Unlocking the Potential of Arginine Deprivation Therapy: Recent Breakthroughs and Promising Future for Cancer Treatment

Arginine is a semi-essential amino acid that supports protein synthesis to maintain cellular functions. Recent studies suggest that arginine also promotes wound healing, cell division, ammonia metabolism, immune system regulation, and hormone biosynthesis-all of which are critical for tumor growth. These discoveries, coupled with the understanding of cancer cell metabolic reprogramming, have led to renewed interest in arginine deprivation as a new anticancer therapy. Several arginine deprivation strategies have been developed and entered clinical trials. The main principle behind these therapies is that arginine auxotrophic tumors rely on external arginine sources for growth because they carry reduced key arginine-synthesizing enzymes such as argininosuccinate synthase 1 (ASS1) in the intracellular arginine cycle. To obtain anticancer effects, modified arginine-degrading enzymes, such as PEGylated recombinant human arginase 1 (rhArg1-PEG) and arginine deiminase (ADI-PEG 20), have been developed and shown to be safe and effective in clinical trials. They have been tried as a monotherapy or in combination with other existing therapies. This review discusses recent advances in arginine deprivation therapy, including the molecular basis of extracellular arginine degradation leading to tumor cell death, and how this approach could be a valuable addition to the current anticancer arsenal.

A novel combination therapy of arginine deiminase and an arginase inhibitor targeting arginine metabolism in the tumor and immune microenvironment

Tumor progression is dependent on tumor cells and their microenvironment. It is important to identify therapies that inhibit cancer cells and activate immune cells. Arginine modulation plays a dual role in cancer therapy. Arginase inhibition induced an anti-tumor effect via T-cell activation through an increase in arginine in the tumor environment. In contrast, arginine depletion by arginine deiminase pegylated with 20,000-molecular-weight polyethylene glycol (ADI-PEG 20) induced an anti-tumor response in argininosuccinate synthase 1 (ASS1)-deficient tumor cells. ADI-PEG 20 did not cause toxicity to normal immune cells, which can recycle the ADI-degraded product citrulline back to arginine. To target tumor cells and their neighboring immune cells, we hypothesized that the combination of an arginase inhibitor (L-Norvaline) and ADI-PEG 20 may trigger a stronger anticancer response. In this study, we found that L-Norvaline inhibits tumor growth in vivo. Pathway analysis based on RNA-seq data indicated that the differentially expressed genes (DEGs) were significantly enriched in some immune-related pathways. Significantly, L-Norvaline did not inhibit tumor growth in immunodeficient mice. In addition, combination treatment with L-Norvaline and ADI-PEG 20 induced a more robust anti-tumor response against B16F10 melanoma. Furthermore, single-cell RNA-seq data demonstrated that the combination therapy increased tumor-infiltrating CD8⁺ T cells and CCR7⁺ dendritic cells. The increase in infiltrated dendritic cells may enhance the anti-tumor response of CD8⁺ cytotoxic T cells, indicating a potential mechanism for the observed anti-tumor effect of the combination treatment. In addition, populations of immunosuppressive-like immune cells, such as S100a8⁺ S100a9⁺ monocytes and Retnla⁺ Retnlg⁺ TAMs, in tumors were dramatically decreased. Importantly, mechanistic analysis indicated that the processes of the cell cycle, ribonucleoprotein complex biogenesis, and ribosome biogenesis were upregulated after combination treatment. This study implied the possibility of L-Norvaline as a modulator of the immune response in cancer and provided a new potential therapy combined with ADI-PEG 20.

Pegylated arginine deiminase drives arginine turnover and systemic autophagy to dictate energy metabolism

Obesity is a multi-systemic disorder of energy balance. Despite intense investigation, the determinants of energy homeostasis remain incompletely understood, and efficacious treatments against obesity and its complications are lacking. Here, we demonstrate that conferred arginine iminohydrolysis by the bacterial virulence factor and arginine deiminase, arcA, promotes mammalian energy expenditure and insulin sensitivity and reverses dyslipidemia, hepatic steatosis, and inflammation in obese mice. Extending this, pharmacological arginine catabolism via pegylated arginine deiminase (ADI-PEG 20) recapitulates these metabolic effects in dietary and genetically obese models. These effects require hepatic and whole-body expression of the autophagy complex protein BECN1 and hepatocyte-specific FGF21 secretion. Single-cell ATAC sequencing further reveals BECN1-dependent hepatocyte chromatin accessibility changes in response to ADI-PEG 20. The data thus reveal an unexpected therapeutic utility for arginine catabolism in modulating energy metabolism by activating systemic autophagy, which is now exploitable through readily available pharmacotherapy.

Phase 1 trial of ADI-PEG 20 and liposomal doxorubicin in patients with metastatic solid tumors

Background

Arginine depletion interferes with pyrimidine metabolism and DNA damage repair pathways. Preclinical data demonstrated that depletion of arginine by PEGylated arginine deiminase (ADI‐PEG 20) enhanced liposomal doxorubicin (PLD) cytotoxicity in cancer cells with argininosuccinate synthase 1 (ASS1) deficiency. The objective of this study was to assess safety and tolerability of ADI‐PEG 20 and PLD in patients with metastatic solid tumors.

Methods

Patients with advanced ASS1‐deficient solid tumors were enrolled in this phase 1 trial of ADI‐PEG 20 and PLD following a 3 + 3 design. Eligible patients were given intravenous PLD biweekly and intramuscular (IM) ADI‐PEG 20 weekly. Toxicity and efficacy were evaluated according to the Common Terminology Criteria for Adverse Events (version 4.0) and Response Evaluation Criteria in Solid Tumors (version 1.1), respectively.

Results

Of 15 enrolled patients, 9 had metastatic HER2‐negative breast carcinoma. We observed no dose‐limiting toxicities or treatment‐related deaths. One patient safely received 880 mg/m² PLD in this study and 240 mg/m² doxorubicin previously. Treatment led to stable disease in 9 patients and was associated with a median progression‐free survival time of 3.95 months in 15 patients. Throughout the duration of treatment, decreased arginine and increased citrulline levels in peripheral blood remained significant in a majority of patients. We detected no induction of anti‐ADI‐PEG 20 antibodies by week 8 in one third of patients.

Conclusion

Concurrent IM injection of ADI‐PEG 20 at 36 mg/m² weekly and intravenous infusion of PLD at 20 mg/m² biweekly had an acceptable safety profile in patients with advanced ASS1‐deficient solid tumors. Further evaluation of this combination is under discussion.

Phase 1b study of pegylated arginine deiminase (ADI-PEG 20) plus Pembrolizumab in advanced solid cancers

Background

Pegylated arginine deiminase (ADI-PEG 20) is a metabolism-based strategy that depletes arginine, resulting in tumoral stress and cytotoxicity. Preclinically, ADI-PEG 20 modulates T-cell activity and enhances the therapeutic efficacy of programmed death-1 (PD-1) inhibition.

Methods

A phase 1b study, including a dose-escalation cohort and an expansion cohort, was undertaken to explore the effects of ADI-PEG 20 in combination with pembrolizumab, an anti-PD-1 antibody, for safety, pharmacodynamics, and response. CD3 levels and programmed death-ligand 1 (PD-L1) expression were assessed in paired biopsies collected prior to and after ADI-PEG 20 treatment but before pembrolizumab.

Results

Twenty-five patients, nine in the dose-escalation cohort and sixteen in the expansion cohort, were recruited. Treatment was feasible with adverse events consistent with those known for each agent, except for Grade 3/4 neutropenia which was higher than expected, occurring in 10/25 (40%) patients. Mean arginine levels were suppressed for 1-3 weeks, but increased gradually. CD3+ T cells increased in 10/12 (83.3%) subjects following ADI-PEG 20 treatment, including in three partial responders (p = .02). PD-L1 expression was low and increased in 3/10 (30%) of subjects. Partial responses occurred in 6/25 (24%) heavily pretreated patients, in both argininosuccinate synthetase 1 proficient and deficient subjects.

Conclusions

The immunometabolic combination was safe with the caveat that the incidence of neutropenia might be increased compared with either agent alone. ADI-PEG 20 treatment increased T cell infiltration in the low PD-L1 tumor microenvironment. The recommended phase 2 doses are 36 mg/m2 weekly for ADI-PEG 20 and 200 mg every 3 weeks for pembrolizumab.

Phase II Study of Arginine Deprivation Therapy With Pegargiminase in Patients With Relapsed Sensitive or Refractory Small-cell Lung Cancer

BACKGROUND

Pre-clinical studies indicated that arginine-deprivation therapy using pegylated arginine deiminase (pegargiminase, ADI-PEG 20) may be effective in patients with argininosuccinate synthetase 1 (ASS1)-deficient small-cell lung cancer (SCLC).

PATIENTS AND METHODS

Patients were enrolled into either a 'sensitive' disease cohort (≥ 90 days response to first-line chemotherapy) or a 'refractory' disease cohort (progression while on chemotherapy or < 90 days afterwards or ≥ third-line treatment). Patients received weekly intramuscular pegargiminase, 320 IU/m² (36.8 mg/m²), until unacceptable toxicity or disease progression. The primary endpoint was tumor response assessed by Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 with secondary endpoints including tolerability, pharmacodynamics, and immunogenicity.

RESULTS

Between January 2011 and January 2014, 22 patients were enrolled: 9 in the sensitive disease cohort and 13 in the refractory disease cohort. At a pre-planned interim analysis, the best overall response observed was stable disease in 2 patients in each cohort (18.2%). Owing to the lack of response and slow accrual in the sensitive disease cohort, the study was terminated early. Pegargiminase treatment was well-tolerated with no unexpected adverse events or discontinuations.

CONCLUSION

Although pegargiminase monotherapy in SCLC failed to meet its primary endpoint of RECIST-confirmed responses, more recent molecular stratification, including MYC status, may provide new opportunities moving forward.

A phase 1 study of ADI-PEG 20 and modified FOLFOX6 in patients with advanced hepatocellular carcinoma and other gastrointestinal malignancies

PURPOSE

Arginine depletion interferes with pyrimidine metabolism as well as DNA damage repair pathways. Preclinical data indicates that pairing pegylated arginine deiminase (ADI-PEG 20) with fluoropyrimidines or platinum enhances cytotoxicity in vitro and in vivo in arginine auxotrophs.

METHODS

This is a single-center, open-label, phase 1 trial of ADI-PEG 20 and modified FOLFOX6 (mFOLFOX6) in treatment-refractory hepatocellular carcinoma (HCC) and other advanced gastrointestinal tumors. A 3 + 3 dose escalation design was employed to assess safety, tolerability, and determine the recommended phase 2 dose (RP2D) of ADI-PEG 20. A RP2D expansion cohort for patients with HCC was employed to define the objective response rate (ORR). Secondary objectives were to estimate progression-free survival (PFS), overall survival (OS), and to explore pharmacodynamics and immunogenicity. Eligible patients were treated with mFOLFOX6 intravenously biweekly at standard doses and ADI-PEG-20 intramuscularly weekly at 18 (Cohort 1) or 36 mg/m² (Cohort 2 and RP2D expansion).

RESULTS

Twenty-seven patients enrolled-23 with advanced HCC and 4 with other gastrointestinal tumors. No dose-limiting toxicities were observed in cohort 1 or 2. The RP2D for ADI-PEG 20 was 36 mg/m² weekly with mFOLFOX6. The most common any grade adverse events (AEs) were thrombocytopenia, neutropenia, leukopenia, anemia, and fatigue. Among the 23 HCC patients, the most frequent treatment-related Grade ≥ 3 AEs were neutropenia (47.8%), thrombocytopenia (34.7%), leukopenia (21.7%), anemia (21.7%), and lymphopenia (17.4%). The ORR for this group was 21% (95% CI 7.5-43.7). Median PFS and OS were 7.3 and 14.5 months, respectively. Arginine levels were depleted with therapy despite the emergence of low levels of anti-ADI-PEG 20 antibodies. Arginine depletion at 4 and 8 weeks and archival tumoral argininosuccinate synthetase-1 levels did not correlate with response.

CONCLUSIONS

Concurrent mFOLFOX6 plus ADI-PEG-20 intramuscularly at 36 mg/m² weekly shows an acceptable safety profile and favorable efficacy compared to historic controls. Further evaluation of this combination is warranted in advanced HCC patients.

A phase 1/1B trial of ADI-PEG 20 plus nab-paclitaxel and gemcitabine in patients with advanced pancreatic adenocarcinoma

BACKGROUND

ADI-PEG 20 is a pegylated form of the arginine-depleting enzyme arginine deiminase. Normal cells synthesize arginine with the enzyme argininosuccinate synthetase (ASS1); ADI-PEG 20 selectively targets malignant cells, which lack ASS1.

METHODS

A single-arm, nonrandomized, open-label, phase 1/1B, standard 3 + 3 dose escalation with an expansion cohort of 9 patients at the recommended phase 2 dose (RP2D) was conducted. Patients who had metastatic pancreatic cancer, up to 1 line of prior treatment (the dose-escalation cohort) or no prior treatment (the expansion cohort), and an Eastern Cooperative Oncology Group performance status of 0 to 1 were included. Patients received both gemcitabine (1000 mg/m² ) and nab-paclitaxel (125 mg/m² ) for 3 of 4 weeks and intramuscular ADI-PEG 20 at 18 mg/m² weekly (cohort 1) or at 36 mg/m² weekly (cohort 2 and the expansion cohort).The primary endpoint was to determine the maximum tolerated dose and RP2D of ADI-PEG 20 in combination with nab-paclitaxel and gemcitabine.

RESULTS

Eighteen patients were enrolled. No dose-limiting toxicities (DLTs) were observed in cohort 1; cohort 2 was expanded to 6 patients because of 1 DLT occurrence (a grade 3 elevation in bilirubin, aspartate aminotransferase, and alanine aminotransferase). The most frequent adverse events (AEs) of any grade were neutropenia, thrombocytopenia, leukopenia, anemia, peripheral neuropathy, and fatigue; all 18 patients experienced grade 3/4 AEs. The most frequent grade 3/4 toxicities, regardless of the relation with any drugs, included neutropenia (12 patients or 67%), leukopenia (10 patients or 56%), anemia (8 patients or 44%), and lymphopenia (6 patients or 33%). The RP2D for ADI-PEG 20 was 36 mg/m² weekly in combination with standard-dose gemcitabine and nab-paclitaxel. The overall response rate among patients treated at the RP2D in the first-line setting was 45.5% (5 of 11).The median progression-free survival time for these patients treated at the RP2D was 6.1 months (95% confidence interval, 5.3-11.2 months), and the median overall survival time was 11.3 months (95% confidence interval, 6.7 months to not reached).

CONCLUSIONS

ADI-PEG 20 was well tolerated in combination with gemcitabine and nab-paclitaxel. Activity was observed in previously treated and untreated patients with advanced pancreatic cancer and in patients with ASS1-deficient and -proficient tumors. Cancer 2017;123:4556-4565. © 2017 American Cancer Society.