Discovery of novel polyamide-pyrrolobenzodiazepine hybrids for antibody-drug conjugates.

Pyrrolobenzodiazepine (PBD) dimers are well-known highly potent antibody drug conjugate (ADC) payloads. The corresponding PBD monomers, in contrast, have received much less attention from the ADC community. We prepared several novel polyamide-linked PBD monomers and evaluated their utility as ADC payloads. The unconjugated polyamide-PBD hybrids exhibited potent antiproliferative activity (IC50 range: 10-11-10-8 M) against a variety of HER2-expressing cancer cell lines. Several peptide-linked variants of the lead compound were prepared and conjugated to trastuzumab to afford ADCs with drug-to-antibody (DAR) ratios ranging from 3 to 5. The ADCs exhibited antigen-dependent cytotoxicity in vitro and potently suppressed tumor xenograft growth in vivo in a target-dependent manner. Moreover, the ADCs were well-tolerated in both mouse and rat. This work demonstrates for the first time that PBD polyamide hybrids can serve as effective ADC payloads.

ABBV-176, a PRLR antibody drug conjugate with a potent DNA-damaging PBD cytotoxin and enhanced activity with PARP inhibition.

BACKGROUND: Prolactin receptor (PRLR) is an attractive antibody therapeutic target with expression across a broad population of breast cancers. Antibody efficacy, however, may be limited to subtypes with either PRLR overexpression and/or those where estradiol no longer functions as a mitogen and are, therefore, reliant on PRLR signaling for growth. In contrast a potent PRLR antibody-drug conjugate (ADC) may provide improved therapeutic outcomes extending beyond either PRLR overexpressing or estradiol-insensitive breast cancer populations. METHODS: We derived a novel ADC targeting PRLR, ABBV-176, that delivers a pyrrolobenzodiazepine (PBD) dimer cytotoxin, an emerging class of warheads with enhanced potency and broader anticancer activity than the clinically validated auristatin or maytansine derivatives. This agent was tested in vitro and in vivo cell lines and patient derived xenograft models. RESULTS: In both in vitro and in vivo assays, ABBV-176 exhibits potent cytotoxicity against multiple cell line and patient-derived xenograft breast tumor models, including triple negative and low PRLR expressing models insensitive to monomethyl auristatin (MMAE) based PRLR ADCs. ABBV-176, which cross links DNA and causes DNA breaks by virtue of its PBD warhead, also demonstrates enhanced anti-tumor activity in several breast cancer models when combined with a poly-ADP ribose polymerase (PARP) inhibitor, a potentiator of DNA damage. CONCLUSIONS: Collectively the efficacy and safety profile of ABBV-176 suggest it may be an effective therapy across a broad range of breast cancers and other cancer types where PRLR is expressed with the potential to combine with other therapeutics including PARP inhibitors.

A first-in-human, phase 1, dose-escalation study of ABBV-176, an antibody-drug conjugate targeting the prolactin receptor, in patients with advanced solid tumors.

ABBV-176 is an antibody-drug conjugate composed of the humanized antibody h16f (PR-1594804) conjugated to a highly potent, cytotoxic cross-linking pyrrolobenzodiazepine dimer (PBD; SGD-1882) targeting the prolactin receptor (PRLR), which is overexpressed in several solid tumor types. This phase 1, dose-escalation study (NCT03145909) evaluated the safety, pharmacokinetics, and preliminary activity of ABBV-176 in patients with advanced solid tumors likely to exhibit elevated levels of PRLR. Patients received ABBV-176 once every 3 weeks. Dose escalation was by an exposure-adjusted, continual reassessment method. Dose-limiting toxicities (DLTs) were assessed from the first day of dosing until the next dose of ABBV-176 to determine the maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D). Nineteen patients received ABBV-176 at doses from 2.7-109.35 µg/kg. Patients enrolled had colorectal cancer (n = 11), breast cancer (n = 6), or adrenocortical carcinoma (n = 2). DLTs occurred in 4 patients and included thrombocytopenia (n = 2; both at 99.9-µg/kg dose level), neutropenia (n = 2; 78.3-µg/kg and 99.9-µg/kg dose levels), and pancytopenia (n = 1; 109.35-µg/kg dose level). The most common treatment-emergent adverse events related to ABBV-176 were thrombocytopenia, neutropenia, increased aspartate aminotransferase, nausea, fatigue, and pleural effusions. Effusions and edema were common, and timing of onset suggested possible cumulative ABBV-176 toxicity. Tumor expression of PRLR varied among patients enrolled and analyzed. No patient had an objective response. MTD was not formally determined, as identification of a tolerable dose was confounded by late-onset toxicities. ABBV-176 was associated with significant toxicity in this phase 1, dose-escalation study. Although cytopenias were often dose limiting, effusions and edema were also common and had late onset that suggested cumulative toxicity. No responses were observed, although data were available from a small number of patients with variable tumor PRLR expression. This study was terminated after the dosing of 19 patients.

Tamrintamab pamozirine (SC-003) in patients with platinum-resistant/refractory ovarian cancer: Findings of a phase 1 study.

OBJECTIVE: Epithelial ovarian carcinoma (EOC) is diagnosed at advanced stage in the majority of women and, despite being initially chemosensitive, eventually recurs and develops resistance to known therapies. SC-003 is a pyrrolobenzodiazepine-based antibody-drug conjugate targeting dipeptidase 3 (DPEP3), a membrane-bound dipeptidase associated with tumor-initiating cells in patient-derived EOC xenograft models. This first-in-human phase 1a/1b study evaluated the safety/tolerability, pharmacokinetics, and preliminary antitumor activity of SC-003 alone or in combination with budigalimab (formerly ABBV-181), an antibody targeting PD-1, in patients with platinum-resistant/refractory EOC (NCT02539719). METHODS: Patients received SC-003 at 1 of 6 dose levels (0.025-0.4 mg/kg) every 3 weeks (Q3W), utilizing a standard 3 + 3 design (dose-limiting toxicity [DLT] period: 21 days). Patients with DPEP3-positive tumors were enrolled in the dose-expansion phase of the study and treated with SC-003 monotherapy or in combination with budigalimab. RESULTS: Seventy-four patients (n = 29, dose escalation; n = 45, dose expansion; n = 3 budigalimab combination) were enrolled and received ≥1 dose of study drug. One DLT occurred (grade 3 ileus) but was considered unrelated to study drug. The MTD for the Q3W schedule was 0.3 mg/kg and the SC-003 doses selected for the dose-expansion phase of the study were 0.3 mg/kg and 0.2 mg/kg. The most common treatment-emergent adverse events were fatigue, nausea, decreased appetite, pleural effusion, abdominal pain, and peripheral edema. The overall response rate was low (4%), and responses were not durable. Post-hoc examination of antitumor activity suggested a higher response rate in patients with higher DPEP3 expression. CONCLUSIONS: SC-003 lacked the requisite safety profile and antitumor activity to warrant further development.

Design and synthesis of a folate-receptor targeted diazepine-ring-opened pyrrolobenzodiazepine prodrug conjugate.

Pyrrolobenzodiazepines (PBDs) and their dimers (bis-PBDs) have emerged as some of the most potent chemotherapeutic compounds and are currently under development as novel payloads in antibody-drug conjugates (ADCs). However, when used as stand-alone therapeutics or as warheads for small molecule drug conjugates (SMDCs), dose-limiting toxicities are often observed. As an elegant solution to this inherent problem, we designed and synthesized a diazepine-ring-opened bis-PBD prodrug (pro-PBD-PBD) folate conjugate lacking the one of the two imine moieties found in the corresponding free bis-PBD. Upon entering a targeted cell, cleavage of the linker system, including the hydrolysis of an oxazolidine moiety, results in the formation of a reactive intermediate which possesses a newly formed aldehyde as well as an aromatic amine. A fast and spontaneous intramolecular ring-closing reaction subsequently takes place as the aromatic amine adds to the aldehyde with the loss of water to give the imine, and as a result, the diazepine ring, thereby delivering the bis-PBD to the targeted cell. The in vitro and in vivo activity of this conjugate has been evaluated on folate receptor positive KB cells. Sub-nanomolar activity with good specificity and high cure rates with minimal toxicity have been observed.

Synthesis and Biological Evaluation of a Novel C8-Pyrrolobenzodiazepine (PBD) Adenosine Conjugate. A Study on the Role of the PBD Ring in the Biological Activity of PBD-Conjugates.

Here we sought to evaluate the contribution of the PBD unit to the biological activity of PBD-conjugates and, to this end, an adenosine nucleoside was attached to the PBD A-ring C8 position. A convergent approach was successfully adopted for the synthesis of a novel C8-linked pyrrolo(2,1-c)(1,4)benzodiazepine(PBD)-adenosine(ADN) hybrid. The PBD and adenosine (ADN) moieties were synthesized separately and then linked through a pentynyl linker. To our knowledge, this is the first report of a PBD connected to a nucleoside. Surprisingly, the compound showed no cytotoxicity against murine cells and was inactive against Mycobacterium aurum and M. bovis strains and did not bind to guanine-containing DNA sequences, as shown by DNase I footprinting experiments. Molecular dynamics simulations revealed that the PBD-ADN conjugate was poorly accommodated in the DNA minor groove of two DNA sequences containing the AGA-PBD binding motif, with the adenosine moiety of the ligand preventing the covalent binding of the PBD unit to the guanine amino group of the DNA duplex. These interesting findings shed further light on the ability of the substituents attached at the C8 position of PBDs to affect and modulate the biological and biophysical properties of PBD hybrids.

A phase 1 trial of SGN-CD70A in patients with CD70-positive diffuse large B cell lymphoma and mantle cell lymphoma.

Purpose This first-in-human study evaluated SGN-CD70A, an antibody-drug conjugate (ADC) directed against the integral plasma membrane protein CD70 and linked to a pyrrolobenzodiazepine (PBD) dimer, in patients with relapsed or refractory (R/R) CD70-positive non-Hodgkin lymphoma (NHL) including diffuse large B cell lymphoma (DLBCL), mantle cell lymphoma (MCL), and Grade 3b follicular lymphoma (FL3b). Methods SGN-CD70A was administered intravenously on Day 1 of 3-week cycles beginning at 8 mcg/kg with planned dose escalation to 200 mcg/kg. Due to observations of prolonged thrombocytopenia, the study was amended to dose every 6 weeks (q6wk). Results Twenty patients were enrolled and treated with SGN-CD70A. The maximum tolerated dose of SGN-CD70A was 30 mcg/kg q6wk. The most common adverse events (AEs) reported were thrombocytopenia (75%), nausea (55%), anemia (50%), and fatigue (50%). The onset for treatment-related thrombocytopenia typically occurred during Cycle 1. Most of the treatment-related events of thrombocytopenia were ≥ Grade 3. Antitumor activity in patients included 1 complete remission (CR) and 3 partial remissions (PRs), 2 of which were ongoing for at least 42.9 weeks. SGN-CD70A exposures were approximately dose proportional, with a mean terminal half-life of 3 to 5 days. Conclusions While modest single-agent activity was observed in heavily pretreated NHL patients, the applicability of SGN-CD70A is limited by the frequency and severity of thrombocytopenia, despite the long-term response with limited drug exposure.

An FDA oncology analysis of toxicities associated with PBD-containing antibody-drug conjugates.

With a new generation of antibody-drug conjugates (ADCs) that contain a drug-to-antibody ratio (DAR) of 2, the question remains whether advances in technology have resulted in more stable and tumor-specific ADCs. These ADCs are anticipated to cause minimal systemic exposures of payloads, with toxicities being evident mainly at tumor sites. We examined 15 ADCs with PBD-dimer payloads and a DAR of 2 and concluded that dose limiting toxicities in animals and in humans are generally related to the payload. Both the payloads and the ADCs had pro-inflammatory responses causing severe toxicities that were at times of low incidence, making it difficult to assess a cause-effect relationship. Due to their low incidence, single-patient cohorts may not detect these events and such design may not be suitable in first-in-human (FIH) trials. The commonly proposed approach by the sponsors for FIH dose selection was 1/6th highest non-severely toxic dose (HNSTD) in monkeys. This approach resulted in an acceptable balance of safety and efficient dose escalation in phase 1 trials, when using data from repeat-dose toxicology studies and body surface area for scaling. No sponsor used the data generated in rodents or proposed novel approaches for FIH dose selection.

Exploration of Pyrrolobenzodiazepine (PBD)-Dimers Containing Disulfide-Based Prodrugs as Payloads for Antibody-Drug Conjugates.

A number of cytotoxic pyrrolobenzodiazepine (PBD) monomers containing various disulfide-based prodrugs were evaluated for their ability to undergo activation (disulfide cleavage) in vitro in the presence of either glutathione (GSH) or cysteine (Cys). A good correlation was observed between in vitro GSH stability and in vitro cytotoxicity toward tumor cell lines. The prodrug-containing compounds were typically more potent against cells with relatively high intracellular GSH levels (e.g., KPL-4 cells). Several antibody-drug conjugates (ADCs) were subsequently constructed from PBD dimers that incorporated selected disulfide-based prodrugs. Such HER2 conjugates exhibited potent antiproliferation activity against KPL-4 cells in vitro in an antigen-dependent manner. However, the disulfide prodrugs contained in the majority of such entities were surprisingly unstable toward whole blood from various species. One HER2-targeting conjugate that contained a thiophenol-derived disulfide prodrug was an exception to this stability trend. It exhibited potent activity in a KPL-4 in vivo efficacy model that was approximately three-fold weaker than that displayed by the corresponding parent ADC. The same prodrug-containing conjugate demonstrated a three-fold improvement in mouse tolerability properties in vivo relative to the parent ADC, which did not contain the prodrug.

Synthesis of a heterotrifunctional linker for the site-specific preparation of antibody-drug conjugates with two distinct warheads.

Codelivery of multiple therapeutic agents with different anticancer mechanisms can overcome drug resistance as well as generate additive or synergistic anticancer effects that may enhance the antitumor efficacy. Antibody-drug conjugates (ADCs) can be used for highly specific delivery of multiple therapeutic agents with different anticancer mechanisms, though more research is required towards designing flexible platforms on which dual drug ADCs could be prepared. Herein, we describe the synthesis of a heterotrifunctional linker that could be used to construct flexible platforms for preparing dual-cytotoxic drug conjugates in a site-specific manner. As a proof of concept, we synthesized dual drug ADCs carrying monomethyl auristain E (MMAE, tubulin polymerization inhibitor) and pyrrolobenzodiazepine dimer (PBD, DNA minor groove alkylator). We then evaluated the dual drug ADCs for in vitro efficacy and confirmed the dual mechanism of action.

A Brief Introduction to Antibody-Drug Conjugates for Toxicologic Pathologists.

Antibody-drug conjugates (ADCs) are an emerging class of anticancer therapeutics, delivering highly cytotoxic molecules directly to cancer cells. ADCs are composed of an antibody, a small molecule drug, and a linker attaching one to another. Antibodies are directed to a large variety of antigens overexpressed on tumor cells, tumor vasculature, or tumor-supporting stroma. After internalization, the ADC is transferred to lysosomes where the cytotoxic component is released, finally killing the target cell. All ADCs are administered via intravenous injection. Once in the circulation, linker stability in plasma is of high importance. In vivo studies in animals address the release of payload over time and typically measure total antibody, conjugated ADC, and free drug. ADC development is driven by ICH (International Council for Harmonisation) guidelines S6(R1) and S9. Dose-limiting toxicities of current ADCs are mainly associated with the payload and correlate well between clinical trials and nonclinical studies in rodents and nonrodents. This mini review is intended to provide general information about ADCs in oncology and shall assist the toxicologic pathologist in correctly interpreting morphological findings acquired in toxicity studies with this entity.

Efficient Preparation of Site-Specific Antibody-Drug Conjugates Using Cysteine Insertion.

Antibody-drug conjugates (ADCs) are a class of biopharmaceuticals that combine the specificity of antibodies with the high-potency of cytotoxic drugs. Engineering cysteine residues in the antibodies using mutagenesis is a common method to prepare site-specific ADCs. With this approach, solvent accessible amino acids in the antibody have been selected for substitution with cysteine for conjugating maleimide-bearing cytotoxic drugs, resulting in homogeneous and stable site-specific ADCs. Here we describe a cysteine engineering approach based on the insertion of cysteines before and after selected sites in the antibody, which can be used for site-specific preparation of ADCs. Cysteine-inserted antibodies have expression level and monomeric content similar to the native antibodies. Conjugation to a pyrrolobenzodiazepine dimer (SG3249) resulted in comparable efficiency of site-specific conjugation between cysteine-inserted and cysteine-substituted antibodies. Cysteine-inserted ADCs were shown to have biophysical properties, FcRn, and antigen binding affinity similar to the cysteine-substituted ADCs. These ADCs were comparable for serum stability to the ADCs prepared using cysteine-mutagenesis and had selective and potent cytotoxicity against human prostate cancer cells. Two of the cysteine-inserted variants abolish binding of the resulting ADCs to FcγRs in vitro, thereby potentially preventing non-target mediated uptake of the ADCs by cells of the innate immune system that express FcγRs, which may result in mitigating off-target toxicities. A selected cysteine-inserted ADC demonstrated potent dose-dependent anti-tumor activity in a xenograph tumor mouse model of human breast adenocarcinoma expressing the oncofetal antigen 5T4.

Design, synthesis, and biological evaluation of pyrrolobenzodiazepine-containing hypoxia-activated prodrugs.

The ability of various pyrrolobenzodiazepine(PBD)-containing cytotoxic compounds to function as hypoxia-activated prodrugs was assessed. These molecules incorporated a 1-methyl-2-nitro-1H-imidazole hypoxia-activated trigger (present in the clinically evaluated compound TH-302) in a manner that masked a reactive imine moiety required for cytotoxic activity. Incubation of the prodrugs with cytochrome P450-reductase under normoxic and hypoxic conditions revealed that some, but not all, were efficient substrates for the enzyme. In these experiments, prodrugs derived from PBD-monomers underwent rapid conversion to the parent cytotoxic compounds under low-oxygen conditions while related PBD-dimers did not. The ability of a given prodrug to function as an efficient cytochrome P450-reductase substrate correlated with the ratio of cytotoxic potencies measured for the compound against NCI460 cells under normoxic and hypoxic conditions.

Synthesis and in vitro evaluation of SG3227, a pyrrolobenzodiazepine dimer antibody-drug conjugate payload based on sibiromycin.

A novel pyrrolobenzodiazepine dimer payload, SG3227, was rationally designed based on the naturally occurring antitumour compound sibiromycin. SG3227 was synthesized from a dimeric core in an efficient fashion. An unexpected room temperature Diels-Alder reaction occurred during the final step of the synthesis and was circumvented by use of an iodoacetamide conjugation moiety in place of a maleimide. The payload was successfully conjugated to trastuzumab and the resulting ADC exhibited potent activity against a HER2-expressing human cancer cell line in vitro.

The use of molecular dynamics simulations to evaluate the DNA sequence-selectivity of G-A cross-linking PBD-duocarmycin dimers.

The pyrrolobenzodiazepine (PBD) and duocarmycin families are DNA-interactive agents that covalently bond to guanine (G) and adenine (A) bases, respectively, and that have been joined together to create synthetic dimers capable of cross-linking G-G, A-A, and G-A bases. Three G-A alkylating dimers have been reported in publications to date, with defined DNA-binding sites proposed for two of them. In this study we have used molecular dynamics simulations to elucidate preferred DNA-binding sites for the three published molecular types. For the PBD-CPI dimer UTA-6026 (1), our simulations correctly predicted its favoured binding site (i.e., 5'-C(G)AATTA-3') as identified by DNA cleavage studies. However, for the PBD-CI molecule ('Compound 11', 3), we were unable to reconcile the results of our simulations with the reported preferred cross-linking sequence (5'-ATTTTCC(G)-3'). We found that the molecule is too short to span the five base pairs between the A and G bases as claimed, but should target instead a sequence such as 5'-ATTTC(G)-3' with two less base pairs between the reacting G and A residues. Our simulation results for this hybrid dimer are also in accord with the very low interstrand cross-linking and in vitro cytotoxicity activities reported for it. Although a preferred cross-linking sequence was not reported for the third hybrid dimer ('27eS', 2), our simulations predict that it should span two base pairs between covalently reacting G and A bases (e.g., 5'-GTAT(A)-3').

Analogues of DNA minor groove cross-linking agents incorporating aminoCBI, an amino derivative of the duocarmycins: Synthesis, cytotoxicity, and potential as payloads for antibody-drug conjugates.

A Pd-catalysed amination method is used to convert seco-CBI, a synthetic analogue of the alkylating subunit of the duocarmycin natural products, from the phenol to amino form. This allows efficient enantioselective access to the more potent S enantiomer of aminoCBI and its incorporation into analogues of DNA minor groove cross-linking agents. Evaluation in a panel of nine human tumour cell lines shows that the bifunctional agents containing aminoCBI are generally less cytotoxic than their phenolCBI analogues and more susceptible to P-glycoprotein-mediated resistance. However, all bifunctional agents are potent cytotoxins, some in the sub-pM IC50 range, with in vitro properties that compare favourably with established microtubule-targeted ADC payloads.

Dithiocarbamate/piperazine bridged pyrrolobenzodiazepines as DNA-minor groove binders: synthesis, DNA-binding affinity and cytotoxic activity.

A new series of C8-linked dithiocarbamate/piperazine bridged pyrrolo[2,1-c][1,4]benzodiazepine conjugates (5a-c, 6a,b) have been synthesized and evaluated for their cytotoxic potential and DNA-binding ability. The representative conjugates 5a and 5b have been screened for their cytotoxicity against a panel of 60 human cancer cell lines. Compound 5a has shown promising cytotoxic activity on selected cancer cell lines that display melanoma, leukemia, CNS, ovarian, breast and renal cancer phenotypes. The consequence of further replacement of the 3-cyano-3,3-diphenylpropyl 1-piperazinecarbodithioate in 5b and 5c with 4-methylpiperazine-1-carbodithioate yielded new conjugates 6a and 6b respectively. In addition, the compounds 5c and 6a,b have been evaluated for their in vitro cytotoxicity on some of the selected human cancer cell lines and these conjugates have exhibited significant cytotoxic activity. Further, the DNA-binding ability of these new conjugates has been evaluated by using thermal denaturation (ΔTm) studies. The correlation between structure and DNA-binding ability has been investigated by molecular modeling studies which predicted that 6b exhibits superior DNA-binding ability and these are in agreement with the experimental DNA-binding studies.

Boseongazepines A-C, pyrrolobenzodiazepine derivatives from a Streptomyces sp. 11A057.

Three new pyrrolobenzodiazepine derivatives, boseongazepines A-C (1-3), were isolated from a culture broth of Streptomyces sp. 11A057, together with the known compound usabamycin B (4). The structures of 1-4 were determined through the analysis of spectroscopic data including extensive 1D-, 2D-NMR, and MS techniques. Cell growth inhibition effects of these compounds were evaluated against Jurkat, K-562, HL-60, and HepG2 cell lines.

An ultrasound assisted, ionic liquid-molecular iodine synergy driven efficient green synthesis of pyrrolobenzodiazepine-triazole hybrids as potential anticancer agents.

Herein, we report an efficient and eco-friendly, ultrasound assisted synthetic strategy for the construction of diversified pyrrolobenzodiazepine-triazole hybrids, which are potentially pharmaceutically important scaffolds, via a domino reaction involving intermolecular electrophilic substitution followed by intramolecular Huisgen 1,3-dipolar azide-alkyne cycloaddition. The USP of the reported protocol is the use of benign and inexpensive, recyclable molecular iodine-ionic liquid synergistic catalytic system cum reaction media for achieving the synthesis. The other salient features of this method are the use of mild reaction conditions, high yield and atom economy, operational simplicity, broad substrate scope and easy workup and purification. All the synthesized compounds were evaluated for in vitro anti-proliferative activity against various cancer cell lines. From among the synthesized title compounds, 9,9-dimethyl-8-phenyl-9H-benzo [b]pyrrolo [1,2-d][1,2,3]triazolo[5,1-g][1,4]diazepine (7) was found most to be the most active compound exhibiting IC50 value of 6.60, 5.45, 7.85, 11.21, 12.24, 10.12, and 11.32 µM against MCF-7, MDA-MB-231, HeLa, SKOV-3, A549, HCT-116 and DLD-1 cell lines, respectively. Further the compounds were found to be non-toxic against normal human embryonic kidney (HEK-293) cell line.

Population pharmacokinetics analysis of camidanlumab tesirine in patients with relapsed or refractory Hodgkin lymphoma and non-Hodgkin lymphoma.

PURPOSE: The objective of this analysis was to develop a population pharmacokinetic (PPK) model to characterize camidanlumab tesirine (Cami) pharmacokinetics based on the phase 1 study in relapsed/refractory lymphoma (NCT02432235). METHODS: An initial PPK model was developed based on a two-compartment model with parallel linear and nonlinear elimination pathways. Pharmacokinetic parameters were evaluated for correlation with potential demographic covariates; significant covariates were retained in the final model. RESULTS: In the final PPK model, baseline weight effects were included on clearance (CL), intercompartmental clearance (Q), and the volumes of distribution in the central (V1) and peripheral (V2) compartments. The baseline soluble CD25 (sCD25) effect was included on CL and maximum velocity of saturable clearance (Vmax); sex effect was included on CL and V1; and ethnicity effect was included on deconjugation clearance (CLdec). For a typical patient, CL and CLdec were 0.516 and 0.21 L/day, respectively (tAb elimination half-life: 18.72 days); V1 and V2 were 4.41 and 2.67 L, respectively; Vmax was 0.49 mg/day; the Michaelis-Menten constant (Km) was 0.409 µg/mL; and the first-order rate for decrease of Vmax (KDES) was 0.0197/day. Cami exposure was higher for patients with low baseline sCD25, higher body weight, and females. CONCLUSIONS: The final model described the observed data well, estimates of PK parameters were obtained, and covariates with significant effects on Cami exposure were identified. Altogether, this final PPK model provides a robust basis for analysis of Cami exposure-response relationships and further supports identification of the optimal Cami dosing schedule for patients with relapsed/refractory lymphoma.