancer therapy. Differential expression of FRα on the surface of malignant cells in selected tumors has enabled the development of antiboy-based therapeutic strategies, including ADCs, BiTEs, and CAR T cells. In addition, FRα's affinity for non-physiological substrates, such as higher levels of folic acid compared to natural folic acid in the diet, enables folic acid conjugators associated with chemotherapy payloads, radioisotopes, and/or fluorescent molecules to further facilitate the development of anticancer drugs and imaging agents.
At present, there is a general lack of effective biomarkers for diagnosis, treatment and prognostic analysis of gynecological tumors in clinical practice. Further studies on the expression and distribution of FRα on the surface of tumor cells can promote the study of gynecological tumor-related antigens, and perhaps FRα can be used as a novel tumor biomarker for gynecological tumors.
FRα is a highly relevant target in cancer therapy. Although it has failed in humanized monoclonal antibodies and small molecule folic acid conjugated drugs due to insufficient single-drug activity, it cannot be denied that it has natural advantages as an anti-cancer target.
It is less expressed in normal tissues, but overexpressed in non-small cell lung cancer, mesothelioma, endometrial cancer and other solid tumors. Although no FRα ADCs are currently available on the global market, positive clinical results have been achieved in clinical trials of IMGN853, MORAb-202, and STRO-002. FRα, as an ADC target with less competition but clear drug potential, can avoid homogeneous competition and form differentiated advantages.
FRα will become another hot target in ADC field. As with PD1, once it is successful in one indication, it can be replicated for more indications. As a lead PEG derivatives, Huateng Pharma is dedicated to being your most reliable partner to provide chemical synthesis and high-quality PEG linkers for ADC drugs.
. NCCN Guidelines Version 1.2023 Ovarian Cancer/Fallopian Tube Cancer/Primary Peritoneal Cancer