Overview of ADC-Based Combination Therapies

Antibody-drug conjugates (ADCs) have now become a popular class of drugs for the treatment of hematologic malignancies and solid tumors, with extensive preclinical and clinical studies. However, as is the case with most cytotoxic drugs, the duration of the objective response or clinical benefit that ADCs can produce as monotherapies remains limited due to the emergence of resistance mechanisms. Therefore, ADC is being actively studied in preclinical and clinical trials in combination with other anticancer agents including chemotherapy, molecularly targeted drugs, and immunotherapy in recent years.

The most attractive drugs to combine with ADCs are those partners with additive or synergistic effects on tumor cells or their microenvironment without unacceptable overlapping toxicities. Drug combination including anti-angiogenic drugs, HER2-targeted drugs, DNA damage response agents and immune checkpoint inhibitors (ICIs) are currently the direction of active research. Here we will overview the research progress of Antibody-Drug Conjugate (ADC)-based combination therapies, such as ADC combination with chemotherapy, ADC combination with targeted drugs and ADC combination with immunotherapy.

ADC-based combination therapies
Rationale for antibody–drug conjugate (ADC)-based combination therapies

Mechanism of ADC-based Combination Therapies

There are four main categories of ADC combination therapies: chemotherapy, targeted therapy, immunotherapy, and anti-angiogenic agents. The mechanism of ADC and its combination is as follows:
(1). Chemotherapy: Up-regulate tumor cell surface antigens, lead to cell cycle arrest, and inhibit DNA repair.
(2). Targeted drugs: The synergistic use of ADCs and targeted drugs can lead to simultaneous stagnation of multiple oncogenic pathways, or double blockage of a specific pathway, thereby more effectively inhibiting downstream signaling.
(3). Immunotherapy: ADC can maintain the immune system of the tumor microenvironment in an activated state through different immune mechanisms, including macrophage reprogramming, generation of T memory cells, induction of increased expression of PD-L1, dendritic and T Cell activation, and these changes may increase the efficacy of immunotherapies that are used synergistically, such as in combination with anti-PD1/PD-L1 antibodies. Furthermore, ADCs can be designed to target specific elements of the tumor microenvironment (TME), such as fibroblasts.
(4). Anti-angiogenic agent: It can restore the normalization of tumor vasculature and help the delivery rate of ADC in the tumor to be higher.

Here we describe the first three ADC-based combination therapies.

ADC Combined With Chemotherapy

The combination of ADC with chemotherapeutic agents requires a better understanding of unique cell cycle interactions and the regulation of surface antigen expression by cytotoxic partners. So far, a growing body of preclinical and clinical data has shown some success, which points the way to further drug development.

1. Cell Cycle Interactions

DNA damaging agents that act in S phase and produce G2/M phase arrest (eg, antimetabolites, platinum, and topoisomerase inhibitors) can be combined with microtubule inhibitors. The successful combination of carboplatin with mirvetuximab soravtansine, anetumab ravtanine, or luveltamab tazevibulin in models of ovarian cancer illustrates this concept.

In early-stage clinical trials, Ravtansine-based ADCs in combination with carboplatin or adriamycin in platinum-sensitive and resistant ovarian cancer patients, and deruxtecan-based ADCs in combination with capecitabine or cisplatin in gastric and lung cancer patients showed significant results.

For blood tumors, representative examples include brentuximab vedotin (CD30-MMAE) combined with CHP (cyclophosphamide, doxorubicin and prednisone) in the treatment of CD30+ peripheral T-cell lymphoma. Polatuzumab vedotin (CD79b–MMAE) combined with rituximab-CHP in the treatment of diffuse large B cell lymphoma.

2. Design of Administration time

The timing of administration may be related to drug combination design. Tubulin polymerization is a key component of the ADC endocytosis mechanism, and DNA damage-mediated G2/M phase arrest may require some time for microtubule destructor sensitization to occur. This has been well demonstrated in studies in colon, lung, and breast cancer models, where continuous administration of SSN-15 (Lewis Y antigen-doxorubicin) and paclitaxel causes more DNA fragmentation than simultaneous administration. This observation suggests that adjusting the timing of dosing, especially delaying dosing of DNA damaging agents after antimicrotubule drugs, may improve therapeutic efficacy.

3. Regulation of surface antigens

Chemotherapy agents modulate the expression of surface antigens targeted by ADCs. In this regard, gemcitabine has been shown to up-regulate HER2 expression in pancreatic adenocarcinoma cells, where the combination of gemcitabine and trastuzumab emtansine (Kadcyla) exerts an enhanced effect. Intertwined with the cell cycle interactions described above, HER2 upregulation occurs particularly in the G2/M population as a result of gemcitabine-mediated inhibition of DNA synthesis.

Therefore, specific chemotherapeutic drugs may be more suitable for combination with ADC, depending on their ability to increase antigen availability. More research is needed to see if the findings are generalised to other AdC-chemotherapy combinations.

4. Overlapping toxicity

ADC is essentially chemotherapy, so the improvement of efficacy in combination regimens is often hampered by unacceptable toxicity. The primary toxicity is driven by cytotoxic payload metabolites and must be carefully considered when designing combination strategies. These toxicities include peripheral neuropathy from MMAE and DM1 derivatives, ocular toxicity from MMAF and DM4, gastrointestinal effects from DM1 or topoisomerase inhibitors, or hepatotoxicity from calicheamicin derivatives, and almost universal neutropenia and thrombocytopenia.

This was demonstrated by two phase 2a/b studies investigating trastuzumab emtansine in combination with docetaxel or paclitaxel in HER2+ advanced breast cancer, in which more than half of patients required dose reduction or discontinuation of taxane. Newer, more tumor-selective ADC drugs such as mirvetuximab soravtansine and datotomab deruxtecan show milder toxicity, making them ideal companions for chemotherapeutic agents with different mechanisms of action.

Overall, despite emerging evidence of enhanced antitumor activity of ADC and chemotherapy in combination, their development may still require substantial optimization of ADC characteristics and careful selection of tumor types and chemotherapy partners to ensure adequate tolerance.

ADC Combined With Targeted Drugs

ADCs have improved therapeutic indices and increased activity against select tumor populations compared to standard chemotherapy, making them ideal partners for targeted agents. One can envision various combinatorial strategies to overcome therapeutic resistance and clonal heterogeneity, elicit stronger inhibition of oncogene-dependent signaling pathways, increase surface antigen availability and sensitize low antigen-expressing tumors, modulate tumor microenvironment .

1. Replacing Chemotherapy With ADC

So far, many studies have attempted to replace standard chemotherapy with ADCs as a combination of targeted drugs, but the results have been disappointing. Clinical trials such as KAITLIN, KRISTINE, and MARIANNE were designed on the basis of synergistic antitumor activity with trastuzumab emtansine in combination with pertuzumab, however in the neoadjuvant and metastatic setting, it was comparable to paclitaxel, trastuzumab, and pertuzumab , which did not show enhanced efficacy. Similarly, in ovarian cancer, anetumab ravtansine was less effective than paclitaxel in combination with bevacizumab.

2. Tyrosine Kinase Inhibitors (TKIs)

Dual-target blockade by adding a TKI could provide greater selectivity and potentially improve the therapeutic index. In the TEAL study, compared with the standard combination of paclitaxel, trastuzumab and pertuzumab, the combination of trastuzumab emtansine, the pan-HER2 inhibitor lapatinib, and albumin-binding paclitaxel improved response to neoadjuvant therapy in patients with HER2+ breast cancer. The combination of Trastuzumab emtansine and tucatinib, a more selective anti-HER2 TKI, achieved an objective response rate (ORR) of 47% in advanced patients who progressed after prior taxane and trastuzumab treatment, Including a 36% brain-specific response rate in patients with BMS. The new generation of ADCs and TKI may get better results.

3. Resistance of Targeted ADC

There is growing evidence that targeted drugs can simultaneously target known ADC resistance mechanisms. For example, CDK4/6 inhibitors have been used in combination with trastuzumab emtansine in HER2-resistant patients because the malignant transformation of HER2 into breast epithelial cells is dependent on cyclin D1.

In addition, another key cell cycle regulator, PLK1, was recently identified as an up-regulated target in acquired and primary trastuzumab emtansine resistance models, and its inhibitor, volasertib, re-sensitized trastuzumab emtansine in vitro and in vivo.

ADCs may also be effective combinations of mechanisms that regulate resistance to targeted drugs. For example, the combination of osimertinib and trastuzumab emtansine produced additional antitumor effects, in which trastuzumab emtansine was able to delay or overcome osimertinib resistance in EGFR mutated non-small cell lung cancer models.

4. Regulation of Surface Antigens

Some TKIs have been shown to modulate surface antigens, potentially promoting further ADC activity and sensitizing low antigen-expressing tumors. In this regard, lapatinib, neratinib, tucatinib, and poziotinib have been shown to enhance the efficacy of trastuzumab emtansine.

However, the exact mechanism is still unclear. lapatinib increases HER2 abundance through strong transcriptional upregulation and reduced ubiquitination, neratinib decreases surface HER2 abundance by stimulating endodification and endocytosis, tucatinib's effect on cell surface HER2 remains elusive, and poziotinib up-regulates exon 20 mutations. However, wild-type HER2 was not upregulated, indicating that the synergistic mechanism was independent of surface HER2 density.

5. Anti-angiogenesis

Anti-angiogenic agents can promote ADC penetration and tumor cell exposure. Combination of anetumab ravtansine or mirvetuximab soravansine with bevacizumab has complete response efficacy in preclinical models of ovarian cancer. A recent Phase 1b study combined mirvetuximab soravtansine and bevacizumab in heavily pretreated, platinum-resistant, high-Frα ovarian cancer patients with 39% ORR exceeding the baseline value (27%) in the pivotal AURELIA trial.

6. DNA Damage Response Agents

Developing synthetic lethality by combining drugs targeting DNA damage response (DDR) with DNA-damaging agent-carrying ADCs may be a promising strategy for the treatment of genomically unstable tumors.

Traditionally, the combination of DDR drugs with chemotherapy has traditionally been hampered by intolerable toxicity. Although topotecan or irinotecan in combination with olaparib or veliparib can result in higher toxicity, the superior activity and tolerance of new generation ADCs carrying topoisomase I inhibitor payloads make them more suitable as joint partners. Several clinical trials are exploring this strategy, including niraparib and trastuzumab duocarmazine, talazoparib and sacituzumab govitecan, and olaparib and trastuzumab deruxtecan.

In addition to PARP inhibition, the increased selectivity of ADCs to chemotherapy will undoubtedly expand the range of DDR drugs that can be combined, for example, a clinical trial of the ATR inhibitor berzosertib combined with sacituzumab govitecan is currently underway (NCT04826341).

ADC Combined With Immunotherapy

More recently, strategies for combining immunotherapy with ADCs have also entered clinical studies. There is growing evidence that ADCs may increase the efficacy of immunotherapy. Its mechanisms are varied, including inducing immunogenic cell death, dendritic cell maturation, increased T-lymphocyte infiltration, and enhanced immune memory and expression of immunomodulatory proteins such as PD-L1 and MHC.

1. Anti-PD-1/PD-L1 And Anti-CTLA-4 Antibodies

There is growing evidence that ADCs may enhance the efficacy of immunotherapy agents. The mechanisms involved are varied, as well as enhancing immune memory and the expression of immunomodulators such as PD-L1 and MHC. Some ADCs showed greater efficacy in preclinical models with intact immune systems, supporting a correlation in their immunomodulatory function.

Multiple HER2-targeting ADCs, including trastuzumab emtansine, trastuzumab deruxtecan, and disitamab vedotin, have been tested in combination with ICIs in vitro and in vivo, demonstrating synergistic activity associated with enhanced homing and immune effector activation.

The KATE2 study, the only published randomized trial testing an ADC plus an ICI, compared T-DM1 plus atezolizumab to T-DM1 plus placebo in patients with HER2+ breast cancer. Combination therapy failed to significantly improve PFS (8.2 vs 6.2 months). However, a trend toward improved PFS was observed in the subgroup of patients with positive PD-L1 expression (8.5 vs 4.1 months), suggesting that the addition of ICIs in targeted therapy for HER2+ breast cancer may only benefit the PD-L1 positive population.

Combination therapy failed to improve progression-free survival (8.2 vs 6.2 months, P=0.33), suggesting that adding ICIs to HER2-targeted therapy may only benefit PD-L1-positive populations. Despite the disappointing results observed in this randomized trial, clinical exploration in multiple tumors is ongoing.

In addition, there is growing preclinical evidence that combination therapies may restore immune sensitivity. For example, in ICI refractory melanoma and non-small cell lung cancer (NSCLC) patient models, the AXL-specific ADC enapotamab vedotin was tested in combination with anti-PD-1 antibodies, where the ADC induced T cell infiltration and enhanced antigen presentation , enhanced ICI activity and resulted in pro-inflammatory changes in the TME.

2. ADC Combined With Other Immunotherapies

Polatuzumab vedotin has been shown to enhance CD20 expression on tumor cells by increasing AKT and ERK signaling, supporting its combination with anti-CD20 antibodies (such as rituximab) and CD20/CD3 bispecific antibody therapy.

In addition, combinations of ADCs and immunomodulators are also being explored in other diseases, such as multiple myeloma. In preclinical models, the combination of belantamab mafodotin with an OX40 agonist produced synergistic antitumor activity, increasing the infiltration and activation of intratumoral T cells and dendritic cells.

A combination regimen of belantamab mafodotin is under active clinical investigation, such as the DREAMM-5 study (NCT04126200), which is administered in combination with a variety of immunotherapeutic agents including anti-ICOS antibodies, OX40 agonists, and gamma-secretase inhibitors, as well as anti-PD-1 antibodies. Preliminary results showed that the combined anti-ICOS antibody had good activity in heavily pretreated patients.

Furthermore, ADCs are designed not only to target cancer cells, but also to modulate elements of the TME, such as immune cells or fibroblasts, thereby altering immune reactivity. For example, ADCs targeting CD73 have shown encouraging preclinical activity. In addition, ADCs targeting cancer-associated fibroblasts demonstrated enhanced CD8+ T-cell-mediated antitumor activity in preclinical models when combined with pembrolizumab.

ADC-based combinations that have been published or are in development

Principles of Clinical Trial Design for ADC Combination Therapies

The principles of clinical trial design evaluating ADC-based combinations are consistent with those published by the National Cancer Institute Investigational Drugs Steering Committee Clinical Trial Design Working Group.

A strong proof premise: why should a drug be used in combination? Expected results and the expected development plan for such combinations need to be provided prior to clinical trials.

If there is concern about dose-limiting toxicity overlap, or a plausible mechanistic basis for a clinically relevant adverse event resulting from a PK or pharmacodynamic interaction, a formal phase 1 joint evaluation of an ADC with another drug is appropriate.

A sequential evaluation of a drug design is recommended, with one drug initially administered as monotherapy in the first cycle and then combined in subsequent cycles. This design allows assessment of PK and pharmacodynamic interactions, which can be compared within each participant and compared with historical data.

To date, the limited success achieved with combination approaches using first-generation ADCs may be attributed to a variety of factors, such as non-specific expression of the target leading to adverse reactions in normal tissues, overlapping toxicity, lack of efficacy in different tumors, and unclear immune mechanisms.

design for combination therapy efficacy and toxicity exploration

Phase I trial design for combination therapy efficacy and toxicity exploration

Conclusion

ADCs as single agents have demonstrated antitumor efficacy and have been approved in a variety of solid and hematologic malignancies. Extensive efforts are currently underway in academia and industry to develop next-generation ADCs by identifying new targets and enhancing their pharmacological effects, as well as combination therapies based on current ADCs.

However, to date, combined approaches using first- and second-generation ADCs have had limited success, which may be attributed to several factors, such as nonspecific expression of the target leading to adverse reactions in normal tissues, overlapping toxicity, inadequate efficacy in different tumor clones, and emerging resistance mechanisms.

Therefore, a deep understanding of ADC pharmacology and associated predictive biomarker combinations is required for preclinical evaluation in well-characterized patient-derived xenotransplantation models to select the most promising AdC-based combinations. It is believed that ADC-based combination therapy will show bright prospects in the future.

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Reference:
Antibody-drug conjugates: in search of partners of choice. Trends Cancer.2023 Feb 4