JP2017081915A - Antitumor agents - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a betulin derivative having water solubility and antitumor effect higher than those of betulin.SOLUTION: An antitumor agent contains as an active ingredient a betulin derivative represented by formula (1) and/or a pharmaceutically acceptable salt thereof [n1 and n2 are each independently 1 or 2].SELECTED DRAWING: None

Description

  The present invention relates to an antitumor agent.

In the local area of cancer, various immunosuppressive factors (TGF-β, PGE ₂ etc.) secreted from cancer cells are intertwined and an immunosuppressive environment is formed. In recent years, it has been found that this is a factor that reduces the therapeutic effect of cancer treatment, particularly cancer immunotherapy. Therefore, a drug that effectively blocks the action of an immunosuppressive factor is required to improve the therapeutic effect. In this research, in order to solve the above-mentioned problems, we started a search for substances that release (block) the function of “immunosuppressive factors”.

In order to find a compound exhibiting a release action against immunosuppression, the present inventors previously screened about 800 kinds of natural products using as an index the cancer cytotoxic activity of mouse NK cells suppressed by TGF-β or PGE _2. did. As a result, the target effectiveness was found for betulin, a white birch component. Although betulin was a known compound, no immunosuppressive release action has been reported, and a patent application was filed because it may be a cancer drug based on a new mechanism of action (May 2014) 30th Patent registration, Patent Document 1).

Japanese Patent No. 5548874

  By the way, since betulin is very difficult to dissolve in water, the absorption in the gastrointestinal tract and the transfer to blood are extremely low in the mouse body, and there is a concern that the blood concentration does not reach the effective range. In fact, LC / MS / MS analysis shows that orally administered betulin is hardly absorbed from the gastrointestinal tract and is hardly detected in blood even when administered intravenously. It has been clarified that the antitumor effect is only about 50%. For this reason, in order to obtain higher effectiveness in animal experiments, it was necessary to develop a derivative that is easily soluble in water and has good blood transportability.

  Therefore, an object of the present invention is to find a betulin derivative having higher water solubility and antitumor effect than betulin and to provide an excellent antitumor agent.

  The present inventors synthesized 82 kinds of betulin derivatives to achieve the above-mentioned object, and compared the effectiveness of 53 main derivatives using a mouse model for cancer transplantation. More specifically, various betulin derivatives with improved water solubility compared to betulin were synthesized, and their effects on tumor suppression in cancer transplanted mouse models and cytotoxicity against cancer cells in vitro were compared and evaluated. . As a result, a remarkable inhibitory action was recognized in the derivative (BD-17) added with succinic acid at the 3rd and 28th positions of betulin and the derivative added with malonic acid (TPU-29), thereby completing the present invention.

  According to the present invention, it is possible to provide an excellent antitumor agent comprising a betulin derivative having higher water solubility and antitumor effect than betulin as an active ingredient.

The antitumor effect of betulin and a betulin derivative (BD-17) is shown. The influence of betulin or betulin derivative (BD-17) on the proliferation ability of cancer cells is shown. Fig. 2 shows the antitumor effect of a betulin derivative (BD-17) in Scid mice. The antitumor effect of a control and a betulin derivative (TPU-29) is shown. The influence of a betulin derivative (TPU-29) on the proliferation ability of cancer cells is shown.

  The present invention relates to an antitumor agent comprising a betulin derivative represented by the following general formula (1) and / or a pharmaceutically acceptable salt thereof as an active ingredient.

(In the formula, n1 and n2 are independently 1 or 2.)

  The present inventors have added amino acids (glycine, phenylalanine, tryptophan, serine, tyrosine, lysine, histidine, aspartic acid), organic acids (benzoic acid), or other amino acids at one or both of positions 3 and 28 of betulin. 89 types of derivatives with functional groups were synthesized, and cytotoxicity in vitro was compared with that of betulin using cancer cells. As a result, the compound BD-17 in which n1 and n2 in the general formula (1) are 2 and the compound TPU-29 in which n1 and n2 in the general formula (1) are 1 are excellent in water solubility, and Specifically, it showed a remarkable cancer suppression effect, and it was found that the cytotoxicity was significantly lower than that of betulin. Furthermore, when the involvement of the immune system in the cancer suppressive effects of these compounds BD-17 and TPU-29 was examined, it was revealed that the acquired immune system greatly contributed, and the compounds BD-17 and TPU- It was also revealed that 29 cancer-suppressing effects involve the acquired immune system.

Compound BD-17 in which n1 and n2 in formula (1) are 2, and the following formula shows the 3rd and 28th positions of the main skeleton of betulin.

Compound TPU-29 in which n1 and n2 in general formula (1) are 1
Methods for the synthesis of compounds BD-17 and TPU-29 are described in Examples 1 and 2.

  The present invention also includes a compound in which n1 in the general formula (1) is 1 and n2 is 2 and a compound in which n1 in the general formula (1) is 2 and n2 is 1. It can be synthesized by reacting betulin with an esterifying agent under appropriate reaction conditions to esterify position 28, protecting the carboxylic acid site, and further reacting with the esterifying agent, followed by deprotection. These compounds can be appropriately synthesized with reference to the methods described in Examples 1 and 2.

  In this specification, a basic salt is mentioned as a pharmaceutically acceptable salt. Basic salts include alkali metal salts, alkaline earth metal salts, transition metal salts, ammonium salts, aliphatic amine salts, aralkylamine salts, heterocyclic aromatic amine salts, quaternary ammonium salts, basic amino acid salts, etc. Is mentioned. Specifically, lithium salt, sodium salt, potassium salt, calcium salt, magnesium salt, barium salt, zinc salt, iron salt, ammonium salt, trimethylamine salt, triethylamine salt, dicyclohexylamine salt, ethanolamine salt, diethanolamine salt, Ethanolamine salt, ethylenediamine salt, meglumine salt, procaine salt, N, N-dibenzylethylenediamine, pyridine salt, picoline salt, quinoline salt, isoquinoline salt, tetramethylammonium salt, tetraethylammonium salt, benzyltrimethylammonium salt, benzyltriethylammonium salt Salt, benzyltributylammonium salt, methyltrioctylammonium salt, tetrabutylammonium salt, arginine salt, lysine salt and the like are used.

  In addition, the compound represented by the general formula (1) and a pharmaceutically acceptable salt thereof can include a solvate, and the solvate is an organic solvate that coordinates an arbitrary number of organic solvent molecules. And hydrates that coordinate any number of water molecules. In the present specification, the “solvate” means, for example, a solvate of the compound represented by the general formula (1) or a pharmaceutically acceptable salt thereof, for example, 1 organic solvate, 2 organic Solvates, monohydrates, dihydrates, 2.5 hydrates, heptahydrates and the like can be mentioned. In addition, pharmaceutically acceptable salts and solvates thereof can be synthesized according to known methods.

  The antitumor agent of the present invention can contain a pharmaceutically acceptable carrier in addition to the betulin derivative of the general formula (1) and the like. Pharmaceutically acceptable carriers that can be used in the antitumor agents of the present invention include ion exchangers, alumina, aluminum stearate, lecithin, serum proteins such as human serum albumin, buffer substances such as phosphate, glycine. , Sorbic acid, potassium sorbate, partial glyceride mixture of saturated vegetable fatty acids, water, salt, or electrolytes such as protamine sulfate, disodium hydrogen phosphate, potassium hydrogen phosphate, sodium chloride, zinc salt, colloidal silica, trisilicate Examples include magnesium acid, polyvinylpyrrolidone, cellulose-based materials, polyethylene glycol, sodium carboxymethylcellulose, polyacrylates, waxes, polyethylene-polyoxypropylene-block polymers, polyethylene glycols and wool oils. But it is not limited to, et al.

  The antitumor agents of the present invention can be administered orally, parenterally, by inhalation spray, topically, rectally, nasally, buccally, vaginally or via an implanted reservoir. As used herein, “parenteral” includes subcutaneous, intravenous, intramuscular, intraarticular, intrasynovial, intrasternal, intrathecal, intrahepatic, intralesional and intracranial infusion or infusion techniques. Preferably, the composition is administered orally, intraperitoneally or intravenously.

  The antitumor agents of the invention can be administered orally in any orally acceptable dosage form including, but not limited to, capsules, tablets, aqueous suspensions or solutions. In the case of tablets for oral use, carriers that are commonly used include lactose and corn starch. A lubricant such as magnesium stearate is also typically added. Useful diluents for oral administration in capsule form include lactose and dried corn starch. When aqueous suspensions are required for oral use, the active ingredient is combined with emulsifying and suspending agents. If desired, certain sweetening, flavoring, or coloring agents can also be added.

  Alternatively, the antitumor agent of the present invention can be administered in the form of a suppository for rectal administration. These can be prepared by mixing the drug with a suitable non-irritating excipient that is solid at room temperature but liquid at the rectal temperature and, therefore, melts in the rectum to release the drug. . Such materials include cocoa butter, beeswax and polyethylene glycols.

  The anti-tumor agents of the present invention can be administered locally, especially when the target of treatment comprises a region or organ that is easily accessible by topical administration, including diseases of the eye, skin, or lower intestinal tract. Appropriate topical formulations are readily prepared for each of these areas or organs.

  Topical application for the lower intestinal tract can be effected in a rectal suppository formulation (see above) or in a suitable enema formulation. Topical transdermal patches can also be used.

  For topical application, the compositions may be formulated in a suitable ointment containing the active component suspended or dissolved in one or more carriers. Carriers for topical administration of the betulin derivative of the general formula (1) of the present invention include mineral oil, liquid paraffin, white petrolatum, propylene glycol, polyoxyethylene, polyoxypropylene compound, emulsified wax and water, It is not limited to these. Alternatively, the composition can be formulated in a suitable lotion or cream containing the active ingredient suspended or dissolved in one or more pharmaceutically acceptable carriers. Suitable carriers include, but are not limited to, mineral oil, sorbitan monostearate, polysorbate 60, cetyl ester wax, cetearyl alcohol, 2-octyldodecanol, benzyl alcohol and water.

  For ophthalmic applications, the composition can be prepared as a pulverized suspension in isotonic, pH-adjusted sterile saline, or preferably as a solution in isotonic, pH-adjusted saline, such as benzalkonium chloride. May be formulated with or without a preservative. Alternatively, for ophthalmic use, the composition may be formulated in an ointment such as petrolatum.

  The antitumor agents of the invention may also be administered by nasal aerosol or inhalation. Such compositions are prepared according to techniques well known in the art of pharmaceutical formulation and include benzyl alcohol or other suitable preservatives, absorption enhancers to enhance bioavailability, fluorocarbons, and / or other conventional May be prepared as a solution in saline using a solubilizing or dispersing agent.

The administration regime (ie, formulation and / or dose and / or administration protocol) for the anti-tumor agent of the present invention can be appropriately selected. For example, the schedule and dose for administration of the antitumor agent of the present invention are appropriately determined according to individual cases in consideration of the age, weight, sex, disease difference, symptom level, route of administration, etc. of the patient. However, it can be delivered at a concentration of 10 mg / mL, for example, in either a 100 mg (10 mL) or 500 mg (50 mL) single use vial. The product is not limited as long as it is generally used as an isotonic agent, pH adjuster, and solubilizer. For example, sodium chloride, sodium citrate, and polysorbate 80 are used. Formulated for intravenous administration in sterile water for injection. The pH is adjusted to 3-8. An exemplary suitable dose range for the betulin derivative of general formula (1) in the antitumor agent of the present invention is about 10 mg / m ^{2 to} 500 mg / m ² , preferably about 20 mg / m ^{2 to} 300 mg / m ^2. It can be. This is administered once or divided into several times a day. However, these schedules are exemplary, and optimal schedules and regimens must be determined in clinical trials. General formula (1) in the antitumor agent of the present invention that saturates all immune cells involved in the efficacy of NK cells, T cells, or other immunotherapeutic agents for 24 hours, 48 hours, 72 hours, or 1 week or 1 month The amount and schedule of injection of the betulin derivative are appropriately determined. Therefore, the preferred dosage ranges, formulations and schedules described above are not intended to limit the invention in any way.

  For example, many therapeutic agents are available for the treatment of cancer. The anti-tumor agents and methods of the present invention may be used in conjunction with any other method commonly used in the treatment of specific diseases, specific tumors, cancer diseases, or other diseases or other disorders that patients present. Unless a particular therapeutic approach is known to be detrimental to the patient's condition itself and does not significantly interfere with the activity of the betulin derivative of general formula (1) in the pharmaceutical composition of the present invention, Is considered.

  In connection with the treatment of solid tumors, the anti-tumor agents of the present invention may be used in combination with classic approaches such as surgery, radiation therapy, chemotherapy and the like. Thus, the present invention provides that the pharmaceutical composition of the present invention is used simultaneously, before, or after surgery or radiotherapy; or conventional chemotherapy, radiotherapeutic or anti-angiogenic agents or targeted immunization A combination therapy is provided that is administered to a patient before or after with a toxin or coaguligand.

  When one or more drugs are used in combination with an anti-tumor agent of the present invention in a therapeutic regimen, the combined results require the addition of the effects observed when each treatment is performed individually Does not exist. Although at least an additive effect is generally desired, an increased anticancer effect over one of a single treatment may be beneficial. There is also no specific requirement for the combined treatment to show a synergistic effect, but this is definitely possible and advantageous.

  In order to practice combined anti-cancer treatment, the anti-tumor agent of the present invention is simply administered to a patient in combination with another anti-cancer agent in an effective manner that produces a combined anti-cancer action within the patient. Thus, the agents are provided in an amount effective as long as they exist in a combined form within the vasculature of the tumor and are effective in their combined action in the tumor environment. To achieve this goal, the anticancer agents of the invention can be administered to a patient simultaneously, either as a single combined composition or as two different compositions using different routes of administration. .

  For surgery, any surgical intervention can be practiced in combination with the anti-tumor agent of the present invention. For radiation therapy, any mechanism that induces DNA damage locally in cancer cells is considered, such as gamma radiation, X-rays, UV radiation, microwaves and electron radiation. Directed delivery of radioisotopes to cancer cells is also contemplated and can be used in conjunction with targeted antibodies or other targeting means.

  Cancer treatment has so far been centered on three major therapies: surgery, radiation therapy, and anticancer drug therapy. In particular, treatments that focus solely on killing cancer cells with high-dose anticancer drugs are expected to be effective, but with significant side effects and greatly reducing patient quality of life (QOL). Has often been viewed as a problem.

  In this respect, the betulin derivative of the general formula (1) found in this study shows remarkable efficacy through the immune system in a mouse model transplanted with cancer, and shows little cytotoxicity since it shows little cytotoxicity. Reduction can be expected.

  More specifically, considering that the acquired immune system is involved in the antitumor effects of BD-17 and TPU-29, cancer therapeutic agents that are involved in the efficacy of the acquired immune system, such as immune checkpoint inhibition Agents (antibody drugs and low molecular weight compounds that inhibit the action of immunosuppressive molecules such as PD-1, PD-L1, PD-L2, CTLA-4, TIM-3, LAG-3, B7-H5, TIGIT), Control of immunosuppressive factor inhibitors (antibody drugs and low molecular weight compounds that inhibit immunosuppressive effects such as TGF-β, prostaglandin E2, VEGF, indoleamine-2,3-dioxygenase-1), anti-CCR4 antibodies, etc. BD-17 and TPU have anti-tumor effects such as drugs that remove sexual T cells, drugs that activate anti-tumor immunity such as anti-CD137 antibody and anti-OX40 antibody, cancer vaccine, cancer antigen-specific T cell transfer therapy, etc. It can be expected that betulin derivatives of general formula (1) such as -29 will be synergistically enhanced.

  Hereinafter, the present invention will be described in more detail based on examples. However, the examples are illustrative of the present invention, and the present invention is not intended to be limited to the examples.

Example 1
<experimental method>
The synthetic melting point (mp) of the betulin derivative (BD-17) was measured using a Yanagimoto melting point measuring device, and the values are uncorrected. Specific rotation ([α]) was measured by Atago using sodium D line. ¹ H and ¹³ C NMR spectra were measured using AVANCE II 400 from Bruker Biospin. The chemical shift value (ppm) was tetramethylsilane or residual proton in the measurement solvent as an internal standard, and the spin coupling constant was indicated by J value (Hz). IR spectrum (ATR-IR) was measured using Spectrum 100 manufactured by PerkinElmer. LRMS and HRMS were measured using a micrOTOF focus manufactured by Burker Dartonics. All of the reaction was monitored using a Merck-made silica gel 60F _254. For column chromatography, silica gel 60N (63-210 mm) manufactured by Kanto Chemical was used.

<3,28-bis [(3-carboxypropanoyl) oxy] betulin (BD-17)>
Betulin (1, 0.50 g, 1.13 mmol) and DMAP (19.5 mg, 0.16 mmol) were dissolved in pyridine (20 mL), succinic anhydride (1.13 g, 11.3 mmol) was added to this solution, The mixture was stirred at 85 ° C. (oil bath) for 24 hours. After confirming the disappearance of betulin by TLC, the solution was cooled with ice and water (250 mL) was added. The solution was acidified with 10% hydrochloric acid and extracted with benzene. All organic layers were washed with water, 5% hydrochloric acid and saturated brine in that order and dried over sodium sulfate. The desiccant was removed by filtration, and the filtrate was distilled off under reduced pressure. The residue was purified by silica gel column chromatography (10% MeOH in CHCl ₃ ) to obtain the target compound (BD-17) as pale orange crystals in 639 mg (88%). The instrumental spectrum of the obtained compound was in good agreement with the literature values.

Rf = 0.33 (10% MeOH in CHCl ₃ ) .Mp = 110-112 ° C (EtOAc). ¹ H NMR (400 MHz, CDCl ₃ ) δ (ppm) = 0.62-1.80 (44H, m), 1.90 (1H, m), 2.37 (1H, dt, J = 10.8 and 10.0 Hz), 2.57-2.70 (7H, m), 3.84 (1H, d, J = 10.8 Hz), 4.27 (1H, d, J = 10.4 Hz), 4.46 (1H, dd, J = 16.4 and 9.2 Hz), 4.56 (1H, s), 4.66 (1H, d, J = 1.6 Hz). ¹³ C NMR (125 MHz, CDCl ₃ ) δ (ppm) = 12.6, 15.0, 16.2, 16.4, 16.7, 18.4, 19.3, 21.0, 23.2, 23.8, 25.4, 27.2, 28.1, 29.3, 29.6, 29.8, 29.9, 34.3, 34.6, 37.3, 37.8, 38.0, 38.6, 41.1, 42.9, 46.6, 47.9, 49.0, 50.5, 55.6, 63.4, 81.8, 110.1, 150.3, 172.0, 172.6, 178.2. ATR-IR ν (cm ^-1 ) = 2942, 2872, 1730, 1709, 1642, 1452, 1390, 1363, 1235, 1159, 1106, 1043, 1007, 975, 915, 882, 843, 802, 748. LRMS (ESI +) m / z 665 ([M + Na] ⁺ , 31). HRMS (ESI +) m / z calcd for C ₃₈ H ₅₈ O ₈ Na 665.4024; found 665.4052.

Example 2
<experimental method>
Synthesis of betulin derivative (TPU-29) Betulin (100 mg, 0.226 mmol) was dissolved in toluene (0.23 ml), and Meldrum's acid (98 mg, 0.678 mmol) was added at 0 ° C, followed by stirring at 113 ° C for 1 hour. After confirming disappearance of the raw material spots by TLC, the reaction solution was concentrated under reduced pressure. The residue was purified by silica gel column chromatography (5% MeOH in CHCl ₃ ) to obtain TPU-29 (134 mg, 95%) as a pale yellow solid.
For use in the activity test, a yellowish white solid was dissolved in ethanol, and water was added little by little at 0 ° C. to precipitate powder crystals. When these were collected by suction filtration, purified TPU-29 (86 mg, 64%) was obtained as white powdery crystals.

Rf: 0.32 (EtOAc: Hex = 3: 1 dropped TFA). Mp: 134-136 ° C (EtOH-H ₂ O). [Α] _D ²⁶ : +11.4 (c 0.88, CHCl ₃ ). ¹ H-NMR ( 400 MHz, CDCl ₃ ) δ = 0.76-1.86 (m, 25H), 0.83 (s, 3H), 0.85 (s, 3H), 0.87 (s, 3H), 0.97 (s, 3H), 1.04 (s, 3H ), 1.68 (s, 3H), 1.91-2.02 (m, 1H), 2.43 (td, J = 10.8 and 5.9 Hz, 1H), 3.41-3.50 (m, 4H), 3.94 (d, J = 10.9 Hz, 1H), 4.41 (d, J = 11.0 Hz, 1H), 4.52-4.62 (m, 1H), 4.56 (s, 1H), 4.69 (s, 1H). 13 C-NMR (100 MHz, CDCl 3) δ = 15.0, 16.2, 16.3, 16.6, 18.3, 19.3, 21.0, 23.7, 25.3, 27.2, 28.1, 29.69, 29.74, 34.3, 34.6, 37.3, 37.9, 38.1, 38.5, 40.9, 41.1, 42.9, 46.7, 47.9, 49.0 , 50.5, 55.6, 64.7, 83.4, 110.2, 150.1, 167.3, 167.8, 170.7, 170.8. IR (neat, cm ^-1 ) ν = 2943, 2872, 1980, 1715, 1643, 1454, 1391, 1375, 1350, 1321 , 1194, 1147, 1006, 982, 881, 797, 745, 661.LRMS (ESI-): m / z = 613 ([MH]-). HRMS (ESI-): m / z calcd for C ₃₆ H ₅₃ O ₈ 613.3746; found 613.3722.

Example 3
Evaluation mouse malignant melanoma cell model (B16F10) prepared in 2 × 10 ⁵ cells / 0.05 ml PBS, C57BL / 6 mice (8 weeks old, female, 8-10 mice / group) or CB -17 Icr scid / scid mice (7-9 weeks old, female, 10 / group) were inoculated subcutaneously into the lower abdomen at 0.05 ml per mouse. The compound was administered into the tumor once a day from the 2nd to 16th day after the cancer inoculation (the day before the end of the experiment). The control group was similarly administered with a solvent (physiological buffer saline containing 0.1% Tween 80) (50 μl / mouse). The tumor diameter was measured every 2 or 3 days, and the apparent tumor volume was calculated by major axis × minor axis × minor axis / 2.

Evaluation of cytotoxicity
B16F10 cells were prepared at 4 × 10 ⁴ cells / ml in DMEM medium (GIBCO) containing 10% FBS, and 4 × 10 ³ cells were seeded per well in a 96-well plate (Corning). After the cells adhered to the plate, compounds were added at various concentrations and cultured in an incubator (37 ° C., 5% CO ₂ ) for 48 hours. Dimethyl sulfoxide was similarly added to the control. After completion of the culture, the medium in each well was replaced with a 10% FBS-DMEM medium containing 5% WST-1 (Wako), and further cultured for 4 hours, and then the absorbance at a wavelength of 450 nm was measured.

<result>
Antitumor effects of betulin and betulin derivatives were examined using a mouse B16F10 malignant melanoma cell subcutaneous transplantation model (FIG. 1 (BD-17) and FIG. 4 (TPU-29)). On the 17th day, the inhibition rate was 31.5% or 47.7% in the betulin 45 nmol or 150 nmol administration group, respectively. On the other hand, in the BD-17 administration group, it was 97.2%, and in the TPU-29 administration group, it was 91.6%.

  Next, in order to clarify whether cytotoxicity is involved in the antitumor effect of BD-17, the effect on the proliferation ability of mouse B16F10 malignant melanoma cells was compared with that of betulin in vitro. As a result, betulin inhibited cell growth depending on the concentration, but BD-17 and TPU-29 had little effect (FIG. 2 (BD-17) and FIG. 5 (TPU-29)). This suggests that the antitumor effects of BD-17 and TPU-29 are different from direct cytotoxicity against cancer cells.

  Therefore, in order to clarify whether the immune system is involved in the antitumor effect of BD-17, the antitumor effect of BD-17 was examined using scid mice lacking T cells and B cells. As in the case of the wild-type mouse shown in FIG. 1, when mouse B16F10 malignant melanoma cells were transplanted subcutaneously and BD-17 was administered, the suppression rate on day 17 was 30.9%, which was shown in FIG. The inhibitory effect was clearly attenuated compared to the results with wild-type mice (FIG. 3). This indicates that the acquired immune system contributes greatly to the antitumor effect of BD-17. These results suggest that BD-17 exerts an anti-tumor effect mainly through the acquired immune system and has very few side effects.

  The present invention is useful in the field of antitumor drugs.

Claims (5)

An antitumor agent comprising a betulin derivative represented by the following general formula (1) and / or a pharmaceutically acceptable salt thereof as an active ingredient.
(In the formula, n1 and n2 are independently 1 or 2.) The antitumor agent according to claim 1, wherein n1 and n2 are 1. The antitumor agent according to claim 1, wherein n1 and n2 are 2. The antitumor agent according to any one of claims 1 to 3, wherein the betulin derivative represented by the general formula (1) and / or a pharmaceutically acceptable salt thereof is a solvate. The antitumor agent according to any one of claims 1 to 4, wherein the tumor is skin cancer.